The Role of Growth Factors in the Activity of Pharmacological Differentiation Agents

Cell Growth & Differentiation : the Molecular Biology Journal of the American Association for Cancer Research. Jun, 2002  |  Pubmed ID: 12114217

Bryostatin-1 inhibits acute myeloid leukemia (AML) in vitroat doses that stimulate the growth of normal hematopoietic progenitors.Although bryostatin-1 has a number of distinct biological activities, those specifically responsible for its antileukemic activity are unclear. We found that bryostatin-1 (10(-8) M) inhibited cell cycling at G(1), induced phenotypic evidence of differentiation, and limited the clonogenic growth of both AML cell lines and patient specimens. This activity was markedly enhanced by granulocyte/macrophage-colony stimulating factor, whereas growth factor-neutralizing antibodies completely inhibited both the differentiating and antileukemic activities of bryostatin-1. Cell cycle inhibition and growth factors were also required for the differentiating activities of two unrelated agents, hydroxyurea and phenylbutyrate. These data suggest that many pharmacological differentiating agents require both cell cycle arrest and lineage-specific growth factors for full activity and may explain why these agents have demonstrated only limited clinical efficacy.

Anti-tumour Activity of Interferon-alpha in Multiple Myeloma: Role of Interleukin 6 and Tumor Cell Differentiation

British Journal of Haematology. Apr, 2003  |  Pubmed ID: 12694246

Interferon-alpha (IFN-alpha) is a pleotropic cytokine that has clinical activity against a wide variety of malignancies, including multiple myeloma (MM). In vitro, IFN-alpha has diverse effects on both normal and malignant cells, however, the exact mechanisms responsible for its clinical anti-tumour activity remain unclear. We found that IFN-alpha inhibited MM cell proliferation in association with cell cycle arrest at G1 and limited the clonogenic growth of both MM cell lines and primary patient specimens. At the doses tested, IFN-alpha was not cytotoxic, but induced terminal plasma cell differentiation resulting in the loss of clonogenicity. These activities were markedly enhanced by the major MM growth factor interleukin 6 (IL-6). Moreover, IL-6 was required for this process, as neutralizing antibodies against IL-6 inhibited the effects of IFN-alpha. IL-6 also induced MM cell terminal differentiation when combined with a second, unrelated, antiproliferative agent bryostatin-1, suggesting that its differentiating activities are preferentially enhanced in the presence of agents that inhibit cell cycling. These results suggest that the differentiating activities of IFN-alpha may play a role in its clinical antimyeloma activity and provide the rationale for clinical differentiation therapy in MM.

Characterization of Clonogenic Multiple Myeloma Cells

Blood. Mar, 2004  |  Pubmed ID: 14630803

The identity of the cells responsible for the initiation and maintenance of multiple myeloma (MM) remains unclear largely because of the difficulty growing MM cells in vitro and in vivo. MM cell lines and clinical specimens are characterized by malignant plasma cells that express the cell surface antigen syndecan-1 (CD138); however, CD138 expression is limited to terminally differentiated plasma cells during B-cell development. Moreover, circulating B cells that are clonally related to MM plasma cells have been reported in some patients with MM. We found that human MM cell lines contained small (< 5%) subpopulations that lacked CD138 expression and had greater clonogenic potential in vitro than corresponding CD138+ plasma cells. CD138- cells from clinical MM samples were similarly clonogenic both in vitro and in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice, whereas CD138+ cells were not. Furthermore, CD138- cells from both cell lines and clinical samples phenotypically resembled postgerminal center B cells, and their clonogenic growth was inhibited by the anti-CD20 monoclonal antibody rituximab. These data suggest that MM "stem cells" are CD138- B cells with the ability to replicate and subsequently differentiate into malignant CD138+ plasma cells.

Cancer Stem Cells: Are We Missing the Target?

Journal of the National Cancer Institute. Apr, 2004  |  Pubmed ID: 15100335

Enhanced Cytotoxicity of Rituximab Following Genetic and Biochemical Disruption of Glycosylphosphatidylinositol Anchored Proteins

Leukemia & Lymphoma. Apr, 2004  |  Pubmed ID: 15160958

Rituximab, an anti-CD20 monoclonal antibody used to treat B cell lymphoproliferative disorders and autoimmune diseases, kills cells through complement dependent cytotoxicity, antibody-dependent cellular toxicity and apoptosis. A mechanism of resistance to rituximab is upregulation of the complement regulatory proteins, CD59 and CD55. Paroxysmal nocturnal hemoglobinuria (PNH) is a hematopoietic disorder caused by PIGA mutations that lead to a loss of all glycosylphospatidylinositol (GPI)-anchored proteins including, CD55 and CD59. We compared the cytotoxic activity of rituximab against a PNH B cell line, LD -, and the isogenic cell line LD - PIGA + in which GPI-anchor expression was restored by stable transfection of PIGA. The PNH cell line was more sensitive to rituximab-mediated killing than the LD - PIGA + cells. Biochemical disruption of GPI anchors with phosphatidylinositol specific phospholipase C (PIPLC), a phospholipase that cleaves GPI-anchored proteins, also increased rituximab-mediated killing. Thus, genetic and biochemical interruption of GPI anchor proteins augments sensitivity to rituximab.

Association of Foxp3 Regulatory Gene Expression with Graft-versus-host Disease

Blood. Oct, 2004  |  Pubmed ID: 15172973

Graft-versus-host disease (GVHD) is characterized by an impairment of mechanisms that underlie the development of immunologic tolerance. Although the cytokine storm associated with GVHD leads to expression of cell surface markers on both effector and regulatory T cells, regulatory CD4+ T cells that play an instrumental role in the maintenance of tolerance appear to uniquely express the Foxp3 transcriptional repressor. Foxp3 mRNA expression was significantly decreased in peripheral blood mononuclear cells from patients with either allogeneic GVHD or autologous GVHD compared with patients without GVHD. Expression of Foxp3 negatively correlated with the severity of GVHD but positively correlated with recent thymic emigrants. The results suggest that defective thymic function contributes to the impaired reconstitution of immune regulatory mechanisms following transplantation. The decrease in regulatory mechanisms after transplantation appears to provide an environment permissive to the development of GVHD.

Activated Marrow-infiltrating Lymphocytes Effectively Target Plasma Cells and Their Clonogenic Precursors

Cancer Research. Mar, 2005  |  Pubmed ID: 15753403

A major limitation of adoptive immunotherapy is the availability of T cells specific for both terminally differentiated tumor cells and their clonogenic precursors. We show here that marrow-infiltrating lymphocytes (MILs) recognize myeloma cells after activation with anti-CD3/CD28 beads with higher frequency than activated peripheral blood lymphocytes from the same patients. Furthermore, activated MILs target both the terminally differentiated CD138+ plasma cells and the myeloma precursor as shown by profound inhibition in a tumor clonogenic assay. The presence of antigen in the marrow microenvironment seems to be important for the maintenance of tumor specificity. Taken together, these results highlight the intrinsic tumor specificity of MILs and describe a novel approach for the generation of tumor-specific T-cell populations suitable for adoptive immunotherapy of multiple myeloma.

Requirement for Myeloid Growth Factors in the Differentiation of Acute Promyelocytic Leukaemia

British Journal of Haematology. Mar, 2005  |  Pubmed ID: 15755292

It is well known that the differentiation of acute promyelocytic leukaemia (APL) cells by all-trans-retinoic acid (ATRA) may be enhanced by myeloid growth factors, but the requirement for growth factors in this process is unclear. Our previous studies in multiple myeloma and non-APL acute myeloid leukaemia demonstrated that lineage-specific growth factors are required for the maximal activity of many pharmacologic differentiating agents in vitro. Thus, we studied whether the differentiation of APL is similarly dependent on growth factors. We found that the myeloid growth factors granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor markedly increased the differentiation of NB4 cells or APL blasts from clinical samples treated with ATRA, arsenic trioxide (ATO), or bryostatin-1 as evidenced by the enhanced expression of myeloid surface antigens and the inhibition of clonogenic growth. Furthermore, myeloid growth factors were necessary for the differentiation of APL cells since the activity of each pharmacologic agent could be blocked by specific growth factor-neutralizing antibodies. Each differentiating agent was active only at concentrations that inhibited cell cycling, suggesting that this property is also required for differentiation. These data demonstrate that both pharmacologic differentiating agents and myeloid growth factors are required, but neither sufficient, for the differentiation of APL cells. The combined use of pharmacologic differentiating agents and growth factors may improve the clinical efficacy of differentiation therapy in APL.

Do Neoplastic Stem Cells Underlie the Pathogenesis of Cutaneous Lymphomas?

Archives of Dermatology. May, 2005  |  Pubmed ID: 15897396

Effects of Imatinib and Interferon on Primitive Chronic Myeloid Leukaemia Progenitors

British Journal of Haematology. Aug, 2005  |  Pubmed ID: 16042686

Imatinib has impressive activity against chronic myeloid leukaemia (CML), but does not appear to completely eradicate the disease. Although responses to interferon-alpha (IFN) are slower and less dramatic than those to imatinib, they can be durable even after discontinuation of the drug. Unlike imatinib, the specific mechanisms responsible for IFN's clinical activity in CML are unknown. We found that IFN induced a G1 cell cycle arrest, as well as terminal differentiation, of the CML cell line KT-1 and CML CD34+ cells from clinical specimens. Myeloid growth factors augmented the antileukaemic activity of IFN, and neutralising antibodies directed against myeloid growth factors inhibited IFN's antileukaemic activity. We next directly compared the effects of imatinib and IFN against differentiated and primitive CML progenitors from newly-diagnosed patients. Although less active against CML granulocyte-macrophage colony forming units than imatinib, IFN was significantly more toxic to primitive CML progenitors responsible for the maintenance of long-term cultures. Imatinib and IFN appear to have divergent effects on CML progenitors at different stages of maturation, with imatinib more active against differentiated CML progenitors and IFN more active against primitive CML progenitors. The different target cells for these agents may explain the disparities in the kinetics and durability of their clinical responses. At least part of the clinical effect of IFN in CML appears to result from its ability to differentiate primitive CML progenitors.

The Paradox of Response and Survival in Cancer Therapeutics

Blood. Jan, 2006  |  Pubmed ID: 16150939

Although most patients with cancer respond to therapy, few are cured. Moreover, objective clinical responses to treatment often do not even translate into substantial improvements in overall survival. For example, patients with indolent lymphoma who achieved a complete remission with conventional-dose therapies in the prerituximab era did not experience a survival advantage over similar patients treated with a "watch and wait" approach. Several studies have also shown that neither the magnitude nor the kinetics of clinical response has an impact on survival in multiple myeloma. Recent data suggesting many malignancies arise from a rare population of cells that exclusively maintains the ability to self-renew and sustains the tumor (ie, "cancer stem cells") may help explain this paradox that response and survival are not always linked. Therapies that successfully eliminate the differentiated cancer cells characterizing the tumor may be ineffective against rare, biologically distinct cancer stem cells. New methods for assessing treatment efficacy must also be developed, as traditional response criteria measure tumor bulk and may not reflect changes in rare cancer stem cell populations. In this article, we discuss the evidence for cancer stem cells in hematologic malignancies and possible ways to begin targeting these cells and measuring clinical effectiveness of such treatment approaches.

Graft-versus-host Reactions and the Effectiveness of Donor Lymphocyte Infusions

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Apr, 2006  |  Pubmed ID: 16545725

We retrospectively analyzed 83 consecutive recipients of donor lymphocyte infusions (DLI) after allogeneic transplantation for factors associated with disease response and graft-versus-host disease (GVHD). DLI was highly effective in relapsed chronic phase chronic myeloid leukemia (CML), with 71% of patients achieving durable complete remissions (CR). In relapsed acute myeloid leukemia, DLI led to durable CRs in 31% of patients; the rate was <20% in all other diseases. Achieving full donor chimerism and GVHD were predictive of CR. Grade II or higher acute or chronic GVHD occurred in 36 (43%) patients and contributed to death in 13 (16%). Even more patients, 33 (40%), died of their underlying malignancy, including 10 who developed active GVHD. In relapsed CML, most durable CRs occurred without clinically apparent GVHD, yet all responders achieved full donor chimerism, including 6 with coincident normal host hematopoiesis at the time of DLI. Thus, in CML, potent lymphohematopoietic graft-versus-host reactions occurred even in the absence of clinically apparent GVHD; this confirms the ability to dissociate these processes and argues against a leukemia-specific immunologic effect. DLI clearly has efficacy in the treatment of relapsed disease after allogeneic transplantation. However, with the exception of CML, most patients die of their underlying disease because of insufficient antitumor activity even with active GVHD.

Strategies to Eliminate Cancer Stem Cells: Clinical Implications

European Journal of Cancer (Oxford, England : 1990). Jun, 2006  |  Pubmed ID: 16644203

Over the past two decades, major advances in our understanding of cancer have translated into only modest increments in survival for the majority of cancer patients. Recent data suggesting cancers arise from rare self-renewing stem cells that are biologically distinct from their more numerous differentiated progeny may explain this paradox. Current anticancer therapies have been developed to decrease the bulk of the tumour mass (i.e. the differentiated cancer cells). Although treatments directed against the bulk of the cancer may produce dramatic responses, they are unlikely to result in long-term remissions if the rare cancer stem cells are also not targeted. Conversely, treatments that selectively attack cancer stem cells will not immediately eliminate the differentiated cancer cells, and might therefore be prematurely abandoned if clinical activity is judged solely by traditional response criteria that reflect changes in the bulk of the tumour. Re-examining both our pre-clinical and clinical drug development paradigms to include the cancer stem cell concept has the potential to revolutionize the treatment of many cancers.

Notch Pathway Inhibition Depletes Stem-like Cells and Blocks Engraftment in Embryonal Brain Tumors

Cancer Research. Aug, 2006  |  Pubmed ID: 16885340

The Notch signaling pathway is required in both nonneoplastic neural stem cells and embryonal brain tumors, such as medulloblastoma, which are derived from such cells. We investigated the effects of Notch pathway inhibition on medulloblastoma growth using pharmacologic inhibitors of gamma-secretase. Notch blockade suppressed expression of the pathway target Hes1 and caused cell cycle exit, apoptosis, and differentiation in medulloblastoma cell lines. Interestingly, viable populations of better-differentiated cells continued to grow when Notch activation was inhibited but were unable to efficiently form soft-agar colonies or tumor xenografts, suggesting that a cell fraction required for tumor propagation had been depleted. It has recently been hypothesized that a small population of stem-like cells within brain tumors is required for the long-term propagation of neoplastic growth and that CD133 expression and Hoechst dye exclusion (side population) can be used to prospectively identify such tumor-forming cells. We found that Notch blockade reduced the CD133-positive cell fraction almost 5-fold and totally abolished the side population, suggesting that the loss of tumor-forming capacity could be due to the depletion of stem-like cells. Notch signaling levels were higher in the stem-like cell fraction, providing a potential mechanism for their increased sensitivity to inhibition of this pathway. We also observed that apoptotic rates following Notch blockade were almost 10-fold higher in primitive nestin-positive cells as compared with nestin-negative ones. Stem-like cells in brain tumors thus seem to be selectively vulnerable to agents inhibiting the Notch pathway.

Blockade of Hedgehog Signaling Inhibits Pancreatic Cancer Invasion and Metastases: a New Paradigm for Combination Therapy in Solid Cancers

Cancer Research. Mar, 2007  |  Pubmed ID: 17332349

In the context of pancreatic cancer, metastasis remains the most critical determinant of resectability, and hence survival. The objective of this study was to determine whether Hedgehog (Hh) signaling plays a role in pancreatic cancer invasion and metastasis because this is likely to have profound clinical implications. In pancreatic cancer cell lines, Hh inhibition with cyclopamine resulted in down-regulation of snail and up-regulation of E-cadherin, consistent with inhibition of epithelial-to-mesenchymal transition, and was mirrored by a striking reduction of in vitro invasive capacity (P < 0.0001). Conversely, Gli1 overexpression in immortalized human pancreatic ductal epithelial cells led to a markedly invasive phenotype (P < 0.0001) and near total down-regulation of E-cadherin. In an orthotopic xenograft model, cyclopamine profoundly inhibited metastatic spread; only one of seven cyclopamine-treated mice developed pulmonary micrometastases versus seven of seven mice with multiple macrometastases in control animals. Combination of gemcitabine and cyclopamine completely abrogated metastases while also significantly reducing the size of "primary" tumors. Gli1 levels were up-regulated in tissue samples of metastatic human pancreatic cancer samples compared with matched primary tumors. Aldehyde dehydrogenase (ALDH) overexpression is characteristic for both hematopoietic progenitors and leukemic stem cells; cyclopamine preferentially reduced "ALDH-high" cells by approximately 3-fold (P = 0.048). We confirm pharmacologic Hh pathway inhibition as a valid therapeutic strategy for pancreatic cancer and show for the first time its particular efficacy against metastatic spread. By targeting specific cellular subpopulations likely involved in tumor initiation at metastatic sites, Hh inhibitors may provide a new paradigm for therapy of disseminated malignancies, particularly when used in combination with conventional antimetabolites that reduce "bulk" tumor size.

Hedgehog Signaling Maintains a Tumor Stem Cell Compartment in Multiple Myeloma

Proceedings of the National Academy of Sciences of the United States of America. Mar, 2007  |  Pubmed ID: 17360475

The cancer stem cell hypothesis suggests that malignant growth depends on a subset of tumor cells with stem cell-like properties of self-renewal. Because hedgehog (Hh) signaling regulates progenitor cell fate in normal development and homeostasis, aberrant pathway activation might be involved in the maintenance of such a population in cancer. Indeed, mutational activation of the Hh pathway is associated with medulloblastoma and basal cell carcinoma; pathway activity is also critical for growth of other tumors lacking such mutations, although the mechanism of pathway activation is poorly understood. Here we study the role and mechanism of Hh pathway activation in multiple myeloma (MM), a malignancy with a well defined stem cell compartment. In this model, rare malignant progenitors capable of clonal expansion resemble B cells, whereas the much larger tumor cell population manifests a differentiated plasma cell phenotype that pathologically defines the disease. We show that the subset of MM cells that manifests Hh pathway activity is markedly concentrated within the tumor stem cell compartment. The Hh ligand promotes expansion of MM stem cells without differentiation, whereas the Hh pathway blockade, while having little or no effect on malignant plasma cell growth, markedly inhibits clonal expansion accompanied by terminal differentiation of purified MM stem cells. These data reveal that Hh pathway activation is heterogeneous across the spectrum of MM tumor stem cells and their more differentiated progeny. The potential existence of similar relationships in other adult cancers may have important biologic and clinical implications for the study of aberrant Hh signaling.

Cyclopamine-mediated Hedgehog Pathway Inhibition Depletes Stem-like Cancer Cells in Glioblastoma

Stem Cells (Dayton, Ohio). Oct, 2007  |  Pubmed ID: 17628016

Brain tumors can arise following deregulation of signaling pathways normally activated during brain development and may derive from neural stem cells. Given the requirement for Hedgehog in non-neoplastic stem cells, we investigated whether Hedgehog blockade could target the stem-like population in glioblastoma multiforme (GBM). We found that Gli1, a key Hedgehog pathway target, was highly expressed in 5 of 19 primary GBM and in 4 of 7 GBM cell lines. Shh ligand was expressed in some primary tumors, and in GBM-derived neurospheres, suggesting a potential mechanism for pathway activation. Hedgehog pathway blockade by cyclopamine caused a 40%-60% reduction in growth of adherent glioma lines highly expressing Gli1 but not in those lacking evidence of pathway activity. When GBM-derived neurospheres were treated with cyclopamine and then dissociated and seeded in media lacking the inhibitor, no new neurospheres formed, suggesting that the clonogenic cancer stem cells had been depleted. Consistent with this hypothesis, the stem-like fraction in gliomas marked by both aldehyde dehydrogenase activity and Hoechst dye excretion (side population) was significantly reduced or eliminated by cyclopamine. In contrast, we found that radiation treatment of our GBM neurospheres increased the percentage of these stem-like cells, suggesting that this standard therapy preferentially targets better-differentiated neoplastic cells. Most importantly, viable GBM cells injected intracranially following Hedgehog blockade were no longer able to form tumors in athymic mice, indicating that a cancer stem cell population critical for ongoing growth had been removed. Disclosure of potential conflicts of interest is found at the end of this article.

Induction of Autologous Graft-versus-host Disease: Results of a Randomized Prospective Clinical Trial in Patients with Poor Risk Lymphoma

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Oct, 2007  |  Pubmed ID: 17889355

The results of blood or marrow transplantation in patients with chemorefractory aggressive lymphoma, that is, those not responding to conventional-dose chemotherapy at the time of transplant, have been poor. The relapse rate has been high after autologous bone marrow transplant, whereas allogeneic transplantation has been associated with excessive transplant-related toxicity. Administration of cyclosporine after autologous transplantation can induce an autoreactive syndrome that resembles graft-versus-host disease (GVHD). This syndrome, named autologous graft-versus-host disease, has clear antitumor activity in animal models that can be enhanced by the addition of cytokines such as gamma-interferon and interleukin-2. A randomized, prospective study was conducted to evaluate the antitumor effect of autologous graft-versus-host disease induced with cyclosporine, and augmented by the administration of gamma-interferon and interleukin-2 in patients with chemorefractory Hodgkin and aggressive non-Hodgkin lymphomas. Fifty-one patients were randomized, 24 to the autologous GVHD induction arm, and 27 to the noninduction arm after autologous transplant using mobilized peripheral blood stem cell (PBSC) grafts. There were no differences in treatment-related mortality, overall and event-free survival (OS, EFS) between both groups; however, in the induction arm, GVHD developed only in 4 patients. The administration of oral cyclosporine followed by interleukin-2 and gamma-interferon is generally not well tolerated, and does not appear to be an effective method to induce autologous GVHD in patients receiving autologous PBSC grafts.

Therapeutic Implications of Leukemic Stem Cell Pathways

Clinical Cancer Research : an Official Journal of the American Association for Cancer Research. Nov, 2007  |  Pubmed ID: 18006753

An emerging concept in cancer biology is that a rare population of cancer stem cells exists among the heterogeneous cell mass that constitutes a tumor. This concept is best understood in human myeloid leukemia. Normal and malignant hematopoietic stem cell functions are defined by a common set of critical stemness genes that regulate self-renewal and developmental pathways. Several stemness factors, such as Notch or telomerase, show differential activation in normal hematopoietic versus leukemia stem cells. These differences could be exploited therapeutically even with drugs that are already in clinical use for the treatment of leukemia. The translation of novel and existing leukemic stem cell-directed therapies into clinical practice, however, will require changes in clinical trial design and the inclusion of stem cell biomarkers as correlative end points.

Cancer Stem Cells: From Bench to Bedside

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Jan, 2007  |  Pubmed ID: 18167509

Objective clinical responses to anticancer treatments often do not translate into substantial improvements in overall survival. Recent data suggesting many cancers arise from rare self-renewing cells (cancer stem cells) that are biologically distinct from their more numerous differentiated progeny, may explain this paradox. Current anticancer therapies have been developed to target the bulk of the tumor mass (i.e., the differentiated cancer cells). Although treatments directed against the bulk of the cancer may produce dramatic responses, they are unlikely to result in long-term remissions if the rare cancer stem cells are also not targeted. Better understanding the biology of cancer stem cells as well reexamining both our preclinical and clinical drug development paradigms to include the cancer stem cell concept, have the potential to revolutionize the treatment of many cancers.

Clonogenic Multiple Myeloma Progenitors, Stem Cell Properties, and Drug Resistance

Cancer Research. Jan, 2008  |  Pubmed ID: 18172311

Many agents are active in multiple myeloma, but the majority of patients relapse. This clinical pattern suggests most cancer cells are eliminated, but cells with the clonogenic potential to mediate tumor regrowth are relatively chemoresistant. Our previous data suggested that CD138(+) multiple myeloma plasma cells cannot undergo long-term proliferation but rather arise from clonogenic CD138(neg) B cells. We compared the relative sensitivity of these distinct cell types to clinical antimyeloma agents and found that dexamethasone, lenadilomide, bortezomib, and 4-hydroxycyclophosphamide inhibited CD138(+) multiple myeloma plasma cells but had little effect on CD138(neg) precursors in vitro. We further characterized clonogenic multiple myeloma cells and stained cell lines using the Hoechst side population and Aldefluor assays. Each assay identified CD138(neg) cells suggesting that they possess high drug efflux capacity and intracellular drug detoxification activity. We also found that multiple myeloma cells expressing the memory B-cell markers CD20 and CD27 could give rise to clonogenic multiple myeloma growth in vitro and engraft immunodeficient nonobese diabetes/severe combined immunodeficient mice during both primary and secondary transplantation. Furthermore, both the side population and Aldefluor assays were capable of identifying circulating clonotypic memory B-cell populations within the peripheral blood of multiple myeloma patients. Our results suggest that circulating clonotypic B-cell populations represent multiple myeloma stem cells, and the relative drug resistance of these cells is mediated by processes that protect normal stem cells from toxic injury.

Myeloablative Allogeneic Bone Marrow Transplant Using T Cell Depleted Allografts Followed by Post-transplant GM-CSF in High-risk Myelodysplastic Syndromes

Leukemia Research. Sep, 2008  |  Pubmed ID: 18261793

Allogeneic blood and marrow transplantation (alloBMT) remains the only curative treatment for patients with myelodysplastic syndromes (MDS), but its application has been limited by the older age range of patients with this disease. T cell depletion decreases transplant-related toxicity related to graft-versus-host disease (GVHD), but does not improve overall survival because of increased risk for relapse and graft failure. Myeloid growth factors have been used to speed engraftment following alloBMT, but data suggest that they may also have anti-tumor properties. We treated 43 patients (median age 56) with MDS/AML with high-risk features using a myeloablative T cell depleted alloBMT followed by prolonged systemic GM-CSF. The current event-free survival at 1 and 3 years was 47% and 34%, respectively with a median follow-up of 22.8 months in surviving patients. The toxicities compared favorably with those seen using reduced intensity conditioning regimens and included grade III/IV GVHD (10%), graft failure (9%), and cumulative treatment-related mortality (28%). The cumulative incidence of relapse remained high at 38%; however, 3/10 patients receiving donor lymphocyte infusions achieved durable complete remissions. These results suggest that it is possible to maintain treatment intensity while minimizing toxicity in older, high-risk MDS patients.

HLA-haploidentical Bone Marrow Transplantation for Hematologic Malignancies Using Nonmyeloablative Conditioning and High-dose, Posttransplantation Cyclophosphamide

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Jun, 2008  |  Pubmed ID: 18489989

We evaluated the safety and efficacy of high-dose, posttransplantation cyclophosphamide (Cy) to prevent graft rejection and graft-versus-host disease (GVHD) after outpatient nonmyeloablative conditioning and T cell-replete bone marrow transplantation from partially HLA-mismatched (haploidentical) related donors. Patients with advanced hematologic malignancies (n = 67) or paroxysmal nocturnal hemoglobinuria (n = 1) received Cy 50 mg/kg i.v. on day 3 (n = 28) or on days 3 and 4 (n = 40) after transplantation. The median times to neutrophil (>500/microL) and platelet recovery (>20,000/microL) were 15 and 24 days, respectively. Graft failure occurred in 9 of 66 (13%) evaluable patients, and was fatal in 1. The cumulative incidences of grades II-IV and grades III-IV acute (aGVHD) by day 200 were 34% and 6%, respectively. There was a trend toward a lower risk of extensive chronic GVHD (cGVHD) among recipients of 2 versus 1 dose of posttransplantation Cy (P = .05), the only difference between these groups. The cumulative incidences of nonrelapse mortality (NRM) and relapse at 1 year were 15% and 51%, respectively. Actuarial overall survival (OS) and event-free survival (EFS) at 2 years after transplantation were 36% and 26%, respectively. Patients with lymphoid malignancies had an improved EFS compared to those with myelogenous malignancies (P = .02). Nonmyeloablative HLA-haploidentical BMT with posttransplantation Cy is associated with acceptable rates of fatal graft failure and severe aGVHD or cGVHD.

Multiple Myeloma Cancer Stem Cells

Journal of Clinical Oncology : Official Journal of the American Society of Clinical Oncology. Jun, 2008  |  Pubmed ID: 18539970

Multiple myeloma is characterized by the clonal expansion of neoplastic plasma cells within the bone marrow, elevated serum immunoglobulin, and osteolytic bone disease. The disease is highly responsive to a wide variety of anticancer treatments including conventional cytotoxic chemotherapy, corticosteroids, radiation therapy, and a growing number of agents with novel mechanisms of action. However, few if any patients are cured with these modalities and relapse remains a critical issue. A better understanding of clonogenic multiple myeloma cells is essential to ultimately improving long-term outcomes, but the nature of the cells responsible for myeloma regrowth and disease relapse is unclear. We review evidence that functional heterogeneity exists in multiple myeloma and discuss potential strategies and clinical implications of the stem-cell model of cancer in this disease.

An Orally Bioavailable Small-molecule Inhibitor of Hedgehog Signaling Inhibits Tumor Initiation and Metastasis in Pancreatic Cancer

Molecular Cancer Therapeutics. Sep, 2008  |  Pubmed ID: 18790753

Recent evidence suggests that blockade of aberrant Hedgehog signaling can be exploited as a therapeutic strategy for pancreatic cancer. Our previous studies using the prototype Hedgehog small-molecule antagonist cyclopamine had shown the striking inhibition of systemic metastases on Hedgehog blockade in spontaneously metastatic orthotopic xenograft models. Cyclopamine is a natural compound with suboptimal pharmacokinetics, which impedes clinical translation. In the present study, a novel, orally bioavailable small-molecule Hedgehog inhibitor, IPI-269609, was tested using in vitro and in vivo model systems. In vitro treatment of pancreatic cancer cell lines with IPI-269609 resembled effects observed using cyclopamine (i.e., Gli-responsive reporter knockdown, down-regulation of the Hedgehog target genes Gli1 and Ptch, as well as abrogation of cell migration and colony formation in soft agar). Single-agent IPI-269609 profoundly inhibited systemic metastases in orthotopic xenografts established from human pancreatic cancer cell lines, although Hedgehog blockade had minimal effect on primary tumor volume. The only discernible phenotype observed within the treated primary tumor was a significant reduction in the population of aldehyde dehydrogenase-bright cells, which we have previously identified as a clonogenic tumor-initiating population in pancreatic cancer. Selective ex vivo depletion of aldehyde dehydrogenase-bright cells with IPI-269609 was accompanied by significant reduction in tumor engraftment rates in athymic mice. Pharmacologic blockade of aberrant Hedgehog signaling might prove to be an effective therapeutic strategy for inhibition of systemic metastases in pancreatic cancer, likely through targeting subsets of cancer cells with tumor-initiating ("cancer stem cell") properties.

The Multiple Myeloma Associated MMSET Gene Contributes to Cellular Adhesion, Clonogenic Growth, and Tumorigenicity

Blood. Jan, 2008  |  Pubmed ID: 17942756

Multiple myeloma (MM) is an incurable hematologic malignancy characterized by recurrent chromosomal translocations. Patients with t(4;14)(p16;q32) are the worst prognostic subgroup in MM, although the basis for this poor prognosis is unknown. The t(4;14) is unusual in that it involves 2 potential target genes: fibroblast growth factor receptor 3 (FGFR3) and multiple myeloma SET domain (MMSET). MMSET is universally overexpressed in t(4;14) MM, whereas FGFR3 expression is lost in one-third of cases. Nonetheless, the role of MMSET in t(4;14) MM has remained unclear. Here we demonstrate a role for MMSET in t(4;14) MM cells. Down-regulation of MMSET expression in MM cell lines by RNA interference and by selective disruption of the translocated MMSET allele using gene targeting dramatically reduced colony formation in methylcellulose but had only modest effects in liquid culture. In addition, MMSET knockdown led to cell-cycle arrest of adherent MM cells and reduced the ability of MM cells to adhere to extracellular matrix. Finally, MMSET knockdown and knockout reduced tumor formation by MM xenografts. These results provide the first direct evidence that MMSET plays a significant role in t(4;14) MM and suggest that therapies targeting this gene could impact this particular subset of poor-prognosis patients.

Cancer Stem Cells in Multiple Myeloma

Cancer Letters. May, 2009  |  Pubmed ID: 18809245

Several key observations providing evidence for the cancer stem cell hypothesis and insights into the unique biology of these cells have come from the study of multiple myeloma. These include evidence that cancer cells may be functionally heterogeneous in spite of their genetic homogeneity and that malignant progenitors share many biological features with normal adult stem cells including drug resistance and regulatory processes governing self-renewal. We review studies that have examined clonogenic cells in multiple myeloma, highlight controversies regarding the cell of origin in multiple myeloma, and discuss potential targeting strategies.

Glycosylphosphatidylinositol-anchored Protein Deficiency Confers Resistance to Apoptosis in PNH

Experimental Hematology. Jan, 2009  |  Pubmed ID: 19013003

Investigate the contribution of PIG-A mutations to clonal expansion in paroxysmal nocturnal hemoglobinuria (PNH).

A Direct Pancreatic Cancer Xenograft Model As a Platform for Cancer Stem Cell Therapeutic Development

Molecular Cancer Therapeutics. Feb, 2009  |  Pubmed ID: 19174553

There is an enormous gap between the antiproliferative and in vivo antitumor efficacy of gemcitabine in cell line-based models and its clinical efficacy. This may be due to insensitiveness of the precursor, cancer stem cell (CSC) compartment to cytotoxic agents. The hedgehog pathway is associated with CSC signaling and control. We used a direct xenograft model of pancreatic cancer and a two-stage approach was used to test the hypotheses that targeting CSC could increase the efficacy of gemcitabine. Tumors from a gemcitabine-sensitive xenograft were treated with gemcitabine first, and randomized, after tumor regression to continuing treatment with gemcitabine, a hedgehog inhibitor alone or in combination with gemcitabine. We tested markers described as associated with CSC such as CD24, CD44, ALDH, nestin, and the hedgehog pathway. After induction with gemcitabine, treated tumor showed an enrichment in CSC markers such as ALDH and CD24. Subsequently, a release from gemcitabine prompted a repopulation of proliferating cells and a decrease in such markers to equilibrate from pretreatment levels. Combined treatment with gemcitabine and cyclopamine induced tumor regression and decrease in CSC markers and hedgehog signaling. Cytoplasmic CD24 and ALDH were inversely and strongly associated with growth and were expressed in a minority of cells that we propose constitute the CSC compartment. Hedgehog inhibitors as part of a dual compartment therapeutic approach were able to further reduce tumor growth and decreased both static and dynamic markers of CSC. Direct tumor xenografts are a valid platform to test multicompartment therapeutic approaches in pancreatic cancer.

Achaete-scute Complex Homologue 1 Regulates Tumor-initiating Capacity in Human Small Cell Lung Cancer

Cancer Research. Feb, 2009  |  Pubmed ID: 19176379

The basic helix-loop-helix transcription factor achaete-scute complex homologue 1 (ASCL1) is essential for the development of normal lung neuroendocrine cells as well as other endocrine and neural tissues. Small cell lung cancer (SCLC) and non-SCLC with neuroendocrine features express ASCL1, where the factor may play a role in the virulence and primitive neuroendocrine phenotype of these tumors. In this study, RNA interference knockdown of ASCL1 in cultured SCLC resulted in inhibition of soft agar clonogenic capacity and induction of apoptosis. cDNA microarray analyses bolstered by expression studies, flow cytometry, and chromatin immunoprecipitation identified two candidate stem cell marker genes, CD133 and aldehyde dehydrogenase 1A1 (ALDH1A1), to be directly regulated by ASCL1 in SCLC. In SCLC direct xenograft tumors, we detected a relatively abundant CD133(high)-ASCL1(high)-ALDH1(high) subpopulation with markedly enhanced tumorigenicity compared with cells with weak CD133 expression. Tumorigenicity in the CD133(high) subpopulation depended on continued ASCL1 expression. Whereas CD133(high) cells readily reconstituted the range of CD133 expression seen in the original xenograft tumor, CD133(low) cells could not. Our findings suggest that a broad range of SCLC cells has tumorigenic capacity rather than a small discrete population. Intrinsic tumor cell heterogeneity, including variation in key regulatory factors such as ASCL1, can modulate tumorigenicity in SCLC.

Circulating Clonotypic B Cells in Classic Hodgkin Lymphoma

Blood. Jun, 2009  |  Pubmed ID: 19188663

Although Hodgkin and Reed-Sternberg (HRS) cells are B lymphoid cells, they are unlike any normal cells of that lineage. Moreover, the limited proliferative potential of HRS cells belies the clinical aggressiveness of Hodgkin lymphoma (HL). More than 20 years ago, the L428 HL cell line was reported to contain a small population of phenotypic B cells that appeared responsible for the continued generation of HRS cells. This observation, however, has never been corroborated, and such clonotypic B cells have never been documented in HL patients. We found that both the L428 and KM-H2 HL cell lines contained rare B-cell subpopulations responsible for the generation and maintenance of the predominant HRS cell population. The B cells within the HL cell lines expressed immunoglobulin light chain, the memory B-cell antigen CD27, and the stem cell marker aldehyde dehydrogenase (ALDH). Clonal CD27(+)ALDH(high) B cells, sharing immunoglobulin gene rearrangements with lymph node HRS cells, were also detected in the blood of most newly diagnosed HL patients regardless of stage. Although the clinical significance of circulating clonotypic B cells in HL remains unclear, these data suggest they may be the initiating cells for HL.

GLI1 is a Direct Transcriptional Target of EWS-FLI1 Oncoprotein

The Journal of Biological Chemistry. Apr, 2009  |  Pubmed ID: 19189974

Ewing sarcoma family of tumors (ESFT) is an undifferentiated neoplasm of the bone and soft tissue. ESFT is characterized by a specific chromosomal translocation occurring between chromosome 22 and (in most cases) chromosome 11, which generates an aberrant transcription factor, EWS-FLI1. The function of EWS-FLI1 is essential for the maintenance of ESFT cell survival and tumorigenesis. The Hedgehog pathway is activated in several cancers. Oncogenic potential of the Hedgehog pathway is mediated by increasing the activity of the GLI family of transcription factors. Recent evidence suggests that EWS-FLI1 increases expression of GLI1 by an unknown mechanism. Our data from chromatin immunoprecipitation and promoter reporter studies indicated GLI1 as a direct transcriptional target of EWS-FLI1. Expression of EWS-FLI1 in non-ESFT cells increased GLI1 expression and GLI-dependent transcription. We also detected high levels of GLI1 protein in ESFT cell lines. Pharmacological inhibition of GLI1 protein function decreased proliferation and soft agar colony formation of ESFT cells. Our results establish GLI1 as a direct transcriptional target of EWS-FLI1 and suggest a potential role for GLI1 in ESFT tumorigenesis.

Ligand-dependent Notch Signaling is Involved in Tumor Initiation and Tumor Maintenance in Pancreatic Cancer

Clinical Cancer Research : an Official Journal of the American Association for Cancer Research. Apr, 2009  |  Pubmed ID: 19258443

Aberrant activation of the Notch signaling pathway is commonly observed in human pancreatic cancer, although the mechanism(s) for this activation has not been elucidated.

Higher Serum Folate Levels Are Associated with a Lower Risk of Atopy and Wheeze

The Journal of Allergy and Clinical Immunology. Jun, 2009  |  Pubmed ID: 19409604

Folic acid is known to be associated with inflammatory diseases, but the relationship between folic acid and allergic diseases is unclear.

Smoothening the Controversial Role of Hedgehog in Hematopoiesis

Cell Stem Cell. Jun, 2009  |  Pubmed ID: 19497273

The role of multiple developmental signaling pathways in the regulation of hematopoiesis has been controversial. In this issue of Cell Stem Cell, two separate reports (Hofmann et al., 2009; Gao et al., 2009) examine whether the Hedgehog signaling pathway modulates normal adult hematopoietic stem cells and blood formation.

DNER, an Epigenetically Modulated Gene, Regulates Glioblastoma-derived Neurosphere Cell Differentiation and Tumor Propagation

Stem Cells (Dayton, Ohio). Jul, 2009  |  Pubmed ID: 19544453

Neurospheres derived from glioblastoma (GBM) and other solid malignancies contain neoplastic stem-like cells that efficiently propagate tumor growth and resist cytotoxic therapeutics. The primary objective of this study was to use histone-modifying agents to elucidate mechanisms by which the phenotype and tumor-promoting capacity of GBM-derived neoplastic stem-like cells are regulated. Using established GBM-derived neurosphere lines and low passage primary GBM-derived neurospheres, we show that histone deacetylase (HDAC) inhibitors inhibit growth, induce differentiation, and induce apoptosis of neoplastic neurosphere cells. A specific gene product induced by HDAC inhibition, Delta/Notch-like epidermal growth factor-related receptor (DNER), inhibited the growth of GBM-derived neurospheres, induced their differentiation in vivo and in vitro, and inhibited their engraftment and growth as tumor xenografts. The differentiating and tumor suppressive effects of DNER, a noncanonical Notch ligand, contrast with the previously established tumor-promoting effects of canonical Notch signaling in brain cancer stem-like cells. Our findings are the first to implicate noncanonical Notch signaling in the regulation of neoplastic stem-like cells and suggest novel neoplastic stem cell targeting treatment strategies for GBM and potentially other solid malignancies.

Differentiation of a Highly Tumorigenic Basal Cell Compartment in Urothelial Carcinoma

Stem Cells (Dayton, Ohio). Jul, 2009  |  Pubmed ID: 19544456

Highly tumorigenic cancer cell (HTC) populations have been identified for a variety of solid tumors and assigned stem cell properties. Strategies for identifying HTCs in solid tumors have been primarily empirical rather than rational, particularly in epithelial tumors, which are responsible for 80% of cancer deaths. We report evidence for a spatially restricted bladder epithelial (urothelial) differentiation program in primary urothelial cancers (UCs) and in UC xenografts. We identified a highly tumorigenic UC cell compartment that resembles benign urothelial stem cells (basal cells), co-expresses the 67-kDa laminin receptor and the basal cell-specific cytokeratin CK17, and lacks the carcinoembryonic antigen family member CEACAM6 (CD66c). This multipotent compartment resides at the tumor-stroma interface, is easily identified on histologic sections, and possesses most, if not all, of the engraftable tumor-forming ability in the parental xenograft. We analyzed differential expression of genes and pathways in basal-like cells versus more differentiated cells. Among these, we found significant enrichment of pathways comprising "hallmarks" of cancer, and pharmacologically targetable signaling pathways, including Janus kinase-signal transducer and activator of transcription, Notch, focal adhesion, mammalian target of rapamycin, epidermal growth factor receptor (erythroblastic leukemia viral oncogene homolog [ErbB]), and wingless-type MMTV integration site family (Wnt). The basal/HTC gene expression signature was essentially invisible within the context of nontumorigenic cell gene expression and overlapped significantly with genes driving progression and death in primary human UC. The spatially restricted epithelial differentiation program described here represents a conceptual advance in understanding cellular heterogeneity of carcinomas and identifies basal-like HTCs as attractive targets for cancer therapy.

Cancer Stem Cells: Controversies in Multiple Myeloma

Journal of Molecular Medicine (Berlin, Germany). Nov, 2009  |  Pubmed ID: 19760278

Increasing data suggest that the initiation, relapse, and progression of human cancers are driven by specific cell populations within an individual tumor. However, inconsistencies have emerged in precisely defining phenotypic markers that can reliably identify these "cancer stem cells" in nearly every human malignancy studied to date. Multiple myeloma, one of the first tumors postulated to be driven by a rare population of cancer stem cells, is no exception. Similar to other diseases, controversy surrounds the exact phenotype and biology of multiple myeloma cells with the capacity for clonogenic growth. Here, we review the studies that have led to these controversies and discuss potential reasons for these disparate findings. Moreover, we speculate how these inconsistencies may be resolved through studies by integrating advancements in both myeloma and stem cell biology.

Urothelial Carcinoma: Stem Cells on the Edge

Cancer Metastasis Reviews. Dec, 2009  |  Pubmed ID: 20012172

Tumors are heterogeneous collections of cells with highly variable abilities to survive, grow, and metastasize. This variability likely stems from epigenetic and genetic influences, either stochastic or hardwired by cell type-specific lineage programs. That differentiation underlies tumor cell heterogeneity was elegantly demonstrated in hematopoietic tumors, in which rare primitive cells (cancer stem cells (CSCs)) resembling normal hematopoietic stem cells are ultimately responsible for tumor growth and viability. Because of the compelling clinical implications CSCs pose--across the entire spectrum of cancers--investigators applied the CSC model to cancers arising in tissues with crudely understood differentiation programs. Instead of relying on differentiation, these studies used empirically selected markers and statistical arguments to identify CSCs. The empirical approach has stimulated important questions about "stemness" in cancer cells as well as the validity and stoichiometry of CSC assays. The recent identification of urothelial differentiation programs in urothelial carcinomas (UroCas) supports the idea that solid epithelial cancers (carcinomas) develop and differentiate analogously to normal epithelia and provides new insights about the spatial localization and molecular makeup of carcinoma CSCs. Importantly, CSCs from invasive UroCas (UroCSCs) appear well situated to exchange important signals with adjacent stroma, to escape immune surveillance, and to survive cytotoxic therapy. These signals have potential roles in treatment resistance and many participate in druggable cellular pathways. In this review, we discuss the implications of these findings in understanding CSCs and in better understanding how UroCas form, progress, and should be treated.

High-dose Cyclophosphamide for Severe Aplastic Anemia: Long-term Follow-up

Blood. Mar, 2010  |  Pubmed ID: 20018919

Severe aplastic anemia (SAA) is a life-threatening bone marrow failure disorder that can be treated with bone marrow transplantation, immunosuppressive therapy, and high-dose cyclophosphamide. Here, we report long-term follow-up on 67 SAA patients (44 treatment-naive and 23 refractory) treated with high-dose cyclophosphamide. At 10 years, the overall actuarial survival was 88%, the response rate was 71% with the majority being complete, and the actuarial event-free survival was 58% in 44 treatment-naive SAA patients. Patients with refractory SAA fared less well after high-dose cyclophosphamide therapy; at 10 years, overall actuarial survival, response, and actuarial event-free survival rates were 62%, 48%, and 27%, respectively. High-dose cyclophosphamide is highly effective therapy for severe aplastic anemia. Large randomized controlled trials will be necessary to establish how results of high-dose cyclophosphamide compare with either bone marrow transplantation or standard immunosuppressive regimens, such as antithymocyte globulin and cyclosporine.

Gli1 Regulates the Proliferation and Differentiation of HSCs and Myeloid Progenitors

Blood. Mar, 2010  |  Pubmed ID: 20107231

The Hedgehog (Hh) pathway is essential for normal embryonic development and tissue repair. The role of Hh signaling in hematopoiesis has been studied primarily by modulating the activity of Patched and Smoothened, but results have been conflicting. Some studies demonstrate a requirement for pathway activity in hematopoiesis, whereas others report that it is dispensable. Hh activity converges on the Gli transcription factors, but the specific role of these downstream effectors in hematopoiesis has not been reported. We have analyzed hematopoietic stem cell (HSC) and progenitor function in mice with a homozygous deletion of Gli1 (Gli1(null)). Gli1(null) mice have more long-term HSCs that are more quiescent and show increased engraftment after transplantation. In contrast, myeloid development is adversely affected with decreased in vitro colony formation, decreased in vivo response to granulocyte colony-stimulating factor (G-CSF), and impaired leukocyte recovery after chemotherapy. Levels of the proto-oncogene Cyclin D1 are reduced in Gli1(null) mice and may explain the loss of proliferation seen in HSCs and progenitor cells. These data demonstrate that Gli1 regulates normal and stress hematopoiesis. Moreover, they suggest that Gli1 and Smoothened may not be functionally redundant, and direct GLI1 inhibitors may be needed to effectively block HH/GLI1 activity in human disease.

High-dose Cyclophosphamide As Single-agent, Short-course Prophylaxis of Graft-versus-host Disease

Blood. Apr, 2010  |  Pubmed ID: 20124511

Because of its potent immunosuppressive yet stem cell-sparing activity, high-dose cyclophosphamide was tested as sole prophylaxis of graft-versus-host disease (GVHD) after myeloablative allogeneic bone marrow transplantation (alloBMT). We treated 117 patients (median age, 50 years; range, 21-66 years) with advanced hematologic malignancies; 78 had human leukocyte antigen (HLA)-matched related donors and 39 had HLA-matched unrelated donors. All patients received conventional myeloablation with busulfan/cyclophosphamide (BuCy) and T cell-replete bone marrow followed by 50 mg/kg/d of cyclophosphamide on days 3 and 4 after transplantation. The incidences of acute grades II through IV and grades III through IV GVHD for all patients were 43% and 10%, respectively. The nonrelapse mortality at day 100 and 2 years after transplantation were 9% and 17%, respectively. The actuarial overall survival and event-free survivals at 2 years after transplantation were 55% and 39%, respectively, for all patients and 63% and 54%, respectively, for patients who underwent transplantation while in remission. With a median follow-up of 26.3 months among surviving patients, the cumulative incidence of chronic GVHD is 10%. These results suggest that high-dose posttransplantation cyclophosphamide is an effective single-agent prophylaxis of acute and chronic GVHD after BuCy conditioning and HLA-matched BMT (clinicaltrials.gov no. NCT00134017).

Prognostic Significance of Tumorigenic Cells with Mesenchymal Features in Pancreatic Adenocarcinoma

Journal of the National Cancer Institute. Mar, 2010  |  Pubmed ID: 20164446

Specific populations of highly tumorigenic cells are thought to exist in many human tumors, including pancreatic adenocarcinoma. However, the clinical significance of these tumor-initiating (ie, cancer stem) cells remains unclear. Aldehyde dehydrogenase (ALDH) activity can identify tumor-initiating cells and normal stem cells from several human tissues. We examined the prognostic significance and functional features of ALDH expression in pancreatic adenocarcinoma.

Multiple Myeloma: a Paradigm for Translation of the Cancer Stem Cell Hypothesis

Anti-cancer Agents in Medicinal Chemistry. Feb, 2010  |  Pubmed ID: 20184542

Despite recent advances in drug development, multiple myeloma (MM) remains incurable for the majority of patients due to relapse and disease progression. The cancer stem cell (CSC) hypothesis may provide an explanation for these clinical findings. It suggests that the long-term proliferative potential responsible for disease initiation, maintenance, and relapse is contained within specific subpopulations of biologically distinct tumor cells. Data in MM suggest that CSCs represent a rare cell population phenotypically resembling normal memory B cells. Compared to MM plasma cells, MM CSCs also appear to be relatively resistant to a wide variety of standard anti-cancer agents suggesting they may persist following treatment and mediate tumor re-growth and relapse. A unique property CSCs share with their normal counterparts is the potential for self-renewal that likely maintains the malignant clone over time. The development of therapeutic strategies targeting the signaling elements contributing to cancer cell self-renewal has been limited primarily because the cellular processes involved are poorly understood. However, it is common that the signaling pathway components regulating normal stem cell self-renewal are aberrantly activated in human cancers and may serve as potential therapeutic targets. One class of shared regulatory pathways are those active during normal embryonic patterning and organ formation such as Hedgehog (Hh), Notch and Wingless (Wnt), and emerging data suggest that these may play a role in CSCs. Here we review the identification and characterization of MM CSCs, the role of Hh in MM, and issues to be considered during the early clinical testing of CSC targeting agents.

Targeting Hedgehog--a Cancer Stem Cell Pathway

Clinical Cancer Research : an Official Journal of the American Association for Cancer Research. Jun, 2010  |  Pubmed ID: 20530699

The Hedgehog (Hh) pathway has been implicated in a wide variety of human tumors, and early clinical trials with pathway antagonists have validated Hh signaling as a bona fide anticancer target. Despite these encouraging results, several issues surrounding the basic biology of the Hh pathway in human cancers remain unclear. These include the influence of specific oncogenic events on Hh signal transduction, the precise mode of Hh signaling (i.e., autocrine or paracrine) that occurs within human tumors, and the best means to inhibit aberrant pathway activity in the clinical setting. The cancer stem cell (CSC) hypothesis may explain a number of clinical phenomena, such as unchecked self-renewal and the development of metastatic disease, and to some extent, the Hh signaling pathway has been implicated in all of these processes. Therefore, Hh pathway inhibitors may also represent some of the first agents to formally examine the CSC hypothesis in the clinical setting. The diverse nature of Hh signaling in human cancers suggests that disease-specific factors must be carefully considered to identify the optimal use of novel pathway inhibitors.

Mantle Cell Lymphoma Activation Enhances Bortezomib Sensitivity

Blood. Nov, 2010  |  Pubmed ID: 20570863

Patients with mantle cell lymphoma (MCL) typically respond to initial treatment but subsequently relapse. This pattern suggests that a population of MCL cells is both drug resistant and capable of clonogenic growth. The intracellular enzyme retinaldehyde dehydrogenase (ALDH) provides resistance to several toxic agents. ALDH can also identify stem cells in normal adult tissues and tumorigenic cancer stem cells in several human malignancies. We studied ALDH expression in MCL and found small populations of ALDH(+) cells that were highly clonogenic. Moreover, ALDH(+) MCL cells were relatively quiescent and resistant to a wide range of agents. Normal B cells can be activated by specific unmethylated cytosine-phosphate-guanosine (CpG) DNA motifs through toll-like receptor 9, and we found that the synthetic CpG oligonucleotide 2006 (CpG) reduced the frequency of quiescent ALDH(+) MCL cells, induced terminal plasma cell differentiation, and limited tumor formation in vitro and in vivo. Treatment with CpG also significantly enhanced the activity of the proteasome inhibitor bortezomib that was associated with induction of the unfolded protein response. Our data suggest that CpG may target clonogenic and resistant ALDH(+) cells as well as improve the activity of proteasome inhibitors in MCL.

Hedgehog Signaling in Hematopoiesis

Critical Reviews in Eukaryotic Gene Expression. 2010  |  Pubmed ID: 21133842

The Hedgehog signaling pathway is highly conserved and plays an essential role in the embryonic development of a wide variety of organs. In adult tissues, such as the central nervous system, it may also be required for homeostasis and repair following injury. The role of Hedgehog signaling in regulating hematopoiesis is not entirely clear. Evidence has shown that Hedgehog signaling is required for both primitive hematopoiesis in the developing embryo, as well as for definitive hematopoiesis in the adult. However, several studies also suggest that Hedgehog pathway activity is completely dispensable in postnatal hematopoiesis. In this review, we discuss the current understanding of Hedgehog signaling in vertebrate hematopoiesis, as well as the contradictory findings that have been reported.

Self-renewal of Acute Lymphocytic Leukemia Cells is Limited by the Hedgehog Pathway Inhibitors Cyclopamine and IPI-926

PloS One. 2010  |  Pubmed ID: 21203400

Conserved embryonic signaling pathways such as Hedgehog (Hh), Wingless and Notch have been implicated in the pathogenesis of several malignancies. Recent data suggests that Hh signaling plays a role in normal B-cell development, and we hypothesized that Hh signaling may be important in precursor B-cell acute lymphocytic leukemia (B-ALL). We found that the expression of Hh pathway components was common in human B-ALL cell lines and clinical samples. Moreover, pathway activity could be modulated by Hh ligand or several pathway inhibitors including cyclopamine and the novel SMOOTHENED (SMO) inhibitor IPI-926. The inhibition of pathway activity primarily impacted highly clonogenic B-ALL cells expressing aldehyde dehydrogenase (ALDH) by limiting their self-renewal potential both in vitro and in vivo. These data demonstrate that Hh pathway activation is common in B-ALL and represents a novel therapeutic target regulating self-renewal and persistence of the malignant clone.

A Combination of DR5 Agonistic Monoclonal Antibody with Gemcitabine Targets Pancreatic Cancer Stem Cells and Results in Long-term Disease Control in Human Pancreatic Cancer Model

Molecular Cancer Therapeutics. Sep, 2010  |  Pubmed ID: 20660600

Pancreatic ductal adenocarcinoma (PDA) is an aggressive malignancy with one of the worst outcomes among all cancers. PDA often recurs after initial treatment to result in patient death despite the use of chemotherapy or radiation therapy. PDA contains a subset of tumor-initiating cells capable of extensive self-renewal known as cancer stem cells (CSC), which may contribute to therapeutic resistance and metastasis. At present, conventional chemotherapy and radiotherapy are largely ineffective in depleting CSC pool, suggesting the need for novel therapies that specifically target the cancer-sustaining stem cells for tumor eradication and to improve the poor prognosis of PDA patients. In this study, we report that death receptor 5 (DR5) is enriched in pancreatic CSCs compared with the bulk of the tumor cells. Treating a collection of freshly generated patient-derived PDA xenografts with gemcitabine, the first-line chemotherapeutic agent for PDA, is initially effective in reducing tumor size, but largely ineffective in diminishing the CSC populations, and eventually culminated in tumor relapse. However, a combination of tigatuzumab, a fully humanized DR5 agonist monoclonal antibody, with gemcitabine proved to be more efficacious by providing a double hit to kill both CSCs and bulk tumor cells. The combination therapy produced remarkable reduction in pancreatic CSCs, tumor remissions, and significant improvements in time to tumor progression in a model that is considered more difficult to treat. These data provide the rationale to explore the DR5-directed therapies in combination with chemotherapy as a therapeutic option to improve the current standard of care for pancreatic cancer patients.

Hypoxia Increases the Expression of Stem-cell Markers and Promotes Clonogenicity in Glioblastoma Neurospheres

The American Journal of Pathology. Sep, 2010  |  Pubmed ID: 20671264

Hypoxia promotes the expansion of non-neoplastic stem and precursor cell populations in the normal brain, and is common in malignant brain tumors. We examined the effects of hypoxia on stem-like cells in glioblastoma (GBM). When GBM-derived neurosphere cultures are grown in 1% oxygen, hypoxia-inducible factor 1alpha (HIF1alpha) protein levels increase dramatically, and mRNA encoding other hypoxic response genes, such as those encoding hypoxia-inducible gene-2, lysyl oxidase, and vascular endothelial growth factor, are induced over 10-fold. Hypoxia increases the stem-like side population over fivefold, and the percentage of cells expressing CD133 threefold or more. Notch pathway ligands and targets are also induced. The rise in the stem-like fraction in GBM following hypoxia is paralleled by a twofold increase in clonogenicity. We believe HIF1alpha plays a causal role in these changes, as when oxygen-stable HIF1alpha is expressed in normoxic glioma cells CD133 is induced. We used digoxin, which has been shown to lower HIF protein levels in vitro and in vivo, to inhibit the hypoxic response. Digoxin suppressed HIF1alpha protein expression, HIF1alpha downstream targets, and slowed tumor growth in vivo. In addition, pretreatment with digoxin reduced GBM flank xenograft engraftment of hypoxic GBM cells, and daily intraperitoneal injections of digoxin were able to significantly inhibit the growth of established subcutaneous glioblastoma xenografts, and suppressed expression of vascular endothelial growth factor.

Tumor-initiating Cells Are Rare in Many Human Tumors

Cell Stem Cell. Sep, 2010  |  Pubmed ID: 20804964

Tumor-initiating cells (TICs) are defined by their ability to form tumors after xenotransplantation in immunodeficient mice and appear to be relatively rare in most human cancers. Recent data in melanoma indicate that the frequency of TICs increases dramatically via more permissive xenotransplantation conditions, raising the possibility that the true frequency of TICs has been greatly underestimated in most human tumors. We compared the growth of human pancreatic, non-small cell lung, and head and neck carcinomas in NOD/SCID and NSG mice. Although TIC frequency was detected up to 10-fold higher in NSG mice, it remained low (<1 in 2500 cells) in all cases. Moreover, aldehyde dehydrogenase-positive (ALDH(+)) and CD44(+)CD24(+) cells, phenotypically distinct cells enriched in TICs, were equally tumorigenic in NOD/SCID and NSG mice. Our findings demonstrate that TICs are rare in these cancers and that the identification of TICs and their frequency in other human malignancies should be validated via primary tumors and highly permissive xenotransplantation conditions.

Telomerase Inhibition Targets Clonogenic Multiple Myeloma Cells Through Telomere Length-dependent and Independent Mechanisms

PloS One. 2010  |  Pubmed ID: 20824134

Plasma cells constitute the majority of tumor cells in multiple myeloma (MM) but lack the potential for sustained clonogenic growth. In contrast, clonotypic B cells can engraft and recapitulate disease in immunodeficient mice suggesting they serve as the MM cancer stem cell (CSC). These tumor initiating B cells also share functional features with normal stem cells such as drug resistance and self-renewal potential. Therefore, the cellular processes that regulate normal stem cells may serve as therapeutic targets in MM. Telomerase activity is required for the maintenance of normal adult stem cells, and we examined the activity of the telomerase inhibitor imetelstat against MM CSC. Moreover, we carried out both long and short-term inhibition studies to examine telomere length-dependent and independent activities.

Cancer-related Epigenome Changes Associated with Reprogramming to Induced Pluripotent Stem Cells

Cancer Research. Oct, 2010  |  Pubmed ID: 20841480

The ability to induce pluripotent stem cells from committed, somatic human cells provides tremendous potential for regenerative medicine. However, there is a defined neoplastic potential inherent to such reprogramming that must be understood and may provide a model for understanding key events in tumorigenesis. Using genome-wide assays, we identify cancer-related epigenetic abnormalities that arise early during reprogramming and persist in induced pluripotent stem cell (iPS) clones. These include hundreds of abnormal gene silencing events, patterns of aberrant responses to epigenetic-modifying drugs resembling those for cancer cells, and presence in iPS and partially reprogrammed cells of cancer-specific gene promoter DNA methylation alterations. Our findings suggest that by studying the process of induced reprogramming, we may gain significant insight into the origins of epigenetic gene silencing associated with human tumorigenesis, and add to means of assessing iPS for safety.

Nonmyeloablative HLA-haploidentical Bone Marrow Transplantation with High-dose Posttransplantation Cyclophosphamide: Effect of HLA Disparity on Outcome

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Apr, 2010  |  Pubmed ID: 19925877

Although some reports have found an association between increasing HLA disparity between donor and recipient and fewer relapses after allogeneic blood or marrow transplantation (BMT), this potential benefit has been offset by more graft-versus-host disease (GVHD) and nonrelapse mortality (NRM). However, the type of GVHD prophylaxis might influence the balance between GVHD toxicity and relapse. The present study analyzed the impact of greater HLA disparity on outcomes of a specific platform for nonmyeloablative (NMA), HLA-haploidentical transplantation. A retrospective analysis was performed of 185 patients with hematologic malignancies enrolled in 3 similar trials of NMA, related donor, haploidentical BMT incorporating high-dose posttransplantation cyclophosphamide for GVHD prophylaxis. No significant association was found between the number of HLA mismatches (HLA-A, -B, -Cw, and -DRB1 combined) and risk of acute grade II-IV GVHD (hazard ratio [HR] = 0.89; P = .68 for 3-4 vs fewer antigen mismatches). More mismatching also had no detrimental effect on event-free survival (on multivariate analysis, HR = 0.60, P = .03 for 3-4 vs fewer antigen mismatches and HR = 0.55, P = .03 for 3-4 vs fewer allele mismatches). Thus, greater HLA disparity does not appear to worsen overall outcome after NMA haploidentical BMT with high-dose posttransplantation cyclophosphamide.

Characterization of Chronic Myeloid Leukemia Stem Cells

American Journal of Hematology. Jan, 2011  |  Pubmed ID: 21132730

Although tyrosine kinase inhibitors have redefined the care of chronic myeloid leukemia (CML), these agents have not proved curative, likely due to resistance of the leukemia stem cells (LSC). While a number of potential therapeutic targets have emerged in CML, their expression in the LSC remains largely unknown. We therefore isolated subsets of CD34(+) stem/progenitor cells from normal donors and from patients with chronic phase or blast crisis CML. These cell subsets were then characterized based on ability to engraft immunodeficient mice and expression of candidate therapeutic targets. The CD34(+)CD38(-) CML cell population with high aldehyde dehydrogenase (ALDH) activity was the most enriched for immunodeficient mouse engrafting capacity. The putative targets: PROTEINASE 3, SURVIVIN, and hTERT were expressed only at relatively low levels by the CD34(+)CD38(-)ALDH(high) CML cells, similar to the normal CD34(+)CD38(-)ALDH(high) cells and less than in the total CML CD34(+) cells. In fact, the highest expression of these antigens was in normal, unfractionated CD34(+) cells. In contrast, PRAME and WT1 were more highly expressed by all CML CD34(+) subsets than their normal counterparts. Thus, ALDH activity appears to enrich for CML stem cells, which display an expression profile that is distinct from normal stem/progenitor cells and even the CML progenitors. Indeed, expression of a putative target by the total CD34(+) population in CML does not guarantee expression by the LSC. These expression patterns suggest that PROTEINASE 3, SURVIVIN, and hTERT are not optimal therapeutic targets in CML stem cells; whereas PRAME and WT1 seem promising.

Concise Review: Emerging Concepts in Clinical Targeting of Cancer Stem Cells

Stem Cells (Dayton, Ohio). Jun, 2011  |  Pubmed ID: 21509907

Cancer stem cells (CSCs) are functionally defined by their ability to self-renew and recapitulate tumors in the ectopic setting. They have been identified in a growing number of human malignancies and their association with poor clinical outcomes has suggested that they are the major factors in dictating clinical outcomes. Moreover, recent studies have demonstrated that CSCs may display other functional attributes, such as drug resistance and invasion and migration, that implicate a broad role in clinical oncology spanning initial tumor formation, relapse following treatment, and disease progression. Although our knowledge regarding the basic biology of CSCs continues to improve, proof that they are clinically relevant is still lacking, and translation of the CSC hypothesis from the laboratory to the clinic is of paramount importance. We will review current evidence supporting the role of CSCs in clinical oncology and discuss potential barriers and strategies in designing trials examining CSC-targeting agents.

Development and Maintenance of Cancer Stem Cells Under Chronic Inflammation

Journal of Nihon Medical School = Nihon Ika Daigaku Zasshi. 2011  |  Pubmed ID: 21720087

In many human cancers, tumorigenic potential is not equally shared by all cells but is restricted to phenotypically distinct subpopulations termed cancer stem cells. Cancer stem cells are also capable of both self-renewal and differentiation, and these functional properties have been suggested to play major roles in tumor initiation and progression. The factors responsible for the development of cancer stem cells and their subsequent regulation are unclear, but several chronic inflammatory states have been associated with an increased risk of malignancy. Therefore, it is possible that specific processes associated with chronic inflammation, as well as the adaptation to cellular stress, regulate cancer stem cells. Several factors associated with chronic inflammation, including cytokines, oxidative stress, and hypoxia, induce the activation of specific cellular response programs that can affect the survival, proliferation, metabolism, and differentiation of cancer cells, as well as the self-renewal and quiescence of normal stem cells. In this review, we discuss how these adaptive processes potentially become subverted to enhance the development and function of cancer stem cells.

High-dose Cyclophosphamide and Rituximab Without Stem Cell Transplant: a Feasibility Study for Low Grade B-cell, Transformed and Mantle Cell Lymphomas

Leukemia & Lymphoma. Nov, 2011  |  Pubmed ID: 21756035

Relapse after autologous stem cell transplant for low grade B-cell lymphoma is common secondary to ineffective conditioning and/or tumor autograft contamination. We investigated high-dose cyclophosphamide and rituximab without stem cell rescue as first-line or salvage therapy in lymphomas. After establishing safety, accrual was increased to evaluate event-free survival (EFS). Eighty-one adults received rituximab (375 mg/m(2) days 1, 4, 8, 11, 45, 52), cyclophosphamide (50 mg/kg days 15-18), and pegfilgrastim (day 20). Forty-two patients had low grade B-cell lymphoma [grade I/II follicular (69%), transformed lymphoma (17%), other (15%)]: 45% were treated without measurable disease. Thirty-nine patients had mantle cell lymphoma: 82% were treated without measurable disease. All achieved hematopoietic recovery; 46% required brief hospitalizations. The 5-year EFS and overall survival (OS) for patients with low grade B-cell and transformed lymphoma were 40% and 72%, respectively. The 5-year EFS and OS for patients with MCL were 39% and 62%, respectively. This low-toxicity therapeutic approach obviates the need for stem cell products and establishes a platform for future therapies.

Cyclin-dependent Kinase Inhibitor Dinaciclib (SCH727965) Inhibits Pancreatic Cancer Growth and Progression in Murine Xenograft Models

Cancer Biology & Therapy. Oct, 2011  |  Pubmed ID: 21768779

Pancreatic cancer is one of the most lethal of human malignancies, and potent therapeutic options are lacking. Inhibition of cell cycle progression through pharmacological blockade of cyclin-dependent kinases (CDK) has been suggested as a potential treatment option for human cancers with deregulated cell cycle control. Dinaciclib (SCH727965) is a novel small molecule multi-CDK inhibitor with low nanomolar potency against CDK1, CDK2, CDK5 and CDK9 that has shown favorable toxicity and efficacy in preliminary mouse experiments, and has been well tolerated in Phase I clinical trials. In the current study, the therapeutic efficacy of SCH727965 on human pancreatic cancer cells was tested using in vitro and in vivo model systems. Treatment with SCH727965 significantly reduced in vitro cell growth, motility and colony formation in soft agar of MIAPaCa-2 and Pa20C cells. These phenotypic changes were accompanied by marked reduction of phosphorylation of Retinoblastoma (Rb) and reduced activation of RalA. Single agent therapy with SCH727965 (40 mg/kg i.p. twice weekly) for 4 weeks significantly reduced subcutaneous tumor growth in 10/10 (100%) of tested low-passage human pancreatic cancer xenografts. Treatment of low passage pancreatic cancer xenografts with a combination of SCH727965 and gemcitabine was significantly more effective than either agent alone. Gene Set Enrichment Analysis identified overrepresentation of the Notch and Transforming Growth Factor-β (TGF-β) signaling pathways in the xenografts least responsive to SCH727965 treatment. Treatment with the cyclin-dependent kinase inhibitor SCH727965 alone or in combination is a highly promising novel experimental therapeutic strategy against pancreatic cancer.

The Redox-sensitive Transcription Factor Nrf2 Regulates Murine Hematopoietic Stem Cell Survival Independently of ROS Levels

Blood. Dec, 2011  |  Pubmed ID: 22039262

Several studies have found that high levels of reactive oxidative species (ROS) are associated with stem cell dysfunction. In the present study, we investigated the role of nuclear factor erythroid-2-related factor 2 (Nrf2), a master regulator of the antioxidant response, and found that it is required for hematopoietic stem progenitor cell (HSPC) survival and myeloid development. Although the loss of Nrf2 leads to increased ROS in most tissues, basal ROS levels in Nrf2-deficient (Nrf2(-/-)) BM were not elevated compared with wild-type. Nrf2(-/-) HSPCs, however, had increased rates of spontaneous apoptosis and showed decreased survival when exposed to oxidative stress. Nrf2(-/-) BM demonstrated defective stem cell function, as evidenced by reduced chimerism after transplantation that was not rescued by treatment with the antioxidant N-acetyl cysteine. Gene-expression profiling revealed that the levels of prosurvival cytokines were reduced in Nrf2(-/-) HSPCs. Treatment with the cytokine G-CSF improved HSPC survival after exposure to oxidative stress and rescued the transplantation defect in Nrf2(-/-) cells despite increases in ROS induced by cytokine signaling. These findings demonstrate a critical role for Nrf2 in hematopoiesis and stem cell survival that is independent of ROS levels.

Perspective: A Model Disease

Nature. Dec, 2011  |  Pubmed ID: 22169808

Differentiation Therapy in Poor Risk Myeloid Malignancies: Results of a Dose Finding Study of the Combination Bryostatin-1 and GM-CSF

Leukemia Research. Jan, 2011  |  Pubmed ID: 20598742

Pharmacologic differentiating agents have had relatively limited clinical success outside of the use of ATRA in acute promyelocytic leukemia and DNA methyltransferase inhibitors in myelodysplastic syndromes. The differentiating effects of such agents can be enhanced in combination with lineage-specific growth factors. We developed a dose finding trial to assess toxicity, differentiating activity, and clinical impact of the combination of bryostatin-1 and GM-CSF.

Autologous Stem Cell Transplantation and Multiple Myeloma Cancer Stem Cells

Biology of Blood and Marrow Transplantation : Journal of the American Society for Blood and Marrow Transplantation. Jan, 2012  |  Pubmed ID: 22226109

It is well established that high-dose therapy (HDT) combined with autologous stem cell transplantation (ASCT) produces superior response rates and progression-free survival compared with conventional chemotherapy in patients with multiple myeloma (MM). Accordingly, MM currently represents the most common indication for ASCT. Despite these clinical improvements, the impact of ASCT on overall survival is unclear because the vast majority of patients eventually experience disease relapse and progression. The continual risk of relapse suggests that malignant cells resistant to HDT possess the clonogenic growth potential to mediate tumor regrowth, and in several diseases cancer stem cells (CSCs) have been identified that are both highly tumorigenic and resistant to standard anticancer approaches. Putative CSCs have been identified in MM, and their characterization may lead to the development of novel maintenance strategies that inhibit the production of new tumor cells, prevent disease relapse, and improve overall survival.

Cancer Stem Cells: Relevance to Clinical Transplantation

Current Opinion in Oncology. Mar, 2012  |  Pubmed ID: 22314617

Despite blood or marrow transplantation (BMT) being arguably the most active modality against hematologic malignancies, relapses remain the major reason for failure. Many cancers have now been shown to harbor cells that are phenotypically and biologically similar to normal cells with self-renewal capacity; these so-called cancer stem cells (CSCs) typically constitute only a small fraction of the total tumor burden, but are hypothesized to be responsible for relapse after conventional-dose therapy. Here, we review whether CSCs may have relevance to BMT.

Biological and Clinical Relevance of Stem Cells in Pancreatic Adenocarcinoma

Journal of Gastroenterology and Hepatology. Mar, 2012  |  Pubmed ID: 22320910

Cancer stem cells (CSC) have been identified in a growing number of human malignancies. CSC are functionally defined by their ability to self-renew and recapitulate tumors in the ectopic setting, and a growing number of studies have shown that they display other functional characteristics, such as invasion and drug resistance. These unique functional properties implicate a role for CSC in clinical consequences, such as initial tumor formation, relapse following treatment, metastasis, and resistance, suggesting they are a major factor in directing clinical outcomes. Pancreatic adenocarcinoma is a highly-aggressive disease with a propensity for early metastasis and drug resistance. Tumorigenic pancreatic cancer cells have been identified using the cell surface antigens CD44, CD24, and CD133, as well as the high expression of aldehyde dehydrogenase (ALDH). In vitro and in vivo studies have shown that ALDH- and CD133-expressing pancreatic CSC have a greater propensity for metastasis, and ALDH-expressing CSC have been shown to be resistant to conventional chemotherapy. In clinical samples from patients with resected pancreatic adenocarcinoma, the presence of ALDH-expressing CSC was associated with worse overall survival. The development of CSC-targeting therapies might be important in changing the clinical outcomes of patients with this disease, and others and we have begun to identify novel compounds that block CSC function. This review will discuss the biological and clinical relevance of CSC in pancreatic cancer, and will discuss novel therapeutic strategies to target them.