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In JoVE (1)
Other Publications (3)
Articles by Kaushal Joshi in JoVE
JoVE Clinical and Translational Medicine
Method for Novel Anti-Cancer Drug Development using Tumor Explants of Surgical Specimens
1Department of Neurological Surgery, The Ohio State University Medical Center, 2Department of Pathology, The Ohio State University Medical Center
Here, we established a method for drug efficacy testing with surgical specimens of brain tumors, termed “tumor explant method”. With this method, we can evaluate drug efficacy without breaking the microenvironment of solid tumors. To validate reliability of this method, we describe representative data with our glioma specimen treated with the current first-line chemotherapeutic agent, temozolomide.
Other articles by Kaushal Joshi on PubMed
Siomycin A Targets Brain Tumor Stem Cells Partially Through a MELK-mediated Pathway
Glioblastoma multiforme (GBM) is a devastating disease, and the current therapies have only palliative effect. Evidence is mounting to indicate that brain tumor stem cells (BTSCs) are a minority of tumor cells that are responsible for cancer initiation, propagation, and maintenance. Therapies that fail to eradicate BTSCs may ultimately lead to regrowth of residual BTSCs. However, BTSCs are relatively resistant to the current treatments. Development of novel therapeutic strategies that effectively eradicate BTSC are, therefore, essential. In a previous study, we used patient-derived GBM sphere cells (stemlike GBM cells) to enrich for BTSC and identified maternal embryonic leucine-zipper kinase (MELK) as a key regulator of survival of stemlike GBM cells in vitro. Here, we demonstrate that a thiazole antibiotic, siomycin A, potently reduced MELK expression and inhibited tumor growth in vivo. Treatment of stemlike GBM cells with siomycin A resulted in arrested self-renewal, decreased invasion, and induced apoptosis but had little effect on growth of the nonstem cells of matched tumors or normal neural stem/progenitor cells. MELK overexpression partially rescued the phenotype of siomycin A-treated stemlike GBM cells. In vivo, siomycin A pretreatment abraded the sizes of stemlike GBM cell-derived tumors in immunodeficient mice. Treatment with siomycin A of mice harboring intracranial tumors significantly prolonged their survival period compared with the control mice. Together, this study may be the first model to partially target stemlike GBM cells through a MELK-mediated pathway with siomycin A to pave the way for effective treatment of GBM.
CD44v6 Regulates Growth of Brain Tumor Stem Cells Partially Through the AKT-mediated Pathway
Identification of stem cell-like brain tumor cells (brain tumor stem-like cells; BTSC) has gained substantial attention by scientists and physicians. However, the mechanism of tumor initiation and proliferation is still poorly understood. CD44 is a cell surface protein linked to tumorigenesis in various cancers. In particular, one of its variant isoforms, CD44v6, is associated with several cancer types. To date its expression and function in BTSC is yet to be identified. Here, we demonstrate the presence and function of the variant form 6 of CD44 (CD44v6) in BTSC of a subset of glioblastoma multiforme (GBM). Patients with CD44(high) GBM exhibited significantly poorer prognoses. Among various variant forms, CD44v6 was the only isoform that was detected in BTSC and its knockdown inhibited in vitro growth of BTSC from CD44(high) GBM but not from CD44(low) GBM. In contrast, this siRNA-mediated growth inhibition was not apparent in the matched GBM sample that does not possess stem-like properties. Stimulation with a CD44v6 ligand, osteopontin (OPN), increased expression of phosphorylated AKT in CD44(high) GBM, but not in CD44(low) GBM. Lastly, in a mouse spontaneous intracranial tumor model, CD44v6 was abundantly expressed by tumor precursors, in contrast to no detectable CD44v6 expression in normal neural precursors. Furthermore, overexpression of mouse CD44v6 or OPN, but not its dominant negative form, resulted in enhanced growth of the mouse tumor stem-like cells in vitro. Collectively, these data indicate that a subset of GBM expresses high CD44 in BTSC, and its growth may depend on CD44v6/AKT pathway.
Telomestatin Impairs Glioma Stem Cell Survival and Growth Through the Disruption of Telomeric G-quadruplex and Inhibition of the Proto-oncogene, C-Myb
PURPOSE: Glioma stem cells (GSCs) are a critical therapeutic target of glioblastoma multiforme (GBM). EXPERIMENTAL DESIGN: The effects of a G-quadruplex ligand, telomestatin (TMS), were evaluated using patient-derived GSCs, non-stem tumor cells (non-GSCs), and normal fetal neural precursors in vitro and in vivo. The molecular targets of TMS were determined by immunofluorescence in situ hybridization (iFISH) and cDNA microarray. The data was then validated by in vitro and in vivo functional assays, as well as by immunohistochemistry against 90 clinical samples.RESULTS: TMS impaired the maintenance of GSC stem cell-state by inducing apoptosis in vitro and in vivo. The migration potential of GSCs was also impaired by TMS treatment. In contrast, both normal neural precursors and non-GSCs were relatively resistant to TMS. Treatment of GSC-derived mouse intracranial tumors reduced tumor sizes in vivo without a noticeable cell death in normal brains. iFISH revealed both telomeric and non-telomeric DNA damage by TMS in GSCs but not in non-GSCs. cDNA microarray identified a proto-oncogene, c-Myb, as a novel molecular target of TMS in GSCs and pharmacodynamic analysis in TMS-treated tumor-bearing mouse brains demonstrated a reduction of c-Myb in tumors in vivo. Knockdown of c-Myb phenocopied TMS-treated GSCs both in vitro and in vivo, and restoring c-Myb by overexpression partially rescued the phenotype. Lastly, c-Myb expression was markedly elevated in surgical specimens of GBM compared to normal tissues. CONCLUSIONS: These data indicate that TMS potently eradicates GSCs through telomere disruption and c-Myb inhibition, and this study suggests a novel GSC-directed therapeutic strategy for GBM.
