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Metabolic Mapping: Quantitative Enzyme Cytochemistry and Histochemistry to Determine the Activity of Dehydrogenases in Cells and Tissues

Altered cellular metabolism is a hallmark of many diseases, including cancer, cardiovascular diseases and infection. The metabolic motor units of cells ...

University of Amsterdam, Amsterdam, The Netherlands

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are key events in the development of glioma, acute myeloid leukemia (AML), chondrosarcoma, intrahepatic cholangiocarcinoma (ICC), and angioimmunoblastic T-cell lymphoma. They also cause D-2-hydroxyglutaric aciduria and Ollier and Maffucci syndromes. IDH1/2 mutations are associated with prolonged survival in glioma and in ICC, but not in AML. The reason for this is unknown. In their wild-type forms, IDH1 and IDH2 convert isocitrate and NADP(+) to α-ketoglutarate (αKG) and NADPH. Missense mutations in the active sites of these enzymes induce a neo-enzymatic reaction wherein NADPH reduces αKG to D-2-hydroxyglutarate (D-2HG). The resulting D-2HG accumulation leads to hypoxia-inducible factor 1α degradation, and changes in epigenetics and extracellular matrix homeostasis. Such mutations also imply less NADPH production capacity. Each of these effects could play a role in cancer formation. Here, we provide an overview of the literature and discuss which downstream molecular effects are likely to be the drivers of the oncogenic and survival-prolonging properties of IDH1/2 mutations. We discuss interactions between mutant IDH1/2 inhibitors and conventional therapies. Understanding of the biochemical consequences of IDH1/2 mutations in oncogenesis and survival prolongation will yield valuable information for rational therapy design: it will tell us which oncogenic processes should be blocked and which "survivalogenic" effects should be retained. 

The driver and passenger effects of isocitrate dehydrogenase 1 and 2 mutations in oncogenesis and survival prolongation.

Type 2 diabetes and cancer as redox diseases?

Acute myeloid leukemia and acute lymphoblastic leukemia cells hijack hematopoietic stem cell (HSC) niches in the bone marrow and become leukemic stem cells (LSCs) at the expense of normal HSCs. LSCs are quiescent and resistant to chemotherapy and can cause relapse of the disease. HSCs in niches are needed to generate blood cell precursors that are committed to unilineage differentiation and eventually production of mature blood cells, including red blood cells, megakaryocytes, myeloid cells and lymphocytes. Thus far, three types of HSC niches are recognized: endosteal, reticular and perivascular niches. However, we argue here that there is only one type of HSC niche, which consists of a periarteriolar compartment and a perisinusoidal compartment. In the periarteriolar compartment, hypoxia and low levels of reactive oxygen species preserve the HSC pool. In the perisinusoidal compartment, hypoxia in combination with higher levels of reactive oxygen species enables proliferation of progenitor cells and their mobilization into the circulation. Because HSC niches offer protection to LSCs against chemotherapy, we review novel therapeutic strategies to inhibit homing of LSCs in niches for the prevention of dedifferentiation of leukemic cells into LSCs and to stimulate migration of leukemic cells out of niches. These strategies enhance differentiation and proliferation and thus sensitize leukemic cells to chemotherapy. Finally, we list clinical trials of therapies that tackle LSCs in HSC niches to circumvent their protection against chemotherapy.

Article	Year
The driver and passenger effects of isocitrate dehydrogenase 1 and 2 mutations in oncogenesis and survival prolongation. Biochimica et biophysica acta\| PubMed ID: 24880135	2014
Type 2 diabetes and cancer as redox diseases? Lancet (London, England)\| PubMed ID: 25209484	2014
Novel therapeutic strategies to target leukemic cells that hijack compartmentalized continuous hematopoietic stem cell niches. Biochimica et biophysica acta\| PubMed ID: 28363872	2017

Remco J. Molenaar

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