Vascular-endothelial response to IDH1 mutant fibrosarcoma secretome and metabolite: implications on cancer microenvironment.

Isocitrate dehydrogenases (IDHs) are enzymes involved in the production of α-ketoglutarate (αkg) in normal cellular metabolism. Cells with IDH mutations reduce αkg to 2-hydroxyglutarate (2HG), an oncometabolite, and 2HG directly transforms normal cells to malignant cells through histone demethylation and epigenetic dysregulation. However, whether IDH mutations affect cancer stromal cells is elusive, and little is known whether 2HG may impact the tumor microenvironment. We hypothesized that the IDH mutant cancer secretome and metabolites would stimulate primitive vascular-endothelial genesis. The secretome of IDH1 mutant human fibrosarcoma cells was harvested following medium starvation and was used to treat vascular-endothelial cells using a tube formation assay. GSK864, an allosteric IDH1 inhibitor, was supplemented to the fibrosarcoma secretome to determine its effects on vascular-endothelial tube formation. Exogenous 2HG or as supplemented in the GSK864-treated secretome was applied to further induce vascular-endothelial perturbation. Total vascular-endothelial tube lengths were quantified using NIH/Image J. Two-sided Student's t-tests and Mann-Whitney U tests were used for statistical analysis. The IDH1 mutant fibrosarcoma secretome stimulated vascular-endothelial tube formation by ~138% relative to control. Remarkably, GSK864 attenuated vascular-endothelial tube formation by ~36%, but 2HG not only reversed GSK864 attenuation of tube formation, but also significantly stimulated vascular-endothelial tubes in the GSK864-treated fibrosarcoma secretome. Importantly, 2HG alone augmented vascular-endothelial tube formation that was equivalent to the fibrosarcoma secretome. Thus, 2HG stimulates vascular-endothelial genesis in conjunction with the fibrosarcoma secretome, despite pre-emptive inhibition of IDH1 mutation with GSK864, suggesting that 2HG enables oncogenic angiogenesis via paracrine signaling. Stimulation of vascular-endothelial genesis by 2HG alone, independent of the cancer secretome, suggests that 2HG also activates oncogenic angiogenic pathways in cancer stromal cells. Thus, the IDH mutant cancer secretome stimulates primitive oncogenic angiogenesis through 2HG and/or paracrine pathways. Taken together, these findings suggest novel mechanisms by which the IDH mutant cancer secretome and/or metabolite, specifically 2HG, interacts with the tumor microenvironment by inducing oncogenic angiogenesis in favor of metastasis.