Isocitrate Dehydrogenase Mutations in Human Cancers: Physiopathologic Mechanisms and Therapeutic Targeting

Abstract

Isocitrate dehydrogenase (IDH) is a metabolic enzyme responsible for the enzymatic conversion of isocitrate to α-ketoglutarate (α-KG). Mutations in the IDH gene result in a novel gain-of-function, with development of neomorphic enzymatic activity determining the pathological reduction of α-KG to (R)-2-hydroxyglutarate. The accumulation of this pathological metabolite (onco-metabolite) in cancer cells is, to a large extent, responsible for the development of several cancers, including acute myeloid leukemia (AML), low-grade gliomas (LGGs) or chondrocytic tumors. Furthermore, various experimental studies have shown that IDH mutations represent an early, driver event, conserved during tumor progression in neoplasias such AML and LGG. Given all these observations, potent and selective IDH inhibitors have been developed and are currently under investigation in phase I/II clinical studies. In particular, AG-221, a first-in-class inhibitor of mutant IDH2, was tested in hematological patients with refractory/relapsing AML or myelodysplasia and showed an overall response rate of 59/159 (37%), as well as a good safety profile. Similarly, AG-120, an inhibitor of mutant IDH1, was tested in 66 relapsing/refractory AML patients and showed an overall response rate of 36%, with a complete response rate of 16%. A new IDH inhibitor, AG-811 displayed the capacity to inhibit both mutants IDH1/2 and to penetrate the blood: brain barrier, a property that would be suitable for treatment of glioma patients. On the other hand, additional observations have suggested that IDH-mutant AMLs are sensitive to treatment with BCL-2 inhibitors and to the differentiative induction with all-trans retinoic acid. In conclusion, the collective studies carried out in recent years on the characterization of IDH-mutant tumors highlight an admirable paradigm of the virtuosic transfer from basic research (with improvements in our understanding of the physio-pathological role played by IDH mutations in the development of some tumors) to clinical studies (with the development of selective, potent and clinically-active IDH inhibitors).