Ivosidenib

Isocitrate dehydrogenase 1 (IDH1) is a metabolic enzyme in the cytoplasm and peroxisomes that plays a role in many cellular processes, including mitochondrial oxidative phosphorylation, glutamine metabolism, lipogenesis, glucose sensing, and regulation of cellular redox status. IDH1 converts isocitrate to α-ketoglutarate (α-KG), a normal metabolite in the carboxylic acid cycle. Multiple cancers are associated with missense mutations in IDH1, leading to the substitution of the amino acid arginine 132 in the enzyme active site, acquired gain-of-function activity, and increased enzyme activity. IDH1 mutation results in the accumulation of D-2-hydroxyglutarate (D-2HG), an oncometabolite that is structurally similar to α-KG. D-2HG inhibits α-KG-dependent dioxygenases, including histone and DNA demethylases, which play a role in histone and DNA demethylation along with other cellular processes. Inhibition of these enzymes leads to histone and DNA hypermethylation and a block in cell differentiation, including hematopoietic differentiation. With histone hypermethylation, methylation-sensitive insulators cannot regulate the activation of oncogenes. Excess D-2HG ultimately interferes with cellular metabolism and alters epigenetic regulation towards oncogenesis.

Ivosidenib inhibits the mutant IDH1 at much lower concentrations than the wild-type enzyme. It targets gene mutations at position R132, with R132H and R132C being the most common mutations. In mouse xenograft models of IDH1-mutated AML, ivosidenib caused a decrease in D-2HG levels in a dose-dependent manner and induced myeloid differentiation in vitro and in vivo. Ivosidenib works to inhibit histone demethylases and restore normal methylation conditions to promote cell differentiation and oncogene regulation.