Introduction: Mutations in the metabolic enzymes, IDH1 and IDH2, are found in 20-25% of intrahepatic cholangiocarcinomas (ICC), a lethal malignancy of the liver bile ducts. Mutant IDH generates high levels of the "oncometabolite" 2-hydroxyglutarate (2HG), which inhibits liver progenitor cells from differentiating into hepatocytes and cooperates with oncogenic KRAS to drive ICC formation in mice. Pharmacologic inhibitors of mutant IDH are currently being tested for ICC treatment in clinical trials. Here, we sought to examine the role of mutant IDH and 2HG in ICC tumor maintenance using a genetically defined murine model. Materials and Methods: We previously generated a genetically engineered mouse model (GEMM) driven by expression of mutant IDH2 and oncogenic KRAS, mutations that coexist in a subset of human ICC. Using a primary ICC cell line (SS49 cells) derived from this model, we tested the impact of the mutant IDH2 inhibitor, AGI-12026, on ICC cell growth in vitro under different conditions (including embedding in matrigel, and cultivation on collagen-coated and uncoated tissue culture dishes, or in suspension). Gene expression analysis and transcriptional profiling was performed by qPCR and RNA-Seq. To test the impact of AGI-12026 in vivo, SS49 cells were injected subcutaneously into SCID mice. Following tumor formation, mice were treated with increasing doses of AGI-12026 for 12 days, and growth monitored by caliper measurements. Analysis of the transcriptome and proteome of vehicle and AGI-12026-treated tumors has been performed by RNA-Seq and mass spectroscopy, respectively. H&E-stained sections of SS49 xenografts were scored by a gastrointestinal pathologist in a blinded manner (V.D.). Results: We found that AGI-12026 had no effect on proliferation of SS49 cells cultivated on collagen-coated dishes or in matrigel, whereas treatment of cells plated on uncoated tissue culture dishes resulted in dose-dependent reductions in growth rate and upregulation of hepatocyte-specific genes. Similarly, AGI-12026 reduced intratumoral 2HG by >88% and slowed the growth of subcutaneous SS49 tumors in a dose-dependent manner. This was associated with induction of hepatocyte-specific genes and a histologic shift toward increased tubular morphology and loss of nested or solid cellular structures, suggesting tumor cell differentiation. Conclusions: Thus, mutant IDH inhibition may lead to morphologic changes that could be consistent with a form of "differentiation therapy" in ICC, slowing the growth of tumor cells even in the context of mutant KRAS. These data are consistent with preliminary reported results from an ongoing phase I clinical trial of AG-120 (ivosidenib, a selective inhibitor of mutant IDH1), where 38.5% of previously treated patients with mutant IDH1 cholangiocarcinoma experienced progression-free survival of 6 months. These data suggest that inhibition of mutant IDH may result in clinical benefit in a significant percentage of IDH mutant ICC patients through disease stabilization.

Citation Format: Supriya K. Saha. Effect of pharmacologic inhibition of mutant IDH in cholangiocarcinoma [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A072.