Abstract 1810: The mutant IDH1 inhibitor ivosidenib promotes tumor cell differentiation and anti-tumor immunity in intrahepatic cholangiocarcinoma
Authors: Wu Meng-Ju , Shi Lei , Dubrot Juan , Hudson Christine , Merritt Joshua , Adil Ramzi , Wu Qibiao , Ronseaux Sebastien , Narayanaswamy Rohini , Manguso Robert , Nicolay Brandon , Bardeesy Nabeel 
Published: September 2020

Abstract
Intrahepatic cholangiocarcinoma (ICC) is a cancer of the liver bile ducts, which has been rising in incidence and carries a 5-year survival rate of less than 10%. Mutations in isocitrate dehydrogenase 1 and 2 (mIDH1/2) are among the most common genetic alterations in ICC, present in 20% patients. The hot-spot point mutations of IDH result in aberrant enzymatic function, reducing alpha-ketoglutarate (alphaKG) to the oncometabolite, 2-hydroxyglutarate (2-HG), which accumulates to millimolar concentrations within the cell. 2-HG competitively inhibits alphaKG-dependent histone and DNA demethylating enzymes, thereby altering chromatin regulation. The first-in-class small molecule selective IDH1m inhibitor, ivosidenib, has shown benefit in phase I and III trials for patients with IDH1m ICC.
In order to gain insight into the mechanisms underlying the response to IDH1m inhibition, we developed the first genetically engineered mouse model (GEMM) of IDH1m ICC. We found that ivosidenib reduced the overall tumor burden and increased overall survival of syngeneic allografts of ICCs derived from the GEMM. The positive response to ivosidenib was associated with an induction of mature hepatocyte lineage markers and a reduction of tumor produced 2-HG &gt;85%, supporting observations from the ivosidenib phase I data in ICC patients that mIDH1 inhibition may promote ICC tumor cell differentiation. In addition, there was pronounced induction of immune stimulatory interferon signaling, increased recruitment of CD8+ T cells to the tumors and strong PD-L1 upregulation. Thus, ivosidenib treatment leads to a sustained inhibition of 2-HG production, which correlated with an increased immune stimulation compared to vehicle treatment. We will present these data as well as ongoing studies interrogating the immune and transcriptomic changes with further resolution via fluorescence-activated cell sorting and single-cell RNA-sequencing analysis, direct functional testing of contributions of specific immune populations to the therapeutic efficacy of ivosidenib, and testing ivosidenib in combination with checkpoint inhibition.
These studies highlight the impact of ivosidenib on hepatocyte differentiation and immune stimulation in IDH1m ICC and support the key role of IDHm in ICC tumor maintenance.
Citation Format: Meng-Ju Wu, Lei Shi, Juan Dubrot, Christine Hudson, Joshua Merritt, Ramzi Adil, Qibiao Wu, Sebastien Ronseaux, Rohini Narayanaswamy, Robert Manguso, Brandon Nicolay, Nabeel Bardeesy. The mutant IDH1 inhibitor ivosidenib promotes tumor cell differentiation and anti-tumor immunity in intrahepatic cholangiocarcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1810.