Abstract 1812: Therapeutic targeting and development of IDH inhibitors for the treatment of chondrosarcoma

Abstract Chondrosarcomas are the second most frequently occurring type of bone malignancy, and account for approximately 25% of all bone sarcomas. They are often highly aggressive neoplasms that rapidly progress and eventually recur and give distant metastases. They are largely considered to be resistant to conventional chemotherapy and radiotherapy. Recurrent somatic mutations in the isocitrate dehydrogenase I (IDH1) genes have been identified in a spectrum of human malignancies, including chondrosarcoma. Mutations in these genes lead to impaired ability of IDH1 to catalyze the conversion of isocitrate to alpha ketoglutarate and to gain of a neomorphic enzymatic activity which results in production of oncometabolite 2-hydroxyglutarate (2HG). Our preliminary data indicated that compared to samples that were wild type, IDH1 mutant samples showed a significant increase in intra-tumoral 2HG levels. In the present study, we hypothesized that 2-HG accumulation induces DNA and histone hypermethylation and altered gene expression, ultimately resulting in a block in cellular differentiation by competitively inhibiting α-ketoglutarate-dependent dioxygenases involved in histone and DNA demethylation. Therefore, we proposed that inhibition of IDH should mediate its antitumor effects through the induction of differentiation. To test this hypothesis, we utilized human chondrosarcoma cell lines including IDH wild type (CH2879) and IDH1 mutant (JJ012) and the IDH1 inhibitor FT6535. Results from our in vitro cell viability assay and histone methylation showed that selective inhibition of IDH1 resulted in modest inhibition of cell proliferation and suppression of histone methylation in IDH1 mutant chondrosarcoma cells. Next we elected to test the IDH inhibitor in combination with differentiating agents including retinoic acid. Cell viability assays showed that when compared to either agent alone, the combination of retinoic acid and FT6535 resulted in a significant decrease in cellular proliferation. Western blot analysis showed induction of COL1A2 and SOX9 (differentiation markers) with suppression of histone methylation H3K27me3 or H3K9me3, Taken together, our data strongly suggests that combination treatment with the IDH1 inhibitor FT6535 and retinoic acid represents a novel approach to suppress cell growth by epigenetic modulation to induce differentiation and merits further evaluation as a potential treatment modality in chondrosarcoma. Citation Format: Tahir N. Sheikh, Chao Lu, Gary K. Schwartz. Therapeutic targeting and development of IDH inhibitors for the treatment of chondrosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1812.