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Prostate cancer cells (PCa) are dependent on the androgen receptor (AR) for their aberrant proliferation and survival. We have recently discovered that AR induces a reprogramming of PCa cell metabolism by controlling the cytoplasmic wild-type enzyme isocitrate dehydrogenase 1 (IDH1), which results in an enhanced proliferation of tumour cells. However, the specific metabolic functions of IDH1 in PCa or how to use the reliance of tumour cells on this enzyme as a therapeutic avenue, is elusive. In in vitro human PCa models, we showed that IDH1 protein levels and activity are increased in an AR-dependent manner. Using pharmacological and genetic tools, we showed that IDH1 is a major contributor to the replenishment of NADPH levels in PCa. This cofactor plays a key role in the synthesis of biomaterials required for cellular division, and our results indicate that IDH1 contribute to 30-40% of total cellular NADPH levels. In that context, blockade of IDH1 was shown to alter the mTOR signaling, a central regulator of cellular anabolism, which is linked to decreased cellular proliferation rates. FDA-approved pharmacological inhibitors of mutant IDH1 significantly inhibited IDH activity and proliferation in PCa cells, suggesting that such inhibitors could be used to treat PCa patients even in absence of IDH1 mutation. Globally, our results demonstrate that IDH1 is a key player in proliferative anabolic pathways in PCa. Importantly, they also support the hypothesis that inhibition of IDH1 using already-approved molecules represents one viable therapeutic solution. Citation Format: Kevin Gonthier, Cindy Weidmann, Lilianne Frégeau-Proulx, Étienne Audet-Walsh. Targeting the isocitrate dehydrogenase 1 (IDH1) metabolic enzyme in prostate cancer [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 3731.

Mutations of the isocitrate dehydrogenase genes IDH1 and IDH2, key enzymes involved in citrate metabolism, are important oncogenic events in several cancer types, including in 1%–3% of all prostate cancer cases. However, if IDH1 and other IDH isoforms are associated with prostate cancer progression, as well as the regulatory factors controlling their expression and activity, remain mostly unknown. Using publicly available datasets, we showed that prostate cancer harbors the highest IDH1 expression across the human cancer spectrum and that IDH1 expression is altered during prostate cancer progression. We showed that the androgen receptor (AR), a key oncogene in prostate cancer, controls multiple IDH isoforms in both in vitro and in vivo models, predominantly positively regulating IDH1. Chromatin immunoprecipitation experiments confirmed the recruitment of AR at several regulatory regions of IDH1 and enzymatic assays demonstrated that AR significantly induces IDH activity. Genetic blockade of IDH1 significantly impaired prostate cancer cell proliferation, consistent with IDH1 having a key function in these cancer cells. Importantly, knockdown of IDH1 blocked the AR-mediated induction in IDH activity, indicating that AR promotes a mitochondrial to cytoplasmic reprogramming of IDH activity. Overall, our study demonstrates that IDH1 expression is associated with prostate cancer progression, that AR signaling integrates one of the first transcriptional mechanisms shown to regulate IDH1, and that AR reprograms prostate cancer cell metabolism by selectively inducing extra-mitochondrial IDH activity. Implications: The discovery that AR reprograms IDH activity highlights a novel metabolic reprogramming necessary for prostate cancer growth and suggests targeting IDH activity as a new therapeutic approach for prostate cancer treatment.

A primary function of the prostate is to synthesize and secrete high levels of citrate by way of a unique metabolic profile regulated by the androgen receptor (AR). Prostate cancer (PCa) is an androgen-dependent disease that is characterized by early reprogramming of citrate metabolism. Accordingly, mutations of the isocitrate dehydrogenase genes IDH1 and IDH2, which are key enzymes involved in the regulation of cellular citrate levels, have been demonstrated as important oncogenic events in several cancer types, including in about 3% of all PCa cases. However, if IDH1 and other IDH isoforms are associated with PCa progression as well as the regulatory factors controlling their expression remain mostly unknown. Across the human cancer spectrum, PCa appears to be the cancer type with the highest expression of IDH1, with levels even higher than common cancers associated with IDH1 mutations such as gliomas. Using publicly available datasets and quantitative PCR, we showed that IDH1 is the predominant IDH isoform expressed in PCa cells. In PCa, the androgen receptor was found to regulate several IDH isoforms in both in vitro and in vivo models of PCa, predominantly positively regulating IDH1. Chromatin immunoprecipitation experiments confirmed the recruitment of AR at several regulatory regions of IDH1 and IDH2. IDH1 and other IDH isoforms were shown to be significantly altered during PCa progression, which is consistent with a reprogramming of citrate metabolism in PCa. In addition, modulation of IDH expression significantly altered PCa cell proliferation and metabolism. Overall, our study indicates that IDH gene regulation is associated with PCa progression and that AR plays a significant role in the regulation of IDH genes. Citation Format: Kevin Gonthier, Raghavendra TK Poluri, Cindy Weidmann, Etienne Audet-Walsh. Association of IDH genes with prostate cancer progression and their regulation by the androgen receptor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1853.