Abstract B014: ONECUT2 activates diverse drug-resistant phenotypes in prostate cancer

Abstract BACKGROUND. Prostate cancer (PC) cells can escape from lineage confinement and be reprogrammed to a drug-resistant, high-plasticity state, however the mechanism underlying this process is not understood. Our group identified the HOX/CUT transcription factor ONECUT2 (OC2) as a mediator of metastatic castration-resistant PC (mCRPC) that can be inhibited with a novel family of small molecules. OC2 was shown to be a lineage plasticity driver that promotes neuroendocrine prostate cancer (NEPC). In this study, we sought to uncover the mechanism whereby OC2 exerts effects on lineage plasticity. METHODS. RNAseq, CUT&RUNseq, scRNAseq, forced expression, shRNA, CRISPR-Cas9, co-precipitation/western blot, PCR, mutagenesis, human PC, PC models, computational modeling. RESULTS. We found that OC2 is capable of activating multiple androgen receptor- (AR)-indifferent, drug-resistant lineages, including programs not associated with NEPC, such as upregulation of the glucocorticoid receptor (GR). Consistent with the GR findings, OC2 regulated genes on the AR cistrome previously shown to be regulated by GR in CRPC, including KLK3/PSA. OC2 activated bivalent promoters of master regulator genes via epigenetic modification, and reprogramed multiple super-enhancers, including those associated with TMPRSS2 and SRRM4. OC2-expressing cells in human CRPC included populations that express AR, NE+/stem-like+, NE-/stem-like+, and “double negative” (NE-/AR-) phenotypes. OC2 also transcriptionally upregulated UDP-glucuronosyltransferase enzymes UGT2B15 and UGT2B17, which inactivate DHT, suggesting that the emergence of phenotypic plasticity also arises from AR suppression by ligand depletion. Consistent with this, low levels of androgen correlated with OC2 activation in human CRPC tumors. Enforced OC2 promoted both enzalutamide and docetaxel resistance in PC models. CONCLUSIONS. These findings identify OC2 as an upstream mediator of many lineage-defining factors that govern drug resistance, including those associated with adenocarcinoma. Because OC2 can be inhibited pharmacologically, these results suggest that suppressing this target may inhibit the emergence of a wide range of drug resistance mechanisms arising from loss of lineage confinement. Citation Format: Chen Qian, Qian Yang, HyoYoung Kim, Yiwu Yan, Elahe Mostaghel, Leigh Ellis, Beatrice Knudsen, Salma Kaochar, Huihui Ye, Isla Garraway, Sungyong You, Michael Freeman. ONECUT2 activates diverse drug-resistant phenotypes in prostate cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr B014.