ABSTRACT: Prostate cancer (PC) typically depends on hormones for growth, with androgen deprivation therapy (ADT) serving as the primary treatment. However, many patients progress to a castration-resistant (CR) stage, where their tumor becomes unresponsive to ADT. Despite the common use of conventional chemotherapeutics like taxanes (docetaxel, cabazitaxel), the majority of patients experience recurrence. To uncover the mechanisms underlying the drug-resistant phenotype, we developed docetaxel-resistant CRPC cell lines, and through a drug library screen, we identified MLL-Menin and MLL-WDR5 inhibitors that overcome taxane resistance and significantly induced G2/M arrest and apoptosis. To determine the roles of individual proteins in the MLL complexes, we silenced several MLL partner proteins , and the absence of Menin and LEDGF particularly halted the growth of the resistant cells while showing no significant effect on parentals. Notably, parental cells with Menin silencing failed to develop resistance even after prolonged exposure, unlike their Menin-expressing counterparts, highlighting the critical role of Menin in the resistance process. Menin knockouts were analyzed through RNA-sequencing, and several gene sets, including E2F targets, G2/M checkpoints, and mTORC1 pathways, were found to be negatively regulated in taxane-resistant cells. The ablation of Menin led to a reduction in mTOR levels, and ChIP-qPCR analysis confirmed that Menin was enriched on the mTOR promoter. According to TCGA clinical data, the correlation between MEN1 and mTOR became stronger as the disease advanced to metastatic stages. Furthermore, the combination of the mTOR inhibitor Torin1 and docetaxel enhanced the sensitivity of our resistant cells. Menin deficiency reduced cell proliferation and key expression of cell cycle genes (Cyclin D1, CDK20). Rescue experiments reversed these effects, and Menin showed significant enrichment of the Cyclin D1 and CDK20 promoters. Finally, Menin loss impaired docetaxel resistant CRPC growth in our in vivo model. Our data demonstrate the essentiality of Menin for docetaxel resistance and suggest a combined approach targeting both Menin and mTOR to improve taxane therapy responses. Additionally, Menin regulates some key cell cycle genes to promote the G1/S transition, emphasizing its critical role in cell cycle regulation and the growth of taxane-resistant CRPC.
