CDK4-selective inhibitor AU2-94 for the treatment of advanced and therapy-resistant prostate cancer

INTRODUCTION: CDK4-selective inhibitors are emerging as promising anticancer agents. Relative to dual CDK4/6 inhibitors, CDK4-selective inhibitors have the potential to retain efficacy while improving tolerability. However, the therapeutic value and mechanistic consequences of selectively targeting CDK4 in prostate cancer remain largely undefined. Here, we investigated the anti-tumour activity and mode of action of the CDK4 inhibitors AU2-94 and atirmociclib across diverse prostate cancer models. METHODS: Antiproliferative activity was assessed in a panel of AR-driven and AR-independent prostate cancer cell lines spanning hormone-sensitive and castration-resistant states. Efficacy was further evaluated in organoids derived from patient-derived xenografts and in xenograft mouse models. Biochemical and molecular analyses were performed to evaluate CDK4 selectivity, RB pathway engagement, transcriptional reprogramming, and downstream effects on cell-cycle regulation, and resistance-associated programmes. AU2-94 was also tested in combination with standard-of-care therapies (enzalutamide and docetaxel) and the PI3K inhibitor alpelisib. RESULTS: AU2-94 exhibited greater selectivity for CDK4 compared with atirmociclib. AU2-94 suppressed proliferation across prostate cancer models irrespective of AR status and retained activity in aggressive and therapy-resistant settings. In RB-proficient in vitro models, AU2-94 reduced RB phosphorylation, attenuated E2F1-dependent transcriptional outputs, activated AR signalling, and decreased expression of proliferation-associated factors such as FOXM1. In vivo, AU2-94 inhibited the growth of both AR-driven (LNCaP) and AR-independent (PC3) xenografts and suppressed RB pathway signalling. Moreover, AU2-94 demonstrated additive or synergistic effects when combined with enzalutamide, docetaxel, or alpelisib that were associated with reinforced cell-cycle blockade and suppression of resistance-associated signalling. CONCLUSION: These findings establish selective CDK4 inhibition as a therapeutically active and mechanistically rational strategy in prostate cancer and support AU2-94 as a candidate for further preclinical and clinical development, including in combination regimens for advanced and therapy-resistant disease.