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

INTRODUCTION: CDK4-selective inhibitors are emerging as promising anti-cancer agents. Relative to dual CDK4/6 inhibitors, CDK4-selective inhibitors have potential to retain efficacy while improving tolerability. However, the therapeutic value and mechanistic consequences of selectively targeting CDK4 in prostate cancer remain undefined. Here, we investigated the therapeutic potential of CDK4 inhibitors AU2-94 and atirmociclib across diverse prostate cancer models. METHODS: Anti-proliferative activity was assessed in a panel of prostate cancer cell lines spanning AR-driven hormone-sensitive and AR-independent castration-resistant states, including therapy-resistant models. Efficacy was further evaluated in organoids from patient-derived xenografts and xenograft mouse models. Biochemical and molecular analyses were performed to define CDK4 selectivity, RB pathway engagement, transcriptional consequences, and downstream effects on cell cycle and resistance-associated programs. AU2-94 was also tested in combination with standard-of-care therapies (enzalutamide, docetaxel) and the PI3K inhibitor alpelisib. RESULTS: AU2-94 exhibited greater selectivity for CDK4 compared to atirmociclib. AU2-94 supressed proliferation across prostate cancer models irrespective of AR status and retained activity in aggressive and therapy-resistant settings. In RB-proficient models, AU2-94 reduced RB phosphorylation, attenuated E2F1-dependent transcriptional outputs, activated AR signalling, and decreased expression of proliferation-associated factors such as c-Myc and FOXM1. In vivo, AU2-94 significantly inhibited tumour growth in both AR-driven (LNCaP) and AR-independent (PC3) xenografts and suppressed RB pathway signalling in tumour tissue. Moreover, AU2-94 enhanced anti-tumour responses in combination with enzalutamide, docetaxel, or alpelisib, demonstrating additive or synergistic effects 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.