CDK4/6 Inhibition Enhances the Efficacy of Standard Chemotherapy Treatment in Malignant Pleural Mesothelioma Cells

Simple Summary Malignant pleural mesothelioma (MPM) is an aggressive disease affecting the pleura, and its incidence is increasing worldwide. Currently, the recommended systemic therapy for MPM is cisplatin/pemetrexed or immunotherapy with nivolumab and ipilimumab. Unfortunately, the prognosis remains poor, and there is an urgent need for new and effective treatments. In this study we investigated the potential antitumoral effects of combining abemaciclib with the standard chemotherapy drugs cisplatin and pemetrexed. Background: The loss of the CDKN2A/ARF (cyclin-dependent kinase inhibitor 2A/alternative reading frame) gene is the most common alteration in malignant pleural mesothelioma (MPM), with an incidence of about 70%, thus representing a novel target for mesothelioma treatment. In the present study, we evaluated the antitumor potential of combining the standard chemotherapy regimen used for unresectable MPM with the CDK4/6 (cyclin-dependent kinase 4 or 6) inhibitor abemaciclib. Methods: Cell viability, cell death, senescence, and autophagy induction were evaluated in two MPM cell lines and in a primary MPM cell culture. Results: The simultaneous treatment of abemaciclib with cisplatin and pemetrexed showed a greater antiproliferative effect than chemotherapy alone, both in MPM cell lines and in primary cells. This combined treatment induced cellular senescence or autophagic cell death, depending on the cell type. More in detail, the induction of cellular senescence was related to the increased expression of p21, whereas autophagy induction was due to the impairment of the AKT/mTOR signaling. Notably, the effect of the combination was irreversible and no resumption in tumor cell proliferation was observed after drug withdrawal. Conclusion: Our results demonstrated the therapeutic potential of CDK4/6 inhibitors in combination with chemotherapy for the treatment of MPM and are consistent with the recent positive results in the MiST2 arm in abemaciclib-treated patients.