Characterization by RNAseq of malignant pleural mesothelioma cell lines and their response to palbociclib

Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited therapeutic options. In this study, we evaluated the impact of CDK4/6 inhibition by palbociclib in established MPM cell lines using a variety of approaches including RNA sequencing. Palbociclib used alone sufficed to strongly and durably inhibit the proliferation of 4 of 6 cell lines. In a parallel study, the efficacy of palbociclib was confirmed in a large panel of patient-derived cell lines indicating a unique sensitivity of MPM to CDK4/6 inhibition. Importantly, insensitivity to palbociclib was mostly explained by the lack of active T172-phosphorylated CDK4, which was associated with the high p16 levels that accompany RB1 defects or inactivation, and also (unexpectely) CCNE1 overexpression in the presence of WT RB1. Prolonged treatment with palbociclib irreversibly inhibited proliferation despite re-induction of cell cycle genes upon drug washout. A senescence-associated secretory phenotype (SASP) including various potentially immunogenic components was also irreversibly induced. Our study strongly supports the clinical evaluation of CDK4/6 inhibitory drugs for MPM treatment including in several combinatorial therapies. 6 cell lines were treated for 9-10 days with 0,1 % DMSO or 1 µM palbociclib. Experiment was performed in duplicate or triplicate except for Met5A which was analyzed only once. For the four sensitive cell lines, the reversibility of the cell cycle arrest imposed by palbociclib was also investigated after a drug washout of 48 hours. This experiment was performed once. Met5A cells were also used in untreated conditions for characterization.