Genetic screens reveal new targetable vulnerabilities in BAP1-deficient Mesothelioma

More than half of malignant mesothelioma patients show alterations in the BAP1 tumour suppressor gene. Being a member of the Polycomb repressive deubiquitinating (PR-DUB) complex, BAP1 loss results in an altered epigenome which may create new vulnerabilities that remain largely unknown. Here we performed a CRISPR/Cas9-kinome screen in mesothelioma cells that identified two kinases in the Mevalonate/Cholesterol biosynthesis pathway. Furthermore, our analysis of chromatin, expression and genetic perturbation data in mesothelioma cells suggests a dependency on Polycomb repressive complex 2 (PRC2) mediated silencing. Pharmacological inhibition of PRC2 elevates the expression of cholesterol biosynthesis genes only in BAP1-deficient mesothelioma, thereby sensitizing these cells to the combined targeting of PRC2 and the mevalonate pathway. Finally, by subjecting autochthonous Bap1-deficient mesothelioma mice or xenografts to mevalonate pathway inhibition (Zoledronic Acid) and PRC2 inhibition (Tazemetostat), we demonstrate a potent anti-tumour effect, suggesting a targeted combination therapy for Bap1-deficient mesothelioma Overall design: mRNA profiles of BNC and NC mesothelioma and H2810, MSTO-211H and H2731 human mesothelioma cells