Data from Functional Genomic Screen in Mesothelioma Reveals that Loss of Function of BRCA1-Associated Protein 1 Induces Chemoresistance to Ribonucleotide Reductase Inhibition

Abstract

<div>Abstract<p>Loss of function of BRCA1-associated protein 1 (BAP1) is observed in about 50% of malignant pleural mesothelioma (MPM) cases. The aim of this study was to investigate whether this aspect could be exploited for targeted therapy. A genetically engineered model was established expressing either functional or nonfunctional BAP1, and whole-genome siRNA synthetic lethality screens were performed assessing differentially impaired survival between the two cell lines. The whole-genome siRNA screen unexpectedly revealed 11 hits (FDR < 0.05) that were more cytotoxic to <i>BAP1</i>-proficient cells. Two actionable targets, ribonucleotide reductase (RNR) catalytic subunit M1 (RRM1) and RNR regulatory subunit M2 (RRM2), were validated. In line with the screen results, primary mesothelioma (<i>BAP1</i><sup>+/−</sup>) overexpressing <i>BAP1</i> C91A (catalytically dead mutant) was more resistant to RNR inhibition, while <i>BAP1</i> knockdown in the <i>BAP1</i>-proficient cell lines rescued the cells from their vulnerability to RNR depletion. Gemcitabine and hydroxyurea were more cytotoxic in <i>BAP1</i>-proficient cell line–derived spheroids compared with <i>BAP1</i> deficient. Upregulation of RRM2 upon gemcitabine and hydroxyurea treatment was more profound in <i>BAP1</i> mut/del cell lines. Increased lethality mediated by RNR inhibition was observed in NCI-H2452 cells reconstituted with <i>BAP1</i>-WT but not with <i>BAP1</i> C91A. Upregulation of RRM2 in NCI-H2452-<i>BAP1</i> WT spheroids was modest compared with control or C91A mutant. Together, we found that BAP1 is involved in the regulation of RNR levels during replication stress. Our observations reveal a potential clinical application where BAP1 status could serve as predictive or stratification biomarker for RNR inhibition-based therapy in MPM.</p></div>