CAMK2D: A Novel Molecular Target for BAP1-Deficient Malignant Mesothelioma

Malignant mesothelioma (MM) is a rare but aggressive malignancy. Although the molecular genetics of MM are known, including BRCA1-associated protein-1 (BAP1) gene alterations, the prognosis of MM patients remains poor. Here we generated BAP1 knockout (BAP1-KO) human mesothelial cell clones to develop molecular-targeted therapeutics based on genetic alterations in MM. cDNA microarray and quantitative RT-PCR (qRT-PCR) analyses revealed high expression of a calcium/calmodulin-dependent protein kinase type II subunit delta (CAMK2D) gene in the BAP1-KO cells. CAMK2D was highly expressed in 70% of the human MM tissues (56/80) and correlated with the loss of BAP1 expression, making it a potential diagnostic and therapeutic target for BAP1-deficient MM. We screened an anticancer drugs library using BAP1-KO cells and successfully identified a CaMKII inhibitor, KN-93, which displayed a more potent and selective antiproliferative effect against BAP1-deficient cells than cisplatin or pemetrexed. KN-93 significantly suppressed the tumor growth in mice xenografted with BAP1-deficient MM cells. This study is the first to provide a potential molecular-targeted therapeutic approach for BAP1-deficient MM.