Dual HDAC and PI3K Inhibitor CUDC-907 Inhibits Growth of Pleural Mesothelioma: The Impact of Cisplatin Sensitivity and Myc Expression

Objectives: Pleural mesothelioma (PM) is a rare cancer that often develops after a decades-long latency period and confers a grim prognosis. Novel, biomarker-based therapeutic modalities are expected to improve the outcome of patients with advanced PM. CUDC-907 (fimepinostat) is a dual inhibitor that affects both histone deacetylases and PI3K enzymes. Its antitumor activity was described in several cancer types, but it has not yet been explored in PM. Materials and Methods: The sensitivity of 22 PM cell lines—including 18 models established in our laboratory—to cisplatin and CUDC-907 was determined using a cell viability assay. BAP1, PTEN, and c-Myc expression, as well as MYC copy number variation, were measured. The effect of combination treatment with cisplatin was assessed with cell viability, cell cycle, and 3D spheroid formation assays. Results: Most PM cell lines were sensitive to CUDC-907 treatment, and the CUDC-907 response was significantly higher in cell lines with higher c-Myc expression due to MYC copy number gain or amplification. Importantly, all cisplatin-insensitive cell lines were sensitive to CUDC-907. Combination treatment with cisplatin synergistically decreased cell viability and induced G2/M arrest or cell death. We tested cisplatin-sensitive P31WT and cisplatin resistant P31cis isogeneic pair and found that in both 2D and 3D assays the cisplatin-resistant cells showed a higher sensitivity to CUDC-907 single treatment. Combining CUDC-907 with cisplatin further decreased cell growth even in cisplatin-resistant cells. Conclusions: The majority of PM cell models are sensitive to CUDC-907, which may be a potent therapeutic agent in PM.