MA17.03 Importance of Cullin4 Ubiquitin Ligase in Malignant Pleural Mesothelioma

Abstract

Loss of the tumor suppressor NF2 is frequent in malignant pleural mesothelioma (MPM). NF2 suppresses tumorigenesis in part by inhibiting Cullin4 ubiquitin ligase (CUL4) complex. Here we aimed to evaluate an importance of CUL4 in MPM. We evaluated the expression of CUL4A and CUL4B in tissue microarrays using immunohistochemistry. We tested the efficacy of cullin inhibition by pevonedistat, a small molecule inhibiting cullin neddylation, in 13 cell lines and 3 primary cells in 2D and 3D culture. Four groups of SCID mice haboring intraperitoneal (ip.) pevonedistat sensitive (MSTO211H) or resistant (ACC-Meso1) cell lines were treated with pevonedistat (50 mg/kg; ip.) on a 5day on/5day off schedule for 3 cycles. Treatment efficacy was assessed by means of overall survival. CUL4B expression was associated with clinical outcomes (figure 1). Five MPM cell lines (38%) were highly sensitive to pevonedistat (IC50<500 nM). This remained true in 3D spheroid culture. The treatment induced S/G2 cell cycle arrest and accumulation of cells undergoing DNA re-replication (containing >4N DNA content) known to be mediated by p21 and CDT1 accumulation. Indeed, the accumulation of p21 and CDT1 was more pronounced in pevonedistat sensitive cell lines after the treatment. Two of primary cells (67%) were sensitive to pevonedistat and also showed higher CDT1 accumulation following the treatment compared to the resistant cells. In vivo, pevonedistat treatment significantly prolonged survival of mice bearing both sensitive and resistant MPM tumors. Pevonedistat treatment reduced growth (phosphorylated histoneH3 positive) in pevonedistat sensitive tumor but increased apoptosis (cleaved–caspase3 positive) in pevonedistat resistant tumor. High CUL4B expression may play a role in MPM progression. Inhibition of cullins by pevonedistat induced growth arrest and DNA re-replication strongly in a subset of MPM. The major mechanism seems to be mediated by p21 and CDT1 accumulation in vitro. Investigation of mechanisms in vivo is ongoing.