Abstract 5191: A combination of Stat3 inhibitor and radiation for the treatment of malignant pleural mesothelioma

Background: Trimodality therapy, including surgery, is the treatment for patients with malignant pleural mesothelioma (MPM). However, the 5-year survival rate remains less than 40%. To improve the survival rate, we investigated Stat3 as a potential therapeutic target for MPM. Methods:Cell viability was assessed using Cell Counting Kit-8 (CCK-8: WST-8 Dojindo). MPM cells (NCI-H28, NCI-H226, NCI-H2052, NCI-H2452, MSTO-211H) were seeded into 96-well plates. After treatment with a Stat3 inhibitor (BBI-608 : napabucasin), Cell Counting Kit-8 solution was added to each well and absorbance was measured using a microplate reader. The level of phosphorylated Stat3 (p-Stat3) in cell lysates was measured by ELISA. ROS level in cells was measured by FACS analysis. In the in vivo study, H226 cells were injected subcutaneously in the flank region of nude mice randomly assigned to four treatment groups (5 mice/group)—(1) treatment with vehicle control, (2) treatment with Stat3 inhibitor, (3) radiation therapy (RT), and (4) Stat3 inhibitor and RT. Tumor size was measured twice/week. Results: Napabucasin decreased the viability of MPM cells (epithelioid, sarcoma, biphasic) in a dose-dependent manner. p-Stat3 levels decreased by 90% after treatment with 10 μM napabucasin in H226 cells. Napabucasin treatment induced more ROS production in MPM cells than did Pemetrexed. Moreover, combinatorial treatment with napabucasin and radiation (2 Gy, 5 Gy) induced more ROS production than did RT alone. In the mouse model, treatment with napabucasin alone significantly suppressed tumor growth (p < 0.05), but napabucasin and RT completely suppressed tumor growth. Conclusion:We showed that napabucasin inhibited proliferation of the MPM cells (epithelial, biphasic, sarcomatoid) and demonstrated that combination therapy with napabucasin and radiation completely suppressed tumor growth in a mouse model. Treatment with the napabucasin alone and the combination of napabucasin and RT induced high ROS production in MPM cells. Collectively, the combination of Stat3 inhibitor with Radiation Therapy (START) is a promising approach for the treatment of MPM.TheA combination of of Stat3 inhibitor and radiation with for the treatment of malignant pleural mesothelioma Citation Format: Seiji Matsumoto, Hiroshi Doi, Akihiro Fukuda, Tohoru Nakamichi, Ayumi Kuroda, Masaki Hashimoto, Teruhisa Takuwa, Nobuyuki Kondo, Seiki Hasegawa. A combination of Stat3 inhibitor and radiation for the treatment of malignant