P3.03-018 Suppression of Tumor Growth by Pegylated Arginase in Malignant Pleural Mesothelioma: Topic: Mesothelioma Transitional

Abstract

Malignant pleural mesothelioma (MPM) is a global health issue. Pegylated arginase (PEG-BCT-100) has shown anti-tumor effects in hepatocellular carcinoma, acute myeloid leukemia and human melanoma. We aimed to study the preclinical anticancer effects of BCT-100 in MPM. A panel of 5 mesothelioma cell lines (from ATCC) was used to study the in vitro effect of BCT-100 by crystal violet staining. The in vivo effects of BCT-100 (± chemotherapy) were studied using two nude mice xenograft models. Protein expression and arginine concentration were evaluated by Western Blot and ELISA respectively. Cellular location of BCT-100 was detected by immunohistochemistry and immunoflorescence staining. TUNEL assay was used to identify cellular apoptotic events. BCT-100 reduced in vitro cell viability (IC50: 13-24 mU/ml) across different cell lines and suppressed tumor growth in both 211H and H226 xenograft models. Argininosuccinate synthetase was expressed in H28, H226, H2452 cells as well as 211H and H266 xenografts. Ornithine transcarbamylase was undetectable in all cell lines and xenograft models. BCT-100 (60 mg/kg) significantly suppressed tumor growth with increased median survival in both xenograft models. No beneficial effect was observed when combining BCT-100 with pemetrexed or cisplatin. BCT-100 decreased serum and intratumoral arginine level. BCT-100 was mainly located in cytosol of tumor cells. Apoptosis (PARP cleavage in 211H xenograft, Bcl-2 downregulation and cleavage of PARP and caspase 3 in H226 xenograft as well as TUNEL-positive staining in both xenografts) and G1 arrest (downregulation of cyclin A2, D3, E1 and CDK4 in 211H xenograft and suppression of cyclin A2, E1, H and CDK4 in H226 xenograft) were evident with BCT-100 treatment. Furthermore, proliferative factor Ki67 was downregulated in BCT-100 treatments arms. MPM tumor growth was suppressed by BCT-100 via apoptosis and G1 arrest in vivo. This provides scientific evidence to support further clinical exploration of BCT-100 in treatment of MPM. (Acknowledgment: This research was supported by Hong Kong Pneumoconiosis Compensation Fund Board, HKSAR.)