The Effects of Pegylated Arginase on Small Cell Lung Cancer in vitro and in vivo

Abstract

Background: Small cell lung cancer (SCLC) accounts for about 15% of all lung cancer cases. SCLC is characterized by frequent relapse, and current treatments lack tumor specificity. Arginase is an important enzyme in human, but it is deficient in some tumors. Arginine deprivation has become a potential therapeutic option in selected tumors. BCT-100 is a pegylated arginase which has demonstrated anticancer activity in arginine auxotrophic tumors, such as melanoma, hepatocellular carcinoma and acute myeloid leukemia. One of resistance mechanisms to arginase is overexpression of argininosuccinate synthetase (ASS1) and ornithine transcarbamylase (OTC). The aim of this study is to determine the effects of BCT-100 on SCLC in vitro and in vivo. Methods: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to detect cell viability of different SCLC cell lines after BCT-100 treatment. Western blotting was employed to evaluate the protein expression. Knockdown of OTC was performed using specific siRNA. Xenograft models were established in nude mice for testing the anticancer effect of BCT-100. Results: The IC50 values of BCT-100 in H69, DMS79, H187, H209, H446, H510A, H526, H841 and SW1271 cells were 462.9±112.2, >1000, 24.9±6.4, 8.6±0.8, 18.0±0.7, 18.2±4.0, 10.1±0.7, >1000 and 49.2±7.4 mU/mL respectively. Knockdown of OTC increased sensitivity to BCT-100 in H841 cells, mediated partially via apoptosis. Mitochondrial membrane depolarization was observed in BCT-100 treatment and cytochrome c and SMAC were released from mitochondria to cytosol. N-acetylcysteine (NAC), the reactive oxygen species (ROS) scavenger, could reverse the apoptosis induced by BCT-100 significantly. Besides, cell cycle specific proteins, cyclin A2, cyclin B1 and CDK4, were downregulated in a time-dependent manner. The tumor growth was inhibited and median survival of mice was prolonged in BCT-100 group in H446 and H510A xenograft models. Serum and intratumoral arginine level was sharply decreased, associated with G1 arrest and apoptosis in H446 and H510A xenografts. Conclusion: The SCLC cell lines with low expression of ASS1 and OTC were susceptible to BCT-100 treatment. ROS was involved in BCT-100 induced-apoptosis. BCT-100 showed potential anticancer activity in SCLC xenograft models.