Effects of pegylated arginase on small cell lung cancer in vitro and in vivo

Background: Small cell lung cancer (SCLC) is characterised by frequent relapse, and current treatments lack tumour specificity. Arginase is an important enzyme in human, but it is deficient in some tumours. Arginine deprivation has become a potential therapeutic option in selected tumours. BCT-100 is a pegylated arginase that has demonstrated anticancer activity in arginine auxotrophic tumours such as melanoma, hepatocellular carcinoma and acute myeloid leukaemia. One of resistance mechanisms to arginase is overexpression of argininosuccinate synthetase (ASS1) and ornithine transcarbamylase (OTC). This study aims 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 assay was used to detect cell viability of different SCLC cell lines after BCT-100 treatment. Western blotting was used 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 half maximal inhibitory concentration (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, partially mediated via apoptosis. Mitochondrial membrane depolarisation was observed in BCT-100 treatment and cytochrome c and SMAC were released from mitochondria to cytosol. Besides, cell cycle–specific proteins, cyclin A2, cyclin B1, and CDK4, were downregulated in a time-dependent manner. The tumour growth was inhibited and median survival of mice was prolonged in BCT-100 group in H446 and H510A xenograft models. Serum and intratumoural 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. Reactive oxygen species was involved in BCT-100 induced-apoptosis. BCT-100 showed potential anticancer activity in SCLC xenograft models