Combination effect of arsenic trioxide and FGFR inhibitor through downregulation of FGFR, Akt and Erk in squamous cell lung carcinoma

Abstract

Background: Lung cancer is the top cancer killer. Squamous cell lung carcinoma (SCC) represents the second most common histologic subtype of lung cancer. Arsenic trioxide (ATO) has been demonstrated to inhibit tumor growth in lung adenocarcinoma and initiate apoptosis in acute promyelocytic leukemia. Fibroblast growth factor (FGF) receptor (FGFR) amplification is shown in some SCC. FGFR inhibitor (e.g. PD173074) has been developed to inhibit FGFR. Methods: The combination effect of ATO and PD173074 was studied using a cell line with FGFR amplification: SK-MES-1. The effect of ATO and/or PD173074 on cell viability and protein expression was studied by MTT assay and Western blot respectively. Cell cycle arrest, phosphatidylserine externalization and mitochondrial membrane depolarization were monitored by flow cytometry. FGFR knockdown was performed with siRNA targeting FGFR. Proteasome inhibitor (MG-132) was used to study the degradation mechanism. The in vivo effect of ATO and/or PD173074 was investigated with a nude mice xenograft model. Results: Combination of ATO and PD173074 reduced cell viability along with increased sub-G1 population, phosphatidylserine externalization and mitochondrial membrane depolarization more significantly than single drug alone. In general, downregulation of FGFR, p-Akt, Akt, p-Src, Src, p-c-Raf, c-Raf, Erk, Bcl-2 and survivin as well as upregulation of p-Erk and cleaved PARP were observed upon ATO and/or PD treatment with or without FGF. MG-132 reversed the degradation of Akt, Src, c-Raf and Erk induced by ATO/PD, but not FGFR, which disclosed proteasome degradation system was involved. Downregulation of FGFR, Akt, Src, c-Raf and Erk as well as cleaved PARP elevation induced by ATO and/or PD were confirmed in vivo. Conclusion: Massive protein degradation (FGFR, Akt, Src, c-Raf and Erk) was induced by ATO and/or PD173074 treatment mainly mediated by activation of proteasome degradation system in SCC cell line SK-MES-1 in vitro and in vivo.