Synergistic combination of DT-13 and topotecan inhibits human gastric cancer via myosin IIA-induced endocytosis of EGF receptor in vitro and in vivo

// Xiao-Wen Yu 1 , Sensen Lin 2 , Hong-Zhi Du 1 , Ren-Ping Zhao 3 , Shu-Yun Feng 1 , Bo-Yang Yu 4 , Lu-Yong Zhang 1 , Rui-Ming Li 5 , Chang-Min Qian 5 , Xue-Jun Luo 5 , Sheng-Tao Yuan 1 , Li Sun 2 1 Jiangsu Center for Pharmacodynamics Research and Evaluation, China Pharmaceutical University, Nanjing, China 2 Jiangsu Key laboratory of Drug Screening, China Pharmaceutical University, Nanjing, China 3 Department of Biophysics, University of Saarland, Homburg, Germany 4 Jiangsu Key Laboratory of TCM Evaluation and Translational Research, Department of Complex Prescription of TCM, China Pharmaceutical University, Nanjing, China 5 Tasly Research Institute, Tianjin Tasly Holding Group Co. Ltd., Tianjin, China Correspondence to: Sheng-Tao Yuan, e-mail: cpuYuanst@163.com Li Sun, e-mail: cpusunli@126.com Keywords: DT-13, topotecan, NM IIA, EGFR, gastric cancer Received: October 10, 2015 Accepted: March 31, 2016 Published: April 20, 2016 ABSTRACT Combination therapy has a higher success rate for many cancers compared to mono-therapy. The treatment of Topotecan (TPT) on gastric cancer (GC) is limited by its toxicity and the potential drug resistance. We found that the combination of the saponin monomer 13 from the dwarf lilyturf tuber (DT-13), performing anti-metastasis and anti-angiogenesis effects, with TPT synergistically induced apoptotic cytotoxicity in GCs with high EGF receptor (EGFR) expression, which was dependent on DT-13-induced endocytosis of EGFR. With TPT, DT-13 promoted EGFR ubiquitin--mediated degradation through myosin IIA-induced and Src/ caveolin-1 (Cav-1)-induced endocytosis of EGFR; inhibited EGFR downstream signalling and then increased the pro-apoptotic effects. Moreover, the synergistic pro-apoptotic efficacy of DT-13 and TPT in GCs with high EGFR expression was eliminated by both the NM II inhibitor (-)-blebbistatin and MYH-9 shRNA. The combination therapy of DT-13 with TPT showed stronger anti-tumour effects in vivo compared with their individual effects. Moreover, the results of combination therapy revealed selective upregulation of pro-apoptotic activity in TUNEL assays and cleaved caspase-3 and NM IIA in immunohischemical analysis; while specific downregulation of p-extracellular regulated kinase 1/2 (p-ERK1/2), EGFR and Cav-1 in immunohischemical analysis. Collectively, these findings have significant clinical implications for patients with tumours harbouring high EGFR expression due to the possible high sensitivity of this regimen.