A recombinant chimeric protein specifically induces mutant KRAS degradation and potently inhibits pancreatic tumor growth

// Ting Pan 1, 2, 3 , Yiwen Zhang 1, 2, 3 , Nan Zhou 1, 2, 3 , Xin He 1, 2, 3 , Cancan Chen 1, 2, 3 , Liting Liang 1, 3 , Xiaobing Duan 1, 2 , Yingtong Lin 1, 3 , Kang Wu 1, 2, 3 , Hui Zhang 1, 2, 3 1 Institute of Human Virology, Sun Yat-Sen University, Guangzhou, Guangdong, China 2 Key Laboratory of Tropical Diseases Control, Ministry of Education, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, Guangdong, China 3 Guangdong Engineering Research Center for Antimicrobial Agent and Immunotechnology, Zhongshan School of Medicine, Sun Yat-Sen University, Guangzhou, Guangdong, China Correspondence to: Hui Zhang, email: zhangh92@mail.sysu.edu.cn Keywords: pancreatic cancer, Vif, Ras binding domain, ubiquitin, KRAS Received: March 01, 2016      Accepted: June 03, 2016      Published: June 14, 2016 ABSTRACT Pancreatic cancer is one of the most lethal human diseases, with an all-stage 5-year survival rate below 5%. To date, no effective and specific therapy is available for this disease. Mutations in KRAS are frequently reported in pancreatic and many other cancers; thus, KRAS is an attractive therapeutic target. Our objective was to specifically eliminate mutant KRAS and induce cell death of tumors expressing this mutant protein. We thus constructed several chimeric proteins by connecting the C-terminal domains of several adaptor proteins of E3 ubiquitin ligases such as CBL, CHIP, E6AP, and VHL, as well as VIF encoded by human immunodeficiency virus type 1 (HIV-1), to the Ras binding domain (RBD) of Raf. Although all of these chimeric proteins caused the degradation of mutant KRAS and the death of KRAS-mutant-tumor cell lines, the RBD-VIF with a protein transduction domain (PTD), named PTD-RBD-VIF, had the strongest tumor-killing effect. Intraperitoneally administered recombinant PTD-RBD-VIF potently inhibited the growth of xenografted KRAS-mutant pancreatic cancer cells. Our findings indicate that recombinant PTD-RBD-VIF, a chimeric protein with a combined cellular-viral origin, could be further developed for the treatment of various tumors harboring mutant or over-activated KRAS, especially for cases presenting with pancreatic cancer recurrence after surgery.