PRSS contributes to cetuximab resistance in colorectal cancer

Tan, Zhaoli; Gao, Lihua; Wang, Yan; Yin, Huihui; Xi, Yongyi; Wu, Xiaojie; Shao, Yong; Qiu, Weiyi; Du, Peng; Shen, Wenlong; Fu, Ling; Jia, Ru; Zhao, Chuanhua; Zhang, Yun; Zhao, Zhihu; Sun, Zhiwei; Chen, Hongxing; Hu, Xianwen; Xu, Jianming; Wang, Youliang

Although PRSS1 in the culture supernatant of colon cancer cells could cleave cetuximab, bevacizumab, and trastuzumab, the cleavage pattern of cetuximab differed from that of completely humanized mAbs such as bevacizumab and trastuzumab, which had almost identical patterns of cleavage ( fig. S4A ). The potential cleavage region of cetuximab differed from the cleavage regions of bevacizumab and trastuzumab by just one amino acid, which was alanine in cetuximab and serine in bevacizumab and trastuzumab ( fig. S3C ). Therefore, we hypothesized that the PRSS1-mediated cleavage of mAbs may be sequence specific and considered whether mutating some amino acids in the potential cleavage region could prevent the PRSS1-mediated cleavage of mAbs. To clarify the sequence specificity, the ZDOCK algorithm (28) (a built-in module of Accelrys Discovery Studio) was used to simulate the docking of cetuximab and PRSS1, whose conformations were derived from the crystal structures PDB:1YY8 and PDB:2RA3, respectively. Then, we designed and purified 10 mutant cetuximab mAbs, which each had a mutation in the cleavage region containing V115 and T116 and a potential recognition region containing S84, L114, and A120 based on the structural modeling and computational design (figs. S3C and S4B). The PRSS1-mediated cleavage of the mutant mAbs containing L114 and T116 was lower than that of cetuximab, while the PRSS1-mediated cleavage of the mutant mAbs containing V115 was greater than that of cetuximab ( fig. S4, C and D) . However, the PRSS1-mediated cleavage of the mutant mAbs containing S84 and A120 was almost identical to that of cetuximab ( fig. S4 , E and F).