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

Our data showed that both PRSS1 in the culture supernatant of colon cancer cells and recombinant human PRSS1 can cleave mAbs (Fig. 3 , A to K). To identify the cleavage site, we analyzed the N-terminal partial sequence of the cleaved heavy chain using the Edman cleavage procedure ( fig. S3A ). The N-terminal sequence of the cleaved heavy chain was Thr-Val-Ser-Ala-Ala-Ser-Thr-Lys-Gly-Pro-Ser-Val-Phe-Pro-Leu ( fig. S3B ), and cleavage occurred between Val 115 and Thr 116 ( fig. S3C ), a cleavage site that has never been reported. The cleavage site is between the variable heavy chain region and constant heavy chain region of the heavy chain, which is found not only in cetuximab but also in a multitude of mAbs, including bevacizumab and trastuzumab ( fig. S3C ). The culture supernatant of colon cancer cells and recombinant human PRSS1 also cleaved both bevacizumab and trastuzumab ( fig. S3 , D and E) and had almost identical cleavage patterns, which again indicated that PRSS1 secreted by the cancer cells cleaved the mAbs. Nevertheless, neither the culture supernatant of colon cancer cells nor recombinant human PRSS1 could cleave aflibercept, which does not have the potential cleavage site ( fig. S3F ). These results all suggest that PRSS1 in the culture supernatant of colon cancer cells can cleave a range of mAbs that harbor the potential cleavage site, including cetuximab, bevacizumab, and trastuzumab ( fig. S3D and E), decreasing the response to these mAbs and ultimately causing resistance to them. These findings all suggest that PRSS1 may cause cetuximab resistance by cleaving cetuximab to increasingly greater degrees.