PGP and colonic neoplasm: However, in the SW620/Ad300 (P-gp-overexpressing) and S1-M1-80 (ABCG2-overexpressing) colon cancer xenograft models, the combination of regorafenib and paclitaxel or the combination of regorafenib and topotecan resulted in a synergistic antitumor effect which demonstrated that regorafenib overcame the resistance of paclitaxel to P-gp-overexpressing SW620/Ad300 tumors and the resistance of topotecan to ABCG2-overexpressing S1-M1-80 tumors in mice (Wang et al., 2017b; Zhang et al., 2019).