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As the representative targeted anticancer drug for colon cancer patients, cetuximab is the EGFR targeted therapeutic antibody and used for treatment of KRAS wild type cancers. Even some patient with KRAS wt gene did not respond cetuximab. However, there is no treatment available for cetuximab-resistant patient group, which is almost 50% of KRAS WT gene holders. Recently, our team identified cetuximab primary resistant related proteins named as mtRTK (mutant receptor tyrosine kinase) by array analysis based cetuximab responder or non-responder colon cancer patient tissues. We investigated mtRTK’s oncogenic potential as a novel anti-cancer target. A large proportion of colon cancer patients (36.2% Caucasian, 56.9% Korean) expressed the mtRTK was identified, using the sequencing analysis of patient samples. Based on these results, our efforts have led to the discovery of WM-S1, mtRTK inhibitor, which is the first mtRTK inhibitor in clinical development. The potent enzyme inhibitor showed a high anticancer activity confirmed in Patient-Derived Cells (PDC) and Patient-Derived Xenograft (PDX) animal models expressing the mutation. In preclinical studies demonstrate that WM-S1 is well tolerated in rats and dogs. Furthermore, WM-S1 has potent anticancer activities for various solid tumor (NSCLC, cholangiocarcinoma, etc.) including activated mtKRAS colon cancer expressing the mtRTK. Currently we are investigating WM-S1 in a phase 1a trial in AUS, which is the first mtRTK inhibitor in clinical development. Meanwhile, the mtRTK inhibitor WM-S1 drives antitumor immunity (with anti-PD-L1) in NSCLC. Combinational approaches with immunotherapy showed that synergistic effect of WM-S1 and anti-PD1 monoclonal antibody, suppressing tumor growth by 75% in anti-PD1 resistance NSCLC-derived humanized mouse model. A phase 1b trial is expected to develop WM-S1 through not only indication expansion but also combination therapy with immuno-checkpoint inhibitors in the USA, AUS and KOR from Q2 2022. In conclusion, mtRTK is a potential oncogenic driver mutation in various solid tumor. A first-in-class anticancer agent WM-S1 targeting mtRTK can be promising therapeutic agents for cetuximab-resistant colon cancer patients regardless of KRAS mutation status and other cancers. Citation Format: Joseph Kim, Jai-Hee Moon, Kyung-Mi Lee, Hyun Ryu, Eun Hye Park, Sang Hee Kim, Jeong Seok Kim, Young Ok Ko, Yong Seok Kim, Hyo Jin Kim, Tae Young Kim Kim, Moon Seong Yoo, Soll Jin, Seongrak Kim, Yoon Sun Park, Min Ki Lee, Mi So Lee, Ji Hyun Go, Yu Geun Ji, Jun Hyung Lee, Haneul Lee, Min Hwa Kim, Eun Hee Ko, Yeo Jin Lee, Seung-Mi Kim, Joon-yee Jeong, Yeon-seoung Choi, Seung-geon Bae, Jinwoo Lee, Won Jun Lee, Min-Kyeong Kim, Ji min Shin, Dong-in Koh, Sun-Chul Hur, Chun-Ho Park, Hyun Ho Lee, Dong-Hoon Jin. WM-S1, the novel small molecule inhibitor of mutant RTK/receptor tyrosine kinase, for the treatment of cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6219.