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Introduction: FGFRs play important roles in cancer development and inhibition of FGFR could disrupt tumor cell proliferation and growth. Four selective FGFR inhibitors have been approved (erdafitinib, pemigatinib, infigratinib, and futibatinib) and several others are in clinical development. Unfortunately upon treatment with these first-generation FGFR inhibitors, acquired resistance often develops and is frequently associated with the emergence of secondary FGFR2/3 kinase domain mutations. Therefore, selectively targeting FGFR2/3 as well as their resistant mutations may render a second-generation treatment approach for the refractory/relapsed patients. Using advanced computation-aided structural analysis and medicinal chemistry design, we have discovered a novel, next-generation, and highly selective FGFR inhibitor, ABSK121. This novel inhibitor demonstrated robust anti-tumor activity in FGFR-dependent tumor models with strong activities against not only de novo but also acquired resistant mutations. Method: ABSK121 was evaluated in biochemical and cellular proliferation experiments for its inhibition on wile type FGFR enzymatic activity and FGFR-dependent cancer cell proliferation. Its potency against FGFR mutations was also analyzed in relevant biochemical and cellular experiments. Efficacy studies were conducted in multiple tumor models to confirm its in vivo activities. Preliminary selectivity profile and ADME profiles were also evaluated. Results: ABSK121 inhibited wild type FGFRs with IC50 Conclusion: ABSK121, presented here by Abbisko Therapeutics, is a highly potent, selective, and next-generation small molecule FGFR inhibitor with great potency against resistant FGFR mutations. Its superior profile supports fast-track preclinical and clinical development. Citation Format: Haiyan Ying, Wenqun Xin, Haibing Deng, Yuan Zhao, Hongping Yu, Zhui Chen, Yao-chang Xu. Discovery and characterization of a next-generation FGFR inhibitor overcoming FGFR resistant mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB317.

Introduction: Aberrant activation of FGF19-FGFR4 signaling pathway plays an essential role in the tumorigenesis of Hepatocellular carcinoma (HCC) and FGFR4 inhibitors have shown preliminary efficacy in recent clinical trials for patients with FGF19 overexpression. However, the observed responses only lasted a few months before tumors relapse. Acquired FGFR4 resistant mutations were found in ~30% of FGFR4 inhibitor responsive patients. Similar FGFR4 mutations haven also been found de novo in about 7-10% of Rhabdomyosarcoma (RMS) and ER-treated invasive lobular carcinoma patients. First generation FGFR4 inhibitors have minimal activity against these de novo or acquired resistant mutations. Therefore, next-generation of FGFR4 inhibitors are needed to overcome these resistant FGFR4 mutations to provide better treatment options for patients. Using advanced computation-aided structural analysis and medicinal chemistry design, we have discovered a next-generation small molecule FGFR4 inhibitor, ABSK012, and demonstrated its strong activities against de novo and acquired resistant FGFR4 mutations while retaining inhibition for wild-type FGFR4. Method: Inhibitory activity of ABSK012 against FGFR4 and FGFR4 mutants was evaluated by MSA assay and its inhibition on FGFR4-dependent cell proliferation was evaluated by Celltiter-Glo assay in wile type FGFR4-dependent cancer cell lines or mutant FGFR4-dependent Ba/f3 cell lines. Its selectivity against other FGFR family member and kinases was analyzed by cellular and KinomeScan profiling. Efficacy studies were conducted in HCC xenograft models and mutant FGFR4-dependent xenograft models including a RMS PDX model harboring FGFR4 V550L mutation. Results: ABSK012 demonstrated strong potency over multiple FGFR4 mutants that are insensitive to a first generation FGFR4 inhibitor BLU-554. It also inhibited wild-type FGFR4 with IC50 Conclusion: ABSK012, presented here by Abbisko Therapeutics, is a highly potent, selective, and next-generation small molecule FGFR4 inhibitor overcoming FGFR4 mutations resistant to first-generation inhibitors. Its superior preclinical profile supports its fast-track development into clinic. Citation Format: Haiyan Ying, Nannan Zhang, Haibing Deng, Fei Yang, Wenqun Xin, Bin Shen, Hongping Yu, Zhui Chen, Yao-chang Xu. Discovery & characterization of a next-generation FGFR4 inhibitor overcoming resistant mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB328.

Epidermal growth factor receptor (EGFR) exon20 insertion mutations and atypical mutations account for about 9% and 20% of EGFR-mutated non-small cell lung cancer (NSCLC), respectively. Currently approved EGFR tyrosine kinase inhibitors (TKIs) have shown efficacy in NSCLC patients with exon20 insertion and atypical mutations, but with limited overall response and high rate of EGFR-related severe adverse events. This may be associated with the inhibition of wild-type (WT) EGFR. ABSK111 is a highly potent, selective, and CNS-penetrable EGFR inhibitor, targeting multiple EGFR and HER2 mutations, including exon20 insertion, atypical, and extracellular mutations. Here we describe the preclinical in vitro and in vivo characterization of ABSK111. ABSK111 potently inhibited the proliferation of BA/F3 cell lines harboring EGFR exon20, atypical and extracellular mutations with higher selectivity for WT EGFR than currently approved EGFR TKIs. ABSK111 also suppressed HER2 atypical and exon20 mutations. Further, ABSK111 potently blocked the phosphorylation of EGFR exon20 insertion mutations and EGFR variant III in BA/F3 cell lines, with less inhibition of WT EGFR signal than the approved TKIs. Moreover, pharmacokinetic and pharmacodynamic studies demonstrated sustained and exposure-dependent suppression of p-ERK in tumor tissue following a single oral dose of ABSK111. Finally, ABSK111 showed dose-dependent anti-tumor activity in BA/F3 tumor models with EGFR exon20 insertion mutations and EGFR variant III without significant body weight loss. Pharmacodynamic analysis of endpoint samples from efficacy study showed sustained inhibition of p-ERK, which was superior to the approved exon20 insertion inhibitor mobocertinib. Taken together, these results demonstrate the ability of ABSK111 to inhibit a broad spectrum of EGFR and HER2 mutations, including exon20 insertions, atypical and extracellular mutations, while sparing the WT form of EGFR. In addition to the application in NSCLC, the activity against EGFR extracellular mutations and the ability to penetrate into brain suggest the application of ABSK111 in glioblastoma multiforme (GBM). Citation Format: Cheng Dai, Juan Peng, Fei Yang, Haibing Deng, Yuan Zhao, Hongping Yu, Yaochang Xu, Zhui Chen, Shuqun Yang. Discovery and characterization of ABSK111, a selective, CNS-penetrable, and broad-spectrum EGFR inhibitor targeting exon20 insertion, atypical and extracellular mutations [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 LB525.