Abstract LB565: Efficacy of a highly potent and selective KIT V654A inhibitor for treatment of imatinib resistant GIST
Authors: Grassian Alexandra R. , Kim Joseph , Ahmad Omar , Barvian Kevin , Davis Alison , Dineen Tom , Hu Wei , Job Ebby , Moine Ludivine , Newberry Kate , Roche Maria , Shorten Doug , Choi Yeon Sook , Wolenski Francis , Bauer Sebastian , Serrano Cesar , Trent Jonathan , George Suzanne 
Published: June 2022

Abstract
Gastrointestinal stromal tumor (GIST) is the most common type of sarcoma, with approximately 5,000 patients diagnosed per year in the US. Approximately 80% of patients with GIST present with mutations in the c-KIT oncogene at exon 9 or 11, which leads to constitutive, ligand-independent activation of the KIT receptor tyrosine kinase. For patients with metastatic GIST, frontline therapy with imatinib is effective, with a response rate of approximately 51-54% and median progression-free survival (PFS) of 19-23 months, in a molecularly unselected population. Other agents are approved for advanced GIST, without molecular selection, after progression on imatinib, including sunitinib, regorafenib, and ripretinib; however, response rates are less than 10% with PFS of approximately 5-6 months. Notably, patients who progress on imatinib and other tyrosine kinase inhibitors may develop a variety of on-target resistance mutations in the KIT oncogene, such as those in exon 17 (including at amino acids D816 and D820, activation loop mutation), exon 13 (V654A, ATP-binding region mutation), and less frequently in exon 14 (T670I, gatekeeper mutation). Several KIT inhibitors have been developed to potently target the exon 17 resistance mutations (avapritinib and ripretinib); however, there remains an important medical need in 2nd- and 3rd-line therapy in a molecularly unselected population of imatinib-resistant GIST. This suggests more broad-spectrum KIT inhibition is likely required, a hypothesis supported by the observation of large inter- and intra-patient heterogeneity of KIT secondary mutations across hundreds of samples obtained from patients with GIST treated with avapritinib. Sequencing data from the NAVIGATOR phase 1 trial (NCT02508532) revealed that patients with KIT mutant GIST and with the KIT V654A secondary resistance mutation had a poor response to treatment with avapritinib. To address this, we developed a highly potent and selective inhibitor of KIT V654A. This inhibitor showed dose-dependent modulation of downstream pharmacodynamic markers and induced tumor regression in a mastocytoma xenograft model driven by an exon 11 plus 13 V654A resistance mutation. Importantly, this inhibitor was generally well-tolerated and showed high selectivity over wild-type KIT. These findings suggest this novel KIT inhibitor has the potential to be used as a single agent or combination therapy for patients with imatinib-resistant GIST harboring the KIT V654A mutation.
Citation Format: Alexandra R. Grassian, Joseph Kim, Omar Ahmad, Kevin Barvian, Alison Davis, Tom Dineen, Wei Hu, Ebby Job, Ludivine Moine, Kate Newberry, Maria Roche, Doug Shorten, Yeon Sook Choi, Francis Wolenski, Sebastian Bauer, Cesar Serrano, Jonathan Trent, Suzanne George. Efficacy of a highly potent and selective KIT V654A inhibitor for treatment of imatinib resistant GIST [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 LB565.