LAUSR

Gastrointestinal stromal tumors are mesenchymal tumors arising in the stomach and small bowel and more rarely in the rectum, esophagus, peritoneum and retroperitoneum. These tumors are characterized by KIT or PDGFRA mutations. KIT mutations are all in frame and lead to constitutive tyrosine kinase domain activation without ligand binding. Mutations concern four exons (9, 11, 13 and 17) but mainly exon 11. In this work we report a case of a GIST patient with wild-type PDGFRA but bearing two mutations in KIT exon 9, i.e., the insertion mutation Y503_F504insAY and the missense mutation K509N. The patient was treated with Imatinib at standard regimen dose (400 mg/day), and responded well. Accordingly, in silico experiments were performed to disclose the effects exerted by these new mutations on the protein structure, its thermodynamic stability, and the ability to promote/interfere with Imatinib binding. Direct drug binding thermodynamics and kinetics of the mutant KIT were measured using isothermal titration calorimetry. FInally, in vitro kinase assays were performed to monitor the phosphorylation status of this new mutant KIT. The prototypical KIT mutations Δ559 and T670I were also analyzed in parallel for comparison. To our knowledge, only AY 502-503 duplication/insertion and K509I substitution have been previously reported. Citation Format: Erik Laurini, Suzana Aulic, Domenico Marson, Maurizio Fermeglia, Roberta Riboni, Marco Lucioni, Elena Dellera, Mario Alessiani, Vittorio Perfetti, Sabrina Pricl. New c-KIT mutations in GISTs: Bad for good [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 812.