LAUSR

Background: NXP900 (formerly known as eCF506) is a novel SRC/YES1 family kinase (SFK) inhibitor that locks SRC into its native closed conformation (= type 1.5), thereby inhibiting both kinase activity and complex formation with protein partners including FAK (Temps et al. Cancer Res. 2021, 81, 5438-5450). This mode of inhibition differentiates it from dasatinib, which blocks SRC into an open conformation (type 1) that promotes SRC-FAK interactions and increases FAK autophosphorylation. According to Watanabe and coworkers (Higuchi et al. Cell Rep 2021, 34, 108876), the enhancement of SRC-protein complex formation makes type 1 SFK inhibitors allosteric facilitators of conformational protein activation. Although dasatinib is a potent inhibitor of kinase activity, because of its allosteric effects, an in vivo decrease in tumor drug exposure below the active threshold could lead to fast activation of SFK-mediated signaling, temporarily promoting cancer growth until the next dose is administered. In contrast, the capacity of NXP900 to inhibit SRC in its inactive conformation should result in a more durable blockade of SFK-induced signaling; a critical advantage to prolong on-target inhibition and improve antitumor efficacy. Materials and Methods: Mice strain: CD1 Nude. Cell line: TOV-21G. Xenograft: bilateral SC implantation of 0.1M cells with matrigel. Groups: Vehicle PO QD; dasatinib 30 mpk PO QD; NXP900 20 mpk PO QD; NXP900 40 mpk PO QD; NXP900 80 mpk PO QD. PD study (n=3): 3 d treatment, tumors retrieved 3 and 24 h after last dose. H&E, IHC. Efficacy (n=5): 28 d treatment. Results: An ovarian clear cell carcinoma (OCCC) cell model, TOV-21G, was implanted subcutaneously in mice to study SRC and FAK phosphorylation (Y419 and Y397, respectively) after oral administration of NXP900 and dasatinib. Tumors were excised 3 and 24 h post-treatment and analyzed by IHC. NXP900 showed lower phosphorylated SRC levels compared to the vehicle control for all doses. Dose response correlation was clearly observed for NXP900 in tumors analyzed 24 h after the last dose, with complete inhibition achieved at 40 mg/Kg. Importantly, comparison between vehicle and dasatinib groups showed that the tumors from the dasatinib-treated group exhibited higher levels of phospho-SRC 24 h after the last dose, evidence of the paradoxical activation of SRC proposed by Watanabe as a consequence of blocking SRC in an open conformation. Analysis of tumor growth showed that treatment with NXP900 resulted in higher anticancer effect than that of dasatinib. Conclusions: NXP900 induces superior target inhibition and anticancer activity than dasatinib in an OCCC xenograft model. The PD study suggests that the conformation selective mode of inhibition of NXP900 is more favorable for clinical development against SFK-driven cancers. Citation Format: Saúl Navarro-Marchal, Carolin Temps, Iñigo Lanzagorta-Calvillo, John C. Dawson, Enrique Poradosu, Neil O. Carragher, Valerie G. Brunton, Asier Unciti-Broceta. In vivo studies demonstrate differences in target inhibition and anticancer efficacy between NXP900 and dasatinib in ovarian clear cell carcinoma model. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4031.