Abstract 615: NXP900, a novel YES1/SRC kinase inhibitor in phase 1, demonstrates potent inhibition of proliferation in cell lines resistant to ALK and EGFR inhibitors
Authors: Carragher Neil O. , Poradosu Enrique , King Ben , Munro Alison F. , Dawson John C. , Unciti-Broceta Asier 
Published: March 2024

Abstract
Background: NXP900 (eCF506) is a novel potent and selective SRC family kinase (SFK) inhibitor, (IC50 of 0.47 nM against YES1). NXP900 locks its target into its native “closed” conformation (type 1.5), thereby inhibiting both kinase activity and complex formation with protein partners (Temps et al. Cancer Res. 2021, 81, 5438). In contrast, multi-kinase inhibitors, including dasatinib and bosutinib, block SRC in the active “open” conformation (type 1) promoting the association of SFK and signaling partners via allosteric facilitation (Higuchi et al. Cell Rep. 2021, 34, 108876). Activation of SFK suggests that NXP900 may have therapeutic potential in cancers with acquired resistance to EGFR and ALK inhibitors.
Methods: Cell lines: Alectinib sensitive (NCI-H2228, ATCC) and osimertinib sensitive (PC9, RIKEN). Alectinib resistant (H2228-ALR1, H2228-ALR2, H2228-ALR3, H2228-ALR4) and osimertinib resistant (PC9-OR1, PC9-OR3) cell lines were generated by treatment of NCI-H2228 or PC9 with increasing concentrations of, respectively, alectinib or osimertinib. Cell proliferation assay: Intracellular ATP (Oncolines B.V.); cells were treated with inhibitors for 120 hours. Reverse Phase Protein Array (RPPA): Protein extracts were prepared from cell lines at sequential timepoints following treatment with NXP900 or a combination of NXP900 and osimertinib. Extracts were printed as a concentration series onto nitrocellulose coated slides across multiple sub-arrays using an Aushon2470 arrayer, each sub-array was addressed with individual mono-specific antibodies to quantify the abundance of SRC, EGFR and other canonical cancer signaling pathway phosphorylation events.
Results: NXP900 single agent potently inhibited cell proliferation of ALK sensitive (GI50=83nM) and all ALK resistant cell lines (GI50=5.8-16nM). GI50 for EGFR sensitive and EGFR resistant cells were 605 nM and 826-4665 nM, respectively. In combination with a fixed concentration of osimertinib (160nM), NXP900 potently reversed osimertinib resistance in both EGFR resistant cell lines (GI50= 43-121 nM).
Conclusions: Despite high response rates to osimertinib and alectinib, acquired resistance almost universally arises. Here we demonstrate that NXP900 can potently inhibit cell proliferation of ALK resistant cell lines as a single agent and EGFR resistant cell lines in combination with osimertinib. Activation of SFK and YAP1 has been shown to be important in the development of resistance to ALK and EGFR treatment. We have previously demonstrated that NXP900 potently inhibits YAP1 nuclear localization and induces tumor regressions in squamous models in vivo providing additional proof of concept for targeting solid tumors with YES1/SRC and Hippo pathway alterations. A FIH, Phase1 dose escalation study for NXP900 has been initiated.
Citation Format: Neil O. Carragher, Enrique Poradosu, Ben King, Alison F. Munro, John C. Dawson, Asier Unciti-Broceta. NXP900, a novel YES1/SRC kinase inhibitor in phase 1, demonstrates potent inhibition of proliferation in cell lines resistant to ALK and EGFR inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 615.