Abstract 5520: NXP900, a phase 1, first-in-class YES1/SRC inhibitor demonstrates potent single agent activity and synergy with ALK inhibitors in ALK resistant NSCLC models

Abstract Background: NXP900 (eCF506) is a novel potent and selective SRC family kinase (SFK) inhibitor, (IC50 of 0.47 nM against YES1) which possesses a unique/first-in-class binding mode-of-action. NXP900 locks its target into its native “closed” conformation, thereby inhibiting both kinase activity and scaffolding function with protein signaling partners (Temps et al. Cancer Res. 2021, 81, 5438-5450). In contrast, multi-kinase inhibitors, including dasatinib and bosutinib, lock SRC in the active “open” conformation (type 1 inhibitors) promoting the association of SFK and signaling partners via allosteric facilitation (Higuchi et al. Cell Rep 2021, 34, 108876). Anaplastic lymphoma kinase (ALK) inhibitors are clinically effective for the treatment of non-small cell lung cancer (NSCLC) patients whose tumors harbor ALK fusion genes. However, the development of resistance to ALK inhibitors in patients is nearly universal. Activation of SFK signaling has previously been shown to mediate acquired resistance to ALK inhibition in NSCLC lines (Yoshida et al. Int J Oncol. 2017, 51, 1533-1540, Sato et al., JCO Precis. Oncol., 2022) indicating a potential for NXP900 to overcome an important bypass resistance mechanism and offer therapeutic potential in cancers with acquired resistance to ALK inhibitors. Materials and Methods: Cell lines: Resistant cell lines to ALK inhibitors were generated from NCI-H2228 (EML4-ALKv3) and NCI-H3122 (EML4-ALKv1). Cell proliferation assays: Cells were diluted in the corresponding ATCC recommended medium and dispensed in a 384-well plate, depending on the cell line used, at a density of 100 - 6400 cells per well. For each cell line the optimal cell density is used and cells were treated with ALK inhibitors lorlatinib and/or NXP900 for 120 h and underwent ATPlite viability assay. Drug combination effects in vitro were studied using synergy scoring methods applied across multiple fixed dose-ratio mixtures. Results: NXP900 single agent potently inhibited cell proliferation of ALK resistant cell lines, with a median GI50=30nM. At the same concentration range, NXP900 potently inhibited the activating SRC autophosphorylation, and demonstrated synergy in combination with lorlatinib in lorlatinib-resistant cell lines derived from NCI-H2228 (EML4-ALKv3) and NCI-H3122 (EML4-ALKv1) cells. Conclusions: Despite high response rates to lorlatinib and long duration of response, 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 is synergistic with lorlatinib in NSCLC models harboring different variants of the ALK gene fusion. Altogether, these data suggest that NXP900 may have therapeutic potential in cancers with acquired resistance to ALK inhibitors. A FIH, Phase1 dose escalation study for NXP900 is ongoing. Citation Format: Neil O. Carragher, Enrique Poradosu, Asier Unciti-Broceta. NXP900, a phase 1, first-in-class YES1/SRC inhibitor demonstrates potent single agent activity and synergy with ALK inhibitors in ALK resistant NSCLC models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5520.