Preclinical efficacy of NXP900, a YES1/SRC kinase inhibitor in esophageal squamous cancer models.

Abstract

e15133 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 inhibitor), thereby inhibiting both kinase activity and complex formation with protein partners (Temps et al. Cancer Res. 2021, 81, 5438-5450). In contrast, multi-kinase inhibitors, including dasatinib and bosutinib, block SRC in the active “open” conformation (type 1 inhibitors) promoting the association of SFK and signaling partners via allosteric facilitation of conformational protein activation (Higuchi et al. Cell Rep 2021, 34, 108876). YES1 gene amplification is prevalent in several squamous cancers including esophageal squamous cell carcinoma (ESCC), lung SCC, head and neck SCC, and bladder cancer, indicating that YES1 would be an attractive target in these cancer types. Moreover, crosstalk between YES1 and the Hippo pathway suggests that NXP900 may have a therapeutic potential in squamous cancers with Hippo pathway alterations. Methods: Animal strain: CD1 Nude mice (Charles River). Human ESCC cancer cell lines: KYSE70, OE21, KYSE410, KYSE30 and OE19 cells (Sigma), TE5, and TE14 (Riken). Xenograft tumors were generated by subcutaneous implantation on the right lower flank of the thigh at a cell density of 2x106 to 1x107 cells/mouse at 0.1 mL Matrigel/cell dilution volume per injection. Experiment groups: Vehicle, NXP900 (40 mg/kg); treatment: QD for 28 days, oral gavage. Colony formation assay: 500 cells of 4 cell lines (KYSE70, OE21, KYSE410 and KYSE30) and 1500 cells of 3 cell lines (OE19, TE5 and TE14) were seeded in 24 well plates in triplicates; and treated with NXP900 for 14 days followed by staining with crystal violet. Results: NXP900 strongly inhibited cell proliferation of KYSE70, KYSE410, KYSE30, OE21, OE19, TE5 and TE14 in a colony formation assay. NXP900 significantly inhibited the activating phosphorylation of SRC in KYSE70 cells at 10 nM, while no effect was observed on the inhibitory tyrosine residues on YES1/FYN at 250 nM. Oral administration of NXP900 in a KYSE70 xenograft mouse model with YES1 gene amplification, resulted in an average decrease of tumor volume of 71% while in the vehicle control group tumor volume increased by 472% (p ≤ 0.001), demonstrating significant tumor regression. On Day 27, a mean increase from baseline in body weight of 2.0% and 3.5% was seen in the NXP900 and control groups respectively, indicating good tolerability. Conclusions: NXP900 is a novel potent and selective YES1/SRC kinase inhibitor with subnanomolar IC50 against YES1. NXP900 has marked antitumor efficacy in esophageal carcinoma models in vitro and in vivo providing substantial proof of concept for targeting solid tumors with YES1 and Hippo pathway alterations. IND enabling studies for NXP900 have been completed.