The SRC family kinase inhibitor NXP900 demonstrates potent antitumor activity in squamous cell carcinomas

Abstract

NXP900 is a selective and potent SRC family kinase (SFK) inhibitor, currently being dosed in a phase 1 clinical trial, that locks SRC in the "closed" conformation, thereby inhibiting both kinase-dependent catalytic activity and kinase-independent functions. In contrast, several multi-targeted kinase inhibitors that inhibit SRC, including dasatinib and bosutinib, bind their target in the active "open" conformation, allowing SRC and other SFKs to act as a scaffold to promote tumorigenesis through non-catalytic functions. NXP900 exhibits a unique target selectivity profile with sub-nanomolar activity against SFK members over other kinases. This results in highly potent and specific SFK pathway inhibition. Here, we demonstrate that esophageal squamous cell carcinomas and head and neck squamous cell carcinomas are exquisitely sensitive to NXP900 treatment in cell culture and in vivo, and we identify a patient population that could benefit from treatment with NXP900.

Keywords: ESCC; HNSCC; Src family kinases; anti-cancer drug; inhibitor.

Figure 1

SFK inhibition by NXP900.A, NXP900 locks SRC in its inactive conformation. B and C, initial screen of squamous cell carcinoma types showed that ESCC cell line KYSE70 and HNSCC cell line CAL27 had a significant reduction in cell viability in response to (B) high and (C) low concentrations of NXP900 in long-term (14-days) colony forming assay. D, activating phosphorylation levels of SRC family kinases were significantly reduced after 24 h of treatment with a low concentration of NXP900 in KYSE70 and CAL27 cells. E, no significant difference in inhibitory phosphorylation levels of YES1/FYN and activation levels of negative SRC regulator, CSK, was observed after NXP900 treatment.

Figure 2

Effect of NXP900 on ESCC cell viability.A, short-term treatment of ESCC cells with NXP900 for 72 h showed substantial reduction in cell viability, except for the KYSE30 cell line. B, long-term treatment of ESCC cells with NXP900 every other day for 14 days showed a significant reduction in cell viability at low concentrations, except for the KYSE30 cell line that showed the presence of a resistant population of cells, even at high concentrations of NXP900.

Figure 3

Effect of NXP900 on HNSCC cell viability.A, short-term treatment of HNSCC cells with NXP900 for 72 h showed a substantial reduction in cell viability, except for FADU and MSK921 cell lines. B, long-term treatment of HNSCC cells with NXP900 every other day for 14 days showed a significant reduction in cell viability at low concentrations, except for FADU and MSK921 cell lines that showed the presence of a resistant population of cells, even at 1 uM NXP900.

Figure 4

In vivo efficacy and YAP1 regulation. Average tumour volumes significantly decreased when mice with (A) KYSE70 and CAL27 xenografts were treated with 40 mg/kg NXP900. B, mice with a FADU cell line xenograft did not show a significant decrease in tumour volume compared to control when treated with NXP900. C, schematic diagram of YAP1 regulation by YES1. D, dose-dependent reduction in high nuclear YAP in the KYSE70 cell line by NXP900 after 24 h of treatment. E, representative images of high (red) and low (green) nuclear YAP in the KYSE70 cell line.