Discovery of ASP6918, a KRAS G12C inhibitor: Synthesis and structure-activity relationships of 1-{2,7-diazaspiro[3.5]non-2-yl}prop-2-en-1-one derivatives as covalent inhibitors with good potency and oral activity for the treatment of solid tumors.

Although KRAS protein had been classified as an undruggable target, inhibitors of KRAS G12C mutant protein were recently reported to show clinical efficacy in solid tumors. In our previous report, we identified 1-{2,7-diazaspiro[3.5]non-2-yl}prop-2-en-1-one derivative (1) as a KRAS G12C inhibitor that covalently binds to Cys12 of KRAS G12C protein. Compound 1 exhibited potent cellular pERK inhibition and cell growth inhibition against a KRAS G12C mutation-positive cell line and showed an antitumor effect on subcutaneous administration in an NCI-H1373 (KRAS G12C mutation-positive cell line) xenograft mouse model in a dose-dependent manner. In this report, we further optimized the substituents on the quinazoline scaffold based on the structure-based drug design from the co-crystal structure analysis of compound 1 and KRAS G12C to enhance in vitro activity. As a result, ASP6918 was found to exhibit extremely potent in vitro activity and induce dose-dependent tumor regression in an NCI-H1373 xenograft mouse model after oral administration.

Mucin 21 confers resistance to apoptosis in an O-glycosylation-dependent manner.

Highly glycosylated mucins protect epithelial surfaces from external insults and are related to malignant behaviors of carcinoma cells. However, the importance of carbohydrate chains on mucins in the process of cellular protection is not fully understood. Here, we investigated the effect of human mucin-21 (MUC21) expression on the susceptibility to apoptosis. MUC21 transfection into HEK293 cells decreased the number of apoptotic cells in culture media containing etoposide or after ultraviolet light irradiation. We used Chinese hamster ovary (CHO) cell variants to investigate the importance of MUC21 glycosylation in the resistance to apoptosis. When MUC21 was expressed in CHO-K1 cells, it was glycosylated with sialyl T-antigen and the cells showed resistance to etoposide-induced apoptosis. MUC21 transfection into Lec2 cells, a variant of CHO cells lacking sialylation of glycans, revealed that the presence of nonsialylated T-antigen also renders cells resistant to etoposide-induced apoptosis. MUC21 was transfected into ldlD cells and the glycosylation was manipulated by supplementation to the medium. Nonsupplemented cells and cells supplemented with N-acetylgalactosamine showed no resistance to etoposide-induced apoptosis. In contrast, these cells supplemented with N-acetylgalactosamine plus galactose expressed sialyl T-antigen and exhibited resistance to etoposide-induced apoptosis. Finally, galectin-3 knockdown in MUC21 transfectants of HEK293 cells did not significantly affect MUC21-dependent induction of apoptosis resistance. The results suggest that T-antigen with or without sialic acid is essential to the antiapoptotic effect of MUC21.

Characterisation of a novel KRAS G12C inhibitor ASP2453 that shows potent anti-tumour activity in KRAS G12C-mutated preclinical models.

BACKGROUND: KRAS is one of the most frequently mutated oncogenes in various cancers, and several novel KRAS G12C direct inhibitors are now in clinical trials. Here, we characterised the anti-tumour efficacy of ASP2453, a novel KRAS G12C inhibitor, in preclinical models of KRAS G12C-mutated cancer. METHODS: We evaluated the in vitro and in vivo activity of ASP2453, alone or in combination with targeted agents and immune checkpoint inhibitors, in KRAS G12C-mutated cancer cells and xenograft models. We also assessed pharmacological differences between ASP2453 and AMG 510, another KRAS G12C inhibitor, using an SPR assay, washout experiments and an AMG 510-resistant xenograft model. RESULTS: ASP2453 potently and selectively inhibited KRAS G12C-mediated growth, KRAS activation and downstream signalling in vitro and in vivo, and improved the anti-tumour effects of targeted agents and immune checkpoint inhibitors. Further, ASP2453 had more rapid binding kinetics to KRAS G12C protein and showed more potent inhibitory effects on KRAS activation and cell proliferation after washout than AMG 510. ASP2453 also induced tumour regression in an AMG 510-resistant xenograft model. CONCLUSIONS: ASP2453 is a potential therapeutic agent for KRAS G12C-mutated cancer. ASP2453 showed efficacy in AMG 510-resistant tumours, even among compounds with the same mode of action.