Discovery of a novel Wnt inhibitor DK419: Reversing temozolomide resistance in glioblastoma by switching off Wnt/β-catenin signaling pathway to inhibit MGMT expression.

Temozolomide (TMZ) remains the primary oral chemotherapeutic agent for glioblastoma, but its efficacy is hampered by resistance mechanisms involving O6-methylguanine-DNA methyltransferase (MGMT). MGMT repairs the TMZ-induced lethal O6-methylguanine (O6-MeG) lesions, leading to treatment resistance. Current small molecule covalent MGMT inhibitors have limited clinical application due to severe hematological toxicity when used with TMZ. Therefore, alternative strategies to overcome MGMT-mediated resistance are critically needed. Targeting the Wnt/β-catenin signaling pathway to suppress MGMT expression presents a promising approach. We synthesized and discovered that a novel Wnt inhibitor, DK419 (6-chloro-2-(trifluoromethyl)-N-(4-(trifluoromethyl)phenyl)-1H -benzimidazole-4-carboxamide), effectively suppressed MGMT expression within 12 h in TMZ-resistant SF763 and SF767 cell lines. DK419 demonstrated synergistic cytotoxic effects with TMZ in these cell lines, while only an additive effect was observed in MGMT-negative SF126 cells. Furthermore, DK419 significantly enhanced TMZ's inhibitory effects on cell proliferation, colony formation, invasion, and migration, while also promoting apoptosis. In a resistant mouse tumor xenograft model, DK419 significantly boosted TMZ's tumor growth suppression, maintaining good biosafety. Western blot analysis revealed that DK419 markedly inhibited the nuclear translocation of β-catenin and decreased the expression of its downstream targets, Cyclin D1 and MGMT. The addition of the Wnt activator LiCl reversed DK419-induced effects on β-catenin nuclear translocation and Cyclin D1 and MGMT expression. For the first time, our findings demonstrate that DK419 can significantly enhance glioblastoma sensitivity to TMZ by modulating the Wnt/β-catenin pathway to downregulate MGMT expression.