Celastrol synergizes with MEK1 inhibitor nedometinib to overcome resistance in bladder cancer via dual suppression of CDK1/CDC5L and feedback-activated Akt/STAT3.

Bladder cancer, particularly in its advanced and cisplatin-resistant forms, poses a significant clinical challenge due to limited therapeutic options. In this study, we demonstrate that concurrent inhibition of cyclin-dependent kinase 1 (CDK1) and cell division cycle 5-like (CDC5L) strongly suppresses bladder cancer cell growth. The natural product celastrol (CST) downregulated both CDK1 and CDC5L expression in cisplatin-resistant and PTEN-mutant bladder cancer cells in a reactive oxygen species-dependent manner. Combining CST with the specific MEK1 inhibitor nedometinib (NB) synergistically enhanced the downregulation of CDK1 and CDC5L, promoted apoptosis and reactive oxygen species accumulation, and significantly inhibited xenograft tumor growth in vivo. Mechanistically, NB monotherapy triggered compensatory activation of the pro-survival Akt and STAT3 pathways, a resistance mechanism effectively counteracted by the addition of CST. Furthermore, the CST + NB combination demonstrated efficacy in rectal adenocarcinoma, that exhibit co-expression of CDK1, CDC5L, and MEK1. The combination regimen displayed a favorable safety profile with no detectable systemic or neurobehavioral toxicity. Our results indicate that CST dually inhibits CDK1 and CDC5L and synergizes with the MEK1 inhibitor by suppressing feedback-driven resistance pathways. These findings support the CST + NB combination as a novel multi-target therapeutic strategy with potent activity against bladder cancer and rectal adenocarcinoma.