Discovery of novel hydroxycamptothecin derivatives as potent Topo I inhibitors for antitumor guided by molecular...

Camptothecin (CPT) and its derivatives are clinically validated topoisomerase I (Topo I) inhibitors with broad-spectrum antitumor activity. Based on the stabilization of the covalent DNA-Topo I complex, modification at the 10-position of the CPT scaffold represents a promising strategy to enhance binding affinity. Herein, the rational design, synthesis, and biological evaluation of novel 10-substituted CPT derivatives guided by molecular dynamics (MD) simulations are presented. A total of 45 derivatives were synthesized and evaluated for their antiproliferative activity against three human cancer cell lines (A549, HCT116, HepG2). Structure-activity relationship (SAR) studies demonstrated that the carbonylmethylene linker and 3-methoxy-4-methylphenyl substitution afforded optimal potency. The most promising compound C6 showed exceptional cytotoxicity against HCT116 cells with an IC₅₀ value of 0.001 μM, 16-fold more potent than that of compound SN-38. Mechanistic studies confirmed that C6 induced S-phase cell cycle arrest and apoptosis in HCT116 cells, suppressed cell migration and invasion, and downregulated Topo I protein expression in a concentration-dependent fashion. Furthermore, compound C6 exhibited significant in vivo antitumor efficacy in an HCT116 xenograft model with a favorable safety profile. Pharmacokinetic evaluation in rats confirmed moderate absolute bioavailability and a reasonable half-life. Collectively, compound C6 was identified as a potent Topo I inhibitor with promising antitumor activity.