Engineering a Redox-Responsive Bimolecular Prodrug for Targeted Gastric Cancer Combination Therapy: Design, Synthesis, and In Vivo Evaluation

Combination chemotherapy often suffers from asynchronous pharmacokinetics and off-target toxicity. To address this, we designed a novel, unreported engineered prodrug—a redox-responsive bimolecular prodrug (CA-4-Gefitinib)—by engineering a disulfide bond as a cleavable linker to covalently conjugate the tubulin inhibitor combretastatin A-4 (CA-4) and the EGFR inhibitor Gefitinib. This molecular-level prodrug design enables tumor-selective drug activation in high-glutathione environments. This prodrug exhibited enhanced cellular uptake and potent antiproliferative activity against SGC-7901 gastric cancer cells, with significantly improved selectivity over normal cells (safety index of 98). Mechanistically, this engineered prodrug disrupted microtubule polymerization, induced G2/M arrest, suppressed ERK signaling, and promoted apoptosis. The prodrug’s pharmacokinetic profile showed prolonged circulation and reduced systemic exposure to free CA-4, indicating favorable biodistribution. In a murine xenograft model, this prodrug demonstrated superior antitumor efficacy and markedly reduced systemic toxicity compared to the combination of free drugs. Our work presents a rational prodrug design strategy—a redox-responsive drug–drug conjugate prodrug—that synchronizes drug delivery, enhances tumor targeting, and maximizes synergistic efficacy, offering a promising platform for advanced cancer combination therapy.