Gemcitabine–Doxorubicin Combination Polymer-Drug Conjugate Prepared by SPAAC Click Chemistry: In Vitro Characterization

Combination chemotherapy is preferred for the treatment of ovarian cancer (OC). Systemic toxicity, however, frequently limits the effectiveness of treatment. Polymer-drug conjugates (PDCs) containing synergistic combinations of chemotherapeutic drugs can be used to enhance therapeutic efficacy. We earlier reported the use of a strain-promoted [3 + 2] azide-alkyne cycloaddition (SPAAC)-mediated polymerization method for the preparation of single-drug PDCs. In this report, the polymerization method was used to prepare gemcitabine-doxorubicin combination PDC. The PDC had a high molecular weight (M_w 1360 kDa) and high drug loading (36.6% weight gemcitabine; 7.0% weight doxorubicin). It demonstrated cathepsin B-catalyzed drug release at pH 5.0 and good hydrolytic stability at pH 7.4. The combination index analysis of free gemcitabine and free doxorubicin showed a concentration-dependent synergism (combination index < 1) in OVCAR-3 OC cells. Compared to individual gemcitabine PDC (the concentration that inhibited 50% growth (IC₅₀) > 50 µg/mL) and doxorubicin PDC (IC₅₀ = 1.79 µg/mL), the combination PDC (IC₅₀ = 0.99 µg/mL) showed greater cytotoxicity against OVCAR-3 cells and was less cytotoxic than the equivalent free drug combination (IC₅₀ = 0.11 µg/mL). The gemcitabine-doxorubicin combination PDC is promising for targeted combination chemotherapy of OC.