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.