For rapid and effective clinical translation, polymer-based anticancer therapeutics need long circulating conjugates that produce a sustained concentration gradient between the vasculature and solid tumor. To this end, we designed second-generation backbone-degradable diblock N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer carriers and evaluated sequential combination therapy of HPMA copolymer-paclitaxel and HPMA copolymer-gemcitabine conjugates against A2780 human ovarian carcinoma xenografts. First, extensive in vitro assessment of administration sequence impact on cell cycle, viability, apoptosis, migration, and invasion revealed that treatment with paclitaxel conjugate followed by gemcitabine conjugate was the most effective scheduling strategy. Second, in an in vivo comparison with first-generation (nondegradable, molecular weight below the renal threshold) conjugates and free drugs, the second-generation degradable high-molecular weight conjugates showed distinct advantages, such as favorable pharmacokinetics (three- to five-times half-life compared with the first generation), dramatically enhanced inhibition of tumor growth (complete tumor regression) by paclitaxel and gemcitabine conjugate combination, and absence of adverse effects. In addition, multimodality imaging studies of dual-labeled model conjugates confirmed the efficacy of second-generation conjugates by visualizing more than five-times enhanced tumor accumulation, rapid conjugate internalization, and effective intracellular release of payload. Taken together, the results indicate that the second-generation degradable HPMA copolymer carrier can provide an ideal platform for the delivery of a range of antitumor compounds, which makes it one of the most attractive candidates for potential clinical application.
Keywords: EPR effect; dual-isotope label; macromolecular therapeutics.