Construction and application of pH-triggered cleavable hyperbranched polyacylhydrazone for drug delivery

Polymeric drug carriers with high stability during long circulation and triggered degradation after drug release are particularly interesting in drug delivery. Here, a novel pH-triggered backbone-cleavable hyperbranched polyacylhydrazone (HPAH) was successfully prepared through a simple polycondensation of 2,3-butanedione and 1-(2-aminoethyl) piperazine tri-propionylhydrazine. The experimental results showed that the degree of branching (DB) of HPAH was 0.60, and the weight-average molecular weight (Mw) of end-capped HPAH was 4.0 × 103 with a polydipersity index (PDI) of 1.6. 2D DOSY NMR degradation experiments demonstrated that HPAH was stable in neutral conditions while cleavable in acidic environments. Owing to the existence of numerous acylhydrazine terminals, the anticancer drug doxorubicin (DOX) was conjugated to hydrophilic HPAH. The obtained HPAH-DOX conjugate could self-assemble into polymeric micelles with an average diameter of 20 nm, which were stable under physiological pH but cleavable after endocytosis. Cell viability of HPAH, monomers, and degradation products was maintained above 70% over the culture periods, even when the concentration was up to 3 mg mL−1 according to methyl tetrazolium (MTT) assay in NIH/3T3 cell line. Both flow cytometry and confocal laser scanning microscopy (CLSM) confirmed the high cellular uptake of HPAH-DOX. Anti-cancer effect was evaluated in HeLa cell line, and the DOX dose required for 50% cellular growth inhibition was found to be 3.5 μg mL−1 by MTT assay.