One-pot synthesis of pH-responsive hyperbranched polymer–peptide conjugates with enhanced stability and loading efficiency for combined cancer therapy

Abstract

Nanoparticles as drug-delivery systems have received significant attention due to their merits such as prolonged circulation time and passive targeting of a tumor site. Polymer–peptide conjugates (PPCs) tend to self-assemble into nanoparticles in an aqueous solution, and the resulting nanoparticles as drug carriers combine the virtues of both the polymers and peptides. In this study, a simple synthetic method based on a thiol–acrylate Michael addition reaction was used for the one-pot synthesis of amphiphilic hyperbranched poly(β-thioester)s (PPHD-PK) conjugated with cytotoxic peptide (KLAKLAK)₂ (denoted as KLAK) and poly(ethylene glycol) (PEG). In aqueous media, PPHD-PK self-assembled into nanoparticles, and the hyperbranched poly(β-thioester)s (PPHD) containing acid-labile β-thiopropionate group acted as the interior of the nanoparticles, whereas PEG and KLAK were employed as the outer shell. The PPHD-PK nanoparticles showed enhanced cellular uptake and favorable antitumor activity, which was attributed to the spherical structure with superficial positive charges and mitochondria-regulated apoptosis of the KLAK peptide. Compared with linear PPCs, the stability of the nanoparticles and the drug-loading efficiency of PPHD-PK were significantly improved, implying that a stronger intermolecular interaction was generated by intertwisting of the branched networks in the nanoparticle core region. Doxorubicin (DOX), as a typical chemotherapeutic drug, was readily released from PPHD-PK under the acidic environment of lysosome, thus leading to efficient nuclear drug translocation and resultant potent drug efficacy. Furthermore, DOX-loaded PPHD-PK nanoparticles showed higher cytotoxic activity than DOX-loaded PPHD-P (without KLAK) and blank PPHD-PK nanoparticles, indicating that the combined treatment of DOX and KLAK was most effective to kill HeLa cells. Therefore, DOX-loaded PPHD-PK nanoparticles with enhanced stability and loading efficiency exhibit great potential as antitumor nanodrugs for efficient cancer therapy.