Preparation of a multifunctional verapamil-loaded nano-carrier based on a self-assembling PEGylated prodrug

In an effort to prove the inherent side effects of doxorubicin (DOX) and potentially revoke the effects of drug resistance exhibited by cancer cells, we have designed a multifunctional DOX-delivery nano-carrier system able to encapsulate the drug resistance reversal agent Verapamil HCl (VRP·HCl). Hydrophilic short-chain polyethylene glycol (i.e., mPEG) was covalently linked to hydrophobic DOX and a benzoic imine linkage was used to form a linear amphiphilic PEGylated prodrug, namely mPEG-b-DOX. In aqueous solution, the amphiphilic PEG-b-DOX is able to self-assemble to form stable nanoparticles with a DOX loading content of approximately 40 wt% and a diameter of ∼ 143 nm. The resulting nanoparticles can simultaneously serve as an anticancer drug conjugate and as a drug carrier system. Here, the hydrophilic VRP could be encapsulated into the nano-carriers via a conventional dialysis method. The loading efficiency in mPEG-b-DOX nano-carrier was determined to be 53.97% and the loading content was found to be 7.71 wt%. The VRP-loaded nano-carriers grew slightly in size, to a diameter of ∼ 177 nm. We found that the release of DOX and VRP was much faster at a lower pH value. The biological activity of the nano-carriers were evaluated in vitro and compared with the DOX-loaded system. In doing so we found that the VRP-loaded nano-carrier features a much higher antitumor activity. Furthermore, the combined-system exhibits a significantly enhanced cytotoxicity with an elevated apoptosis rate observed for MCF-7/ADR used as a cell line in this in vitro study. This combinatory system and promising candidate for applications involving DOX chemotherapy proved to be easy to prepare and could be characterized in terms of biocompatibility, biodegradability, loading capacity, pH responsiveness and reversal of drug resistance.