PEGylated reduced graphene oxide as nanoplatform for targeted gene and drug delivery

Abstract

Combination therapies involving anticancer drugs and gene therapy agents have become a potential treatment for different cancer types reducing the side effects of anticancer drugs while enhancing their effectiveness. Here, we improved our previously published strategy that uses multiple pyrene groups of poly(ethylene glycol) (PEG) brushed graft copolymer to enhance the biological use of reduced graphene oxide (rGO) and introduced an azide containing monomer in the copolymer for further modifications to carry hydrophobic drugs like doxorubicin (Dox) along with oligonucleotides such as small interfering RNAs (siRNA). Azide functionality on the side chain of coated copolymer enables not only the conjugation of alkyne end group functional cationic copolymer but also allows the addition of targeting moieties like EPPT1 peptide that selectively binds MUC1, an early hallmark of tumorigenesis. To achieve the outlined carrier, first, a well-defined PEG, pyrene, azide, and methyl methacrylate containing poly[(poly(ethylene glycol) methyl ether methacrylate)-co-(3-azidopropyl methacrylate)-co-(methyl methacrylate)-co-(1-pyrenemethyl methacrylate)] (P(PEGMA-co-AzPMA-co-MMA-co-PMA), PAMP) copolymer was synthesized via ATRP and through its azide group another well-defined, cationic copolymer composed of hexyl methacrylate, 2-dimethyl amino ethyl methacrylate, and N,N,N-trimethylaminoethyl methacrylate iodide (P(HMA-co-DMAEMA-co-TMAEMA) was coupled via copper-catalyzed azide-alkyne cycloaddition (CuAAC). This cationic copolymer was synthesized using a unique ATRP initiator to allow click reaction as described as well as pH-dependent degradation through its hydrazone linkage. The obtained graft copolymer (PAMP-CP) was then coated on a graphene oxide (GO) surface and GO was in situ reduced to rGO (PAMP-CP-rGO) to have an rGO-based PEGylated nanoplatform that can be highly loaded with doxorubicin and successfully condensed with anti-GAPDH siRNA. Consequently, this dual drug delivery nanoplatform showed a controlled drug release that switches between release kinetics by the change of pH and high transfection efficiency regarding targeted GAPDH protein levels. Moreover, in vitro cytotoxicity tests showed that EPPT1-targeted Dox-loaded PAMP-CP-rGO shows concentration-dependent and selective cellular toxicity against cancer cells compared to its non-targeted versions. These results demonstrated the potential of a highly adaptable, multifunctional nanoplatform for safely and selectively transporting different cargoes to the tumor site.