Increasing the anticancer performance of bufalin (BUF) by introducing an endosome-escaping polymer and tumor-targeting peptide in the design of a polymeric prodrug

A well-defined multifunctional brush-type polymeric prodrug covalently linked with an anticancer drug (bufalin, BUF), a tumor-targeting peptide (RGD), and an endosome-escaping polymer, poly( N,N -diethylaminoethyl methacrylate- co -butyl methacrylate (P(DEA- co -BMA)), was developed. Its anticancer performance against colon cancer was investigated in vitro and in vivo. Reversible addition-fragmentation transfer (RAFT) polymerization of oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA), 2-((3-( tert -butoxy)-3-oxopropyl)thio)ethyl methacrylate (BSTMA), and 2-(2-bromoisobutyryloxy)ethylmethacrylate (BIEM) afforded the multifunctional random copolymer, P(OEGMA- co -BSTMA- co -BIEM), in which hydrophilic POEGMA can stabilize nanoparticles in water, PBSTMA can be converted into carboxyl groups, and PBIEM can be employed as a macromolecular atom radical transfer polymerization (ATRP) initiator. The ATRP of DEA and BMA using P(OEGMA- co -BSTMA- co -BIEM) as a macromolecular ATRP initiator led to the formation of the pH-responsive brush-type copolymer, P(OEGMA- co -BSTMA)- g -P(DEA- co - BMA). After hydrolysis by trifluoroacetic acid and post-functionalization the final polymeric prodrug, P(OEGMA- co -BUF- co -RGD)- g -P(DEA- co -BMA), was obtained with a drug content of ∼7.8 wt%. P(OEGMA- co -BUF- co -RGD)- g -P(DEA- co -BMA) can be assembled into nanoparticles (BUF- NP-RGD) in aqueous solution with a diameter of 148.4 ± 0.7 nm and a zeta potential of −7.6 ± 0.4 mV. BUF-NP-RGD exhibited controlled drug release in the presence of esterase. Additionally, P(OEGMA- co - BSMA)- g -P(DEA- co -BMA) showed a significant hemolysis effect at a pH comparable to that of endosomes/lysosomes. Cell viability and a tumor-bearing nude mouse model were employed to evaluate the anticancer efficacy of BUF-NP-RGD. It was revealed that BUF-NP-RGD showed improved anticancer performance compared with that of free BUF both in vitro and in vivo. Histological and immunochemical analysis further demonstrated that BUF-NP-RGD exhibited improved cell apoptosis, angiogenesis inhibition, and an anti-proliferation effect.