Drug-free neutrally charged polypeptide nanoparticles as anticancer agents.

Cationic synthetic anticancer polymers and peptides have attracted increasing attention for advancing cancer treatment without causing drug resistance development. To circumvent in vivo instability and toxicity caused by cationic charges of the anticancer polymers/peptides, we report, for the first time, a nanoparticulate delivery system self-assembled from a negatively charged pH-sensitive polypeptide poly(ethylene glycol)-b-poly(ʟ-lysine)-graft-cyclohexene-1,2-dicarboxylic anhydride and a cationic anticancer polypeptide guanidinium-functionalized poly(ʟ-lysine) (PLL-Gua) via electrostatic interaction. The formation of nanoparticles (Gua-NPs) neutralized the positive charges of PLL-Gua. Both PLL-Gua and Gua-NPs killed cancer cells in a dose- and time-dependent manner, and induced cell death via apoptosis. Confocal microscopic studies demonstrated that PLL-Gua and Gua-NPs readily entered cancer cells, and Gua-NPs were taken up by the cells via endocytosis. Notably, Gua-NPs and PLL-Gua exhibited similar in vitro anticancer efficacy against MCF-7 and resistant MCF-7/ADR. PLL-Gua and Gua-NPs also induced similar morphological changes in MCF-7/ADR cells compared to MCF-7 cells, further indicating their ability to bypass drug resistance mechanisms in the MCF-7/ADR cells. More importantly, Gua-NPs with higher LD50 and enhanced tumor accumulation significantly inhibited tumor growth with negligible side effects in vivo. Our findings shed light on the in vivo delivery of anticancer peptides and opened a new avenue for cancer treatment.

Antimicrobial Polypeptides Capable of Membrane Translocation for Treatment of MRSA Wound Infection In Vivo.

Multidrug resistant infections are plaguing the healthcare sector over the past few decades with limited treatment options. To overcome this problem, the authors synthesize a series of novel guanidinium-functionalized polypeptides. Specifically, poly(l-lysine) (PLL) with different lengths is first synthesized by ring-opening polymerization of Nε -benzyloxycarbonyl-l-lysine-N-carboxyanhydride (Lys(Z)-NCA) followed by functionalization with a guanidinium-functional group to obtain guanidinium-functionalized PLL (PLL-Gua). To study the effect of hydrophobicity on antimicrobial activity, relatively more hydrophobic leucine-NCA monomer or hydrophobic vitamin E moiety is introduced to PLL-Gua. These polypeptides are characterized for antimicrobial activity against a panel of microbes including multidrug-resistant bacteria, and hemolytic activity. Among all the polypeptides, PLL22 -Gua is most effective against bacteria and yeast. Particularly, excellent bactericidal activity is observed against Staphylococcus aureus and MRSA. PLL22 -Gua kills bacteria mainly by membrane translocation. In addition, PLL22 -Gua kills MRSA with low resistance frequency (<3.3 × 10-8 ). In an MRSA-caused wound infection mouse model, two-day treatment (twice daily) with 10, 20, or 40 mg per kg of PLL22 -Gua shows up to 99.5% bacterial removal. Moreover, no acute dermal toxicity is observed even at a dose of 200 mg per kg. These promising results show the excellent potential of PLL22 -Gua as an antimicrobial agent against multidrug-resistant infection in vivo.