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Antibiotic resistance in bacteria, especially Gram-positive bacteria like

Safe and effective antimicrobials are needed to combat emerging antibiotic-resistant bacteria. Structurally nanoengineered antimicrobial peptide polymers (termed SNAPPs) interact with bacterial cell membranes to potently kill bacteria but may also interact at some level with human cell membranes. We studied the association of four different SNAPPs with six different white blood cells within fresh whole human blood by flow cytometry. In whole human blood, SNAPPs had detectable association with phagocytic cells and B cells, but not natural killer and T cells. However, without plasma proteins and therefore no protein corona on the SNAPPs, a greater marked association of SNAPPs with all white blood cell types was detected, resulting in cytotoxicity against most blood cell components. Thus, the formation of a protein corona around the SNAPPs reduced the association and prevented human blood cell cytotoxicity of the SNAPPs. Understanding the bio-nano interactions of these SNAPPs will be crucial to ensuring that the design of next-generation SNAPPs and other promising antimicrobial nanomaterials continues to display high efficacy toward antibiotic-resistant bacteria while maintaining a low toxicity to primary human cells.

Synthetic polypeptide-based macroporous cryogels with inherent antimicrobial properties were prepared for potential water purification applications. Gels were chemically cross-linked through the amine residue of a polycationic polylysine-b-polyvaline block copolymer with glutaraldehyde as cross-linker under cryogenic conditions. These cryogels exhibited excellent water swelling and highly compressible mechanical properties owing to their macroporous structure. The antibacterial performance was evaluated based on E. coli viability, with cryogels exhibiting up to 95.6% reduction in viable E. coli after a brief 1 h incubation. In comparison to the hydrogel control, the presence of macropores is shown to be vital to the antimicrobial effect of the gels. The confined environment and increased antimicrobial surface area of the macropores is believed to result in a “trap and kill” mechanism. Mechanical strength and pore integrity of cryogels were also found to be determinants for antibacterial activity. Along wi...

Synthetic polypeptides are a class of bioinspired polymers with well demonstrated biocompatibility, enzyme biodegradability, and cell adhesive properties, making them promising materials for the preparation of macroporous hydrogels as 3D cellular scaffolds. Three-dimensional macroporous hydrogels composed entirely of biocompatible and enzyme biodegradable synthetic polypeptides have thus been prepared. Under cryoconditions, macroporous hydrogels in the form of macroporous cryogels were prepared using a single copolymer component through direct EDC/sulfo-NHS zero-length cross-linking between poly(l-glutamic acid) (PLG) and poly(l-lysine) (PLL) residues on a PLG-r-PLL random copolypeptide chain. The resulting macroporous cryogels were found to contain large interconnected pores (≥100 μm) highly suitable for tissue engineering applications. Tuning the relative ratios of the amino acid components could result in cryogels with very different pore structures, swelling, and mechanical properties, suitable for developing gels for a range of possible soft tissue engineering applications. These cryogels were shown to be enzymatically biodegradable and demonstrated excellent biocompatibility, cell attachment and cell proliferation profiles with mammalian fibroblast (NIH-3T3) cells, demonstrating the appeal of these novel cryogels as highly suitable cellular scaffolds.

In this work, the effect of two key structural parameters, number of arms and arm length, of star-shaped "structurally nanoengineered antimicrobial peptide polymers" (SNAPPs) on their antimicrobial activity and biocompatibility, is investigated. A library of star-shaped SNAPPs is prepared, containing varying arm numbers and arm lengths. Antimicrobial assays are then performed to assess the capacity of the SNAPPs to disrupt the membrane, inhibit the growth, and kill pathogenic bacteria. A major finding of the study is that increasing arm number and length of SNAPPs enhanced antimicrobial activity, which can be respectively attributed to the higher local concentrations of polypeptide arms and increased α-helical content. SNAPP architecture is shown to affect the bacteria membrane state and therefore mechanism of killing. Two more potent structures with up to twice the antimicrobial activity of the previously reported SNAPP are discovered in this process. Toxicities of the SNAPPs also increase with arm number and arm length, however therapeutic index calculations identified a 16-arm SNAPP and an easier to prepare 4-arm SNAPP as the best therapeutic agents. The biocompatibility of the SNAPP with the best biological activity is also evaluated in vivo, showing no markers of systemic damage in mice.

Aryl imidazylates are effective electrophilic partners in copper-free palladium-catalyzed Hiyama and Sonogashira cross-coupling reactions. The Sonogashira cross-coupling of estron-3-yl imidazylate afforded the corresponding phenylacetylene derivative in excellent yield.

Novel cisplatin (CDDP)-loaded, polypeptide-based vesicles for the targeted delivery of cisplatin to cancer cells have been prepared. These vesicles were formed from biocompatible and biodegradable maleimide-poly(ethylene oxide)114-b-poly(L-glutamic acid)12 (Mal-PEG114-b-PLG12) block copolymers upon conjugation with the drug itself. CDDP conjugation forms a short, rigid, cross-linked, drug-loaded, hydrophobic block in the copolymer, and subsequently induces self-assembly into hollow vesicle structures with average hydrodynamic diameters (Dh) of ∼ 270 nm. CDDP conjugation is critical to the formation of the vesicles. The reactive maleimide-PEG moieties that form the corona and inner layer of the vesicles were protected via formation of a reversible Diels-Alder (DA) adduct throughout the block copolymer synthesis so as to maintain their integrity. Drug release studies demonstrated a low and sustained drug release profile in systemic conditions (pH = 7.4, [Cl(-)] = 140 mM) with a higher "burst-like" release rate being observed under late endosomal/lysosomal conditions (pH = 5.2, [Cl(-)] = 35 mM). Further, the peripheral maleimide functionalities on the vesicle corona were conjugated to thiol-functionalized folic acid (FA) (via in situ reduction of a novel bis-FA disulfide, FA-SS-FA) to form an active targeting drug delivery system. These targeting vesicles exhibited significantly higher cellular binding/uptake into and dose-dependent cytotoxicity toward cancer cells (HeLa) compared to noncancerous cells (NIH-3T3), which show high and low folic acid receptor (FR) expression, respectively. This work thus demonstrates a novel approach to polypeptide-based vesicle assembly and a promising strategy for targeted, effective CDDP anticancer drug delivery.

Sonogashira coupling of various imidazylates including the estrone derivative (IV) with phenylacetylene afford the desired products with good to excellent yields.