Michelle T. Dohm

Antimicrobial Peptoids Are Effective Against Pseudomonas aeruginosa Biofilms

ABSTRACT The resistance of biofilms to conventional antibiotics complicates the treatment of chronic cystic fibrosis (CF). We investigated the effects of peptoids, peptides, and conventional antibiotics on the biomass and cell viability within Pseudomonas aeruginosa biofilms. At their MICs, peptoids 1 and 1-C134mer caused maximum reductions in biomass and cell viability, respectively. These results suggest that peptoids of this class could be worth exploring for the treatment of pulmonary infections occurring in CF patients.

Peptoids: Bio-Inspired Polymers as Potential Pharmaceuticals

Peptoids are a developing class of peptide-like oligomers originally invented for drug discovery in the early 1990s. While peptides hold great promise for therapeutic applications, current development of peptide-based pharmaceuticals is hindered by their potential for misfolding and aggregation, and particularly, for rapid in vivo degradation post-administration. Researchers have investigated alternative peptide-like constructs that may be able to circumvent such complications. Peptoids comprise a peptide-based backbone and N-substituted glycines for side chain residues, resulting in complete protease-resistance. Synthesis of peptoid sequences up to 50 units in length allows for controlled sequence composition and incorporation of diverse side chain chemistries. Though the landscape of peptoid structure is not clearly defined, secondary, tertiary, loop, turn, and random structures have been identified. As protease-resistant isomers of peptides, peptoids are being developed as versatile molecular tools in biochemistry and biophysics, and are becoming attractive candidates for therapeutic and diagnostic applications. Peptoids have thus far demonstrated bioactivity as protein mimics and as replacements for small molecule drugs. In this review, we discuss the most recent advances in peptoid research on the therapeutic front in the last few years, including in vitro and in vivo studies in the fields of lung surfactant therapy, antimicrobial agents, diagnostics, and cancer. We particularly focus on the biophysical activity of lipid-associated peptoids and their potential therapeutic applications.

Biophysical mimicry of lung surfactant protein B by random nylon-3 copolymers

Non-natural oligomers have recently shown promise as functional analogues of lung surfactant proteins B and C (SP-B and SP-C), two helical and amphiphilic proteins that are critical for normal respiration. The generation of non-natural mimics of SP-B and SP-C has previously been restricted to step-by-step, sequence-specific synthesis, which results in discrete oligomers that are intended to manifest specific structural attributes. Here we present an alternative approach to SP-B mimicry that is based on sequence-random copolymers containing cationic and lipophilic subunits. These materials, members of the nylon-3 family, are prepared by ring-opening polymerization of beta-lactams. The best of the nylon-3 polymers display promising in vitro surfactant activities in a mixed lipid film. Pulsating bubble surfactometry data indicate that films containing the most surface-active polymers attain adsorptive and dynamic-cycling properties that surpass those of discrete peptides intended to mimic SP-B. Attachment of an N-terminal octadecanoyl unit to the nylon-3 copolymers, inspired by the post-translational modifications found in SP-C, affords further improvements by reducing the percent surface area compression to reach low minimum surface tension. Cytotoxic effects of the copolymers are diminished relative to that of an SP-B-derived peptide and a peptoid-based mimic. The current study provides evidence that sequence-random copolymers can mimic the in vitro surface-active behavior of lung surfactant proteins in a mixed lipid film. These findings raise the possibility that random copolymers might be useful for developing a lung surfactant replacement, which is an attractive prospect given that such polymers are easier to prepare than are sequence-specific oligomers.

Close mimicry of lung surfactant protein B by "clicked" dimers of helical, cationic peptoids.

A family of peptoid dimers developed to mimic SP‐B is presented, where two amphipathic, cationic helices are linked by an achiral octameric chain. SP‐B is a vital therapeutic protein in lung surfactant replacement therapy, but its large‐scale isolation or chemical synthesis is impractical. Enhanced biomimicry of SP‐Bs disulfide‐bonded structure has been previously attempted via disulfide‐mediated dimerization of SP‐B1‐25 and other peptide mimics, which improved surface activity relative to the monomers. Herein, the effects of disulfide‐ or “click”‐mediated (1,3‐dipolar cycloaddition) dimerization, as well as linker chemistry, on the lipid‐associated surfactant activity of a peptoid monomer are described. Results revealed that the ‘clicked’ peptoid dimer enhanced in vitro surface activity in a DPPC:POPG:PA lipid film relative to its disulfide‐bonded and monomeric counterparts in both surface balance and pulsating bubble surfactometry studies. On the pulsating bubble surfactometer, the film containing the “clicked” peptoid dimer outperformed all presented peptoid monomers and dimers, and two SP‐B derived peptides, attaining an adsorbed surface tension of 22 mN m−1, and maximum and minimum cycling values of 42 mN m−1 and near‐zero, respectively.

Opinion: Why we need a centralized repository for isotopic data

Organizational structure for the proposed IsoBank. A central executive group would oversee four subcommittees (SC): Information technology, integrative disciplinary, education and training, and analytical expertise. GNIP, Global Network of Isotopes in Precipitation; IAEA, International Atomic Energy Association; QA/QC, quality assurance/quality control.

Biomimetic N-terminal alkylation of peptoid analogues of surfactant protein C.

Surfactant protein C (SP-C) is a hydrophobic lipopeptide that is critical for lung function, in part because it physically catalyzes the formation of surface-associated surfactant reservoirs. Many of SP-Cs key biophysical properties derive from its highly stable and hydrophobic α-helix. However, SP-Cs posttranslational modification with N-terminal palmitoyl chains also seems to be quite important. We created a new (to our knowledge) class of variants of a synthetic, biomimetic family of peptide mimics (peptoids) that allow us to study the functional effects of biomimetic N-terminal alkylation in vitro. Mimics were designed to emulate the amphipathic patterning, helicity, and hydrophobicity of SP-C, and to include no, one, or two vicinal amide-linked, N-terminal octadecyl chains (providing a reach equivalent to that of natural palmitoyl chains). Pulsating bubble surfactometry and Langmuir-Wilhelmy surface balance studies showed that alkylation improved biomimetic surface activities, yielding lower film compressibility and lower maximum dynamic surface tensions. Atomic force microscopy studies indicated that alkyl chains bind to and retain segregated interfacial surfactant phases at low surface tensions by inducing 3D structural transitions in the monolayers fluid-like phase, forming surfactant-associated reservoirs. Peptoid-based SP-C mimics are easily produced and purified, and offer much higher chemical and secondary structure stability than polypeptide-based mimics. In surfactant replacements intended for medical use, synthetic SP mimics reduce the odds of pathogen contamination, which may facilitate the wider use of surfactant treatment of respiratory disorders and diseases.

Effective in vivo treatment of acute lung injury with helical, amphipathic peptoid mimics of pulmonary surfactant proteins

Acute lung injury (ALI) leads to progressive loss of breathing capacity and hypoxemia, as well as pulmonary surfactant dysfunction. ALI’s pathogenesis and management are complex, and it is a significant cause of morbidity and mortality worldwide. Exogenous surfactant therapy, even for research purposes, is impractical for adults because of the high cost of current surfactant preparations. Prior in vitro work has shown that poly-N-substituted glycines (peptoids), in a biomimetic lipid mixture, emulate key biophysical activities of lung surfactant proteins B and C at the air-water interface. Here we report good in vivo efficacy of a peptoid-based surfactant, compared with extracted animal surfactant and a synthetic lipid formulation, in a rat model of lavage-induced ALI. Adult rats were subjected to whole-lung lavage followed by administration of surfactant formulations and monitoring of outcomes. Treatment with a surfactant protein C mimic formulation improved blood oxygenation, blood pH, shunt fraction, and peak inspiratory pressure to a greater degree than surfactant protein B mimic or combined formulations. All peptoid-enhanced treatment groups showed improved outcomes compared to synthetic lipids alone, and some formulations improved outcomes to a similar extent as animal-derived surfactant. Robust biophysical mimics of natural surfactant proteins may enable new medical research in ALI treatment.