Poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) block co-polymers (PEO-PPO-PEO, sold as Pluronics, Poloxamers, Tetronics) are a widely used class of amphiphilic materials for different biological applications. In fact for certain members of the Pluronics series, the interactions of block segments with living cells alter the lipid membrane properties and facilitate the permeation of drugs. A fuller understanding of the molecular mechanisms underpinning these interactions is essential for ensuring their safety and efficacy in biomedical applications and to inform the design of new amphiphilic copolymers for potential use in a clinical setting. In this paper, by means of atomistic molecular dynamics simulations and membrane lysis assays, we investigate the relationship between the molecular conformations of a subset of the Pluronic copolymers (L31, L61, L62 and L64) and their haemolytic activity. Our computational studies suggest that the hydrophilic blocks in these copolymers interact with the polar head groups of lipid molecules, resulting in a predicted modification of the structure of the membranes. Parallel membrane lysis assays in human erythrocytes indicate differences in the rates of haemolysis, as a result of incubation with these polymers, that correlate well with the predicted interactions from the atomistic simulations. The computational data thus provide a putative mechanism to rationalize the available experimental data on membrane lysis by these copolymers and quantitatively agree with haemoglobin release endpoints measured when copolymers with the same molecular weight and structure as of those modelled are incubated with erythrocytes. The data further suggest some new structure-function relationships at the nanoscale that are likely to be of importance in determining the biological activity of these otherwise inert copolymers.

A new polymer poly(N-vinylpiperidone) (PVPip) (2 x , M n NMR 4.5-83 kDa) has been prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization using a xanthate as a chain-transfer agent. These polymers all exhibited sharp reversible cloud points (in the range 87 and 68°C) which depended on the molecular weight of the polymer and showed no apparent hysteresis. Furthermore, cytotoxicity studies of the PVPip showed that the polymer is noncytotoxic. Chain extension of PVPip 62 with vinyl acetate afforded well-defined amphiphilic diblock copolymers: poly(N-vinylpiperidone) x -block-poly-(vinyl acetate) y (PVPip x -b-PVAc y ) (for 3, x:y = 62:21; for 4, x:y = 62:32). Both 3 and 4 exhibit phase transitions of 62 and 55°C, respectively, in water, with the latter showing evidence of a slight hysteresis. Direct dissolution of 3 in nanopure water at 1 mg/mL gave spherical micelles (ca. 24 nm), as confirmed by DLS, TEM, and AFM analysis, which could be reversibly disassembled upon heating above the cloud point of the diblock. The block copolymer 4 was hydrolyzed under basic conditions to give the double hydrophilic biocompatible diblock copolymer poly(N-vinylpiperidone) 62 -block-poly(vinyl alcohol) 32 (5).

The data suggest a link between the affinity of certain Pluronics for biological membranes and their cellular adverse effects. This first cell-based investigation of the interactions of Pluronics with biological membranes is an important step towards unravelling the complex mechanisms which govern the biological effects of widely used amphiphilic materials.

Effective agents to treat coronavirus infection are urgently required, not only to treat COVID-19, but to prepare for future outbreaks. Repurposed anti-virals such as remdesivir and human anti-inflammatories such as barcitinib have received emergency approval but their overall benefits remain unclear. Vaccines are the most promising prospect for COVID-19, but will need to be redeveloped for any future coronavirus outbreak. Protecting against future outbreaks requires the identification of targets that are conserved between coronavirus strains and amenable to drug discovery. Two such targets are the main protease (Mpro) and the papain-like protease (PLpro) which are essential for the coronavirus replication cycle. We describe the discovery of two non-antiviral therapeutic agents, the caspase-1 inhibitor SDZ 224015 and Tarloxotinib that target Mpro and PLpro, respectively. These were identified through extensive experimental screens of the drug repurposing ReFRAME library of 12,000 therapeutic agents. The caspase-1 inhibitor SDZ 224015, was found to be a potent irreversible inhibitor of Mpro (IC50 30 nM) while Tarloxotinib, a clinical stage epidermal growth factor receptor inhibitor, is a sub micromolar inhibitor of PLpro (IC50 300 nM, Ki 200 nM) and is the first reported PLpro inhibitor with drug-like properties. SDZ 224015 and Tarloxotinib have both undergone safety evaluation in humans and hence are candidates for COVID-19 clinical evaluation.

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