Abstract:

Lipid nanoparticles (LNPs) for drug-delivery applications are largely derived from natural lipids. Synthetic lipids, particularly those incorporating branched hydrocarbons and hyper-branched hydrocarbon architectures, may afford enhanced lipophilicity with enhanced fluidity and thereby lead to LNP stabilization. Hydrocarbon anchors based on serinol diesters were prepared from linear C_n (n = 14, 16, 18) and branched (n = 16) acids with Boc-protected serinol. These diesters were further dimerized on an iminodiacetamide backbone to provide eight branched-chain and dendritic lipid anchors. Derivatization of these core structures provided eight PEG-lipids and seven thiopurine linked lipid–drug conjugates. LNPs were prepared by microfluidic mixing from mixed lipids in ethanol diluted into aqueous media. The lipid–drug conjugates incorporated 5 mol% of a phosphocholine and 5 mol% of a commercial PEG-lipid to form LNPs with a thiopurine drug loading of 15 wt%. The PEG–lipids prepared were formulated at 1.5 mol% as a surface stabilizer to LNPs containing dsDNA lipoplexes. The stability of the LNPs was assessed under different storage conditions through monitoring of particle size. For both LNPs from lipid–thiopurine conjugates and the PEG-lipid systems, there is strong preliminary evidence that hydrocarbon branching results in LNP stabilization. Four of the lipid–drug conjugate formulations were stable to cell culture conditions (10% serum, 37 °C) and the toxicity of these LNPs was assessed in two cell lines relative to the free thiopurines in the medium. The observed toxicity is consistent with cellular uptake of the LNPs and reductive release of the cargo thiopurine within the cell.