Synthesis, Characterization, and Evaluation of Sulfonium Lipids as Potential Nonviral Gene Vectors

<xp>Background: Non-viral gene vectors have attracted much attention in the last few decades because of their potential activity and fewer side effects. Headgroup chemistry is a key aspect of lipid design.Methods: In this study, a group of sulfonium lipids were designed and constructed by combining tetrahydrothiophene or tetrahydrothiopyran with an ethoxy linker and carbon aliphatic chains and were evaluated in terms of their ability as potential gene vectors. The sulfonium lipids were synthesized and characterized by ¹H NMR, ¹³C NMR, and Mass. Condensates of sulfonium lipids (SL) and DNA were examined by gel electrophoresis and particle size and zeta potential were measured. Sulfonium compounds were tested on HepG2 cells for cytotoxicity. SL/DNA condensates were studied in cellular uptake and distribution using fluorescent microscopy.Results: 12 sulfonium lipids were obtained. Gel electrophoresis experiments showed that sulfonium cation can effectively interact with phosphorous in DNA. Compounds containing longer lipid chains can effectively retard DNA at an S/P ratio higher than 10/1 and can condense DNA into nano size particles with particle size in the range of 150 nm ∼ 300 nm and zeta potential in the range of +20∼+40. Sulfonium compounds were calculated against HepG2 cells in the range of 0.035 μg/mL to 1.64 μg/mL. The intracellular uptake experiments revealed that SL/DNA nanoparticle was taken into the cell at low efficiency.Conclusion: Sulfonium head group can interact with the phosphates of DNA. The structural environment of sulfonium ions influences the DNA bonding effect. The designed cyclic sulfonium ion was buried in the middle of the structure and thus hindered interaction with DNA. This type of molecule is worthy of further modification to increase DNA capacity and reduce cell cytotoxicity.