517. Lipopolythioureas: Non Cationic System for Gene Delivery

Abstract

The positive charge of cationic-lipid/DNA cationic polymer/DNA complexes renders them highly susceptible to interactions with the biological milieu, leading to aggregation and destabilization, and rapid clearance from the blood circulation. To overcome such drawback we have investigated the possibility to deliver DNA using non- cationic synthetic vectors. We have previously demonstrated that neutral lipopolythioureas DT3TU bind to DNA leading to small particles. These new DNA binding agents lack non-specific accumulation in the lung and increasing circulation time in the bloodstream compared to cationic liposomes. However DT3TU is highly hydrophobic and are inefficient for gene delivery. To improve lipopolythiourea efficiency we have synthesized a series of new lipopolythioureas (LPT) build around two di-thiourea scaffolds derived from (2-amino-3-thiocarbamoylamino- propyl)thiourea or from 2,6-bis(thiocarbamoylamino)hexanoic acid. Variation of hydrophobic anchor size and linker has also been investigated. We have found that derivative ended with an N-diol could be formulated without helper lipid. On the other hand LPT with methyl terminus yielded also small particles when formulated with DPPC. Ten compounds were evaluated for their transfection efficiency against B16 or Eahycell line in the presence of serum. The results revealed that (2-amino-3-thiocarbamoylamino-propyl)thioureas, elicited transfection activity with the same level as cationic lipids. Intratumoral injection of thiourea lipoplex was used to evaluate gene expression on 3LL tumor in C57BL\6 mice. The luciferase reporter gene revealed that LPT express the protein with a similar level as cationic lipid. Finally, pharmacokinetics and biodistribution in mice showed that 10 % of the complexes were still circulating after two hours (3% for other cationic lipid vectors). To the best of our knowlege these new LPT are the first examples of non-cationic transfecting lipids.