Biologically active bisquaternary ammonium chlorides: physico–chemical properties of long chain amphiphiles and their evaluation as non-viral vectors for gene delivery

The biological properties of bisquaternary ammonium salts, which are derivatives of N,N-bisdimethyl-1,2-ethanediamine (bis-C_nBEC), of general formula /C_nH_2n+1OOCCH₂(CH₃)₂N⁺CH₂CH₂N⁺(CH₃)₂CH₂COOC_nH_2n+1/2Cl⁻, were investigated (n=10, 12, 14). The interaction with model membrane was studied by differential scanning calorimetry experiments, and the apparent adiabatic molar compressibility of their solution as a function of concentration was obtained by sound velocity measurements. Their biological activities were assayed by Electrophoresis Mobility Shift, MTT proliferation, and transient transfection. All the investigated compounds interact with the DNA and are able to transfect DNA, when they are coformulated with DOPE, with an efficiency significantly greater than that of a standard commercial transfection reagent. Bis-C₁₄BEC is the only molecule able to deliver DNA inside the cells without a helper lipid, as shown by EGFP expression, albeit with a low efficiency in comparison with a standard commercial transfection reagent. This may be due to a slightly different interaction of bis-C₁₄BEC from bis-C₁₀BEC and bis-C₁₂BEC with phospholipid bilayers. Bis-C₁₀BEC and bis-C₁₂BEC show a slight fluidising effect, while bis-C₁₄BEC increases stability of both the gel and the rippled gel phases.