COMB-TYPE COPOLYMER - STABILIZATION OF TRIPLEX DNA AND POSSIBLE APPLICATION IN ANTIGENE STRATEGY

By employing a reductive amination reaction between the epsilon-amino groups of poly(L-lysine) (PLL) and the reductive ends of the hydrophil ic dextran (Dex) side chain, we have prepared different comb-type copo lymers which varied in the degree of grafting and the length of the hy drophilic Dex chains. The resulting copolymers, poly(L-lysine)-graft-d extran (PLL-g-Dex), were tested for their ability to stabilize tripler DNA in vitro under physiologically relevant conditions. Thermal denat uration (UV-T-m) and circular dichroism experiments revealed that the graft copolymer with the higher degree of grafting of long Der chains significantly increased the thermal stability of tripler structure of poly(dA).2poly(dT) by more than 50 degrees C without affecting the tra nsition between tripler and single-stranded DNA or the native structur e of DNA. Of importance is that when tripler formation involving a 30- mer target duplex from rat alpha 1 (I) collagen promoter was analyzed by an in vitro electrophoretic mobility shift assay,the graft copolyme r also remarkably diminished potassium inhibition of the purine motif tripler formation up to 200 mM as well as pH-dependence of the pyrimid ine motif tripler formation. Moreover the tripler-stabilizing efficien cy of the copolymer was significantly higher than that of other oligoc ations like spermine and spermidine. We suggest that a molecular desig n of comb-type copolymers consisting of various types of polycation ba ckbones (e.g., PLL) grafted with different hydrophilic side chains (e. g., Dex) is a novel strategy to create efficient tripler stabilizers t hat will certainly shed light on possible in vivo application of the a ntigene strategy.