CYTOTOXICITY OF POLYAMINE ANALOGS IS DIRECTLY RELATED TO THEIR DNA AFFINITY AS DETERMINED BY POLYACRYLAMIDE GEL COELECTROPHORESIS (PACE) METHOD

Polyamines are essential for cell growth. Polyamine analogs that can replace intracellular polyamines inhibit tumor cell proliferation both in culture as well as in animal models. The positively charged polyamines interact with the negatively charged DNA backbone both in a nonspecific manner, as well as sequence specifically through direct or water mediated hydrogen bonds. Therefore, it is difficult to ascertain the exact interactions that regulate the biological functions of polyamines. Several attempts have been made to determine the thermodynamic parameters of polyamine-DNA interactions with conflicting results. Here, we report a simple method of determining the apparent association constants for polyamine-DNA interaction by using polyacrylamide gel coelectrophoresis (PACE). We have used several cytotoxic polyamine analogs of different conformations and chain lengths. We observed that polyamine analogs with higher charge density or with conformational restrictions, which are absent in the naturally occurring polyamines, interact with DNA more strongly than do natural polyamines. A comparison of the cytotoxicities of the polyamine analogs against human tumor cell lines with their DNA affinities revealed that the higher the DNA affinity the more the cytoxicity of the analogs. The direct correlation between DNA affinities and cytotoxities provides a novel method for a rational design of therapeutically effective cytotoxic polyamine analogs.