Polyamines to target drugs to DNA.
In neutral solutions polyamines are fully protonated, and hence are really polyammonium cations (PAC). Spermine, for example, carries four positive charges in a linear system, H3N+(CH2)3N+H2(CH2)4N+H2 (CH2)3N+H3. There is a very powerful coulombic interaction between aqueous DNA and such cations, thus the cations are attracted to the DNA over large distances, and once close to the DNA normally remain there for long periods. A key issue is; are the cations mobile, or do they remain at one preferred site for significant periods? The latter is the currently preferred concept, but NMR and EPR evidence will be presented in favour of the former. If the former is correct, then PACs may be able to act as good drug delivery systems. In its simple form the concept is that any drug that acts directly on DNA can be chemically bound to a PAC. Once in the cell, this PAC-drug complex (PAC-D) will be carried to DNA and will move very rapidly along the exposed strands until it recognises the site of action. This may be some special base sequence region, a damaged site, or the PAC-D unit may simply be present prior to potential damage, so that this can be repaired very rapidly. Some of our current studies on these systems are described.