The porphyrins in cancer and virus research.

Compounds with extended conjugated electron-system are under constant study in view of their numerous biological functions. Among them natural and synthetic porphyrins are of particular interest because of their activity in photodynamic treatment of cancer and virus infection. Recently, many modifications in tetrapyrrole ring system have been reported, which are briefly reviewed. Among the tetracationic porphyrins, T theta OPP, a compound having four electron-sending tentacle side chains, exhibits large aggregation tendency in the presence of DNA of different base-sequence. The aggregation tendency of T theta OPP can be attributed to its relatively basic core (pKa is approximately 4.6) which is also responsible for the existence of a T theta OPP-DNA adduct where the core is protonated. This protonation, observed even at physiological pH, alters T theta OPP binding mode on the surface of the DNA.