Cationic porphyrin TMPyP4 redox behaviour and interaction with nucleic acids: Towards a new methodology for screening porphyrin-based anticancer drugs

The cationic meso-substituted porphyrin 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin (TMPyP4) is considered an excellent model compound for the development of new porphyrin-based anticancer drugs able to inhibit the telomerase in cancer cells. Drug development testing methods are nowadays laborious and timeconsuming; hence, the development of rapid, sensitive, selective, low-cost techniques of testing the effectiveness of drugs acting on specific DNA sequences is essential. TMPyP4 oxidation behavior and its interaction with different nucleic acid sequences were electrochemically investigated, aiming to develop an easy, label free and low cost electrochemical methodology of fast screening porphyrin-based anticancer drugs, by differentiating their affinity to different nucleic acid structures.TMPyP4 undergoes an irreversible, pH dependent, two-step oxidation at glassy carbon electrode, each step occurring with the loss of one electron and one proton from the nitrogen atoms of the porphine central ring. DPV was able to discriminate between TMPyP4 binding to different nucleic acid sequences, in agreement with models existent in the literature: (i) TMPyP4 interaction with DNA double-helix is fast and occurs by intercalation, preferentially at the G-C base pairs, but does not cause oxidative DNA damage, (ii) TMPyP4 interaction with polyadenylic acid single-helices formed at neutral pH occurs by pseudo-intercalation, and with single- and double-helices formed at mild acidic pH occurs by side-binding, and (iii) TMPyP4 interaction with polyguanylic acid promotes the formation of G-quadruplexes. The voltammetric results represent a proof of concept, confirming the ability of the proposed electrochemical methodology to screen porphyrin-based anticancer drugs in the process of drug development, allowing the drug easy classification in terms of intercalation and selectivity for different nucleic acid structures.