Photodynamic Studies of Metallo Porphyrins: Biological Consequences in a Human Carcinoma Cell Line

M.MILANESIO,E.YSLAS,M.ALVAREZ,C.BORSARELLI,J.SILVER,V.RIVAROLA, E.DURANTINI

Ascochinga, Córdoba

Conferencia; XII th Inter-American Photochemical Conference, en Ascochinga; 2001

  The photodynamic activities of the free-base 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (TMP) and their metal complexes with zinc(II) (ZnTMP), copper(II) (CuTMP) and cadmium(II) (CdTMP) have been compared in two systems: reverse micelle of n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/water bearing photo-oxidizable substrates and on Hep-2 human larynx-carcinoma cell line. The quantum yields of singlet molecular oxygen, O2(1Dg), production (FD) of TMP, ZnTMP and CdTMP in tetrahydrofuran, were determined yielding values of 0.65, 0.73, and 0.73, respectively; while O2(1Dg) formation was not detected for CuTMP. In the reverse micellar system, the amino acid L-tryptophan (Trp) was used as biological substrate to analyze the O2(1Dg)-mediated photooxidation. The observed rate constants for Trp photooxidation (kobsTrp) were proportional to the sensitizer quantum yield of O2(1Dg). A value of ~2x107 s-1M-1 was found for the second order rate constant of Trp (krTry) in this system. In biological medium, the response of Hep-2 cells to cytotoxicity photoinduced by these agents was studied. The Hep-2 cultures were treated with 1 mM of porphyrin for 24 h at 37 ºC and the cells exposed to visible light. The cell survival at different light doses was dependent on the FD. Under these conditions, the cytotoxic effect increases in the order: CuTMP<<TMP<ZnTMP~CdTMP, correlating with the production of O2(1Dg). The similar behavior observed in both chemical and biological media indicates that the O2(1Dg) mediation appears to be mainly responsible for the cell inactivation.