STRUCTURE-ACTIVITY RELATIONSHIP OF PORPHINES FOR PHOTOINACTIVATION OFBACTERIA

The antibacterial photodynamic effects of uncharged (o-tetrahydroxyphe nyl porphine [THPP], m-THPP and p-THPP), cationic (5,10,15,20-tetra[4- N-methylpyridyl]porphine [TMPyP]) and anionic (5,10,15,20-tetra[4-sulf onatophenyl porphine] [TPPS4]) porphines on Staphylococcus aureus and Escherichia ici coli bacteria inactivation were examined. The results show that uncharged porphines provoked antibacterial photodynamic acti vity on S. aureus, and also on E. coli in the presence of the membrane -disorganizing peptide polymixin B nonapeptide (PMNP). The TMPyP compo und was highly photoactive toward gram-positive bacteria but only marg inally effective on gram-negative cells, whereas TPPS, showed no activ ity on either gram-positive or gram-negative bacteria. The photoactivi ty of TMPyP is due to the electrostatic attraction between the positiv ely charged sensitizer molecule and the negatively charged membrane of the gram-positive target cells. For TPPS4, the inactivity toward gram -positive bacteria is due to electrostatic repulsion between the charg ed sensitizer molecule and the cell membrane. For gram-negative bacter ia, the inactivity is conceivably due to preferential (electrostatic) binding to the positively charged PMNP, which is an adjuvant for membr ane disorganization, but has a no effect on cell viability. For hydrop hobic sensitizers, the photoactivity depends on the state of aggregati on, The extent of deaggregation of the different THPP isomers was dete rmined by fluorescence measurements of bound sensitizers and could be positively correlated with their photoinactivation capacity. We conclu de that the structure-activity relationships of these porphines are af fected by their net charge and by aggregation.