Optimization of cellular uptake of zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine for maximal photoinactivation of Candida albicans

Abstract

Cellular uptake and photodynamic action of zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc4+) was examined in Candida albicans. In vitro investigations showed that ZnPPc4+ was rapidly bound to C. albicans cells. The binding of phthalocyanine to cells was dependent on ZnPPc4+ concentrations (1–10 μM) and cells densities (106–108 cells mL−1). A high amount of ZnPPc4+ retained in the cells after two washing steps, indicating a strong interaction between the photosensitizer and C. albicans. The uptake was temperature dependent, although the difference between 37 °C and 4 °C was about 10 %. Also, the amount of ZnPPc4+ bound to C. albicans was affected when the cells were incubated for a longer time with azide and 2,4-dinitrophenol (DNP) prior to treatment with ZnPPc4+. Cell survival after irradiation was dependent on the irradiation period, ZnPPc4+ concentration and cells density. Photoinactivation of C. albicans cells was elevated even after two washing steps. The strong dependence of uptake on cell density reveals the strength and avidity of the binding of ZnPPc4+ to C. albicans cells. The accumulation behaviour of ZnPPc4+ suggests that mainly an affinity-mediated binding mechanism can be involved. Therefore, ZnPPc4+ is an interesting phthalocyanine for photodynamic inactivation (PDI) of yeasts in liquid suspensions.