Soybean oil as a possible solubilizing and vehicular medium for zinc phthalocyanine in photodynamic therapy

Soybean oil (SBO) is used as a medium to solubilize zinc phthalocyanine (ZnPc), a known photosensitizer, which has been found to be of potential use in photodynamic therapy. It absorbs red light in this medium at 670 nm with good molar absorptivity comparable to its value in most organic solvents (2.45 x 10(5) M(-1) cm(-1)). The wavelength of the fluorescence emission band peaked at 700 nm when excited at 591 nm, and when excited at 560 nm, the emission band was observed at 680 nm. The characteristic emission band of ZnPc at the near end of the visible spectral region suggests that this compound exists in this medium in a monomeric form, a form most useful in photo therapeutic applications. Moreover, the excitation wavelength, observed in the far-red region, precludes minimal effect, if any, of skin photonecrosis if this medium is used in PDT. A fluorescence spectral analysis of the ZnPc-SBO solution carried out for thirty-eight days indicates that this solution is stable within this time frame. No toxicity was detected when this solution was seeded in human endothelial cells in a culture well for 36 hr and also when injected subcutaneously into the nude and Balb C mice. In both cases the ZnPc was observed to clear from the injected area in a reasonable time. This fact coupled with its good solubilizing property for ZnPc and its virtual nontoxicity may make soybean oil a possible vehicular medium for transporting useful photosensitizers to target cells in photodynamic therapy and related applications.