13 2 -Hydroxy-Bacteriopheophorbide a Methyl Ester Pharmacokinetics Measurements with Fluorescence Versus Absorption Spectroscopy. Is There a Difference?

Abstract

Objective: Quantification of photosensitizer concentration in tissue improves the planning and, subsequently, the outcome of photodynamic therapy. This study was designed to determine if the method of photosensitizer evaluation influences the accuracy of pharmacokinetic results. Materials and Methods: In vivo 13²-Hydroxybacteriopheophorbide a methyl ester (13²-OH-BPME) pharmacokinetics in mice bearing LEWIS lung carcinoma was studied using fluorescence in situ and absorption spectroscopy (following photosensitizer chemical extraction) as photosensitizer quantification methods. The correlation of 13²-OH-BPME fluorescence intensity and its concentration using the absorption spectroscopy were determined for each tissue. Results: The parenchymatous organs showed maximum 13²-OH-BPME concentration and fluorescence intensity at 2h post-injection (lung, liver, spleen), and at 2h post-injection in the kidney with both quantification methods (identical correlation). There was a difference in the time of maximum photosensitizer fluorescence intensity and its concentration in tumor, muscle, and skin (low correlation). The time of maximum fluorescence intensity in muscle, skin, and tumor was at 4h, 12h, and 12h post injection respectively while its maximum concentration was at 2h, 4h, and 8h post-injection. Conclusion: The method of photosensitizer evaluation affects the accuracy of its pharmacokinetic results.