A direct sensitized fluorimetric determination of 5,10,15,20-tetra(m-hydroxyphenyl)chlorin [m-THPC (Foscan)®] in human plasma using a cyclodextrin inclusion complex

The 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (m-THPC) (Foscan (R)) is a photosensitizer used in the photodynamic therapy (PDT) of cancers which is currently under clinical trial. The formation of a m-THPC inclusion complex with dimethyl-beta -cyclodextrin (Me-beta -CD) in solution was demonstrated on the basis of circular dichroism experiments. A 1:2 complex stoichiometry was found and an inclusion constant beta (2) = 2.8(+/-0.4) x 10(10) M-2 was determined. The formation of such a complex was shown to enhance the m-THPC fluorescence intensity. It could be exploited to improve the sensitivity of the direct m-THPC detection in human plasma. Optimization of the operating conditions shows that the best results were obtained by the addition of 100 muL of a concentrated Me-beta -CD solution (3.2 x 10(-2) M) to 1 mL plasma samples. Compared to the standard conditions, a 90% increase in sensitivity was obtained. The proposed analytical method which showed a linear response function [0-300 ng mL(-1) (440 pM)] and a low limit of detection [1.5 ng mL(-1) (2 pM) (S/N = 3)] appears, especially due to the absence of metabolism, a simple and specific method suitable for pharmacokinetics studies in patients.