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

Abstract

The 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (m-THPC) (Foscan®) 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-β-cyclodextrin (Me-β-CD) in solution was demonstrated on the basis of circular dichroism experiments. A 1∶2 complex stoichiometry was found and an inclusion constant β₂ = 2.8(±0.4) × 10¹⁰ 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 μL of a concentrated Me-β-CD solution (3.2 × 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.