Pharmacokinetic and biodistribution study following systemic administration of Fospeg®--a Pegylated liposomal mTHPC formulation in a murine model.

Fospeg (R) is a newly developed photosensitizer formulation based on meso-tetra(hydroxyphenyl) chlorin (mTHPC), with hydrophilic liposomes to carry the hydrophobic photosensitizer to the target tissue. In this study the pharmacokinetics and biodistribution of Fospeg (R) were investigated by high performance liquid chromatography at various times (0.5-18 hours) following systemic i.v. administration. As a model an experimental HT29 colon tumor in NMRI nu/nu mice was employed. Our study indicates a higher plasma peak concentration, a longer circulation time and a better tumor-to-skin ratio than those of Foslip (R), another liposomal mTHPC formulation. Data from ex vivo tissue fluorescence and reflectance imaging exhibit good correlation with chemical extraction. Our results have shown that optical imaging provides the potential for fluorophore quantification in biological tissues.