Combination of photodynamic therapy (PDT) and melphalan in experimental tumors.

Abstract

To investigate whether application of "early" photodynamic therapy (PDT) using a disulphonated aluminium phthallocyanine photosensitizer can potentiate the action of melphalan in experimental RIF-1 tumors in vivo. Tumors were irradiated with laser light of wavelength 675 nm 60 min after treatment with the photosensitizer and 15 min after melphalan. Melphalan pharmacokinetics were measured using high performance liquid chromatography with optical detection. Melphalan and PDT when given alone, caused a significant delay in tumor growth. This was increased for the combined treatment. Pharmacokinetic analyses showed that levels of free, unreacted melphalan in freely circulating blood are unaffected by combined treatment. However, significant differences in tumor levels were observed between treatment with melphalan alone or in combination. Whereas in the former, melphalan is still present in tumors after 2 h, it was not detectable even at the earliest time of 15-23 min for the combined treatment. The antitumor effects were additive with no evidence of significant potentiation.