CAROTENOPORPHYRINS AS SELECTIVE PHOTODIAGNOSTIC AGENTS FOR TUMORS

The covalent binding of a carotene moiety to one phenyl ring and meso- tetraphenyl-substituted porphyrins (see Figure 1) efficiently quenches the photosensitising activity of the porphyrin while a relatively lar ge yield of fluorescence emission around 650 nm is retained. Pharmacok inetic studies performed with two carolenoporphyrins (CPs) and the cor responding porphyrins (Ps) in Balb/c mice bearing an MS-2 fibrosarcoma show that the two Ps give a high selectivity of tumour localisation ( tumour/peritumoral tissue ratios of dye concentration ranging between c. 30 and 90 al 24 h after injection of 4.2-8.4 mu mol kg(-1) in a Cre mophor emulsion) and photosensitise tumour necrosis upon red light irr adiation. For the same injected doses, the two CPs show no tumour-phot osensitising activity even though they localise in the tumour in conce ntrations of the order of 10-40 mu g g(-1) at 24 h with tumour/peritum oral ratios larger than 10. Thus, the fluorescence emitted by these CP s in the tumour can be used for photodiagnostic purposes with no risk of skin photosensitisation. However, this approach is presently limite d by the large accumulation and prolonged retention of the CPs in the liver and spleen.