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.