Tetra-n-propylporphycene as a tumour localizer: pharmacokinetic and phototherapeutic studies in mice.

The porphin isomer tetra-n-propyl-porphycene (TPP) was incorporated into unilamellar liposomes of dipalmitoylphosphatidylcholine and intravenously injected at a dose of 2 mg/kg to BALB/c mice bearing a MS-2 fibrosarcoma. Pharmacokinetic studies show that TPP is selectively transported by serum lipoproteins and delivered to the tumour tissue with good efficiency (approx. 1 microgram of the TPP per g of tissue at 24 h after injection) and selectivity (ratio of TPP concentration in the tumour to the peritumoural tissue 16.7 at 24 h). Large doses of TPP are also accumulated by the liver, in agreement with the elimination of the drug via the biliary route, while no TPP is recovered from the brain. Red light-irradiation (300 J/cm2) of the tumour area caused extensive necrosis, while only little cutaneous photosensitivity was observed. Since TPP has a large absorbance in the 630-640 nm region, can be synthesized with a high degree of purity and is an efficient generator of singlet oxygen, this drug represents a potential candidate as a phototherapeutic agent for tumours.