Liposome- or LDL-administered Zn (II)-phthalocyanine as a photodynamic agent for tumours. I. Pharmacokinetic properties and phototherapeutic efficiency.

The pharmacokinetics of Zn-phthalocyanine (Zn-Pc) in mice bearing a transplanted MS-2 fibrosarcoma has been studied using dipalmitoyl-phosphatidylcholine (DPPC) liposomes and low density lipoproteins (LDL) as drug delivery systems. LDL induce a higher Zn-Pc uptake by the tumour and improve the selectivity of tumour targeting as compared to DPPC liposomes. Experimental photodynamic therapy (PDT) of the MS-2 fibrosarcoma has been performed using liposome-delivered Zn-Pc and the efficiency of tumour necrosis has been measured following four different irradiation protocols. We found that Zn-Pc doses as low as 0.07-0.35 mg kg-1 are sufficient for inducing an efficient tumour response that is linearly dependent on the injected dose. The amount of Zn-Pc in the tumour decreases very slowly as a function of time, hence PDT gives satisfactory results even if performed at relatively long time intervals after administration.