Interaction of human serum low density lipoproteins with porphyrins: a spectroscopic and photochemical study

Porphyrin-lipoprotein association as a factor in porphyrin localization

Systemic administration of the tumor-localizing product hematoporphyrin derivative (HPD) to mice bearing the Lewis-Lung tumor leads to an initial distribution of porphyrins among plasma lipoproteins and albumin. The more hydrophobic components of HPD (including the tumor-localizing fraction) preferentially bind to plasma low density lipoprotein (LDL) and high density lipoprotein (HDL). After 48 h, the remaining plasma porphyrins are mainly bound to HDL. The distribution pattern of HPD is correlated with the relative numbers of LDL receptors in different tissues.

In vitro interaction of the photoactive anticancer porphyrin derivative photofrin II with low density lipoprotein, and its delivery to cultured human fibroblasts

Low density lipoprotein (LDL) doped with the anticancer mixture of hematoporphyrin derivatives Photofrin II (P2) competes with native LDL for binding to fibroblast receptors, despite a slight increase in the negative net charge related to the presence of acidic residues of porphyrins. P2 delivery to fibroblasts can be achieved by LDL, HDL3 or albumin doped with P2 (LDL-P2, HDL-P2 or A-P2, respectively). P2 delivery to cells assessed by fluorescence measurement, is much more efficient, at low protein concentrations (10-20 micrograms/ml) by LDL-P2 than by HDL-P2 or A-P2. Moreover, P2 delivery to cells by LDL-P2 as a function of protein concentration is a saturable process, whereas P2 delivery by HDL-P2 or A-P2 is a linear process. Finally, reduction of the LDL-receptor number by preincubation of fibroblasts in medium supplemented with lipoproteins results in a decrease of P2 delivery by LDL-P2. These results suggest a special role of the LDL-receptor pathway in P2 delivery to cells and could be of interest in cancer phototherapy by porphyrins.

Role of high-, low- and very low-density lipoproteins in the transport and tumor-delivery of hematoporphyrin in vivo

Free hematoporphyrin administered intravenously to healthy rabbits (1-28 mg/kg body weight) is bound by the 3 major lipoprotein components of plasma (VLDL, LDL and HDL) with different efficiency. In vitro-prepared complexes of hematoporphyrin (Hp) with lipoprotein fractions isolated from mouse serum have been injected intracardiacally into mice affected by MS-2 fibrosarcoma (1 mg of Hp per kg body weight). LDL appear to allow a more specific delivery of the complexed Hp to the tumor tissue as compared with HDL, VLDL or free Hp. The different behavior of VLDL, LDL and HDL as carriers of Hp in vivo is also discussed.

Photosensitization with derivatives of haematoporphyrin

This review describes recent progress in delineation of the structure of the active component(s) in the tumour-localizing photosensitizer HPD (haematoporphyrin derivative), along with suggestions concerning the likely determinants of accumulation of this product by different tissues.

Fundamental aspects in tumor photochemotherapy: interactions of porphyrins with membrane model systems and cells

Some molecular aspects underlying photochemotherapy and photodiagnosis of tumors with porphyrins are reviewed. The nature of the clinically used photosensitizer HpD is first presented along with structures of molecules found to be efficient in vitro. The possible role of pH in the preferential retention of dicarboxylic porphyrins by tumors is discussed in light of results obtained with membrane models. The uptake of dicarboxylic porphyrins by cells most likely involves passive mechanisms. Cell photoinactivation using a purified porphyrin does not depend upon the incubation time but only on the intracellular concentration of the dye. This likely reflects a poor specificity of the photoinactivation processes with regard to the cellular localization of the dye. The properties which should be presented by more efficient photosensitizers are discussed.