Biomimetic liposomes and planar supported bilayers for the assessment of glycodendrimeric porphyrins interaction with an immobilized lectin.

Photodynamic therapy is a potentially efficient treatment for various solid tumours, among which retinoblastoma. Its efficacy depends on the preferential accumulation of photosensitizers in the malignant tissues and their accessibility to light. The specificity of drugs for retinoblastoma cells can be improved by targeting a mannose receptor overexpressed at their surface. With the aim of assessing the recognition of newly synthesized glycodendrimeric porphyrins by such receptors, we have built and characterized an original synthetic biomimetic membrane having similar lipidic composition to that of the retinal cell membranes and bearing Concanavalin A, as a model of the mannose receptor. The interaction of the porphyrin derivatives with liposomes and supported planar bilayers has been studied by dynamic light scattering and quartz crystal microbalance with dissipation monitoring (QCM-D). Only mannosylated porphyrins interacted significantly with the membrane model. The methodology used proved to be efficient for the selection of potentially active compounds.

[Interfacial behaviour of glycoconjugated tetraphenylporphyrins and their interaction with biomimetic models of the cell membrane]. / Comportement interfacial de tétraphénylporphyrines glycoconjuguées et leur interaction avec des modèles biomimétiques de la membrane cellulaire.

INTRODUCTION: Porphyrins are photosensitizers usable in photodynamic therapy. Although these molecules are clinically effective, their low water solubility and their lack of specificity are major drawbacks to their development. Our study was aimed at analysing the interfacial behaviour of glycoconjugated tetraphenylporphyrins newly synthesized at the Curie Institute, and their interaction with model membranes bearing a specific lectin mimicking a mannose membrane receptor in retinoblastoma. MATERIAL AND METHODS: The interfacial behaviour of the porphyrins was analysed by surface pressure measurements, and their specific interaction with the lectin, by dynamic light scattering (liposomes) and the quartz crystal microbalance technique (supported bilayers). RESULTS: All porphyrin derivatives were able to organize at the air/liquid interface. The dendrimeric compounds formed more stable monolayers than the others, and generally showed good mixing properties with the phospholipid used for liposome preparation. In the presence of concanavalin A, the porphyrin bearing-liposomes behaved differently depending on the nature (mannosylated or not) of the porphyrins. DISCUSSION: The interfacial behaviour of the tetraphenylporphyrins is directly related to the orientation of the tetrapyrrolic macrocycle controlled by the grafted groups. Incorporated into a liposome bilayer, glycodendrimeric porphyrins expose their sugar moieties at the vesicle surface. The spacer length plays a crucial role by increasing sugars freedom and enhancing glycosylated liposomes interaction with the lectin. CONCLUSION: Compared to the other studied compounds, the glycodendrimeric porphyrins seem very promising compounds and are now evaluated on cell cultures.

Effect of cholesterol and sugar on the penetration of glycodendrimeric phenylporphyrins into biomimetic models of retinoblastoma cells membranes.

Photodynamic therapy (PDT) is considered one efficient treatment against retinoblastoma. The specificity of a photosensitizer and its penetration into cancerous cells are crucial for achieving tumor necrosis. The selection of photosensitizers such as porphyrin derivatives by tumor cells thus depends to a large extent on their ability to interact with the biological membrane. In this work, we have studied by surface pressure measurements and fluorescence spectroscopy the interaction between three newly synthesized dendrimeric phenylporphyrins and monolayers or liposomes with increasing cholesterol content mimicking the retinoblastoma cell membrane. The morphology of phospholipid-cholesterol-porphyrin mixed monolayers was also analyzed by Brewster angle microscopy. The results showed that the increase in cholesterol content in the model membranes had almost no effect on the effective penetration of the drugs into the lipid layers. Conversely, the chemical structure of the glycodendrimeric phenylporphyrins and the presence of sugar moieties especially appeared to play a crucial role. Although the non-glycoconjugated phenylporphyrin penetrated to a greater extent than glycodendrimeric ones into the liposome membrane, this could be achieved at a high lipid/porphyrin ratio only. Glycodendrimeric porphyrins exhibited improved surface properties compared to the non-glycoconjugated derivative and could penetrate into lipid layers even at low lipid/porphyrin ratios and high surface pressures. Our work highlights the role in the passive diffusion of porphyrins into biomimetic cancer cell membranes, of complex interactions among the lipid molecules, the sugar moieties, and the hydrophobic macrocycle of the porphyrins.

Evaluation of the specific interactions between glycodendrimeric porphyrins, free or incorporated into liposomes, and concanavalin A by fluorescence spectroscopy, surface pressure, and QCM-D measurements.

In photodynamic therapy, the specificity of a photosensitizer and its penetration into tumor cells are crucial. We have analyzed the ability of newly synthesized meso-(tetraphenyl)porphyrins to be recognized by a model of mannose-specific proteins overexpressed at the surface of retinoblastoma cells. The specific interaction of porphyrin with Con A was studied by surface pressure measurements, fluorescence spectroscopy, dynamic light scattering, and QCM-D. The extent of porphyrins binding to Con A was highly dependent upon their chemical structure. Glycodendrimeric porphyrins showed the higher binding constant to Con A. The length of the spacer separating the sugar from the tetrapyrrolic ring appeared to be crucial in controlling the interaction of the compounds with the lectin in solution or immobilized onto a solid substrate. The methodology used proved to be efficient for the selection of potentially active compounds. The glycodendrimeric porphyrins, especially the derivative having the longer spacer, interacted more significantly with the lectin than the compound devoid of any sugar.