Neuropilin-1 targeting photosensitization-induced early stages of thrombosis via tissue factor release.

PURPOSE: This article characterizes the vascular effects following vascular-targeted photodynamic therapy with a photosensitizer which actively targets endothelial cells. METHODS: This strategy was considered by coupling a chlorin to a heptapeptide targeting neuropilin-1 in human malignant glioma-bearing nude mice. A laser Doppler microvascular perfusion monitor was used to monitor microvascular blood perfusion in tumor tissue. Endothelial cells' ultra structural integrity was observed by transmission electron microscopy. The consequences of photosensitization on tumor vessels, tissue factor expression, fibrinogen consumption, and thrombogenic effects were studied by immunohistochemical staining. RESULTS: Treatment of glioma-bearing mice with the conjugate showed a statistically significant tumor growth delay. Vascular effect was characterized by a decrease in tumor tissue blood flow at about 50% baseline during treatment not related to variations in temperature. This vascular shutdown was mediated by tumor blood vessels' congestion. A pro-thrombotic behavior of targeted endothelial cells in the absence of ultra structural changes led to the induction of tissue factor expression from the earliest times post-treatment. Expression of tissue factor-initiated thrombi formation was also related to an increase in fibrinogen consumption. CONCLUSION: Using a peptide-conjugated photosensitizer targeting neuropilin-1, induction of tissue factor expression immediately post-treatment, led to the establishment of thrombogenic effects within the vessel lumen.

A peptide competing with VEGF165 binding on neuropilin-1 mediates targeting of a chlorin-type photosensitizer and potentiates its photodynamic activity in human endothelial cells.

Destruction of the neovasculature is essential for efficient tumor eradication by photodynamic therapy (PDT). Since the over-expression of receptors for vascular endothelial growth factor (VEGF) is correlated with tumor angiogenesis and subsequent growth, we conjugated a photosensitizer (5-(4-carboxyphenyl)-10,15,20-triphenyl-chlorin, TPC), via a spacer (6-aminohexanoic acid, Ahx), to a VEGF receptor-specific heptapeptide (ATWLPPR). ATWLPPR and TPC-Ahx-ATWLPPR bound exclusively to neuropilin-1 (NRP-1) recombinant chimeric protein (IC50=19 and 171 microM, respectively) but were devoid of affinity for VEGF receptor type 2 (VEGFR-2, KDR), to which ATWLPPR was initially thought to bind. TPC-Ahx-ATWLPPR was incorporated up to 25-fold more in human umbilical vein endothelial cells (HUVEC) than TPC over a 24-h period, and the addition of 8 mM ATWLPPR induced a significant decrease of this uptake (P<0.05), corroborating a receptor-mediated incorporation. Slightly less cytotoxic in the dark, TPC-Ahx-ATWLPPR exhibited enhanced in vitro photodynamic activity (10.4-fold), compared to TPC. Pharmacokinetic analysis in nude mice xenografted with U87 human malignant glioma cells revealed relevant tumor levels as soon as 1 h after intravenous injection of TPC-Ahx-ATWLPPR, and a rapid elimination from the blood compartment. Moreover, TPC-Ahx-ATWLPPR was not degraded in vivo up to 2 h after intravenous injection. Taken together, our results demonstrate that TPC-Ahx-ATWLPPR is a much more potent photosensitizer in vitro than TPC, in NRP-1-expressing cells. Thus, it may efficiently potentiate the vascular effect of PDT in vivo.

Peptide-conjugated chlorin-type photosensitizer binds neuropilin-1 in vitro and in vivo.

The strategy developed aims to favor the vascular effect of photodynamic therapy (PDT) by targeting tumor vasculature. This approach is considered by coupling a photosensitizer (PS) to an heptapeptide targeting neuropilin-1 (NRP-1). We previously demonstrated that this new conjugated PS, which binds to recombinant NRP-1 protein, was a much more potent PS compared to the non-conjugated PS in human umbilical vein endothelial cells (HUVEC) expressing NRP-1, due to the coupling of the peptide moiety. To argue the involvement of NRP-1 in the conjugated PS cellular uptake, MDA-MB-231 breast cancer cells were used, strongly over-expressing NRP-1 receptor, and we evidenced a significant decrease of the conjugated PS uptake after RNA interference-mediated silencing of NRP-1. In mice xenografted ectopically with U87 human malignant glioma cells, we demonstrated that only the conjugated PS allowed a selective accumulation in endothelial cells lining tumor vessels. Vascular endothelial growth factor (VEGF) plasma and tumor levels could not prevent the recognition of the conjugate by NRP-1. The vascular effect induced by the conjugated PS, was characterized by a reduction in tumor blood flow around 50% during PDT. In vivo, the photodynamic efficiency with the conjugated PS induced a statistically significant tumor growth delay compared to the non-coupled PS. The peptide-conjugated chlorin-type PS uptake involves NRP-1 and this targeting strategy favors the vascular effect of PDT in vivo.

Response surface methodology: an extensive potential to optimize in vivo photodynamic therapy conditions.

PURPOSE: Photodynamic therapy (PDT) is based on the interaction of a photosensitizing (PS) agent, light, and oxygen. Few new PS agents are being developed to the in vivo stage, partly because of the difficulty in finding the right treatment conditions. Response surface methodology, an empirical modeling approach based on data resulting from a set of designed experiments, was suggested as a rational solution with which to select in vivo PDT conditions by using a new peptide-conjugated PS targeting agent, neuropilin-1. METHODS AND MATERIALS: A Doehlert experimental design was selected to model effects and interactions of the PS dose, fluence, and fluence rate on the growth of U87 human malignant glioma cell xenografts in nude mice, using a fixed drug-light interval. All experimental results were computed by Nemrod-W software and Matlab. RESULTS: Intrinsic diameter growth rate, a tumor growth parameter independent of the initial volume of the tumor, was selected as the response variable and was compared to tumor growth delay and relative tumor volumes. With only 13 experimental conditions tested, an optimal PDT condition was selected (PS agent dose, 2.80 mg/kg; fluence, 120 J/cm(2); fluence rate, 85 mW/cm(2)). Treatment of glioma-bearing mice with the peptide-conjugated PS agent, followed by the optimized PDT condition showed a statistically significant improvement in delaying tumor growth compared with animals who received the PDT with the nonconjugated PS agent. CONCLUSIONS: Response surface methodology appears to be a useful experimental approach for rapid testing of different treatment conditions and determination of optimal values of PDT factors for any PS agent.

Tissue distribution and pharmacokinetics of an ATWLPPR-conjugated chlorin-type photosensitizer targeting neuropilin-1 in glioma-bearing nude mice.

Destruction of the neovasculature is essential for efficient tumor eradication by photodynamic therapy (PDT). The PDT anti-vascular effect can be promoted by developing addressed photosensitizers localized preferentially to the tumor vascular compartment. A new photosensitizer conjugated to an heptapeptide [H-Ala-Thr-Trp-Leu-Pro-Pro-Arg-OH (ATWLPPR)] targeting neuropilin-1, a Vascular Endothelial Growth Factor (VEGF) co-receptor, has been synthesized. It was administered intravenously for an easier access to endothelial cells lining the vasculature in human malignant glioma-bearing nude mice. Plasma pharmacokinetic parameters were derived from plasma concentration-time data using a non-compartmental analysis and validated a relatively rapid elimination from the blood compartment with an elimination rate constant of 0.062 h(-1) and a biological half-life of 11.0 h. The photosensitizer was mainly concentrated in organs such as liver, spleen and kidneys, which are rich in reticuloendothelial cells. In these organs, the elimination profiles of the photosensitizer were comparable, with half-lives as short as 12.2, 15.1 and 19.7 h, respectively. The peptidic moiety of the conjugated photosensitizer was degraded to various rates depending on the organ considered, most of the degradation process occurred in organs of the reticuloendothelial system. A metabolic product resulting from the enzymatic cleavage of the peptide bond between Ala and Thr was detected in plasma at all the examined time points from 2 h post-injection. The conjugated photosensitizer accumulated rapidly and at high levels in the tumor, with 2.3% of injected dose per gram of tumor tissue at 1 h after injection. Taking into account the aspecific uptake of the degradation product, the tumor levels of total photoactivable compounds might exhibit an interesting photodynamic activity. On the contrary, levels of total photoactivable compounds remained low in the skin. This study provides essential information for the choice of the time interval not to exceed to activate the photosensitizer.

Metabolic profile of a peptide-conjugated chlorin-type photosensitizer targeting neuropilin-1: an in vivo and in vitro study.

Because angiogenic endothelial cells of the tumor vasculature represent an interesting target to potentiate the antivascular effect of photodynamic therapy, we recently described the conjugation of a photosensitizer [5-(4-carboxyphenyl)-10,15,20-triphenylchlorin (TPC)], via a spacer [6-aminohexanoic acid (Ahx)], to a vascular endothelial growth factor receptor-specific heptapeptide [H-Ala-Thr-Trp-Leu-Pro-Pro-Arg-OH (ATWLPPR)] and showed that TPC-Ahx-ATWLPPR binds to neuropilin-1. Because peptides often display low stability in biological fluids, we examined the in vivo and in vitro stability of this conjugate by high-performance liquid chromatography and matrix-assisted laser desorption ionization/time of flight mass spectrometry. TPC-Ahx-ATWLPPR was stable in vitro in human and mouse plasma for at least 24 h at 37 degrees C but, following i.v. injection in glioma-bearing nude mice, was degraded in vivo to various rates, depending on the organ considered. TPC-Ahx-A was identified as the main metabolic product, and biodistribution studies suggested that its appearance in plasma mainly resulted from the degradation of the peptidic moiety into organs of the reticuloendothelial system. According to in vitro cell culture experiments, TPC-Ahx-ATWLPPR was also significantly degraded after incorporation in human umbilical vein endothelial cells (HUVEC), mainly into TPC-Ahx-A and to a lesser extent into TPC-Ahx-AT and TPC-Ahx-ATWLPP. TPC-Ahx-ATWLPPR mostly localized into lysosomes, and when HUVEC were treated with the lysosomal enzymes' inhibitor ammonium chloride, this resulted in a significant decrease of the peptide degradation. This study provides essential information for the choice of the time of activation of the photosensitizer (drug-light interval) not to be exceeded and for the future design of more stable molecules.

Recent improvements in the use of synthetic peptides for a selective photodynamic therapy.

Photodynamic therapy (PDT) is a relatively new cytotoxic treatment, predominantly used in anti-cancer approaches, that depends on the retention of photosensitizers in tumor and their activation after light exposure. Photosensitizers are photoactive compounds such as porphyrins and chlorins that upon photoactivation, effect strongly localized oxidative damage within the target cells. The ability to confine activation of the photosensitizer by restricting illumination to the tumor allows for a certain degree of selectivity. Nevertheless, the targeted delivery of photosensitizers to defined cells is a major problem in PDT of cancer, and one area of importance is photosensitizer targeting. Alterations or increased levels in receptor expression of specific cellular type occur in the diseased tissues. Therefore, photosensitizers can be covalently attached to molecules such as peptides, leading to a receptor-mediated targeting strategy. These active-targeting approaches may be particularly useful for anti-vascular PDT. Moreover, it has been shown that the photocytotoxicity of photodynamic drugs could be enhanced by delivering high amounts of a photosensitizer into subcellular organelles such as the nucleus where nucleic acids represent target molecules sensitive to photodamage. The recent progresses in the use of active-targeting strategy with synthetic peptides and the interest of using an active-targeting strategy in PDT, which could allow efficient cellular internalization of photosensitizers, are described in this review.