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

DA7R: A 7-Letter Zip Code to Target PDAC

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, and is among the most aggressive and still incurable cancers. Innovative and successful therapeutic strategies are extremely needed. Peptides represent a versatile and promising tool to achieve tumor targeting, thanks to their ability to recognize specific target proteins (over)expressed on the surface of cancer cells. A7R is one such peptide, binding neuropilin-1 (NRP-1) and VEGFR2. Since PDAC expresses these receptors, the aim of this study was to test if A7R-drug conjugates could represent a PDAC-targeting strategy. PAPTP, a promising mitochondria-targeted anticancer compound, was selected as the cargo for this proof-of-concept study. Derivatives were designed as prodrugs, using a bioreversible linker to connect PAPTP to the peptide. Both the retro-inverso (DA7R) and the head-to-tail cyclic (cA7R) protease-resistant analogs of A7R were tested, and a tetraethylene glycol chain was introduced to improve solubility. Uptake of a fluorescent DA7R conjugate, as well as of the PAPTP-DA7R derivative into PDAC cell lines was found to be related to the expression levels of NRP-1 and VEGFR2. Conjugation of DA7R to therapeutically active compounds or nanovehicles might allow PDAC-targeted drug delivery, improving the efficacy of the therapy and reducing off-target effects.

A Photosensitized Singlet Oxygen (1O2) Toolbox for Bio-Organic Applications: Tailoring 1O2 Generation for DNA and Protein Labelling, Targeting and Biosensing

Singlet oxygen (1O2) is the excited state of ground, triplet state, molecular oxygen (O2). Photosensitized 1O2 has been extensively studied as one of the reactive oxygen species (ROS), responsible for damage of cellular components (protein, DNA, lipids). On the other hand, its generation has been exploited in organic synthesis, as well as in photodynamic therapy for the treatment of various forms of cancer. The aim of this review is to highlight the versatility of 1O2, discussing the main bioorganic applications reported over the past decades, which rely on its production. After a brief introduction on the photosensitized production of 1O2, we will describe the main aspects involving the biologically relevant damage that can accompany an uncontrolled, aspecific generation of this ROS. We then discuss in more detail a series of biological applications featuring 1O2 generation, including protein and DNA labelling, cross-linking and biosensing. Finally, we will highlight the methodologies available to tailor 1O2 generation, in order to accomplish the proposed bioorganic transformations while avoiding, at the same time, collateral damage related to an untamed production of this reactive species.

The Importance of 6-Aminohexanoic Acid as a Hydrophobic, Flexible Structural Element

6-aminohexanoic acid is an ω-amino acid with a hydrophobic, flexible structure. Although the ω-amino acid in question is mainly used clinically as an antifibrinolytic drug, other applications are also interesting and important. This synthetic lysine derivative, without an α-amino group, plays a significant role in chemical synthesis of modified peptides and in the polyamide synthetic fibers (nylon) industry. It is also often used as a linker in various biologically active structures. This review concentrates on the role of 6-aminohexanoic acid in the structure of various molecules.

Strategies for optimizing the delivery to tumors of macrocyclic photosensitizers used in photodynamic therapy (PDT)

This review briefly summaries the principles and mechanisms of action of photodynamic therapy (PDT) as concerns its application in the oncological field, highlighting its drawbacks and some of the strategies that have been or are being explored to overcome them. The major aim is to increase the efficiency and selectivity of the photosensitizer (PS) uptake in the cancer cells for optimizing the PDT effects on tumors while sparing normal cells. Some attempts to achieve this are based on the conjugation of the PS to biomolecules (small ligands, peptides) functioning as carriers with the ability to efficiently penetrate cells and/or specifically recognize and bind proteins/receptors overexpressed on the surface of cancer cells. Alternatively, the PS can be entrapped in nanocarriers derived from various types of materials that can target the tumor by exploiting the enhanced permeability and retention (EPR) effects. The use of nanocarriers is particularly attractive because it allows the simultaneous delivery of more than one drug with the possibility of combining PDT with other therapeutic modalities.

A stabilized peptide ligand for multifunctional glioma targeted drug delivery

Peptide ligands consisting of l-amino acids are subject to proteolysis in vivo. When modified on the surface of nanocarriers, those peptide ligands would readily degrade and the targeting efficacy is significantly attenuated. It has received increasing scrutiny to design stable peptide ligands for targeted drug delivery. Here, we present the design of a stable peptide ligand by the formation of a head-to-tail amide bond as an example. Even though the linear l-peptide A7R (termed ^LA7R) can bind specifically to vascular endothelial growth factor receptor 2 (VEGFR2) and neuropilin-1 (NRP-1) that are overexpressed on glioma cells, neovasculature and glioma vasculogenic mimicry (VM), the tumor-homing capacity of ^LA7R is greatly impaired in vivo due to proteolysis (e.g. in the serum). A cyclic A7R (cA7R) peptide was identified by computer-aided peptide design and synthesized with high yield by combining solid phase peptide synthesis and native chemical ligation. The binding of cA7R to both receptors was theoretically and experimentally assessed. In our simulated model hydrophobic and ionic interactions dominated the binding of ^LA7R to receptors. It is very interesting that cA7R adopting a different structure from ^LA7R retained high binding affinities to receptors without affecting the hydrophobic and ionic interactions. After head-to-tail cyclization by the formation of an amide bond, cA7R exhibited exceptional stability in mouse serum. Either cA7R or ^LA7R was conjugated on the surface of doxorubicin (DOX) loaded liposomes (cA7R-LS/DOX or ^LA7R-LS/DOX). The results of in vitro cellular assays indicated that cA7R-LS/DOX not only displayed stronger anti-proliferative effect against glioma cells, but also demonstrated to be more efficient in destruction of VM and HUVEC tubes in comparison to ^LA7R-LS/DOX and plain liposomes (LS/DOX, without peptide conjugation). cA7R conjugation could achieve significantly higher accumulation of liposomes in glioma than did ^LA7R conjugation, which in turn, cA7R-LS/DOX could substantially suppress subcutaneous tumor growth when compared with other DOX formulations (free DOX, LS/DOX and ^LA7R-LS/DOX). The designed cyclic A7R exhibited the capability of targeting glioma cells, neovasculature and VM simultaneously in vivo. Considering the ease of synthesis, high binding affinity to receptors and increased stability of cA7R peptide in the present study, the design of head-to-tail cyclized peptides by the formation of amide bond based on computer-aided peptide design presents an alternative method to identify proteolytically stable peptide ligands.

New Peptide-Conjugated Chlorin-Type Photosensitizer Targeting Neuropilin-1 for Anti-Vascular Targeted Photodynamic Therapy

Photodynamic therapy (PDT) is a cancer treatment modality that requires three components, namely light, dioxygen and a photosensitizing agent. After light excitation, the photosensitizer (PS) in its excited state transfers its energy to oxygen, which leads to photooxidation reactions. In order to improve the selectivity of the treatment, research has focused on the design of PS covalently attached to a tumor-targeting moiety. In this paper, we describe the synthesis and the physico-chemical and photophysical properties of six new peptide-conjugated photosensitizers designed for targeting the neuropilin-1 (NRP-1) receptor. We chose a TPC (5-(4-carboxyphenyl)-10,15, 20-triphenyl chlorine as photosensitizer, coupled via three different spacers (aminohexanoic acid, 1-amino-3,6-dioxaoctanoic acid, and 1-amino-9-aza-3,6,12,15-tetraoxa-10-on-heptadecanoic acid) to two different peptides (DKPPR and TKPRR). The affinity towards the NRP-1 receptor of the conjugated chlorins was evaluated along with in vitro and in vivo stability levels. The tissue concentration of the TPC-conjugates in animal model shows good distribution, especially for the DKPPR conjugates. The novel peptide-PS conjugates proposed in this study were proven to have potential to be further developed as future NRP-1 targeting photodynamic therapy agent.

Multifunctional Peptide-conjugated hybrid silica nanoparticles for photodynamic therapy and MRI

Photodynamic therapy (PDT) is an emerging theranostic modality for various cancer as well as non-cancer diseases. Its efficiency is mainly based on a selective accumulation of PDT and imaging agents in tumor tissue. The vascular effect is widely accepted to play a major role in tumor eradication by PDT. To promote this vascular effect, we previously demonstrated the interest of using an active- targeting strategy targeting neuropilin-1 (NRP-1), mainly over-expressed by tumor angiogenic vessels. For an integrated vascular-targeted PDT with magnetic resonance imaging (MRI) of cancer, we developed multifunctional gadolinium-based nanoparticles consisting of a surface-localized tumor vasculature targeting NRP-1 peptide and polysiloxane nanoparticles with gadolinium chelated by DOTA derivatives on the surface and a chlorin as photosensitizer. The nanoparticles were surface-functionalized with hydrophilic DOTA chelates and also used as a scaffold for the targeting peptide grafting. In vitro investigations demonstrated the ability of multifunctional nanoparticles to preserve the photophysical properties of the encapsulated photosensitizer and to confer photosensitivity to MDA-MB-231 cancer cells related to photosensitizer concentration and light dose. Using binding test, we revealed the ability of peptide-functionalized nanoparticles to target NRP-1 recombinant protein. Importantly, after intravenous injection of the multifunctional nanoparticles in rats bearing intracranial U87 glioblastoma, a positive MRI contrast enhancement was specifically observed in tumor tissue. Real-time MRI analysis revealed the ability of the targeting peptide to confer specific intratumoral retention of the multifunctional nanoparticles.

Denis TG, Hamblin MR. Photodynamic Therapy for Cancer and for Infections: What Is the Difference?

Photodynamic therapy (PDT) was discovered over one hundred years ago when it was observed that certain dyes could kill microorganisms when exposed to light in the presence of oxygen. Since those early days, PDT has mainly been developed as a cancer therapy and as a way to destroy proliferating blood vessels. However, recently it has become apparent that PDT may also be used as an effective antimicrobial modality and a potential treatment for localized infections. This review discusses the similarities and differences between the application of PDT for the treatment of microbial infections and for cancer lesions. Type I and type II photodynamic processes are described, and the structure-function relationships of optimal anticancer and antimicrobial photosensitizers are outlined. The different targeting strategies, intracellular photosensitizer localization, and pharmacokinetic properties of photosensitizers required for these two different PDT applications are compared and contrasted. Finally, the ability of PDT to stimulate an adaptive or innate immune response against pathogens and tumors is also covered.

Functionalized silica-based nanoparticles for photodynamic therapy

AIM

The strategy developed aims to favor the vascular effect of photodynamic therapy by targeting tumor-associated vascularization using peptide-functionalized nanoparticles. We previously described the conjugation of a photosensitizer to a peptide targeting neuropilin-1 overexpressed in tumor angiogenic vessels.

MATERIALS & METHODS

In this study, we have designed and photophysically characterized a multifunctional nanoparticle consisting of a surface-localized tumor vasculature targeting peptides and encapsulated photodynamic therapy and imaging agents.

RESULTS & CONCLUSION

The elaboration of these multifunctional silica-based nanoparticles is reported. Nanoparticles functionalized with approximately 4.2 peptides bound to recombinant neuropilin-1 protein. Nanoparticles conferred photosensitivity to cells overexpressing neuropilin-1, providing evidence that the chlorin grafted within the nanoparticle matrix can be photoactivated to yield photocytotoxic effects in vitro.

Stability of peptides and therapeutic success in cancer

INTRODUCTION

Although naturally occurring peptides have been widely used as drugs, their rapid in vivo degradation by proteolysis and their interactions at multiple receptors are part of the reason for the limitation of their clinical applications.

AREAS COVERED

This paper reviews peptide-metabolizing enzymes in the brain and intestinal brush-border membranes, and discusses potential strategies to improve biological activity, specificity and stability of peptides. The reader will gain, via some examples, an appreciation of the challenges involved in identifying peptides stability to improve their biological properties such as selectivity.

EXPERT OPINION

Due to the metabolic process, it is crucial to follow the biodistribution of a peptide drug and/or a peptidic moiety in order to improve its biological properties such as selectivity. To these purposes, pseudopeptides and peptidomimetics preserving the biological properties of native peptides have been developed to increase their resistance to degradation and elimination, bioavailability and selectivity to become good drug candidates.

[Towards a new treatment of retinoblastoma?]

Photodynamic therapy (PDT) is a recent approach for the treatment of small cancerous tumours, on-surface or accessible by endoscopy in which a dye (usually a tetrapyrrolic macrocycle) absorbs light and generates cytotoxic reactive oxygen species leading to cellular damage. Retinoblastoma (Rb) is a rare intraocular tumour of childhood. All the multifocal forms are hereditary and constitute a syndrome of genetic predisposition in the cancer. The current treatments with etoposide or carboplatine expose the patient to the late risk of second cancer. The use of PDT as cancer therapy is particularly attractive due to the use of few mutagenic and non-toxic photosensitizers (PS) prior light excitation and to the localized tumour illumination. The photoefficiency towards Rb of a glycoconjugated porphyrin is discussed and compared with the results obtained with a second-generation photosensitizer, the Foscan. Some in vivo results on an animal model of Rb are presented by a point of view of photoefficiency, biodistribution, pharmacokinetic and longitudinal follow-up of the PDT effect using a new non-invasive method of magnetic resonance imaging of real-time. Photodynamic treatments in association with non-invasive sodium imaging open ways for new treatment tailoring or treatment individualization of retinoblastoma in clinic.

Photodynamic therapy targeting neuropilin-1: Interest of pseudopeptides with improved stability properties

The general strategy developed aims to favor the vascular effect of photodynamic therapy by targeting tumor vasculature. Since angiogenic endothelial cells represent an interesting target to potentiate this vascular effect, we previously described the conjugation of a photosensitizer to a peptide targeting neuropilins (NRPs) over-expressed specially in tumor angiogenic vessels and we recently characterized the mechanism of photosensitization-induced thrombogenic events. Nevertheless, in glioma-bearing nude mice, we demonstrated that the peptide moiety was degraded to various rates according to time after intravenous administration. In this study, new peptidases-resistant pseudopeptides were tested, demonstrating a molecular affinity for NRP-1 and NRP-2 recombinant chimeric proteins and devoid of affinity for VEGF receptor type 1 (Flt-1). To argue the involvement of NRP-1, MDA-MB-231 breast cancer cells were used, strongly over-expressing NRP-1 receptor. We evidenced a statistically significant decrease of the different peptides-conjugated photosensitizers uptake after RNA interference-mediated silencing of NRP-1. Peptides-conjugated photosensitizers allowed a selective accumulation into cells. In mice, no degradation was observed in plasma in vivo 4h after intravenous injection by MALDI-TOF mass spectrometry. This study draws attention to this potential problem with peptides, especially in the case of targeting strategies, and provides useful information for the future design of more stable molecules.

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.

Phenomenological modeling of tumor diameter growth based on a mixed effects model

Over the last few years, taking advantage of the linear kinetics of the tumor growth during the steady-state phase, tumor diameter-based rather than tumor volume-based models have been developed for the phenomenological modeling of tumor growth. In this study, we propose a new tumor diameter growth model characterizing early, late and steady-state treatment effects. Model parameters consist of growth rhythms, growth delays and time constants and are meaningful for biologists. Biological experiments provide in vivo longitudinal data. The latter are analyzed using a mixed effects model based on the new diameter growth function, to take into account inter-mouse variability and treatment factors. The relevance of the tumor growth mixed model is firstly assessed by analyzing the effects of three therapeutic strategies for cancer treatment (radiotherapy, concomitant radiochemotherapy and photodynamic therapy) administered on mice. Then, effects of the radiochemotherapy treatment duration are estimated within the mixed model. The results highlight the model suitability for analyzing therapeutic efficiency, comparing treatment responses and optimizing, when used in combination with optimal experiment design, anti-cancer treatment modalities.

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.

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.