Novel Foscan®-derived ring-fused chlorins for photodynamic therapy of cancer

Photodynamic therapy (PDT) is an established anticancer treatment that combines the use of a photosensitiser (PS) and a light source of a specific wavelength for the generation of reactive oxygen species (ROS) that are toxic to the tumour cells. Foscan® (mTHPC) is a clinically-approved chlorin used for the PDT treatment of advanced head and neck, prostate and pancreatic cancers but is characterized by being photochemically unstable and associated with prolonged skin photosensitivity. Herein, we report the synthesis of new 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins, having the meso-tetra(3-hydroxyphenyl)macrocycle core of mTHPC, by exploring the [8π + 2π] cycloaddition of a meso-tetra(3-hydroxyphenyl)porphyrin derivative with diazafulvenium methides. These chlorins have photochemical properties similar to Foscan® but are much more photostable. Among the novel compounds, two chlorins with a hydroxymethyl group and its azide derivative present in the 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused system, are promising photodynamic agents with activity in the 100 nM range against triple-negative breast cancer cells and, in the case of azidomethyl chlorin, a safer phototherapeutic index compared to Foscan®.

Ligand-Targeted Delivery of Photosensitizers for Cancer Treatment

Photodynamic therapy (PDT) is a promising cancer treatment which involves a photosensitizer (PS), light at a specific wavelength for PS activation and oxygen, which combine to elicit cell death. While the illumination required to activate a PS imparts a certain amount of selectivity to PDT treatments, poor tumor accumulation and cell internalization are still inherent properties of most intravenously administered PSs. As a result, common consequences of PDT include skin photosensitivity. To overcome the mentioned issues, PSs may be tailored to specifically target overexpressed biomarkers of tumors. This active targeting can be achieved by direct conjugation of the PS to a ligand with enhanced affinity for a target overexpressed on cancer cells and/or other cells of the tumor microenvironment. Alternatively, PSs may be incorporated into ligand-targeted nanocarriers, which may also encompass multi-functionalities, including diagnosis and therapy. In this review, we highlight the major advances in active targeting of PSs, either by means of ligand-derived bioconjugates or by exploiting ligand-targeting nanocarriers.

Lipid monolayer as a simple model membrane for comparative assessment of the photodynamic therapy photosensitizer efficiency via macroscopic measurements

Cellular membrane is one of the main targets of photodynamic therapy. Its high complexity has led to the study of the efficiency of photosensitizers on artificial lipid systems mimicking membranes. However, the preliminary analysis of this efficiency remains limited due to difficulty of the model construction and/or implementation of the required measurement techniques. Hereby, we propose a quite simple way for the rapid comparative assessment of novel photosensitizers in terms of membrane photodegradation, based on simple and fast measurements, such as wetting angle and surface plasmon resonance spectroscopy. As a proof of concept, we applied this methodology to two bacteriopurpurinimide derivatives. We have shown in particular that such complementary techniques can be employed not only for the multiparametric monitoring of the kinetics of the photodegradation, but also for the comparison of the damaging efficiency of the photosensitizers in the lipid structures as well.

Synthesis and Characterization of an Epidermal Growth Factor Receptor-Selective RuII Polypyridyl-Nanobody Conjugate as a Photosensitizer for Photodynamic Therapy

There is a current surge of interest in the development of novel photosensitizers (PSs) for photodynamic therapy (PDT), as those currently approved are not completely ideal. Among the tested compounds, we have previously investigated the use of RuII polypyridyl complexes with a [Ru(bipy)2 (dppz)]2+ and [Ru(phen)2 (dppz)]2+ scaffold (bipy=2,2'-bipyridine; dppz=dipyrido[3,2-a:2',3'-c]phenazine; phen=1,10-phenanthroline). These complexes selectively target DNA. However, because DNA is ubiquitous, it would be of great interest to increase the selectivity of our PDT PSs by linking them to a targeting vector in view of targeted PDT. Herein, we present the synthesis, characterization, and in-depth photophysical evaluation of a nanobody-containing RuII polypyridyl conjugate selective for the epidermal growth factor receptor (EGFR) in view of targeted PDT. Using ICP-MS and confocal microscopy, we could demonstrate that our conjugate has high selectivity for the EGFR receptor, which is a crucial oncological target because it is overexpressed and/or deregulated in a variety of solid tumors. However, in contrast to expectations, this conjugate was found to not produce reactive oxygen species (ROS) in cancer cells and is therefore not phototoxic.

Fluorescent glycoconjugates and their applications

Fluorescent glycoconjugates are discussed for their applications in biology in vitro, in cell assays and in animal models. Advantages and limitations are presented for each design using a fluorescent core conjugated with glycosides, or vice versa.

Multilayer photodynamic therapy for highly effective and safe cancer treatment

Recent efforts to develop tumor-targeted photodynamic therapy (PDT) photosensitizers (PSs) have greatly advanced the potential of PDT in cancer therapy, although complete eradication of tumor cells by PDT alone remains challenging. As a way to improve PDT efficacy, we report a new combinatory PDT therapy technique that specifically targets multilayers of cells. Simply mixing different PDT PSs, even those that target distinct receptors (this may still lead to similar cell-killing pathways), may not achieve ideal therapeutic outcomes. Instead, significantly improved outcomes likely require synergistic therapies that target various cellular pathways. In this study, we target two proteins upregulated in cancers: the cannabinoid CB2 receptor (CB₂R, a G-protein coupled receptor) and translocator protein (TSPO, a mitochondria membrane receptor). We found that the CB₂R-targeted PS, IR700DX-mbc94, triggered necrotic cell death upon light irradiation, whereas PDT with the TSPO-targeted IR700DX-6T agent led to apoptotic cell death. Both PSs significantly inhibited tumor growth in vivo in a target-specific manner. As expected, the combined CB₂R- and TSPO-PDT resulted in enhanced cell killing efficacy and tumor inhibition with lower drug dose. The median survival time of animals with multilayer PDT treatment was extended by as much as 2.8-fold over single PDT treatment. Overall, multilayer PDT provides new opportunities to treat cancers with high efficacy and low side effects.

STATEMENT OF SIGNIFICANCE

Photodynamic therapy (PDT) is increasingly used as a minimally invasive, controllable and effective therapeutic procedure for cancer treatment. However, complete eradication of tumor cells by PDT alone remains challenging. In this study, we investigate the potential of multilayer PDT in cancer treatment with high efficacy and low side effects. Through PDT targeting two cancer biomarkers located at distinct subcellular localizations, remarkable synergistic effects in cancer cell killing and tumor inhibition were observed in both in vitro and in vivo experiments. This strategy may be widely applied to treat various cancer types by using strategically designed PDT photosensitizers that target corresponding upregulated receptors at tactical subcellular localization.

Synthesis of BODIPY-Peptide Conjugates for Fluorescence Labeling of EGFR Overexpressing Cells

Regioselective functionalization of 2,3,5,6,8-pentachloro-BODIPY 1 produced unsymmetric BODIPY 5, bearing an isothiocyanate group suitable for conjugation, in only four steps. The X-ray structure of 5 reveals a nearly planar BODIPY core with aryl dihedral angles in the range 47.4-62.9°. Conjugation of 5 to two EGFR-targeting pegylated peptides, 3PEG-LARLLT (6) and 3PEG-GYHWYGYTPQNVI (7), under mild conditions (30 min at room temperature), afforded BODIPY conjugates 8 and 9 in 50-80% isolated yields. These conjugates showed red-shifted absorption and emission spectra compared with 5, in the near-IR region, and were evaluated as potential fluorescence imaging agents for EGFR overexpressing cells. SPR and docking investigations suggested that conjugate 8 bearing the LARLLT sequence binds to EGFR more effectively than 9 bearing the GYHWYGYTPQNVI peptide, in part due to the lower solubility of 9, and its tendency for aggregation at concentrations above 10 μM. Studies in human carcinoma HEp2 cells overexpressing EGFR demonstrated low dark and photo cytotoxicities for BODIPY 5 and the two peptide conjugates, and remarkably high cellular uptake for both conjugates 8 and 9, up to 90-fold compared with BODIPY 5 after 1 h. Fluorescence imaging studies in HEp2 cells revealed subcellular localization of the BODIPY-peptide conjugates mainly in the Golgi apparatus and the cell lysosomes. The low cytotoxicity of the new conjugates and their remarkably high uptake into EGFR overexpressing cells renders them promising imaging agents for cancers overexpressing EGFR.

Highly water-soluble and tumor-targeted photosensitizers for photodynamic therapy

Biological uses of photosensitizers in photodynamic therapy (PDT) often suffer from a lack of tumor selectivity; a strategy based on molecule-targeted cancer therapies could provide a promising solution. To synthesize new water-soluble phthalocyanines (Pcs) for bio-conjugation with peptides or antibodies, we developed a method to synthesize asymmetrically substituted Pcs with both high water solubility and one monoamino group for conjugation with biological agents for tumor homing, using folic acid as the ligand model to direct the modified Pcs into target cells. Here, we report studies on the syntheses and characterization of these Pcs. In vitro and in vivo assays prove that the high solubility characteristic can greatly increase the tumor targeting capability of Pcs by reducing non-specific uptake. This newly designed photosensitizer accumulated almost completely in tumor regions, with a negligible signal found in other tissues in the xenograft tumor model. These initial data provide strong evidence of the high specificity tumor targeting of Pcs with folate and tri-glycerol substitutions. Theoretically, the synthesized Pcs could be conveniently conjugated to many other ligands, endorsing the broad applicability of this method for tumor-targeted PDT.

Synthesis and biological evaluation of peptide-conjugated phthalocyanine photosensitizers with highly hydrophilic modifications

Highly hydrophilic modification enhances the selectivity of targeted photosensitizer delivery.

The translocator protein as a potential molecular target for improved treatment efficacy in photodynamic therapy

Since its serendipitous discovery over 30 years ago, the translocator protein (18 kDa) has been demonstrated to play an important role in a multitude of critical biological processes. Although implemented as a novel therapeutic and diagnostic tool for a variety of disease states, its most promising role is as a molecular target for anticancer treatments such as photodynamic therapy (PDT). This review gives an overview of the attempts made by researchers to design porphyrin-based photosensitizers for use as anticancer therapeutics in PDT as well as improved imaging agents for diagnostic purposes. With a better understanding of the structure and function of the translocator protein, the synthesis of porphyrins for use in PDT with optimum binding affinities will become ever more possible.

Zinc phthalocyanine conjugated with the amino-terminal fragment of urokinase for tumor-targeting photodynamic therapy

Photodynamic therapy (PDT) has attracted much interest for the treatment of cancer due to the increased incidence of multidrug resistance and systemic toxicity in conventional chemotherapy. Phthalocyanine (Pc) is one of main classes of photosensitizers for PDT and possesses optimal photophysical and photochemical properties. A higher specificity can ideally be achieved when Pcs are targeted towards tumor-specific receptors, which may also facilitate specific drug delivery. Herein, we develop a simple and unique strategy to prepare a hydrophilic tumor-targeting photosensitizer ATF-ZnPc by covalently coupling zinc phthalocyanine (ZnPc) to the amino-terminal fragment (ATF) of urokinase-type plasminogen activator (uPA), a fragment responsible for uPA receptor (uPAR, a biomarker overexpressed in cancer cells), through the carboxyl groups of ATF. We demonstrate the high efficacy of this tumor-targeting PDT agent for the inhibition of tumor growth both in vitro and in vivo. Our in vivo optical imaging results using H22 tumor-bearing mice show clearly the selective accumulation of ATF-ZnPc in tumor region, thereby revealing the great potential of ATF-ZnPc for clinical applications such as cancer detection and guidance of tumor resection in addition to photodynamic treatment.

Cannabinoid CB2 receptor as a new phototherapy target for the inhibition of tumor growth

The success of targeted cancer therapy largely relies upon the selection of target and the development of efficient therapeutic agents that specifically bind to the target. In the current study, we chose a cannabinoid CB2 receptor (CB2R) as a new target and used a CB2R-targeted photosensitizer, IR700DX-mbc94, for phototherapy treatment. IR700DX-mbc94 was prepared by conjugating a photosensitizer, IR700DX, to mbc94, whose binding specificity to CB2R has been previously demonstrated. We found that phototherapy treatment using IR700DX-mbc94 greatly inhibited the growth of CB2R positive tumors but not CB2R negative tumors. In addition, phototherapy treatment with nontargeted IR700DX did not show significant therapeutic effect. Similarly, treatment with IR700DX-mbc94 without light irradiation or light irradiation without the photosensitizer showed no tumor-inhibitory effect. Taken together, IR700DX-mbc94 is a promising phototherapy agent with high target-specificity. Moreover, CB2R appears to have great potential as a phototherapeutic target for cancer treatment.

Synthesis and biological investigations of a ZnPc-antiCEA bioconjugate for imaging of colorectal cancer

Two zinc(II) phthalocyanines (ZnPcs) were conjugated with a monoclonal antibody (MAb) directed against carcinoembryonic antigen (CEA), using an in situ activated carboxylic acid on the ZnPcs. The bioconjugate with the highest ZnPc/MAb ratio of 3 was investigated in vitro for its ability to target and fluorescently label human colorectal HT-29 cells. The ZnPc-CEA MAb 2 was observed to efficiently target HT-29 cells, about 37 times more than unconjugated ZnPc. Furthermore, in the presence of a 4-fold excess of unlabelled anti-CEA antibody, the fluorescence signal of 2 was reduced by ~90% showing that the targeting is CEA-mediated. These studies further confirm the high specificity of Pc-antibody conjugates for antigens over-expressed on tumor cells and warrant further investigations of these immunoconjugates and their derivatives for imaging of colorectal cancer.

Assessment of new cationic porphyrin binding to plasma proteins by planar microarray and spectroscopic methods

Porphyrins have a unique aromatic structure determining particular photochemical properties that make them promising photosensitizers for anticancer therapy. Previously, we synthesized a set of artificial porphyrins by modifying side-chain functional groups and introducing different metals into the core structure. Here, we have performed a comparative study of the binding properties of 29 cationic porphyrins with plasma proteins by using microarray and spectroscopic approaches. The porphyrins were noncovalently immobilized onto hydrogel-covered glass slides and probed to bio-conjugated human and bovine serum albumins, as well as to human hemoglobin. The signal detection was carried out at the near-infrared fluorescence wavelength (800 nm) that enabled the effect of intrinsic visible wavelength fluorescence emitted by the porphyrins tested to be discarded. Competition assays on porphyrin microarrays indicated that long-chain fatty acids (FAs) (palmitic and stearic acids) decrease porphyrin binding to both serum albumin and hemoglobin. The binding affinity of different types of cationic porphyrins for plasma proteins was quantitatively assessed in the absence and presence of FAs by fluorescent and absorption spectroscopy. Molecular docking analysis confirmed results that new porphyrins and long-chain FAs compete for the common binding site FA1 in human serum albumin and meso-substituted functional groups in porphyrins play major role in the modulation of conformational rearrangements of the protein.

Phthalocyanine-peptide conjugates for epidermal growth factor receptor targeting

Four phthalocyanine (Pc)-peptide conjugates designed to target the epidermal growth factor receptor (EGFR) were synthesized and evaluated in vitro using four cell lines: human carcinoma A431 and HEp2, human colorectal HT-29, and kidney Vero (negative control) cells. Two peptide ligands for EGFR were investigated: EGFR-L1 and -L2, bearing 6 and 13 amino acid residues, respectively. The peptides and Pc-conjugates were shown to bind to EGFR using both theoretical (Autodock) and experimental (SPR) investigations. The Pc-EGFR-L1 conjugates 5a and 5b efficiently targeted EGFR and were internalized, in part due to their cationic charge, whereas the uncharged Pc-EGFR-L2 conjugates 4b and 6a poorly targeted EGFR maybe due to their low aqueous solubility. All conjugates were nontoxic (IC(50) > 100 μM) to HT-29 cells, both in the dark and upon light activation (1 J/cm(2)). Intravenous (iv) administration of conjugate 5b into nude mice bearing A431 and HT-29 human tumor xenografts resulted in a near-IR fluorescence signal at ca. 700 nm, 24 h after administration. Our studies show that Pc-EGFR-L1 conjugates are promising near-IR fluorescent contrast agents for CRC and potentially other EGFR overexpressing cancers.

Silica nanoparticles functionalized with porphyrins and analogs for biomedical studies

This review focus on the preparation of silica nanoparticles functionalized with porphyrins and related compounds. It is aimed to highlight their features as photosensitizers in the area of photodynamic therapy. In this field, photosensitizers have been covalently and non-covalently linked to silica nanoparticles, in order to study their photophysical and biological properties. Another fascinating scenario for photosensitizer-silica nanoparticles hybrids involves the possibility of including metal cores for conditioning the uptake in the target cells, allowing most of the times the combination of therapies and in certain conditions to facilitate the removal and reutilization of the photosensitizer in environmental applications.

A first ABAC phthalocyanine

The derouting of the selective synthesis of crosswise phthalocyanines (Pcs) applied to a statistical precursors mixture leads to the first member of a new family of Pcs bearing three different substituents: the ABAC phthalocyanines. By playing on the precursors' relative ratio, the yields and selectivity of the method have been optimized.

Synthetic porphyrins in experimental photodynamic therapy induce a different antitumoral effect

The aim of the study was to investigate the influence of discrete structural differences in synthetic porphyrins on the antineoplastic effect induced in myelocitic cell line K562 after experimental photodynamic therapy procedure. For this study, we used 5,10,15,20-tetra(1-naphthyl)porphyrin, 5,10,15,20-tetra(4-sulfonatophenyl)porphyrin and their Zn complexes. For all these compounds, the following photodynamic therapy parameters were optimized: cell concentration, dye loading concentration, loading time and irradiation procedure. The non-toxic doses of porphyrins were different according to their structure: for 5,10,15,20-tetra(1-naphthyl)porphyrin compounds, the dose was of 10 μg.mL-1, and for 5,10,15,20-tetra(4-sulfonatophenyl)porphyrin compounds, the dose was 20 μg.mL-1. Cell functionality was assessed as membrane integrity, viability, and number of metabolically active cells. Photodynamic cell degradation kinetics showed that during irradiation tumor cells are actively destroyed, in contrast to unloaded cells. K562 cells loaded with the above-mentioned compounds and subjected to irradiation, displayed lower proliferative capacity compared to the control, for a period of 72 h after irradiation. The proliferative capacity of K562 cell line was more strongly inhibited by the 5,10,15,20-tetra(1-naphthyl)porphyrin family of compounds than by the 5,10,15,20-tetra(4-sulfonatophenyl)porphyrin family. The tested synthetic porphyrins showed effective antineoplastic activity against K562 leukemia cells in our in vitro photodynamic therapy experimental model.

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

Mono- and tri-cationic porphyrin-monoclonal antibody conjugates: photodynamic activity and mechanism of action

Two cationic porphyrins bearing an isothiocyanate group for conjugation to monocolonal antibodies have been synthesized. The two porphyrins conjugated efficiently to three monoclonal antibodies (anti-CD104, anti-CD146 and anti-CD326), which recognize antigens commonly over-expressed on a range of tumour cells. In vitro, all conjugates retained the phototoxicity of the porphyrin and the immunoreactivity of the antibody. Mechanistic studies showed that conjugates formed from the mono- and tri-cationic porphyrin and anti-CD104 antibody mediated apoptosis following irradiation with non-thermal red light of 630 ± 15 nm wavelength. In vivo antibody conjugates caused suppression of human LoVo tumour growth in immunodeficient NIH III mice, similar to the commercial photodynamic therapy (PDT) agent Photofrin®, but at administered photosensitizer doses that were more than two orders of magnitude lower. Positron emission tomography (PET) following PDT showed a large, early increase in uptake of ¹⁸fluorodeoxyglucose (FDG) by tumours treated with the anti-CD104 conjugates. This effect was not observed with Photofrin® or with conjugates formed from the same photosensitizers conjugated to an irrelevant antibody.

Synthesis and stereochemistry of highly unsymmetric beta,meso-linked porphyrin arrays

Porphyrin arrays with tailor-made photophysical properties and well-defined three-dimensional geometries constitute attractive synthetic targets in porphyrin chemistry. The paper describes a variable, straightforward synthetic procedure for the construction of beta,meso-linked porphyrin multichromophores in good to excellent yields. In a Suzuki-type coupling reaction beta-borylated 5,10,15,20-tetraarylporphyrins (TAPs) served as versatile building blocks for the preparation of a plethora of directly linked, unsymmetrically substituted di- and triporphyrins. Besides their interesting photophysical properties, especially the trimeric porphyrin arrays show exciting stereochemical features. The established protocols thus open a convenient entry into the synthesis of achiral and chiral, unsymmetrically substituted beta,meso-linked oligoporphyrins, e.g., for applications in biomedicine or nonlinear optics.

A fluorinated ruthenium porphyrin as a potential photodynamic therapy agent: synthesis, characterization, DNA binding, and melanoma cell studies

When the new porphyrin 5,10-(4-pyridyl)-15,20-(pentafluorophenyl)porphyrin is reacted with 2 equiv of Ru(bipy)(2)Cl(2) (where bipy = 2,2'-bipyridine) formation of the target ruthenated porphyrin is achieved with 40% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrin Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dpi) to bipy(pi*) metal to ligand charge transfer (MLCT) band. The bipyridyl pi to pi* transition occurs at 295 nm. Cyclic voltammetry experiments reveal two single-electron redox couples in the cathodic region at E(1/2) = -0.80 and -1.18 V vs Ag/AgCl associated with the porphyrin. Two overlapping redox couples at E(1/2) = 0.83 V vs Ag/AgCl due to the Ru(III/II) centers is also observed. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give a K(b) = 7.6 x 10(5) M(-1) indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 400 nm), complete nicking of the DNA is observed. Cell studies show that the ruthenated porphyrin is more toxic to melanoma skin cells than to normal fibroblast cells. When irradiated with a 60 W tungsten lamp, the ruthenium porphyrin preferentially leads to apoptosis of the melanoma cells over the normal skin cells.

Photodynamic Therapy: Porphyrins and Phthalocyanines as Photosensitizers

The present work is focussed on the principles of photodynamic therapy (PDT), emphasizing the photochemical mechanisms of reactive oxygen species formation and the consequent biochemical processes generated by the action of reactive oxygen species on various biological macromolecules and organelles. This paper also presents some of the most used photosensitizers, including Photofrin, and the new prototypes of photosensitizers, analysing their physicochemical and spectroscopic properties. At this point, the review discusses the therapeutic window of absorption of specific wavelengths involving first- and second-generation photosensitizers, as well as the principal light sources used in PDT. Additionally, the aggregation process, which consists in a phenomenon common to several photosensitizers, is studied. J-aggregates and H-aggregates are discussed, along with their spectroscopic effects. Most photosensitizers have a significant hydrophobic character; thus, the study of the types of aggregation in aqueous solvent is very relevant. Important aspects of the coordination chemistry of metalloporphyrins and metallophthalocyanines used as photosensitizers are also discussed. The state-of-the-art in PDT is evaluated, discussing recent articles in this area. Furthermore, macrocyclic photosensitizers, such as porphyrins and phthalocyanines, are specifically described. The present review is an important contribution, because PDT is one of the most auspicious advances in the therapy against cancer and other non-malignant diseases.

In vivo and in vitro characterisation of a protoporphyrin IX-cyclic RGD peptide conjugate for use in photodynamic therapy

Increasing treatment specificity is one of the major aims of cancer research. Photodynamic therapy is a clinically proven treatment for some cancers and certain other diseases. Photosensitisers generally have little intrinsic selectivity for tumours and any accumulation is dependent upon the type of tumour involved. Increasing tumour selective accumulation could improve the efficacy of PDT and reduce any risk of side effects caused by photosensitiser accumulation in non-target tissue. In order to target photosensitisers to tumours, a cyclic peptide, cRGDfK (arginine-glycine-aspartic acid-phenylalanine-lysine) has been synthesised using solid phase peptide chemistry and conjugated to the porphyrin photosensitiser, protoporphyrin IX. The arginine-glycine-aspartic acid (RGD) motif has been shown to specifically bind alphavbeta3 integrins, heterodimeric glycoproteins upregulated on the surface of proliferating endothelial cells such as those in tumour neovasculature. This study reports the synthesis, in vitro and in vivo characterisation of this novel compound and compares its properties to the free photosensitiser. The individual components in our system, protoporphyrin IX and cRGDfK retain their respective photodynamic and integrin binding activity following the coupling step and produce a conjugate of high purity. The PpIX:cRGDfK conjugate is shown to be a good photosensitiser in vitro in the integrin positive human SiHa cell line and in vivo in a mouse CaNT tumour model. Moreover, pharmacokinetic analysis of PpIX:cRGDfK treated mice shows significant retention and accumulation of photosensitiser in tumour tissue with higher tumour : normal tissue ratios than the free photosensitiser. However, although the conjugate shows this higher accumulation and improved tumour : non-target tissue ratios, the overall in vivo PDT effect, between dose-light intervals of 0 and 6 h, is not significantly better than for free protoporphyrin IX This is possibly due to differences in the target environment or in the subcellular localisation of the compounds.

Model Systems for Fluorescence and Singlet Oxygen Quenching by Metalloporphyrins

Next-generation photodynamic therapy agents will minimize extraneous phototoxicity by being active only at the target site. To this end, we have developed a model system to systematically investigate the excited-state quenching ability of a number of metalloporphyrins. Central metal ions that prefer four-coordinate, square planar orientations (Ag(II), Cu(II), Ni(II), Pd(II), and Zn(II)) were used. Porphyrin dimers based on 5-(4-aminophenyl)-10,15,20-triphenylporphyrin and comprising both a free base porphyrin and a metalloporphyrin covalently linked through a five-carbon alkyl chain were synthesized. The fluorescence and singlet oxygen quantum yields for the dimers were probed at 630 and 650 nm, respectively, resulting in the excitation of only the free base porphyrin and allowing a comparison of the quenching efficacy of each central metal ion. These results demonstrate that metalloporphyrins can serve as efficient quenchers, and may be useful in the design of novel light-activated therapeutic agents.

Enhanced cellular uptake with a cobaltacarborane-porphyrin-HIV-1 Tat 48-60 conjugate

A series of four porphyrin-cobaltacarborane conjugates have been synthesized, containing three or four cobaltabisdicarbollide anions linked by O(CH(2)CH(2)O)(2) groups to the porphyrin macrocycle and one of them containing a HIV-1 Tat 48-60 peptide sequence linked via a low molecular weight poly(ethylene glycol) (PEG) spacer. The cellular uptake, cytotoxicity, and preferential sites of intracellular localization of the conjugates were evaluated in human HEp2 cells. All conjugates are nontoxic in the dark at the concentrations studied. Upon exposure to low light dose (1 J cm(-)(2)) only the porphyrin-cobaltacarborane-HIV-1 Tat 48-60 conjugate showed 30% inhibition of cell proliferation at a concentration of 10 microM. The cellular uptake was dependent on the number of carborane cages and was significantly enhanced by the presence of the cell penetrating peptide sequence HIV-1 Tat 48-60. All conjugates preferentially localized in the cell lysosomes.

DNA damaging capability of hematoporphyrin towards DNAs of various accessibilities

In this work we wanted to verify that photoactivation of DNA-non-binding porphyrin derivative hematoporphyrin IX (Hp) is able to induce damages in DNAs of various accessibilities such as B-conformation and superhelical isolated DNA, nucleoprotein complex and intracellular DNAs. It was found that photodynamic reaction of Hp results significant changes in thermal stability of isolated T7 DNA and induces single strand breaks in supercoiled Bluescript plasmid isolated from Escherichia coli cells. As optical melting measurements revealed, the irradiation of photosensitized T7 nucleoprotein complex leads to a destabilization of the protein capsid. The photodynamic reaction affected both the protein structure and DNA-protein interaction, however, the parameters corresponding to the DNA denaturation are not influenced. The accumulation of Hp in HeLa cells was followed by laser scanning confocal microscopy. The picture received is typical for lipophilic dyes. When Hp loaded cells were irradiated, a reduction of viability could be observed in a concentration and a light dose dependent manner; 12microM porphyrin induced almost complete cell killing after 30min irradiation. After similar treatment, alkaline agarose gel electrophoresis of isolated nuclear DNA did not show the presence of single strand breaks. The alkaline comet assay also failed to demonstrate any DNA damage in HeLa cells. We also considered the possibility of the generation of damages in intracellular SV40 DNA. According to the electropherograms there was no difference between the patterns of DNAs from treated and control samples.

Peptide-mediated cell transport of water soluble porphyrin conjugates

Five new porphyrin-peptide conjugates bearing a nuclear localizing sequence SV40 or a fusogenic peptide (HIV-1Tat 40-60 or octa-arginine) linked by low molecular weight poly(ethylene glycol) have been synthesized. In vitro studies using human HEp2 cells show that the cellular uptake of the conjugates depends significantly on the nature and sequence of amino acids in the peptide and on the nature of the substituents on the porphyrin macrocycle. The fusogenic peptide sequences HIV-1Tat 40-60 and octa-arginine were the most effective in delivering the conjugates to the cells. The subcellular distribution of the conjugates was found to be dependent on the nature of substituents on the porphyrin macrocycle. The conjugates bearing a hydrophobic porphyrin localized preferentially in the endoplasmic reticulum and were significantly more phototoxic to HEp2 cells than the carboxylic acid functionalized porphyrin conjugates, which localized mainly in the lysosomes.

Polymeric nanoparticle preparation that eradicates tumors

We report the production of poly(lactic-co-glycolic acid) nanoparticles that encapsulate the photosensitizer meso-tetraphenylporpholactol. These nanoparticles are stable and nonphototoxic upon systemic administration. Upon cellular internalization, the photosensitizer is released from the nanoparticle and becomes highly phototoxic. Irradiation with visible light results in cell-specific killing of several cancer cell lines. Importantly, in vivo experiments show complete eradication of cancers in mouse models. The concept of photosensitizers with selective phototoxicity should have widespread applications in cancer therapy.

Near IR emitting isothiocyanato-substituted fluorophores: their synthesis and bioconjugation to monoclonal antibodies

Two near IR emitting fluorophores, based on the phthalocyanine and naphthalocyanine chromophores, which also bear a single isothiocyanato group suitable for conjugation to proteins are reported; their utility as luminescent probes is demonstrated by conjugation to monoclonal antibodies and the ability of these conjugates to selectively bind cells bearing the relevant antigen.