Synthesis of new representatives of A3B-type carboranylporphyrins based on meso-tetra(pentafluorophenyl)porphyrin transformations.

A carboranylporphyrin of A3B-type bearing a single pentafluorophenyl ring was prepared through the regioselective nucleophilic aromatic substitution reaction of the p-fluorine atoms in 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin with 9-mercapto-m-carborane. The reaction of this porphyrin with sodium azide led to the selective substitution of the p-fluorine atom in the pentafluorophenyl substituent with an azide functionality which upon reduction with SnCl2 resulted in the formation of the corresponding porphyrin with an amino group. Pentafluorophenyl-substituted A3B-porphyrins were studied and transformed to thiol and amino-substituted compounds allowing for the preparation of porphyrins with different reactive groups such as hydroxy and amino derivatives capable for further functionalization and conjugation of these porphyrins to other substrates. In addition, conjugates containing maleimide or biotin entities in the structure of carborane A3B-porphyrin were also synthesized based on the amino-substituted A3B-porphyrin. The structures of the prepared carboranylporphyrins were determined by UV-vis, IR, 1H, 19F, 11B NMR spectroscopic data and MALDI mass spectrometry.

The Copper Reduction Potential Determines the Reductive Cytotoxicity: Relevance to the Design of Metal-Organic Antitumor Drugs.

Copper-organic compounds have gained momentum as potent antitumor drug candidates largely due to their ability to generate an oxidative burst upon the transition of Cu2+ to Cu1+ triggered by the exogenous-reducing agents. We have reported the differential potencies of a series of Cu(II)-organic complexes that produce reactive oxygen species (ROS) and cell death after incubation with N-acetylcysteine (NAC). To get insight into the structural prerequisites for optimization of the organic ligands, we herein investigated the electrochemical properties and the cytotoxicity of Cu(II) complexes with pyridylmethylenethiohydantoins, pyridylbenzothiazole, pyridylbenzimidazole, thiosemicarbazones and porphyrins. We demonstrate that the ability of the complexes to kill cells in combination with NAC is determined by the potential of the Cu+2 → Cu+1 redox transition rather than by the spatial structure of the organic ligand. For cell sensitization to the copper-organic complex, the electrochemical potential of the metal reduction should be lower than the oxidation potential of the reducing agent. Generally, the structural optimization of copper-organic complexes for combinations with the reducing agents should include uncharged organic ligands that carry hard electronegative inorganic moieties.

BODIPY derivatives modified with carborane clusters: synthesis, characterization and DFT studies.

An efficient approach for the preparation of 3,5-dicarborane-substituted BODIPY conjugates was developed via the functionalization of 3,5-dibromo-8-pentafluorophenyl-BODIPY with neutral and anionic carborane S-nucleophiles. It was found that 3,5-dicarborane-substituted BODIPYs could be easily modified with a third carborane cluster using SNAr substitution reactions of the para-fluorine atom in the meso-pentafluorophenyl BODIPY substituent with the corresponding carborane S-nucleophile affording boron-enriched BODIPYs in good yields. The influence of bromine atom substitution with carborane moieties on the position of absorption and fluorescence bands and the fluorescence quantum yields of the prepared BODIPYs were analyzed. The crystal structures of BODIPYs 4 and 8 were investigated. Density functional theory methods (DFT wb97xd/6-31G* and wb97xd/lanl2dz) were performed to study the geometrical structures, electronic characteristics, the highest occupied and the lowest unoccupied molecular orbitals (HOMOs and LUMOs) and other chemical descriptors of the synthesized compounds.

Multistep synthesis and X-ray structures of carboxyl-terminated hybrid iron(II) phthalocyaninatoclathrochelates and their postsynthetic transformation into polytopic carboranyl-containing derivatives.

A multistep general synthetic strategy towards polytopic carboranyl-containing (semi)clathrochelate metal complexes, based on the template synthesis, transmetallation, amide condensation and 1,3-dipolar cycloaddition reactions, is developed. Their mono(semi)clathrochelate precursors with a single reactive group were obtained using a transmetallation of the triethylantimony-capped macrobicyclic precursor. The thus obtained carboxyl-terminated iron(II) semiclathrochelate underwent a macrobicyclization with zirconium(IV) phthalocyaninate to form the corresponding phthalocyaninatoclathrochelate. The direct one-pot template condensation of the suitable chelating and cross-linking ligand synthons on the Fe2+ ion as a matrix was also used for its preparation. Further amide condensation of the aforementioned semiclathrochelate and hybrid complexes with propargylamine in the presence of carbonyldiimidazole gave the (pseudo)cage derivatives with a terminal CC bond. Their "click" reaction with an appropriate carboranylmethyl azide afforded the ditopic carboranosemiclathrochelates and the tritopic carboranyl-containing phthalocyaninatoclathrochelates with a flexible spacer fragment between their polyhedral entities. The obtained new complexes were characterized using elemental analysis, MALDI-TOF mass spectrometry, multinuclear NMR, and UV-vis spectroscopy, and by single crystal X-ray diffraction experiments. Their FeN6-coordination polyhedra show a truncated trigonal-pyramidal geometry, while the cross-linking heptacoordinate Zr4+ or Hf4+ cations in the hybrid compounds form the MIVN4O3-coordination polyhedra with the geometry of a capped trigonal prism.

Synthesis, Characterization and DFT Study of a New Family of High-Energy Compounds Based on s-Triazine, Carborane and Tetrazoles.

An efficient one-pot synthesis of carborane-containing high-energy compounds was developed via the exploration of carbon-halogen bond functionalization strategies in commercially available 2,4,6-trichloro-1,3,5-triazine. The synthetic pathway first included the substitution of two chlorine atoms in s-triazine with 5-R-tetrazoles (R = H, Me, Et) units to form disubstituted tetrazolyl 1,3,5-triazines followed by the sequential substitution of the remaining chlorine atom in 1,3,5-triazine with carborane N- or S-nucleophiles. All new compounds were characterized by IR- and NMR spectroscopy. The structure of four new compounds was confirmed by single crystal X-ray diffraction analysis. The density functional theory method (DFT B3LYP/6-311 + G*) was used to study the geometrical structures, enthalpies of formation (EOFs), energetic properties and highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energies and the detonation properties of synthesized compounds. The DFT calculation revealed compounds processing the maximum value of the detonation velocity or the maximum value of the detonation pressure. Theoretical terahertz frequencies for potential high-energy density materials (HEDMs) were computed, which allow the opportunity for the remote detection of these compounds.

Multicomponent Molecular Systems Based on Porphyrins, 1,3,5-Triazine and Carboranes: Synthesis and Characterization.

2,4,6-Trichloro-1,3,5-triazine (cyanuric chloride) is an excellent coupling reagent for the preparation of highly structured multifunctional molecules. Three component systems based on porphyrin, cyanuric chloride and carborane clusters were prepared by a one-pot stepwise amination of cyanuric chloride with 5-(4-aminophenyl)-10,15,20-triphenylporphyrin, followed by replacement of the remaining chlorine atoms with carborane S- or N-nucleophiles. Some variants of 1,3,5-triazine derivatives containing porphyrin, carborane and residues of biologically active compounds such as maleimide, glycine methyl ester as well as thioglycolic acid, mercaptoethanol and hexafluoroisopropanol were also prepared. A careful control of the reaction temperature during the substitution reactions will allow the synthesis of desired compounds in a good to high yields. The structures of synthesized compounds were determined with UV-vis, IR, 1H NMR, 11B NMR, MALDI-TOF or LC-MS spectroscopic data. The dark and photocytotoxicity as well as intracellular localization and photoinduced cell death for compounds 8, 9, 17, 18 and 24 were evaluated.

Copper-Containing Nanoparticles and Organic Complexes: Metal Reduction Triggers Rapid Cell Death via Oxidative Burst.

Copper-containing agents are promising antitumor pharmaceuticals due to the ability of the metal ion to react with biomolecules. In the current study, we demonstrate that inorganic Cu2+ in the form of oxide nanoparticles (NPs) or salts, as well as Cu ions in the context of organic complexes (oxidation states +1, +1.5 and +2), acquire significant cytotoxic potency (2-3 orders of magnitude determined by IC50 values) in combinations with N-acetylcysteine (NAC), cysteine, or ascorbate. In contrast, other divalent cations (Zn, Fe, Mo, and Co) evoked no cytotoxicity with these combinations. CuO NPs (0.1-1 µg/mL) together with 1 mM NAC triggered the formation of reactive oxygen species (ROS) within 2-6 h concomitantly with perturbation of the plasma membrane and caspase-independent cell death. Furthermore, NAC potently sensitized HCT116 colon carcinoma cells to Cu-organic complexes in which the metal ion coordinated with 5-(2-pyridylmethylene)-2-methylthio-imidazol-4-one or was present in the coordination sphere of the porphyrin macrocycle. The sensitization effect was detectable in a panel of mammalian tumor cell lines including the sublines with the determinants of chemotherapeutic drug resistance. The components of the combination were non-toxic if added separately. Electrochemical studies revealed that Cu cations underwent a stepwise reduction in the presence of NAC or ascorbate. This mechanism explains differential efficacy of individual Cu-organic compounds in cell sensitization depending on the availability of Cu ions for reduction. In the presence of oxygen, Cu+1 complexes can generate a superoxide anion in a Fenton-like reaction Cu+1L + O2 → O2-. + Cu+2L, where L is the organic ligand. Studies on artificial lipid membranes showed that NAC interacted with negatively charged phospholipids, an effect that can facilitate the penetration of CuO NPs across the membranes. Thus, electrochemical modification of Cu ions and subsequent ROS generation, as well as direct interaction with membranes, represent the mechanisms of irreversible membrane damage and cell death in response to metal reduction in inorganic and organic Cu-containing compounds.

Fluorinated maleimide-substituted porphyrins and chlorins: synthesis and characterization.

Maleimide-containing fluorinated porphyrins and chlorins were prepared based on the reaction of Zn(II) or Ni(II) complexes of 5,10,15,20-tetrakis(4-amino-2,3,5,6-tetrafluorophenyl)porphyrin and chlorin with maleic anhydride. Porphyrin maleimide derivatives were also prepared by the reaction of 5,10,15,20-tetrakis(4-azido-2,3,5,6-tetrafluorophenyl)porphyrinato Zn(II) or Ni(II) with N-propargylmaleimide via the CuAAC click reaction to afford fluorinated porphyrin-triazole-maleimide conjugates. New maleimide derivatives were isolated in reasonable yields and identified by UV-vis, 1H NMR, 19F NMR spectroscopy and mass-spectrometry.

Carborane derivatives of 1,2,3-triazole depolarize mitochondria by transferring protons through the lipid part of membranes.

Boron containing polyhedra (carboranes) are three-dimensional delocalized aromatic systems. These structures have been shown to transport protons through lipid membranes and mitochondria. Conjugation of carboranes to various organic moieties is aimed at obtaining biologically active compounds with novel properties. Taking advantage of 1,2,3-triazoles as the scaffolds valuable in medicinal chemistry, we synthesized 1-(o-carboranylmethyl)-4-pentyl-1,2,3-triazole (c-triazole) and 1-(o-carboranylmethyl)-4-pentyl-1,2,3-triazolium iodide (c-triazolium). Both compounds interacted with model lipid membranes and exhibited a proton carrying activity in planar bilayers and liposomes in a concentration- and pH-dependent manner. Importantly, mechanisms of the protonophoric activity differed; namely, protonation-deprotonation reactions of the triazole and the o-carborane moieties were involved in the transport cycles of c-triazole and c-triazolium, respectively. At micromolar concentrations, c-triazole and c-triazolium stimulated respiration of isolated rat liver mitochondria and depolarized their membrane potential, with c-triazole being more potent. In living K562 (human chronic myelogenous leukemia) cells, both c-triazolium and c-triazole altered the mitochondrial membrane potential as determined by a decreased intracellular accumulation of the potential-dependent dye tetramethylrhodamine ethyl ester. Finally, cell viability testing demonstrated a cytotoxic potency of c-triazolium and, to a lesser extent, of c-triazole against K562 cells, whereas non-malignant fibroblasts were much less sensitive. In all tests, the reference boron-free benzyl-4-pentyl-1,2,3-triazole showed little-to-no effects. These results demonstrated that carboranyltriazoles carry protons across biological membranes, a property potentially important in anticancer drug design.

Weak C-H acids as protonophores can carry hydrogen ions through lipid membranes and mitochondria: a case of o-carborane.

ortho-Carborane (1,2-C2B10H12) was found to be a carrier of protons in both mitochondrial and artificial lipid membranes, suggesting that this dicarborane can reversibly release hydrogen ions and diffuse through the membranes in neutral and anionic forms. Similar to conventional uncouplers (e.g. 2,4-dinitrophenol), o-carborane stimulated mitochondrial respiration and decreased the membrane potential at concentrations of tens of micromoles. Protonophoric activity of o-carborane was observed both by a fluorometric assay using pyranine-loaded liposomes and electrical current measurements across planar lipid bilayers. Substantial contribution of the proton flux to the o-carborane-mediated current was proved by a shift of the zero current voltage upon imposing a pH gradient across the membrane. Meta-carborane (1,7-C2B10H12) lacked the protonophoric activity in line with its reduced C-H acidity. The results suggest that weak C-H acids can exhibit protonophoric activity in the biological environment. The finding of a new class of protonophoric compounds is of substantial interest due to promising anti-obesity and anti-diabetic properties of uncouplers.

Carboranyl-Chlorin e6 as a Potent Antimicrobial Photosensitizer.

Antimicrobial photodynamic inactivation is currently being widely considered as alternative to antibiotic chemotherapy of infective diseases, attracting much attention to design of novel effective photosensitizers. Carboranyl-chlorin-e6 (the conjugate of chlorin e6 with carborane), applied here for the first time for antimicrobial photodynamic inactivation, appeared to be much stronger than chlorin e6 against Gram-positive bacteria, such as Bacillus subtilis, Staphyllococcus aureus and Mycobacterium sp. Confocal fluorescence spectroscopy and membrane leakage experiments indicated that bacteria cell death upon photodynamic treatment with carboranyl-chlorin-e6 is caused by loss of cell membrane integrity. The enhanced photobactericidal activity was attributed to the increased accumulation of the conjugate by bacterial cells, as evaluated both by centrifugation and fluorescence correlation spectroscopy. Gram-negative bacteria were rather resistant to antimicrobial photodynamic inactivation mediated by carboranyl-chlorin-e6. Unlike chlorin e6, the conjugate showed higher (compared to the wild-type strain) dark toxicity with Escherichia coli ΔtolC mutant, deficient in TolC-requiring multidrug efflux transporters.

Preferential DNA photocleavage potency of Zn(II) over Ni(II) derivatives of carboxymethyl tetracationic porphyrin: the role of the mode of binding to DNA.

The porphyrin-based photosensitizers capable of binding to DNA are perspective drug candidates. Here we report the interactions with calf thymus DNA of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium)porphyrin (P1) and its derivatives containing Zn(II) or Ni(II) in the coordination sphere. These interactions were studied with absorption and circular dichroism spectroscopy. NiP1 and ZnP1 formed different types of complexes with DNA. NiP1 intercalated into the double helix, whereas ZnP1 bound the DNA groove. Compound P1 displayed both binding modes. The ZnP1-DNA binding constant was approximately three times smaller than the respective values for P1-DNA and NiP1-DNA complexes. Light induced degradation of the reactive oxygen species (ROS) trap 1,3-diphenylisobenzofuran in the presence of P1 and its metal derivatives revealed that NiP1 was a weaker photooxidative agent, whereas P1 and ZnP1 generated ROS to similar extents. Nevertheless, the DNA photodamaging effect of ZnP1 was the most pronounced. Illumination of the supercoiled plasmid caused single-strand DNA photocleavage in the presence of P1 and ZnP1; double strand breaks were detectable with micromolar concentrations of ZnP1. The concentration of ZnP1 required for plasmid photonicking was two times smaller than that of P1 and ~20 times lower than that for NiP1. Thus, the modes of P1, NiP1 and ZnP1 binding to DNA determine the differential photodamaging potency of these porphyrins. A greater accessibility to the solvent of the groove binder ZnP1, compared to the shielded intercalator NiP1 and the intercalated P1 molecules, allows for an efficient local generation of ROS followed by DNA photocleavage.

Photodynamic activity of the boronated chlorin e6 amide in artificial and cellular membranes.

Photodynamic tumor-destroying activity of the boronated chlorin e6 derivative BACE (chlorin e6 13(1)-N-{2-[N-(1-carba-closo-dodecaboran-1-yl)methyl]aminoethyl}amide-15(2), 17(3)-dimethyl ester), previously described in Moisenovich et al. (2010) PLoS ONE 5(9) e12717, was shown here to be enormously higher than that of unsubstituted chlorin e6, being supported by the data on much higher photocytotoxicity of BACE in M-1 sarcoma cell culture. To validate membrane damaging effect as the basis of the enhanced tumoricidal activity, BACE was compared with unsubstituted chlorin e6 in the potency to photosensitize dye leakage from liposomes, transbilayer lipid flip-flop, inactivation of gramicidin A ionic channels in planar lipid membranes and erythrocyte hemolysis. In all the models comprising artificial and cellular membranes, the photodynamic effect of BACE exceeded that of chlorin e6. BACE substantially differed from chlorin e6 in the affinity to liposomes and erythrocytes, as monitored by fluorescence spectroscopy, flow cytometry and centrifugation. The results support the key role of membrane binding in the photodynamic effect of the boronated chlorin e6 amide.

Differential binding preference of methylpheophorbide a and its diboronated derivatives to albumin and low density lipoproteins.

The tetrapyrrolic macrocycle and the functional groups at its periphery allow for a variety of modifications aimed at multifunctional therapeutic compounds. In particular, conjugation of boron polyhedra yields dual efficacy antitumor photo/ radiosensitizers. Structural optimization of these agents presumes the identification of macromolecules that bind and transport boronated tetrapyrroles. Using spectroscopic methods we demonstrated that methylpheophorbide a forms complexes with serum albumin and low density lipoproteins (LDL) whereas two diboronated derivatives, 13(2),17(3)-[di(o-carboran-1-yl)methoxycarbonyl]pheophorbide a and 13(2),17(3)-[di(1-carba-closo-dodecaboran-1-yl)methoxycarbonyl]pheophorbide a, were capable of binding to LDL but not to albumin. Molecular modeling showed a mode of interaction of methylpheophorbide a with the amino acid residues in the albumin's hemin binding site. In contrast, for diboronated derivatives such interactions are sterically hindered by boron polyhedra, in line with experimentally determined lack of complex formation with albumin. These data strongly suggest that LDL might be the preferred carrier for polycarborane containing methylpheophorbide a derivatives.

The role of carboxymethyl substituents in the interaction of tetracationic porphyrins with DNA.

Cationic porphyrin-based compounds capable of interacting with DNA are currently under extensive investigation as prospective anticancer and anti-infective drugs. One of the approaches to enhancing the DNA-binding affinity of these ligands is chemical modification of functional groups of the porphyrin macrocycle. We analyzed the interaction with DNA of novel derivatives containing carboxymethyl and ethoxycarbonylmethyl substituents at quaternary nitrogen atoms of pyridinium groups at the periphery of the porphyrin macrocycle. The parameters of binding of 5,10,15,20-tetrakis(N-carboxymethyl-4-pyridinium)porphyrin (P1) and 5,10,15,20-tetrakis(N-ethoxycarbonylmethyl-4-pyridinium)porphyrin (P2) to double-stranded DNA sequences of different nucleotide content were determined using optical spectroscopy. The association constant of P1 interaction with calf thymus DNA (K = 3.4 × 10(6) M(-1)) was greater than that of P2 (K = 2.8 × 10(5) M(-1)). Preferential binding of P1 to GC- rather than AT-rich oligonucleotides was detected. In contrast, P2 showed no preference for particular nucleotide content. Modes of binding of P1 and P2 to GC and AT duplexes were verified using the induced circular dichroism spectra. Molecular modeling confirmed an intercalative mode of interaction of P1 and P2 with CpG islands. The carboxyl groups of the peripheral substituent in P1 determine the specific interactions with GC-rich DNA regions, whereas ethoxycarbonylmethyl substituents disfavor binding to DNA. This study contributes to the understanding of the impact of peripheral substituents on the DNA-binding affinity of cationic porphyrins, which is important for the design of DNA-targeting drugs.

Novel photosensitizers trigger rapid death of malignant human cells and rodent tumor transplants via lipid photodamage and membrane permeabilization.

BACKGROUND: Apoptotic cascades may frequently be impaired in tumor cells; therefore, the approaches to circumvent these obstacles emerge as important therapeutic modalities. METHODOLOGY/PRINCIPAL FINDINGS: Our novel derivatives of chlorin e(6), that is, its amide (compound 2) and boronated amide (compound 5) evoked no dark toxicity and demonstrated a significantly higher photosensitizing efficacy than chlorin e(6) against transplanted aggressive tumors such as B16 melanoma and M-1 sarcoma. Compound 5 showed superior therapeutic potency. Illumination with red light of mammalian tumor cells loaded with 0.1 µM of 5 caused rapid (within the initial minutes) necrosis as determined by propidium iodide staining. The laser confocal microscopy-assisted analysis of cell death revealed the following order of events: prior to illumination, 5 accumulated in Golgi cysternae, endoplasmic reticulum and in some (but not all) lysosomes. In response to light, the reactive oxygen species burst was concomitant with the drop of mitochondrial transmembrane electric potential, the dramatic changes of mitochondrial shape and the loss of integrity of mitochondria and lysosomes. Within 3-4 min post illumination, the plasma membrane became permeable for propidium iodide. Compounds 2 and 5 were one order of magnitude more potent than chlorin e(6) in photodamage of artificial liposomes monitored in a dye release assay. The latter effect depended on the content of non-saturated lipids; in liposomes consisting of saturated lipids no photodamage was detectable. The increased therapeutic efficacy of 5 compared with 2 was attributed to a striking difference in the ability of these photosensitizers to permeate through hydrophobic membrane interior as evidenced by measurements of voltage jump-induced relaxation of transmembrane current on planar lipid bilayers. CONCLUSIONS/SIGNIFICANCE: The multimembrane photodestruction and cell necrosis induced by photoactivation of 2 and 5 are directly associated with membrane permeabilization caused by lipid photodamage.

Novel boronated chlorin e6-based photosensitizers: synthesis, binding to albumin and antitumour efficacy.

Chlorins, a class of plant porphyrins, are perspective as photosensitizing agents due to light absorption in the long wavelength spectral region and deeper photodamage of tissues. Aiming at optimization of antitumour properties of chlorins, we synthesized a series of boronated derivatives of chlorin e(6) and their complexes containing Zn(II), Pd(II) or Sn(IV). The compounds were synthesized by alkylation of amino or hydroxy derivatives of chlorin e(6) with 1-trifluoromethanesulfonylmethyl-o-carborane. Chlorin e(6) 13(1)-N-{2-[N-(o-carboran-1-yl)methyl]aminoethyl}amide-15(2), 17(3)-dimethyl ester (compound 5) formed complexes with serum albumin, a major porphyrin carrier. The binding constant of these complexes was approximately 4 times bigger than the respective value for the complexes of albumin with boron-free aminochlorin e(6). Compound 5 potently sensitized rat fibroblasts to illumination with monochromatic red light: >98% of cells were necrotic by 24h post-illumination with 1 microM of 5. This compound demonstrated high efficacy in photodynamic therapy of rat M-1 sarcoma. After PDT with 25mg/kg of 5 the residual tumours were significantly smaller than in animals subjected to PDT with equal concentration of boron-free aminochlorin e(6). No signs of general toxicity were detectable after PDT with 5. Thus, boronation can enhance the potency of chlorins in PDT, in particular, due to an increased binding to albumin. Our data expand the therapeutic applicability of boronated chlorins beyond boron neutron capture therapy; these agents emerge as dual efficacy photoradiosensitizers.

Boronated protohaemins: synthesis and in vivo antitumour efficacy.

The conjugates of porphyrin macrocycles with boron-containing polyhedra are under investigation as agents for binary treatment strategies of cancer. Aiming at the design of photoactive compounds with low-to-zero dark toxicity, we synthesized a series of carboranyl and monocarbon-carboranyl derivatives of protohaemin IX using the activation of porphyrin carboxylic groups with di-tert-butyl pyrocarbonate or pivaloyl chloride. The water-soluble 1,3,5,8-tetramethyl-2,4-divinyl-6(7)-[2'-(closo-monocarbon-carborane-1''-yl)methoxycarbonylethyl]-7(6)-(2'-carboxyethyl)porphyrin Fe(III) (compound 9) exerted no discernible cytotoxicity for cultured mammalian cells, nor did it cause general toxicity in rats. Importantly, 9 demonstrated dose-dependent activity as a phototoxin in photodynamic therapy of M-1 sarcoma-bearing rats. In animals injected with 20 mg kg(-1) of 9, the tumours shrank by day 3 after one single irradiation of the tumour with red laser light. Between 7 and 14 days post-irradiation, 88.9% of rats were tumour-free; no recurrence of the disease was detectable within at least 90 days. Protohaemin IX alone was without effect, indicating that boronation is important for the phototoxic activity of 9. This is the first study that presents the synthesis and preclinical in vivo efficacy of boronated derivatives of protohaemin as phototoxins. The applicability in photodynamic treatment broadens the therapeutic potential of boronated porphyrins beyond their conventional role as radiosensitizers in boron neutron capture therapy.

Novel boronated derivatives of 5,10,15,20-tetraphenylporphyrin: synthesis and toxicity for drug-resistant tumor cells.

We have developed the synthesis of boronated porphyrins for potential application in cancer treatment, based on the functional derivatives of 5,10,15,20-tetraphenylporphyrin. Boronated amide derivatives starting from 5,10,15,20-tetra(p-aminophenyl)porphyrin and 9-o- and 9-m-carborane carboxylic acid chlorides were prepared. Also, the reaction of 2-formyl-5,10,15,20-tetraphenylporphyrin with closo-C-lithium-o- and m-carboranes, as well as with closo-C-lithium monocarbon carborane, yielded neutral and anionic boronated hydroxy derivatives of 5,10,15,20-tetraphenylporphyrin, respectively. Water-soluble forms of neutral compounds were prepared by deboronation of closo-polyhedra with Bu4NF into nido-7,8- and nido-7,9-dicarbaundecaborate anions. Monocarbon carborane conjugated with copper (II) complex of 5,10,15,20-tetraphenylporphyrin was active for a variety of tumor cell lines (IC50 approximately 5 microM after 48-72 h of exposure) but was inert for non-malignant fibroblasts at up to 100 microM. At low micromolar concentrations, this compound caused the death of cells that express P-glycoprotein and other mechanisms of resistance to conventional anticancer drugs.

Carboranylporphyrins for boron neutron capture therapy of cancer.

A major challenge for cancer treatment is the preferential and irreversible killing of tumor cells and minimal damage of normal tissues, both in the site of the malignancy and in the body. The agents used in boron neutron capture therapy (BNCT) are supposed to have the following advantages over many conventional chemotherapeutics: 1) when irradiated with thermal neutrons, an unstable isotope (11)B is formed whose rapid decay yields local and a thermal effect; 2) because the free path of the released particles is close to the cell diameter, the tissues outside the tumor should gain less damage; 3) local radioactivity and heat should be harmful for cells that, in the course of their natural history, acquired the determinants of altered response to many toxic stimuli. However, a higher specificity of damage would be achieved if the drugs accumulate mostly in cancer cells rather than in non-malignant counterparts. Therefore, optimization of agents for BNCT presumes the design of chemicals with improved accumulation/ retention in cancer cells. In particular, carboranyl-substituted porphyrins, the stable conjugates of macrocyclic porphyrins with complex boron-containing polyhedra, are considered good candidates for BNCT due to their uptake by cancer cells and high boron content. Importantly, the proposed mechanisms of pharmacological effects of carboranylporphyrins make these compounds potentially appropriate for elimination of pleiotropically resistant tumor cells.