Oxovanadium(IV)-based near-IR PDT agents: design to biological evaluation

An oxovanadium(IV) complex of dipyridophenazine, as a potent metal-based PDT agent, shows efficient DNA photocleavage activity at near-IR region and high photocytotoxicity in both UV-A and visible light in HeLa cells.

Cation-induced crown porphyrin dimers of oxovanadium(IV)

Oxovanadium(1V) porphyrins appended with crown ether (benzo-15-crown-5) at the 5 (mono), the 5 and 10115 (cis/trans bis), the 5, 10, and 15 (tris), and the 5, 10, 15, and 20 (tetrakis) positions have been synthesized. The cation complexation behavior of these cavity-bearing porphyrins has been studied by using optical aborption and ESR spectral methods. The cations K+, Cs+, NH4+, and Ba2+, which require two crown ether cavities for complexation, induce dimerization of the porphyrins. The cation-induced dimerization constants for a representative tetrasubstituted porphyrin vary as K+ > Ba2+ > Cs+ - NH4+, and the relative stabilities of the dimers are dependent on the type of the substitution, tetrakis > tris > cis bis. ESR spectra recorded at a sample temperature of 77 K have low-field components attributed to Ah& = f 2 transitions, providing further evidence for the existence of dimers in solutions. The eclipsed sandwich dimers have V-V distances in the range 4.70 A. The relative distributions of oxovanadium crown porphyrins in terms of monomeric and dimeric forms rest on the geometric dispositions of the crown ether appendages.

Oxalato complexes of oxovanadium (IV)

Oxalato oxovanadium (IV) complexes with neutral ligand molecules like dimethyl sulphoxide (DMSO) and antipyrine (Apy), VOOX·2DMSO and VOOX·2Apy and complex oxalates of oxovanadium (IV)-(NH4)2[VOOX2]·2H2O, (NH4)2[(VO)2OX3]·6H2O and (NH4)2[(VO)2OX3] have been prepared and characterized by different methods. In the divanadyl complexes, V-V and V-O-V-O types of bonding are shown to be absent by magnetic and spectral data and a bridged oxalato group co-ordinated to the two vanadium atoms is shown to be present, in addition to the usual bidentate oxalate groups. The possible stereochemical arrangements are indicated for the complexes.

Photocytotoxicity and DNA cleavage activity of L-arg and L-lys Schiff base oxovanadium(IV) complexes having phenanthroline bases

Oxovanadium(IV) complexes [VO(sal-argH)(B)] Cl (1-3) and [VO(sal-lysH)(B)] Cl (4-6), where sal-argH2 and sal-lysH(2) are N-salicylidene-L-arginine and N-salicylidene-L-lysine Schiff bases and B is a phenanthroline base, viz. 1,10-phenanthroline (phen in 1 and 4); dipyrido[3,2-d: 2', 3'-f] quinoxaline (dpq in 2 and 5) and dipyrido[3,2-a: 2', 3'-c] phenazine (dppz in 3 and 6), have been prepared, characterized and their DNA photocleavage activity studied. Complex 1, characterized by X-ray crystallography, shows the presence of a vanadyl group in VIVO3N3 coordination geometry with a tridentate Schiff base having a pendant guanidinium moiety and bidentate phen ligand. The complexes exhibit a d-d band at similar to 715 nm in 20% DMF-Tris-HCl buffer. The complexes are redox active showing cathodic and anodic responses near -1.0 V and 0.85 V (vs. SCE) for the V(IV)-V(III) and V(V)-V(IV) couples, respectively, in DMF-Tris-HCl buffer. The complexes bind to calf thymus DNA giving Kb values in the range of 3.8 x 10(4) to 1.6 x 10(5) M-1. Thermal denaturation and viscosity data suggest DNA groove binding nature of the complexes. The complexes do not show any `chemical nuclease'' activity in dark in the presence of 3-mercaptopropionic acid or H2O2. The dpq and dppz complexes are efficient photocleavers of plasmid DNA in UV-A (365 nm) and red light (676 nm) via singlet oxygen pathway. The dppz complexes exhibit photocytotoxicity in HeLa cancer cells giving IC50 values of 15.4 mu M for 3 and 17.5 mu M for 6 in visible light while being non-toxic in dark giving IC50 values of > 100 mu M.

Photocytotoxicity and near-IR light DNA cleavage activity of oxovanadium(IV) Schiff base complexes having phenanthroline bases

Oxovanadium(IV) complexes VO(L)(B)] (1-3), where H2L is a Schiff base ligand 2-(2-hydroxybenzylideneamino) phenol and B is 1,10-phenanthroline (phen for 1), dipyrido3,2-d:2',3'-f]quinoxaline (dpq for 2) or dipyrido3,2-a:2',3'-c]phenazine (dppz for 3), have been prepared, characterized and their DNA binding property and photo-induced DNA cleavage activity studied. Complex 3 which is structurally characterized by X-ray crystallography shows the presence of an oxovanadium(IV) moiety in a six coordinate VO3N3 coordination geometry. The complexes show a d-d band within 800-850 nm in DMF. The complexes display an oxidative response near 0.7 V versus SCE for V(V)-V(IV) and a reductive response within -1.1 to -1.3 V due to V(IV)-V(III) couple in DMF-0.1 M TBAP. The complexes are avid binders to calf thymus DNA giving binding constant values of 4.2 x 10(4) to 1.2 x 10(5) M (1). The complexes do not show any ``chemical nuclease'' activity in dark. The dpq and dppz complexes are photocleavers of plasmid DNA in UV-A light of 365 nm via O-1(2) pathway and in near-IR light (752.5 to 799.3 nm IR optics) by HO* pathway. Complex 3 exhibits significant photocytotoxicity in visible light in HeLa cells giving IC50 value of 13 mu M, while it is less toxic in dark (IC50 = 97 mu M). (C) 2010 Elsevier B.V. All rights reserved.

Terpyridine Oxovanadium(IV) Complexes of Phenanthroline Bases for Cellular Imaging and Photocytotoxicity in HeLa Cells

Oxovanadium(IV) complexes VO(N-N-N)(N-N)](NO3)(2) (1-4) of (4'-phenyl)-2,2': 6',2 `'-terpyridine (ph-tpy in 1 and 2) or (4'-pyrenyl)-2,2':6',2 `'-terpyridine (py-tpy in 3 and 4) having N-N as 1,10-phenanthroline (phen in 1 and 3) or dipyrido3,2-a:2',3'-c]phenazine (dppz in 2 and 4) are prepared and characterized. The crystal structure of 1 has VO2+ group in VN5O coordination geometry. The terpyridine ligand coordinates in a meridional binding mode. The phen ligand displays a chelating mode of binding with an N-donor site trans to the vanadyl oxo group. The complexes show a d-d band in the range of 710-770 nm in aqueous DMF (4:1 v/v). The complexes exhibit an irreversible V-IV/V-III redox response near -1.0 V vs. SCE in aqueous DMF/0.1 M KCl. The complexes bind to CT DNA giving K-b values within 3.5 x 10(5) to 1.2 x 10(6) M-1. The complexes show poor chemical nuclease activity in dark. Complexes 2-4 show photonuclease activity in UV-A light of 365 nm forming O-1(2) and (OH)-O-center dot. Complex 4 shows DNA photocleavage activity at near-IR light of 785 nm forming (OH)-O-center dot radicals. Complexes 2 and 4 show significant photocytotoxicity in HeLa cancer cells. Uptake of the complexes in HeLa cells, studied by fluorescence imaging, show predominantly cytosolic localization inside the cells.

Schiff base oxovanadium(IV) complexes of phenanthroline bases showing DNA photocleavage activity at near-IR light and photocytotoxicity

Oxovanadium(IV) complexes VO(L)(B)](ClO4) (1-3) of N-2-pyridylmethylidine-2-hydroxyphenylamine (HL) Schiff base and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido3,2-d: 2',3'-f] quinoxaline (dpq in 2) or dipyrido3,2-a: 2',3'-c] phenazine (dppz in 3), were prepared, characterized and their DNA binding property, photo-induced DNA cleavage activity and photocytotoxicity in HeLa cells studied. The crystal structure of 1 shows the presence of a VO2+ moiety in VO2N4 coordination geometry. The complexes show a d-d band at similar to 830 nm in DMF. The complexes display an oxidative V(V)-V(IV) response near 0.5 V versus SCE and a reductive V(IV)/V(III) response near -0.65 V in DMF -0.1 M TBAP. The complexes that are avid binders to CT DNA giving K-b values within 7.1 x 10(4) to 3.2 x 10(5) M-1, do not show any significant chemical nuclease activity in presence of 3-mercaptopropionic acid or glutathione. The dpq and dppz complexes are photocleavers of pUC19 DNA in UV-A light of 365 nm forming both O-1(2) and (OH)-O-center dot radicals and in near-IR light of 785 nm forming (OH)-O-center dot radicals. The dppz complex exhibits photocytotoxicity in visible light in HeLa cells (IC50 = 6.8 mu M). Flow-cytometric study on this complex shows a high sub-G1 phase in light compared to dark indicating PDT effect. (C) 2011 Elsevier B. V. All rights reserved.

Cellular uptake and remarkable photocytotoxicity of pyrenylter pyridine oxovanadium(IV) complexes of dipyridophenazine bases

Pyrenylterpyridine (pytpy) oxovanadium(IV) complexes VO(pytpy)(L)]Cl-2 (1-6) of the dipyridophenazine bases (L), viz., dipyrido-6,7,8,9-tetrahydrophenazine (dpqC in 1), dipyrido3,2-a:2',3'-c]phenazine-2-carboxylic acid (dppzc in 2), dipyrido3,2-a:2',3'-c]phenazine-11-sulfonic acid (dppzs in 3), 7-aminodipyrido3,2-a:2',3'-c]phenazine (dppza in 4), benzo-i]dipyrido3,2-a:2',3'-c]phenazine (dppn in 5) and dipyrido3,2-a:2',3'-c]phenazine (dppz in 6) were prepared, characterized and their DNA binding, photocleavage activity and photocytotoxicity studied. The complexes which showed a d-d band near 750 nm in DMF are efficient binders to calf thymus DNA (K-b: 3.2 x 10(5)-2.9 x 10(6) M-1). The complexes showed significant pUC19 DNA cleavage in near-IR light of 785 nm forming center dot OH radicals and photocytotoxicity in HeLa cells in visible light with the benzo-i] dipyrido3,2-a:2',3'-c]phenazine complex 5 showing a remarkably low IC50 value of 0.036 mu M. Flow-cytometric analysis shows a high sub-G1 phase cell cycle arrest in HeLa cells by the complexes on photo-irradiation. The photocytotoxicity correlates well with the hydrophobicity, photosensitizing ability and DNA binding propensity of the complexes. (C) 2012 Elsevier B.V. All rights reserved.

Carbohydrate-appended photocytotoxic (imidazophenanthroline)-oxovanadium(IV) complexes for cellular targeting and imaging

Oxovanadium(IV) complexes VO(aip)(L)](ClO4)(2) (L = phtpy, 1; stpy, 2) and VO(pyip)(L)](ClO4)(2) (L = phtpy, 3; stpy, 4), where aip is 2-(9-anthryl)-1H-imidazo4,5-f]1,10] phenanthroline, pyip is 2-(1-pyrenyl)-1Himidazo4,5-f]1,10] phenanthroline, phtpy is (4'-phenyl)-2,2': 6',2 `'-terpyridine and stpy is (2,2': 6', 2 `'-terpyridin-4'-oxy) ethyl-beta-D-glucopyranoside, were prepared, characterized and their DNA binding and photocleavage activity, cellular uptake and photocytotoxicity in visible light were studied. The complexes are avid binders to calf thymus DNA (K-b similar to 10(5) mol(-1)). They efficiently cleave pUC19 DNA in red light of 705 nm via the formation of HO center dot species. The glucose appended complexes 2 and 4 showed higher photocytotoxicity in HeLa and Hep G2 cells over the normal HEK 293T cells. No such preference was observed for the phtpy complexes 1 and 3. No significant difference in IC50 values was observed for the HEK 293T cells. Cell cycle analysis showed that the glucose appended complexes 2 and 4 are more photocytotoxic in cancer cells than in normal cells. Fluorescence microscopy was done to study the cellular localization of complex 4 having a pendant pyrenyl group.

Oxovanadium(IV) complexes of curcumin for cellular imaging and mitochondria targeted photocytotoxicity

Oxovanadium(IV) complexes VO(R-tpy)(cur)](ClO4) (1, 2) of curcumin (Hcur) and terpyridine ligands (R-tpy) where R is phenyl (phtpy in 1) or p-triphenylphosphonium methylphenyl bromide (C6H4CH2PPh3Br) (TPP-phtpy in 2) were prepared and characterized and their DNA photocleavage activity, photocytotoxicity and cellular localization in cancer cells (HeLa and MCF-7) were studied. Acetylacetonate (acac) complexes VO(R-tpy)(acac)](ClO4) of phtpy (3) and TPP-phtpy (4) were prepared and used as the control species. These complexes showed efficient cleavage of pUC19 DNA in visible light of 454 nm and near-IR light of 705 rim. Complexes 1 and 2 showed significant photocytotoxicity in visible light of 400-700 nm. FACS analysis showed sub-G1/G0 phase cell-cycle arrest in cancer cells when treated with 1 and 2 in visible light in comparison with the dark controls. Fluorescence microscopic studies revealed specific localization of the p-triphenylphosphonium complex 2 in the mitochondria of MCF-7 cancer cells whereas no such specificity was observed for complex 1.

Remarkable enhancement in photocytotoxicity and hydrolytic stability of curcumin on binding to an oxovanadium(IV) moiety

Oxovanadium(IV) complexes of polypyridyl and curcumin-based ligands, viz. VO(cur)(L)Cl] (1, 2) and VO(scur)(L)Cl] (3, 4), where L is 1,10-phenanthroline (phen in 1 and 3), dipyrido3,2-a:2',3'-c]phenazine (dppz in 2 and 4), Hcur is curcumin and Hscur is diglucosylcurcumin, were synthesized and characterized and their cellular uptake, photocytotoxicity, intracellular localization, DNA binding, and DNA photo-cleavage activity studied. Complex VO(cur)(phen)Cl] (1) has (VN2O3Cl)-N-IV distorted octahedral geometry as evidenced from its crystal structure. The sugar appended complexes show significantly higher uptake into the cancer cells compared to their normal analogues. The complexes are remarkably photocytotoxic in visible light (400-700 nm) giving an IC50 value of <5 mu M in HeLa, HaCaT and MCF-7 cells with no significant dark toxicity. The green emission of the complexes was used for cellular imaging. Predominant cytosolic localization of the complexes 1-4 to a lesser extent into the nucleus was evidenced from confocal imaging. The complexes as strong binders of calf thymus DNA displayed photocleavage of supercoiled pUC19 DNA in red light by generating (OH)-O-center dot radicals as the ROS. The cell death is via an apoptotic pathway involving the ROS. Binding to the VO2+ moiety has resulted in stability against any hydrolytic degradation of curcumin along with an enhancement of its photocytotoxicity.

Endoplasmic reticulum targeting tumour selective photocytotoxic oxovanadium(IV) complexes having vitamin-B6 and acridinyl moieties

Oxovanadium(IV) complexes of vitamin-B6 Schiff base, viz., VO(HL1/L-2/L-3)(B)] Cl (1-4), where B is 2,2'-bipyridine (bpy in 1 and 2), 11-(9-acridinyl)dipyrido3,2-a:2',3'-c]phenazine (acdppz in 3 and 4), H2L1 center dot HCl is 3-hydroxy-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylp yridin-1-ium chloride (in 1 and 4), HL2 is 2-(((2-(1H-imidazol-4-yl)ethyl) imino)methyl) phenol (in 2) and HL3 is 4-(((2-(1H-imidazol-4- yl)ethyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol (in 3) were synthesized, characterized and their cellular uptake, photo-activated cytotoxicity and intracellular localization were studied. Complexes 1a, as the perchlorate salt of 1, and 2a, as the hexafluorophosphate salt of 2, were structurally characterized. Vitamin-B6 transporting membrane carrier (VTC) mediated entry into tumour cells in preference to the normal ones seems to be responsible for the higher cellular uptake of the complexes into HeLa and MCF-7 cells over MCF-10A cells. Complexes 3 and 4 having acdppz as the photosensitizer exhibit remarkable photocytotoxicity in these cancer cells giving IC50 of < 0.9 mu M. The complexes remain non-toxic in the dark. The complexes show photo-induced apoptotic cell death via singlet oxygen (O-1(2)) generation. Fluorescence microscopy reveals specific localization of complex 4 to endoplasmic reticulum (ER) and generation of O-1(2) possibly leads to apoptotic cell death by triggering ER stress response (ERSR).

Endoplasmic reticulum targeting tumour selective photocytotoxic oxovanadium(IV) complexes having vitamin-B6 and acridinyl moieties

Oxovanadium(IV) complexes of vitamin-B6 Schiff base, viz., VO(HL1/L-2/L-3)(B)] Cl (1-4), where B is 2,2'-bipyridine (bpy in 1 and 2), 11-(9-acridinyl)dipyrido3,2-a:2',3'-c]phenazine (acdppz in 3 and 4), H2L1 center dot HCl is 3-hydroxy-5-(hydroxymethyl)-4-(((2-hydroxyphenyl)imino)methyl)-2-methylp yridin-1-ium chloride (in 1 and 4), HL2 is 2-(((2-(1H-imidazol-4-yl)ethyl) imino)methyl) phenol (in 2) and HL3 is 4-(((2-(1H-imidazol-4- yl)ethyl)imino)methyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol (in 3) were synthesized, characterized and their cellular uptake, photo-activated cytotoxicity and intracellular localization were studied. Complexes 1a, as the perchlorate salt of 1, and 2a, as the hexafluorophosphate salt of 2, were structurally characterized. Vitamin-B6 transporting membrane carrier (VTC) mediated entry into tumour cells in preference to the normal ones seems to be responsible for the higher cellular uptake of the complexes into HeLa and MCF-7 cells over MCF-10A cells. Complexes 3 and 4 having acdppz as the photosensitizer exhibit remarkable photocytotoxicity in these cancer cells giving IC50 of < 0.9 mu M. The complexes remain non-toxic in the dark. The complexes show photo-induced apoptotic cell death via singlet oxygen (O-1(2)) generation. Fluorescence microscopy reveals specific localization of complex 4 to endoplasmic reticulum (ER) and generation of O-1(2) possibly leads to apoptotic cell death by triggering ER stress response (ERSR).

Synthesis, structure and solution chemistry of mixed-ligand oxovanadium(IV) and oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands

In the title family, the ONO donor ligands are the acetylhydrazones of salicylaidehyde (H2L1) and 2-hydroxyacetophenone (H2L2) (general abbreviation, H2L). The reaction of bis(acetylacetonato)oxovanadium(IV) with a mixture of tridentate H2L and a bidentate NN donor [e.g., 2,2'-bipyridine(bpy) or 1,10-phenanthroline(phen), hereafter B] ligands in equimolar ratio afforded the tetravalent complexes of the type [(VO)-O-IV(L)(B)]; complexes (1)-(4) whereas, if B is replaced by 8-hydroxyquinoline(Hhq) (which is a bidentate ON donor ligand), the above reaction mixture yielded the pentavalent complexes of the type [(VO)-O-V(L)(hq)]; complexes (5) and (6). Aerial oxygen is most likely the oxidant (for the oxidation of V-IV -> V-V) in the synthesis of pentavalent complexes (5) and (6). [(VO)-O-IV(L)(B)] complexes are one electron paramagnetic and display axial EPR spectra, while the [(VO)-O-V(L)(hq)] complexes are diamagnetic. The X-ray structure of [(VO)-O-V(L-2)(hq)] (6) indicates that H2L2 ligand is bonded with the vanadium meridionally in a tridentate dinegative fashion through its phenolic-O, enolic-O and imine-N atoms. The general bond length order is: oxo < phenolato < enolato. The V-O (enolato) bond is longer than V-O (phenolato) bond by similar to 0.07 angstrom and is identical with V-O (carboxylate) bond. H-1 NMR spectrum of (6) in CDCl3 solution indicates that the binding nature in the solid state is also retained in solution. Complexes (1)(4) display two ligand-field transitions in the visible region near 820 and 480 nm in DMF solution and exhibit irreversible oxidation peak near +0.60 V versus SCE in DMSO solution, while complexes (5) and (6) exhibit only LMCT band near 535 nm and display quasi-reversible one electron reduction peak near -0.10 V versus SCE in CH2Cl2 solution. The VO3+-VO2+ E-1/2 values shift considerably to more negative values when neutral NN donor is replaced by anionic ON donor species and it also provides better VO3+ binding via phenolato oxygen. For a given bidentate ligand, E-1/2 increases in the order: (L-2)(2-) < (L-1)(2-). (c) 2004 Elsevier B.V. All rights reserved.

Oxovanadium(IV) and (V) complexes of acetylpyridine-derived semicarbazones exhibit insulin-like activity

Reaction of 2-acetylpyridine semicarbazone (H2APS), 3-acetylpyridine semicarbazone (H3APS) and 4-acetylpyridine semicarbazone (H4APS) with [VO(acac)(2)] (acac = acetylacetonate) gave [VO(H2APS)(acac)(2)] (1), (VO(H3APS)(acac)(2)] (2) and [VO(4APS)(acac) (H2O)] center dot 1/2H(2)O (3). Oxidation of complex 1 in acetonitrile gave [VO2(2APS)] (4). The crystal structures of complexes 1 and 4 have been determined. Complexes 1-3 were able to enhance glucose uptake and to inhibit glycerol release from adipocytes, which indicate their potential to act as insulin-mimics. (C) 2008 Elsevier Ltd. All rights reserved.