Interactions of Vanadocene(IV)-Chelated Complexes with Artificial Membranes

Antiretroviral spermicide WHI-07 prevents vaginal and rectal transmission of feline immunodeficiency virus in domestic cats

WHI-07 [5-bromo-6-methoxy-5,6-dihydro-3'-azidothymidine-5'-(p-bromophenyl)-methoxy alaninyl phosphate] is a novel dual-function aryl phosphate derivative of zidovudine with potent anti-human immunodeficiency virus (HIV) and spermicidal activities. WHI-07 was active against the feline immunodeficiency virus (FIV). This study evaluated whether topical application of WHI-07 as a single agent and in combination with an organometallic vanadium complex, vanadocene dithiocarbamate (VDDTC), via a nontoxic gel microemulsion can block vaginal as well as rectal transmission of feline AIDS (FAIDS) by chronically FIV-infected feline T cells in the natural host model. Genital transmission of FIV was monitored in recipient cats by the appearance of viral antibodies to FIV Gag proteins and by virus isolation of blood leukocytes as measured by FIV reverse transcriptase activity and FIV-specific PCR. Microbicidal activity was considered effective when the treated cats did not show evidence of FIV infection for up to 18 weeks postchallenge. An aggregate analysis of 46 specific-pathogen-free cats revealed that a single dose of the infected cell inoculum efficiently transmitted FIV infection when delivered into the vagina (100%) or rectum (66%). Pretreatment of the vagina or rectum with 2% WHI-07 alone or in combination with 0.25% VDDTC significantly (P = 0.004) protected cats from genital transmission by the highly infectious inoculum (7 million FIV(Bangston)-infected feline T cells). Collectively, using the vaginal and rectal transmucosal model for FAIDS, our studies demonstrated that WHI-07 either alone or in combination with a vanadocene has clinical potential for the development of a dual-function anti-HIV microbicide for sexually active women.

Potent dual anti-HIV and spermicidal activities of novel oxovanadium(V) complexes with thiourea non-nucleoside inhibitors of HIV-1 reverse transcriptase

We have previously demonstrated that tetrahedral bis(cyclopentadienyl)vanadium(IV) complexes and square pyramidal oxovanadium(IV) complexes of vanadium are rapid and selective spermicidal agents at low micromolar concentrations. This study investigated the potential utility of oxovanadium in combination with thiourea non-nucleoside inhibitors (NNIs) of HIV-1 reverse transcriptase (RT) for the development of an effective dual-function anti-HIV spermicide. Two rationally designed substituted phenyl-ring containing pyridyl thiourea NNIs, N-[2-(2-chlorophenethyl)]-N(')-[2-(5-bromopyridyl)-thiourea) [1] and N-[2-(2-methoxyphenethyl)]-N(')-[2-(pyridyl)-thiourea [2] that exhibited subnanomolar IC(50) values against the drug-sensitive, drug-resistant, and multidrug-resistant strains of HIV-1, were complexed with oxovanadium. The oxovanadium-thiourea [OVT] NNIs, C(29)H(27)Br(2)Cl(2)N(6)O(2)S(2)V [3], and C(31)H(35)N(6)O(4)S(2)V [4], were synthesized by reacting VOSO(4), a V(IV) compound, with the corresponding deprotonated thiourea NNI compounds as ligands. Elemental analysis showed that each OVT-NNI used two thiourea molecules as ligands. The existence of the Vz.dbnd6;O bond (968cm(-1)) was confirmed by IR spectroscopy. No d-d bands were observed in the visible spectra of OVT-NNIs and their EPR spectra were featureless, indicating that the vanadium centers were oxidized to V(V). The new OVT-NNIs as well as their thiourea NNI ligands were evaluated for (i) anti-HIV activity using the cell-free recombinant RT inhibition assays, (ii) cellular HIV replication assays, (iii) spermicidal activity against human sperm by computer-assisted sperm analysis (CASA), and (iv) cytotoxicity against normal human female genital tract epithelial cell using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) dye-reduction assays. Similar to thiourea NNIs 1 and 2, the OVT-NNIs 3 and 4, exhibited potent anti-HIV activity with submicromolar IC(50[p24]) values (0.08 and 0.128 microM, respectively) and submicromolar IC(50[RT]) values (2.1 and 0.87 microM, respectively). Notably, OVT-NNIs were spermicidal against human sperm at low micromolar concentrations (IC(50)=34 and 55 microM, respectively) and induced rapid sperm immobilization (T(1/2)=12 and 240s) when compared with their respective thiourea NNI ligands (EC(50)=>400 microM and T(1/2)=>180min). Moreover, OVT-NNIs displayed high selectivity indices against normal female genital tract epithelial cells (IC(50) values >250 microM) when compared to the detergent-type spermicide, nonoxynol-9, which was cytotoxic at spermicidal concentrations (IC(50) values 32-64 microM). This is the first report on the dual anti-HIV and spermicidal activities of a vanadium/oxovanadium complex. Our discovery of potent anti-HIV and rapid spermicidal activities of OVT-NNIs may be useful for the development of an effective and safe vaginal anti-HIV spermicide for women who are at high risk for acquiring HIV/AIDS by heterosexual transmission.

2,3-Bifunctionalized Quinoxalines: Synthesis, DNA Interactions and Evaluation of Anticancer, Anti-tuberculosis and Antifungal Activity

A variety of 2,3-bifunctionalized quinoxalines (6-14) have been prepared by the condensation of 1,6-disubstituted-hexan-1,3,4,6-tetraones (1-4) with o-phenylenediamine, (R,R)-1,2-diaminocyclohexane and p-nitro-o-phenylenediamine. It is concluded that strong intramolecular N-H----O bonds in the favoured keto-enamine form may be responsible for the minimal biological activities observed in DNA footprinting, anti-tubercular, anti-fungal and anticancer tests with these hyper π-conjugated quinoxaline derivatives. However, subtle alteration by addition of a nitro group affecting the charge distribution confers significant improvements in biological effects and binding to DNA.

Subchronic (13-week) toxicity studies of intravaginal administration of spermicidal vanadocene acetylacetonato monotriflate in mice

Bis-cyclopentadienyl complexes of vanadium(IV) or vanadocenes are rapid and potent inhibitors of human sperm motility with potential as a new class of contraceptive agents. In this study, groups of 10 B(6)C(3)F(1) and 20 CD-1 female mice were exposed intravaginally to a gel-microemulsion containing 0, 0.06, 0.12, or 0.25% of a representative vanadocene, vanadocene acetylacetonato monotriflate (VDACAC), five days per week for 13 consecutive weeks. The doses of VDACAC used were nearly 300- to 1250-fold higher than its in vitro spermicidal EC(50) value. After 13 weeks of intravaginal treatment, B(6)C(3)F(1) mice were evaluated for survival, body weight gain, absolute and relative organ weights, and systemic toxicity. Blood was analyzed for hematological and clinical chemistry profiles. Microscopic examination was performed on hematoxylin- and eosin-stained tissue sections from each study animal. Vanadium content in tissues was determined by atomic absorption spectroscopy. Gel-microemulsion (placebo) control and VDACAC dosed female CD-1 mice were mated with untreated males in order to evaluate if VDACAC has any adverse effects on the reproductive outcome. There were no treatment-related mortalities in either study. Mean body weight gain during the dosing period was not reduced by VDACAC treatment. Hemograms or clinical chemistry profiles did not reveal any toxicologically significant changes attributed to VDACAC treatment. No clinically significant dose-dependent changes in absolute and relative organ weights were noted in VDACAC dose groups. Extensive histopathological examination of tissues revealed no treatment-related abnormalities in any of the three VDACAC dose groups. Vanadium was not incorporated in mouse tissues at levels above 1 microg/g. Repeated intravaginal exposure of CD-1 mice to increasing concentrations of VDACAC for 13 weeks had no adverse effect on their subsequent reproductive capability (100% fertile), neonatal survival (>96%) or pup development. Collectively, these findings demonstrate that repetitive intravaginal administration of VDACAC to yield effective spermicidal concentrations (<0.1%) in the vagina was not associated with systemic toxicity and did not adversely affect the reproductive performance in mice. The spermicidal vanadocene-chelated complex, VDACAC, may be useful as a safe vaginal contraceptive.

Subchronic (13-week) toxicity studies of intravaginal administration of spermicidal vanadocene dithiocarbamate in mice

Spermicidal organometallic complexes of vanadium(IV) with bis(cyclopentadienyl) rings or vanadocenes are a new class of experimental contraceptive agents. In a systematic search for vanadocenes with selective spermicidal activity, we identified vanadocene dithiocarbamate (VDDTC) as the most potent and stable spermicidal compound. In this study, groups of 10 B(6)C(3)F(1) and 20 female CD-1 mice were exposed intravaginally to a gel-microemulsion containing 0, 0.06, 0.12, and 0.25% VDDTC 5 days per week for 13 consecutive weeks. The doses of VDDTC used were nearly 1250- to 5000-fold higher than its in vitro spermicidal EC(50) value. After 13 weeks of intravaginal treatment, B(6)C(3)F(1) mice were evaluated for survival, body weight gain, absolute and relative organ weights, and systemic toxicity. Blood was analyzed for hematologic and clinical chemistry parameters. Microscopic examination was performed on hematoxylin and eosin-stained tissue sections from each study animal. Vanadium content in tissues was determined by atomic absorption spectroscopy. Placebo control and VDDTC-dosed female CD-1 mice were mated with untreated males to evaluate whether VDDTC has any deleterious effects on the reproductive performance. There were no treatment-related effects on survival and mean body weight and mean body weight gain during the dosing period. The blood chemistry or hemogram profiles did not reveal any toxicologically significant changes that could be attributed to VDDTC treatment. No clinically significant changes in absolute and relative organ weights were noted in VDDTC dose groups. Extensive histopathological examination of tissues revealed no treatment-related abnormalities in any of the three VDDTC dose groups. The vanadium content of all mouse tissue analyzed was <1 microg/g. Repeated intravaginal exposure of CD-1 mice to increasing concentrations of VDDTC for 13 weeks had no adverse effect on their subsequent reproductive capability (100% fertile), neonatal survival (>90%), or pup development. Collectively, these findings demonstrate that repetitive intravaginal administration of VDDTC to yield effective spermicidal concentrations (<0.1%) in the vagina was not associated with systemic toxicity and did not adversely affect the reproductive performance in mice. VDDTC may have clinical utility as an active ingredient of non-detergent type, safe, vaginal spermicidal contraceptives.

Apoptosis inducing novel anti-leukemic agent, bis(4,7-dimethyl-1,10 phenanthroline) sulfatooxovanadium(IV) [VO(SO4)(Me2-Phen)2] depolarizes mitochondrial membranes

Bis(4,7-dimethyl-1,10 phenanthroline) sulfatooxovanadium(IV) [VO(SO(4) )(Me(2)-Phen)(2)] induces apoptosis in human NALM-6 leukemia cells. In the present report, we demonstrate that VO(SO(4) )(Me(2)-Phen)(2)-induced apoptosis is mediated through the generation of reactive oxygen species (ROS), depletion of glutathione and depolarization of mitochondrial membrane potential (DeltaPsim). Using multilaser flow cytometry methods, we further mapped out the death sequence that occurs in VO(SO(4))(Me(2)-Phen)(2)-treated leukemic cells. Triple labeling method to measure ROS, DeltaPsim and glutathione coupled with multilaser excitation flow cytometry showed that induction of ROS took place before the loss of mitochondrial permeability transition and depletion of glutathione. Correlated two parameter plots of glutathione content versus DeltaPsim showed that loss of DeltaPsim and depletion of glutathione closely follows each other. Translocation of phosphatidylserine to the outer leaflet of the cell membrane was the final step in the process before the cells became apoptotic. These results demonstrate that the mitochondrial permeability transition takes place during VO(SO(4))(Me(2)-Phen)(2)-induced apoptosis and is mediated through induction of ROS and depletion of glutathione.

Induction of aerobic peroxidation of liposomal membranes by bis(cyclopentadienyl)-vanadium(IV) (acetylacetonate) complexes

The ability of bis(cyclopentadienyl)-vanadium(IV) (acetylacetonate) (1) to initiate oxygen-dependent lipid peroxidation in zwitterionic liposomal membranes was examined in detail. A comparison of the rates of the lipid peroxidation reaction demonstrated that the electron-donating capacity of the substituted acetylacetonate ligand significantly influences the rate of reaction. An increase in the rate of lipid peroxidation correlated to a decrease in the V(IV)/V(V) redox potential. Notably, lipid peroxidation initiated with 1 proceeded without the formation of radicals as shown by EPR spin trap techniques. In contrast, lipid peroxidation initiated with non-chelated bis(cyclopentadienyl)-vanadium(IV) dichloride (6) was associated with the production of radicals under similar experimental conditions. There also was a significant pH effect on the extent of peroxidation initiated with 6 versus the reaction initiated with 1. The mode of action of 1 likely involves the activation of molecular oxygen by the vanadium(IV) center followed by allylic hydrogen atom abstraction from the lipid.

Studies in humans on the mechanism of potent spermicidal and apoptosis-inducing activities of vanadocene complexes

We previously demonstrated that bis-cyclopentadienyl (Cp) complexes of vanadium(IV) (vanadocenes) are potent spermicidal and apoptosis-inducing agents. To gain further insight into the structure-function relationships controlling these two properties of vanadocenes, we have synthesized analogues in which the bis-Cp rings were substituted with one or five electron-donating methyl groups. The three complexes included vanadocene dichloride (VDC), bis(methylcyclopentadienyl) vanadium dichloride (VMDC), and bis(pentamethylcyclopentadienyl) vanadium dichloride (VPMDC). The concentration-dependent effect of these vanadocenes on sperm-immobilizing activity (SIA), mitochondrial membrane potential (DeltaPsim), axonemal dynein ATPase activity, and tyrosine phosphorylation of global and axoneme-specific sperm proteins was assessed by computer-assisted sperm analysis, flow cytometry, colorimetry, and immunoblotting, respectively. Apoptosis-inducing ability was quantitated by the two-color flow cytometric terminal dideoxynucleotidyl transferase-based assay that labels 3'-hydroxyl ends of fragmented DNA. All three vanadocenes induced rapid sperm immobilization (T(1/2) < 15 sec). Substitution of the bis-Cp rings by five methyl groups augmented the SIA of VDC by 10-fold. The EC(50) values (50% inhibitory concentration) for VDC, VMDC, and VPMDC were 7.5 microM, 4.3 microM, and 0.7 microM, respectively. Whereas SIA of vanadocenes was apparent at low micromolar concentrations, the apoptosis-inducing property was evident only at higher micromolar concentrations. The concentrations of VDC, VMDC, and VPMDC required for 50% apoptosis were 49 microM, 67 microM, and 153 microM, and for 50% reduction in sperm DeltaPsim were 435 microM, 173 microM, and 124 microM, respectively. Spermicidal activity of vanadocenes was not dependent on the inhibition of ATPase or tyrosine phosphorylation of global and sperm axonemal proteins. Due to the ability of these vanadocene complexes to rapidly generate hydroxyl radicals in the presence of oxidant, our findings provide unprecedented evidence for a novel mechanism of action for spermicidal vanadocenes. The differential concentration-dependent spermicidal and apoptosis-inducing properties of vanadocenes gives them particular utility as a new class of vaginal contraceptives.

Synthesis and Structure of Bis(pi-cyclopentadienyl)vanadium(IV) 1,10-Phenanthroline and 2,2'-Bipyridine Compounds and Their Interactions with Artificial Membranes

The reaction of in situ generated Cp(2)V(OTf)(2) (Cp = cyclopentadienyl; OTf = O(3)SCF(3)) with excess 1,10-phenanthroline and 2,2'-bipyridine yields the d(1) vanadocene coordination compounds [Cp(2)V(phen)][OTf](2) (1) and [Cp(2)V(bpy)][OTf](2) (2), respectively. The compounds have been characterized by UV-vis and EPR spectroscopy and by cyclic voltammetry. The complexes have relatively low vanadium(IV)-vanadium(III) reduction potentials (-0.62 V vs Cp(2)Fe(+/0) in acetonitrile). Structures of 1 and 2 have been determined by X-ray crystallography. Compound 1 crystallized in a monoclinic system, space group P2(1)/n, with a = 10.2763(5) Å, b = 18.1646(9) Å, c = 13.5741(7) Å, beta = 99.4150(10) degrees, and Z = 4. Refinement of its structure by full-matrix least-squares techniques gave final residuals R = 0.040 and R(w) = 0.096. Compound 2 crystallized in a monoclinic system, space group P2(1)/c, with a = 10.6451(6) Å, b = 18.3863(10) Å, c = 12.6993(7) Å, beta = 98.6220(10) degrees, and Z = 4. Refinement of its structure by full-matrix least-squares techniques gave final residuals R = 0.046 and R(w) = 0.101. The two nitrogen atoms and centroids of the two cyclopentadienyl rings for both compounds occupy a distorted tetrahedral geometry around the vanadium(IV) center. The chelated ring plane is inclined closer to one of the neighboring Cp rings with the tilt more evident in 1 ( approximately 8 degrees ) than 2 ( approximately 4 degrees ). The membrane interactions of these compounds and the titanium analogues, [Cp(2)Ti(phen)][OTf](2) (3) and [Cp(2)Ti(bpy)][OTf](2) (4), have been studied with zwitterionic unilamellar liposomes as artificial membranes. We show that the ability of metallocenes to enhance the permeability of a liposomal membrane depends on the hydrophobicity, as well as the size and planarity of the ancillary chelated ligands, but not the nature of the central metal ion. Also provided is evidence that metallocene-induced permeability changes in artificial membranes are not caused by lipid peroxidation.