Structure-activity correlationship and strain specificity of polyoxometalates in anti-human immunodeficiency virus activity

Inhibition of Human Immunodeficiency Virus Type 1 Entry by a Keggin Polyoxometalate

Here, we report the anti-human immunodeficiency virus (HIV) potency and underlying mechanisms of a Keggin polyoxometalate (PT-1, K₆HPTi₂W₁₀O₄₀). Our findings showed that PT-1 exhibited highly potent effects against a diverse group of HIV type 1 (HIV-1) strains and displayed low cytotoxicity and genotoxicity. The time-addition assay revealed that PT-1 acted at an early stage of infection, and these findings were supported by the observation that PT-1 had more potency against Env-pseudotyped virus than vesicular stomatitis virus glycoprotein (VSVG) pseudotyped virus. Surface plasmon resonance binding assays and flow cytometry analysis showed that PT-1 blocked the gp120 binding site in the CD4 receptor. Moreover, PT-1 bound directly to gp41 NHR (N36 peptide), thereby interrupting the core bundle formation of gp41. In conclusion, our data suggested that PT-1 may be developed as a new anti-HIV-1 agent through its effects on entry inhibition.

Toxicity evaluation of two polyoxotungstates with anti-acetylcholinesterase activity

A toxicity evaluation of two Keggin-type heteropolytungstates, K₇[Ti₂PW₁₀O₄₀]·6H₂O and K₆H[SiV₃W₉O₄₀]·3H₂O, with different inhibitory potencies toward acetylcholinesterase activity (IC₅₀ values of 1.04×10^-6 and 4.80×10^-4mol/L, respectively) was performed. Wistar albino rats were orally treated with single doses (5 and 50mg/kg) of both investigated compounds. The biochemical parameters of renal (serum urea and creatinine) and liver function (direct and total bilirubin, alanine transaminase, and aspartate aminotransferase) were determined after 24h and 14days. A histopathological analysis of liver tissue was carried out 14days after the polyoxotungstate administration. Both applied doses of the investigated compounds did not induce statistically significant alterations of the renal function markers. However, the polyoxotungstate treatment caused an increase in the activities of serum alanine transaminase and aspartate aminotransferase in a time- and concentration-dependent manner, although statistically significant changes in bilirubin concentrations were not observed. Furthermore, the detected hepatotoxic effect was confirmed by histhopathological analysis that suggested some reversible liver tissue damage two weeks after the treatment, especially in the case of K₆H[SiV₃W₉O₄₀]·3H₂O. Accordingly, the toxicity of these two polyoxotungstates with anti-acetylcholinesterase effect cannot be considered as a severe one, but their potential clinical application would require a more complex toxicological study.

Polyoxometalates active against tumors, viruses, and bacteria

Polyoxometalates (PMs) as discrete metal-oxide cluster anions with high solubility in water and photochemically and electrochemically active property have a wide variety of structures not only in molecular size from sub-nano to sub-micrometers with a various combination of metals but also in symmetry and highly negative charge. One of the reasons for such a structural variety originates from their conformation change (due to the condensed aggregation and the structural assembly) which strongly depends on environmental parameters such as solution pH, concentration, and coexistent foreign inorganic and/or organic substances. In the course of the application of the physicochemical properties of such PMs to the medical fields, antitumoral, antiviral, and antibacterial activities have been developed for realization of a novel inorganic medicine which provides a biologically excellent activity never replaced by other approved medicines. Several PMs as a candidate for clinical uses have been licensed toward the chemotherapy of solid tumors (such as human gastric cancer and pancreatic cancer), DNA and RNA viruses (such as HSV, HIV, influenza, and SARS), and drug-resistant bacteria (such as MRSA and VRSA) in recent years: [NH3Pr(i)]6[Mo7O24]∙3H2O (PM-8) and [Me3NH]6[H2Mo(V) 12O28(OH)12(Mo(VI)O3)4]∙2H2O (PM-17) for solid tumors; K7[PTi2W10O40]∙6H2O (PM-19), [Pr(i)NH3]6H[PTi2W10O38(O2)2]∙H2O (PM-523), and K11H[(VO)3(SbW9O33)2]∙27H2O (PM-1002) for viruses; and K6[P2W18O62]∙14H2O (PM-27), K4[SiMo12O40]∙3H2O (SiMo12), and PM-19 for MRSA and VRSA. The results are discussed from a point of view of the chemotherapeutic clarification in this review.

Targeted delivery of polyoxometalate nanocomposites

Polyoxometalate/carboxymethyl chitosan nanocomposites with an average diameter of 130 nm are synthesized and labeled with fluorescein isothiocyanate (FITC) for a combined drug-carrier and cellular-monitoring approach. [Eu(β(2) -SiW(11) O(39) )(2) ](13-) /CMC nanospheres as a representative example do not display cytotoxicity for POM concentrations up to 2 mg mL(-1) . Cellular uptake of fluoresecently labelled {EuSiW(11) O(39) }/FITC-CMC nanoparticles is monitored with confocal laser scanning microscopy. Nanoparticle uptake occurs after incubation times of around 1 h and no cyctotoxic effects are observed upon prolonged treatment. The preferential location of the POM/CMC nanocomposites in the perinuclear region is furthermore verified with transmission electron microscopy investigations on unlabeled nanoparticles. Therefore, this approach is a promising dual strategy for the safe cellular transfer and monitoring of bioactive POMs.

HIV-1 protease inhibition potential of functionalized polyoxometalates

Polyoxometalates (POMs) are interesting biomedical agents due to their versatile anticancer and antiviral properties, such as remarkable anti-HIV activity. Although POMs are tunable and easily accessible inorganic drug prototypes in principle, their full potential can only be tapped by enhancing their biocompatibility, for example, through organic functionalization. We have therefore investigated the HIV-1 protease inhibition potential of functionalized Keggin- and Dawson-type POMs with organic side chains. Their inhibitory performance was furthermore compared to other POM types, and the buffer dependence of the results is discussed. In addition, chemical shift mapping NMR experiments were performed to exclude POM–substrate interactions. Whereas the introduction of organic side chains into POMs is a promising approach in principle, the influence of secondary effects on the reaction system also merits detailed investigation.

Does speciation matter for tungsten ecotoxicology?

Tungsten is a widely used transition metal that has not been thoroughly investigated with regards to its ecotoxicological effects. Tungsten anions polymerize in environmental systems as well as under physiological conditions in living organisms. These polymerization/condensation reactions result in the development of several types of stable polyoxoanions. Certain chemical properties (in particular redox and acidic properties) differentiate these polyanions from monotungstates. However, our current state of knowledge on tungsten toxicology, biological and environmental effects is based entirely on experiments where monotungstates were used and assumed by the authors to be the form of tungsten that was present and that produced the observed effect. Recent discoveries indicate that tungsten speciation may be important to ecotoxicology. New results obtained by different research groups demonstrate that polytungstates develop and persist in environmental systems, and that polyoxotungstates are much more toxic than monotungstates. This paper reviews the available toxicological information from the standpoint of tungsten speciation and identifies knowledge gaps and pertinent future research directions.

Studies on the interactions of Ti-containing polyoxometalates (POMs) with SARS-CoV 3CLpro by molecular modeling

Ti-containing alpha-Keggin polyoxometalates (POMs) have been proved with properties of both anti-tumor and anti-HIV (human immunodeficiency virus). The potential anti-SARS (severe acute respiratory syndrome) activity of the POMs [alpha-PTi(2)W(10)O(40)](7-) isomers was investigated in this paper by molecular modeling method. The SARS 3c like protease, namely the SARS 3CL(pro) is the key function protease for virus replication as well as transcription and thus can be taken as one of the key targets for anti-SARS drug design. Affinity/Insight II was used to explore possible binding locations for POMs/3CL(pro) interaction. Charges in the POMs were obtained from density-functional theory (DFT) method. The results show that POMs bind with 3CL(pro) in the active site region with high affinity; POMs are more prone to bind with 3CL(pro) than with some organic compounds; for the POMs/3CL(pro)complex, the OTi(2) in POMs is the vital element for electrostatic interaction, and the electrostatic binding energy is strong enough to keep the complex stable.

Enhancement Effect of Polyoxometalates on NGF-Induced Neurite-Outgrowth of PC12 Cells

Nerve growth factor (NGF)-induced neurite-outgrowth of PC12 cells was enhanced by polyoxometalates such as Na9[SbW(9)O(33)].19.5H(2)O (SbW(9)) and (NH(3)Pr(i))6[Mo(7)O(24)].3H(2)O (Mo(7)). Western blotting analysis of polyoxometalate/NGF-treated PC12 cells showed a strong expression of growth-associated protein 43 (GAP-43), which is associated with the neurite outgrowth. Similar effects were observed for other polyoxometalates, K(11)H[(VO)3(SbW(9)O(33))2].27H(2)O ((VO)3(SbW(9))2), K6[P(2)W(18)O(62)].14H(2)O (P(2)W(18)), and K7[PTi(2)W(10)O(40)].6H2O (PTi(2)W(10)), in contrast with little effect for monomeric tungstate and molybdate. Of the polyoxometalates tested in this study, SbW(9) and Mo(7) were the most potent.

Antitumor activity of polyoxomolybdate, [NH3Pri]6[Mo7O24].3H2O, against, human gastric cancer model

Polyoxometalates are negatively charged inorganic compounds which contain metal ions such as tungsten, molybdenum, vanadium etc. and which make clusters with the surrounding oxygen atoms. [NH3Pri]6[Mo7O24].3H2O (PM-8) was found to be a significant antitumor polyoxomolybdates. It had already been reported that the PM-8 suppressed the growth of Co-4 human colon cancer, MX-1 human breast cancer and OAT human lung cancer xenografted in nude mice. However, the mechanism of the antitumor activity has not been clarified. In this study, the antitumor activity of one of the metal oxide clusters (polyoxometalates), hexabis(isopropylammonium) heptamolybdate trihydrate, [NH3Pri]6[Mo7O24].3H2O (PM-8) were shown in an MTS assay. DNA ladder formation and detection of apoptotic bodies in nuclei were revealed that antitumor activity of PM-8 in MKN45 cells was due to apoptosis. It is concluded that the observation of significant tumor growth suppression of PM-8 in MKN45-bearing mice results from the induction of apoptosis. PM-8 shows promise as a novel anti-cancer agent.

Anticancer activity of polyoxomolybdate

Anticancer polyoxomolybdates have been investigated for medical application of polyoxometalates as discrete cluster anions of metal oxides. [NH3Pri]6[Mo7O24].3H2O (PM-8) has been recognized as one of significant antitumoral polyoxomolybdates. PM-8 had shown the growth suppression against several tumors, for examples, Co-4, human colon cancer, MX-1, human breast cancer, and OAT, human lung cancer. PM-8 showed the tumor growth suppression for MKN-45 human gastric cancer in tumor bearing mice. PM-8 inhibited the cell growth of AsPC-1 which depended on the dose with showing DNA ladder formation and DNA fragmentation, and positive Hoechst staining indicating apoptosis. The ratio of apoptotic cells on flow cytometry analysis were 35%, and 57% with treatment of PM-8 after 48, and 72 h, respectively. One of the anti-tumor activity of PM-8 result from the activation of apoptotic pathway. It is thought that polyoxomolybdates will be applied as a novel anti-tumor agent especially against cancers which are difficult to be treated clinically.

A novel anti-tumor agent, polyoxomolybdate induces apoptotic cell death in AsPC-1 human pancreatic cancer cells

Anti-tumoral polyoxomolybdates have been investigated in the course of study of the medical application of polyoxometalates as discrete cluster anions of metal oxides. [NH(3)Pr(i)](6)[Mo(7)O(24)].3H(2)O (PM-8) has been recognized as one of significantly anti-tumoral polyoxomolybdates. PM-8 inhibited the cell growth of human pancreatic cells (AsPC-1) depending on the dose. DNA ladder formation and DNA fragmentation were observed by Hoechst and TUNEL staining and flowcytometry analysis. The ratio of apoptotic cells were 29%, 35%, and 57% with treatment of PM-8 after 24, 48, and 72 h, respectively, which suggested that the anti-tumor activity of PM-8 results from the activation of the apoptotic pathway. Polyoxomolybdates provide promising, novel anti-tumor agent, especially for the treatment of cancers that are difficult to treat.

Broad spectrum anti-RNA virus activities of titanium and vanadium substituted polyoxotungstates

Seven polyoxotungstates substituted with vanadium or titanium atoms were examined for their activity against Flaviviridae (Dengue fever virus, DFV), Orthomyxoviridae (influenza virus type A, fluV-A), Paramyxoviridae (respiratory syncytial virus, RSV, parainfluenza virus type 2, PfluV-2 and canine distemper virus, CDV) and Lentiviridae (human immunodeficiency virus type 1, HIV-1) families. Among the seven polyoxotungstates examined, PM-43 [K(5)[SiVW(11)O(40)]], PM-47 [K(7)[BVW(11)O(40)]], and PM-1001 [K(10)Na(VO)(3)(SbW(9)O(33))(2)]26H(2)O contained vanadium. PM-1002 had the same core structure of (VO)(3)(SbW(9)O(33))(2) as PM-1001; however, three V atoms of PM-1001 consisted of two V(IV) and one V(V) and those of PM-1002 consisted of three V(IV). On the other hand, PM-518 [[Et(2)NH(2)](7)[PTi(2)W(10)O(40)]], PM-520 [Pri(2)NH(2)](5)[PTiW(11)O(40)] and PM-523 [PriNH(3)](6)H[PTi(2)W(10)O(38)(O(2))(2)]H(2)O all contained titanium. All compounds showed broad spectrum antiviral activity against all viruses examined except for PMs-43, -518 and -523 which did not exhibit inhibitory activity at >/=50 microM against PfluV-2, CDV and DFV, respectively. All compounds were inhibitory against HIV replication at an EC(50) of less than 2.0 microM. Among them, PMs-1001 and -1002 showed the most potent inhibition. The compounds were not toxic for MDCK, HEp-2 and Vero cells at a concentration of 200 microM. For the exponentially growing MT-4 cells, the vanadium containing polyoxometalates (PMs-43, 47, 1001, 1002) showed toxicity at concentrations between 41 and 47 microM. On the other hand, titanium containing polyoxometalates (PMs-518, -520, -523) were not toxic at 100 microM. The mechanism of anti-HIV action of PM-1001 was analyzed: it affected the binding of HIV to the cell membrane and syncytium formation between HIV-infected and uninfected cells.

Layer-by-Layer Self-Assembled Ultrathin Multilayer Films of Lanthanide Polyoxometalates and Poly(allylamine Hydrochloride) and Their Photoluminescent Properties

Ultrathin multilayer films of two lanthanide polyoxometalates (LPOMs), K(17)[Eu(P(2)W(17)O(61))(2)] (EPW) and K(13)[Eu(SiW(11)O(39))(2)] (ESW), and poly(allylamine hydrochloride) (PAH) have been prepared by layer-by-layer self-assembly from dilute aqueous solutions. UV-vis spectroscopy and ellipsometry respectively show that the absorbance values at characteristic wavelengths and the thicknesses of the multilayer films increase linearly with the number of LPOM/PAH bilayers, suggesting that the deposition process is linear and highly reproducible from layer to layer. Average thicknesses of ca. 3.4 and 2.4 nm were determined for the EPW/PAH and ESW/PAH bilayers by ellipsometry, respectively. In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) images provide the surface morphology of the LPOM/PAH films, indicating that the film surface is relatively uniform and smooth. The photoluminescent properties of these films have also been investigated by fluorescence spectroscopy. The LPOM/PAH multilayer film has a good thermal stability as shown by UV-vis, X-ray photoelectron, and fluorescence spectra.

RANTES and MCP-3 inhibit the replication of T-cell-tropic human immunodeficiency virus type 1 strains (SF-2, MN, and HE)

The effects of the C-C chemokines RANTES (regulation upon activation normal T-cell expressed and secreted) and MCP-3 (monocyte chemotactic protein 3) on human immunodeficiency virus (HIV) replication in normal human peripheral blood mononuclear cells (PBMC) activated in vitro with phytohemagglutinin (PHA) were investigated. The following T-cell line-tropic (T-tropic) HIV strains were tested: HIV type 1 (HIV-1) SF-2, HIV-1 IIIB, HIV-1 MN, HIV-1 NDK, HIV-1 HE, HIV-1 NL4-3, HIV-2 ROD, and HIV-2 EHO. The strain most sensitive to the antiviral effects of RANTES and MCP-3 appeared to be HIV-1 SF-2. A 50% inhibitory concentration for HIV-1 SF-2 of 4 ng of RANTES per ml was obtained, and that of MCP-3 was about 1 ng/ml. However, MCP-3 was inactive at 100 ng/ml. Other HIV-1 strains, such as MN and HE, were less sensitive to the antiviral effects of RANTES and MCP-3, whereas all the other HIV strains tested were insensitive. Although the ratio of CD3+ CD4+ to CD3+ CD8+ T cells was the same in HIV-infected PBMC cultures treated or untreated with the chemokines, RANTES and MCP-3 interfered with the binding of monoclonal antibody (MAb) OKT4 to the CD4 receptor on T cells but not with the binding of MAb OKT4A. Therefore, RANTES and MCP-3 not only interfere with the HIV-induced fusion process but also have some modulating effect on the CD4 cell receptor. The chemokines did not affect HIV-1 binding to PHA-stimulated PBMC. Taken together, our observations point to the important role that both RANTES and MCP-3 may play in inhibiting HIV-1 replication of certain T-tropic strains in primary PBMC cultures. This may have important implications for immunotherapeutic strategies designed to slow down disease progression in AIDS.