Gabriele Rispoli

HIV-1 in strand transfer chelating inhibitors: A focus on metal binding

Most active and selective strand transfer HIV-1 integrase (IN) inhibitors contain chelating functional groups that are crucial feature for the inhibition of the catalytic activities of the enzyme. In particular, diketo acids and their derivatives can coordinate one or two metal ions within the catalytic core of the enzyme. The present work is intended as a contribution to elucidate the mechanism of action of the HIV-IN inhibitors by studying the coordinative features of H₂L¹ (L-708,906), an important member of the diketo acids family of inhibitors, and H₂L₂, a model for S-1360, another potent IN inhibitor. Magnesium(II) and manganese(II) complexes of H₂L¹ and H₂L² were isolated and fully characterized in solution and in the solid state. The crystal structures of the manganese complex [Mn(HL₂)₂(CH₃OH)₂]·2CH₃OH were solved by X-ray diffraction analysis. Moreover, the speciation models for H₂L₂ with magnesium(II) and manganese(II) ions were performed and the formation constants of the complexes were measured. M(HL₂)₂ (M = Mg²+, Mn²+) was the most abundant species in solution at physiological pH. All the synthesized compounds were tested for their anti-IN activity, showing good results both for the ligand and the corresponding complexes. From analysis of the speciation models and of the biological data we can conclude that coordination of both metal cofactors could not be strictly necessary and that inhibitors can act as complexes and not only as free ligands.

Investigating the Role of Metal Chelation in HIV-1 Integrase Strand Transfer Inhibitors

HIV-1 integrase (IN) has been validated as an attractive target for the treatment of HIV/AIDS. Several studies have confirmed that the metal binding function is a crucial feature in many of the reported IN inhibitors. To provide new insights on the metal chelating mechanism of IN inhibitors, we prepared a series of metal complexes of two ligands (HL1 and HL2), designed as representative models of the clinically used compounds raltegravir and elvitegravir. Potentiometric measurements were conducted for HL2 in the presence of Mg(II), Mn(II), Co(II), and Zn(II) in order to delineate a metal speciation model. We also determined the X-ray structures of both of the ligands and of three representative metal complexes. Our results support the hypothesis that several selective strand transfer inhibitors preferentially chelate one cation in solution and that the metal complexes can interact with the active site of the enzyme.

Investigation of the salicylaldehyde thiosemicarbazone scaffold for inhibition of influenza virus PA endonuclease.

AbstractThe influenza virus PA endonuclease is an attractive target for the development of novel anti-influenza virus therapeutics, which are urgently needed because of the emergence of drug-resistant viral strains. Reported PA inhibitors are assumed to chelate the divalent metal ion(s) (Mg2+ or Mn2+) in the enzyme’s catalytic site, which is located in the N-terminal part of PA (PA-Nter). In the present work, a series of salicylaldehyde thiosemicarbazone derivatives have been synthesized and evaluated for their ability to inhibit the PA-Nter catalytic activity. Compounds 1–6 have been evaluated against influenza virus, both in enzymatic assays with influenza virus PA-Nter and in virus yield assays in MDCK cells. In order to establish a structure–activity relationship, the hydrazone analogue of the most active thiosemicarbazone has also been evaluated. Since chelation may represent a mode of action of such class of molecules, we studied the interaction of two of them, one with and one without biological activity versus the PA enzyme, towards Mg2+, the ion that is probably involved in the endonuclease activity of the heterotrimeric influenza polymerase complex. The crystal structure of the magnesium complex of the o-vanillin thiosemicarbazone ligand 1 is also described. Moreover, docking studies of PA endonuclease with compounds 1 and 2 were performed, to further analyse the possible mechanism of action of this class of inhibitors.

Ruthenium arene complexes as HIV-1 integrase strand transfer inhibitors

The quinolone HL(1) and the hydroxypyrimidine-carboxamide HL(2) were designed and synthesized as models of the HIV integrase strand transfer inhibitors Elvitegravir and Raltegravir (brand name Isentress), with the aim to study their complexing behavior and their biological activity. The Ru(arene) complexes [RuCl(η(6)-p-cym)L(1)], [RuCl(η(6)-p-cym)L(2)] and [RuCl(hexamethylbenzene)L(2)] were also synthesized and spectroscopically characterized and their X-ray diffraction structures were discussed. The ligands and the complexes showed inhibition potency in the sub/low-micromolar concentration range in anti-HIV-1 integrase enzymatic assays, with selectivity toward strand transfer catalytic process, without any significant cytotoxicity on cancer cells.

Diketoacid chelating ligands as dual inhibitors of HIV-1 integration process

HIV-1 Integrase (IN) represents a very attractive pharmacological target for the development of new and more efficient drugs. Recently, an allosteric inhibitory approach also emerged, that targets the interaction between IN and cellular cofactors, such as LEDGF/p75. Small molecules based on the diketoacid pharmachophore were studied for their ability to inhibit at the same time integration and IN-LEDGF/p75 interaction (dual inhibitors): in this study, we evaluated three indole diketoacid derivatives and their magnesium(II) complexes for their ability to act as dual inhibitors. Effectively, the metal complexes exhibited IN inhibition potency in low nanomolar/micromolar concentration range; both the complexes and the free ligands are also able to inhibit the IN-LEDGF/p75 interaction at low μM values. Moreover, these magnesium compounds showed good antiviral activity, suggesting the possibility to exploit metal coordination for the design of new antivirals.

Antiretroviral activity of metal-chelating HIV-1 integrase inhibitors.

Data regarding the activity of metal complexes against HIV virus in cell are surprisingly scarce. In this study, we present the antiviral activity against HIV-infected cells of different types of chelating ligands and of their metal complexes. In particular, the carboxamide chelating scaffold and the corresponding coordination compounds demonstrated an interesting antiviral profile in the nanomolar range. These molecules inhibit not only HIV integrase catalytic activity, but they also interfere with the function of the RNase H component of the HIV reverse transcriptase. Here we also discuss the thermodynamic characterization in solution of the metal complexes of the most active ligands, affording to the best of our knowledge for the first time this type of data for complexes with anti-HIV activity.