Characterization of HIV-1 entry inhibitors with broad activity against R5 and X4 viral strains.

BACKGROUND: Combined antiretroviral therapy has drastically reduced mortality and morbidity of HIV-infected individuals. Nevertheless long-term toxicity and appearance of viral resistance hampers the prolonged effectiveness of combination therapy, requiring a continuous input of drugs to replace those utilized in combination regimens. We here investigated the anti-HIV activity of novel derivatives of the suradista chemical class. METHODS: Compounds were tested on acute HIV-1 infection of activated peripheral blood mononuclear cells. HIV production was monitored by enzyme-linked immunosorbent assay measuring the protein p24 released in culture supernatants. Fusion assays were carried out to study the mechanism of action of these compounds. A modified version of a previously established recombinant vaccinia virus-based assay was used measuring activation of a reporter gene upon fusion of two distinct cell populations. Flow cytometry was performed in competition assays for the binding of several antibodies targeting different sites of the viral envelope glycoprotein gp120, or the receptor CD4, or the coreceptors CXCR4 and CCR5. RESULTS: Four compounds inhibited replication of a prototypic R5 (BaL) and X4 (IIIB) laboratory-adapted HIV-1 strain at low micromolar concentrations, in the absence of cytotoxicity. Approximately a ten fold greater activity was achieved against the X4 as compared to the R5 strain. The compounds blocked X4 and R5 HIV-1 fusion, a step of viral entry. This activity appeared specific for HIV-1, as entry of human herpesvirus 6 (HHV-6) and influenza virus was not substantially affected. Further investigation of the inhibitory mechanism revealed that these new molecules target the viral envelope, rather than the coreceptors, as previously shown for a congener of the same class characterized by a long plasmatic half-life. Indeed ND-4043, the most active compound, specifically competed with binding of monoclonal antibodies against the CD4-binding site (CD4-BS) and coreceptor-binding site (CoR-BS) of gp120. These compounds displayed broad anti-HIV activity, as they inhibited various primary R5, X4 and, importantly, dualtropic R5X4 HIV-1 isolates. Of the four derivatives tested, the dimeric compounds were consistently more potent than the monomeric ones. CONCLUSIONS: Given their unique features, these molecules represent promising candidates for further development and exploitation as anti-HIV therapeutics.

Role of glutathione transferases in the mechanism of brostallicin activation.

Brostallicin is a novel and unique glutathione transferase-activated pro-drug with promising anticancer activity, currently in phase I and II clinical evaluation. In this work, we show that, in comparison with the parental cell line showing low GST levels, the cytotoxic activity of brostallicin is significantly enhanced in the human breast carcinoma MCF-7 cell line, transfected with either human GST-pi or GST-mu. Moreover, we describe in detail the interaction of brostallicin with GSH in the presence of GSTP1-1 and GSTM2-2, the predominant GST isoenzymes found within tumor cells. The experiments reported here indicate that brostallicin binds reversibly to both isoenzymes with K(d) values in the micromolar range (the affinity being higher for GSTM2-2). Direct evidence that both GSTP1-1 and GSTM2-2 isoenzymes catalyze the Michael addition reaction of GSH to brostallicin has been obtained both by an HPLC-MS technique and by a new fluorometric assay. We also saw the rapid formation of an intermediate reactive species, which is slowly converted into the final products. This intermediate, identified as the alpha-chloroamido derivative of the GSH-brostallicin adduct, is able to alkylate DNA in a sequence-specific manner and appears to be the active form of the drug. The kinetic behavior of the reaction between brostallicin and GSH, catalyzed by GSTP1-1, has been studied in detail, and a minimum kinetic scheme that suitably describes the experimental data is provided. Overall, these data fully support and extend the findings that brostallicin could be indicated for the treatment of tumor overexpressing the pi or mu class GST.

Improved synthesis of polyfluorinated L-lysine for 19F NMR-based screening.

Polyfluorinated N-alpha-Fmoc-is an element of-Boc-L-lysine represents the best-in-class among a set of polyfluorinated amino acids (PFAs) which are useful tools for (19)F NMR-Based Screening. In this communication, optimized reaction conditions that allowed for the multi-gram preparation of this unnatural amino acid are reported.

Polyfluorinated amino acids for sensitive 19F NMR-based screening and kinetic measurements.

Two novel series of polyfluorinated amino acids (PFAs) were designed and synthesized according to a very short and scalable synthetic sequence. The advantages and limitations of these moieties for screening purposes are presented and discussed. The potential applications of these PFAs were tested with their incorporation into small arginine-containing peptides that represent suitable substrates for the enzyme trypsin. The enzymatic reactions were monitored by 19F NMR spectroscopy, using the 3-FABS (three fluorine atoms for biochemical screening) technique. The high sensitivity achieved with these PFAs permits a reduction in substrate concentration required for 3-FABS. This is relevant in the utilization of 3-FABS in fragment-based screening for identification of small scaffolds that bind weakly to the receptor of interest. The large dispersion of 19F isotropic chemical shifts allows the simultaneous measurement of the efficiency of the different substrates, thus identifying the best substrate for screening purposes. Furthermore, the knowledge of KM and Kcat for the different substrates allows the identification of the structural motifs responsible for the binding affinity to the receptor and those affecting the chemical steps in enzymatic catalysis. This enables the construction of suitable pharmacophores that can be used for designing nonpeptidic inhibitors with high affinity for the enzyme or molecules that mimic the transition state. The novel PFAs can also find useful application in the FAXS (fluorine chemical shift anisotropy and exchange for screening) experiment, a 19F-based competition binding assay for the detection of molecules that inhibit the interaction between two proteins.

Serum fetuin-A levels link inflammation and cardiovascular calcification in hemodialysis patients.

BACKGROUND: Cardiovascular disease (CVD) is the leading cause of mortality in hemodialysis (HD). An elevated incidence of cardiovascular calcifications (CVC) is observed in HD. Fetuin-A is an important inhibitor of CVC. Reduced fetuin-A levels associate with inflammation and increased cardiovascular (CV) mortality in HD. In this study we investigated the association of fetuin-A levels and CVC. METHOD: We evaluated a cohort of 115 patients (67 males), aged 63 +/- 16 years with a HD vintage >or=9 months. Presence of CVC was assessed by ultrasound imaging of the abdominal aorta, common carotid arteries, bilateral ilio-femoral axis, aortic and mitral cardiac valves. The presence of CVC was analyzed as a CVC score (CVCS) (0-7) according to the number of CVC sites. Patients were arbitrary stratified in three groups: group I (CVCS = 0), group II (0 < CVCS < 6) and group III (CVCS >or= 6). Patients without CVC were younger, non-diabetic and with a negative history for CV events. RESULTS: Patients with evidence of CVC in more than 5 sites had lower serum fetuin-A levels (0.41 +/- 0.22 g/l) compared to patients with CVCS = 0 (0.51 +/- 0.17 g/l, p = 0.048). In addition a worse CVCS was associated with higher serum levels of C-reactive protein (p = 0.002) and fibrinogen (p < 0.001). Serum fetuin-A levels lower than 0.290 g/l were associated with higher risk of a worse CVCS, independently from traditional risk factors. CONCLUSION: Chronic inflammation in HD patients leads to lower serum fetuin-A levels. The present study confirms the independent and significant association between reduced serum fetuin-A levels and multi-site CVC in HD.

NMR-based quality control approach for the identification of false positives and false negatives in high throughput screening.

The quality of the data generated in a high throughput screening (HTS) run is fundamental for selecting bona fide inhibitors and for ensuring the capture of the full richness of inhibitors present in a chemical library. For this purpose a quality control filter based on three one dimensional (1D) proton NMR experiments is proposed. The approach called SPAM (Solubility, Purity and Aggregation of the Molecule) Filter requires the acquisition of a 1D reference spectrum, a WaterLOGSY spectrum and/or a selective longitudinal relaxation filter spectrum for the identified hits dissolved in aqueous solution and in the presence of a water soluble reference molecule. This palette of experiments permits the rapid characterization of the identity, purity, solubility and aggregation state of the active compound. This knowledge is crucial for deriving accurate IC(50) and K(1) values of the inhibitors, for identifying false negatives and for detecting promiscuous inhibitors. Only compounds that pass through the SPAM Filter can be considered as starting points for medicinal chemistry efforts directed toward lead optimization. Examples of this approach in the identification of false positives in a screening run against the enzyme thymidine phosphorylase (TP) and the rescue of a false negative in a screening run against the Ser/Thr kinase AKT1 are presented.

Sensitivity improvement in 19F NMR-based screening experiments: theoretical considerations and experimental applications.

NMR-based binding and functional screening performed with FAXS (fluorine chemical shift anisotropy and exchange for screening) and 3-FABS (three fluorine atoms for biochemical screening) represents a potential alternative approach to high-throughput screening for the identification of novel potential drug candidates. The major limitation of this method in its current status is its intrinsic low sensitivity that limits the number of tested compounds. One approach for overcoming this problem is the use of a cryogenically cooled (19)F probe that reduces the thermal noise in the receiver circuitry. Sensitivity improvement in the two screening techniques achieved with the novel cryogenic (19)F probe technology permits an increased throughput, detection of weaker binders and inhibitors (relevant in a fragment-based lead discovery program), detection of slow binders, and reduction in protein and substrate consumption. These aspects are analyzed with theoretical simulations and experimental quantitative performance evaluation. Application of 3-FABS combined with the cryogenic (19)F probe technology to rapid screening at very low enzyme concentrations and the current detection limits reached with this approach are also presented.

Reliable high-throughput functional screening with 3-FABS.

An NMR method called 3-FABS has extended the capabilities of NMR, enabling rapid, efficient and reliable high-throughput functional screening for the identification of inhibitors and for measuring their 50% mean inhibition concentration (IC(50)) with accuracy. The substrate is tagged with a CF(3) moiety and (19)F NMR spectroscopy is used for the detection of the substrate and product components. We provide comprehensive insight into 3-FABS, a discussion of its strength and weakness when compared with other HTS techniques and a presentation of some of its applications to the screening of different enzymes and to multiple screening.

Cytotoxic alpha-halogenoacrylic derivatives of distamycin A and congeners.

The mechanism of action of many antitumor agents involves DNA damage, either by direct binding of the drug to DNA or to DNA-binding proteins. However, most of the DNA-interacting agents have only a limited degree of sequence specificity, which implies that they may hit all the cellular genes. DNA minor groove binders, among which the derivatives of distamycin A play an important role, could provide significant improvement in cancer management, increasing gene specificity, due to high selectivity of interaction with thymine-adenine (TA) rich sequences. We now report and discuss the synthesis, the in vitro and in vivo activities, and some mechanistic features of alpha-halogenoacrylamido derivatives of distamycin A. The final result of this work was the selection of brostallicin 17 (PNU-166196). Brostallicin, presently in phase II clinical trials, shows a broad spectrum of antitumor activity and an apoptotic effect higher than distamycin derivative tallimustine. An important in vitro toxicological feature of brostallicin is the very good ratio between myelotoxicity on human haematopoietic progenitor cells and cytotoxicity on tumor cells, in comparison with clinically tested DNA minor groove binders. A peculiarity of brostallicin is its in vitro reactivity in the DNA alkylation assays only in the presence of glutathione. Moreover brostallicin's antitumor activity, both in in vitro and in vivo tumor models, is higher in the presence of increased levels of glutathione/glutathione-S-tranferases. These findings contribute to the definition of brostallicin as a novel anticancer agent that differs from other minor groove binders and alkylating agents for both the profile of activity and the mechanism of action and to classify the alpha-bromoacrylamido derivatives of distamycin as a new class of cytotoxics. Moreover, due to its interaction with glutathione, brostallicin may have a role for the tailored treatment of tumors characterized by constitutive or therapy-induced overexpression of glutathione/glutathione-S-tranferase levels.

Recent anticancer cytotoxic agents.

In spite of the impressive progress in diagnosis, surgery and therapy that occurred since the Sixties, the overall cancer mortality is still high and the medical need is largely unmet. A number of innovative strategies, aimed to target malignant abnormalities of tumor cells are in development and begin to give important results. In alternative, angiogenesis inhibition has been addressed with the aim to limit the tumor ability to grow and metastasize. However, it will likely take some years to fully define the therapeutic role of different innovative drugs. Therefore, cytotoxic drugs will continue to represent a chief part of the therapy in the forthcoming years, possibly in combination with innovative agents addressing molecular targets. Most important traditional chemotherapeutic drugs or investigational anticancer agents were derived from natural sources also through synthetic structural modifications. In the Nineties, taxanes and camptothecins represented important success stories of this approach, while among DNA interacting agents anthracyclines continued to represent a structural platform for discovering new drugs and DNA minor groove binders represented a new field of investigation. Combinatorial chemistry combined with high-throughput screening programs are an important source of totally synthetic new agents, however, it should not be disregarded the fact that nature already performed combinatorial chemistry and leads selection through the ages. New natural or semisynthetic agents acting as tubulin stabilizers or DNA interactive agents of various mechanisms of action are presently investigated and will probably continue to give important contribution to cancer therapy in the near future. In this review, the medicinal chemistry and the development status of these anticancer cytotoxic agents are focused and discussed.

A general NMR method for rapid, efficient, and reliable biochemical screening.

High-throughput screening is usually the method of drug-lead discovery. It is now well accepted that, for a functional assay, quality is more important than quantity. The ligand-based or protein-based NMR screening methodologies for detecting compounds binding to the macromolecular target of interest are now well established. A novel and sensitive NMR method for rapid, efficient, and reliable biochemical screening is presented. The method named 3-FABS (three fluorine atoms for biochemical screening) requires the labeling of the substrate with a CF(3) moiety and utilizes (19)F NMR spectroscopy for the detection of the starting and enzymatically modified substrates. The method allows for high-quality screening of large compound or natural product extract collections and for measuring their IC(50) values. Applications of this technique to the screening of inhibitors of the Ser/Thr kinase AKT1 and the protease trypsin are presented. In addition, an interesting application of 3-FABS to functional genomics is also presented.

Cytotoxic alpha-bromoacrylic derivatives of low molecular weight.

In vitro and in vivo activities of a small series of alpha-bromoacrylic derivatives of low molecular weight (MW) are described and compared with those of alpha-bromoacrylic derivatives of distamycin-like frames. Low MW compounds, when lacking of a strong basic moiety, are potent cytotoxics, while analogues bearing a strong basic moiety are not. This suggests the existence of an active transport mechanism for distamycin-derived cytotoxics characterized by strong basic amidino or guanidino moieties. Low MW compounds are inactive in vivo, possibly because of the metabolic lability of alpha-bromoacrylic moiety. The same moiety is however present in a series of potent anticancer distamycin-like minor groove binders, for example, PNU-166196 (brostallicin), a fact that underlines the features of the latter.