Repositioning organohalogen drugs: a case study for identification of potent B-Raf V600E inhibitors via docking and bioassay.

Drug repositioning has been attracting increasingly attention for its advantages of reducing costs and risks. Statistics showed that around one quarter of the marketed drugs are organohalogens. However, no study has been reported, to the best of our knowledge, to aim at efficiently repositioning organohalogen drugs, which may be attributed to the lack of accurate halogen bonding scoring function. Here, we present a study to show that two organohalogen drugs were successfully repositioned as potent B-Raf V600E inhibitors via molecular docking with halogen bonding scoring function, namely D(3)DOCKxb developed in our lab, and bioassay. After virtual screening by D(3)DOCKxb against the database CMC (Comprehensive Medicinal Chemistry), 3 organohalogen drugs that were predicted to form strong halogen bonding with B-Raf V600E were purchased and tested with ELISA-based assay. In the end, 2 of them, rafoxanide and closantel, were identified as potent inhibitors with IC50 values of 0.07 µM and 1.90 µM, respectively, which are comparable to that of vemurafenib (IC50: 0.17 µM), a marketed drug targeting B-Raf V600E. Single point mutagenesis experiments confirmed the conformations predicted by D(3)DOCKxb. And comparison experiment revealed that halogen bonding scoring function is essential for repositioning those drugs with heavy halogen atoms in their molecular structures.

Halide ion effects on human Ether-à-go-go related gene potassium channel properties.

The human Ether-à-go-go related gene (hERG) potassium channel has been widely used to counter screen potential pharmaceuticals as a biomarker to predict clinical QT prolongation. Thus, higher throughput assays of hERG are valuable for early in vitro screening of drug candidates to minimize failure in later-stage drug development due to this potentially adverse cardiac risk. We have developed a novel method utilizing potassium fluoride to improve throughput of hERG counter screening with an automated patch clamp system, PatchXpress 7000A. In that method, ∼50% substitution of internal Cl(-) with F(-) greatly increases success rate without substantially altering the biophysical properties of the hERG channel or compromising data quality. However, effect of F(-) or other halide ions on hERG channel properties has not been studied in detail. In this study, we examined effects of complete replacement of Cl(-) in internal solution with halide ions, F(-), or Br(-). We found that (1) F(-) slightly shifts the voltage dependence of hERG channel activation to more positive voltages, while Br(-) shifts it to more negative voltages; (2) Br(-) shifts to more positive voltages both the inactivation-voltage relationship and the peak position of channel full activation of hERG; (3) F(-) slows hERG activation, while both F(-) and Br(-) make the channel close faster; (4) neither F(-) nor Br(-) have any effect on hERG inactivation kinetics. In conclusion, compared to Cl(-), F(-) has subtle effect on hERG activation, while Br(-) has distinct effects on certain, but not all biophysical properties of hERG channel.

Antibacterial activity of extracellular compounds produced by a Pseudomonas strain against methicillin-resistant Staphylococcus aureus (MRSA) strains.

BACKGROUND: The emergence of multidrug-resistant bacteria is a world health problem. Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) strains, is one of the most important human pathogens associated with hospital and community-acquired infections. The aim of this work was to evaluate the antibacterial activity of a Pseudomonas aeruginosa-derived compound against MRSA strains. METHODS: Thirty clinical MRSA strains were isolated, and three standard MRSA strains were evaluated. The extracellular compounds were purified by vacuum liquid chromatography. Evaluation of antibacterial activity was performed by agar diffusion technique, determination of the minimal inhibitory concentration, curve of growth and viability and scanning electron microscopy. Interaction of an extracellular compound with silver nanoparticle was studied to evaluate antibacterial effect. RESULTS: The F3 (ethyl acetate) and F3d (dichloromethane- ethyl acetate) fractions demonstrated antibacterial activity against the MRSA strains. Phenazine-1-carboxamide was identified and purified from the F3d fraction and demonstrated slight antibacterial activity against MRSA, and synergic effect when combined with silver nanoparticles produced by Fusarium oxysporum. Organohalogen compound was purified from this fraction showing high antibacterial effect. Using scanning electron microscopy, we show that the F3d fraction caused morphological changes to the cell wall of the MRSA strains. CONCLUSIONS: These results suggest that P. aeruginosa-produced compounds such as phenazines have inhibitory effects against MRSA and may be a good alternative treatment to control infections caused by MRSA.

Halogen-enriched fragment libraries as leads for drug rescue of mutant p53.

The destabilizing p53 cancer mutation Y220C creates a druggable surface crevice. We developed a strategy exploiting halogen bonding for lead discovery to stabilize the mutant with small molecules. We designed halogen-enriched fragment libraries (HEFLibs) as starting points to complement classical approaches. From screening of HEFLibs and subsequent structure-guided design, we developed substituted 2-(aminomethyl)-4-ethynyl-6-iodophenols as p53-Y220C stabilizers. Crystal structures of their complexes highlight two key features: (i) a central scaffold with a robust binding mode anchored by halogen bonding of an iodine with a main-chain carbonyl and (ii) an acetylene linker, enabling the targeting of an additional subsite in the crevice. The best binders showed induction of apoptosis in a human cancer cell line with homozygous Y220C mutation. Our structural and biophysical data suggest a more widespread applicability of HEFLibs in drug discovery.

Nontuberculous mycobacteria in aerosol droplets and bulk water samples from therapy pools and hot tubs.

Hot tub exposure has been causally associated with a steroid-responsive, granulomatous lung disease featuring nontuberculous mycobacterial (NTM) growth in both clinical and environmental samples. Little is known regarding prevalence of and risk factors for NTM-contamination and associated illness in these settings. In this study, the frequency of NTM growth and aerosolization in 18 public hot tubs and warm water therapy pools and the factors associated with mycobacterial growth were analyzed. Each site was characterized by water chemistry analysis; a questionnaire on maintenance, disinfection, and water quality; and air and water sampling for quantitative NTM culture. NTM were detected in air or water from 13/18 (72%) sites; a strong correlation was found between the maximum air and water NTM concentrations (rho 0.49, p = 0.04). Use of halogen (chlorine or bromine) disinfection was associated with significantly lower air and water concentrations of NTM compared with disinfection using ultraviolet light and hydrogen peroxide (p = 0.01-0.04). Higher water turnover rates were also associated with lower air and water NTM concentrations (p = 0.02-0.03). These findings suggest that NTM are frequently detectable in the air and water of spas and therapy pools and that particular maintenance and disinfection approaches affect NTM bioaerosol concentrations in these settings.

Mutagenic potency of haloacroleins and related compounds.

2-Chloroacrolein, the ultimate mutagen, formed on metabolism of the carcinogenc herbicides, diallate and sulfallate, and its 2-bromo-, 2,3-dichloro- and 2,3,3-trichloro- analogs are much more potent mutagens in the Ames Salmonella typhimurium strain TA1U0 assay than any other aldehydes examined previously or in this study. Polymer formation on reaction of deoxyadenosine with the difunctional 2-chloroacrolein probably involves crosslinking via Schiff base formation at the carbonyl group and Michael addition at the doubts bond.

Cytostatic activity of pyridazine derivatives. I. In vitro studies on 1-methoxyphenylpyridazine-6-ones.

Cytotoxicity of 15 pyridazine derivatives was studied by tissue method on human KB and HeLA cell lines. Six compounds with ED50 activity values between 0.025 and 1.1 micrograms/ml/5.7 X 10(8) - 3.2 X 10(-6) M/were classified for further in vivo investigations. It seems that the halogen in C-5 position plays the main role in the cytotoxic activity of pyridazine-6-ones. The para position of methoxy C-4 group in the lateral benzene ring may be assumed as the next determinant of activity. On the basis of theoretical possibilities a hypothetical model of the role of C-5 halogen substituent in complementary hydrogen bonds with the purines of DNA has been proposed.

The mutagenicity of halogenated alkanols and their phosphoric acid esters for Salmonella typhimurium.

9 halogenated alkanols, 9 corresponding tris (haloalkyl)phosphates, and 2 bis-(2,3-dibromopropyl)phosphate salts were evaluated for mutagenicity against Salmonella typhimurium TA98, TA100, TA1535, TA1537 and TA1538, with and without rat liver in vitro metabolic activation system (S9 mix). Most of the test samples showed mutagenic activity in the strains TA100 and TA1535, but not in the strains TA98, TA1537 and TA1538. In general, the mutagenic activities of the phosphates obtained with S9 mix were greater than the activities obtained without S9 mix. Among the phosphates, several structure--activity relationships were found; i.e., (i) the bromoalkyl derivatives were more mutagenic than the corresponding chloroalkyl derivatives, (ii) the beta-haloethyl derivatives were more mutagenic than the gamma-halopropyl derivatives, (iii) the phosphates having adjacent beta and gamma halogen atoms in the alkyl moiety, e.g., tris-(2,3-dibromopropyl)phosphate, were particularly potent mutagens, (iv) the branched carbon chain reduced the mutagenic activities in spite of the presence of beta-halogen atoms, e.g., tris(1-bromomethyl-2-bromoethyl)phosphate. However, such relations did not necessarily apply to the halogenated alkanols. It is concluded that the metabolic activation pathway via haloalkanols to mutagens must not be in common with all tris-BP-like phosphates.