Pharmacological approach towards the development of indolequinone bioreductive drugs based on the clinically inactive agent EO9.
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The bioreductive drug EO9 (3-hydroxy-5-aziridinyl-1-methyl-2[indole-4,7-dione]-prop-beta-en-alpha-ol) has good pharmacodynamic properties in vitro, modest anti-tumour activity in experimental tumour models, but failed to show activity in clinical trials. Understanding the reasons for its poor efficacy in vivo is important in terms of progressing second generation analogues into the clinic. In two human tumour xenografts, direct intra-tumoural injection resulted in improved anti-tumour activity compared with intravenous administration suggesting that drug delivery to tumours is suboptimal. Compared with Mitomycin C (MMC) and the experimental agent MeDZQ, EO9 was rapidly cleared from the systemic circulation (t1/2=1.8 min) whereas MMC and MeDZQ had significantly increased plasma t1/2 values (14 and 22 min respectively). These three compounds demonstrated similar pharmacodynamic properties in terms of potency towards the NQO1 (NAD(P)H:Quinone oxidoreductase) rich H460 cell line in vitro but differed significantly in their in vivo activity with growth delays of 17.7, 4.5 and 1.0 days for MMC, MeDZQ and EO9 respectively. EO9 was rapidly metabolized by red blood cells in vitro (t1/2=14.5 min) which must contribute to its rapid pharmacokinetic elimination in vivo whereas MMC and MeDZQ were metabolized at comparatively slower rates (t1/2>120 min and 77.0 min respectively). In conclusion, the development of second generation EO9 analogues should address the issue of drug delivery and analysis of drug metabolism by murine whole blood in vitro could be utilized as a preliminary screen to identify lead compounds that are likely to have improved pharmacokinetic profiles in vivo. (+info)
Development of a selective photoactivatable antagonist for corticotropin-releasing factor receptor, type 2 (CRF2).
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A novel photoactivatable analog of antisauvagine-30 (aSvg-30), a specific antagonist for corticotropin-releasing factor (CRF) receptor, type 2 (CRF2), has been synthesized and characterized. The N-terminal amino-acid d-Phe in aSvg-30 [d-Phe11,His12]Svg(11-40) was replaced by a phenyldiazirine, the 4-(1-azi-2,2,2-trifluoroethyl)benzoyl (ATB) residue. The photoactivatable aSvg-30 analog ATB-[His12]Svg was tested for its ability to displace [125I-Tyr0]oCRF or [125I-Tyr0]Svg from membrane homogenates of human embryonic kidney (HEK) 293 cells stably transfected with cDNA coding for rat CRF receptor, type 1 (rCRF1) or mouse CRF receptor, type 2beta (mCRF2beta). Furthermore, the ability of ATB-[His12]Svg(12-40) to inhibit oCRF- or Svg-stimulated cAMP production of transfected HEK 293 cells expressing either rCRF1 (HEK-rCRF1 cells) or mCRF2beta (HEK-mCRF2beta cells) was determined. Unlike astressin and photo astressin, ATB-[His12]Svg(12-40) showed high selective binding to mCRF2beta (Ki = 3.1 +/- 0.2 nm) but not the rCRF1 receptor (Ki = 142.5 +/- 22.3 nm) and decreased Svg-stimulated cAMP activity in mCRF2beta-expressing cells in a similar fashion as aSvg-30. A 66-kDa protein was identified by SDS/PAGE, when the radioactively iodinated analog of ATB-[His12]Svg(12-40) was covalently linked to mCRF2beta receptor. The specificity of the photoactivatable 125I-labeled CRF2beta antagonist was demonstrated with SDS/PAGE by the finding that this analog could be displaced from the receptor by antisauvagine-30, but not other unrelated peptides such as vasoactive intestinal peptide (VIP). (+info)
Effect of morphine-induced antinociception is altered by AF64A-induced lesions on cholinergic neurons in rat nucleus raphe magnus.
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AIM: To examine the role of cholinergic neurons in the nucleus raphe magnus (NRM) in noxious heat stimulation and in the effects of morphine-induced antinociception by rats. METHODS: After the cholinergic neuron selective toxin, AF64A, was microinjected into the NRM, we examined changes in the antinociceptive threshold and effects of morphine (5 mg/kg, ip) using the hot-plate (HP) and tail-flick (TF) tests. RESULTS: Systemic administration of morphine inhibited HP and TF responses in control rats. Microinjection of AF64A (2 nmol/site) into the NRM significantly decreased the threshold of HP response after 14 d, whereas the TF response was not affected. Morphine-induced antinociception was significantly attenuated in rats administered AF64A. Extracellular acetylcholine was attenuated after 14 d to below detectable levels in rats given AF64A. Naloxone (1 microg/site) microinjected into control rat NRM also antagonized the antinociceptive effect of systemic morphine. CONCLUSION: These findings suggest that cholinergic neuron activation in the NRM modulates the antinociceptive effect of morphine simultaneously with the opiate system. (+info)
Inducible ablation of adipocytes in adult transgenic mice expressing the E. coli nitroreductase gene.
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We describe the use of an enzyme prodrug system based on E. coli nitroreductase (NTR) to achieve the specific ablation of adipose tissue. Transgenic mice expressing the NTR gene specifically in the adipose tissue were generated using the adipocyte specific promoter aP2. After treatment with the prodrug CB1954 these mice showed extensive cell depletion in all fat depots; this was directly correlated to both the dose of prodrug and the levels of NTR expression. Higher doses of CB1954 resulted in complete disappearance of visible adipose stores in some transgenic mice. These mice exhibited an impaired ability to thermoregulate body temperature. Lower doses of CB1954 resulted in a partial reduction of the adipose tissue leaving non-expressing cells that escape ablation. These animals show normal levels of blood glucose and triglycerides but have reduced leptin levels. After 30 days they were able to regenerate the fat depots and leptin levels returned to normal but, interestingly, no NTR-expressing cells were detectable. The present model provides a new approach to manipulate the number of adipocytes at different stages of mouse development and provides a new system for the study of fat metabolism especially in abnormal conditions such as obesity and its modulation through manipulation of the target cell population. (+info)
Ethylenimine-inactivated rabies vaccine of tissue culture origin.
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The replication of seven rabies virus strains (CVS, HEP, PV, ERA, WIRAB, CPZ and BOLIVAR) in BHK cells and the inactivation dynamics of these strains by beta-propiolactone, acetylethylenimine, and ethylenimine were studied to find the most immunogenic strain and the most economic and stable inactivating agent for the production of an inactivated tissue culture rabies vaccine for animal use. The seven strains reached the peak of virus production 3 to 5 days after inoculation of the cell culture; PV yielded the highest virus titer (10(9) plaque-forming units/ml). The infectivity of virus suspensions containing 10(7) to 10(8) plaque-forming units/0.1 ml was inactivated by beta-propiolactone in 0.5 h, acetylethylenimine in 3.0 h, and ethylenimine in 1.0 h. Most of the vaccine lots prepared with the different strains and inactivating agents passed a modified National Institutes of Health potency test. The vaccines prepared with the PV strain had consistently higher antigenic values (equal or better than four) than the other six strains. This difference was highly significant (F6,12=59.8), whereas there were no statistically significant differences among the antigenic values of the vaccine lots prepared with the three inactivating agents. Batches of lyophilized and liquid vaccine stored at 4 C maintained potency for over 1 year. Ten dogs vaccinated with a vaccine prepared with the PV strain and inactivated with ethylenimine developed a good antibody response and resisted challenge 60 days after vaccination, while seven of eight nonvaccinated controls died of rabies. This information indicates that an inactivated, stable, economic, and easy-to-prepare rabies vaccine can be produced in BHK cells by using the PV strain and ethylenimine as an inactivating agent. (+info)
Photoaffinity labeling with a neuroactive steroid analogue. 6-azi-pregnanolone labels voltage-dependent anion channel-1 in rat brain.
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Neuroactive steroids modulate the function of gamma-aminobutyric acid, type A (GABA(A)) receptors in the central nervous system by an unknown mechanism. In this study we have used a novel neuroactive steroid analogue, 3 alpha,5 beta-6-azi-3-hydroxypregnan-20-one (6-AziP), as a photoaffinity labeling reagent to identify neuroactive steroid binding sites in rat brain. 6-AziP is an effective modulator of GABA(A) receptors as evidenced by its ability to inhibit binding of [(35)S]t-butylbicyclophosphorothionate to rat brain membranes and to potentiate GABA-elicited currents in Xenopus oocytes and human endothelial kidney 293 cells expressing GABA(A) receptor subunits (alpha(1)beta(2)gamma(2)). [(3)H]6-AziP produced time- and concentration-dependent photolabeling of protein bands of approximately 35 and 60 kDa in rat brain membranes. The 35-kDa band was half-maximally labeled at a [(3)H]6-AziP concentration of 1.9 microM, whereas the 60-kDa band was labeled at higher concentrations. The photolabeled 35-kDa protein was isolated from rat brain by two-dimensional PAGE and identified as voltage-dependent anion channel-1 (VDAC-1) by both matrix-assisted laser desorption ionization time-of-flight and ESI-tandem mass spectrometry. Monoclonal antibody directed against the N terminus of VDAC-1 immunoprecipitated labeled 35-kDa protein from a lysate of rat brain membranes, confirming that VDAC-1 is the species labeled by [(3)H]6-AziP. The beta(2) and beta(3) subunits of the GABA(A) receptor were co-immunoprecipitated by the VDAC-1 antibody suggesting a physical association between VDAC-1 and GABA(A) receptors in rat brain membranes. These data suggest that neuroactive steroid effects on the GABA(A) receptor may be mediated by binding to an accessory protein, VDAC-1. (+info)
Mechanism of charging and supercharging molecules in electrospray ionization.
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The origin of the extent of charging and the mechanism by which multiply charged ions are formed in electrospray ionization have been hotly debated for over a decade. Many factors can affect the number of charges on an analyte ion. Here, we investigate the extent of charging of poly(propyleneimine) dendrimers (generations 3.0 and 5.0), cytochrome c, poly(ethylene glycol)s, and 1,n-diaminoalkanes formed from solutions of different composition. We demonstrate that in the absence of other factors, the surface tension of the electrospray droplet late in the desolvation process is a significant factor in determining the overall analyte charge. For poly(ethylene glycol)s, 1,n-diaminoalkanes, and poly(propyleneimine) dendrimers electrosprayed from single-component solutions, there is a clear relationship between the analyte charge and the solvent surface tension. Addition of m-nitrobenzyl alcohol (m-NBA) into electrospray solutions increases the charging when the original solution has a lower surface tension than m-NBA, but the degree of charging decreases when this compound is added to water, which has a higher surface tension. Similarly, the charging of cytochrome c ions formed from acidified denaturing solutions generally increases with increasing surface tension of the least volatile solvent. For the dendrimers investigated, there is a strong correlation between the average charge state of the dendrimer and the Rayleigh limiting charge calculated for a droplet of the same size as the analyte molecule and with the surface tension of the electrospray solvent. A bimodal charge distribution is observed for larger dendrimers formed from water/m-NBA solutions, suggesting the presence of more than one conformation in solution. A similar correlation is found between the extent of charging for 1,n-diaminoalkanes and the calculated Rayleigh limiting charge. These results provide strong evidence that multiply charged organic ions are formed by the charged residue mechanism. A significantly smaller extent of charging for both dendrimers and 1,n-diaminoalkanes would be expected if the ion evaporation mechanism played a significant role. (+info)
Plasticity in action of intrathecal clonidine to mechanical but not thermal nociception after peripheral nerve injury.
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BACKGROUND: Intrathecal clonidine reduces tactile allodynia in animal models of neuropathic pain, and this effect is blocked by atropine. However, the role of tonic spinal cholinergic activity and its interaction with alpha2-adrenergic systems in normal and neuropathic conditions and to different sensory methods has not been systematically examined. The authors examined cholinergic receptor involvement in thermal and mechanical sensitivity in normal and neuropathic animals and its interaction with intrathecal clonidine. METHODS: Normal rats and rats that received L5/L6 spinal nerve ligation were tested with acute radiant heat, paw pressure, and punctate mechanical stimulation before and after the intrathecal administration of saline, the muscarinic receptor antagonist, atropine, or a toxin to destroy cholinergic neurons, and then after intrathecal clonidine. RESULTS: Atropine, the cholinergic neuronal toxin, and saline did not alter baseline withdrawal thresholds. In nerve-injured rats, neither saline nor atropine altered antinociception from clonidine to a thermal stimulus, but atropine reduced the effect of clonidine to von Frey filament withdrawal threshold (34 +/- 5.6 vs. 14 +/- 5.8 g [mean +/- SEM], saline vs. atropine; P < 0.05) and to withdrawal threshold to paw pressure after clonidine (174 +/- 18 g vs. 137 +/- 16 g, saline vs. atropine; P < 0.05). CONCLUSIONS: These data suggest that after nerve injury, mechanical but not thermal antinociception from intrathecal clonidine relies on a muscarinic interaction, because only mechanical antinociception was antagonized by atropine. These results do not favor a regulation of nociceptive transmission by a tonic release of acetylcholine in nerve-injured rats. (+info)