Reactivity of Zinc Finger Cysteines: Chemical Modifications Within Labile Zinc Fingers in Estrogen Receptor

Estrogen receptor (ER, alpha isoform) is a 67 kDa zinc finger transcription factor that plays a fundamental role in both normal reproductive gland development and breast carcinogenesis, and also represents a critical molecular target for breast cancer therapy. We are investigating the structural consequences of chemical exposures thought to modify essential zinc finger cysteine residues in human ER. The current study employs mass spectrometry to probe ER zinc finger structural changes induced by a redox-reactive vitamin K3 analog, menadione; a commonly used cysteine alkylator, iodoacetic acid; and a thiol alkylating fluorophore, monobromobimane. Although they are slower to react, the sterically bulkier reagents, monobromobimane and menadione, effectively alkylate the most susceptible ER zinc finger cysteine sulfhydryl groups. Menadione arylation results first in Michael addition of the hydroquinone followed by rapid oxidation to the corresponding quinone, evidenced by a 2 Da mass loss per cysteine residue. Mass spectrometric analysis performed under MALDI conditions reveals both hydroquinone and quinone forms of arylated menadione, whereas only the quinone product is detectable under ESI conditions. Tandem mass spectrometry of a synthetic peptide encompassing the C-terminal half of the structurally more labile second zinc finger of ER (ZnF2B) demonstrates that the two nucleophilic thiols in ZnF2B (Cys-237, Cys-240) are not chemically equivalent in their reactivity to bromobimane or menadione, consistent with their unequal positioning near basic amino acids that affect thiol pKa, thereby rendering Cys-240 more reactive than Cys-237. These findings demonstrate important differential susceptibility of ER zinc finger cysteine residues to thiol reactions

Insulin-like growth factor - Oestradiol crosstalk and mammary gland tumourigenesis

Development and differentiation of the mammary gland are dependent on the appropriate temporal expression of both systemically acting hormones and locally produced growth factors. A large body of evidence suggests that molecular crosstalk between these hormonal and growth factor axes is crucial for appropriate cell and tissue function. Two of the most important trophic factors involved in this process are the oestrogen (E) and insulin-like growth factor (IGF) molecular axes. The reciprocal crosstalk that exists between these pathways occurs at transcriptional/post-transcriptional and translational/post-translational levels regulate the expression and activity of genes involved in this process. In a clinical context an important consequence of such crosstalk in the mammary gland is the role which it may play in the aetiology, maintenance and development of breast tumours. Although oestradiol (E2) acting through oestrogen receptors α and β (ERα/β) is important for normal mammary gland function it can also provide a mitogenic drive to ER+ breast tumours. Therefore over several years anti-oestrogen therapeutic regimens in the form of selective oestrogen receptor modulators (SERMs - e.g. tamoxifen), aromatase inhibitors (AI e.g. anastrozole) or selective oestrogen receptor down regulators (SERDs - e.g. fulvestrant) have been used in an adjuvant setting to control tumour growth. Although initial response is usually encouraging, large cohorts of patients eventually develop resistance to these treatments leading to tumour recurrence and poor prognosis. There are potentially many routes by which breast cancer (BC) cells could escape anti-oestrogen based therapeutic strategies and one of the most studied is the possible growth factor mediated activation of ER(s). Because of this, growth factor modulation of ER activity has been an intensively studied route of molecular crosstalk in the mammary gland. The insulin-like growth factors (IGF-1 and -2) are amongst the most potent mitogens for mammary epithelial cells and there is accumulating evidence that they interact with the E2 axis to regulate mitogenesis, apoptosis, adhesion, migration and differentiation of mammary epithelial cells. Such interactions are bi-directional and E2 has been shown to regulate the expression and activity of IGF axis genes with the general effect of sensitising breast epithelial cells to the actions of IGFs and insulin. In this short review we discuss the evidence for the involvement of crosstalk between the insulin-like growth factor (IGF) and oestrogen axes in the mammary gland and comment on the relevance of such studies in the aetiology and treatment of BC

Titanium nanoparticles (TiO2)/graphene oxide nanosheets (GO): an electrochemical sensing platform for the sensitive and simultaneous determination of benzocaine in the presence of antipyrine.

An effective electrochemical sensing platform for the simultaneous determination of benzocaine (BEN) and antipyrine (ANT) based upon titanium dioxide nanoparticle (TiO2)/graphene oxide nanosheet (GO) bulk modified carbon paste electrodes (TiO2-GO/CPE) is reported. The TiO2-GO/CPE electrochemical sensing platform is found to exhibit linear ranges from 1.0 × 10-6 to 1.0 × 10-4 M and 1.2 × 10-8 to 8.0 × 10-5 M for BEN and ANT, respectively. The TiO2-GO/CPE sensor is explored towards the analysis of BEN and ANT in oral fluid (saliva) and pharmaceutical products. The synergy between the graphene oxide nanosheets and titanium dioxide nanoparticles results in a dramatic enhancement in the sensitivity of the sensor through a combination of increased surface area and improved electron transfer kinetics compared to other electrode alternatives. The fabricated TiO2-GO/CPE exhibits high sensitivity and good stability towards the sensing of BEN and ANT and has the potential to be utilised as a clinical assay and QA in pharmaceutical products

Analytical and metabolic studies of the trypanocidal diamidines

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The effects of inducing agents on the metabolism of pentamidine in isolated hepatocytes

The aromatic diamidine, pentamidine isethionate, has been used for over four decades for the chemotherapy of African human trypanosomiasis (sleeping sickness) in affected areas world-wide (Goa and Campoli-Richards, 1987). Pentamidine (P) is also used for the treatment of Pneumocyctis carinii pneumonia commonly associated with AIDS victims and over 45% of patients who receive the drug are known to suffer severe adverse reactions (Sands et al., 1985). However, emergence of drug resistant strains of trypanosomes has become a major barrier to the efficacy of trypanocidal diamidines (Peregrine, 1994). In view of poor prospects for new drug development, attempts to sustain efficacy of the drug have focussed on research into the causes of parasite drug resistance as well as drug toxicity. The inhibition or induction of hepatic drug metabolising enzymes following multiple drug therapy or exposure to environmental chemicals can alter the metabolism profile and pharmacokinetics of a given drug, leading to either a toxicological response or therapeutic failure. The aim of this study was to investigate the effects of two classical cytochrome P450 inducers, phenobarbitone (PB) and 3-methylcholanthrene (3MC), as well as a pyrethroid insecticide, deltamethrin (DM), on the metabolism of P by isolated rat hepatocytes

RP-HPLC determination of dimanazene aceturate in pharmaceutical preparations

This presentation looks at RP-HPLC determination of dimanazene aceturate in pharmaceutical preparation

High-performance liquid chromatographic determination of diminazene aceturate in the presence of its related substances

This presentation looks at high-performance liquid chromatographic determination of diminazene aceturate in the presence of its related substance

The effects of inducing agents on the metabolism of trypanocidal diamidines by isolated rat hepatocytes

This study has investigated the effect of phenobarbitone (PB), 3-methylcholanthrene (3-MC), and deltamethrin (DM) on the metabolism of two trypanocidal diamidines; pentamidine isethionate and diminazene aceturate in freshly isolated Sprague-Dawley rat hepatocytes. There were significant increases in the total cytochrome P450 content of hepatocytes obtained from rats pre-treated with PB and 3-MC, whereas pre-treatment with DM did not produce any significant induction of cytochrome P450. However, pre-treatment of rats with each of the three agents led to inhibition of pentamidine metabolism following a 3 h incubation of pentamidine (100 muM) with freshly isolated rat hepatocytes (5 x 10(6) Cells ml(-1)). Pre-treatment with 3-MC caused the highest inhibitory effect on pentamidine metabolism (8-fold inhibition), compared with PB (4.8-fold) and DM (2.2-fold). Six previously reported phase I metabolites of pentamidine were identified in cells from all the pre-treated animals as well as controls. When compared to the control group, there were significant differences between the profiles of the three major metabolites of pentamidine, 1,5-di(4'-amidinophenoxy)-2-pentanol, 1,5-di(4'-amidinophenoxy)-3-pentanol and 5-(4'-amidinophenoxy) pentanoic acid, in hepatocytes from the DM and 3-MC pre-treated rats, whereas no significant differences were observed in the cells from the PB pre-treated group. In contrast, diminazene was not metabolised with the same experimental conditions. Differences in the metabolic profiles of pentamidine and its metabolites as a result of concomitant exposure to environmental xenobiotics could have important toxicological and pharmacological implications for patients that receive the drug

The effect of inducing agents on the metabolism of trypanocidal diamidines by isolated rat hepatocytes

This study has investigated the effect of phenobarbitone (PB), 3-methylcholanthrene (3-MC), and deltamethrin (DM) on the metabolism of two trypanocidal diamidines; pentamidine isethionate and diminazene aceturate in freshly isolated Sprague-Dawley rat hepatocytes. There were significant increases in the total cytochrome P450 content of hepatocytes obtained from rats pre-treated with PB and 3-MC, whereas pre-treatment with DM did not produce any significant induction of cytochrome P450. However, pre-treatment of rats with each of the three agents led to inhibition of pentamidine metabolism following a 3 h incubation of pentamidine (100 μM) with freshly isolated rat hepatocytes (5×106 cells ml−1). Pre-treatment with 3-MC caused the highest inhibitory effect on pentamidine metabolism (8-fold inhibition), compared with PB (4.8-fold) and DM (2.2-fold). Six previously reported phase I metabolites of pentamidine were identified in cells from all the pre-treated animals as well as controls. When compared to the control group, there were significant differences between the profiles of the three major metabolites of pentamidine, 1,5-di(4′-amidinophenoxy)-2-pentanol, 1,5-di(4′-amidinophenoxy)-3-pentanol and 5-(4′-amidinophenoxy) pentanoic acid, in hepatocytes from the DM and 3-MC pre-treated rats, whereas no significant differences were observed in the cells from the PB pre-treated group. In contrast, diminazene was not metabolised with the same experimental conditions. Differences in the metabolic profiles of pentamidine and its metabolites as a result of concomitant exposure to environmental xenobiotics could have important toxicological and pharmacological implications for patients that receive the drug

The effects of inducing agents on the metabolism of pentamidine by isolated rat hepatocytes

Abstract of toxicology paper. The aromatic diamidine, pentamidine isethionate, has been used for over four decades for the chemotherapy of African human trypanosomiasis (sleeping sickness) in affected areas world-wide (Goa and Campoli-Richards, 1987). Pentamidine (P) is also used for the treatment of Pneumocyctis carinii pneumonia commonly associated with AIDS victims and over 45% of patients who receive the drug are known to suffer severe adverse reactions (Sands et al., 1985). However, emergence of drug resistant strains of trypanosomes has become a major barrier to the efficacy of trypanocidal diamidines (Peregrine, 1994). In view of poor prospects for new drug development, attempts to sustain efficacy of the drug have focussed on research into the causes of parasite drug resistance as well as drug toxicity. The inhibition or induction of hepatic drug metabolising enzymes following multiple drug therapy or exposure to environmental chemicals can alter the metabolism profile and pharmacokinetics of a given drug, leading to either a toxicological response or therapeutic failure. The aim of this study was to investigate the effects of two classical cytochrome P450 inducers, phenobarbitone (PB) and 3-methylcholanthrene (3MC), as well as a pyrethroid insecticide, deltamethrin (DM), on the metabolism of P by isolated rat hepatocytes