Drug bioactivation, covalent binding to target proteins and toxicity relevance.
ABSTRACT A number of therapeutic drugs with different structures and mechanisms of action have been reported to undergo metabolic activation by Phase I or Phase II drug-metabolizing enzymes. The bioactivation gives rise to reactive metabolites/intermediates, which readily confer covalent binding to various target proteins by nucleophilic substitution and/or Schiff's base mechanism. These drugs include analgesics (e.g., acetaminophen), antibacterial agents (e.g., sulfonamides and macrolide antibiotics), anticancer drugs (e.g., irinotecan), antiepileptic drugs (e.g., carbamazepine), anti-HIV agents (e.g., ritonavir), antipsychotics (e.g., clozapine), cardiovascular drugs (e.g., procainamide and hydralazine), immunosupressants (e.g., cyclosporine A), inhalational anesthetics (e.g., halothane), nonsteroidal anti-inflammatory drugs (NSAIDSs) (e.g., diclofenac), and steroids and their receptor modulators (e.g., estrogens and tamoxifen). Some herbal and dietary constituents are also bioactivated to reactive metabolites capable of binding covalently and inactivating cytochrome P450s (CYPs). A number of important target proteins of drugs have been identified by mass spectrometric techniques and proteomic approaches. The covalent binding and formation of drug-protein adducts are generally considered to be related to drug toxicity, and selective protein covalent binding by drug metabolites may lead to selective organ toxicity. However, the mechanisms involved in the protein adduct-induced toxicity are largely undefined, although it has been suggested that drug-protein adducts may cause toxicity either through impairing physiological functions of the modified proteins or through immune-mediated mechanisms. In addition, mechanism-based inhibition of CYPs may result in toxic drug-drug interactions. The clinical consequences of drug bioactivation and covalent binding to proteins are unpredictable, depending on many factors that are associated with the administered drugs and patients. Further studies using proteomic and genomic approaches with high throughput capacity are needed to identify the protein targets of reactive drug metabolites, and to elucidate the structure-activity relationships of drug's covalent binding to proteins and their clinical outcomes.
SourceAvailable from: Soumendranath Bhakat[Show abstract] [Hide abstract]
ABSTRACT: he present art of drug discovery and design of new drugs is based on suicidal irreversible inhibitors. Covalent inhibition is the strategy that is used to achieve irreversible inhibition. Irreversible inhibitors interact with their targets in a time-dependent fashion, and the reaction proceeds to completion rather than to equilibrium. Covalent inhibitors possessed some significant advantages over non-covalent inhibitors such as covalent warheads can target rare, non-conserved residue of a particular target protein and thus led to development of highly selective inhibitors, covalent inhibitors can be effective in targeting proteins with shallow binding cleavage which will led to development of novel inhibitors with increased potency than non-covalent inhibitors. Several computational approaches have been developed to simulate covalent interactions; however, this is still a challenging area to explore. Covalent molecular docking has been recently implemented in the computer-aided drug design workflows to describe covalent interactions between inhibitors and biological targets. In this review we highlight: (i) covalent interactions in biomolecular systems; (ii) the mathematical framework of covalent molecular docking; (iii) implementation of covalent docking protocol in drug design workflows; (iv) applications covalent docking: case studies and (v) shortcomings and future perspectives of covalent docking. To the best of our knowledge; this review is the first account that highlights different aspects of covalent docking with its merits and pitfalls. We believe that the method and applications highlighted in this study will help future efforts towards the design of irreversible inhibitors.
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ABSTRACT: Liver plays a key role in metabolism and detoxification, therefore analysis of its proteome is relevant for toxicology and drug discovery studies. To optimize for high proteome coverage, protein and peptide-level ion exchange fractionation were assessed using rat liver microsomes and S9 fractions. 2D-(SCX-RP)-LC–MS/MS analysis with peptide fractionation was subsequently employed for rat, mouse and human samples, yielding between 1400 and 1939 identified proteins, 58% of which were shared between species, and with relatively high sequence coverage. This rich dataset is specifically interesting for the toxicology community, and could serve as an excellent source for targeted assay development.
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ABSTRACT: Cytochrome P450 (CYP) is a super family of phase I enzyme in the biotransformation of xenobiotics and medications. Most medications undergo deactivation by CYP, and then are eliminated through either bile or kidneys from the body. CYP isozymes play a crucial role in drug interactions that may result in enhanced toxicity, reduced efficacy or onset of adverse reactions. On the other hand, many agents affecting CYP expression and activity may alter metabolic rate of different medications co-administrated. Therefore, the molecular basis, regulation by inducers or inhibitors, and pharmacologic reaction of specific CYP isozymes are the key issues of biochemical mechanisms, pharmaceutical development and safe use of various medications. This book is to meet the needs from basic molecular biochemists, pharmacologists, pharmacists, medical students, clinical practitioners and scientists, as well as broad readers who wish to understand how an herbal extract, medication or natural supplement is metabolized or transformed in the liver or other sites for deactivation and elimination. Special focuses are paid to herbal extracts and medications in the treatment of neuro-psychiatric or cardiovascular disorders, diabetes and viral hepatitis. Detailed dissection of drug interactions in a particular field intends to provide rationales for useful guidance of safe drug use in daily practice. The contributing authors are basic scientists, pharmacists, pharmacologists and on-service physicians in cardiovascular, neuro-psychiatric, gastroenterologic and hepatologic fields from Europe (Germany, France, Portugal), Australia, the US and China. Thus, the book is the collection of master pieces by well-known experts from various regions of the world, and represents the current understanding of CYP enzyme reaction and a contemporary coverage of possible drug interactions in involved fields. The featured chapters are scientific elucidation of basic biochemistry, pharmacology and clinical investigations in the interest of drug metabolism, interaction and safe use guidance in the single focus of this microsomal enzyme with multi-facet metabolic function.First edited by Jian Wu, 09/2014; Nova Science Publishers, Inc.., ISBN: 978-1-61942-209-4