Info Jph
aCompounds with public structures from the set of Bergstrom et al.27 excluded SKF105657 n 78 . SKF105657 is included for values in parentheses n 79 . b Pharma Algorithms, www.ap-algorithms.com. cVCC-LAB, www.vcclab.org. dCompumine AB, www.compumine.com. eQikProp 1.6, Schrodinger, Inc. f Interactive Analysis, www.logP.com. 9Average prediction of seven models. Considering the results discussed above, an RMSE in the range of 1-1.5 log units seems likely for a test set representing broadly druglike...
Pulmonary Route
The inhalation route has been developed primarily for the treatment of respiratory disorders that today affect two hundred million people worldwide. Pulmonary drug administration allows locally acting drugs to be administered directly to their site of action such as asthma and chronic obstructive pulmonary disease COPD treatments. More recently, pulmonary drug delivery has gained interest for the administration of systemic drugs, due to the large absorptive surface of the lung, the high...
Info Cfh
a25 C, 0.15 M KCl ionic strength, solubility determined by the DTT method,31 unless otherwise noted. b Instrinsic solubility, based on molar units. cKsp BH Cl , the solubility product. d25 C, 0.5 M KCl .42 e25 C, 0.1 M KCl .46 f37 C, 0.15 M KCl pION, unpublished work . 9 Re-analysis of 37 C data of Jinno et a .58 h37 C, no ionic strength adjuster added.53 '25 C, 0.01 M ionic strength, determined by the UV method pION, unpublished work .
ADMET Predictor
Methods and models used by ADMET Predictor to predict pKa have been described in Section 5.25.3.1.2. Since its inception, the program has been coded with high-throughput batch prediction of a variety of molecular properties in mind. Even though full microspeciation puts exponential demands on the computer's CPU, it is calculated completely for each compound. In a recent test, all 65 536 microstates of the 16-group viomycin were processed in 2 min 2 s version 1.1.4, Pentium IV 512MB RAM . In the...
Figure 5 Major peptidases acting on oxytocin Descending arrows represent
Oxytocin Figure 5 is a potent and specific stimulant of myometrial contractions commonly used to induce labor. This peptide is of interest here due to it being a natural peptide and being degraded by a variety of peptidases. Thus, cleavage of the N-terminal cysteine is catalyzed by an aminopeptidase now known as cystinyl aminopeptidase EC 3.4.11.3 oxytocinase , an enzyme found in the placenta and in the serum of pregnant women.23 The enzyme acts efficiently to hydrolyze the Cys1-Tyr2 bond, thus...
Conclusion 1
The explosion of metabolic information since the 1990s has served to accentuate the importance of drug metabolism to clinical pharmacology and therapeutics. This new knowledge emphasizes the need for a common understanding among investigators of the different disciplines that impact drug development. To help meet that need, my goal in writing this chapter was to provide a comprehensive overview of the scope of the chemistry and major enzyme systems involved in drug metabolism. Many of the...
Conclusion Evt
This chapter was written with a number of objectives in mind. As a priority, it was felt necessary to demonstrate to medicinal chemists the fact that metabolic reactions of hydrolysis and conjugation are not second in importance to the redox reactions comprehensively surveyed in 5.05 Principles of drug metabolism 1 Redox reactions The variety of substrates and products presented here is just as ample as that discussed in 5.05 Principles of drug metabolism 1 Redox reactions, and the...
In Silico Methods for the Prediction of Aqueous Solubility
Since the turn of the millenium, about half a dozen new QSPR methods have been published yearly for the in silico prediction of aqueous solubility. The published methods represent greatly varying approaches as to the selection of the experimental database, description of chemical structures, model selection and fitting, and validation of the prediction power. In the following discussion the methods are grouped together based on the type of structure representation, and representative examples...
Arene oxide substrates
Together with glutathione conjugation, hydration is a major pathway in the inactivation and detoxification of arene oxides. As a rule, these are good substrates of microsomal epoxide hydrolase. But when reading the literature, the Figure 7 A simplified model showing that the nucleophilic attack of the substrate is mediated by a carboxylate group in the catalytic site to form an ester intermediate. Only in the second step is the intermediate hydrolyzed by an activated water molecule, leading to...
References Jjt
1. Kola, I. Landis, J. Nat. Rev. Drug Disc. 2004, 3, 711-715. 2. Kennedy, T Drug Disc. Today 1997, 2, 436-444. 3. Prentis, R. A. Lis, Y Walker, S. R. Br. J. Clin. Pharmacol. 1988, 25, 387-396. 4. Artursson, P Borchardt, R. T. Pharm. Res. 1997, 14, 1655-1658. 5. Artursson, P J. Pharm. Sci. 1990, 79, 476-482. 6. Hilgers, A. R. Conradi, R. A. Burton, P. S. Pharm. Res. 1990, 7, 902-910. 7. Hidalgo, I. J. Raub, T J. Borchardt, R. T Gastroenterology 1989, 96, 736-749. 8. Wilson, G. Hassan, I. F Dix,...
In Vitro Surrogate BloodBrain Barrier Models
In spite of the documented value of cultured brain endothelial cells as BBB models, they have not been universally popular with pharmaceutical companies. This is largely due to the labor-intensive nature of their preparation, and the fact that the expertise needed to prepare reproducible cultures is greater than for commonly used epithelial models such as Caco-2 and MDCK. These are widely used as assay systems to predict gastrointestinal permeability of a compound or drug see 5.11 Passive...
The Prohapten Concept
Many low-molecular-weight chemicals are not protein reactive themselves. However, they can become subject to cell metabolism by the xenobiotic metabolizing enzymes cytochrome P450, glutathione S-transferases, N-acetyltrans-ferases, quinone reductases, etc. . Haptenic reactive intermediates can form and cause adverse immune reactions Table 4 . The chemicals are often called prohaptens and the process bioactivation. While the liver is the major detoxifying organ and expresses the necessary...
References Ffn
1. Peppas, N. A. Buri, P. A. J. Control. Release 1985, 2, 257-275. 2. Peppas, N. A. Int. J. Pharm. 2004, 277, 11-17. 3. Rathbone, M. J. Drummond, B. K. Tucker, I. G. Adv. Drug Deliv. Rev. 1994, 13, 1-22. 4. Squier, C. A. Wertz, P W Structure and Function of the Oral Mucosa and Implications for Drug Delivery. In Oral Mucosal Drug Delivery Rathbone, M. J., Ed. Marcel Dekker New York, 1996, pp 1-26. 5. Squier, C. A. Hall, B. K. Arch. Oral Biol. 1985, 30, 485-491. 6. De Vries, M. E. Bodde, H. E....
Outlook
Due to the high attrition rate in late stage development, the pharmacokinetic and pharmacodynamic profiles of new compounds are obtained at an earlier stage than ever before. In order to fully understand these data, plasma protein binding and tissue studies are in greater demand than ever before. Understanding of the properties controlling plasma and tissue binding is increasing dramatically. Studies are now being undertaken on the crystallization of albumin and a1-acid glycoprotein with...
Nomenclature Exe
Human UGTs are composed of two gene families, UGT1 and UGT2, and three subfamilies that are designated UGT1A, UGT2A, and UGT2B. Within each family, individual enzymes, e.g., UGT2A1, UGT2B4, share at least 45 sequence homology and subfamily members, e.g., UGT1A1 and UGT1A3, share at least 60 homology. The human UGT1 gene locus is located on the long arm of chromosome 2, and the UGT2 genes are found on the long arm of chromosome 4. UGT2 enzymes are each conventionally encoded by separate genes,...
Info Ldo
80 100 120 140 160 180 200 Time min Figure 8 Water solubility of compound Q as a hydrate and an anhydrous form. Table 2 Some examples of the impact of amorphous solid form on solubility Glibenclamide Griseofulvin Indometacin Iopanoic acid MK0591 sodium Amorphous crystalline Amorphous crystalline Amorphous gamma Amorphous crystalline I Amorphous crystalline 4.5 in water 5 C and 25 C 3.7 37 C phosphate buffer Approx. 1000 Mosharraf and Nystrom ' Flammin et al.69 Hancock and Parks70 Stagner and...
Hammett and Taft Equations
Values can be predicted using linear free energy relationships, from the class of compound, and also by analogy and extrapolation. The change in free energy AG that is produced by adding a substituent leads to a corresponding change in pKa, and the effects are additive, more or less. This observation forms the basis of the Hammett and Taft equations that are the most widely used methods of prediction. As seen in Figures 7-13, pKa values change according to the class of compound. An example is...
Software for Predicting pKa Values
Several vendors, including Compudrug Pallas , Simulations Plus, ACD, and Pharma Algorithms supply software for the calculation of pKa values. Software predicts values very well for simple molecules, but for more complex or novel structures, the prediction may be suspect. Many software developers are keen to improve their predictions by taking advantage of published, measured pKa values for new compounds, and it seems likely that predictions will improve considerably during the coming years see...
Structure
In general, P450s are 450-500-amino-acid 55-60 kDa proteins with a completely conserved C-terminal cysteine residue that provides the thiolate coordinate bond to the iron atom which tethers the heme prosthetic group. Intracellularly, P450s reside in the soluble fraction of the cell bacterial enzymes , the inner membrane of the mitochondrion several steroid-metabolizing P450s , or the endoplasmic reticulum drug-metabolizing P450s targeting is dependent on the nature of the N-terminal leader...
ADME Boxes
ADME Boxes from Pharma Algorithms includes the Ionization Filter a model that counts the total number of ionizable groups and estimates one or two primary pKa values for the strongest acid and the strongest base, where applicable. The program uses database lookup approach recognizing over 100 electrolyte groups and over 1300 generic skeleton fragment classes. On average a skeleton has been derived from five compounds with known pKa values. Nearest neighbors are found based on fragment...
The Effect of CoSolvents on pKa
Methods of pKa of measurement were developed using water-soluble samples. However, many drugs are poorly soluble in water alone, and require the presence of a water-miscible co-solvent to keep them in aqueous solution. The solvent affects the pKa in two ways. It causes the pH scale to shift, and it causes the pKa to shift. The consequence is that apparent pKa values measured in the presence of solvent are different from aqueous values. For the sake of improving throughput, it is tempting to...
In Vivo Absorption Distribution Metabolism and Excretion Studies in Discovery
T Lave and C Funk, F. Hoffmann-La Roche Ltd, Basel, Switzerland 2007 Elsevier Ltd. All Rights Reserved. 5.03.1 Objectives of Absorption, Distribution, Metabolism, and Excretion ADME Studies 32 5.03.1.1 Support to Drug Discovery 32 5.03.1.2 Support to Drug Metabolism 32 5.03.1.3 Support to Pharmacodynamics 32 5.03.1.4 Support to Toxicology 32 5.03.1.5 Support to Formulation Testing 32 5.03.2 In Vivo Drug Metabolism and Pharmacokinetics Screening Studies 33 5.03.3 Pharmacokinetic Studies 33...
pHMetric Titration
The pH-metric method can be used to measure all pKa values between 2 and 12, with or without a UV chromophore, provided the sample can be dissolved in water or water co-solvent over the pH range of interest. Albert and Serjeant9 described a simple pH-metric method for measuring pKa values, illustrated here for a sample of 30.9 mg of boric acid in 47.5 mL of water at 20 C. Ten aliquots of NaOH titrant are added, and the pH measured after each addition. The results are calculated as shown in...
Hybrid pHMetricUltraviolet Method
Significantly smaller sample concentrations 10 5m or below are required for pKa measurement by the hybrid pH-metric UV method, in which multiwavelength UV absorbance of the sample solution is monitored throughout the titration. Samples must have a chromophore, and the absorbance must change as a function of ionization. Recent advances in this method have enabled pKa measurement in volumes less than 8 mL by the use of a fiber-optic dip probe in a titration cell, and has been automated on the...
Routes Across the BloodBrain Barrier
For drug discovery programs involving compounds designed to target or avoid the central nervous system CNS , several potential routes for permeation across the BBB are relevant.1,8,9 The brain endothelial tight junctions severely restrict the penetration of hydrophilic solutes via the intercellular cleft paracellular pathway , forcing molecular traffic between blood and brain to take a largely transcellular route Figure 3 .2,3 Gaseous molecules such as O2 and CO2, and small lipophilic agents,...
Progress in Bioanalytics and Automation Robotics for Absorption Distribution
J Wang, Novartis Institutes for Biomedical Research, Cambridge, MA, USA B Faller, Novartis Institutes for Biomedical Research, Basel, Switzerland 2007 Elsevier Ltd. All Rights Reserved. 5.15.1 The Automated Absorption, Distribution, Metabolism, and Excretion ADME Screening Era 341 5.15.1.1 Is Automation Absolutely Necessary for High-Throughput In Vitro Absorption, Distribution, Metabolism, and Excretion Assays 342 5.15.1.2 Automation Strategy 343 5.15.1.2.1 Shared assay workstations 344...
Dehydrogenases and reductases
Alcohol dehydrogenase E.C. 1.1.1 ADH 32 toxifies ethanol to acetaldehyde, which is then predominantly detoxified by an aldehyde dehydrogenase E.C. 1.2.1 to acetic acid. The second step, the aldehyde dehydrogenase-mediated oxidation to acetic acid, is inhibited by disulfiram Antabus , which is used in the treatment of alcohol addiction. After alcohol consumption disulfiram leads to the accumulation of the toxic acetaldehyde. The resulting toxicity provokes headache and nausea, which is intended...
Epoxide hydrolases EC 3323
Epoxide hydrolases EHs 38 catalyze the hydrolytic cleavage of oxirane rings. Because of the higher electron attracting force of the oxygen atom compared with the two carbon atoms of oxirane rings, epoxides possess two electrophilic carbon atoms, the electrophilic reactivity of which is enhanced by the tension of the three-membered oxirane ring. Depending on the influences of the rest of the molecule this can make epoxides highly cytotoxic, genotoxic, and carcinogenic. Therefore, the...
References Gqr
1. Hodgson, J. Nature Biotech. 2001, 19, 722-726. 2. Li, A. P Drug Disc. Today 2001, 6, 357-366. 3. Kerns, E. H. Di, L. Drug Disc. Today Technol. 2004, 1, 343-348. 4. Roberts, S. A. Curr. Opin. Drug Disc. Dev. 2003, 6, 66-80. 5. Wang, J. Urban, L. Drug Disc. World 2004, 5, 73-86. 6. Biller, S. A. Custer, L. Dickinson, K. E. Durham, S. K. Gavai, A. Hamann, L. G. Josephs, J. L. Moulin, F Pearl, G. M. Flint, O. P et al. In Pharmaceutical Profiling in Drug Discovery for Lead Selection Borchardt, R....
HighThroughput and Diagnostic Chemical Stability Methods
In vitro assays are used to test compounds rapidly against key stability challenges. The following sections discuss methods to screen stability under physicochemical conditions in the chemical laboratory solution pH, light, heat and humidity, and oxidation. Then methods for chemical stability in biological systems are discussed biological assay matrices, and plasma and gastrointestinal. Compounds are exposed to various pHs in the laboratory, in biological testing, and in vivo efficacy and...
Choice of Stability Conditions to Monitor
The study of chemical stability requires analytical methodology. In considering what methods to implement or have access to, it is useful to consider the various stability challenges that compounds encounter in the laboratory, during in vitro testing and in vivo.3 Even before testing, chemists can consider if these conditions could be anticipated to cause compound reaction. In the laboratory, compounds are exposed to light, oxygen, and water. As compounds are stored in solid or solution form,...
References Leg
1. Leuner, C. Dressmann, J. Eur. J. Pharm. Biopharm. 2000, 50, 47-60. 2. Lipper, R. A. Mod. Drug Disc. 1999, 2, 55-60. 3. Stahl, P H. Wermuth, C. G., Eds. Handbook of Pharmaceutical Salts Properties, Selection and Use IUPAC, Verlag Helvetica Chimica Acta Z rich, Switzerland, 2002. 4. Haleblian, J. McCrone, W J. Pharm. Sci. 1969, 58, 911-929. 5. Haleblian, J. J. Pharm. Sci. 1975, 64, 1269-1288. 6. International Conference on Harmonization ICH . Guideline Specification Q6A, October 1999. 7....
pH Gradient Titration
A technique called pH gradient titration can be used for the rapid measurement of pKa. In this technique, samples are injected into a flowing pH gradient, which is created by mixing an acidified and a basified linear buffer together using syringe pumps running at inversely varying speeds. During the gradient the pH varies linearly, and the pH at any given time may be predicted from the time elapsed since the start of gradient generation. This eliminates the need for pH measurement, which is one...
Surface Activity
Surface activity parameters may be classified as a family of purely physicochemical parameters i.e., the bulk organic solvent water partition coefficient, hydrogen bond acidity basicity, etc. rather than as biomimetic physicochemical parameters. Nevertheless, surface activity parameters are closely related to membrane partition and permeation. Surface activity parameters have been studied for their relevance to in vivo BBB penetration,160-162 and Km of the P-gp substrate.163,164 Surface...
Rectal Route
Rectal route for drug administration has been proposed to complement the classical GI way for systemic delivery of drugs either in cases of peculiar patient conditions, such as nausea, vomiting or convulsions, or, more importantly, for treating children.77 From an anatomical point of view, the rectal mucosa differs slightly from other mucosal epithelia of the GI tract. However, the dense vascular network of the rectum potentially allows the systemic distribution of absorbed drugs while...
UDPglucuronosyltransferases EC 24117
Conjugation with glucuronic acid is the most abundant phase-II reaction see 5.06 Principles of Drug Metabolism 2 Hydrolysis and Conjugation Reactions . UDP-glucuronosyltransferases UGTs 52 catalyze the formation of beta-D-glucuronides from a large variety of xenobiotics by their reaction with UDP-glucuronic acid UDPGA . Hydroxyl-, thiol-, amino-, hydroxylamino- and carboxyl-substituents serve as the anchor to which glucuronic acid can be conjugated also C-glucuronides can be formed if the...
Passive Transcellular Transport
The passive transcellular pathway is still by far the most important absorption pathway for drugs. Drug transport via the passive transcellular route requires that the solute permeates the apical cell membrane. The composition of the phospholipids and proteins of the cell membranes varies from cell type to cell type, and may, theoretically, give rise to different permeability properties depending on the cell type. In addition, monolayer-forming cells such as the intestinal enterocytes have a...
Theory
So far, we have considered intrinsic dissolution of compounds from rotating planar surfaces, where, at steady state, the classical Nernst-Brunner thin-film model predicts a linear decrease in concentration of the dissolving species throughout the ABL. With a spherical particle, on the other hand, the concentration gradient is nonlinear bowed in the ABL, and decreases proportionately with the inverse distance from the surface of the particle. Dissolution of a spherical surface will not reach a...
Pka Of Clioquinol
Figure 3 Distribution of species of clioquinol, an ampholyte with base pKa 2.96 and acid pKa 7.60. Clioquinol is unionized at intestinal pH. Figure 3 Distribution of species of clioquinol, an ampholyte with base pKa 2.96 and acid pKa 7.60. Clioquinol is unionized at intestinal pH. Figure 4 Distribution of species of ampicillin, a zwitterion with base pKa 7.14 and acid pKa 2.55. Ampicillin is ionized across the entire pH range. Figure 4 Distribution of species of ampicillin, a zwitterion with...
S
Equilibrative nucleoside transporter family SLC29 Figure 2 The classification of modes of solute S transport translocation between the extracellular out and intracellular iri compartments. A few examples of transporter families are included. primary active transport systems are coupled to an energy source that results in solar, electrical or chemical reactions, such as the hydrolysis of ATP by ion pumps ATPases and the ATP-binding cassette ABC transporters that transport the substrate in one...
Ionization and Lipophilicity
Molecules are most lipophilic when they are unionized, and their lipophilicity decreases rapidly when they are ionized. This has an important implication for the absorption and transport of drugs as a result of their permeability by passive diffusion through membranes and lipid bilayers. Figure 14 shows the lipophilicity expressed as octanol water partition of three ionizable drugs as a function of pH. Significant variations in lipophilicity occur over the physiological pH range. The pH of...
A
The relative position of the G-isobars AGa-B of different modifications can be determined by solubility experiments in a given solvent SA is the saturation solubility of the modification A and SB the saturation solubility of the modification B Each crystal form has its own heat capacity, which is a function of the enthalpy H and the temperature. The heat capacities of solids at constant volume and constant pressure are about the same. The H isobars of two modifications are parallel. Their...
Alkene oxide substrates
Alkene oxides are generally quite stable chemically, indicating a much reduced chemical reactivity compared to arene oxides. Under physiologically relevant conditions, they have little capacity to undergo rearrangement reactions and are resistant to uncatalyzed hydration. As a result, many alkene oxides formed as metabolites are stable enough to allow their isolation in the absence of degrading enzymes. Some drugs contain an unconjugated alkene group undergoing CYP-catalyzed epoxidation...
Info Bho
A methylene dioxy group in aromatic compounds is subject to O-dealkylation e.g., 3,4-methylenedioxyampheta-mine 53 78 eqn 18 . The process generates formic acid and the catechol metabolite 54 as final products. However, in the course of the reaction a portion of the enzyme can be inactivated by formation of what has been termed a metabolic intermediate MI complex79,80 characterized by an absorption peak maximum at 455 nm in the difference spectrum of reduced cytochrome P450. The complexing...
NonMichaelisMenten Kinetics
The observation of atypical enzyme kinetics, particularly involving CYP, has become relatively common. Since predictions of in vivo clearances are based on kinetic parameters observed during in vitro experiments, misidentification of the drug kinetic profile can lead to inaccurate predictions of intrinsic clearance.34 The atypical kinetic profiles include autoactivation sigmoidal kinetics or homotropic cooperativity , substrate inhibition, heteroactivation heterotropic cooperativity , partial...
Lipophilicity and Hydrophobicity
Lipophilicity, the 'love of fat,' and hydrophobicity, the 'fear of water,' are often taken as synonyms, but do not exactly describe the same property hydrophobicity considers the interaction between the compound and water, whereas lipophilicity is a measure of the interaction with a lipid. It has been suggested that hydrophobicity may be a component lipophilicity hydrophobicity polarity and that lipophilicity may consist of a cavity volume or size related and a polarity term the combination of...
Drug Binding with Membranes Membrane Analogs and Proteins
Changes in the fluorescence properties of quinine after association with neutral and negatively charged small unilamellar lipid vesicles at pH 7 and 37 C were used to obtain binding isotherms over a range of phospholipid compositions at different ionic strengths. All the findings suggested that the association of quinine to liposomes is controlled primarily through electrostatic attractions, and, to a lesser extent, by hydrophobic forces. Electrostatic and hydrophobic interactions play a...
Info Jqk
Figure 3 A schematic representation of modern drug research and development a , presented in parallel with the layout of this volume b . a The major steps in drug R amp D, showing target validation, discovery, and development, followed by the clinical phases and the postmarketing phase. Note the overlaps, which reflect the fact that many knowledge-expanding investigations are carried out after the next phases have begun, e.g., in vivo research in animals continues during the clinical phases,...
Artificial Membrane Technologies to Assess Transfer and Permeation of Drugs in
K Sugano, Pfizer Inc., Aichi, Japan 2007 Elsevier Ltd. All Rights Reserved. 5.19.1 Permeability An Intersection of Biology and Physicochemistry 454 5.19.2 Biological Membranes Constituents, Morphology, and Physicochemistry 455 5.19.2.1 Chemical Components 455 5.19.2.2 Physicochemical Properties of Lipid Bilayers 456 5.19.2.3 Intestinal Membrane Morphology, Physicochemistry, and Lipid Composition 458 5.19.2.3.2 pH and transit time at each gastrointestinal site 458 5.19.2.3.3 Lipid composition...
Ph. Eur. Monograph 1339
1. Van de Waterbeemd, H. Smith, D. A. Beaumont, K. Walker, D. K. J. Med. Chem. 2001, 44, 1313-1333. 2. Van de Waterbeemd, H. Smith, D. A. Jones, B. C. J. Comput.-AidedMol. Design 2001, 15, 273-286. 3. Lombardo, F Obach, R. Shalaeva, M. Y Gao, F J. Med. Chem. 2002, 45, 2867-2876. 4. Lipinski, C. A. Lombardo, F Dominy, B. W Feeney, P J. Adv. Drug Delia. Rev. 1997, 23, 3-25. 5. Wenlock, M. C. Austin, R. P. Barton, P Davis, A. M. Leeson, P D. J. Med. Chem. 2003 , 46, 1250-1256. 6. Vieth, M. Siegel,...