Parent Drug Molecule Research Articles

Review On Prodrug : An Advance Approach for The Drug Design to Enhance the Therapeutic Efficacy

Prodrugs are derivatives of drug molecules that are pharmacologically inactive but require either chemical or enzymatic transformation to release the active drug in vivo in order to exert a pharmacological effect. Prodrugs have better delivery properties that surpass the parent drug molecule. Prodrug concept is justified because it enables the active drug to overcome the barrier that would impede it from reaching the site of action to exert the required pharmacological activity. Some of the barriers that the prodrug approach helps to surmount are as follows, low bioavailability due to poor aqueous solubility (corticosteroids); poor permeability or absorption (ampicillin); high first pass metabolism (propranolol); metabolic instability leading to short half- life, (dopamine); poor site specificity (anticancer agents); incomplete absorption (epinephrine); unfavorable organoleptic properties (chloramphenicol); difficulties during formulation and adverse effects and toxicity. The prodrug approach is rapidly becoming a crucial part in the stratagem of delivery of drugs. The prodrug strategy implementation in the last 20 y has led to a steady advancement in the biopharmaceutical, physicochemical and/or pharmacokinetic attributes of the pharmacologically active compounds

Opportunistic Challenges of Computer-aided Drug Discovery of Lipopeptides: New Insights for Large Molecule Therapeutics.

Computer-aided drug designing is a promising approach to defeating the dry pipeline of drug discovery. It aims at reduced experimental efforts with cost-effectiveness. Naturally occurring large molecules with molecular weight higher than 500 Dalton such as cationic peptides, cyclic peptides, glycopeptides and lipopeptides are a few examples of large molecules which have successful applications as the broad spectrum antibacterial, anticancer, antiviral, antifungal and antithrombotic drugs. Utilization of microbial metabolites as potential drug candidates incur cost effectiveness through large scale production of such molecules rather than a synthetic approach. Computational studies on such compounds generate tremendous possibilities to develop novel leads with challenges to handle these complex molecules with available computational tools. The opportunities begin with the desired structural modifications in the parent drug molecule. Virtual modifications followed by molecular interaction studies at the target site through molecular modeling simulations and identification of structure-activity relationship models to develop more prominent and potential drug molecules. Lead optimization studies to develop novel compounds with increased specificity and reduced off targeting is a big challenge computationally for large molecules. Prediction of optimized pharmacokinetic properties facilitates development of a compound with lower toxicity as compared to the natural compounds. Generating the library of compounds and studies for target specificity and ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) for large molecules are laborious and incur huge cost and chemical wastage through in-vitro methods. Hence, computational methods need to be explored to develop novel compounds from natural large molecules with higher specificity. This review article is focusing on possible challenges and opportunities in the pathway of computer-aided drug discovery of large molecule therapeutics.

Characterizing aripiprazole and its ester derivatives, lauroxil and cavoxil, in interaction with dopamine D2 receptor: Molecular docking and dynamics simulations with physicochemical appraisals

Among second-generation (atypical) antipsychotic medications, aripiprazole (ARP) is of major importance as the partial agonist of the D2 receptor (D2R). Long-standing efforts in the field of a long-acting injectable formulation of aripiprazole have led to its two ester derivatives, aripiprazole lauroxil (ARP-L) and aripiprazole cavoxil (ARP-C), as prodrugs and also as atypical antipsychotics. However, information regarding the D2R binding of ARP-L and ARP-C is limited. Herein, chemoinformatics appraisal, molecular docking, and molecular dynamics (MD) simulations of ARP-L and ARP-C are presented in this study to gain insights into their physicochemical properties-activity relationship and their detailed interaction with D2R in comparison with its parent drug molecule (ARP). Both ARP derivatives, exactly like ARP itself, are not PAIN and have stronger interactions with D2R/D4R in comparison with D3R. The order of binding free energy of these antipsychotics with D2R is as follows: ARP > ARP-C ≅ ARP-L. The analysis of RMSD, RMSF, Rg, and SASA indicate that due to antipsychotic ligand binding, the stability/fluctuation, flexibility/rigidity, compactness, and solvent accessible surface area change in the intracellular regions, while intracellular residues (ICL1: 29–32, ICL2: 103–114, ICL3: 188–348) have no contribution in ΔGBinding. This perception points to the existence of allosteric communications that transforms the small changes in the orthosteric binding pocket into noticeable rearrangements in intracellular regions. Most of this orthosteric–allosteric dual effect is observed in the D2R/ARP-C complex. This work could be useful in guiding future drug discovery and development studies aimed at better-tolerated aripiprazole-based antipsychotics.

Crystal products of lamotrigine-citric acid for improvement of in vitro drug release in simulated gastric fluid

Crystal engineering is an integral part of the drug development research. Crystal forms can modify the physicochemical properties of the parent drug molecule. The present work was aimed at the synthesis and characterization of crystalline product of lamotrigine (LT), an U.S. Food and Drug Administration approved anti-epileptic drug, with citric acid (CA) to improve its release in gastric region and oral absorption. The crystalline products of LT?CA were developed by solvent evaporation method using ethanol-water as the solvent system. Appearance of new characteristic peaks in the FTIR spectra for the crystal products indicated formation of new crystal state. In DSC thermogram, melting point of the experimental crystal products was different than that of the pure drug. Further, formation of new crystalline phase was confirmed from XRD data through the identification of new sharp peaks for the selected crystal products. A higher cumulative percentage of drug release was observed for the crystal products than for the free drug within 60 min of drug release in simulated gastric fluid. However, in vivo studies are warranted for the future technology transfer of the product at industrial scale.

Approaches of Prodrug Designing to Treat Cancer, Neurodegenerative Disorders and Viral Diseases

Classical prodrug design is a sweeping approach to throw away futile side effects related to drug therapy. The main purpose of prodrug designing is to ameliorate physicochemical, pharmaceutical, and pharmacokinetic characteristics of particular compounds to resolve issues like formulation, delivery to the target site, and toxicity limitations. To fabricate the pharmacological action in CNS, drugs must cross the blood-brain barrier (BBB). Therefore, prodrug strategies are designed which include lipidization and the use of carriers and transporters. In this article, we have reviewed different anticancer, neuroprotective, and antiviral prodrugs. Flurbiprofen prodrugs, glycosylated prodrugs, resveratrol prodrugs, levodopa, etc., are mapped out for neurodegenerative disorders in CNS. Due to the poor oral pharmacokinetic properties of antiviral agents, drug design methods are performed by combining the parent drug molecule with a number of active components such as dipeptide esters, amino acids, nucleosides, and macromolecular-based prodrugs.

Computational and spectral studies of 3,3'-(propane-1,3-diyl)bis(7,8-dimethoxy-1,3,4,5-tetrahydro-2H-benzo[d]azepin-2-one)

Detection and qualification of unknown impurities during commercial drug synthesis have been mandated by the regulatory authorities. 3,3'-(propane-1,3-diyl)bis(7,8-dimethoxy-1,3,4,5-tetrahydro-2H-benzo [d]azepin-2-one) in short IVA-9, is one such process-related impurity formed during the synthesis of cardiotonic drug Ivabradine. The structure and properties of this molecule have not been explored yet. A suggestive reaction route for the chance formation of IVA-9 during the commercial synthesis of parent drug molecule has been reported in this article. Further, the optimized geometry and vibrational studies have been computed using Gaussian 09. Experimental FTIR scan has also been performed and values show satisfactory consilience with the computational data. The frontier orbital energies and energy band gaps of the reaction fragments and products were computed. The evaluation of ADME parameters such as absorption, distribution, metabolism, and excretion are performed using SwissADME tool to assess the drug-likeness and medicinal chemistry friendliness. Six physiochemical parameters namely flexibility, lipophilicity, size, polarity, solubility and saturation and their critical limits are depicted using the bioavailability radar of the programme to provide insights into pharmacokinetic properties such as human gastrointestinal absorption (HIA), blood-brain-barrier (BBB) permeability, total polar surface area (TPSA) and inhibitor action to important cytochromes etc.

SPECTROSCOPIC AND VOLUMETRIC TECHNIQUES FOR THE ESTIMATION OF IVABRADINE IMPURITY 3,3'-(PROPANE-1,3-DIYL)BIS(7,8-DIMETHOXY-1,3,4,5-TETRAHYDRO-2H-BENZO[D]AZEPIN-2-ONE)

Objective: Two simple and sensitive techniques - one spectrophotometric and one titrimetric- have been developed for the determination of 3,3'-(propane-1,3-diyl)bis(7,8-dimethoxy-1,3,4,5-tetrahydro-2H-benzo[d]azepin-2-one) commonly known as ivabradine impurity-9 (IVA-9).
 Methods: The spectrophotometric method is based on the oxidation of drug impurity by excess cerium (IV) sulphate in acidic medium and the subsequent reaction of the remaining Ce(IV) with a known amount of ferrous ammonium sulphate. The resultant ferric ion is then made to react with thiocyanate in acid medium to form a brown coloured complex which is analyzed spectrophotometrically against the reagent blank. In the volumetric method, the un-reacted Ce(IV) is titrated against standard ferrous ammonium sulphate to estimate the quantity of IVA-9.
 Results: The colored complex showed an absorption maximum at 479 nm when measured spectrophotometrically. The stated methods are validated statistically using the International Council for Harmonization guidelines-ICH Q2(R1) for precision and accuracy. The method showed a linear response from 0.5 to 100µg/ml with a correlation coefficient of 0.9985
 Conclusion : No estimation techniques have been reported to date for the determination of this molecule. The proposed techniques may be used for the routine quantification in its pure form and also in presence of its parent drug molecule Ivabradine.

Analysis of Chloramphenicol and Two Metabolites in Crab and Shrimp Following Waterborne Exposure

The use of chloramphenicol (CAP) in aquaculture products is banned in many countries, including the United States, due to human health issues. Very few depletion and metabolism studies of CAP in seafood have been performed. Current detection methods for CAP residues in food are directed toward the parent drug molecule, but rapid elimination following treatment suggests the need for an alternative marker residue. We identified, characterized, and determined the persistence of two CAP metabolites, CAP-base (CAP-B) and CAP-alcohol (CAP-OH), in crab and shrimp. Interday recoveries of CAP, CAP-B, and CAP-OH in muscle fortified ( n = 9) at levels of 0.15 to 0.60 ng/g ranged from 95 to 127% and 101 to 119% for crab and shrimp, respectively, with repeatability ranging from 4 to 19%. The limit of detection for CAP and metabolites in crab and shrimp ranged from 0.05 to 0.11 ng/g. We also monitored the depletion of CAP, CAP-B, and CAP-OH in crab following waterborne exposures. To our knowledge, we present the first CAP depletion and metabolite study following waterborne exposure in crabs, with the aim of identifying alternative marker residues.

Transition Metal Complexes of Naproxen: Synthesis, Characterization, Forced Degradation Studies, and Analytical Method Verification.

The aim of our current research was to synthesize some transition metal complexes of Naproxen, determine their physical properties, and examine their relative stability under various conditions. Characterizations of these complexes were done by 1H-NMR, Differential Scanning Calorimetry (DSC), FT-IR, HPLC, and scanning electron microscope (SEM). Complexes were subjected to acidic, basic, and aqueous hydrolysis as well as oxidation, reduction, and thermal degradation. Also the reversed phase high-performance liquid chromatography (RP-HPLC) method of Naproxen outlined in USP was verified for the Naproxen-metal complexes, with respect to accuracy, precision, solution stability, robustness, and system suitability. The melting points of the complexes were higher than that of the parent drug molecule suggesting their thermal stability. In forced degradation study, complexes were found more stable than the Naproxen itself in all conditions: acidic, basic, oxidation, and reduction media. All the HPLC verification parameters were found within the acceptable value. Therefore, it can be concluded from the study that the metal complexes of Naproxen can be more stable drug entity and offer better efficacy and longer shelf life than the parent Naproxen.

Discovery and Characterization of a Water-Soluble Prodrug of a Dual Inhibitor of Bacterial DNA Gyrase and Topoisomerase IV.

Benzimidazole 1 is the lead compound resulting from an antibacterial program targeting dual inhibitors of bacterial DNA gyrase and topoisomerase IV. With the goal of improving key drug-like properties, namely, the solubility and the formulability of 1, an effort to identify prodrugs was undertaken. This has led to the discovery of a phosphate ester prodrug 2. This prodrug is rapidly cleaved to the parent drug molecule upon both oral and intravenous administration. The prodrug achieved equivalent exposure of 1 compared to dosing the parent in multiple species. The prodrug 2 has improved aqueous solubility, simplifying both intravenous and oral formulation.

Degradation of anti-inflammatory drug ketoprofen by electro-oxidation: comparison of electro-Fenton and anodic oxidation processes.

The electrochemical degradation of the nonsteroidal anti-inflammatory drug ketoprofen in tap water has been studied using electro-Fenton (EF) and anodic oxidation (AO) processes with platinium (Pt) and boron-doped diamond (BDD) anodes and carbon felt cathode. Fast degradation of the parent drug molecule and its degradation intermediates leading to complete mineralization was achieved by BDD/carbon felt, Pt/carbon felt, and AO with BDD anode. The obtained results showed that oxidative degradation rate of ketoprofen and mineralization of its aqueous solution increased by increasing applied current. Degradation kinetics fitted well to a pseudo-first-order reaction. Absolute rate constant of the oxidation of ketoprofen by electrochemically generated hydroxyl radicals was determined to be (2.8 ± 0.1) × 10(9) M(-1) s(-1) by using competition kinetic method. Several reaction intermediates such as 3-hydroxybenzoic acid, pyrogallol, catechol, benzophenone, benzoic acid, and hydroquinone were identified by high-performance liquid chromatography (HPLC) analyses. The formation, identification, and evolution of short-chain aliphatic carboxylic acids like formic, acetic, oxalic, glycolic, and glyoxylic acids were monitored with ion exclusion chromatography. Based on the identified aromatic/cyclic intermediates and carboxylic acids as end products before mineralization, a plausible mineralization pathway was proposed. The evolution of the toxicity during treatments was also monitored using Microtox method, showing a faster detoxification with higher applied current values.

Nanotechnology Versus other Techniques in Improving Drug Dissolution

Many newly discovered drug molecules have low aqueous solubility, which results in low bioavailability. One way to improve their dissolution is to formulate them as nanoparticles, which have high specific surface areas, consequently increasing the dissolution rate and solubility. Nanoparticles can be produced via top-down or bottom-up methods. Top-down techniques such as wet milling and high pressure homogenisation involve reducing large particles to nano-sizes. Some pharmaceutical products made by these processes have been marketed. Bottom-up methods such as precipitation and controlled droplet evaporation form nanoparticles from molecules in solution. To minimise aggregation upon drying and promote redispersion of the nanoparticles upon reconstitution or administration, hydrophilic matrix formers are added to the formulation. However, the nanoparticles will eventually agglomerate together after dispersing in the liquid and hinders dissolution. Currently there is no pharmacopoeial method specified for nanoparticles. Amongst the current dissolution apparatus available for powders, the flow-through cell has been shown to be the most suitable. Regulatory and pharmacopoeial standards should be established in the future to standardise the dissolution testing of nanoparticles. More nanoparticle formulations of new hydrophobic drugs are expected to be developed in the future with the advancement of nanotechnology. However, the agglomeration problem is inherent and difficult to overcome. Thus the benefit of dissolution enhancement often cannot be fully realised. On the other hand, chemical strategies such as modifying the parent drug molecule to form a more soluble salt form, prodrug, or cyclodextrin complexation are well established and have been shown to be effective in enhancing dissolution. Thus the value of nanoformulations needs to be interpreted in the light of their limitations. Chemical approaches should also be considered in new product development.

Which Metabolites Circulate?

Characterization of the circulating metabolites for a new chemical entity in humans is essential for safety assessment, an understanding of their contributions to pharmacologic activities, and their potential involvement in drug-drug interactions. This review examines the abundance of metabolites relative to the total parent drug [metabolite-to-parent (M/P) ratio] from 125 drugs in relation to their structural and physicochemical characteristics, lipoidal permeability, protein binding, and fractional formation from parent (fm). Our analysis suggests that fm is the major determinant of total drug M/P ratio for amine, alcohol, N- and S-oxide, and carboxylic acid metabolites. Passage from the hepatocyte to systemic circulation does not appear to be limiting owing to the vast majority of metabolites formed being relatively lipid permeable. In some cases, active transport plays an important role in this process (e.g., carboxylic acid metabolites). Differences in total parent drug clearance and metabolite clearance are attenuated by the reduction in lipophilicity introduced by the metabolic step and resultant compensatory changes in unbound clearance and protein binding. A small subclass of these drugs (e.g., terfenadine) is unintentional prodrugs with very high parent drug clearance, resulting in very high M/P ratios. In contrast, arenol metabolites show a more complex relationship with fm due largely to the new metabolic routes (conjugation) available to the metabolite compared with the parent drug molecule. For these metabolites, a more thorough understanding of the elimination clearance of the metabolite is critical to discern the likelihood of whether the phenol will constitute a major circulating metabolite.

Methemoglobin incites primaquine toxicity through single-electron oxidation and modification

Primaquine (Pq) metabolic products are responsible for drug-associated hemotoxicity and limit primaquine usage. Methemoglobin (MetHb)-Pq molecular modeling was used to identify the Pq binding pocket. UPLC, mass spectrometry, and other indirect analytical methods were used to predict the metabolite. MetHb generation, development of oxidative stress, inhibition of antioxidant enzymes, and scanning electron microscope (SEM) were used to characterize the hemotoxic potentials of oxidized Pq (Pqox). MetHb binded Pq at the heme site with KD =6.4 μM as evidenced by a difference spectroscopy study. MetHb oxidized Pq through a single e-transfer mechanism to form Pqox. The analysis of Pq from MetHb-H2O2 peroxidase reaction mixture gave peaks at m/z 300.53 and m/z 243.42, corresponding to the hydroxyl and desamino derivative of Pq, respectively. Similar peaks were absent in Pq or Pq incubated with H2O2 in the same buffer system. A robust increase in MetHb formation, reactive oxygen species generation, and inhibition of antioxidant enzymes were found in red blood cells (RBCs) exposed to Pqox compared with a parent drug molecule. The RBC membrane exhibited visible damages to plasma membrane (holes) as evidenced by SEM analysis of Pqox-exposed RBCs. The MetHb-H2O2 system transforms quiescent parent drug molecule to a highly reactive oxidative form to exhibit severe hemolysis. MetHb-H2O2-mediated Pq hemolytic potentiation that is sensitive to spin trap indicates the role of Pq* radical or other single e-species in the process. The result suggests that MetHb incites the molecular property of the Pq and peroxidase inhibitors can be explored to control drug-associated toxicity.

Targeted lipid based drug conjugates: A novel strategy for drug delivery

A majority of studies involving prodrugs are directed to overcome low bioavailability of the parent drug. The aim of this study is to increase the bioavailability of acyclovir (ACV) by designing a novel prodrug delivery system which is more lipophilic, and at the same time site specific. In this study, a lipid raft has been conjugated to the parent drug molecule to impart lipophilicity. Simultaneously a targeting moiety that can be recognized by a specific transporter/receptor in the cell membrane has also been tethered to the other terminal of lipid raft. Targeted lipid prodrugs i.e., biotin-ricinoleicacid-acyclovir (B-R-ACV) and biotin-12hydroxystearicacid-acyclovir (B-12HS-ACV) were synthesized with ricinoleicacid and 12hydroxystearicacid as the lipophilic rafts and biotin as the targeting moiety. Biotin-ACV (B-ACV), ricinoleicacid-ACV (R-ACV) and 12hydroxystearicacid-ACV (12HS-ACV) were also synthesized to delineate the individual effects of the targeting and the lipid moieties. Cellular accumulation studies were performed in confluent MDCK-MDR1 and Caco-2 cells. The targeted lipid prodrugs B-R-ACV and B-12HS-ACV exhibited much higher cellular accumulation than B-ACV, R-ACV and 12HS-ACV in both cell lines. This result indicates that both the targeting and the lipid moiety act synergistically toward cellular uptake. The biotin conjugated prodrugs caused a decrease in the uptake of [3H] biotin suggesting the role of sodium dependent multivitamin transporter (SMVT) in uptake. The affinity of these targeted lipid prodrugs toward SMVT was studied in MDCK-MDR1 cells. Both the targeted lipid prodrugs B-R-ACV (20.25±1.74μM) and B-12HS-ACV (23.99±3.20μM) demonstrated higher affinity towards SMVT than B-ACV (30.90±4.19μM). Further, dose dependent studies revealed a concentration dependent inhibitory effect on [3H] biotin uptake in the presence of biotinylated prodrugs. Transepithelial transport studies showed lowering of [3H] biotin permeability in the presence of biotin and biotinylated prodrugs, further indicating a carrier mediated translocation by SMVT. Overall, results from these studies clearly suggest that these biotinylated lipid prodrugs of ACV possess enhanced affinity towards SMVT. These prodrugs appear to be potential candidates for the treatment of oral and ocular herpes virus infections, because of higher expression of SMVT on intestinal and corneal epithelial cells. In conclusion we hypothesize that our novel prodrug design strategy may help in higher absorption of hydrophilic parent drug. Moreover, this novel prodrug design can result in higher cell permeability of hydrophilic therapeutics such as genes, siRNA, antisense RNA, DNA, oligonucleotides, peptides and proteins.

Prodrug Strategies for Antihypertensives

There is a great emphasis on research to discover methods aimed at enhancing the efficacy of drugs and reducing their toxicity and unwanted side effects. Prodrugs are biologically inactive compounds that are converted to actual drug molecule, through biotransformation, that combine with the receptors to produce the biological action. Prodrugs can thus be considered as drugs containing specialized nontoxic protective groups utilized in a transient manner to alter or eliminate the undesirable properties of the parent drug molecule. Hypertension is one of the leading risk factors for cardiovascular disease and represents a major health and economic burden. Most of the drugs for cardiovascular diseases have low oral bioavailability, short duration of action, first pass metabolism and variable lipohilicities. Out of the need to overcome these limitations, various prodrugs have been designed for antihypertensive agents. This review extensively focuses on various strategies used for design and development of prodrugs for the various classes of antihypertensives, emphasizing on the details regarding the need for prodrug synthesis for each class, structure, type of modification and goal achieved. It also provides an insight into the major advances in the field of antihypertensive prodrug research.

Intact human holo‐transferrin interaction with oxaliplatin

We report the interaction of intact human holo-transferrin (holo-Tf) with oxaliplatin (an anticancer drug), and the characterization of a complex composed of (1:1) intact holo-Tf and the parent oxaliplatin molecule using nanoelectrospray ionization quadrupole time-of-flight mass spectrometry (nanoESI-QTOF-MS). The molecular weight of this complex was determined to be 80,077 Da, which was an increase of 397 mass units compared to the protein alone (79,680 Da), suggesting that a parent drug molecule was bound to the intact protein. We further examined the interaction between the intact protein and oxaliplatin using size-exclusion high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS). The protein complex and free oxaliplatin were separated by HPLC and quantitatively determined by simultaneous monitoring of both 195Pt and 56Fe using ICPMS. The HPLC/ICPMS detected both Pt and Fe signals at retention time of 2.6 min, identifying the protein-drug complex. The Fe signal at 2.6 min did not change with the increase in incubation time of the reaction mixture containing holo-Tf and oxaliplatin, while the Pt signal at the same retention time increased over time, further demonstrating that the formation of this complex does not affect the protein-bound Fe. The binding constant of the (1:1) intact human holo-Tf-oxaliplatin complex was determined to be 7.7x10(5) M-1. Both nanoESI-MS and HPLC/ICPMS results support that the holo-Tf and parent oxaliplatin molecules form complexes through non-covalent binding, suggesting that holo-Tf may be a useful carrier for oxaliplatin delivery.

Characterization of the Formation and Localization of Sulfamethoxazole and Dapsone-Associated Drug-Protein Adducts in Human Epidermal Keratinocytes

Sulfonamide- and sulfone-induced hypersensitivity reactions are thought to be mediated through bioactivation of parent drug molecule(s) to their respective reactive metabolite(s). Recent studies have demonstrated that keratinocytes can bioactivate sulfonamides and sulfones. Using enzyme-linked immunosorbent assay and hapten-specific rabbit antisera developed in our laboratory, we found that incubation of either normal human epidermal keratinocytes (NHEKs) or an immortalized human keratinocyte cell line (HaCaT) with sulfamethoxazole (SMX) or dapsone (DDS) resulted in the formation of drug/metabolite protein adducts. The formation of these adducts with SMX was increased in the presence of ascorbic acid, whereas N-acetylcysteine decreased adduct formation with both SMX and DDS. Adduct formation was confirmed using confocal microscopy when NHEKs were incubated with SMX, DDS, or their respective arylhydroxylamine metabolites. Cellular distribution of adducts was compared in permeable versus nonpermeable NHEKs. Exposure to SMX, DDS, or dapsone hydroxylamine resulted in the formation of intracellular adducts, whereas SMX hydroxylamine also resulted in the presence of adducts on the cell surface. In summary, our work shows that keratinocytes can bioactivate SMX/DDS to form drug-protein adducts, which may be acquired by antigen-presenting cells upon keratinocyte cell death, evoking an immune response. In addition, keratinocytes may themselves present antigen to hapten-specific cytotoxic T lymphocytes. Furthermore, our results also suggest that different sulfonamides/sulfones may have different protein targets for in situ haptenation in keratinocytes.

Stability and in vitro metabolism of dipeptide model prodrugs with affinity for the oligopeptide transporter

One approach to increase drug stability and to facilitate oral absorption of low bioavailability drugs may be to design oligopeptide ester prodrugs which are stable in the gastrointestinal tract, are transported via the oligopeptide transporter, and finally release the parent drug molecule into the blood circulation and/or by its site of action. In these kinds of prodrugs the ester linkage may be broken by pH dependent and/or enzyme catalyzed hydrolysis. The objective of the present study was to investigate the degradation mechanism and rate of the model compounds Glu(OBzl)–Sar, d-Glu(OBzl)–Ala and Asp(OBzl)–Sar in aqueous solution and in relevant biological media and to compare these results with those of our previous study of d-Asp(OBzl)–Ala. Furthermore, the resulting aqueous stability and in vitro metabolism data are related to our previous affinity data to evaluate if Glu–Sar, d-Glu–Ala, and Asp–Sar have potential as pro-moieties in these kinds of prodrugs. The degradation rates follow first-order kinetics, show maximun stability at pH 4–5 with maximum half-lives for Asp(OBzl)–Sar, Glu(OBzl)–Sar, and d-Glu(OBzl)–Ala of 115 h, 30 days and 152 days, respectively. The stability was dependent on buffer concentration, temperature, pH, and ionic strength. In biological media such as 80% human plasma, human gastric juice and intestinal fluid, and 10% rat jejunal homogenate at 37°C, the half-lives were greater than 1 h except for the hydrolysis of Glu(OBzl)–Sar in 10% rat jejunal homogenate, where the half-life was approximately 16 min. All the stabilized dipeptides may have potential as drug carriers targeting hPepT1.

Photosensitive Lichenoid Reaction to Torsemide—a Loop Diuretic

Photosensitive Lichenoid Reaction to Torsemide—a Loop Diuretic