Potent Reversible Inhibitor Research Articles

Systematic Comparison of Peptidic Proteasome Inhibitors Highlights the α‐Ketoamide Electrophile as an Auspicious Reversible Lead Motif

The ubiquitin-proteasome system (UPS) has been successfully targeted by both academia and the pharmaceutical industry for oncological and immunological applications. Typical proteasome inhibitors are based on a peptidic backbone endowed with an electrophilic C-terminus by which they react with the active proteolytic sites. Although the peptide moiety has attracted much attention in terms of subunit selectivity, the target specificity and biological stability of the compounds are largely determined by the reactive warheads. In this study, we have carried out a systematic investigation of described electrophiles by a combination of in vitro, in vivo, and structural methods in order to disclose the implications of altered functionality and chemical reactivity. Thereby, we were able to introduce and characterize the class of α-ketoamides as the most potent reversible inhibitors with possible applications for the therapy of solid tumors as well as autoimmune disorders.

Inhibition of Human Neutrophil Elastase by Pentacyclic Triterpenes

ScopeInhibiting human neutrophil elastase (HNE) is a promising strategy for treating inflammatory lung diseases, such as H1N1 and SARS virus infections. The use of sivelestat, the only clinically registered synthesized HNE inhibitor, is largely limited by its risk of organ toxicity because it irreversibly inhibits HNE. Therefore, potent reversible HNE inhibitors are promising alternatives to sivelestat.Methods and ResultsAn in vitro HNE inhibition assay was employed to screen a series of triterpenes. Six pentacyclic triterpenes, but not tetracyclic triterpenes, significantly inhibited HNE. Of these pentacyclic triterpenes, ursolic acid exhibited the highest inhibitory potency (IC50 = 5.51 µM). The HNE inhibitory activity of ursolic acid was further verified using a mouse model of acute smoke-induced lung inflammation. The results of nuclear magnetic resonance and HNE inhibition kinetic analysis showed that the pentacyclic triterpenes competitively and reversibly inhibited HNE. Molecular docking experiments indicated that the molecular scaffold, 28-COOH, and a double bond at an appropriate location in the pentacyclic triterpenes are important for their inhibitory activity.ConclusionOur results provide insights into the effects of pentacyclic triterpenes on lung inflammatory actions through reversible inhibition of HNE activity.

Potent Reversible Inhibition of Myeloperoxidase by Aromatic Hydroxamates

The neutrophil enzyme myeloperoxidase (MPO) promotes oxidative stress in numerous inflammatory pathologies by producing hypohalous acids. Its inadvertent activity is a prime target for pharmacological control. Previously, salicylhydroxamic acid was reported to be a weak reversible inhibitor of MPO. We aimed to identify related hydroxamates that are good inhibitors of the enzyme. We report on three hydroxamates as the first potent reversible inhibitors of MPO. The chlorination activity of purified MPO was inhibited by 50% by a 5 nm concentration of a trifluoromethyl-substituted aromatic hydroxamate, HX1. The hydroxamates were specific for MPO in neutrophils and more potent toward MPO compared with a broad range of redox enzymes and alternative targets. Surface plasmon resonance measurements showed that the strength of binding of hydroxamates to MPO correlated with the degree of enzyme inhibition. The crystal structure of MPO-HX1 revealed that the inhibitor was bound within the active site cavity above the heme and blocked the substrate channel. HX1 was a mixed-type inhibitor of the halogenation activity of MPO with respect to both hydrogen peroxide and halide. Spectral analyses demonstrated that hydroxamates can act variably as substrates for MPO and convert the enzyme to a nitrosyl ferrous intermediate. This property was unrelated to their ability to inhibit MPO. We propose that aromatic hydroxamates bind tightly to the active site of MPO and prevent it from producing hypohalous acids. This mode of reversible inhibition has potential for blocking the activity of MPO and limiting oxidative stress during inflammation.

Abstract B98: Development and evaluation of selective, reversible LSD1 inhibitors from fragment startpoints.

Abstract There is currently considerable interest in lysine-specific histone demethylase 1 (LSD1) as a therapeutic target in human malignancies. Specifically LSD1 has been demonstrated to be an essential regulator of leukaemia stem cell potential, inhibiting differentiation and apoptosis in the MLL-AML setting. There are a variety of potent irreversible LSD1 inhibitors available but here we present two series of reversible aminothiazole inhibitors obtained through the expansion of hits derived from a high concentration biochemical screen of a fragment library. The potency of the initial fragment hits was increased 32-fold through synthesis, with one series of compounds showing clear structure activity relationships (SAR) and inhibitory activities in the range of 7 to 187 µM in a biochemical assay. This series also showed selectivity against the homologous amine oxidase enzyme monoamine oxidase A (MAO-A). This work represents one of the first reported examples of a reversible small molecule inhibitor of LSD1 with clear SAR and selectivity against MAO-A, and could provide a platform for the development of more potent reversible inhibitors. We also report the first Proof of Mechanism (POM) cell based assay utilizing CD86 expression as a surrogate marker of LSD1 activity in THP1 cells and its use to evaluate both our compounds and some recently reported reversible LSD1 inhibitors. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B98. Citation Format: Alex Stowell, Niall Hamilton, James Hitchin, Julian Blagg, Rosemary Burke, Samantha Burns, Mark J. Cockerill, Emma Fairweather, Colin Hutton, Allan Jordan, Daniel Mould, Graeme Thomson, Ian Waddell, Donald Ogilvie. Development and evaluation of selective, reversible LSD1 inhibitors from fragment startpoints. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B98.

The pre-clinical absorption, distribution, metabolism and excretion properties of IPI-926, an orally bioavailable antagonist of the hedgehog signal transduction pathway

1. IPI-926 is a novel semisynthetic cyclopamine derivative that is a potent and selective Smoothened inhibitor that blocks the hedgehog signal transduction pathway.2. The in vivo clearance of IPI-926 is low in mouse and dog and moderate in monkey. The volume of distribution is high across species. Oral bioavailability ranges from moderate in monkey to high in mouse and dog. Predicted human clearance using simple allometry is low (24 L h−1), predicted volume of distribution is high (469 L) and predicted half-life is long (20 h).3. IPI-926 is highly bound to plasma proteins and has minimal interaction with human α-1-acid glycoprotein.4. In vitro metabolic stability ranges from stable to moderately stable. Twelve oxidative metabolites were detected in mouse, rat, dog, monkey and human liver microsome incubations and none were unique to human.5. IPI-926 is not a potent reversible inhibitor of CYP1A2, 2C8, 2C9 or 3A4 (testosterone). IPI-926 is a moderate inhibitor of CYP2C19, 2D6 and 3A4 (midazolam) with KI values of 19, 16 and 4.5 µM, respectively. IPI-926 is both a substrate and inhibitor (IC50 = 1.9 µM) of P-glycoprotein.6. In summary, IPI-926 has desirable pre-clinical absorption, distribution, metabolism and excretion properties.

Development and evaluation of selective, reversible LSD1 inhibitors derived from fragments

Two series of aminothiazoles have been developed as reversible inhibitors of lysine specific demethylase 1 (LSD1) through the expansion of a hit derived from a high concentration biochemical fragment based screen of 2466 compounds. The potency of the initial fragment hit was increased 32-fold through synthesis, with one series of compounds showing clear structure–activity relationships and inhibitory activities in the range of 7 to 187 μM in a biochemical assay. This series also showed selectivity against the related FAD-dependent enzyme mono-amine oxidase A (MAO-A). Although a wide range of irreversible inhibitors of LSD1 have been reported with activities in the low nanomolar range, this work represents one of the first reported examples of a reversible small molecule inhibitor of LSD1 with clear SAR and selectivity against MAO-A, and could provide a platform for the development of more potent reversible inhibitors. Herein, we also report the use of a recently developed cell-based assay for profiling LSD1 inhibitors, and present results on our own compounds as well as a selection of recently described reversible LSD1 inhibitors.

A combination of [+] and [−]-Huperzine A improves protection against soman toxicity compared to [+]-Huperzine A in guinea pigs

The neuropathologic mechanisms after exposure to lethal doses of nerve agent are complex and involve multiple biochemical pathways. Effective treatment requires drugs that can simultaneously protect by reversible binding to the acetylcholinesterase (AChE) and blocking cascades of seizure related brain damage, inflammation, neuronal degeneration as well as promoting induction of neuroregeneration. [−]-Huperzine A ([−]-Hup A), is a naturally occurring potent reversible AChE inhibitor that penetrates the blood–brain barrier. It also has several neuroprotective effects including modification of beta-amyloid peptide, reduction of oxidative stress, anti-inflammatory, anti-apoptotic and induction and regulation of nerve growth factor. Toxicities at higher doses restrict the neuroporotective ability of [−]-Hup A for treatment. The synthetic stereoisomer, [+]-Hup A, is less toxic due to poor AChE inhibition and is suitable for both pre-/post-exposure treatments of nerve agent toxicity. [+]-Hup A block the N-methyl-d-aspartate (NMDA)-induced seizure in rats, reduce excitatory amino acid induced neurotoxicity and also prevent soman induced toxicity with minimum performance decrement. Unique combinations of two stereo-isomers of Hup A may provide an excellent pre/post-treatment drug for the nerve agent induced seizure/status epilepticus. We investigated a combination of [+]-Hup A with a small dose of [−]-Hup A ([+] and [−]-Hup A) against soman toxicity. Our data showed that pretreatment with a combination [+] and [−]-Hup A significantly increased the survival rate and reduced behavioral abnormalities after exposure to 1.2×LD50 soman compared to [+]-Hup A in guinea pigs. In addition, [+] and [−]-Hup A pretreatment inhibited the development of high power of EEG better than [+]-Hup A pretreatment alone. These data suggest that a combination of [+] and [−]-Hup A offers better protection than [+]-Hup A and serves as a potent medical countermeasure against lethal dose nerve agent toxicity in guinea pigs.

The Inhibition of Monoamine Oxidase by 8-(2-Phenoxyethoxy)Caffeine Analogues

Previous studies have documented that substituted 8-oxycaffeines act as inhibitors of human monoamine oxidase (MAO) B. A particularly potent inhibitor among the reported compounds was 8-(2-phenoxyethoxy)caffeine with an IC50 value of 0.383 µM towards MAO-B. In an attempt to improve on the inhibition potency of this compound and to discover highly potent reversible MAO-B inhibitors, in the present study, a series of 8-(2-phenoxyethoxy)caffeine analogues containing various substituents on C4 of the phenoxy ring, were synthesized and evaluated as inhibitors of human MAO-A and -B. The results show that the 8-(2-phenoxyethoxy)caffeine analogues are selective and reversible MAO-B inhibitors with the most potent homologue, 8-{2-[4-(trifluoromethyl)phenoxy]ethoxy}caffeine, exhibiting an IC50 value of 0.061 μM. These highly potent inhibitors are useful leads in the design of therapies for neurodegenerative disorders such as Parkinson's disease.

Selected C7-substituted chromone derivatives as monoamine oxidase inhibitors

A series of C7-substituted chromone (1-benzopyran-4-one) derivatives were synthesized and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The chromones are structurally related to a series of C7-functionalized coumarin (1-benzopyran-2-one) derivatives which has been reported to act as potent MAO inhibitors. The results of the current study document that the chromones are highly potent reversible inhibitors of MAO-B with IC50 values ranging from 0.008 to 0.370μM. While the chromone derivatives also exhibit affinities for MAO-A, with IC50 values ranging from 0.495 to 8.03μM, they are selective for the MAO-B isoform. Structure–activity relationships (SAR) show that 7-benzyloxy substitution of chromone is suitable for MAO-B inhibition with tolerance for a variety of substituents and substitution patterns on the benzyloxy ring. It may be concluded that 7-benzyloxychromones are appropriate lead compounds for the design of reversible and selective MAO-B inhibitors. With the aid of modeling studies, potential binding orientations and interactions of selected chromone derivatives in the MAO-A and -B active sites are examined.

Selected chromone derivatives as inhibitors of monoamine oxidase

A previous study has shown that a series of C6-benzyloxy substituted chromones exhibit high binding affinities for human monoamine oxidase (MAO) B. In an attempt to discover additional chromones with potent and selective MAO-B inhibitory potencies and to further examine the structure–activity relationships of MAO-B inhibition by chromones, the series was expanded with homologues containing polar functional groups on C3 of the chromone ring. The results demonstrate that 6-[(3-bromobenzyl)oxy]chromones containing acidic and aldehydic functional groups on C3 act as potent reversible MAO-B inhibitors with IC50 values of 2.8 and 3.7nM, respectively. Interestingly, a 2-hydroxy-2,3-dihydro-1-benzopyran-4-one derivative as well as open-ring 2-acetylphenol analogues of the chromones also were potent MAO-B inhibitors with IC50 values ranging from 4 to 11nM. Chromone derivatives containing the benzyloxy substituent on C5 of the chromone ring, however, exhibit MAO-B inhibition potencies that are several orders of magnitude weaker. High potency inhibitors of MAO-B may find application in the therapy of neurodegenerative disorders such as Parkinson’s disease.

Inhibition of monoamine oxidase by 8-phenoxymethylcaffeine derivatives

A recent study has reported that a series of 8-benzyloxycaffeines are potent and reversible inhibitors of both human monoamine oxidase (MAO) isoforms, MAO-A and -B. In an attempt to discover additional caffeine derivatives with potent MAO inhibitory activities, and to contribute to the known structure–activity relationships of MAO inhibition by caffeine derived compounds, the present study investigates the MAO inhibitory potencies of series of 8-phenoxymethylcaffeine and 8-[(phenylsulfanyl)methyl]caffeine derivatives. The results document that the 8-phenoxymethylcaffeine derivatives act as potent reversible inhibitors of MAO-B, with IC50 values ranging from 0.148 to 5.78μM. In contrast, the 8-[(phenylsulfanyl)methyl]caffeine derivatives were found to be weak inhibitors of MAO-B, with IC50 values ranging from 4.05 to 124μM. Neither the 8-phenoxymethylcaffeine nor the 8-[(phenylsulfanyl)methyl]caffeine derivatives exhibited high binding affinities for MAO-A. While less potent than the 8-benzyloxycaffeines as MAO-B inhibitors, this study concludes that 8-phenoxymethylcaffeines may act as useful leads for the design of MAO-B selective inhibitors. Such compounds may find application in the therapy of neurodegenerative disorders such as Parkinson’s disease. Using molecular docking experiments, this study also proposes possible binding orientations of selected caffeine derivatives in the active sites of MAO-A and -B.

Inhibition of human glutathione transferases by pesticides: Development of a simple analytical assay for the quantification of pesticides in water

The insecticides dieldrin and spiromesifen were identified as potent reversible inhibitors toward hGSTA1-1. Based on in silico docking analysis and kinetic inhibition studies it was concluded that dieldrin and spiromesifen bind specifically to the enzyme presumably at a distinct position that partially overlaps the substrates binding site. The ability of dieldrin and spiromesifen to inhibit hGSTA1-1 activity was exploited for the development of analytical quantification assays for these two pesticides. The reproducibility of the assay response, expressed by relative standard deviation (RSD), was in the order of 4.1% ( N = 28). The method was successfully applied to the determination of these pesticides in real water samples without sample preparation steps. The proposed assay offers clear and distinct advantages, such as low cost, real-time detection with minimum sample preparation and sample handling, over standard analytical methods for the direct monitoring of dieldrin and spiromesifen. ► The ability of dieldrin and spiromesifen to inhibit hGSTA1-1 was exploited. ► Analytical assays for dieldrin and spiromesifen were developed. ► The reproducibility, expressed by RSD, was in the order of 4.1% ( N = 28). ► Determination of pesticides in water without sample preparation steps was achieved. Glutathione transferases (GSTs; EC 2.5.1.18) form a group of multifunctional enzymes that are involved in phase II cellular detoxification mechanism. Here, screening of the inhibition potency of a wide range of pesticides toward selected human GST isoenzymes (hGSTA1-1, hGSTP1-1, hGSTT2-2 and hGSTO1-1) was carried out. hGSTA1-1 was found more susceptible to inhibition by pesticides than other isoenzymes. The insecticides dieldrin and spiromesifen were identified as potent reversible inhibitors toward hGSTA1-1 with IC 50 values equal to 17.9 ± 1.7 μM and 12.1 ± 3.4 μM, respectively. Based on in silico docking analysis and kinetic inhibition studies it was concluded that dieldrin and spiromesifen bind specifically to the enzyme presumably at a distinct position that partially overlaps with both the G- and H-site. The ability of dieldrin and spiromesifen to inhibit hGSTA1-1 activity was exploited for the development of analytical quantification assays for these two pesticides. Linear calibration curves were obtained for dieldrin and spiromesifen, with useful concentration in the range of 0–10 μM. The reproducibility of the assay response, expressed by relative standard deviation, was in the order of 4.1% ( N = 28). The method was successfully applied to the determination of these pesticides in real water samples without sample preparation steps.

Lapatinib for advanced or metastatic breast cancer.

Lapatinib is a potent reversible and selective inhibitor of the tyrosine kinase domains of epidermal growth factor receptor and human epidermal growth factor receptor (HER)-2 that exerts its action by competitive binding to the intracellular ATP-binding site of the receptor. It is registered for the treatment of advanced or metastatic HER-2+ breast cancer in combination with capecitabine and for hormone receptor-positive breast cancer in combination with an aromatase inhibitor. Lapatinib administered orally once daily is moderately to well tolerated, with rash and gastrointestinal adverse events as the main toxicities. In studies on the efficacy of lapatinib, direct comparisons between lapatinib and trastuzumab are lacking. Results of ongoing randomized phase III studies with lapatinib or trastuzumab in combination with taxanes as first-line agents for metastatic breast cancer as well as in the neoadjuvant and adjuvant settings are awaited.

Inhibition of monoamine oxidase by selected C6-substituted chromone derivatives

Chromone has been reported to be a useful scaffold for the design of monoamine oxidase (MAO) inhibitors. In an attempt to discover highly potent MAO inhibitors and to contribute to the known structure–activity relationships (SAR) of MAO inhibition by chromones, in the present study, we have synthesized a series of chromone derivatives substituted at C6 with a variety of alkyloxy substituents, and evaluated the resulting compounds as inhibitors of recombinant human MAO-A and -B. The results document that the C6-substituted chromones are potent reversible MAO-B inhibitors with IC50 values in the low nM range (2–76 nM). The chromones were also found to bind reversibly to MAO-A, but with lower affinities compared to MAO-B. It may therefore be concluded that C6-substituted chromones are highly potent MAO-B selective inhibitors and promising lead compounds for the development of therapy for neurodegenerative disorders such as Parkinson’s disease. The results of this study are discussed with reference to possible binding orientations of a selected C6-substituted chromone in the active site cavities of MAO-A and -B.

17β-Arylsulfonamides of 17β-aminoestra-1,3,5(10)-trien-3-ol as highly potent inhibitors of steroid sulfatase

Steroid sulfatase (STS) catalyzes the desulfation of biologically inactive sulfated steroids to yield biologically active desulfated steroids and is currently being examined as a target for therapeutic intervention for the treatment of breast and other steroid-dependent cancers. Here we report the synthesis of a series of 17β-arylsulfonamides of 17β-aminoestra-1,3,5(10)-trien-3-ol and their evaluation as inhibitors of STS. Some of these compounds are among the most potent reversible STS inhibitors reported to date. Introducing n-alkyl groups into the 4′-position of the 17β-benzenesulfonamide derivative resulted in an increase in potency with the n-butyl derivative exhibiting the best potency with an IC50 of 26nM. A further increase in carbon units (to n-pentyl) resulted in a decrease in potency. Branching of the 4′-n-propyl group resulted in a decrease in potency while branching of the 4′-n-butyl group (to a tert-butyl group) resulted in a slight increase in potency (IC50=18nM). Studies with 3′- and 4′-substituted substituted 17β-benzenesulfonamides with small electron donating and electron withdrawing groups revealed the 3′-bromo and 3′-trifluoromethyl derivatives to be excellent inhibitors with IC50’s of 30 and 23nM, respectively. The 17β-2′-naphthalenesulfonamide was also an excellent inhibitor (IC50=20nM) while the 17β-4′-phenylbenzenesulfonamide derivative was the most potent inhibitor of all the compounds studied with an IC50 of 9nM.

Apixaban

Apixaban is a potent reversible inhibitor of the activated human coagulation factor X. This new oral anticoagulant has favourable pharmacokinetic and pharmocodynamic properties which include a concentration-dependent anticoagulant effect, good oral bioavailability, balanced elimination and excretion, infrequent drug or food interactions, and the lack of liver toxicity. Apixaban has already completed a large part of its phase 3 clinical trial programme. In the ARISTOTLE study, which focused on stroke prevention in atrial fibrillation, apixaban showed a balanced efficacy and safety profile, being superior to warfarin both in the prevention of strokes and in the risk of causing major bleeding. A further trial related to this indication, AVERROES, demonstrated the clear superiority of apixaban compared to aspirin treatment. In the primary prophylaxis of venous thromboembolism after orthopaedic surgery, apixaban successfully completed the ADVANCE study programme and was approved in Europe for patients undergoing elective hip or knee replacement. The results of the AMPLIFY and AMPLIFY-EXT studies will soon show whether the inhibitor is also effective in the treatment and secondary prophylaxis after acute deep vein thrombosis and pulmonary embolism. On the other hand, the use of apixaban in the primary prophylaxis of venous thrombosis in hospitalised medical patients, and its administration on top of antiplatelet therapy to patients who have suffered an acute coronary syndrome, have not received support by the results of ADOPT and APPRAISE-II, respectively. In conclusion, on the basis of the available evidence, apixaban appears to be a valuable therapeutic option for the prevention of venous thrombosis and embolic stroke.

Monoamine oxidase inhibition by C4-substituted phthalonitriles

It was recently reported that a series of C5-substituted phthalimides are remarkably potent reversible inhibitors of recombinant human monoamine oxidase (MAO) B. Modeling studies suggested that the phthalimide ring forms numerous polar interactions with the polar region of the MAO-B substrate cavity while the C5 side chain extends to, and interacts via Van der Waals interactions with the hydrophobic regions of the enzyme entrance cavity. Interactions with both cavities appear to be requirements for high affinity binding. In the present study we have examined an analogs series of C4-substituted phthalonitriles as potential human MAO inhibitors. The phthalonitriles were found to be highly potent reversible MAO-B inhibitors with most analogs exhibiting IC50 values in the low nM range. The phthalonitriles also interacted with human MAO-A, although with lower binding affinities compared to MAO-B. Modeling studies suggest that the high binding affinities of the phthalonitriles to MAO-B may depend, at least in part, on the formation of polar interactions between the nitrile functional groups and the enzyme substrate cavity. Examination of a homologs series of benzonitriles established that the phthalonitrile moiety is more optimal for MAO-B inhibition than the corresponding benzonitrile moiety, and that C3-substituted benzonitriles are better MAO-B inhibitors than C4-substituted benzonitriles. Since elimination of the nitrile functional group yielded compounds with only moderate MAO-B inhibition potencies, it may be concluded that this functional group is privileged for MAO-B inhibition.

Thio- and aminocaffeine analogues as inhibitors of human monoamine oxidase

In a recent study it was shown that 8-benzyloxycaffeine analogues act as potent reversible inhibitors of human monoamine oxidase (MAO) A and B. Although the benzyloxy side chain appears to be particularly favorable for enhancing the MAO inhibition potency of caffeine, a variety of other C8 oxy substituents of caffeine also lead to potent MAO inhibition. In an attempt to discover additional C8 substituents of caffeine that lead to potent MAO inhibition and to explore the importance of the ether oxygen for the MAO inhibition properties of C8 oxy-substituted caffeines, a series of 8-sulfanyl- and 8-aminocaffeine analogues were synthesized and their human MAO-A and -B inhibition potencies were compared to those of the 8-oxycaffeines. The results document that the sulfanylcaffeine analogues are reversible competitive MAO-B inhibitors with potencies comparable to those of the oxycaffeines. The most potent inhibitor, 8-{[(4-bromophenyl)methyl]sulfanyl}caffeine, exhibited an IC50 value of 0.167μM towards MAO-B. While the sulfanylcaffeine analogues also exhibit affinities for MAO-A, they display in general a high degree of MAO-B selectivity. The aminocaffeine analogues, in contrast, proved to be weak MAO inhibitors with a number of analogues exhibiting no binding to the MAO-A and -B isozymes. The results of this study are discussed with reference to possible binding orientations of selected caffeine analogues within the active site cavities of MAO-A and -B. MAO-B selective sulfanylcaffeine derived inhibitors may act as lead compounds for the design of antiparkinsonian therapies.

HIV Protease Inhibitors Act as Competitive Inhibitors of the Cytoplasmic Glucose Binding Site of GLUTs with Differing Affinities for GLUT1 and GLUT4

The clinical use of several first generation HIV protease inhibitors (PIs) is associated with the development of insulin resistance. Indinavir has been shown to act as a potent reversible noncompetitive inhibitor of zero-trans glucose influx via direct interaction with the insulin responsive facilitative glucose transporter GLUT4. Newer drugs within this class have differing effects on insulin sensitivity in treated patients. GLUTs are known to contain two distinct glucose-binding sites that are located on opposite sides of the lipid bilayer. To determine whether interference with the cytoplasmic glucose binding site is responsible for differential effects of PIs on glucose transport, intact intracellular membrane vesicles containing GLUT1 and GLUT4, which have an inverted transporter orientation relative to the plasma membrane, were isolated from 3T3-L1 adipocytes. The binding of biotinylated ATB-BMPA, a membrane impermeable bis-mannose containing photolabel, was determined in the presence of indinavir, ritonavir, atazanavir, tipranavir, and cytochalasin b. Zero-trans 2-deoxyglucose transport was measured in both 3T3-L1 fibroblasts and primary rat adipocytes acutely exposed to these compounds. PI inhibition of glucose transport correlated strongly with the PI inhibition of ATB-BMPA/transporter binding. At therapeutically relevant concentrations, ritonavir was not selective for GLUT4 over GLUT1. Indinavir was found to act as a competitive inhibitor of the cytoplasmic glucose binding site of GLUT4 with a KI of 8.2 µM. These data establish biotinylated ATB-BMPA as an effective probe to quantify accessibility of the endofacial glucose-binding site in GLUTs and reveal that the ability of PIs to block this site differs among drugs within this class. This provides mechanistic insight into the basis for the clinical variation in drug-related metabolic toxicity.

Determining the Time Course of CYP3A Inhibition by Potent Reversible and Irreversible CYP3A Inhibitors Using A Limited Sampling Strategy

We established a new limited sampling strategy to assess CYP3A activity and evaluated the time course of reversible (voriconazole) and irreversible (ritonavir) CYP3A inhibition. In this randomized trial, two groups, each with eight healthy participants, received CYP3A inhibitors voriconazole or ritonavir orally for 9 days, with 3 mg midazolam (MDZ) administered before the inhibitor treatment, on days 1, 2, 3, 5, 8, and 9 during inhibitor treatment, and on days 10, 11, and 12 (3 days) after discontinuation. Plasma MDZ area under the curve (AUC) between 2 and 4 h after oral administration in the form of a solution strongly correlated with MDZ clearance. Using this parameter, maximum inhibition of voriconazole and ritonavir was calculated to have occurred only 48 h after starting of the inhibitor (percentage of baseline MDZ clearance, voriconazole: 10.6%; ritonavir: 8.4%). Recovery of CYP3A activity occurred with a half-life of 24 h after voriconazole, whereas ritonavir inhibition was still strong 3 days after discontinuation. These findings underscore the substantial and gradual alterations in dose requirements in the first days of and after such combination therapies.