Toward Reducing hERG Affinities for DAT Inhibitors with a Combined Machine Learning and Molecular Modeling Approach

Psychostimulant drugs, such as cocaine, inhibit dopamine reuptake via blockading the dopamine transporter (DAT), which is the primary mechanism underpinning their abuse. Atypical DAT inhibitors are dissimilar to cocaine and can block cocaine- or methamphetamine-induced behaviors, supporting their development as part of a treatment regimen for psychostimulant use disorders. When developing these atypical DAT inhibitors as medications, it is necessary to avoid off-target binding that can produce unwanted side effects or toxicities. In particular, the blockade of a potassium channel, human ether-a-go-go (hERG), can lead to potentially lethal ventricular tachycardia. In this study, we established a counter screening platform for DAT and against hERG binding by combining machine learning-based quantitative structure-activity relationship (QSAR) modeling, experimental validation, and molecular modeling and simulations. Our results show that the available data are adequate to establish robust QSAR models, as validated by chemical synthesis and pharmacological evaluation of a validation set of DAT inhibitors. Furthermore, the QSAR models based on subsets of the data according to experimental approaches used have predictive power as well, which opens the door to target specific functional states of a protein. Complementarily, our molecular modeling and simulations identified the structural elements responsible for a pair of DAT inhibitors having opposite binding affinity trends at DAT and hERG, which can be leveraged for rational optimization of lead atypical DAT inhibitors with desired pharmacological properties.

Tropane-Based Ibogaine Analog Rescues Folding-Deficient Serotonin and Dopamine Transporters

Missense mutations that give rise to protein misfolding are rare, but collectively, defective protein folding diseases are consequential. Folding deficiencies are amenable to pharmacological correction (pharmacochaperoning), but the underlying mechanisms remain enigmatic. Ibogaine and its active metabolite noribogaine correct folding defects in the dopamine transporter (DAT), but they rescue only a very limited number of folding-deficient DAT mutant proteins, which give rise to infantile Parkinsonism and dystonia. Herein, a series of analogs was generated by reconfiguring the complex ibogaine ring system and exploring the structural requirements for binding to wild-type transporters, as well as for rescuing two equivalent synthetic folding-deficient mutants, SERT-PG^601,602AA and DAT-PG^584,585AA. The most active tropane-based analog (9b) was also an effective pharmacochaperone in vivo in Drosophila harboring the DAT-PG^584,585AA mutation and rescued 6 out of 13 disease-associated human DAT mutant proteins in vitro. Hence, a novel lead pharmacochaperone has been identified that demonstrates medication development potential for patients harboring DAT mutations.

New Drugs, Old Targets: Tweaking the Dopamine System to Treat Psychostimulant Use Disorders

The abuse of illicit psychostimulants such as cocaine and methamphetamine continues to pose significant health and societal challenges. Despite considerable efforts to develop medications to treat psychostimulant use disorders, none have proven effective, leaving an underserved patient population and unanswered questions about what mechanism(s) of action should be targeted for developing pharmacotherapies. As both cocaine and methamphetamine rapidly increase dopamine (DA) levels in mesolimbic brain regions, leading to euphoria that in some can lead to addiction, targets in which this increased dopaminergic tone may be mitigated have been explored. Further, understanding and targeting mechanisms underlying relapse are fundamental to the success of discovering medications that reduce the reinforcing effects of the drug of abuse, decrease the negative reinforcement or withdrawal/negative affect that occurs during abstinence, or both. Atypical inhibitors of the DA transporter and partial agonists/antagonists at DA D₃ receptors are described as two promising targets for future drug development.

Structure-activity relationships for a series of (Bis(4-fluorophenyl)methyl)sulfinylethyl-aminopiperidines and -piperidine amines at the dopamine transporter: Bioisosteric replacement of the piperazine improves metabolic stability

Despite considerable efforts to develop medications to treat psychostimulant use disorders, none have proven effective, leaving an underserved patient population and unanswered questions as to what mechanism(s) of action should be targeted for developing pharmacotherapies. Atypical dopamine transporter (DAT) inhibitors, based on (±)modafinil, have shown therapeutic potential in preclinical models of psychostimulant abuse. However, metabolic instability among other limitations to piperazine analogues 1-3 have impeded further development. Herein, bioisosteric substitutions of the piperazine ring were explored with a series of aminopiperidines (A) and piperidine amines (B) wherein compounds with either a terminal tertiary amine or amide were synthesized. Several lead compounds showed high to moderate DAT affinities and metabolic stability in rat liver microsomes. Aminopiperidines 7 (DAT Ki = 50.6 nM), 21b (DAT Ki = 77.2 nM) and 33 (DAT Ki = 30.0 nM) produced only minimal stimulation of ambulatory activity in mice, compared to cocaine, suggesting an atypical DAT inhibitor profile.

Novel Fluorescent Ligands Enable Single-Molecule Localization Microscopy of the Dopamine Transporter

The dopamine transporter (DAT) is critical for spatiotemporal control of dopaminergic neurotransmission and is the target for therapeutic agents, including ADHD medications, and abused substances, such as cocaine. Here, we develop new fluorescently labeled ligands that bind DAT with high affinity and enable single-molecule detection of the transporter. The cocaine analogue MFZ2-12 (1) was conjugated to novel rhodamine-based Janelia Fluorophores (JF₅₄₉ and JF₆₄₆). High affinity binding of the resulting ligands to DAT was demonstrated by potent inhibition of [³H]dopamine uptake in DAT transfected CAD cells and by competition radioligand binding experiments on rat striatal membranes. Visualization of binding was substantiated by confocal or TIRF microscopy revealing selective binding of the analogues to DAT transfected CAD cells. Single particle tracking experiments were performed with JF₅₄₉-conjugated DG3-80 (3) and JF₆₄₆-conjugated DG4-91 (4) on DAT transfected CAD cells enabling quantification and categorization of the dynamic behavior of DAT into four distinct motion classes (immobile, confined, Brownian, and directed). Finally, we show that the ligands can be used in direct stochastic optical reconstruction microscopy (dSTORM) experiments permitting further analyses of DAT distribution on the nanoscale. In summary, these novel fluorescent ligands are promising new tools for studying DAT localization and regulation with single-molecule resolution.

Synthesis of distal and proximal fleximer base analogues and evaluation in the nucleocapsid protein of HIV-1

Anti-HIV-1 drug design has been notably challenging due to the virus’ ability to mutate and develop immunity against commercially available drugs. The aims of this project were to develop a series of fleximer base analogues that not only possess inherent flexibility that can remain active when faced with binding site mutations, but also target a non-canonical, highly conserved target: the nucleocapsid protein of HIV (NC). The compounds were predicted by computational studies not to function via zinc ejection, which would endow them with significant advantages over non-specific and thus toxic zinc-ejectors. The target fleximer bases were synthesized using palladium-catalyzed cross-coupling techniques and subsequently tested against NC and HIV-1. The results of those studies are described herein.

Bicyclic and Tricyclic "Expanded" Nucleobase Analogues of Sofosbuvir: New Scaffolds for Hepatitis C Therapies

Given the impressive success of Gilead's Sofosbuvir, many laboratories, including ours, have explored the unique 2'-sugar modification (2'-Me, 2'-F) of nucleoside analogues in the hopes of exploiting the biological activity that this unique modification has imparted to the nucleoside scaffold. In that regard, we have combined our tricyclic "expanded" purine base motif with the 2'-Me, 2'-F sugar modification. Although the synthesis of these complex molecules proved to be nontrivial, with the best results coming from a linear approach, the overall strategy resulted in highly promising biological results for several of the target compounds, including their corresponding McGuigan ProTides. Modest activity against HCV was observed with inhibitory concentrations of as low as 20 μM.

Shaping quality: the use of performance polygons for multidimensional presentation and interpretation of qualitative performance data

BACKGROUND

Measuring outcomes and quality in anaesthesia is challenging. In the UK, there is increased focus on these as a result of changes in Department of Health strategy and the imminent introduction of mandatory revalidation for all doctors. A definition of quality may differ according to the observer's standpoint and numerous performance measures may contribute to overall quality. Patients, surgeons, anaesthetic assistants, recovery nurses, managers, and anaesthetic peers are each likely to have their own perspective on 'anaesthetic quality' and would perhaps suggest different metrics to measure it. Speed, efficiency, cost, interpersonal skills, complication rates, patient recorded outcome measures, and satisfaction are all valid as quality measures, but none alone captures anaesthetic quality. Performance data are frequently presented as single-dimension measurements (e.g. pain, postoperative nausea and vomiting, patient satisfaction), but this does not address the fact that two or more domains may be closely related (e.g. use of regional anaesthesia and quality of analgesia) or in opposition (e.g. use of regional anaesthesia and speed).

METHODS

We introduce the concept of a 'performance polygon' as a tool to represent multidimensional performance assessment. This method of data presentation encourages balanced appraisal of anaesthetic quality.

RESULTS

Performance polygons may be used to compare individual performance with peers, published outcome norms, trends in performance over time, to explore aspects of team performance and potentially capture data that are required for medical revalidation.

CONCLUSIONS

Performance polygons enable easy comparison with any relevant data set and are a visual tool that potentially has wider applications in healthcare quality improvement.

Angiotensin receptor blockade attenuates cigarette smoke-induced lung injury and rescues lung architecture in mice

Chronic obstructive pulmonary disease (COPD) is a prevalent smoking-related disease for which no disease-altering therapies currently exist. As dysregulated TGF-β signaling associates with lung pathology in patients with COPD and in animal models of lung injury induced by chronic exposure to cigarette smoke (CS), we postulated that inhibiting TGF-β signaling would protect against CS-induced lung injury. We first confirmed that TGF-β signaling was induced in the lungs of mice chronically exposed to CS as well as in COPD patient samples. Importantly, key pathological features of smoking-associated lung disease in patients, e.g., alveolar injury with overt emphysema and airway epithelial hyperplasia with fibrosis, accompanied CS-induced alveolar cell apoptosis caused by enhanced TGF-β signaling in CS-exposed mice. Systemic administration of a TGF-β-specific neutralizing antibody normalized TGF-β signaling and alveolar cell death, conferring improved lung architecture and lung mechanics in CS-exposed mice. Use of losartan, an angiotensin receptor type 1 blocker used widely in the clinic and known to antagonize TGF-β signaling, also improved oxidative stress, inflammation, metalloprotease activation and elastin remodeling. These data support our hypothesis that inhibition of TGF-β signaling through angiotensin receptor blockade can attenuate CS-induced lung injury in an established murine model. More importantly, our findings provide a preclinical platform for the development of other TGF-β-targeted therapies for patients with COPD.

Oxidative mechanisms for the biotransformation of 1-methyl-1,6-dihydropyridine-2-carbaldoxime to pralidoxime chloride

AIMS

Due to pralidoxime chloride's (2-PAM) positive charge, it's penetration through the blood brain barrier (BBB) and reactivation of organophosphate (OP) inhibited central nervous system (CNS) acetylcholinesterase (AChE) is poor. The results of CNS inhibited AChE are seizures. Pro-2-PAM (1-methyl-1,6-dihydropyridine-2-carbaldoxime), a pro-drug of 2-PAM, due to higher hydrophobicity, penetrates the BBB better but must be oxidized to 2-PAM, the active form of the oxime to reactivate CNS AChE in order to abrogate seizures. In this study, we characterize the in vivo mechanism of pro-2-PAM oxidation.

MAIN METHODS

A high pressure liquid chromatography (HPLC) assay was developed to quantify the conversion of pro-2-PAM to 2-PAM. NADPH oxidase activity was measured by a photo-luminescence assay using lucigenin substrate. Upon analysis, the rate of NADPH induced oxidation suggested that an alternate mechanism may be involved. Therefore, various enzyme co-factors of oxidation-reduction enzyme systems were evaluated, including nicotinamide adenine dinucleotide (NAD), nicotinamide adenine dinucleotide phosphate (NADP), flavin adenine dinucleotide (FAD), riboflavin 5'-phosphate (FMN), and riboflavin. Next, a spectrophotometric assay was developed to measure the conversion of pro-2-PAM to 2-PAM in the presence of riboflavin.

KEY FINDINGS

In guinea pig brain homogenate, diphenyleneiodonium (DPI), a specific NADPH oxidase inhibitor, reduced pro-2-PAM to 2-PAM conversion to less than 25%. In contrast, riboflavin, FAD, and FMN rapidly oxidized all pro-2-PAM to 2-PAM in an in vitro assay. Riboflavin oxidized pro-2-PAM reactivated diisopropylfluorophosphate (DFP) inhibited AChE.

SIGNIFICANCE

The present study shows that pro-2-PAM was rapidly oxidized by riboflavin to 2-PAM, which reactivated organophosphate (OP)-inhibited AChE.

Critical transition in tissue homeostasis accompanies murine lung senescence

Background

Respiratory dysfunction is a major contributor to morbidity and mortality in aged populations. The susceptibility to pulmonary insults is attributed to “low pulmonary reserve”, ostensibly reflecting a combination of age-related musculoskeletal, immunologic and intrinsic pulmonary dysfunction.

Methods/Principal Findings

Using a murine model of the aging lung, senescent DBA/2 mice, we correlated a longitudinal survey of airspace size and injury measures with a transcriptome from the aging lung at 2, 4, 8, 12, 16 and 20 months of age. Morphometric analysis demonstrated a nonlinear pattern of airspace caliber enlargement with a critical transition occurring between 8 and 12 months of age marked by an initial increase in oxidative stress, cell death and elastase activation which is soon followed by inflammatory cell infiltration, immune complex deposition and the onset of airspace enlargement. The temporally correlative transcriptome showed exuberant induction of immunoglobulin genes coincident with airspace enlargement. Immunohistochemistry, ELISA analysis and flow cytometry demonstrated increased immunoglobulin deposition in the lung associated with a contemporaneous increase in activated B-cells expressing high levels of TLR4 (toll receptor 4) and CD86 and macrophages during midlife. These midlife changes culminate in progressive airspace enlargement during late life stages.

Conclusion/Significance

Our findings establish that a tissue-specific aging program is evident during a presenescent interval which involves early oxidative stress, cell death and elastase activation, followed by B lymphocyte and macrophage expansion/activation. This sequence heralds the progression to overt airspace enlargement in the aged lung. These signature events, during middle age, indicate that early stages of the aging immune system may have important correlates in the maintenance of tissue morphology. We further show that time-course analyses of aging models, when informed by structural surveys, can reveal nonintuitive signatures of organ-specific aging pathology.

Lavage administration of dilute recombinant surfactant in acute lung injury in piglets

In an acute lung injury model, we previously observed reversal of pulmonary dysfunction with natural surfactant administered by lavage (dose = 18 mg/kg phospholipid). The present study questioned whether a lower dose of phospholipid would be effective if a recombinant preparation rather than natural surfactant were used. Acute lung injury was induced by repeated saline lung lavage in ventilated, sedated, and paralyzed piglets. Three concentrations of recombinant surfactant were studied (low phospholipid, 1 mg/mL; medium phospholipid, 4 mg/mL; high phospholipid, 13.5 mg/mL). Control piglets received no surfactant. Thirty-five milliliters per kilogram of surfactant was administered by gravity, followed by passive drainage of excess fluid. All treatment groups retained similar volumes (4.7+/-0.3 mL/ kg), corresponding to phospholipid doses of 4+/-0.4, 22+/-3, and 67+/-4 mg/kg in low, medium, and high-dose groups, respectively. Treatment groups showed significant improvement in Pao2 compared with controls. Other parameters different from controls were found in only the medium and high-dose groups. All surfactant-treated groups showed improvement over time in Pao2, Paco2, lung resistance mean airway pressure, functional residual capacity, and dynamic compliance. These data support the statement that whereas there is a dose response to exogenous surfactant, the effective dose of recombinant surfactant in acute lung injury may be as low as 4 mg/kg phospholipid when administered by lavage.

Mutations in ribosomal protein L10e confer resistance to the fungal-specific eukaryotic elongation factor 2 inhibitor sordarin

The natural product sordarin, a tetracyclic diterpene glycoside, selectively inhibits fungal protein synthesis by impairing the function of eukaryotic elongation factor 2 (eEF2). Sordarin and its derivatives bind to the eEF2-ribosome-nucleotide complex in sensitive fungi, stabilizing the post-translocational GDP form. We have previously described a class of Saccharomyces cerevisiae mutants that exhibit resistance to varying levels of sordarin and have identified amino acid substitutions in yeast eEF2 that confer sordarin resistance. We now report on a second class of sordarin-resistant mutants. Biochemical and molecular genetic analysis of these mutants demonstrates that sordarin resistance is dependent on the essential large ribosomal subunit protein L10e in S. cerevisiae. Five unique L10e alleles were characterized and sequenced, and several nucleotide changes that differ from the wild-type sequence were identified. Changes that result in the resistance phenotype map to 4 amino acid substitutions and 1 amino acid deletion clustered in a conserved 10-amino acid region of L10e. Like the previously identified eEF2 mutations, the mutant ribosomes show reduced sordarin-conferred stabilization of the eEF2-nucleotide-ribosome complex. To our knowledge, this report provides the first description of ribosomal protein mutations affecting translocation. These results and our previous observations with eEF2 suggest a functional linkage between L10e and eEF2.

Elongation factor 2 as a novel target for selective inhibition of fungal protein synthesis

Elongation factor 2 (EF2) is an essential protein catalyzing ribosomal translocation during protein synthesis and is highly conserved in all eukaryotes. It is largely interchangeable in translation systems reconstituted from such divergent organisms as human, wheat, and fungi. We have identified the sordarins as selective inhibitors of fungal protein synthesis acting via a specific interaction with EF2 despite the high degree of amino acid sequence homology exhibited by EF2s from various eukaryotes. In vitro reconstitution assays using purified components from human, yeast, and plant cells demonstrate that sordarin sensitivity is dependent on fungal EF2. Genetic analysis of sordarin-resistant mutants of Saccharomyces cerevisiae shows that resistance to the inhibitor is linked to the genes EFT1 and EFT2 that encode EF2. Sordarin blocks ribosomal translocation by stabilizing the fungal EF2-ribosome complex in a manner similar to that of fusidic acid. The fungal specificity of the sordarins, along with a detailed understanding of its mechanism of action, make EF2 an attractive antifungal target. These findings are of particular significance due to the need for new antifungal agents.

Promoting meconium clearance from the lungs of the neonatal piglet with asymmetric high frequency oscillation

To investigate the role of high frequency oscillation (HFO) in promoting meconium clearance from the airway, we used a commercially available ventilator configured with maximal expiratory flow exceeding inspiratory flow (asymmetric HFO or AHFO). We hypothesized that AHFO would move meconium in an expiratory direction (toward the ventilator). We first tested our hypothesis in vitro and, later, in vivo using the neonatal piglet. In vitro experiments using a Plexiglas airway confirmed meconium movement in an expiratory direction when bias ratio was > or = 2. For in vivo experiments, each piglet received a 3 mL/kg intratracheal bolus of a 44 g/100 mL meconium mixture followed by 45 min of mechanical ventilation. Then, in part 1, the piglet was placed in a 15 degree head down tilt position and randomized to either AHFO [ratio of inspiratory time/expiratory time (I:E) of 70:30] or HFO (I:E ratio of 30:70). After 30 min of either AHFO or HFO, the piglet was crossed over to the alternate strategy for an additional 30 min. For part 2, we maintained the piglet on either AHFO or HFO continuously for 4 h. Results demonstrate that, although there was a tendency for larger volumes of meconium to be aspirated from the airway during AHFO in part 1 experiments, there was no difference found in part 2. We also found no significant differences in blood gases or hemodynamic measurements between AHFO and HFO during the prolonged observation period in part 2 of our study. We conclude that AHFO is of no benefit in the treatment of meconium aspiration syndrome.

Chemical approaches to improve the oral bioavailability of peptidergic molecules

This review discusses both tools and strategies that may be employed as approaches towards the pursuit of orally active compounds from peptidergic molecules. Besides providing a review of these subjects, this paper provides an example of how these were utilized in a research programme at SmithKline Beecham involving the development of orally active GPIIb/IIIa antagonists. The tools for studying oral drug absorption in-vitro include variants of the Ussing chamber which utilize either intestinal tissues or cultured epithelial cells that permit the measurement of intestinal permeability. Example absorption studies that are described are mannitol, cephalexin, the growth hormone-releasing peptide SK&F 110679 and two GPIIb/IIIa antagonist peptides SK&F 106760 and SK&F 107260. With the exception of cephalexin, these compounds cross the intestine by passive paracellular diffusion. Cephalexin, on the other hand, crosses the intestine via the oligopeptide transporter. Structure-transport studies are reviewed for this transporter. The tools for studying oral drug absorption in-vivo involve animals bearing in-dwelling intestinal or portal vein catheters. A study of the segmental absorption of SK&F 106760 is provided. The review concludes with two chemical strategies that may be taken towards the enhancement of oral bioavailability of peptidergic molecules. The first strategy involves the chemical modification of peptides which enhance intestinal permeability, specifically the modification of amide bonds. The second strategy involves the design of compounds bearing nonpeptide templates, which are more amenable to the discovery of compounds with oral activity, from peptide pharmacophore models. An example is given regarding the discovery of SB 208651, a potent orally active GPIIb/IIIa antagonist, designed from the peptides SK&F 106760 and SK&F 107260.

Myocardial positron tomography with manganese-52m

The biodistribution of radiomanganese (54Mn) was studied in mice, rats, and dogs. Disappearance of radioactivity from the blood was extremely rapid, with a half-time of approximately 0.8 minutes. This resulted in very favorable myocardium-to-blood ratios, even at early times after administration. The myocardial uptake in dogs was greater than 3% at three and 15 minutes, with myocardium-to-blood ratios of about 40:1 at 15 minutes. Positron tomograms obtained with 52mMn clearly demonstrated regional myocardial perfusion. There was good correlation (r = 0.89) of microsphere-to-radiomanganese distribution in the infarcted dog heart.