Glenmar P. Obedencio

Efficacy of telavancin (TD-6424), a rapidly bactericidal lipoglycopeptide with multiple mechanisms of action, in a murine model of pneumonia induced by methicillin-resistant Staphylococcus aureus.

ABSTRACT The efficacy of telavancin, a bactericidal lipoglycopeptide, was compared to that of vancomycin and linezolid against methicillin-resistant Staphylococcus aureus (MRSA) in a murine pneumonia model. Telavancin produced greater reductions in lung bacterial titer and mortality than did vancomycin and linezolid at human doses equivalent to those described by the area under the concentration-time curve. These results suggest the potential utility of telavancin for treatment of MRSA pneumonia.

Pharmacodynamics of TD-1792, a Novel Glycopeptide-Cephalosporin Heterodimer Antibiotic Used against Gram-Positive Bacteria, in a Neutropenic Murine Thigh Model

ABSTRACT TD-1792 is a novel glycopeptide-cephalosporin heterodimer investigational antibiotic that displays potent bactericidal effects against clinically relevant Gram-positive organisms in vitro. The present studies evaluated the in vivo pharmacokinetics (PK) and pharmacodynamics (PD) of TD-1792 in the neutropenic murine thigh infection animal model. TD-1792, dosed subcutaneously (SC), produced dose-dependent reduction in the thigh bacterial burden of several organisms, including methicillin-susceptible and -resistant strains of Staphylococcus aureus and Staphylococcus epidermidis (MSSA, MRSA, MSSE, MRSE, respectively), penicillin-susceptible strains of Streptococcus pneumoniae (PSSP), Streptococcus pyogenes, and vancomycin-intermediate-susceptible Staphylococcus aureus (VISA). In single-dose efficacy studies, the 1-log10 CFU kill effective dose (ED1-log kill) estimates for TD-1792 ranged from 0.049 to 2.55 mg/kg of body weight administered SC, and the bacterial burden was reduced by up to 3 log10 CFU/g from pretreatment values. Against S. aureus ATCC 33591 (MRSA), the total 24-h log10 stasis dose (EDstasis) and ED1-logkill doses for TD-1792 were 0.53 and 1.11 mg/kg/24 h, respectively, compared to 23.4 and 54.6 mg/kg/24 h for vancomycin, indicating that TD-1762 is 44- to 49-fold more potent than vancomycin. PK-PD analysis of data from single-dose and dose-fractionation studies for MRSA (ATCC 33591) demonstrated that the total-drug 24-h area under the concentration-time curve-to-MIC ratio (AUC/MIC ratio) was the best predictor of efficacy (r2 = 0.826) compared to total-drug maximum plasma concentration of drug-to-MIC ratio (Cmax/MIC ratio; r2 = 0.715) and percent time that the total-drug plasma drug concentration remains above the MIC (%Time>MIC; r2 = 0.749). The magnitudes of the total-drug AUC/MIC ratios associated with net bacterial stasis, a 1-log10 CFU reduction from baseline and near maximal effect, were 21.1, 37.2, and 51.8, respectively. PK-PD targets based on such data represent useful inputs for analyses to support dose selection decisions for clinical studies of patients.

Prediction of Human Serotonin and Norepinephrine Transporter Occupancy of Duloxetine by Pharmacokinetic/Pharmacodynamic Modeling in the Rat

Translation of central nervous system occupancy and clinical effect from animal models to humans has remained elusive for many pharmacological targets. The current studies evaluate the ability of a rodent pharmacokinetic/pharmacodynamic (PK/PD) modeling approach to translate ex vivo occupancy determined in rats to that observed after positron emission tomography (PET) imaging in humans for the dual serotonin transporter (SERT) and norepinephrine transporter (NET) inhibitor duloxetine. Ex vivo transporter occupancy in rat spinal cord was evaluated after single oral doses of 0.3 to 60 mg/kg. A novel methodology, based on the initial rates of association of transporter selective radioligands to tissue homogenates, was developed and validated for the assessment of ex vivo transporter occupancy. Duloxetine exhibited selectivity for occupancy of SERT over NET in rat spinal cord with ED50 values of 1 and 9 mg/kg, respectively. Corresponding EC50 values for the inhibition of SERT and NET based on unbound duloxetine spinal cord concentrations were 0.5 and 8 nM. An effect compartment PK/PD modeling approach was used to analyze the relationship between the time course of duloxetine plasma concentration and SERT and NET occupancy. Duloxetine inhibited SERT and NET in rat spinal cord with a plasma EC50 of 2.95 and 59.0 ng/ml, respectively. Similar plasma EC50 values for the inhibition of SERT (2.29–3.7 ng/ml) have been reported from human PET studies. This study illustrates the value of translational PK/PD modeling approaches and suggests that the preclinical modeling approach used in the current study is capable of predicting plasma concentrations associated with 50% occupancy of SERT in the human central nervous system.

Relative Contributions of Norepinephrine and Serotonin Transporters to Antinociceptive Synergy between Monoamine Reuptake Inhibitors and Morphine in the Rat Formalin Model

Multimodal analgesia is designed to optimize pain relief by coadministering drugs with distinct mechanisms of action or by combining multiple pharmacologies within a single molecule. In clinical settings, combinations of monoamine reuptake inhibitors and opioid receptor agonists have been explored and one currently available analgesic, tapentadol, functions as both a µ-opioid receptor agonist and a norepinephrine transporter inhibitor. However, it is unclear whether the combination of selective norepinephrine reuptake inhibition and µ-receptor agonism achieves an optimal antinociceptive synergy. In this study, we assessed the pharmacodynamic interactions between morphine and monoamine reuptake inhibitors that possess different affinities and selectivities for norepinephrine and serotonin transporters. Using the rat formalin model, in conjunction with measurements of ex vivo transporter occupancy, we show that neither the norepinephrine-selective inhibitor, esreboxetine, nor the serotonin-selective reuptake inhibitor, fluoxetine, produce antinociceptive synergy with morphine. Atomoxetine, a monoamine reuptake inhibitor that achieves higher levels of norepinephrine than serotonin transporter occupancy, exhibited robust antinociceptive synergy with morphine. Similarly, a fixed-dose combination of esreboxetine and fluoxetine which achieves comparable levels of transporter occupancy potentiated the antinociceptive response to morphine. By contrast, duloxetine, a monoamine reuptake inhibitor that achieves higher serotonin than norepinephrine transporter occupancy, failed to potentiate the antinociceptive response to morphine. However, when duloxetine was coadministered with the 5-HT3 receptor antagonist, ondansetron, potentiation of the antinociceptive response to morphine was revealed. These results support the notion that inhibition of both serotonin and norepinephrine transporters is required for monoamine reuptake inhibitor and opioid-mediated antinociceptive synergy; yet, excess serotonin, acting via 5-HT3 receptors, may reduce the potential for synergistic interactions. Thus, in the rat formalin model, the balance between norepinephrine and serotonin transporter inhibition influences the degree of antinociceptive synergy observed between monoamine reuptake inhibitors and morphine.

In Vivo Pharmacological Characterization of TD-4208, a Novel Lung-Selective Inhaled Muscarinic Antagonist with Sustained Bronchoprotective Effect in Experimental Animal Models

Tiotropium is currently the only once-daily, long-acting muscarinic antagonist (LAMA) approved in the United States and other countries for the treatment of chronic obstructive pulmonary disease (COPD). Glycopyrronium has shown promise as a LAMA and was recently approved for once-daily maintenance treatment of COPD in the European Union. Here, we describe the in vivo preclinical efficacy and lung selectivity of a novel inhaled muscarinic antagonist, TD-4208 (biphenyl-2-ylcarbamic acid 1-(2-{[4-(4-carbamoylpiperidin-1-ylmethyl)benzoyl]methylamino}ethyl)piperidin-4-yl ester) and compare its profile to tiotropium and glycopyrronium. In anesthetized dogs, TD-4208, along with tiotropium and glycopyrronium, produced sustained inhibition of acetylcholine-induced bronchoconstriction for up to 24 hours. In anesthetized rats, inhaled TD-4208 exhibited dose-dependent 24-hour bronchoprotection against methacholine-induced bronchoconstriction. The estimated 24-hour potency (expressed as concentration of dosing solution) was 45.0 µg/ml. The bronchoprotective potencies of TD-4208 and tiotropium were maintained after 7 days of once-daily dosing, whereas glycopyrronium showed a 6-fold loss in potency after repeat dosing. To assess systemic functional activity using a clinically relevant readout, the antisialagogue effect of compounds was also evaluated. The calculated lung selectivity index (i.e., ratio of antisialagogue and bronchoprotective potency) of TD-4208 was superior to glycopyrronium after both single and repeat dosing regimens and was superior to tiotropium after repeat dosing. In conclusion, the in vivo preclinical profile suggests that TD-4208 has the potential to be a long-acting bronchodilator for once-daily treatment of respiratory diseases. Its greater functional selectivity for the lung in preclinical models may translate to an improved tolerability profile compared with marketed muscarinic receptor antagonists.

Preclinical to Clinical Translation of CNS Transporter Occupancy of TD-9855, a Novel Norepinephrine and Serotonin Reuptake Inhibitor

Background: Monoamine reuptake inhibitors exhibit unique clinical profiles that reflect distinct engagement of the central nervous system (CNS) transporters. Methods: We used a translational strategy, including rodent pharmacokinetic/pharmacodynamic modeling and positron emission tomography (PET) imaging in humans, to establish the transporter profile of TD-9855, a novel norepinephrine and serotonin reuptake inhibitor. Results: TD-9855 was a potent inhibitor of norepinephrine (NE) and serotonin 5-HT uptake in vitro with an inhibitory selectivity of 4- to 10-fold for NE at human and rat transporters. TD-9855 engaged norepinephrine transporters (NET) and serotonin transporters (SERT) in rat spinal cord, with a plasma EC50 of 11.7ng/mL and 50.8ng/mL, respectively, consistent with modest selectivity for NET in vivo. Accounting for species differences in protein binding, the projected human NET and SERT plasma EC50 values were 5.5ng/mL and 23.9ng/mL, respectively. A single-dose, open-label PET study (4–20mg TD-9855, oral) was conducted in eight healthy males using the radiotracers [11C]-3-amino-4- [2-[(di(methyl)amino)methyl]phenyl]sulfanylbenzonitrile for SERT and [11C]-(S,S)-methylreboxetine for NET. The long pharmacokinetic half-life (30–40h) of TD-9855 allowed for sequential assessment of SERT and NET occupancy in the same subject. The plasma EC50 for NET was estimated to be 1.21ng/mL, and at doses of greater than 4mg the projected steady-state NET occupancy is high (>75%). After a single oral dose of 20mg, SERT occupancy was 25 (±8)% at a plasma level of 6.35ng/mL. Conclusions: These data establish the CNS penetration and transporter profile of TD-9855 and inform the selection of potential doses for future clinical evaluation.

Comparative efficacy of AHU-377, a potent neprilysin inhibitor, in two rat models of volume-dependent hypertension

Background Progressive hypertension and deteriorating renal function are hallmarks of cardio-renal syndromes. Historically, the deoxycorticosterone acetate (DOCA)-salt model has been used to assess the therapeutic potential of antihypertensives in the setting of low renin and volume-dependent hypertension. Dahl-salt-sensitive (Dahl-SS) rats represent a genetic model of volumedependent hypertension and possess similar features to the DOCA model, including higher natriuretic peptide tone. Neprilysin inhibitors (NEPi) prevent the degradation of natriuretic peptides and activate cGMP signalling pathways that regulate volume and blood pressure. Antihypertensive effects of NEPi have been demonstrated in both DOCA and Dahl-SS models; however, the relative efficacy of NEPi in these two models has not been studied directly. Here, we characterized the natriuretic peptide tone in DOCA and Dahl-SS rats and compared antihypertensive effects of a NEPi, (AHU-377).

Pharmacological properties of TD-6301, a novel bladder selective muscarinic receptor antagonist.

Existing antimuscarinic drugs for overactive bladder have high affinity for M(3)/M(1) muscarinic receptors and consequently produce M(3)/M(1)-mediated adverse effects including dry mouth, constipation, mydriasis and somnolence. TD-6301 is a M(2/4) muscarinic receptor-selective antagonist developed for the treatment of overactive bladder. The present studies characterize the in vitro and in vivo pharmacological properties of this molecule in comparison to other marketed antimuscarinics agents. In radioligand binding studies, TD-6301 was found to possess high affinity for human M(2) muscarinic receptor (K(i)=0.36 nM) and was 31, 36, 2 and 128-fold selective for the human M(2) muscarinic receptor compared to the M(1), M(3), M(4) and M(5) muscarinic receptors, respectively. The in vivo bladder selectivity of TD-6301 in rats was determined to be 26, 28, >100, 16 and 0.4-fold, respectively, assessed by comparing its potency for inhibition of volume-induced bladder contractions to that for inhibition of oxotremorine-induced salivation, inhibition of small-intestinal transit, decreases in locomotor activity, increases in pupil diameter and increases in heart rate. TD-6301 was more potent in inhibiting volume-induced bladder contractions (ID(50)=0.075 mg/kg) compared to oxotremorine-induced salivation (ID(50)=1.0 mg/kg) resulting in a bladder/salivary gland selectivity ratio greater than that observed for tolterodine, oxybutynin, darifenacin and solifenacin. The preclinical properties of TD-6301 suggest that this molecule is likely to be efficacious in overactive bladder patients with a lower propensity to cause M(3) muscarinic receptor mediated adverse effects.

Discovery of N-substituted-endo-3-(8-aza-bicyclo[3.2.1]oct-3-yl)-phenol and -phenyl carboxamide series of μ-opioid receptor antagonists

Gastrointestinal dysfunction as a consequence of the use of opioid analgesics is of significant clinical concern. First generation drugs to treat these opioid-induced side-effects were limited by their negative impact on opioid receptor agonist-induced analgesia. Second generation therapies target a localized, peripherally-restricted, non-CNS penetrant drug distribution of opioid receptor antagonists. Herein we describe the discovery of the N-substituted-endo-3-(8-aza-bicyclo[3.2.1]oct-3-yl)-phenol and -phenyl carboxamide series of μ-opioid receptor antagonists. This report highlights the discovery of the key μ-opioid receptor antagonist pharmacophore and the optimization of in vitro metabolic stability through the application of a phenol bioisostere. The compounds 27a and 31a with the most attractive in vitro profile, formed the basis for the application of Theravance Biopharmas multivalent approach to drug discovery to afford the clinical compound axelopran (TD-1211), targeted for the treatment of opioid-induced constipation.