Gut-Selective Design of Orally Administered Izencitinib (TD-1473) Limits Systemic Exposure and Effects of Janus Kinase Inhibition in Nonclinical Species.

Izencitinib (TD-1473), an oral, gut-selective pan-Janus kinase (JAK) inhibitor under investigation for treatment of inflammatory bowel diseases, was designed for optimal efficacy in the gastrointestinal tract while minimizing systemic exposures and JAK-related safety findings. The nonclinical safety of izencitinib was evaluated in rat and dog repeat-dose and rat and rabbit reproductive and developmental toxicity studies. Systemic exposures were compared with JAK inhibitory potency to determine effects at or above pharmacologic plasma concentrations (≥1× plasma average plasma concentration [Cave]:JAK 50% inhibitory concentration [IC50] ratio). In rats and dogs, 1000 and 30 mg/kg/day izencitinib, respectively, produced minimal systemic findings (ie, red/white cell changes) and low systemic concentrations (approximately 1× plasma Cave:JAK IC50 ratio) with an 8× nonclinical:clinical systemic area under the curve (AUC) margin compared with exposures at the highest clinically tested dose (300 mg, quaque die, once daily, phase 1 study in healthy volunteers). In dogs, it was possible to attain sufficient systemic exposures to result in immunosuppression characteristic of systemic JAK inhibition, but at high AUC margins (43×) compared with systemic exposures observed at the highest tested dose in humans. No adverse findings were observed in the gastrointestinal tract or systemic tissues. Izencitinib did not affect male or female fertility. Izencitinib did not affect embryonic development in rats and rabbits as commonly reported with systemic JAK inhibition, consistent with low maternal systemic concentrations (2-6× plasma Cave:JAK IC50 ratio, 10-33× nonclinical:clinical AUC margin) and negligible fetal exposures. In conclusion, the izencitinib gut-selective approach resulted in minimal systemic findings in nonclinical species at pharmacologic, clinically relevant systemic exposures, highlighting the impact of organ-selectivity in reducing systemic safety findings.

Discovery of Axelopran (TD-1211): A Peripherally Restricted µ-Opioid Receptor Antagonist.

The effects of opioids in the central nervous system (CNS) provide significant benefit in the treatment of pain but can also lead to physical dependence and addiction, which has contributed to a growing opioid epidemic in the United States. Gastrointestinal dysfunction is an additional serious consequence of opioid use, and this can be treated with a localized drug distribution of a non-CNS penetrant, peripherally restricted opioid receptor antagonist. Herein, we describe the application of Theravance's multivalent approach to drug discovery coupled with a physicochemical property design strategy by which the N-substituted-endo-3-(8-aza-bicyclo[3.2.1]oct-3-yl)-phenyl carboxamide series of µ-opioid receptor antagonists was optimized to afford the orally absorbed, non-CNS penetrant, Phase 3 ready clinical compound axelopran (TD-1211) 19i as a potential treatment for opioid-induced constipation.

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 Biopharma's multivalent approach to drug discovery to afford the clinical compound axelopran (TD-1211), targeted for the treatment of opioid-induced constipation.

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.

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 ED(50) values of 1 and 9 mg/kg, respectively. Corresponding EC(50) 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 EC(50) of 2.95 and 59.0 ng/ml, respectively. Similar plasma EC(50) 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.

Pharmacodynamics of TD-1792, a novel glycopeptide-cephalosporin heterodimer antibiotic used against Gram-positive bacteria, in a neutropenic murine thigh model.

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-log(10) CFU kill effective dose (ED(1-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 log(10) CFU/g from pretreatment values. Against S. aureus ATCC 33591 (MRSA), the total 24-h log(10) stasis dose (ED(stasis)) and ED(1-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 (r(2) = 0.826) compared to total-drug maximum plasma concentration of drug-to-MIC ratio (Cmax/MIC ratio; r(2) = 0.715) and percent time that the total-drug plasma drug concentration remains above the MIC (%Time>MIC; r(2) = 0.749). The magnitudes of the total-drug AUC/MIC ratios associated with net bacterial stasis, a 1-log(10) 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.

5-HT(4) receptor agonist mediated enhancement of cognitive function in vivo and amyloid precursor protein processing in vitro: A pharmacodynamic and pharmacokinetic assessment.

There remains an urgent need for therapeutic agents that provide improved symptomatic treatment and attenuate disease progression in patients with Alzheimer's disease (AD). 5-HT(4) receptors are widely expressed in those CNS areas which receive substantial cholinergic input and are involved in cognition. The ability of 5-HT(4) receptor agonists to increase acetylcholine (ACh) release and reduce cognitive impairment in both animals and humans has been demonstrated. In addition, 5-HT(4) receptor agonist modulation of levels of the amyloid precursor protein (APP) derived peptides, soluble amyloid precursor protein (sAPPα) and amyloid beta protein (Aß) in the CNS has been reported. In this study, the preclinical properties of three structurally-distinct 5-HT(4) receptor selective agonists, PRX-03140, velusetrag and TD-8954, were studied to assess their potential for symptomatic and disease-modifying benefit in the treatment of AD. All three compounds exhibited high affinity for the rat 5-HT(4) receptor but could be discriminated on the basis of their agonist activity. In cAMP accumulation and sAPPα secretion assays using recombinant HEK293f-5-HT(4(d))-APP(695) cells, velusetrag and TD-8954 were potent, full agonists, relative to 5-HT, whereas PRX-03140 was a partial agonist (intrinsic activity 18%, relative to 5-HT). In a guinea pig colon isolated tissue preparation, TD-8954 exhibited lower intrinsic activity than velusetrag, and PRX-03140 had negligible agonist activity. In the rat Morris water maze (MWM) cognition test, velusetrag and TD-8954 (0.1 mg/kg), but not PRX-03140 (0.03-1 mg/kg), significantly reversed the scopolamine-induced spatial learning deficit via activation of 5-HT(4) receptors. Coadministration of subefficacious doses of the acetylcholinesterase inhibitor (AChEi), donepezil (0.1 mg/kg, i.p.), and either velusetrag or TD-8954 (0.01 mg/kg i.p.) resulted in reversal of the scopolamine-induced cognitive deficit. Pharmacokinetic data indicated that the CNS penetration for all three 5-HT(4) receptor agonists was relatively low. However, the pharmacodynamic-pharmacokinetic relationships in the MWM model for velusetrag and TD-8954 were consistent with their respective receptor pharmacology (binding affinity and intrinsic efficacy) and CNS penetration properties. Collectively, these findings support a potential role for potent and efficacious 5-HT(4) receptor agonists in the treatment of AD.

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.

Efficacy of telavancin in a murine model of bacteraemia induced by methicillin-resistant Staphylococcus aureus.

OBJECTIVES: The efficacy of telavancin, a bactericidal lipoglycopeptide, was compared with vancomycin against methicillin-resistant Staphylococcus aureus (MRSA) in an immunocompromised murine model of bacteraemia. METHODS: Immunocompromised mice were inoculated intraperitoneally with S. aureus ATCC 33591 and treated with two subcutaneous doses (once every 12 h) of vehicle or test compound. Mouse pharmacokinetic data were generated and used to choose doses of telavancin (40 mg/kg) and vancomycin (110 mg/kg) in order to equate clinical exposures. Reduction in bacterial titre (in blood and spleen) and mortality were the two pharmacodynamic endpoints of the study. RESULTS: Mortality was 100% in animals treated with vehicle or vancomycin but was significantly lower (7%) in telavancin-treated animals. Telavancin produced significantly greater reductions in blood and spleen bacterial titres compared with vancomycin. CONCLUSIONS: The data described here demonstrate that telavancin's in vivo bactericidal activity is superior to that of vancomycin against a single strain of MRSA and results in successful infection resolution and, consequently, improved survival in the murine bacteraemia model.

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.

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.