No abstract

Opioids provide powerful analgesia but also efficacy-limiting adverse effects, including severe nausea, vomiting, and respiratory depression, by activating μ-opioid receptors. Preclinical models suggest that differential activation of signaling pathways downstream of these receptors dissociates analgesia from adverse effects; however, this has not yet translated to a treatment with an improved therapeutic index. Thirty healthy men received single intravenous injections of the biased ligand TRV130 (1.5, 3, or 4.5mg), placebo, or morphine (10mg) in a randomized, double-blind, crossover study. Primary objectives were to measure safety and tolerability (adverse events, vital signs, electrocardiography, clinical laboratory values), and analgesia (cold pain test) versus placebo. Other measures included respiratory drive (minute volume after induced hypercapnia), subjective drug effects, and pharmacokinetics. Compared to morphine, TRV130 (3, 4.5mg) elicited higher peak analgesia (105, 116 seconds latency vs 75 seconds for morphine, P<.02), with faster onset and similar duration of action. More subjects doubled latency or achieved maximum latency (180 seconds) with TRV130 (3, 4.5mg). Respiratory drive reduction was greater after morphine than any TRV130 dose (-15.9 for morphine versus -7.3, -7.6, and -9.4 h*L/min, P<.05). More subjects experienced severe nausea after morphine (n=7) than TRV130 1.5 or 3mg (n=0, 1), but not 4.5mg (n=9). TRV130 was generally well tolerated, and exposure was dose proportional. Thus, in this study, TRV130 produced greater analgesia than morphine at doses with less reduction in respiratory drive and less severe nausea. This demonstrates early clinical translation of ligand bias as an important new concept in receptor-targeted pharmacotherapy.

Efficacy of conventional opioids can be limited by adverse events (AEs). TRV130 is a structurally novel biased ligand of the μ-opioid receptor that activates G protein signaling with little β-arrestin recruitment. In this phase 2, randomized, placebo- and active-controlled study, we investigated the efficacy and tolerability of TRV130 in acute pain after bunionectomy. We used an adaptive study design in which 144 patients experiencing moderate-to-severe acute pain after bunionectomy were randomized to receive double-blind TRV130, placebo, or morphine in a pilot phase. After pilot phase analysis, 195 patients were randomized to receive double-dummy TRV130 0.5, 1, 2, or 3 mg every 3 hours (q3h); placebo; or morphine 4 mg q4h intravenously. The primary end point was the time-weighted average change in numeric rating scale pain intensity over the 48-hour treatment period. Secondary end points included stopwatch and categorical assessments of pain relief. Safety and tolerability were also assessed. TRV130 2 and 3 mg q3h, and morphine 4 mg q4h produced statistically greater mean reductions in pain intensity than placebo over 48 hours (P < 0.005). TRV130 at 2 and 3 mg produced significantly greater categorical pain relief than morphine (P < 0.005) after the first dose, with meaningful pain relief occurring in under 5 minutes. TRV130 produced no serious AEs, with tolerability similar to morphine. These results demonstrate that TRV130 rapidly produces profound analgesia in moderate-to-severe acute pain, suggesting that G-protein-biased μ-opioid receptor activation is a promising target for development of novel analgesics.

Abstract-Acute ␤-adrenergic stimulation enhances cardiac contractility, accelerates muscle relaxation, and amplifies the inotropic and lusitropic response to increased stimulation frequency. These effects are modulated by phosphorylation of calcium handling and myofilament proteins such as troponin I (TnI) by protein kinase A (PKA). To more directly delineate the role of TnI PKA phosphorylation, transgenic mice were generated that overexpress cardiac TnI in which the serine residues normally targeted by PKA are mutated to aspartic acid to mimic constitutive phosphorylation (TnIDD 22,23 ). Native cardiac TnI was near completely replaced in one transgenic line as assessed by in vitro phosphorylation, and this led to reduced calcium sensitivity of myofibrillar MgATPase, as expected. TnIDD 22,23 mice had mildly enhanced basal systolic and diastolic function, and displayed marked augmentation of frequency-dependent inotropy and relaxation, with a peak frequency response 2-fold greater in mutants than controls (PϽ0.005). Increasing afterload prolonged relaxation more in nontransgenic than TnIDD 22,23 (PϽ0.02), whereas contractile responses to afterload were similar between these strains. Isoproterenol treatment eliminated the differential force-frequency and afterload response between TnIDD 22,23 and controls. In contrast to in vivo studies, isolated isometric trabeculae from nontransgenic and TnIDD 22,23 mice had similar basal, isoproterenol-, and frequency-stimulated function, suggesting that muscle shortening may be important to TnI PKA effects. These results support a novel role for cardiac TnI PKA phosphorylation in the rate-dependent enhancement of systolic and diastolic function in vivo and afterload sensitivity of relaxation. These results have implications for cardiac failure in which force-frequency modulation is blunted and afterload relaxation sensitivity increased in association with diminished PKA TnI phosphorylation. Key Words: troponin I Ⅲ protein kinase A Ⅲ cardiac function Ⅲ myofilament S timulation of cardiac ␤-adrenergic receptors augments myocardial contractility, accelerates the rate of force development and relaxation, and amplifies the positive inotropic and lusitropic effects of higher stimulation frequency. 1 In addition, the load dependence of cardiac relaxation is influenced by cardiac contractility and level of ␤-stimulation. 2,3 These effects are thought to be mediated by the phosphorylation of target proteins by protein kinase A (PKA), including the myofilament proteins cardiac troponin I (cTnI) and myosin binding protein-C (MyBP-C), sarcoplasmic reticulum (SR) regulatory proteins phospholamban (PLB) and ryanodine receptor channel, and the sarcolemmal calcium channel. The net result is greater availability of intracellular calcium during systole, more rapid calcium removal from the cytosol into the SR, and enhanced calcium dissociation from myofilaments during diastole (reviewed by Bers 4 ). Of these PKA target proteins, strong evidence exists for potent regulation by PLB and calcium ch...