Conrad L. Cowan

A G Protein-Biased Ligand at the μ-Opioid Receptor Is Potently Analgesic with Reduced Gastrointestinal and Respiratory Dysfunction Compared with Morphine

The concept of ligand bias at G protein-coupled receptors broadens the possibilities for agonist activities and provides the opportunity to develop safer, more selective therapeutics. Morphine pharmacology in β-arrestin-2 knockout mice suggested that a ligand that promotes coupling of the μ-opioid receptor (MOR) to G proteins, but not β-arrestins, would result in higher analgesic efficacy, less gastrointestinal dysfunction, and less respiratory suppression than morphine. Here we report the discovery of TRV130 ([(3-methoxythiophen-2-yl)methyl]({2-[(9R)-9-(pyridin-2-yl)-6-oxaspiro[4.5]decan-9-yl]ethyl})amine), a novel MOR G protein-biased ligand. In cell-based assays, TRV130 elicits robust G protein signaling, with potency and efficacy similar to morphine, but with far less β-arrestin recruitment and receptor internalization. In mice and rats, TRV130 is potently analgesic while causing less gastrointestinal dysfunction and respiratory suppression than morphine at equianalgesic doses. TRV130 successfully translates evidence that analgesic and adverse MOR signaling pathways are distinct into a biased ligand with differentiated pharmacology. These preclinical data suggest that TRV130 may be a safer and more tolerable therapeutic for treating severe pain.

First Clinical Experience With TRV130: Pharmacokinetics and Pharmacodynamics in Healthy Volunteers

TRV130 is a G protein‐biased ligand at the µ‐opioid receptor. In preclinical studies it was potently analgesic while causing less respiratory depression and gastrointestinal dysfunction than morphine, suggesting unique benefits in acute pain management. A first‐in‐human study was conducted with ascending doses of TRV130 to explore its tolerability, pharmacokinetics, and pharmacodynamics in healthy volunteers. TRV130 was well‐tolerated over the dose range 0.15 to 7 mg administered intravenously over 1 hour. TRV130 geometric mean exposure and Cmax were dose‐linear, with AUC0–inf of 2.52 to 205.97 ng h/mL and Cmax of 1.04 to 102.36 ng/mL across the dose range tested, with half‐life of 1.6–2.7 hours. A 1.5 mg dose of TRV130 was also well‐tolerated when administered as 30, 15, 5, and 1 minute infusions. TRV130 pharmacokinetics were modestly affected by CYP2D6 phenotype: clearance was reduced by 53% in CYP2D6 poor metabolizers.TRV130 caused dose‐ and exposure‐related pupil constriction, confirming central compartment µ‐opioid receptor engagement. Marked pupil constriction was noted at 2.2, 4, and 7 mg doses. Nausea and vomiting observed at the 7 mg dose limited further dose escalation. These findings suggest that TRV130 may have a broad margin between doses causing µ‐opioid receptor‐mediated pharmacology and doses causing µ‐opioid receptor‐mediated intolerance.

Biased ligands: pathway validation for novel GPCR therapeutics

G protein-coupled receptors (GPCRs), in recent years, have been shown to signal via multiple distinct pathways. Furthermore, biased ligands for some receptors can differentially stimulate or inhibit these pathways versus unbiased endogenous ligands or drugs. Biased ligands can be used to gain a deeper understanding of the molecular targets and cellular responses associated with a GPCR, and may be developed into therapeutics with improved efficacy, safety and/or tolerability. Here we review examples and approaches to pathway validation that establish the relevance and therapeutic potential of distinct pathways that can be selectively activated or blocked by biased ligands.

Long-Term Biased β-Arrestin Signaling Improves Cardiac Structure and Function in Dilated Cardiomyopathy

Background: Biased agonism of the angiotensin II receptor is known to promote cardiac contractility. Our laboratory indicated that these effects may be attributable to changes at the level of the myofilaments. However, these signaling mechanisms remain unknown. Because a common finding in dilated cardiomyopathy is a reduction in the myofilament-Ca2+ response, we hypothesized that &bgr;-arrestin signaling would increase myofilament-Ca2+ responsiveness in a model of familial dilated cardiomyopathy and improve cardiac function and morphology. Methods: We treated a dilated cardiomyopathy–linked mouse model expressing a mutant tropomyosin (Tm-E54K) for 3 months with either TRV120067, a &bgr;-arrestin 2–biased ligand of the angiotensin II receptor, or losartan, an angiotensin II receptor blocker. At the end of the treatment protocol, we assessed cardiac function using echocardiography, the myofilament-Ca2+ response of detergent-extracted fiber bundles, and used proteomic approaches to understand changes in posttranslational modifications of proteins that may explain functional changes. We also assessed signaling pathways altered in vivo and by using isolated myocytes. Results: TRV120067- treated Tm-E54K mice showed improved cardiac structure and function, whereas losartan-treated mice had no improvement. Myofilaments of TRV120067-treated Tm-E54K mice had significantly improved myofilament-Ca2+ responsiveness, which was depressed in untreated Tm-E54K mice. We attributed these changes to increased MLC2v and MYPT1/2 phosphorylation seen only in TRV120067-treated mice. We found that the functional changes were attributable to an activation of ERK1/2-RSK3 signaling, mediated through &bgr;-arrestin, which may have a novel role in increasing MLC2v phosphorylation through a previously unrecognized interaction of &bgr;-arrestin localized to the sarcomere. Conclusions: Long-term &bgr;-arrestin 2–biased agonism of the angiotensin II receptor may be a viable approach to the treatment of dilated cardiomyopathy by not only preventing maladaptive signaling, but also improving cardiac function by altering the myofilament-Ca2+ response via &bgr;-arrestin signaling pathways.

Cardiac myosin light chain phosphorylation and inotropic effects of a biased ligand, TRV120023, in a dilated cardiomyopathy model

AIMS Therapeutic approaches to treat familial dilated cardiomyopathy (DCM), which is characterized by depressed sarcomeric tension and susceptibility to Ca(2+)-related arrhythmias, have been generally unsuccessful. Our objective in the present work was to determine the effect of the angiotensin II type 1 receptor (AT1R) biased ligand, TRV120023, on contractility of hearts of a transgenic mouse model of familial DCM with mutation in tropomyosin at position 54 (TG-E54K). Our rationale is based on previous studies, which have supported the hypothesis that biased G-protein-coupled receptor ligands, signalling via β-arrestin, increase cardiac contractility with no effect on Ca(2+) transients. Our previous work demonstrated that the biased ligand TRV120023 is able to block angiotensin-induced hypertrophy, while promoting an increase in sarcomere Ca(2+) response. METHODS AND RESULTS We tested the hypothesis that the depression in cardiac function associated with DCM can be offset by infusion of the AT1R biased ligand, TRV120023. We intravenously infused saline, TRV120023, or the unbiased ligand, losartan, for 15 min in TG-E54K and non-transgenic mice to obtain left ventricular pressure-volume relations. Hearts were analysed for sarcomeric protein phosphorylation. Results showed that the AT1R biased ligand increases cardiac performance in TG-E54K mice in association with increased myosin light chain-2 phosphorylation. CONCLUSION Treatment of mice with an AT1R biased ligand, acting via β-arrestin signalling, is able to induce an increase in cardiac contractility associated with an increase in ventricular myosin light chain-2 phosphorylation. AT1R biased ligands may prove to be a novel inotropic approach in familial DCM.

TRV0109101, a G protein-biased agonist of the µ-opioid receptor, does not promote opioid-induced mechanical allodynia following chronic administration

Prescription opioids are a mainstay in the treatment of acute moderate to severe pain. However, chronic use leads to a host of adverse consequences including tolerance and opioid-induced hyperalgesia (OIH), leading to more complex treatment regimens and diminished patient compliance. Patients with OIH paradoxically experience exaggerated nociceptive responses instead of pain reduction after chronic opioid usage. The development of OIH and tolerance tend to occur simultaneously and, thus, present a challenge when studying the molecular mechanisms driving each phenomenon. We tested the hypothesis that a G protein-biased µ-opioid peptide receptor (MOPR) agonist would not induce symptoms of OIH, such as mechanical allodynia, following chronic administration. We observed that the development of opioid-induced mechanical allodynia (OIMA), a model of OIH, was absent in β-arrestin1−/− and β-arrestin2−/− mice in response to chronic administration of conventional opioids such as morphine, oxycodone and fentanyl, whereas tolerance developed independent of OIMA. In agreement with the β-arrestin knockout mouse studies, chronic administration of TRV0109101, a G protein-biased MOPR ligand and structural analog of oliceridine, did not promote the development of OIMA but did result in drug tolerance. Interestingly, following induction of OIMA by morphine or fentanyl, TRV0109101 was able to rapidly reverse allodynia. These observations establish a role for β-arrestins in the development of OIH, independent of tolerance, and suggest that the use of G protein-biased MOPR ligands, such as oliceridine and TRV0109101, may be an effective therapeutic avenue for managing chronic pain with reduced propensity for opioid-induced hyperalgesia.