The novel μ‐opioid receptor agonist PZM21 depresses respiration and induces tolerance to antinociception

Abstract

Background and PurposePZM21 is a novel μ‐opioid receptor ligand that has been reported to induce minimal arrestin recruitment and be devoid of the respiratory depressant effects characteristic of classical μ receptor ligands such as morphine. We have re‐examined the signalling profile of PZM21 and its ability to depress respiration.Experimental ApproachG protein (Gi) activation and arrestin‐3 translocation were measured in vitro, using BRET assays, in HEK 293 cells expressing μ receptors. Respiration (rate and tidal volume) was measured in awake, freely moving mice by whole‐body plethysmography, and antinociception was measured by the hot plate test.Key ResultsPZM21 (10−9 – 3 × 10−5 M) produced concentration‐dependent Gi activation and arrestin‐3 translocation. Comparison with responses evoked by morphine and DAMGO revealed that PZM21 was a low efficacy agonist in both signalling assays. PZM21 (10–80 mg·kg−1) depressed respiration in a dose‐dependent manner. The respiratory depression was due to a decrease in the rate of breathing not a decrease in tidal volume. On repeated daily administration of PZM21 (twice daily doses of 40 mg·kg−1), complete tolerance developed to the antinociceptive effect of PZM21 over 3 days but no tolerance developed to its respiratory depressant effect.Conclusion and ImplicationsThese data demonstrate that PZM21 is a low efficacy μ receptor agonist for both G protein and arrestin signalling. Contrary to a previous report, PZM21 depresses respiration in a manner similar to morphine, the classical opioid receptor agonist.

The G‐protein‐biased agents PZM21 and TRV130 are partial agonists of μ‐opioid receptor‐mediated signalling to ion channels

“…They also showed that PZM21 had substantially lower efficacy than DAMGO, using a BRET-based assay to detect the dissociation of G αi1 and G γ2 (Hill et al, 2018). Our data are also consistent with another recent publication, which using conformational biosensor binding to the purified μ receptor, showed that PZM21 had lower efficacy than morphine, or fentanyl, two opioids used clinically (Livingston et al, 2018).…”

“…A recent report showed that PZM21 induced respiratory depression similar to that evoked by morphine (Hill et al, 2018), which is in contrast to the earlier report describing this biased agonist (Manglik et al, 2016).…”

“…A recent report showed that PZM21 induced respiratory depression similar to that evoked by morphine (Hill et al, ), which is in contrast to the earlier report describing this biased agonist (Manglik et al, ). They also showed that PZM21 had substantially lower efficacy than DAMGO, using a BRET‐based assay to detect the dissociation of G αi1 and G γ2 (Hill et al, ).…”

“…A recent report showed that PZM21 induced respiratory depression similar to that evoked by morphine (Hill et al, ), which is in contrast to the earlier report describing this biased agonist (Manglik et al, ). They also showed that PZM21 had substantially lower efficacy than DAMGO, using a BRET‐based assay to detect the dissociation of G αi1 and G γ2 (Hill et al, ). Our data are also consistent with another recent publication, which using conformational biosensor binding to the purified μ receptor, showed that PZM21 had lower efficacy than morphine, or fentanyl, two opioids used clinically (Livingston et al, ).…”

Molecular mechanisms of fentanyl mediated β-arrestin biased signaling

“…where ligand potency increased as a function of aliphatic group size (Figure 6c). One compound in particular, propyl substituted FD-3, retained partial-agonist properties comprising a mid-nanomolar EC 50 with a maximal coupling efficiency that is approximately 67% that of morphine [16] and comparable to the Figure 6c). Taken together with our prior mutational analysis, these experiments suggest that the n-aniline ring is required for fentanyl mediated β-arrestin, but not Gi coupling, and this effect is mediated through an interaction with M153 3.36 .…”