Behavioral pharmacology of the mixed-action delta-selective opioid receptor agonist BBI-11008: studies on acute, inflammatory and neuropathic pain, respiration, and drug self-administration

Rationale and objectives: The present study characterized the behavioral pharmacology of a novel, mixed-action delta-selective (78:1) opioid receptor agonist, BBI-11008. This glycopeptide drug candidate was tested in assays assessing antinociception (acute, inflammatory, and neuropathic pain-like conditions) and side-effect endpoints (respiratory depression and drug self-administration). Results: BBI-11008 had a 78-fold greater affinity for the delta opioid receptor than the mu receptor, and there was no binding to the kappa opioid receptor. BBI-11008 (3.2–100; 10–32 mg kg⁻¹, i.v.) and morphine (1–10; 1–3.2 mg kg⁻¹, i.v.) produced antinociceptive and anti-allodynic effects in assays of acute thermal nociception and complete Freund’s adjuvant (CFA)-induced inflammatory pain, with BBI-11008 being less potent than morphine in both assays. BBI-11008 (1–18 mg kg⁻¹, i.v.) had similar efficacy to gabapentin (10–56 mg kg⁻¹, i.v.) in a spinal nerve ligation (SNL) model of neuropathic pain. In the respiration assay, with increasing %CO₂ exposure, BBI-11008 produced an initial increase (32 mg kg⁻¹, s.c.) and then decrease (56 mg kg⁻¹, s.c.) in minute volume (MV) whereas morphine (3.2–32 mg kg⁻¹, s.c.) produced dose-dependent decreases in MV. In the drug self-administration procedure, BBI-11008 did not maintain self-administration at any dose tested. Conclusions: These results suggest that the glycopeptide drug candidate possesses broad-spectrum antinociceptive and anti-allodynic activity across a range of pain-like conditions. Relative to morphine or fentanyl, the profile for BBI-11008 in the respiration and drug self-administration assays suggests that BBI-11008 may have less pronounced deleterious side effects. Continued assessment of this compound is warranted.