Assessment of potentially abuse-related events in two phase 3 studies of NKTR-181, a novel opioid analgesic, using the MADDERS® system (Misuse, Abuse, and Diversion Drug Event Reporting System)

In vivo and in vitro Characterization of a Partial Mu Opioid Receptor Agonist, NKTR-181, Supports Future Therapeutic Development

Mu opioid receptor (MOPr) agonists are well-known and frequently used clinical analgesics but are also rewarding due to their highly addictive and often abusive properties. This may lead to opioid use disorder (OUD) a disorder that effects millions of people worldwide. Therefore, novel compounds are urgently needed to treat OUD. As opioids are effective analgesics and OUD often occurs in conjunction with chronic pain, these novel compounds may be opioids, but they must have a low abuse liability. This could be mediated by diminishing or slowing blood-brain barrier transport, slowing target receptor binding kinetics, and showing a long half-life. NKTR-181 is a PEGylated oxycodol and a MOPr agonist that has slowed blood-brain barrier transport, a long half-life, and diminished likeability in clinical trials. In this study, we examined the signaling and behavioral profile of NKTR-181 in comparison with oxycodone to determine whether further therapeutic development of this compound may be warranted. For this preclinical study, we used a number of in vitro and in vivo assays. The signaling profile of NKTR-181 was determined by the electrophysiological assessment of MOPr-Ca2+ channel inhibition in the nociceptive neurons of rodent dorsal root ganglia. Heterologous cell-based assays were used to assess biased agonism and receptor trafficking. Different rodent behavioral models were used to define the NKTR-181-induced relief of effective and reflexive nociception and drug-seeking behavior as assessed by an intravenous self-administration (IVSA) of NKTR-181. We found that NKTR-181 and oxycodone are partial agonists in G-protein signaling and Ca2+ channel inhibition assays and promote limited MOPr desensitization. However, NKTR-181 inhibits Ca2+ channels by a different mechanism than oxycodone and induces a different pattern of arrestin recruitment. In addition, NKTR-181 has a slower receptor on-rate and a slower rate of Ca2+ channel coupling than oxycodone. This signaling profile is coupled with a slower onset of antinociception and limited drug-seeking behavior in comparison with oxycodone. Together with its known long half-life and slow blood-brain barrier transport, these data suggest that NKTR-181 could be further studied as a pharmacotherapeutic treatment modality for OUD.

Long-term Safety and Tolerability of NKTR-181 in Patients with Moderate to Severe Chronic Low Back Pain or Chronic Noncancer Pain: A Phase 3 Multicenter, Open-Label, 52-Week Study (SUMMIT-08 LTS)

OBJECTIVE

To evaluate the long-term safety of NKTR-181, a novel mu-opioid receptor agonist that may have reduced human abuse potential, in patients with moderate to severe chronic low back pain (CLBP) or other chronic noncancer pain (CNP).

DESIGN

Uncontrolled, multicenter, open-label, long-term study of NKTR-181 comprised of three periods: screening (≤21 days), treatment (52 weeks), and safety follow-up (∼14 days after the last dose of NKTR-181).

SETTING

Multicenter, long-term clinical research study.

METHODS

NKTR-181 administered at doses of 100-600 mg twice daily (BID) was evaluated in opioid-naïve and opioid-experienced patients. Patients were enrolled de novo or following completion of the randomized, placebo-controlled phase 3 efficacy study (SUMMIT-07). Safety assessments included adverse event documentation, measurements of opioid withdrawal, and clinical laboratory tests. Effectiveness was assessed using the modified Brief Pain Inventory Short Form (mBPI-SF).

RESULTS

The study enrolled 638 patients. The most frequently reported treatment-emergent adverse events (TEAEs) were constipation (26%) and nausea (12%). Serious TEAEs, reported in 5% of patients, were deemed by investigators to be unrelated to NKTR-181. There were no deaths or reported cases of respiratory depression. A sustained reduction in mBPI-SF pain intensity and pain interference from baseline to study termination was observed throughout treatment. Only 2% of patients discontinued NKTR-181 due to lack of efficacy, and 11% discontinued due to treatment-related AEs. NKTR-181 doses of up to 600 mg BID were generally well tolerated, and patients experienced low rates of opioid-related adverse events.

CONCLUSIONS

The study results support the premise that NKTR-181 is a safe and effective option for patients with moderate to severe CLBP or CNP.

Peripherally acting opioid analgesics and peripherally-induced analgesia

The management of pain, particularly chronic pain, is still an area of medical need. In this context, opioids remain a gold standard for the treatment of pain. However, significant side effects, mainly of central origin, limit their clinical use. Here, we review recent progress to improve the therapeutic and safety profiles of opioids for pain management. Characterization of peripheral opioid-mediated pain mechanisms have been a key component of this process. Several studies identified peripheral µ, δ, and κ opioid receptors (MOR, DOR, and KOR, respectively) and nociceptin/orphanin FQ (NOP) receptors as significant players of opioid-mediated antinociception, able to achieve clinically significant effects independently of any central action. Following this, particularly from a medicinal chemistry point of view, main efforts have been directed towards the peripheralization of opioid receptor agonists with the objective of optimizing receptor activity and minimizing central exposure and the associated undesired effects. These activities have allowed the characterization of a great variety of compounds and investigational drugs that show low central nervous system (CNS) penetration (and therefore a reduced side effect profile) yet maintaining the desired opioid-related peripheral antinociceptive activity. These include highly hydrophilic/amphiphilic and massive molecules unable to easily cross lipid membranes, substrates of glycoprotein P (a extrusion pump that avoids CNS penetration), nanocarriers that release the analgesic agent at the site of inflammation and pain, and pH-sensitive opioid agonists that selectively activate at those sites (and represent a new pharmacodynamic paradigm). Hopefully, patients with pain will benefit soon from the incorporation of these new entities.

Measuring Opioid Withdrawal in a Phase 3 Study of a New Analgesic, NKTR-181 (Oxycodegol), in Patients with Moderate to Severe Chronic Low Back Pain

OBJECTIVE

To evaluate the SUMMIT-07 trial opioid withdrawal results of NKTR-181 (oxycodegol), a new molecular entity mu-opioid receptor agonist.

DESIGN

Phase 3, enriched-enrollment, double-blind, randomized-withdrawal study in patients with chronic low back pain (CLBP).

SETTING

Conducted in the United States at multiple sites.

METHODS

SUMMIT-07 was comprised of five periods: screening; NKTR-181 open-label titration (100 to 400 mg twice daily); 12-week randomized, double-blind study drug (NKTR-181 or placebo); one-week study drug taper; and two-week safety follow-up. Permitted rescue medication included hydrocodone 5 mg/acetaminophen 300 mg (two tablets daily) for two weeks after randomization, then acetaminophen 1.0 gm daily for the remainder of the trial. Signs and symptoms of drug withdrawal were evaluated using the Clinical Opiate Withdrawal Scale (COWS); Subjective Opiate Withdrawal Scale (SOWS); Misuse, Abuse, and Diversion Drug Event Reporting System (MADDERS); and withdrawal-related adverse events.

RESULTS

Of 1,190 patients entering titration, one patient had moderate withdrawal (COWS score 13/48 maximum) three days after discontinuing NKTR-181. Of 610 patients randomized (N = 309, NKTR-181; N = 301, placebo), no COWS scores indicating withdrawal at a moderate level or greater (i.e., score ≥13) were observed at any time point. At day 8 after randomization, week 12, and the end of tapering, COWS scores indicating mild withdrawal (<13) were observed in seven (2.4%), one (0.4%), and one (0.5%) placebo patients, respectively, and three (1.0%), one (0.4%), and five (2.3%) NKTR-181 patients, respectively. Mean SOWS scores in both arms were ≤2.8 of 64 possible points at all time points. During the randomized period, of 35 events identified by MADDERS, adjudicators identified 20 possible "withdrawal" events (9 [2.9%] NKTR-181 and 11 [3.7%] placebo).

CONCLUSIONS

NKTR-181 exhibited a low rate and severity of opioid withdrawal in SUMMIT-07 patients with CLBP.

Photochemical fluoro-amino etherification reactions of aryldiazoacetates with NFSI under stoichiometric conditions

A photochemical three-component reaction is reported that allows the introduction of fluorine and a short polyether side chain in high efficiency under metal-free conditions.