A Novel Reversal Agent for Treatment of Overdose from the Combination of Fentanyl and Xylazine

PROJECT SUMMARY Co-use of fentanyl with the animal tranquilizer xylazine, a compound for which naloxone, the standard of care for opioid intoxication is ineffective, is a major cause of overdose death in the US. Co-use of fentanyl and xylazine (an adulterant) has reached crisis levels, with xylazine-positive overdose deaths increasing by 1,127% in the South and over 100% in all other regions between 2020 and 2021. In July 2023 the White House released the “Fentanyl Adulterated or Associated with Xylazine Response Plan,” a first-of-its-kind National Response effort. A key part of the Plan is reversal agents for overdose from fentanyl/xylazine combinations. Our goal is to develop a reversal agent for combinations of xylazine and fentanyl, delivered by intramuscular (IM) injection, that is compatible with naloxone. Our antidote is a small molecule sequestrant that encapsulates intoxicants, immediately reversing their toxidrome, followed by accelerated clearance into urine. The indication is to simultaneously reduce the level of fentanyl and xylazine in the human body, with restoration of respiration and reversal of sedation. We envision two use cases: (1) use alone if sedation is the major symptom, and (2) use after naloxone if respiratory depression is also present. In the R43 we identified five compounds with good binding to both fentanyl and xylazine. Two candidates were selected for further study: (1) CS-1103, an acyclic cucurbituril compound, currently in advanced development to treat methamphetamine and fentanyl intoxication, and (2) CS-1105, a CS-1103 analogue. CS-1103 and CS- 1105 are highly effective against fentanyl, restoring breathing in 2-3 min in rat, and compatible with naloxone. Both significantly reduce xylazine level and duration of sedation in rat, with about equal effectiveness. For combinations of fentanyl and xylazine, CS-1103 restored respiration in 2-3 min, reversed sedation caused by xylazine in 10-20 min, and accelerated clearance of fentanyl and xylazine into urine 73-fold and 7-fold, respectively, in 2 hr, vs saline control. Naloxone was less effective in restoring respiration, and showed no improvement in sedation reversal or intoxicant clearance vs saline control. In the R44, the first Aim will study the effect of CS-1105 on fentanyl/xylazine combinations, to select a lead candidate. The R44 will address four key questions: (1) Does xylazine affect the dose response of candidate against fentanyl, and vice versa?; (2) Does candidate simultaneously restore respiration and reverse sedation?; (3) Is the candidate compatible with naloxone?; (4) What is the regulatory pathway for treating polysubstance overdose? Aim 1 will select a candidate against co-use of fentanyl and xylazine, in rat. Aim 2 will optimize formulation of lead candidate for IM injection. Aim 3 will establish the dose response of lead candidate against combinations of fentanyl and xylazine in rat. Aim 4 will establish the dose response of lead candidate against co-use of fentanyl and xylazine, in canine. Aim 5 will complete pre-IND package, including nonclinical plan and clinical strategy.