Project Summary/Abstract This effort addresses the urgent need for a safe rapidly acting reversal agent for fentanyl and its analogues (F/FA) with a mechanism of action that differs from the µ-opioid receptor (MOR) antagonists including naloxone. Abuse of F/FA is now a major cause of death that is increasing yearly. Centers for Disease Control and Prevention data show that between 2013 and 2020 fentanyl-linked deaths have increased 10-fold; fentanyl related deaths now are double those caused by heroin. Naloxone, currently the standard of care to reverse respiratory depression caused by opioid overdose, is highly effective against heroin and many opioids derived from natural products, but is far less effective against F/FA. The long-term objective is to obtain FDA approval for sale and marketing of CS-1103, a small-molecule sequestrant, formulated for intramuscular injection, as a rescue drug to treat F/FA toxicity in the commonly encountered emergency scenarios of mixtures of multiple F/FA and co-use of F/FA with stimulants. CS-1103 is well tolerated, selectively binds F/FA in blood and dramatically accelerates its removal from the body by clearance into the urine, representing a new approach to reversal of drug effect: remove the cause and remove the effect. It is proposed here to continue development of CS-1103 as a rescue drug to treat opioid toxicity in emergency scenarios. Formulation of CS-1103 for IM administration will be optimized and a safe and effective IM dose that rapidly reverses physiological effects of opioids in these scenarios will be determined. These significant milestones on the path to FDA approval will be achieved via completion of the following Aims: Aim 1 will optimize a stable formulation of CS-1103 suitable for IM injection with rapid appearance in the plasma compartment. The formulation will be adjusted to maximize stability, tolerability, and speed of appearance of CS-1103 in plasma, and evaluated in rat and canine. Expected outcome is a formulation appropriate for use in human studies. Aim 2 will establish the efficacy profile of CS-1103 for IM injection for reversal of F/FA intoxication in real-world scenarios, in pre-clinical studies. Three scenarios: 1) multiple F/FA, 2) fentanyl in the presence of stimulants, and 3) use in conjunction with naloxone, will be evaluated. A detailed dose-ranging study in rat and canine will be conducted to establish an effective dose. Endpoints are restoration of adequate ventilation and clearance of opioid from plasma into urine. Expected outcome is CS-1103 dose for reversal of toxic effects and rapid opioid clearance. Aim 3 will establish the safety profile of CS-1103 for IM injection in pre-clinical Investigational New Drug Application (IND)-enabling studies. Standard Good Laboratory Practice (GLP) toxicology and pharmacokinetic studies per FDA requirements will be performed in rat and canine to establish a safe initial human dose; the endpoint will be the maximum safe dose. A pre-IND meeting will be conducted with the FDA. Successful completion of Aims 1-3 is anticipated to yield a drug candidate ready for further IND-enabling pre-clinical studies.

PROJECT NARRATIVE Deaths linked to the synthetic opioids fentanyl and its derivatives increased over 10-fold between 2013 and 2020, and are now double those caused by heroin. The proposed work addresses the urgent need for a safe rapidly acting reversal agent for synthetic opioids with a new mechanism of action that improves treatment compared to the standard of care, naloxone. Such an agent would save lives and improve patient outcomes.