Cyanide is a metabolic poison that inhibits the utilization of oxygen to form ATP. The consequences of acute cyanide exposure are severe, and result in loss of consciousness, cardiac and respiratory failure, hypoxic brain injury, and dose-dependent death within minutes to hours. In a mass-casualty scenario, such as an industrial accident or terrorist attack, currently available cyanide antidotes would leave many victims untreated in the short time available for successful administration of a medical countermeasure. This restricted therapeutic window reflects the rate-limiting step of intravenous administration, which requires both time and trained medical personnel. Therefore, there is a need for rapidly acting antidotes that can be quickly administered to large numbers of people. To meet this need, our lab is developing sulfanegen, a potential antidote for cyanide poisoning with a novel mechanism based on 3-mercaptopyruvate sulfurtransferase (3-MST) for the detoxification of cyanide. Additionally, sulfanegen can be rapidly administered by intramuscular injection and has shown efficacy in many species of animal models. The following summarizes the journey from concept to clinical leads for this promising antidote.

Bupropion is an atypical antidepressant that is biotransformed in humans to its major active metabolite hydroxybupropion by cytochrome P450 2B6 (CYP2B6). Co-administration of bupropion with an inhibitor of CYP2B6 can result in a serious drug interaction, leading to bupropion related adverse effects (e.g. seizures). The antiplatelet agent ticlopidine has been identified as a potent in vitro inhibitor of bupropion hydroxylation, however it is unknown if it interacts in vivo in rodents. In this study we investigated the potential pharmacokinetic (PK) drug interaction between bupropion and ticlopidine in mice. Using a destructive sampling design, male CF-1 mice were administered ticlopidine 1.0 mg/kg daily for 5 d, followed by single-dose bupropion 50 mg/kg. Bupropion and hydroxybupropion levels were measured by HPLC-UV in plasma and brain tissues at 30, 60, 90, 120 and 180 min post-dose, and compared between treatment groups. There was a strong trend in both plasma and brain data towards greater bupropion levels and smaller hydroxybupropion levels in ticlopidine treated mice. Analysis of variance indicated statistical differences (pϽ Ͻ0.05) at many time points. The variance associated with the area under the curve was calculated using Bailer's method and significant differences were found between treatment groups. Taken together, the concentration time point statistical analysis followed by PK modeling demonstrate a significant PK drug interaction between bupropion and ticlopidine. To our knowledge, this is the first study to document an in vivo drug interaction between these drugs in mice. Our findings support future in vivo drug interaction studies in mice between bupropion and CYP2B6 inhibitors.

Aim: Sulfanegen has been shown to be an effective next generation cyanide antidote in multiple animal studies. Sulfanegen detoxifies cyanide by acting as a sulfur donor, converting cyanide to thiocyanate through the enzyme 3-mercaptopyruvate (3-MP) sulfurtransferase. The current study was performed to determine the PK behavior of sulfanegen in rabbits and compare it to current US FDA-approved cyanide therapeutics. Methods: Plasma sulfanegen concentrations, as 3-MP (i.e., sulfanegen is a prodrug that converts to the active sulfur donor, 3-MP, upon administration), were monitored using LC-MS/MS following intramuscular administration of sulfanegen in rabbits. Results: Concentrations of 3-MP rapidly increased following sulfanegen administration, indicating rapid absorption and distribution of 3-MP throughout the body. Elimination of 3-MP was also relatively rapid; the calculated half-life was approximately 114 min. A one-compartment model with first-order distribution and elimination was used to describe the PK behavior of 3-MP. Conclusion: Overall, the PK characteristics of sulfanegen were found to be well suited for the rapid treatment of cyanide poisoning.

Cyanide is a metabolic poison that inhibits cytochrome c oxidase. Its broad applications in manufacturing and history as an agent of warfare/terror highlight the limitations in approved cyanide antidotes for mass casualties. Sulfanegen, a pre-clinical antidote for cyanide poisoning, exploits an endogenous detoxification pathway and should be amenable to mass-casualty scenarios. Because human studies are unethical, determination of appropriate animal species as models in translational studies for FDA approval under the “Animal Rule” are critical. Here, we compared the specific activities of mercaptopyruvate sulfurtransferase (MST, required for sulfanegen’s activity), across common laboratory models of cyanide intoxication, and humans. Human MST activities in erythrocytes (measured as micromole pyruvate/min/106 rbc) were closest to those of Swiss-Webster mice and NZW rabbits. Similar species were selected for a more detailed tissue-specific comparison of MST activities. NZW Rabbits were closest to humans in the liver and kidney mitochondrial fractions, the Swiss-Webster mouse was closest to humans in the liver cytosolic fraction, while C57BL/6 mouse was closest in the kidney cytosolic fraction. These data comparing MST activities in animal models will help justify the use of those specific animals per the animal rule. Interestingly, statistically significant differences were found in MST activities of liver mitochondria between human smokers and non-smokers (p= 0.0030).

Bupropion is a popular antidepressant that is also prescribed in the management of smoking cessation. In humans, bupropion is predominantly metabolized to its active metabolite hydroxybupropion by CYP2B6. Inhibitors of CYP2B6 have the potential to decrease the clearance of bupropion, leading to adverse drug toxicity. We sought to develop a sensitive HPLC‐UV assay to quantify plasma and brain concentrations of bupropion and hydroxybupropion; and apply the assay to assess in vivo pharmacokinetic (PK) drug‐drug interaction (DDI) studies between bupropion and potent CYP2B6 inhibitors. Tissue extraction followed by HPLC‐UV detected timolol (IS), hydroxybupropion and bupropion at 6, 11 and 36 minutes, respectively. The LOD for both compounds was 6.0 ng/ml, and the intra‐day and inter‐day coefficients of variation was ±12% in plasma and ±15% in whole brain tissue. We then utilized this novel technique to evaluate the PK of bupropion and hydroxybupropion following repeated administration of the known CYP2B6 inhibitor ticlopidine (5 mg/kg daily x 5 days) in CF‐1 mice. Ticlopidine increased the plasma area under the concentration curve (AUC) of bupropion (2.0‐fold, p< 0.01) and decreased the plasma AUC of hydroxybupropion (1.2‐fold;p< 0.05). In whole brain tissue, ticlopidine increased the AUC of bupropion (1.3‐fold;p> 0.05)and decreased the AUC of hydroxybupropion (2.0‐fold;p< 0.001). In summary, we have developed a sensitive HPLC assay and suitable rodent model to evaluate in vivo PK DDI between bupropion and CYP2B6 inhibitors. Support: Drake Univ COPHS Intramural Research Grants.