Antidotal efficacies of the cyanide antidote candidate dimethyl trisulfide alone and in combination with cobinamide derivatives

Abstract

Formulation optimization and antidotal combination therapy are the two important tools to enhance the antidotal protection of the cyanide (CN) antidote dimethyl trisulfide (DMTS). The focus of this study is to demonstrate how the formulation with polysorbate 80 (Poly80), an excipient used in pharmaceutical technology, and the combinations with other CN antidotes having different mechanisms of action enhance the antidotal efficacy of the unformulated (neat) DMTS. The LD₅₀ for CN was determined by the statistical Dixon up-and-down method on mice. Antidotal efficacy was expressed as antidotal potency ratio (APR). CN was injected subcutaneously one minute prior to the antidotes’ injection intramuscularly. The APR values of 1.17 (dose: 25 mg/kg bodyweight) and 1.45 (dose: 50 mg/kg bodyweight) of the neat DMTS were significantly enhanced by the Poly80 formulation at both investigated doses to 2.03 and 2.33, respectively. The combination partners for the Poly80 formulated DMTS (DMTS-Poly80; 25 and 50 mg/kg bodyweight) were 4-nitrocobinamide (4NCbi) (20 mg/kg bodyweight) and aquohydroxocobinamide (AHCbi; 50, 100, and 250 mg/kg bodyweight). When DMTS-Poly80 (25 and 50 mg/kg bodyweight; APR = 2.03 and 2.33, respectively) was combined with 4NCbi (20 mg/kg bodyweight; APR = 1.35), significant increase in the APR values were noted at both DMTS doses (APR = 2.38 and 3.12, respectively). AHCbi enhanced the APR of DMTS-Poly80 (100 mg/kg bodyweight; APR = 3.29) significantly only at the dose of 250 mg/kg bodyweight (APR = 5.86). These studies provided evidence for the importance of the formulation with Poly80 and the combinations with cobinamide derivatives with different mechanisms of action for DMTS as a CN antidote candidate.

Keywords:

• Combination therapy
• intramuscular antidote injection
• subcutaneous cyanide exposure
• cobinamide
• dimethyl trisulfide

Acknowledgements

The authors are thankful for Ms. Ashley C. Whiteman, Ms. Anna Duke, and Mr. Stephen Lee, for technical assistance. Special thanks to Dr. David Thompson for scientific discussions.

Disclosure statement

The authors declare no conflicts of interest associated with this study. Two patents by two coauthors, related to DMTS are: (1) Gary A. Rockwood, Ilona Petrikovics (SHSU) and Steven I. Baskin (USAMRICD): Dimethyl Trisulfide as a Cyanide Antidote. U.S. Patent No. 9,375,407, 2016, (2) Ilona Petrikovics and Kristóf Kovács (SHSU). Formulations of Dimethyl Trisulfide for Use as a Cyanide Antidote. U.S. Patent No. 9,456,996, 2016.

Additional information

Funding

This research was supported by the CounterACT Program, National Institutes of Health Office of the Director, and the National Institute of Allergy and Infectious Diseases, NIH/Department of Defence Interagency Agreement [AOD14020-001-00000/A120-B.P2014-01], and the Robert A. Welch Foundation [X-0011] at Sam Houston State University, Huntsville, TX.