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Soligenix (SNGX): Identifies Biomarkers for Ricin Toxin Vaccine Testing under the FDA Animal Rule

By Grant Zeng, CFA


On Dec. 21, 2017, SNGX (NASDAQ:SNGX) announced the successful identification of biomarkers for ricin toxin vaccine (RiVax®) testing. This could facilitate the approval of the testing under the FDA "Animal Rule".

The FDA Animal Rule is used to tests/products where testing in humans would be unethical or impossible.  In the case of a ricin toxin vaccine studies, clinical efficacy testing of the vaccine is unethical since exposing unvaccinated humans to ricin toxin would be fatal.  

The Animal Rule then allows efficacy testing in animals instead, typically in non-human primates (NHPs), to facilitate approval.  One key requirement for the animal rule is to establish a correlation between the response observed in clinical trials in healthy volunteers with the response demonstrated in animal efficacy studies.  

Identification of a biomarker to facilitate demonstrating the correlation between animal and human studies is a significant accomplishment in the RiVax® development program.

Soligenix studies have demonstrated the unique expression profile of ricin antibodies. Key biomarkers of these profiles have been identified and include in order of increasing sensitivity:
• antibody titers (the ability of antibodies to recognize ricin),
• neutralizing antibody activity (the ability of antibodies to prevent ricin toxicity), and
• SyH7 antibody epitope competition profile (the ability of antibodies to bind to the SyH7 binding site on the ricin protein, a key binding site that neutralizes the toxicity of the ricin protein).

These biomarkers are consistent across mice, NHPs and humans, supporting the application of the Animal Rule.

In Soligenix previous studies, RiVax is not only protective and thermostable, but also demonstrated that a reduced number of vaccinations may be ok to establish protection, potentially utilizing only two doses instead of three.  Further efficacy studies in NHPs evaluating potential dosing regimens are anticipated in 2018, in addition to continued human safety testing evaluating the thermostable RiVax® formulation.

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