Soligenix Demonstrates Extended Protection with RiVax Ricin Toxin Vaccine

Soligenix has demonstrated extended protection with its heat stable ricin toxin vaccine, RiVax®. Mice, vaccinated twice on Days 1 and 21 were protected for at least 365 days against subsequent ricin challenge. These results demonstrate that the thermostabilized vaccine formulation is capable of eliciting enduring protection in mice. Coupled with previous demonstration of efficacy in mice and non-human primates (NHPs) as well as long-term thermostability (at least 1 year at 40°C or 104°F), these results reinforce the practicality of stockpiling and potentially utilizing the RiVax® vaccine in warfighters and civilian first responders without the complexities that arise for vaccines that require cold chain handling. This same thermostabilization approach is also being advanced in the development of Soligenix's CiVax™ vaccine for COVID-19.

RiVax® is the Company's vaccine candidate for the prevention of death following exposure to a lethal dose of ricin toxin using a unique antigen that is completely devoid of the toxic activity of ricin. Formulated by Soligenix to have enhanced thermostability, RiVax® has demonstrated up to 100% protection in mice and NHPs subsequently exposed to lethal doses of ricin toxin either systemically or by aerosol. Most recently, mice have been shown to be protected from ricin challenge at 10 times the lethal dose for at least 12 months post-vaccination.

"These results continue to reinforce the convenience and practicality of the RiVax® vaccine," said Dr. Oreola Donini, Chief Scientific Officer of Soligenix. "This, and other ongoing work, has continued to corroborate the efficacy of RiVax® and will facilitate its potential approval."

Approval for RiVax® will be pursued under the US Food and Drug Administration (FDA) "Animal Rule," which is applied to products where testing in clinical efficacy trials would be unethical. In the case of a ricin toxin vaccine, clinical efficacy testing of the vaccine is unethical since it would require intentionally exposing humans to ricin toxin. The Animal Rule is generally associated with the approval of medical countermeasures for biodefense purposes. The Animal Rule requires the evaluation of efficacy in animals (RiVax® has demonstrated up to 100% protection in NHPs exposed to lethal aerosolized ricin), safety in humans (the RiVax® antigen has been demonstrated to be well-tolerated in human Phase 1 clinical studies) and immunogenicity correlated between animal models and humans (biomarkers have been identified, see publication here).

RiVax® studies are supported by a contract (# HHSN272201400039C) award of approximately $21.2 million from the National Institute of Allergy and Infectious Diseases (NIAID). Non-dilutive funding for the development of RiVax® has exceeded $40 million to date.

RiVax® has received Orphan Drug and Fast Track designations from the FDA, and, upon approval, has the potential to qualify for a biodefense Priority Review Voucher (PRV). In addition, RiVax® has received Orphan Drug designation from the European Medicines Agency (EMA).

Ricin toxin is a lethal plant-derived toxin and is considered both a bioterrorism agent and a chemical warfare agent because of its stability and high potency, and the fact that it is readily extracted from by-products of castor oil production. Ricin comes in many forms including powder, mist or pellet. Ricin can also be dissolved in water and other liquids. The US Centers for Disease Control and Prevention estimates that the lethal dose in humans is about the size of a grain of salt. Ricin toxin illness causes tissue necrosis and general organ failure leading to death within several days of exposure. Ricin is especially toxic when inhaled. Ricin works by entering cells of the body and preventing the cells from making the proteins they need. Without the proteins, cells die, which is eventually harmful to the entire body.

There are currently no effective treatments for ricin poisoning. The successful development of an effective vaccine against ricin toxin may act as a deterrent against the actual use of ricin as a biological weapon and could be used to vaccinate military personnel and civilian emergency responders at high risk of potential exposure in the event of a biological attack.