Promising results from Soligenix' RiVax vaccine trials against ricin toxin

Feb 3 2010

Soligenix, Inc. (OTC Bulletin Board: SNGX) (Soligenix or the Company), a late-stage biotechnology company, announced today the publication of an article in the February 2010 edition of Vaccine, which describes preclinical formulations of RiVax™, its ricin toxin vaccine, with heightened stability. The article was authored by the Company's collaborators at the University of Texas Southwestern Medical Center at Dallas (UT Southwestern) where the vaccine originated. RiVax™ is currently being evaluated in Phase 1 human safety and immunogenicity trials, as well as non-human primate trials for efficacy.

The purpose of this study was to establish preliminary conditions for long-term stability of RiVax™ with the intent of avoiding the cold chain usually required for storage of vaccines. In this publication, a series of formulations of the RiVax™ immunogen, a modified recombinant ricin A chain protein, were examined for comparative effects of storage at room temperature versus refrigeration. The formulations were designed with excipients expected to add to protein stability and then processed by lyophilization to remove water. One combination of lyophilization conditions and excipients was found to result in a vaccine that retained immunogenicity in animals, an index of vaccine potency, for one year at room temperature (the longest time tested). The lead formulation showed no evidence of degradation, whereas unstable control formulations aggregated when reconstituted with water. Moreover, the stabilized vaccine formulation was potent when adsorbed to aluminum hydroxide adjuvant, which is used in many approved vaccines. As shown previously, the aluminum adjuvant enhanced the immunogenicity and potency of RiVax™. The lyophilized vaccine was also tested for immunogenicity in mouse challenge models, in which vaccinated mice were exposed to ricin by the aerosol or oral route. In each case, the reconstituted vaccine was demonstrably protective in comparison to control vaccine preparations.

"We know that the ricin subunit vaccine itself is very sensitive to denaturation, and we are very encouraged to find lyophilization conditions that aid in the long-term stability of the vaccine," stated Dr. Ellen Vitetta, Director of the Cancer Immunobiology Center at UT Southwestern and an author of the study. "We are also pleased to see that in our study storage for over one year at ambient conditions resulted in no apparent degradation of potency or the integrity of the protein immunogen."

"These results are very promising not only for the future development of RiVax™ in particular, but also for the potential development of other vaccines with long-term stability, especially those using conventional adjuvants composed of aluminum salts," stated Robert N. Brey, Ph.D., Chief Scientific Officer of Soligenix. "Our current efforts are centered on combining conventional adjuvant and scalable lyophilization techniques to examine formulations that retain stability at elevated temperatures, building on the results that Dr. Vitetta and her colleagues have reported in this publication."

The article, entitled "A lyophilized formulation of RiVax™, a recombinant ricin subunit vaccine, retains immunogenicity," was authored by Drs. Joan Smallshaw and Ellen Vitetta at UT Southwestern. The research was funded directly by an NIH grant to UT Southwestern and complements the NIH funding to Soligenix for the development of RiVax™. The full article (Smallshaw and Vitetta, "A lyophilized formulation of RiVax, a recombinant ricin subunit vaccine, retains immunogenicity," Vaccine) is available online at http://dx.doi.org/10.1016/j.vaccine.2009.12.081.