Soligenix Announces Publication of Positive Stability Results with RiVax(TM), its Vaccine Against Ricin Toxin

Preclinical data demonstrate the potential for long-term stability of RiVax(TM)

PRINCETON, NJ, USA | February 2, 2010 | Soligenix, Inc. (OTC Bulletin Board: SNGX) (Soligenix or the Company), a late-stageruary biotechnology company, announced today the publication of an article in the February 2010 edition of Vaccine, which describes preclinical formulations of RiVaxâ„¢, 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. RiVaxâ„¢ 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 RiVaxâ„¢ with the intent of avoiding the cold chain usually required for storage of vaccines. In this publication, a series of formulations of the RiVaxâ„¢ 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 RiVaxâ„¢. 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 RiVaxâ„¢ 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 RiVaxâ„¢, 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 RiVaxâ„¢. 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.

About RiVaxâ„¢

RiVaxâ„¢ is Soligenix's proprietary vaccine developed to protect against exposure to ricin toxin and is the most advanced vaccine in the company's portfolio. RiVaxâ„¢ induces a protective immune response in animal models of ricin exposure and is currently being evaluated in humans. One human Phase 1 clinical trial has been completed and a second trial is currently being conducted.

Results of the first Phase 1 clinical trial of RiVaxâ„¢ indicated that the immunogen was safe and induced antibodies anticipated to protect humans from ricin exposure. The outcome of the study was published in the Proceedings of the National Academy of Sciences (Vitetta et al., 2006, PNAS, 105:2268-2273). The second trial, sponsored by UT Southwestern, is currently evaluating a more potent formulation of RiVaxâ„¢. Soligenix has developed processes for large-scale manufacturing and is further establishing correlates of the human immune response in non-human primates.

The development of RiVaxâ„¢ has been sponsored through a series of overlapping challenge grants (UC1) and cooperative grants (U01) from the NIH, granted to Soligenix and to UT Southwestern where the vaccine originated. The second clinical trial is being supported by a grant to UT Southwestern from the US Food and Drug Administration's Office of Orphan Products Development. Soligenix and UT Southwestern have collectively received approximately $25 million in grant funding from the NIH for development of RiVaxâ„¢ and related vaccine technologies.

About Ricin Toxin

Ricin toxin is a plant toxin thought to be a bioterror threat because of its stability and high potency as well as the large worldwide reservoir created as a by-product of castor oil production. Exposure to ricin results in local tissue necrosis, and general organ failure leading to death within several days of exposure. The potential use of ricin toxin as a biological weapon has been highlighted in an FBI terrorism report, which states that "Ricin and the bacterial agent anthrax are emerging as the most prevalent agents involved in WMD investigations" (http://www.fbi.gov/publications/terror/terrorism2002_2005.pdf).

There are currently no effective means to prevent the effects of ricin intoxication. 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 in rapid deployment scenarios in the event of a biological attack. RiVaxâ„¢ would potentially be added to the Strategic National Stockpile and dispensed in the event of a terrorist attack.

About Soligenix, Inc.

Soligenix, Inc. (Soligenix) is a late-stage biopharmaceutical company developing products to treat life-threatening side effects of cancer treatments and serious gastrointestinal diseases, and vaccines for certain bioterrorism agents. Soligenix's lead product, orBec® (oral beclomethasone dipropionate or BDP), is a potent, locally acting corticosteroid being developed for the treatment of acute gastrointestinal Graft-versus-Host-Disease (GI GVHD), a common and potentially life-threatening complication of hematopoietic cell transplantation. orBec® is currently the subject of a confirmatory Phase 3 clinical trial for the treatment of acute GI GVHD and an NIH-supported, Phase 2, randomized, double-blind, placebo-controlled trial in the prevention of acute GVHD. Both of these trials are actively enrolling patients. Soligenix has also recently initiated an NIH-supported Phase 1/2 clinical trial of SGX201 in the prevention of acute radiation enteritis. Additionally, Soligenix has a Lipid Polymer Micelle (LPM™) drug delivery technology for the oral delivery of leuprolide for the treatment of prostate cancer and endometriosis.

Through its Biodefense Division, Soligenix is developing biomedical countermeasures pursuant to the Project BioShield Act of 2004. Soligenix's lead biodefense product in development is a recombinant subunit vaccine called RiVaxâ„¢, which is designed to protect against the lethal effects of exposure to ricin toxin. RiVaxâ„¢ has been shown to be well tolerated and immunogenic in a Phase 1 clinical trial in normal volunteers. RiVaxâ„¢ will also be the subject of a recent $9.4 million NIH grant received by the Company supporting development of new heat stable vaccines.

SOURCE: Soligenix, Inc.,

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