Soligenix Announces Publication of Article Identifying Domains Within the Ricin Toxin A Subunit as Targets of Protective Antibodies

Paper describes the partial immunological structure of ricin and identifies neutralizing domains

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Sep 02, 2010, 08:00 ET

PRINCETON, N.J., Sept. 2 /PRNewswire-FirstCall/ -- Soligenix, Inc. (OTC Bulletin Board: SNGX) (Soligenix or the Company), a late-stage biopharmaceutical company, announced today the publication of an article online in Vaccine. The article describes the systematic identification of neutralizing and non-neutralizing B-cell epitopes on ricin toxin's enzymatic A subunit (RTA). An inactivated form of RTA is the primary component of RiVax™, the Company's proprietary vaccine against ricin toxin. RiVax™ is currently being evaluated in Phase 1 human safety and immunogenicity trials, as well as non-human primate trials for efficacy.

The results of this study indicate that there are "hot spots" on RTA responsible for eliciting neutralizing antibodies associated with protective immunity to ricin toxin. These results suggest that there are distinct regions of RTA that are responsible for eliciting protective immunity. Importantly, the recognition of immunodominant epitopes was similar between mice and rabbits, suggesting that different species including humans develop similar immune response to RTA.

The major findings to emerge from this study are as follows:

Identification of six immunodominant linear B cell epitopes on RTA
Production of monoclonal antibodies (MAbs) against five of the six immunodominant regions
Identification of several neutralizing "hot spots" on RTA in specific folding domains (termed domain 1 and 2)
Demonstration that non-neutralizing Mabs are directed at domain 3
Convergence of immunodominant epitopes recognized by several animal species

"Efforts to develop an effective vaccine against ricin toxin are focused on the engineering of attenuated and stable recombinant forms of the toxin's RTA," stated Dr. Nicholas Mantis, Research Scientist at the Division of Infectious Disease, Wadsworth Center, New York State Department of Health, and senior author of the study. "These data offer insights into the immunodominant and structural determinants on RTA that give rise to protective immunity, and for the first time provide an immunological rationale for ricin vaccine design."

"We are providing further detail of the immunological structure of RTA in order to define additional correlates of protective immunity," stated Robert N. Brey, PhD, Chief Scientific Officer of Soligenix, a co-author of the study. "Such correlates are important in understanding immune responses from human studies and how they relate to protective immunity in animals when vaccines cannot be directly tested for efficacy."

The article, entitled "Folding domains within the ricin toxin A subunit as targets of protective antibodies," was authored by Drs. O'Hara, Neal, McCarthy, Kasten-Jolly, Brey and Mantis. The article represents a collaborative research effort between Soligenix and the Wadsworth Center, and signifies research was supported by grants to Soligenix and to Wadsworth from the National Institutes of Health. The full article (O'Hara et. al., "Folding domains within the ricin toxin A subunit as targets of protective antibodies," Vaccine) is available online doi:10.1016/j.vaccine.2010.08.020.

About RiVax™

RiVax™ is Soligenix's proprietary vaccine developed to protect against exposure to ricin toxin and is the most advanced vaccine in the company's portfolio. RiVax™ 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 RiVax™ 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 RiVax™. 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 RiVax™ 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 RiVax™ 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. RiVax™ 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. 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 RiVax™, which is designed to protect against the lethal effects of exposure to ricin toxin. RiVax™ has been shown to be well tolerated and immunogenic in a Phase 1 clinical trial in normal volunteers. RiVax™ is also the subject of a $9.4 million NIH grant received by the Company supporting development of new heat stable vaccines.

For further information regarding Soligenix, Inc., please visit the Company's website at www.soligenix.com.

This press release contains forward-looking statements that reflect Soligenix, Inc.'s current expectations about its future results, performance, prospects and opportunities. Statements that are not historical facts, such as "anticipates," "believes," "intends," or similar expressions, are forward-looking statements. These statements are subject to a number of risks, uncertainties and other factors that could cause actual events or results in future periods to differ materially from what is expressed in, or implied by, these statements. Soligenix cannot assure you that it will be able to successfully develop or commercialize products based on its technology, including orBec®, SGX201, RiVax™, and LPM™, particularly in light of the significant uncertainty inherent in developing vaccines against bioterror threats, manufacturing and conducting preclinical and clinical trials of vaccines, and obtaining regulatory approvals, that its cash expenditures will not exceed projected levels, that product development and commercialization efforts will not be reduced or discontinued due to difficulties or delays in clinical trials or due to lack of progress or positive results from research and development efforts, that it will be able to successfully obtain any further grants and awards, maintain its existing grants which are subject to performance, enter into any biodefense procurement contracts with the US Government or other countries, that the US Congress may not pass any legislation that would provide additional funding for the Project BioShield program, that it will be able to patent, register or protect its technology from challenge and products from competition or maintain or expand its license agreements with its current licensors, or that its business strategy will be successful. Important factors which may affect the future use of orBec® for gastrointestinal GVHD include the risks that: the FDA's requirement that Soligenix conduct additional clinical trials to demonstrate the safety and efficacy of orBec® will take a significant amount of time and money to complete and positive results leading to regulatory approval cannot be assumed; Soligenix is dependent on the expertise, effort, priorities and contractual obligations of third parties in the clinical trials, manufacturing, marketing, sales and distribution of its products; orBec® may not gain market acceptance if it is eventually approved by the FDA; and others may develop technologies or products superior to orBec®. Factors affecting the development and use of SGX201 and LPM™ are similar to those affecting orBec®. These and other factors are described from time to time in filings with the Securities and Exchange Commission, including, but not limited to, Soligenix's reports on Forms 10-Q and 10-K. Unless required by law, Soligenix assumes no obligation to update or revise any forward-looking statements as a result of new information or future events.

SOURCE Soligenix, Inc.