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May 21, 2003
SARS: Newly NIH Sponsored Studies of Potential Therapies for SARS now Finds Hemispherx' Ampligen® among the Most Active from a Large Pool of 70 (Seventy) Drug Candidates
Philadelphia, PA, Wednesday, May 21, 2003: Hemispherx Biopharma, Inc. (AMEX: HEB) announced today that the Institute for Antiviral Research, sponsored by the National Institutes of Health (NIAID, Virology Branch, Contract No. 1-AI-85348) have just reported a comprehensive new study which screened many test compounds for potential therapy against SARS. The results of the study entitled “Potential therapies for SARS: Inhibitors of Human Coronavirus Strain OC43 by Antiviral Agents” have identified Ampligen®, a flagship investigational immunotherapeutic of the Company, as having unusually high and consistent antiviral activity against human coronavirus.

About the Assay Method
Human coronavirus (strain OC43) in different amounts was grown in African green monkey kidney cells and thereafter potential antiviral therapies (“the test compounds”) were added. Each of the approximately 70 new drug candidates for SARS were introduced to determine levels of possible reduction in virus growth (called “virus yield reduction assay”). Thereafter, these drugs were ranked by their relative ability to inhibit virus and for their ability to protect the target cells from death or severe damage.

About the Compounds Screened for Inhibiting Human Coronavirus
A. “Traditional” Antivirals
An unusual broad array of candidates was selected including many new drugs, submitted by various drug manufacturers, to NIH for screening (18 cpds), also many nucleoside analogues (21 cpds) known to be potentially active against HBV, HIV, herpes, etc.; marketed (FDA approved) antivirals, including ribavirin (for RSV, respiratory syncytal virus) and related compounds (5 cpds); formycin analogs and polyoxometalates and dendrimers and 5 non carbocyclic adenosine analogues (totaling 11 new cpds); new apoptosis inhibitors and new cyclin-dependent kinase inhibitors (6 cpds) as well as adenosine kinase inhibitors (3 cpds); plus miscellaneous phospolipase, attachment / penetration and bunga virus inhibitors, plus cyclohexamide and a coumadin analog (totaling 7 cpds). In total, these compounds represent multiple mechanisms of action designed to stop the human coronavirus at virtually every step of its multiplication within cells.
B. Immune Modulators and Interferons
Human Interferon gamma (recombinant) from Interimmune Corp. and Interferon – alpha consensus (recombinant, Intergen) from Amgen Corp. were also evaluated both alone and in combination. Both are FDA approved products widely used for the treatment of chronic granulomatous disease of lungs and hepatitis C, respectively. Ampligen®, an experimental immunotherapeutic in Phase 3 clinical testing, was provided by the Company under a research collaboration agreement with the NIH. A structurally related compound, termed PolyIC:LC, developed by the NIH scientists and widely available in the Republic of China as a potential broad-spectrum antiviral, was also tested.
About the Results
As compared to all therapeutic products tested, Ampligen ranked with the highest antiviral activity.

Ampligen® was the most consistently active compound tested in the various assay methods used. A structurally related dsRNA compound, poly IC:LC, presently available in China, was not demonstrated to have any significant activity against human coronavirus.

Similarly, ribavirin, which has been widely reported in the media to have been used in the SARS epidemic in Asia (alone or in combination with steroids), was also devoid of significant viral inhibitory activity.
In contrast, Ampligen® demonstrated very high potency at low concentrations (0.4 micrograms per milliliter) and had a favorable safety profile (the ratio of concentration to damage normal cells relative to that necessary to stop viral growth). Only 1 compound, termed iodotubercidin, demonstrated similar potency, however, the results with this compound were very inconsistent within the multiple assay systems of viral inhibition, suggesting that it may provide unpredictable antiviral benefits, in contrast to Ampligen®.

Relative Potency within the Immune Modulator Class: Ampligen® surpassed Recombinant IFN
Both recombinant interferons given alone, provided less antiviral protection than Ampligen (>50%) with the trademarked Intergen (Amgen Corp., originally selected for its high potency) providing only 28% protection and interferon gamma, trademarked Actimune, providing only 18% protection. In fact, to achieve antiviral protection against human coronavirus similar to Ampligen® alone, it was necessary to combine these two different recombinant IFNs, thereby achieving 52% antiviral protection. Except as occurs in the natural antiviral cocktail of alpha interferon, termed Alferon and owned by Hemispherx, the combination of two or more IFNs (recombinant) has been generally deemed too potentially toxic to justify human exposure.

About Hemispherx
Hemispherx Biopharma, based in Philadelphia, is a biopharmaceutical company engaged in the manufacture and clinical development of new drug entities for treatment of viral and immune-based chronic disorders. Its flagship products include Alferon and the experimental immunotherapeutics/antivirals Ampligen and Oragens. These novel proteins, approved for a category of STD infection, and experimental nucleic acids are being developed for globally important chronic viral diseases and disorders of the immune system including HPV, HIV, CFS and Hepatitis. Its platform technology includes large and small agent components for potential treatment of various chronic viral infections. Hemispherx has approximately 400 patents comprising its core intellectual property estate, a fully commercialized product (Alferon N) and GMP certified manufacturing facilities for its novel pharma products. For more information please visit www.hemispherx.net

Hemispherx Biopharma, Inc.,
Dianne Will, Investor Relations
(518) 398-6222, Fax: (518) 398-6223

HEB's Web Site: www.hemispherx.net

Information contained in this news release other than historical information, should be considered forward-looking and is subject to various risk factors and uncertainties. For instance, the strategies and operations of Hemispherx involve risk of competition, changing market conditions, change in laws and regulations affecting these industries and numerous other factors discussed in this release and in the Company's filings with the Securities and Exchange Commission. Any specifically referenced investigational drugs and associated technologies of the company (including AmpligenÒ and Oragensä) are experimental in nature and as such are not designated safe and effective by a regulatory authority for general use and are legally available only through clinical trials with the referenced disorders. The forward-looking statements represent the Company's judgment as of the date of this release. The Company disclaims, however, any intent or obligation to update these forward-looking statements. Clinical trials for other potential indications of the approved biologic AlferonÒ do not imply that the product will ever be specifically approved commercially for these other treatment indications. The Alferon® asset for overseas sales for a category of STD is currently being acquired by the Company as part of a multi-step purchase contract of inventory, intellectual property, commercial licenses and GMP approved facilities, which house the biological operations.