Aphton Announces Clinical Proof of Concept in Prostate Cancer Patients Equivalent to Surgical Castration is Achieved in Phase I/II Trial.

MIAMI--(BW HealthWire)--March 31, 1999--In an on-going Phase I/II safety/dose-ranging clinical trial in patients with advanced prostate cancer, Aphton's GnRH pharmaccine reduced, in some patients at the lowest dose level, gonadal testosterone to levels achieved by surgical castration. This demonstrated clinical "proof of concept" in man. In addition to this proof of concept marker, the cancer "progression" marker Prostate Specific Antigen (PSA) was reduced markedly in these patients to very low levels.

The immunological neutralization of Gonadotropin Releasing Hormone (GnRH) by the antibodies induced by GnRH pharmaccine shuts down the production of testosterone in the testes. Testosterone fuels prostate cancer, both early stage, primary cancer and metastatic (spreading) cancer. Like physical castration, hormonal, or biological blockage of testosterone has been shown to be efficacious in humans for the treatment of both early and late state prostate cancer. Aphton's GnRH pharmaccine, which is expected to be reversible based on the mechanism of action (in contrast to surgical castration), induces hormonal, or biological blockage of testosterone.

The GnRH pharmaccine, for which Aphton was granted a US patent in November, 1997, consists of synthetic peptides (constructed to "look like" GnRH), which are bound chemically to a carrier and suspended in a proprietary "delivery vehicle". The pharmaccine is administered intramuscularly to the patient by injection and induces an immune response or production of antibodies in the patient, which neutralize GnRH thus removing it from circulation. After immunity has been established from an initial series of injections, follow-up injections will be given regularly to maintain high levels of neutralizing antibodies directed against GnRH.

There is a need for an improved therapy for prostate cancer patients, particularly for those whose cancer has spread or can be expected to spread. The number of new cases of prostate cancer in the US and Western Europe (WE) exceeds 370,000 annually; thenumber of existing prostate cancer cases in the US and WE is estimated to exceed 2,300,000. Until very recently, only a small fraction of these large numbers of patients were treated with anti-GnRH drugs, primarily those in late-stage disease. However, in July 1998, it was announced that FDA approval to market one of them, in combination therapy, was granted to treat early stage prostate cancer (locally confined to the prostate gland). These drugs, called GnRH agonists, have a net benefit -- but cause an initial "surge," or "flare," in testosterone. This "surge" is the opposite of the desired effect, namely testosterone suppression, which can fuel the cancer. (Aphton's GnRH pharmaccine, in contrast, is a"pure" antagonist with no "surge".) The annual revenues for such anti-GnRH drugs already were in excess of a billion US dollars per year and can be expected to increase significantly, given the FDA's recent approval to treat early stage prostate cancer with them.

On June 19, 1998, Aphton and SmithKline Beecham announced a strategic alliance under an exclusive collaboration and licensing agreement to develop and market GnRH pharmaccine worldwide, for various indications.

Aphton Corporation is a biopharmaceutical company developing products using its innovative vaccine-like technology for neutralizing hormones that participate in gastrointestinal system and reproductive system cancer and non-cancer diseases; and the prevention of pregnancy. In addition to SmithKline Beecham PLC, Aphton has strategic alliances with Pasteur Merieux Connaught (Rhone-Poulenc Group), Schering Plough Animal Health and the World Health Organization (WHO). Aphton's Web page, describing the company, its technology, products, strategic alliances, news releases and listing reports of independent brokerage firm analysts, can be visited at: www.aphton.com

Except for the historical information herein, the matters discussed herein include forward-looking statements that may involve a number of risks and uncertainties. Future results may vary significantly based on a number of factors including, but not limited to, intellectual property risks, risks in regulatory and market acceptance of new products and continuing demand for same, the impact of competitive products and pricing, changing economic conditions and other risk factors detailed in Aphton's most recent 10-K and other filings with the Securities and Exchange Commission.