Ligand Receives Milestone for AHP Breast Cancer Product; Marks Second IND of Ligand/Wyeth-Ayerst Collaboration.

SAN DIEGO--(BW HealthWire)--March 1, 1999--Ligand Pharmaceuticals Incorporated (Nasdaq: LGND) announced today that Wyeth-Ayerst Laboratories, the pharmaceutical division of American Home Products (NYSE: AHP), has submitted an Investigational New Drug Application (IND) with the U.S. Food and Drug Administration (FDA) for the compound ERA-923, a tissue selective estrogen receptor (ER) modulator for the treatment of breast cancer.

Phase I clinical trials of ERA-923 are expected to commence during the first quarter 1999. In accordance with the terms of the collaborative research agreement between Ligand and Wyeth-Ayerst, Wyeth-Ayerst made an undisclosed milestone payment to Ligand as a result of the IND filing; Ligand may qualify for additional milestone payments through NDA approval if development continues.

The IND for ERA-923 is the second IND submitted for a compound emanating from the Ligand / Wyeth-Ayerst collaboration. On March 26, 1998, Wyeth-Ayerst submitted an IND for the tissue selective estrogen (TSE), TSE-424, for the treatment of post-menopausal osteoporosis. At that time, Wyeth-Ayerst also made an undisclosed milestone payment to Ligand as a result of the IND filing. Phase II clinical trials of TSE-424 are expected to commence shortly.

"Ligand is pleased with the emerging success of its partnership with Wyeth-Ayerst. In only four years, our collaboration has brought two new compounds into human clinical trials. The two INDs for selective estrogen receptor modulators (SERMs) further substantiate the importance of Ligand's technology in the identification and/or characterization of molecules that may provide benefit in hormone replacement therapy and breast cancer treatment and prevention," said Andres Negro-Vilar, M.D., Ph.D., Ligand Senior Vice President and Chief Scientific Officer. "These compounds join a growing pipeline of SERMs in human clinical development with our partners, giving Ligand a leading position in major growth markets," Dr. Negro-Vilar said.

"Recent clinical trials conducted for the National Cancer Institute and different national and multi-national consortia have established the therapeutic and preventive benefit of anti-estrogen therapy for many breast cancer sufferers," said C. Richard Lyttle, PhD, Vice President, Discovery, Women's Health Research Institute at Wyeth-Ayerst. "ERA-923, a second-generation compound, offers the potential of diminished side effects generally associated with prolonged therapy with existing drugs of this type."

According to the National Cancer Institute (NCI), approximately 2.0 million Americans have been diagnosed with breast cancer. The NCI estimates that one woman in nine will get breast cancer during her lifetime, making breast cancer the most common non-skin cancer among women in the United States. The Cancer Journal for Clinicians estimates that in 1999 there will be 176,300 new cases of breast cancer diagnosed and 43,900 deaths resulting from this disease.

Wyeth-Ayerst Laboratories is a major research-oriented pharmaceutical company with leading products in the areas of women's health care, cardiovascular, and metabolic disease therapies, central nervous system drugs, anti-inflammatory agents, vaccines, and generic pharmaceuticals. American Home Products Corporation is one of the world's largest research-based pharmaceutical and health care products companies. It is a leader in the discovery, development, manufacturing, and marketing of prescription drugs and over-the-counter medications. It is also a global leader in vaccines, biotechnology, agricultural products, and animal health care.

Since 1989, Ligand Pharmaceuticals Incorporated has established a leadership position in gene transcription technology, particularly intracellular receptor (IR) technology and Signal Transducers and Activators of Transcription (STATs). Ligand has applied IR and STATs technology to the discovery and development of small molecule drugs to enhance therapeutic and safety profiles, and to address unmet patient needs in cancer, women's and men's health and skin diseases, as well as osteoporosis, metabolic, cardiovascular and inflammatory diseases.

This news release may contain certain forward looking statements by Ligand and actual results could differ materially from those described as a result of factors including, but not limited to, the following. There can be no assurance that any product in Ligand's or any partner's pipeline will be successfully developed, that regulatory approvals will be granted in a timely manner or at all, that patient and/or physician's acceptance of these products will be achieved, that results of human clinical trials will be consistent with any pre-clinical results, or that any results will be supportive of regulatory approvals required to market products. Additional information concerning these factors can be found in press releases as well as in Ligand's public periodic filings with the Securities and Exchange Commission. Ligand undertakes no obligation to update the statements contained in this press release after the date hereof.

For information about Wyeth-Ayerst, contact Douglas Petkus at 610/971-4980.

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