Ligand Earns $2 Million Milestone as GlaxoSmithKline Begins Phase I Development Of a Second Oral Drug for Thrombocytopenia Markets; Potential for Future Double-Digit Royalties if Successful.

SAN DIEGO -- Ligand Pharmaceuticals Incorporated (Nasdaq:LGNDE) announced today that the company has earned a $2 million milestone payment from GlaxoSmithKline (NYSE:GSK) with that company's filing of an IND for SB-559448, a small-molecule drug that mimics the activity of thrombopoietin (TPO), a protein factor that promotes growth and production of blood platelets. If the drug continues in development and ultimately is approved and marketed, Ligand could receive additional milestone payments and double-digit royalties on product sales.

In February 2005 Ligand earned a $1 million milestone payment from GlaxoSmithKline with that company's commencement of Phase II trials of another TPO product, SB-497115.

Thrombocytopenia (decreased platelet count) is a common side effect of many chemotherapies and can lead to uncontrolled bleeding, thus representing a significant problem in the treatment of cancer patients. Similarly, thrombocytopenia is commonly seen in patients undergoing myeloablative therapies or in those with leukemias or metastatic tumors. Ligand estimates, based on available data, that approximately 20 to 25 per cent of the more than one million patients who undergo chemotherapy each year experience thrombocytopenia. These estimates do not include patients suffering from idiopathic thrombocytopenia or the large number of patients -- estimated at more than two million -- with hepatitis or other diseases affecting liver function. Currently, thrombocytopenia patients have few therapeutic options other than frequent platelet transfusions. The frequency and chronicity of treatment with platelet restoring factors such as TPO could vary depending on the underlying cause of thrombocytopenia.

There are no approved TPO agents for the treatment or prevention of thrombocytopenias. SB-497115 is being developed for the treatment of thrombocytopenia associated with chemotherapy or disease states such as immune thrombocytopenic purpura and chronic liver disease.

SB-497115 is the first, and most advanced in human development, non-peptide small molecule TPO receptor agonist with demonstrated activity in human bone marrow in vitro assays and pharmacological activity in humans. Data from a Phase I study in healthy volunteers presented at the 2004 annual meeting of the American Society of Hematology in San Diego, California, (ASH Abstract #2916) show that SB-497115 increased platelet counts in a dose-dependent fashion when administered orally.

"GSK's decision to move a second, small-molecule TPO growth factor into human development is an exciting further evolution of products from our collaborative research programs, especially following so quickly after SB-497115 moving into Phase II," said Andres Negro-Vilar, M.D. PhD, Ligand's executive vice president of research and development and chief scientific officer. "Either or both of these drugs, if successful, will add a key component to the hematopoietic factors (EPO, G-CSF) that have proven so useful in the treatment of anemias and neutropenias in cancer patients and in those with different hematopoietic disorders. This also underscores the continued maturation of our portfolio of 12 'big drugs' in human development which resulted from our first decade of collaborative research programs."

About the GSK-Ligand Growth Factor Collaboration

The GSK-Ligand collaboration began in 1995 to capitalize on Ligand's proprietary expertise and technology to discover small molecule drugs to control hematopoiesis and treat patients with cancer, anemia or platelet deficiencies. The research phase of the collaboration ended in 2001. GSK is responsible for the development and registration of products resulting from the collaboration, and Ligand may earn milestone payments of up to a combined $8 million as a product moves through development. GSK has exclusive worldwide marketing rights to products resulting from the research, and will pay Ligand royalties on a sliding scale up to low double digits on sales of products that make it to market.

About Ligand

Ligand discovers, develops and markets new drugs that address critical unmet medical needs of patients in the areas of cancer, pain, skin diseases, men's and women's hormone-related diseases, osteoporosis, metabolic disorders, and cardiovascular and inflammatory diseases. Ligand's proprietary drug discovery and development programs are based on its leadership position in gene transcription technology, primarily related to Intracellular Receptors (IRs). For more information, go to www.ligand.com.

Caution Regarding Forward-Looking Statements

This news release contains certain forward-looking statements that involve risks and uncertainties and reflect Ligand's judgment as of the date of this release. These statements include those related to clinical trials, product approval and marketing, further development, milestone and royalty payments, benefits and usefulness of SB-559448 and SB-497115, market size, registration opportunities, potential success of these drugs and maturation of our portfolio. Actual events or results may differ from our expectations. For example, there can be no assurance that SB-559448 or SB-497115 or other potential drugs will progress through Phase I, Phase II or later clinical development or receive required regulatory approvals within the expected time lines or at all, that future milestones or royalties will be earned, or that any such drugs will be beneficial or successfully marketed. Additional information concerning these and other risk factors affecting Ligand can be found in prior press releases as well as in public periodic filings with the Securities and Exchange Commission, available via www.ligand.com. Ligand disclaims any intent or obligation to update these forward-looking statements beyond the date of this release. This caution is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.