Ligand Announces Initiation of Clinical Trials for Thrombocytopenia Drug, LGD 4665.

SAN DIEGO -- Ligand Pharmaceuticals Incorporated (NASDAQ:LGND) (the "Company" or "Ligand") announced today that the Company is initiating Phase I clinical trials of LGD 4665, an oral, small molecule drug that mimics the activity of thrombopoietin (TPO), a growth factor that promotes growth and production of blood platelets.

Thrombocytopenia or low platelet count is a common clinical finding associated with a diverse group of clinical disorders or conditions affecting platelet production and/or survival. Prevalent clinical disorders where platelet loss or dysfunction leads to significant morbidity include idiopathic thrombocytopenia purpura (ITP), myelodysplastic syndrome, liver dysfunction associated with hepatitis C viral and severe cirrhosis, chemotherapy-induced thrombocytopenia (CIT) as well as a number of other disorders. Current therapeutic options are mostly palliative, including steroids, immunosuppresants, splenectomy and, for the most severe thrombocytopenias, platelet transfusion.

Thrombopoietin (TPO) is the key hematopoietic growth factor responsible for platelet production. There are currently no approved TPO molecules available but there are both peptides and oral TPO mimetics in late-stage clinical development, the latter class including molecules developed by GSK in collaboration with Ligand.

While the size of the emerging thrombopoietin market is difficult to estimate, previous published estimates in research analyst reports at Merrill Lynch and Lehman Brothers suggest the potential worldwide market could be between $2.5 and $4.5 billion dollars per year.

LGD 4665 was selected from a group of novel oral TPO mimetics synthesized at Ligand, for which Ligand has retained exclusive worldwide rights. These molecules were profiled to have in vitro efficacy and selectivity equal to or better than TPO in predictive human cell models and to have a better profile for efficacy and potency than other oral mimetics currently in clinical development.

"We are very pleased that LGD 4665, a novel, second generation, orally active thrombopoietin mimetic is advancing to human clinical trials," said Andres Negro-Vilar, MD, PhD, Executive Vice President, R&D and Chief Scientific Officer, Ligand Pharmaceuticals. "LGD 4665 has shown an excellent profile of activity in preclinical studies, and has the potential to become, in terms of efficacy, potency and selectivity, a competitive molecule for the treatment of different forms of thrombocytopenias. Potential disease targets under consideration by Ligand for advanced clinical development include idiopathic thrombocytopenia purpura (ITP), myelodysplastic syndrome and leukemias, platelet dysfunction associated with hepatitis C and chronic liver disease and chemotherapy-induced thrombocytopenia, among others."

"LGD 4665 targets a number of platelet disorders of different etiologies, in what represents an underserved, large pool of patients frequently requiring long-term treatment for chronic, debilitating conditions associated with platelet loss and dysfunction," said Andres Negro-Vilar, MD, PhD.

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 forward-looking statements within the meaning of section 21E of the Securities Exchange Act of 1934, as amended, 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 of LGD 4665, other TPO related drugs or mimetics, market size and potential, LGD 4665 profile, efficacy, potency, selectivity, competitiveness and potential, and number of patients. Actual events or results may differ from our expectations. For example, there can be no assurance that LGD 4665 or other potential drugs will progress through clinical development or receive required regulatory approvals within the expected time lines or at all, that clinical trials will confirm any characteristics or profile presented here, that there will be a market of any size for LGD 4665, nor that LGD 4665 or any drugs will be beneficial to patients 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.