By Lisa Seachrist

Washington Editor

WASHINGTON - The FDA granted marketing approval to Ligand Pharmaceuticals Inc.'s first drug, Panretin (aliretinoin) gel, as a topical treatment for Kaposi's sarcoma (KS), a cancer common in people who have AIDS.

While not a blockbuster drug, the Panretin gel approval serves as an important milestone for Ligand, said Mike King, senior analyst with BancBoston Robertson Stephens, in New York.

"KS is a small market," King said. "It's really important more for getting a sales force in place and showing that they can negotiate the FDA approval process. It's good practice; they're walking before they run."

San Diego-based Ligand said it will deliver Panretin gel to its distributor, Integrated Commercialization Solutions, within five business days. With the treatment, Ligand is hoping to provide an important, less-invasive option to KS patients.

A spokesman for Ligand said the main advantage of Panretin gel is that it is a self-applied treatment. Other cutaneous therapies, such as radiation, cryotherapy or laser surgery, require the time and expertise of health professionals and entail the costs of the clinical setting, he said. With Panretin gel, those costs are reduced.

Price, Side-Effect Profile Could Offer Advantages

Panretin also avoids some of the disfiguring and toxic side effects of other therapies.

Ligand estimates the cost of treatment with Panretin gel at $3,900 to $5,800 for a four-to-six-month course of therapy. Currently, intravenously administered liposomal anthracycline formulations used to treat KS cost between $8,000 and $12,000 for the drug used in the standard course of treatment, not including collateral clinical costs.

Panretin gel is a 0.1 percent topical formulation of 9-cis retinoic acid. It is a small-molecule, non-peptide hormone isolated and characterized by Ligand in collaboration with scientists at the Salk Institute, in La Jolla, Calif., and Baylor College of Medicine, in Houston, Texas. It is a derivative of vitamin A, and has a broad range of biological activities that affect cell growth, differentiation and apoptosis.

In November, Panretin gel cleared the FDA's Oncologic Drugs Advisory Committee by a vote of 8 to 1. The company at that time presented two Phase III clinical studies, one conducted in North America and the other internationally. (See BioWorld Today, Nov. 17, 1998, p. 1.)

In the North American study of 268 patients, 35 percent of the patients using Panretin gel showed a complete or partial response compared to 16 percent of the placebo patients. The international study included only 82 patients, because it reached a protocol-specified stopping point when 36 percent of patients in the Panretin group showed a response to therapy, compared to 7 percent of the placebo group.

With the advent of highly aggressive antiretroviral therapy, the incidence of KS has been dropping. However, Ligand estimates that between 30,000 and 50,000 patients in the U.S. and Western Europe suffer from the disease.

In addition to Panretin gel, Ligand has an oral formulation, Panretin capsules, in Phase II studies for the treatment of AIDS-related KS. The company is also conducting Phase II trials of Panretin capsules in breast and pediatric cancers, and in bronchial metaplasia. The company is testing the formulation as a therapy for myelodysplastic syndrome, severe plaque psoriasis, and in combination with interferon as a treatment for renal cell carcinoma.

Ligand's stock (NASDAQ:LGND) closed Wednesday at $11.75, down $0.375.