By Mary Welch

After one patient out of 1,400 developed low platelet counts and neutralizing antibodies in trials of Amgen Inc.'s megakaryocyte growth and development factor (MGDF), the company pulled the plug on platelet donation clinical trials with the product.

However, Thousand Oaks, Calif.-based Amgen's trials using MGDF for cancer patients receiving chemotherapy — including a Phase III trial for bone marrow transplantation — will continue.

In laboratory tests, MGDF induced bone marrow progenitor cells to become megakaryocytes, the large cells that make platelets. Platelets are needed for the blood to clot, and a shortage can place cancer patients at risk of serious bleeding.

In earlier tests with platelet donors, MGDF seemed well tolerated and effective in increasing platelet counts and the yields of platelets obtained in platelet donation. Based on this preliminary evidence, the larger trials were started.

The purpose of these trials was to grow a higher platelet yield in healthy people. Enriching the donors' platelets would reduce the number of donations needed.

"We were hoping to obtain the number of platelets that are needed for medical reasons while using the least number of people being exposed to any safety risks [involved in donating platelets]," said David Kaye, spokesman for Amgen.

Using healthy donors posed unique problems.

"We set high hurdles for ourselves," Kaye said. "When you have a healthy individual, the tolerance level for adverse effects is zero. You have to have a squeaky clean product and very few of us have that."

One patient in 1,400 developed low platelet counts and neutralizing antibodies, which are antibodies that cross-react with a natural protein and hinder its effects.

Analysts did not seem surprised by Amgen's news.

"I've always indicated that I was skeptical about MGDF in platelet donations," said Matthew Geller, with Oppenheimer & Co., in New York. "You can't take healthy people and make them sick."

David Crossen, an analyst with Montgomery Securities in San Francisco, said he too never believed MGDF in platelet donations would be an important product for the company. "We had been hearing about side effects way back," Crossen said.

For cancer patients, the picture is much different. Low platelet levels are a complication of cancer chemotherapy, and chemotherapy-induced thrombocytopenia often delays or prevents further cancer therapy.

Amgen's Pipeline Is Weak, Analyst Says

The analysts believe Amgen's MGDF setback is just a blip on a larger screen of problems for Amgen. "The only issue for Amgen that I see is that their pipeline is full of holes, and MGDF doesn't look like it's going to fill [them]," said Geller.

Crossen noted that the company's stock has been "stilted and languishing for two years, and the only upswings have come as a result of takeover rumors, which I don't see [happening], or in overly optimistic views of Epogen sales."

Epogen is a red blood cell booster used for the treatment of anemia in dialysis patients.

The Phase III trial of MGDF in chemotherapy patients was launched in the fourth quarter of 1997. Earlier last year, Amgen reported MGDF was shown to boost platelet levels by 70 percent in a Phase I/II trial.

Amgen's stock (NASDAQ:AMGN) closed Tuesday at $70.50, down $0.375. *