By Frances Bishopp

ImmunoGen Inc.'s stock dropped 37.5 percent Tuesday after the company reported it would discontinue development of its most advanced product, Oncolysin B, based on preliminary data from Phase III clinical trials.

The Cambridge, Mass., company's shares (NASDAQ: IMGN) ended the day at $1.562, down $0.938.

The Phase III data, reviewed by an independent monitoring committee after enrollment of 155 patients, indicated Oncolysin B offered no advantage when compared to the control arm of the study. The drug was being studied in a 47-center trial funded by the National Cancer Institute for the treatment of lymphoma patients following autologous bone marrow transplants.

"We feel these results are at best ambiguous and with our limited resources lead us to not be able to continue to commit both economic and intellectual resources to the product," ImmunoGen CEO Mitchel Sayare told BioWorld Today.

"If we were a huge company with unrestricted amounts of cash, then perhaps we would," he continued. "But we're not."

Oncolysin B combines a monoclonal antibody with a modified form of the plant toxin ricin to attack B-cell lymphomas and leukemias. Oncolysin B has been in the clinic since the end of 1988 and in Phase III studies since the end of 1993.

The Phase III study focused on patients with non-Hodgkin's B-cell lymphoma who had had many cycles of relapse and remission on conventional chemotherapy, leading eventually to a bone marrow transplant. These patients were randomized to one of two groups, one that received the drug and one that didn't,

"What the statistical analysis showed at this stage," Sayare said, "was that there was no clinical benefit for the drug."

ImmunoGen, Sayare said, has enough financial resources to cover 12 to 16 months of operation. The company also is working diligently to negotiate corporate partnerships around other ImmunoGen products in the areas of colon cancer, small cell lung cancer and apoptosis research.

"We expect to bring not only these deals home, and the validation that comes with these deals, but also cash into the company," Sayare.

ImmunoGen is developing a drug candidate for the treatment of colorectal cancer based on targeting the powerful chemotherapeutic agent DM1 directly to cancer cells through its attachment to an antibody that binds to a protein found on the surface of tumor cells. DM1 is a toxin derived from maytansine, a natural product found in an African shrub.

By linking the antibody to DM1, ImmunoGen has produced a product 100 times more potent than established cytotoxic agents in animal tests.

In published mouse studies, this product eliminated transplanted human colon tumors. The company, which has two patents covering the use of DM1 in conjugated forms, plans to begin human trials on the drug in 1998.

ImmunoGen also is delivering DM1 directly to small cell lung cancer with a humanized version of an antibody that binds specifically to small cell lung cancer cells. In preclinical studies, this product eradicated small cell lung cancer tumors in mouse models. It currently is in advanced preclinical studies.

Apoptosis Technology Inc., founded by ImmunoGen in 1993, develops screens to identify chemicals that reverse the suppression of apoptosis in cancer cells.

In October 1996, ImmunoGen, faced with dwindling cash reserves, obtained $12 million in equity financing to support development of its oncology drugs. (See BioWorld Today, Oct. 24, 1996, p. 2.)

In 1994, the company slashed its staff by 60 percent, reduced senior management salaries by 20 percent and suspended new product programs to conserve resources for continued clinical production of Oncolysin B.

"The decision to discontinue development of Oncolysin B permits us to put our economic and intellectual resources behind things that have real value to ImmunoGen," Sayare said, "and to make a clean statement about where we are going." *