By Mary Welch

Xenova Group plc. said a Phase II colorectal cancer study with XR5000 failed to produce a complete or partial response to treatment, and as a result the trial has been stopped.

Patients received XR5000, a topoisomerase I and II inhibitor, in a 120-hour intravenous infusion every three weeks. Of those patients studied, two have shown stable disease and 13 patients have had disease progression.

"We are not particularly disheartened," said Hilary Reid Evans, the company's head of corporate communications. "We're pretty realistic and know that if you are going to do several trials the probability is that you're not going to have 100 percent success in all indications. You face it and go from there."

The company's stock (NASDAQ:XNVA) took the news a little harder, closing Thursday at $1.218, down 31.25 cents, or 20 percent.

Xenova, based in Slough, UK, is conducting three other Phase II trials with XR5000 in ovarian and non-small-cell lung cancer and glioblastoma. Recruitment is substantially complete for two of these studies, the company said. All four trials are being carried out in conjunction with the European Organization for the Research and Treatment of Cancer.

"What we are going to do is wait until we get data from these studies, which will probably be in Q3 or maybe early into Q4, and then review each trial and the drug's progress as a whole," Evans said. "We will not make any decisions before then."

She said the company does not know if another dosage would have made a difference or whether the drug is just not suitable for the colorectal indication.

"Approximately the same dosage is being used in the other three trials," Evans said. "We will wait until all the data is in before deciding what the situation is. There may be no relationship between the colorectal indication and the other three indications. What works in one may not work in another. We don't know yet ."

XR5000 acts as an inhibitor of both topoisomerases I and II, enzymes that are critically involved in the replication of DNA during the process of cell division. XR5000 is potentially the first in a new class of compounds that exhibit a novel mechanism of action through both topoisomerases.