Cytogen Corp. said Monday that it has begun Phase I trials ofits ThromboScan cardiovascular imaging agent.

ThromboScan, which is linked to technetium, targets fibrinogenreceptors on platelets in order to detect blood clots in thecirculatory system. The trials are testing ThromboScan for deepvenous thrombosis and pulmonary emboli.

ThromboScan uses a molecular recognition unit (MRU) insteadof a much larger monoclonal antibody. MRUs are short chains ofamino acids that have the ability to bind with specific targetsites. The ThromboScan MRU is only 17 amino acids long,compared with the 1,320 amino acids of a typical MAb.

Other companies, including Centocor Inc., American BiogeneticSciences Inc. and Bio-Technology General Corp., are usingantibody fragments, which are larger than MRUs, for blood clotimaging. Centocor, which is farthest ahead, filed in Decemberfor Food and Drug Administration marketing approval of itsFibriscint imaging agent. Fibriscint binds to a portion of thefibrin molecule only in new clots.

Cytogen shares (NASDAQ:CYTO) closed down $4 at $24.75. Thestock climbed as high as $31.50 last week upon the FDA'smarketing approval of Cytogen's OncoScint imaging agent.

In a separate announcement, the Princeton, N.J., companyreported that 1991 revenues rose to $10.9 million, 132 percentabove 1990 revenues of $4.7 million. The 1991 figure included$4 million from two one-time milestone payments, fromEuroCetus for the approval of the company's colorectal imagingproduct in Germany and Luxembourg, and from KnollPharmaceuticals upon finalizing a U.S. co-promotion agreementwith Knoll.

Net loss for 1991 was $15.3 million, or 98 cents per share,compared with a loss of $17.3 million, or $1.36 per share, in1990.

For the fourth quarter ended Dec. 28, its net loss was $3.1million, or 19 cents per share, on revenues of $5 million. Forthe comparable 1990 quarter, the company had a net loss of$4.6 million, or 32 cents per share, on revenues of $900,000. --KB

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