Single-chain antigen-binding (SCA) proteins were shown inresearch at the National Cancer Institute (NCI) to have the edgeover monoclonal antibodies in delivering anti-cancer agents totumor cells.

The SCA research, conducted in a collaboration betweenscientists at Enzon Inc. and Jeffrey Schlom, chief of thelaboratory of tumor immunology and biology at the NCI, waspublished in the June 15 issue of Cancer Research.

Enzon's SCAs consist of a whole chain of an antibody and have ahigher affinity for their targets than either whole antibodies orantibody fragments. Their high binding rates also give SCAs ashort circulating life, reducing the chances of immuneresponses.

"These SCA proteins penetrate the tumor in a massive wave,"said Marc Whitlow, group leader of protein engineering atEnzon, who presented the study's results at the 39th AnnualMeeting of the Society of Nuclear Medicine last week in LosAngeles. "They radiate out uniformly from the blood vesselsand rapidly reach areas deep within the tumor," he said. "As aresult, SCA proteins have an edge over conventionalmonoclonal antibodies in cancer imaging and therapy."

The NCI study compared tumor penetration of the SCAproteins, MAbs and antibody fragments in human colon tumorsin mice.

"The tumor-to-normal tissue ratio is higher with SCA proteinsthan monoclonal antibodies," said Robert Shorr, vice presidentof research at Enzon. "The higher the ratio, the more specificthe desired result," he said. "If we're looking to image a tumor,the image will be sharper. If we're delivering a drug, theincreased ratio lowers the possiblility of side effects."

SCAs have potential applications in the diagnosis and treatmentof cardiovascular, infectious, autoimmune and inflammatorydiseases, as well as cancer.

Enzon signed an exclusive licensing agreement with NeoprobeCorp. in January to combine the SCA technology withNeoprobe's radioimmuneoguided surgery (RIGS). Enzon said ithas no products using SCA under development.

(c) 1997 American Health Consultants. All rights reserved.