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In its march toward gaining more product candidates, Exelixis Inc. signed a deal with Invitrogen Corp. under which Invitrogen will help with lead development and optimization by providing validated high-throughput screening assays in single live cells.

"Basically what we're buying from them are cell lines used in assay development," said Jane Green, vice president of corporate communications for South San Francisco-based Exelixis. "But there is also some custom work they'll be doing with us. In that instance, there are specific cell lines we would want developed, and they would make those available to us, but it's nonexclusive so they would be able to utilize the reagents with other customers."

Financial terms were not disclosed.

Product and service provider Invitrogen's Drug Discovery Solutions group (formerly called PanVera) offers Exelixis the GeneBLAzer and Voltage Sensor Probe technologies for compound screening.

The GeneBLAzer cell-based (beta)-lactamase system combines traditional molecular and cellular biology with a fluorescence resonance energy transfer (FRET) detection method for high-throughput screening experiments, allowing researchers to get more precise measurements of subtle functional cellular responses related to specific drug targets, in living cells and in highly miniaturized formats.

FRET has been around for decades but lately has become steadily more refined, thanks to improvements in dyes and instruments. It involves non-radiative transfer of energy from a fluorophore (or fluorescent molecule) in an excited state to a nearby acceptor fluorophore, thus providing important details about molecules' interactions.

"We've really established a beachhead in kinase drug discovery," Green said. "One of the company's strategies is to broaden discovery and development and explore other targets outside of cancer, and increasingly we will be focusing on these additional targets" in drug classes such as nuclear hormone receptors and G protein-coupled receptors, she said, and the deal with Invitrogen will help.

"I wouldn't say it was predominantly why [the deal] was done," Green told BioWorld Today. "The strategy has been in our long-term plan for quite a while, so it wasn't as though they had the product and the strategy was based on the product."

The process, she noted, already has begun, and the firm's "large and diverse high-throughput screening library of more than 4 million compounds is particularly well-suited to these target classes."

Meanwhile, the first generation of what Exelixis calls Spectrum Selective Kinase Inhibitors is moving along, and the firm continues to aim for at least two investigational new drug applications per year. In late June, Exelixis disclosed its plan to restructure and consolidate, cutting 62 positions, or 11 percent of the company's work force, as a way of intensifying the bid for more INDs. (See BioWorld Today, July 1, 2004.)

Exelixis' pipeline already features one Phase III candidate, XL119 (becatecarin) for bile-duct tumors, in-licensed from Bristol-Myers Squibb Co., of New York, which got it from the National Cancer Institute in Bethesda, Md. The compound is semi-synthetic and a topoisomerase II inhibitor. (See BioWorld Today, June 24, 2004.)

Rounding out the drug roster is Exelixis' proprietary collection of earlier-stage compounds. One has finished Phase I testing, another is undergoing Phase I, and more are preclinical. The company's collaborators include London-based GlaxoSmithKline plc, Bristol-Myers, and Merck & Co. Inc., of Whitehouse Station, N.J.

Exelixis' stock (NASDAQ:EXEL) closed Thursday at $6.75, down 4 cents. Carlsbad, Calif.-based Invitrogen's shares (NASDAQ:IVGN) ended the day at $49.13, down 71 cents.

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