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Biological Chemistry

New Tool For Drug Delivery Kinetics

Uptake and release of drug-carrier's cargo in cells is quantified in real time

by Michael Freemantle
May 8, 2006 | A version of this story appeared in Volume 84, Issue 19

A novel molecular transporter system carries probe molecules across cell membranes and allows the uptake of the transporter and the release of its molecular cargo to be monitored as the processes occur. The method could one day ferry drugs into cells.

The system, developed by chemistry professor Paul A. Wender and coworkers at Stanford University, consists of a peptide transporter linked by a disulfide bond to luciferin, a drug stand-in that is exploited to study the kinetics of the delivery system.

The researchers administer the luciferin-transporter conjugate to cells stably transfected with luciferase (J. Am. Chem. Soc., published online April 25, dx.doi.org/10.1021/ja0586283). They also can administer the conjugate to transgenic animals that express luciferase in all their cells, but that work has yet to be published.

In the cells, Wender explains, the conjugate encounters a reducing environment that cleaves the disulfide bond and releases its cargo of luciferin. Each molecule of free luciferin generates a photon when it interacts with luciferase, the enzyme responsible for the luminescent glow of the firefly. The Stanford team uses a special camera to measure the luminescent signal from the cells.

"The camera allows us to quantify precisely the timing and amount of the release in real time," Wender says. "The assay is fast and should facilitate studies on new transporters and linkers. Importantly, it does not require sacrifice of the animals.

"We now have a powerful tool that could greatly impact fundamental research by enabling the use of a wider range of probes," he continues. "It could also impact therapy by enabling a broader range of molecules to be used for intervention in various diseases."

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