George Hess: Technique aids treatment for epilepsy, cocaine poisoning

George P. Hess, professor of molecular biology and genetics, speaks during a press conference at the AAAS meeting in Denver, Feb. 15. David Brand/Cornell News Service

By Roger Segelken

Discovery of drugs to treat generalized epilepsy with febrile seizures (GEFS), a genetic disorder that affects 4 million Americans, could now advance more rapidly, predicts Cornell biochemist George P. Hess.

A professor of molecular biology and genetics, Hess invented a laser-based technique to study signal transmission between cells of the nervous system. The same technique, called laser-pulse photolysis, already has identified a cocainelike analog compound to block the effects of cocaine poisoning on the nervous system.

Hess discussed his laser technique, which could enable drug design and testing for a variety of neurological disorders, in a press briefing on Feb. 15 and in a lecture on Feb. 16 at the American Association for the Advancement of Science annual meeting. His lecture was given in a session titled "Shining Light on Signal Transmission Between Cells of the Nervous System."

"Mechanism-based drug design can proceed more rationally, knowing the exact roles and timing of all the chemical players at the junctions between neurons and muscle cells or between neurons and other neurons," Hess said.

The recent discovery of cocaine analogs, one application of the laser-pulse photolysis technique, will be reported in the scientific literature, Hess said, adding: "These compounds are not ready for clinical use, but they do pro-vide a lead for pharmaceutical development."

Laser-pulse photolysis allows neuroscientists to look at entire ensembles of molecules -- not just single channels or single molecules -- during split-second chemical reactions that relay electrical signals through the nervous system, Hess explained. "These reactions can be over and done in 0.3 millisecond. To observe them in detail, we need to equilibrate [balance] the receptor with the neurotransmitter in much shorter time frames," he said. One way to beat the clock and test the effects of a potential therapeutic agent is to present the compound as a "caged neurotransmitter," a specially constructed molecule that has no effect on receptor proteins so it can be mixed with a cell without triggering reactions.

Once the caged neurotransmitter is in place, said Hess, a single pulse of laser light can cleave the protective cage within microseconds, allowing the neurotransmitter to bind to receptors. As the freshly exposed neurotransmitter opens transmembrane channels through which electrical currents flow, investigators can watch the millisecond shifts -- between open and closed states of channels -- and determine whether a drug, such as a cocaine analog, is having the desired effect.

In the case of GEFS epilepsy, a genetic mutation is believed to be responsible for a single, inappropriate amino acid in the so-called GABA receptor in brain cells. (The disorder is called febrile because, out of the approximately 5 percent of young children who experience seizures during a high fever, a small proportion with a genetic predisposition later develop epilepsy.) Using laser-pulse photolysis, Hess and his students discovered the reason for the receptor malfunction: a shift in the equilibrium from the open-channel form toward the closed-channel form. They also tested several compounds with high molecular weights that can shift the channel-opening equilibrium -- an encouraging indication that small-molecule drugs can be found to overcome mutations in the GABA receptor and halt the raging "electrical storms" that characterize epilepsy.

Also valuable would be a treatment to short-circuit the electro-chemical effects of cocaine, Hess said. "During the past two decades, many attempts have been made to find compounds that prevent cocaine's inhibition of proteins that are essential in brain function, but compounds that alleviate cocaine inhibition have not been identified -- until now."