August 18, 2009

Will New Insect Repellent Fly?

After searching for 50 years, scientists finally have discovered new mosquito repellents that beat DEET for warding off those pesky, disease-carrying insects. The stuff seems like a dream come true. It makes mosquitoes buzz off three times longer than DEET, the active ingredient in many of today's bug repellents. It does not have the unpleasant odor and it does not cause DEET's sticky-skin sensation.

But there's a fly in the ointment. The odds are against any of the new repellents finding a place on store shelves this year or next "” or ever.
According to Ulrich Bernier, Ph.D., lead researcher for the repellent study, the costly, time-consuming pre-market testing and approval process is a hurdle that will delay availability of the repellents, which were discovered last year.

"Commercial availability of topical repellents can take years and a significant investment . . ." Bernier was quoted as saying. "Once you determine that the repellent works through some screening process, we then have to go through a toxicological hazard evaluation involving numerous toxicological tests."

Provided the repellents continue to work when tested in the laboratory on human skin, and if they pass the battery of toxicological tests, they would still face a series of tests to prove their effectiveness in making mosquitoes bug off, Bernier said. "Clearly, the odds are stacked against new repellent products making it to market."

Bernier and his team discovered the repellents with the application of a computer model using the molecular structures of more than 30,000 chemical compounds tested as repellents over the last 60 years. Using 11 known compounds, they synthesized 23 new ones. Of those, 10 gave about 40 days protection, compared to 17.5 days for DEET, when a soaked cloth was worn by a human volunteer. When applied directly to the skin, DEET lasts about five hours.

Bernier participates in repellency studies, in which about 500 mosquitoes try to land on his arm and bite through a repellent-soaked cloth. "If the mosquitoes don't even land, we know the repellent is surely working," he explained. "If they walk around on the cloth-covered-arm, they are on the verge of being repelled. If they bite"¦ on to the next repellent." He said that extended studies are now evaluating the effectiveness of the repellents against flies and ticks.

"This was quite an ambitious project," Bernier said. "The USDA historical archives and repellents database we used consisted of more than 30,000 chemical structures tested over the past six decades."

To search for the best repellents, the team devised software that recognized structural features of chemicals that effectively kept the bugs away. They trained the program by feeding it the molecular structures of 150 known repellents. The program learned to identify the chemical traits of a good repellent without the chemists even having to know what those traits were. For example, the program checked out 2,000 variants of a compound found in black pepper that repels insects.

SOURCE: Presented at the National Meeting of the American Chemical Society (ACS), Washington, D.C., August 16, 2009