3.4: Is It Chemistry or Genetics?

Regardless of the way researchers find new medicines, drug discovery often takes many unexpected twists and turns. Scientists must train their eyes to look for new opportunities lurking in the outcomes of their experiments. Sometimes, side trips in the lab can open up entirely new avenues of discovery.

Take the case of cyclosporine, a drug discovered three decades ago that suppresses the immune system and thereby prevents the body from rejecting transplanted organs. Still a best-selling medicine, cyclosporine was a research breakthrough. The drug made it possible for surgeons to save the lives of many critically ill patients by transplanting organs. But it's not hard to imagine that the very properties that make cyclosporine so powerful in putting a lid on the immune system can cause serious side effects, by damping immune function too much.

Years after the discovery of cyclosporine, researchers looking for less toxic versions of this drug found a natural molecule called FK506 that seemed to produce the same immune-suppressing effects at lower doses. The researchers found, to their great surprise, that cyclosporine and FK506 were chemically very different. To try to explain this puzzling result, Harvard University organic chemist Stuart Schreiber (then at Yale University in New Haven, Connecticut) decided to take on the challenge of figuring out how to make FK506 in his lab, beginning with simple chemical building blocks.

Schreiber succeeded, and he and scientists at Merck & Co., Inc. (Whitehouse Station, New Jersey) used the synthetic FK506 as a tool to unravel the molecular structure of the receptor for FK506 found on immune cells. According to Schreiber, information about the receptor's structure from these experiments opened his eyes to consider an entirely new line of research.

Schreiber reasoned that by custom-making small molecules in the lab, scientists could probe the function of the FK506 receptor to systematically study how the immune system works. Since then, he and his group have continued to use synthetic small molecules to explore biology. Although Schreiber's strategy is not truly genetics, he calls the approach chemical genetics, because the method resembles the way researchers go about their studies to understand the functions of genes.

In one traditional genetic approach, scientists alter the "spelling" (nucleotide components) of a gene and put the altered gene into a model organism—for example, a mouse, a plant, or a yeast cell—to see what effect the gene change has on the biology of that organism. Chemical genetics harnesses the power of chemistry to custom-produce any molecule and introduce it into cells, then look for biological changes that result. Starting with chemicals instead of genes gives drug development a step up. If the substance being tested produces a desired effect, such as stalling the growth of cancer cells, then the molecule can be chemically manipulated in short order since the chemist already knows how to make it.

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Blending Science

These days, it's hard for scientists to know what to call themselves. As research worlds collide in wondrous and productive ways, the lines get blurry when it comes to describing your expertise. Craig Crews of Yale University, for example, mixes a combination of molecular pharmacology, chemistry, and genetics. In fact, because of his multiple scientific curiosities, Crews is a faculty member in three different Yale departments: molecular, cellular, and developmental biology; chemistry, and pharmacology. You might wonder how he has time to get anything done.

The herb feverfew (bachelor's button) contains a substance called parthenolide that appears to block inflammation.

He's getting plenty done—Crews is among a new breed of researchers delving into a growing scientific area called chemical genetics (see main text). Taking this approach, scientists use chemistry to attack biological problems that traditionally have been solved through genetic experiments such as the genetic engineering of bacteria, yeast, and mice. Crews' goal is to explore how natural products work in living systems and to identify new targets for designing drugs. He has discovered how an inflammation-fighting ingredient in the medicinal herb feverfew may work inside cells. He found that the ingredient, called parthenolide, appears to disable a key process that gets inflammation going. In the case of feverfew, a handful of controlled scientific studies in people have hinted that the herb, also known by its plant name "bachelor's button," is effective in combating migraine headaches, but further studies are needed to confirm these preliminary findings.