By William Wells
Somehow the brain classifies the thousands of smells we encounter every day. Finding out how this works may bring biologists not only intellectual satisfaction, but also money.
"There reigned in the cities a stench barely conceivable to us modern men and women. The streets stank of manure, the courtyards of urine, the stairwells of moldering wood and rat droppings, the kitchens of spoiled cabbage and mutton fat."*
Somehow the nose can differentiate these aldehydes, and it doesnt stop there. The caraway smell of (+)-carvone is distinct from the spearmint smell of (-)-carvone, its mirror image. The orange, rose-like smell of octanol contrasts with the rancid, sweaty odor of its chemical relative octanoic acid. Even relative dose matters. Indoles have a pleasant floral scent when diluted, but, according to Paul Grayson, a concentrated hit "makes cat urine smell pretty good."
As CEO of Senomyx, Inc. (La Jolla, Calif.), Grayson hopes to make sense of this vast and confusing odiferous world. Senomyx is unusual in the world of biotechs because it is focussing not on miracle medical cures, but on improving consumer products. Bringing logic to smelly science could save Calvin Klein millions of dollars if perfumes could be made with fewer or cheaper ingredients. "Weve put together big pharmas tools," says Grayson, "to come up with our discovery engine for smell and taste."
*Quotations are from "Perfume : the story of a murderer" © 1986 Patrick Süskind, published by Alfred A. Knopf, Inc.
"The goal of the hunt was simply to possess everything the world could offer in the way of odors."
"When Baldini assigned him a new scent ... Grenouille no longer reached for flacons and powders, but instead simply sat himself down at the table and wrote the formula straight out."
The first task for Senomyx is to come up with an olfactory code: a matrix in which every smelly chemical can be expressed as a pattern of activated olfactory receptors. This coding of smells should allow Senomyx to replace expensive chemicals with cheaper ones, or a complicated mixture with one chemical, as long as the final pattern of receptor activation is the same. "If we can mimic the way that natural products work in terms of activating the receptors then our brain wont know the difference between a natural odor and a synthetic," says Senomyxs vice-president of research Mark Zoller. "The million dollar question is whether we can get chemicals that look different but smell the same."
The receptor activation patterns will act as a replacement human nose, capable of screening the thousands of novel chemicals that Senomyx is generating. "If you could screen 50,000 compounds a day with 1 microliter of fragrance per assay in human subjects we would be out of business," says Grayson. "But you cant."
Before it tests its novel chemicals, Senomyx needs a matrix describing the effect of known smelly chemicals. "The proximal problem of what odors go with what receptor I think will be solved in the next two to four years," says Larry Katz (Duke University, Durham, North Carolina). "Relatively soon well have a molecular fingerprint of what an odorant looks like to the olfactory epithelium."
Whether those matrices make any sense is another matter. "Are there such things as primary odors?" asks Stuart Firestein of Columbia University in New York. "In vision you have red, green and blue [receptors] but you can see thousands of hues. The question is whether there are similar things in the olfactory system."
From Bucks work we know that each olfactory receptor recognizes multiple odorants (some clearly related, some not) and that each odorant is recognized by multiple receptors. Everyone involved is hoping that some sense of order falls out of this combinatorial code. Based on the psychophysics of smell and the psychobabble of perfumers "there are all these odor categories," says Katz, "and I think they must have correlations with groups of receptors."
Senomyx will use receptor patterns in several of their projects, including screens for inhibitors of malodors. Perhaps the most lucrative application will be in establishing the code for a best-selling perfume, and then ensuring that the code is maintained even as the chemical mix is changed. Unnecessary components of complex perfume mixtures could be removed, expensive or unstable components replaced with cheaper, more stable chemicals, and new scent combinations devised to transmit the same odor signature from the far less volatile emulsion of a shampoo. In the land of Calvin Klein et al., its all about brand extension.
What Grayson cannot yet know is how exact his receptor patterns will have to be and how exact of a match will have to be maintained to preserve the precise scent of his choice. The work of Katz and Buck suggest that the number of receptors activated by any single odorant will be manageable. But establishing how sensitive the code is to altered affinities or failure to bind 1 of 10 previously occupied receptors will only come once the code is established and the system tested. Unfortunately, as Senomyx co-founder Lubert Stryer (Stanford University, Stanford, California) says, "Its easy to say in a sentence, but its a vast project to determine the olfactory response spectrum. Its the most complex combinatorial recognition project."
What no one is promising, at least so far, is mind control. "The emotional content, how odors bring back memories and make one feel, are very important, but receptors will not code all of that," says Stryer. "Im not in the position to say that a given receptor activation will seem pleasant." But Zoller feels that medical applications may come in time. "We know that olfaction and memory are linked," he says. "Maybe there are certain areas of pain and memory that could be accessed with odorants."
"The persuasive power of an odor cannot be fended off, it enters us like breath into our lungs, it fills us up, imbues us totally. There is no remedy for it"
This may be one of the few biotechnology companies whose FAQ list includes the question, "Is this some kind of joke?" And what other company can lay claim to having its founding technology parodied before the real company even existed? Now that DigiScents is operational, however, it is busy promoting a test process named FirstWhiff, electing a vice president of scentography, and building a website called, you guessed it, The Snortal
Distribution of the necessary software will be easy it is being bundled with RealPlayer but the hardware (with its cartridge of 128 odorants, combinable in millions of permutations) presents more of a challenge. "The focus studies weve done have been very very successful," says DigiScents co-founder and CEO Joel Bellenson. "The response rate has been over 90% once people experience it." The trick may be to get people to try it in the first place to get them past their memories of the classic John Waters film Polyester, a scratch-and-sniff extravaganza presented in "Odorama."
The iSmell will be available soon, but in the meantime DigiScents is busy cloning olfactory receptor genes (with the help of CLONTECH Laboratories, Inc. of Palo Alto, California) and determining an olfactory code akin to that being derived by Senomyx. "Those patterns become a fingerprint for an odor, which allows us to reproduce that odor later," says Bellenson. "We pull the subjectivity out of the problem."
For all its interest in olfaction, Senomyx may get its start in modifying taste. The simplest of all its proposed projects involves blocking the response of bitter taste receptors to products such as processed foods, nutraceuticals, antibiotics, and artificial sweeteners. The number of bitter taste receptors appears to be manageable (perhaps 2040), and any given bitter chemical may target only one receptor. "Its more like a classical target," says Zoller. In contrast, devising something new say a tofu with meat flavor involves creating new volatile and non-volatile components, and "thats a really difficult problem." Other projects for the future include novel sweeteners (based on putative sweet receptors isolated by Zuker and Ryba), and modifiers of possible taste receptors for umami (the flavor of monosodium glutamate) and salt.
"The meaning and goal and purpose of his life had a higher destiny: nothing less than to revolutionize the odiferous world.."
As a refugee from pharmaceutical science, Zoller has certainly thought about the contrast between his old and new goals. "When I tell non-scientists what Im doing everybody thinks it is unbelievably cool," he says. "When I tell scientists they think, Youre not curing osteoporosis or cancer."
The new science "is very much targeted to enhancing the enjoyment of life," says Stryer. "It relates to day-to-day living rather than the amelioration of suffering."
Stryer says he has more than paid his dues in medical science and is happy to be focussing on satisfaction rather than suffering. Besides, more serious applications may come, such as the modification of plant smells to repel insect predators.
But that project is not top of the list for now. With the current fuss over genetically modified foods "were not even going down that road," says Grayson. "Well revolutionize one industry at a time."