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UNCOVERING LINKS BETWEEN CANCER GENES AND POTENTIAL DRUGS
GASSING UP A VINTAGE BUG
Reprinted from Cell, 154, Basu, A., et al., An interactive resource to identify cancer genetic and lineage dependencies targeted by small molecules. 1151−1161, Copyright 2013, with permission from Elsevier.
Most successful new cancer drugs have been agents that target specific mutations, but resistance can crop up. Therefore researchers would like to have screening methods that allow them to look at a full range of cellular targets that might respond to therapies. One option is cancer cell-line profiling, a high throughput approach to probe the mutations that help the cancer cell survive while screening for molecules that target those mutations. In a new study, Basu et al. describe the Cancer Therapeutics Response Portal (CTRP), an interactive and expandable online database that allows researchers to examine these types of interactions based on an initial set of 242 cancer cell lines and 354 small molecules (Cell 2013, 154, 1151− 1161). The researchers used this tool to pull out a novel pairing of an oncogene, a mutation of β-catenin and a small molecule drug, navitoclax. To create the database, Basu et al. initially focused on small molecules with high specificity for their targets or members of a distinct protein family. More than two-thirds of the molecules were chemical probes, some of which were synthesized for this project, while the remaining molecules were FDA-approved drugs or clinical candidates. The cell lines have been extensively characterized as part of the Cancer Cell Line Encyclopedia collection. The researchers carried out their screens using the CellTiter-Glo assay, which measures ATP in a cell, to examine cell viability after treatment with the small molecules. Initially they validated the database by making sure that known relationships between drugs and mutations showed up. Then they looked for undiscovered relationships. The CTRP points to a connection between mutations in β-catenin and supporting proteins, which are involved in cell adhesion and transcription, and the small molecule navitoclax, a drug developed to target mutations in the apoptosis regulator gene Bcl-2. Further testing showed that mutations that boosted β-catenin levels also increased sensitivity to navitoclax. Other similar studies have found connections between β-catenin mutations and Bcl-2 family inhibitors. Overall, the CTRP could serve as a powerful tool for forming new hypotheses and investigating new cancer therapies.
With a rising demand for alternative energy solutions that do not rely on fossil fuels, many biotechnologists have looked to microbes as sustainable factories for fuel. Given a suitable host and some clever genetic engineering, scientists have successfully produced long-chain hydrocarbons of 13−17 carbons in length. These products of fatty acid synthesis pathways can substitute for the diesel fuel. While such biodiesel microbes are promising, the modern world still relies upon burning gasoline for most transportation applications. Gasoline, or petrol, differs from diesel in that it is made up of short-chain alkanes less than 12 carbons in length. Now, a promising new study (Choi and Lee, Nature 2013, 502, 571−574) bends the rules of what an E. coli can produce by engineering enzyme systems to favor the build up of short-chain alkanes instead. To make these biogasoline-producing bacteria, the researchers relied upon deleting the activity of several E. coli metabolic enzymes while increasing the activity of others and expressing genes borrowed from other organisms. To keep the bacteria from favoring longer-chain molecules, it was critical to delete the native fadE enzyme, a key catalyst for converting shortchain fatty acyl-CoA molecules into longer chain molecules via b-oxidation. To further increase the synthesis of free fatty acids, the fadR gene was also deleted. This gene acts as a transcriptional regulator for the unsaturated fatty acid biosynthesis pathways. This was important because those unsaturated molecules will inhibit enzymes involved in producing the desired short-chain fatty acids. With the unsaturated fatty acid
Sarah A. Webb, Ph.D.
Published: November 15, 2013 © 2013 American Chemical Society
Reprinted by permission from Macmillan Publishers Ltd.: Nature, Choi and Lee, 502, 571−574, copyright 2013.
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dx.doi.org/10.1021/cb4008138 | ACS Chem. Biol. 2013, 8, 2351−2353
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pathway toned down, the fadD enzyme, which generates the reactive acyl-CoA intermediates from free fatty acids, was overexpressed to increase flux through the proper pathway. To go from these intermediates to saturated hydrocarbons, the final engineering strain also expressed a reductase from Clostridium to produce the fatty aldehyde and an aldehyde decarbonylase from Arabidopsis to generate alkanes. The resulting bacterium could produce over 0.5 g of mixed shortchain alkanes per liter of optimized culture. While these results will not be filling fuel tanks anytime soon, they indicate another new route for biofuel production that certainly warrants further investigation.
mice than in awake mice. Further analysis suggested that signaling through the adrenergic pathway likely plays an important role in regulating the volume of interstitial space. Taken together, the data suggest that a key function of sleep may be to promote the clearance of potentially neurotoxic waste products that accumulate as a result of brain activity while awake. Eva J Gordon, Ph.D.
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MAKING MYELIN
Jason G. Underwood, Ph.D.
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THE PURPOSE OF SLEEP
Reprinted by permission from Macmillan Publishers Ltd.: Nature, Deshmukh, V. A., et al., 502, 327−332, copyright 2013.
It is estimated that 1.3 million people across the globe are afflicted with multiple sclerosis. This devastating disease is characterized by damage to the myelin sheath, the protective coating along nerve cells that facilitates communication between the brain and the rest of the body. A special type of brain cell called an oligodendrocyte is responsible for remyelinating nerve cells. However, their precursors, oligodendrocyte precursor cells (OPCs), must be recruited to sites of injury and then undergo differentiation to the mature oligodendrocytes, which ultimately remyelinate the nerves. In multiple sclerosis, lack of remyelination is thought to result from failure of OPCs to differentiate, intimating that small molecules capable of inducing the differentiation of OPCs might be potential therapies for multiple sclerosis and other myelination disorders. Deshmukh et al. (Nature 2013, 502, 327−332) now report their discovery that the Parkinson’s drug benztropine effectively promotes the differentiation of OPCs. Using a high content imaging assay, the authors screened approximately 100,000 small molecules to find those capable of inducing the expression of myelin basic protein, which is an indication of differentiation, in cultured OPCs. The azabicycloctane benztropine was among the most effective inducers of OPC differentiation. In two mouse models, the experimental autoimmune encephalomyelitis (EAE) model of multiple sclerosis and the cuprizone model of demyelination, treatment with benztropine led to an increase in the number of mature oligodendrocytes as well as enhanced remyelination. In addition, when tested in combination with immunosuppressive agents used clinically for multiple sclerosis, benztropine worked synergistically with these drugs to decrease the clinical severity
From Xie, L., et al., Science, 2013, 342, 373. Reprinted with permission from AAAS.
The purpose of sleep has longed puzzled biologists. It is wellknown that lack of sleep impairs brain function, but the molecular processes that govern this phenomenon have not been elucidated. Numerous potentially neurotoxic proteins, such as β-amyloid (notorious for its role in Alzheimer’s disease), reside in the interstitial fluid that surrounds cells in the brain. The interstitial fluid continuously exchanges components with the cerebrospinal fluid (CSF) that circulates through the brain. Interestingly, β-amyloid concentrations are higher in the interstitial fluid in awake rodents than in sleeping ones, but it is unclear whether the higher concentrations are due to increased production of the protein during wakefulness or increased removal during sleep. To explore this question, Xie et al. (Science 2013, 342, 373−377) examine the CSF influx into the brain of awake, anesthetized, and sleeping mice. Using methods such as two-photon imaging, electrocorticography, and electromyography, the authors monitor activity, the volume of interstitial fluid, and the amount of β-amyloid in the brains of mice at different states of arousal. They discover that CSF influx is strikingly reduced in awake mice compared with sleeping or anesthetized animals. They also observe that the volume of interstitial space is reduced in awake versus sleeping mice. Notably, this volume difference likely strongly influences the diffusion of important neurotransmitters in the brain during different states of arousal. Examination of the rate of clearance of β-amyloid indicated that the protein is cleared twice as fast in sleeping or anesthetized 2352
dx.doi.org/10.1021/cb4008138 | ACS Chem. Biol. 2013, 8, 2351−2353
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observed in EAE mice. These findings provide a compelling starting point for the development of new strategies to treat multiple sclerosis. Eva J. Gordon, Ph.D.
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ANOTHER REASON TO EAT YOUR VEGETABLES Cruciferous vegetables such as broccoli, cauliflower, and cabbage are loaded with vitamins, minerals, and other phytochemicals, including a compound called indole-3-carbinol. In the stomach, indole-3-carbinol is metabolized to 3,3′-diindolylmethane (DIM); both compounds have been linked to cancer prevention. Toward understanding the mechanism behind their potential anticancer activity, Fan et al. (Proc. Natl. Acad. Sci. U.S.A., Epub ahead of print Oct 14, 2013; DOI: pnas.1308206110) explore the molecular basis by which DIM might contribute to preventing radiation-induced cancer in mice. The authors find that administration of DIM significantly increases survival rates in mice subjected to lethal doses of total body irradiation, especially when given prior to the radiation exposure. Radiation is known to promote signaling by the nuclear kinase ataxia-telangiectasia (ATM), a nuclear kinase involved in regulating the response to DNA damage. Analysis of tumor tissue from irradiated mice and phosphorylation patterns in irradiated cells suggested that DIM enhances radiationinduced ATM signaling. In addition, evaluation of DNA damage and apoptosis indicators suggested that DIM stimulates DNA repair and cell survival signaling pathways. Together, the data support that DIM acts as a potent radioprotector via stimulation of the DNA damage response, promoting both DNA repair and cell survival. This unique mechanism could be exploited in the management of various types of radiation-induced damage, such as that incurred by whole body exposure or during cancer treatment. Eva J. Gordon, Ph.D.
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