Cryo-electron microscopy, whose pioneers won the 2017 Nobel Prize in Chemistry, is gaining favor among scientists as a tool to probe cancer at the molecular level. To that end, the NCI recently launched a centralized, free service facility to better meet the needs of researchers interested in utilizing this otherwise highly expensive technology.

Over the last several years, cryo-electron microscopy (cryo-EM) has steadily gained ground on X-ray crystallography as a tool for visualizing proteins and other molecules in fine detail. That cryo-EM's pioneers were awarded the 2017 Nobel Prize in Chemistry is therefore both timely and exciting, says Sriram Subramaniam, PhD, of the NCI.

The three winners—Jacques Dubochet, PhD; Joachim Frank, PhD; and Richard Henderson, PhD—“laid the foundation, back in the 1980s, for what's become modern cryo-EM,” he says. Today's scientists can study biological molecules in near-native states, at atomic resolution, by flash-freezing a given sample in under a millisecond and bombarding it with electrons. A special camera then captures 2-D images from different angles that are aligned into a 3-D map.

Until recently, however, cryo-EM remained on the fringes, Subramaniam observes, because it produced fuzzy and blob-like images on film that required development in a darkroom. The advent of direct electron detectors in 2013 revolutionized cryo-EM's data quality and inspired other technical advances in the field. Taking advantage of these improvements, Subramaniam's group became the first to solve the single-particle cryo-EM structures of beta-galactosidase, followed by the protein p97 and several dehydrogenases.

“The latter examples provided proof of principle that cryo-EM could be applied to clinical targets,” he says. The therapeutic potential of blocking p97, a regulator of protein homeostasis—on which cancer cells can become overly dependent—is being investigated. Earlier attempts to study p97 using X-ray crystallography were limited to a resolution of 3.5 Å; Subramaniam's team successfully imaged it at 2.3 Å, and “we'll be using this structural information to inform better drug design,” he says.

Besides running his own cryo-EM lab, Subramaniam recently established the National Cryo-Electron Microscopy Facility (NCEF; www.cancer.gov/research/resources/cryoem) at the NCI's Frederick National Laboratory for Cancer Research (FNLCR). “The idea is to democratize access to this technology,” he explains. “There are dozens of cancer targets that should be worked on, but expense is a big bottleneck—cryo-EM infrastructure costs millions of dollars, and it takes months to get these instruments installed and working properly.”

NCEF, which officially launched in May, currently houses one powerful, state-of-the-art Titan Krios microscope; another will be added in June 2018. This facility is one of the NCI's “national mission projects” based at FNLCR, with another being the RAS Initiative, says Sara Hook, PhD, the program officer for NCEF. “We recognized the need for an extramural resource so researchers across the country—with or without NCI funding—could easily use cryo-EM for their work, without cost being a barrier.” Any researcher can submit a request to use NCEF for free, she says.

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The protein p97 is trapped in an inactive state by a new inhibitor (red) and the molecule cannot proceed into its normal reaction cycle.

“We ask them to briefly describe why their work is relevant to cancer,” Subramaniam says, “but there's no need for a lengthy proposal, and no extended committee review process.” That said, he adds, “researchers can't be purely aspirational—they need to use a lower-end feeder microscope, which is cheaper and much more widely available, to produce evidence that they have a specimen ready for top-of-the-line imaging and data collection at NCEF.”

Centralized cryo-EM resources such as NCEF have been a growing trend for some time, Subramaniam observes. Howard Hughes Medical Institute's service facility in Ashburn, VA, and the Electron Bio-Imaging Center in Oxfordshire, UK, were among the first to emerge. The New York Structural Biology Center's National Resource for Automated Molecular Microscopy is another facility providing access to researchers who seek to apply this method to important biological problems.

“Cryo-EM is a rapidly evolving field, so it's important to have a shared resource run by qualified experts who can keep pace,” he says. “We'll see further advances over the next few years, whether it's hardware, software, or biochemistry. This is just the beginning; it's ready for takeoff.” –Alissa Poh

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