Big pharma is big for a reason. According to the Pharmaceutical Research and Manufacturers of America – the main representative of US drug companies and scientists – it takes on average 10 years to develop a new medicine, at a cost of roughly $2.6bn. Faced with such eye-watering numbers, it is clear why pharma is such a high-risk business – and why drugs often come at such a steep cost to those who need them.

But what if ill-fated drug candidates could be rooted out earlier? That is the promise of a new type of high-speed, high-mass-resolution spectroscopy technique that has been developed by physicist Ian Gilmore of the National Physical Laboratory (NPL) in Teddington, UK, and others. Unlike that mainstay of cell biology – super-resolution fluorescence microscopy – Gilmore’s “OrbiSIMS” technique has no need for fluorescent tagging. In principle, it can therefore be directed at objects that are incompatible with that approach – and in particular metabolites, the conveyors of all metabolic processes.

OrbiSIMS could spot previously undetectable signs of failure in the first phase of drugs testing

By tracking how metabolites change in response to new drugs, OrbiSIMS could let researchers spot previously undetectable signs of failure in the first phase of drugs testing, freeing up time and money to be redirected elsewhere. “It could open up completely new discoveries,” Gilmore claims.

Old idea, new direction

The first mass spectrometer was invented by the British physicist Francis William Aston a century ago. It enabled him to identify many of the first isotopes, and win the 1922 Nobel Prize for Chemistry just three years later. The concept was simple: he passed ions through a tube between the poles of a magnet and measured the degree of deflection using a photographic plate. The smaller an ion’s deflection, the greater its mass.

Today, the technique is rather more sophisticated and has a great variety of applications, from police forensics and the detection of environmental toxins, to cancer screening, protein characterization and drug development. It is no longer limited to identifying pure elements but can also be applied to any complex synthetic or biological materials whose molecules can be ionized. In this popular version of the surface-analysis technique – known as secondary ion mass spectroscopy (SIMS) – some sort of ionization source, or probe, is scanned over the material’s surface, raster fashion. This yields an image of the material, where every pixel has a mass spectrum. And if another ion beam shaves off a fine layer of the material’s surface between each 2D image, it is even possible to build up a 3D picture.

The most popular type of mass spectrometer used for imaging involves a time-of-flight (TOF) analyser, which accelerates the ionized molecules along a straight path to a detector with an electrostatic field. A timing system starts a clock once the molecules are ionized and stops it once they strike the detector, with their flight time being proportional to the square root of their mass. The system is so fast that it can complete, say, a 256 × 256 pixel image in minutes. The problem is that it is not all that accurate, because the flight time depends not only on mass, but also on the kinetic energy with which the molecules originally left their sample. The result appears as a spread of masses equivalent to a chromatic aberration, and limits the resolving power of TOF analysers to about 15,000.

“The huge frustration [with TOF] is that although we get images, we have no confidence of what they are of,” says Gilmore. “You can get around that in [synthetic] materials, because you have reference samples and so on, but in biology you really don’t stand a chance – the mass spectrum you get from a cell is so, so complicated. It’s like the Hubble Space Telescope before the lens was improved: the images looked pretty, but they were just a blur, and you couldn’t discover anything.”

In the late 1990s, building on work by other inventors, a Russian physicist called Alexander Alexeyevich Makarov developed an analyser for mass spectroscopy with much better mass resolution. Rather than send molecular ions to a detector, Makarov directed them into an electrostatic trap shaped like a tulip, or a shallot, around which they simultaneously orbited and precessed. Crucially, the frequency of precession – which could be measured via an induced current in an electrode and converted to mass via a Fourier transform – was independent of the spread in kinetic energy of the molecules entering. Makarov could therefore raise the mass resolving power into the hundreds of thousands. His system, the Orbitrap, was ultimately bought by the US equipment manufacturer Thermo Fisher Scientific.

Unfortunately, the Orbitrap solved the resolution problem at one great expense: speed. “Orbitrap takes a long time to take a 2D image, never mind a 3D image,” says Gilmore.

Original interest

Although Gilmore has had an interest in clinical science from a young age, he was “too squeamish” to study biology at university, and so embarked on a career as a physicist, becoming an expert in mass spectrometry. When he set up the National Centre of Excellence in Mass Spectrometry Imaging at NPL in partnership with the University of Nottingham in 2012, however, a path back to his original interest presented itself, for the technique is used by life scientists more than any others. In particular, Gilmore established a working relationship with Colin Dollery, a leading pharmacologist formerly at the British pharmaceutical giant Glaxo Smith Kline (GSK), which “had this drive to better understand how drugs got into cells, and where they went, to try to reduce the attrition problem in drug testing”.

One evening in May 2011, Gilmore was preparing a presentation about the fundamental compromise scientists are forced to make in mass spectrometry imaging: fast but low resolution with TOF, or slow but high resolution with the Orbitrap and other Fourier-transform methods. One or two glasses of pinot later, he struck upon an idea: why not combine them? “We scientists should have more wine!” he reflects.

Bringing the idea of a combined TOF/Orbitrap instrument to fruition was no smooth ride, not least because of the need to share sensitive intellectual property between Thermo Fisher Scientific and the manufacturer of TOF analysers chosen by Gilmore, IONTOF, based in Germany. “I needed to bring these guys together, which is not as easy as it sounds,” says Gilmore. “But it was really fortunate that I already worked a lot with GSK, which was a great help, especially because it could show the need for this new technology.” The project started in 2013. Four years later, OrbiSIMS was born.

In essence, OrbiSIMS consists of a single sample and ionization stage that can feed either a TOF or Orbitrap analyser via an electrostatic switch (figure 1). Typically, a user performs an initial scan in TOF mode (rather like a “preview scan” on a document scanner), identifies a small area of interest, and then explores it in more detail in Orbitrap mode. Such a methodology would be impossible with separate TOF and Orbitrap instruments, as the sample would have to be moved from the former to the latter, and the location of the area of interest would be lost. OrbiSIMS can perform 3D scans, too. In this set-up, the TOF analyser takes a 2D scan before a layer of material is removed; that layer of material is then sent over to the Orbitrap analyser, which gives an average (but precise) mass spectrum, and the process repeats (Nature Methods 14 1175). “We’re mostly looking at biological systems, but it’s also very powerful for looking at organic electronic systems and multi-layered systems, for example,” says Gilmore.

Broad applications

Ricky Wildman, an engineer at Nottingham, has already been using one of the first OrbiSIMS instruments to investigate the curing of new polymer materials in 3D printing. “One of the difficulties we have is that the structures that we are resolving are small – potentially down to 100 nm – and consist of materials that have very similar [chemical] fingerprints,” he explains. “For us, already, we are beginning to see that the increased spatial and mass resolution of [OrbiSIMS] is shedding light on the curing mechanisms. This is tremendously exciting.”

Meanwhile, Lucy Collinson, a microbiologist who runs the Electron Microscopy Science Technology Platform at the Francis Crick Institute in London, wonders whether OrbiSIMS could complement electron microscopy, which currently struggles to identify molecules in cells. One reason she and her colleagues want to do this is to understand whether a drug has reached the right location to fight a bacterial infection. “OrbiSIMS, and other spatial elemental analysis techniques, may allow us to do this at the nanoscale,” she says – adding, however, that it would require the development of specific sample-preparation techniques.

The chief competition for OrbiSIMS comes from super-resolution fluorescence microscopy, in which a fluorescent tag, or fluorophore, is attached to a biological macromolecule – a certain protein, for instance. This method allows a user to observe and track the macromolecule with an optical microscope, despite that macromolecule being smaller than the diffraction limit of visible light, about 200 nm. Developed in the early 2000s, it is incredibly powerful, and won its inventors Eric Betzig of the Howard Hughes Medical Institute in Virginia, US, Stefan Hell of the Max Planck Institute for Biophysical Chemistry in Göttingen, Germany, and William Moerner of Stanford University in California, US, the 2014 Nobel Prize for Chemistry.

What fluorescence microscopy cannot do, however, is track metabolites – the reactants and products of metabolic processes, including drug molecules themselves – because they do not simply move around, but are actually created by cells. Spotting and tracking metabolites would be highly valuable to pharmacologists, because changes in them provide one of the first clues that something in the body is going awry. Since such tracking is not usually available, failures in potential drugs are often only picked up at later stages of testing, at great cost. “If a drug fails at a late stage in a clinical trial, you’ve probably already spent a billion on R&D,” says Gilmore.

Since it requires no fluorescent tagging, OrbiSIMS potentially offers a way to track metabolites. The catch is that its spatial resolution, at about 1.4 µm, currently lags well behind fluorescence microscopy. The limiting factor, according to Gilmore, is in the initial ionization of the sample: the smaller the area focused on, the greater the density of ions required. But ionization is a murky process. Scientists know that an ion probe sets up a chain reaction among atoms and molecules inside a sample until the energy eventually returns to the surface, ejecting one of the molecules there. Quite how this molecule becomes ionized, however, is poorly understood.

Gilmore and his colleagues are performing synchrotron-based experiments to see whether a laser system could work with a traditional ion probe to improve the ionization efficiency. If it succeeds, an ion probe would eject the sample’s molecules, while a laser would photo-ionize them. “That sounds simple, but people have been trying to do it for a long time,” says Gilmore. “But laser technology is improving.”

In the meantime, he and his colleagues are welcoming scientists from all disciplines to consider the benefits of OrbiSIMS at one of the two instruments currently in existence: the original at NPL, and the first production model at the University of Nottingham. “People in the UK are lucky,” he says. “It has two, and there are only two in the world!”