Fingerprinting cells

Anthony King

Scientists in the UK have reported a technique to isolate individual living cells and evaluate how they absorb drugs. They also generated a lipid fingerprint for mammalian cells given a tuberculosis drug.

The approach could reveal how individual cells respond to infection or to a drug, while examining nearby cells for bystander effects. It could also be used to investigate responses to radiation during cancer treatment.

The University of Surrey researchers used a nanocapillary to extract individual human pancreatic cancer cells from a dish. The cell contents were separated using liquid chromatography (LC), and individual components were fed into a mass spectrometer (MS) for analysis (Analyst, doi: 10.1039/d2an01732f).

Scientists previously measured the contents of cells by spraying them directly into a mass spectrometer. However, the issue with spraying directly is that molecules compete for ionisation, meaning molecules with the lowest ionisation potential and less abundant components can be overlooked, says research leader Melanie Bailey. ‘[Instead] we separated the contents of the cells, before we sprayed them into the mass spectrometer, and that helps us do quantitative analysis.’

The method was applied to 30 living cells grown in media spiked with five compounds active against tuberculosis bacteria – isoniazid, rifampicin, ethambutol, pyrazinamide, and bedaquiline. Variations were found in how much drug was in each cell.

Between 14 and 158 lipid features were detected per single cell, and the research revealed an association between bedaquiline uptake and the cell’s lipid fingerprint. ‘When we split the cells into high drug uptake versus lower drug uptake, we saw differences in their lipid profile,’ says Bailey, suggesting lipid content can reflect drug uptake. She is especially interested in exploring radiation effects. It is well known that when a cell is hit by a proton beam, it signals to neighbouring cells, which may then self-destruct. ‘That process, the bystander effect, is not very well understood,’ says Bailey.

Proton beams are used in medicine to destroy hard-to-reach cancers such as brain tumours, but bystander effects can accentuate side effects. ‘This type of system could start to unravel new information about the way that individual cells respond to radiation,’ says Bailey.

Biochemist Edward Emmott at the University of Liverpool notes that working out why certain cancer cells are resistant to treatment could allow the approach to be tailored to make them more susceptible. ‘Currently [this method] is very manual and requires some skill to take the samples and for this reason can look at only limited sample numbers, although the authors do mention an automated system in development,’ he adds.

‘One can have high confidence in what a molecule is, using LCMS for example, but as a bulk technique we have no localisation, so no confidence where it is,’ comments Ian Gilmore, a physicist at the UK’s National Physical Laboratory in London. ‘This paper is a great help to the community in the important field of single-cell omics and will enhance the uptake of the very nice live-cell imaging method,’ as initially reported by a group in Japan (Anal. Sci., doi: 10.2116/analsci.25.953).