by ecancer reporter Clare Sansom

The spread of cancer throughout a patient’s body is driven by cells that break off from the primary tumour and circulate in the bloodstream.

These circulating tumour cells (CTCs) express proteins that can be used as biomarkers for disease detection and diagnosis.

However, patients with early stage cancer carry only a small number of circulating tumour cells, and these cells express cancer biomarkers such as the epithelial cell adhesion molecule (EpCAM) in a heterogeneous manner.

It is therefore particularly difficult to detect and characterise CTCs reliably in these patients. 

Current methods of CTC detection based on microfluidic devices are more reliable than the preceding ones but downstream analysis of the cells is still quite limited.

Nano-scale materials such as graphene oxide, which have a high surface area to volume ratio and are similar in size to biological macromolecules, are considered promising candidates for the development of novel methods for the capture of these cells.

Sunita Nagrath of the University of Michigan, Ann Arbor, MI, USA and her colleagues have now developed and tested a chip that can identify and capture CTCs in the bloodstream,

The device they developed consists of graphene oxide nanosheets adsorbed onto a patterned gold surface on a base layer of silicon.

The nanosheets were functionalized with biotinylated antibodies to EpCAM, bound to them via avidin and a cross-linker.

Scanning electron micrographs of the gold surface revealed it to be covered with a uniform pattern of treated nanosheets.

Firstly, buffer containing fluorescently labelled human breast and prostate cancer cells was flowed through the chips, and the cells that were captured on the nanosheets and collected in the waste were counted.

Tumour cells expressing EpCAM were captured effectively by the nanosheets at flow rates of between 1 and 3 ml per hour with yields of over 82%, whereas fewer than 10% of control cells that did not express EpCAM were captured under the same conditions.

Low concentrations of breast cancer cells from the MCF-7 cell line, which express EpCAM, were then spiked into human blood and flowed through the chips, and the tumour cells were recovered with fairly high sensitivity and specificity.

The graphene oxide chips with the gold patterns were able to detect low numbers of tumour cells with higher sensitivity than other types of silicon-based device tested, and with an average recovery rate over all samples of 73%.

Captured tumour cells were also seen to spread and proliferate on the surface of these devices.

The researchers next tested the chips using blood samples from cancer patients.

Blood obtained from seven patients with metastatic breast cancer, four with early-stage lung cancer, nine with metastatic pancreatic cancer and six age-matched healthy controls was passed through the graphene oxide chips.

The chips captured EpCAM-expressing circulating tumour cells from all the patient samples, with at least 2 CTCs per ml of blood identified in each; in contrast, no CTCs were detected in any of the samples taken from healthy controls.

Tumour cells were extracted as successfully from samples taken from patients with early stage lung cancer as they were from those taken from patients with metastatic disease.

Most of the captured tumour cells stained negative for the antigen CD45, and most of the breast cancer cells were herceptin receptor (HER2) positive.

RNA extracted from cells captured from four of the six breast cancer patients also showed HER2 gene expression.

Interestingly, HER2 expression was detected in some CTCs isolated from the blood of patients diagnosed with HER2 negative disease.

Taken together, these results show that the functionalized graphic oxide nanodevices developed by Nagrath and her co-workers can capture circulating tumour cells from the blood of cancer patients with high sensitivity and in greater numbers than those generally reported in the literature.

Although further clinical development is necessary, it is likely that this technique will prove valuable in differential diagnosis and perhaps in the selection of the optimum treatment for an individual patient’s tumour.

Reference

Yoon, H.Y., Kim, T.H., Zhang, Z. and 9 others (2013). Sensitive capture of circulating tumour cells by functionalized graphene oxide nanosheets. Nature Nanotechnology, published online ahead of print 29 September 2013. doi:10.1038/nnano.2013.194