Circulating tumor cells (CTCs) are cells that begin as part of a tumor, but then break free into the bloodstream of a patient. It is thought that these cells can initiate metastases elsewhere in the body, but the question remains: are all CTCs able to create new tumors? A research collaboration between several schools in Massachusetts created an assay to detect these malignant CTCs on an individual basis, as reported in the April 2014 cover article of Integrative Biology.
Previously, only entire populations of CTCs were examined, and therefore it could not be determined if all cells or only a subset contributed to metastasis. To be classified as metastasis causing a cell needs to;
- beviable after breaking off from the tumor,
- be able to invade new tissue,
- secrete active proteases associated with cancer cells.
The new assay uses nano wells to isolate individual CTCs or small clusters from blood samples of cancer patients. The viability and location of the cell over time (a measure of invasiveness) were determined by fluorescence analysis, while the secreted compounds of the same cells were detected with antibodies.
Figure 1 below shows functional measurements of viability, invasion and secretory profiles of CTCs using arrays of nanowells. (a) Scheme for the enrichment and functional characterization of CTCs using nanowells for (1) viability, (2) invasion, or (3) secretion of soluble factors. (b) Scatter plot (left) is generated from on-chip imaging cytometry of 50 C4-2 cells spiked into 5 ml of whole blood. Image analysis software extracted the fluorescence intensities of all the cells on the array, and plotted as a scatter plot similar to that used in flow cytometry. A single cell can be mapped back to its original image (middle) or secretion event determined by microengraving (right) based on its unique well ID. (c) Eﬃciency of recovery of tumor cells from whole blood is about 30% using spiked HT29 and C4-2 cells.
In comparing the number of persistent CTCs with patient outcomes, the researchers found that larger numbers of viable cells may be correlated to poor outcomes. Surprisingly, they found that the invasiveness of CTCs ranged from no movement at all to 100 μm for a single patient’s cells. This shows that not all CTCs have identical properties, and some are indeed more invasive, and therefore more likely to cause metastases. Approximately 2% of CTCs were found to possess malignant traits, demonstrating the need for individual screening.
The researchers also note that there is a high level of apoptosis and dormancy present in a population of CTCs. This presents an additional challenge for treatment, as dormant cells can lead to residual and/or recurrent disease in patients. Combined with the rarity of dangerous CTCs, it is understandable that traditional chemotherapies are often not enough.
Read the full paper by downloading your copy using the following link:
Functional analysis of single cells identifies a rare subset of circulating tumor cells with malignant traits – Cover Article, Integrative Biology, 2014, 6, 388
Xiaosai Yao, Atish D. Choudhury, Yvonne J. Yamanaka, Viktor A. Adalsteinsson, Todd M. Gierahn, Christina A. Williamson, Carla R. Lamb, Mary-Ellen Taplin, Mari Nakabayashi, Matthew S. Chabot, Tiantian Li, Gwo-Shu M. Lee, Jesse S. Boehm, Philip W. Kantoﬀ, William C. Hahn, K. Dane Wittrup and J. Christopher Love