Korean and Singaporean scientists have recently proposed a new probe to detect cancer stem cells, and it might be an effective seek-and-destroy weapon against a variety of cancer types.
In a paper published in the journal Angewandte Chemie earlier this month, the researchers describe a fluorescent dye that they created to highlight cancer stem cells, and, as it turns out, the dye does more than that—it may actually be lethal to the cells it binds to .
Cancer stem cells in brief
Cancer stem cells (CSCs, also known as TICs, tumor-initiating cells) are exactly what they sound like; they are cancerous cells that exhibit stem cell-like abilities to self-renew and differentiate into the other cell types found in a given tumor. Discovered at the end of the 90s, these cells are the real culprit behind cancerous growth, being able to give rise to both to other CSCs and cells that, while non-tumorigenic themselves, are still part of a tumor—they descend from a cancer stem cell but do not have the same ability to divide uncontrollably. This is according to the CSC model of cancer; according to the stochastic model, it might be possible that every cell in a tumor has the ability to self-renew and differentiate, not only cancer stem cells, and the truth might be not so clear-cut, with some tumors following one model and others following the other .
However, according to the CSC model, solely attacking cancer stem cells may be a better strategy than attacking the whole tumor, as once its stem cells are eliminated, the other, non-CSC cancer cells will eventually hit the Hayflick limit and stop replicating.
It is commonplace to use fluorescent dyes (also called “probes”) to highlight specific types of cells, proteins or tissues. To do so, scientists make use of dyes that stain the targets but nothing else. This makes it far easier to highlight structures in biological tissues for viewing, often with the aid of different types of microscopes.
In the case of this particular CSC marker, the team led by Drs. Nam-Young Kang and Young-Tae Chang devised a probe that binds to vimentin, a specific protein in the cytoskeleton of the cell. Every cell has a cytoskeleton, which is a protein network that acts as a scaffolding, allowing cells to maintain their shapes, compartmentalize their contents, and migrate, among other functions.
As the authors of the study themselves have pointed out in their paper, previous studies have shown a strong correlation between high levels of cellular vimentin and aggressive epithelial tumors and invasive cancer cell lines. Thus, the researchers decided to try their probe, tumor-initiating cell probe yellow (TiY), on several different kinds of human cancer cell lines. They found that their dye successfully stains, and thus detects, CSCs and that, perhaps more importantly, higher levels of TiY appear to be cytotoxic to CSCs while leaving other cells essentially alone; this means that, in the right amount, this particular dye kills off several types of cancer stem cells without harming healthy cells. This is of special interest because other approaches to treating high-vimentin cancers entail the use of drugs with higher cytotoxicity to normal cells.
The elimination of CSCs is important in preventing cancer relapses; killing off all the other cancer cells while leaving even just one CSC around might mean that the cancer will grow right back one day. This is why TiY might prove useful in the future as both a detection tool and as the basis for the development of vimentin-targeting drugs that are useful against multiple cancers.
 Lee, Y. A., Kim, J. J., Lee, J., Lee, J. H. J., Sahu, S., Kwon, H. Y., … & Tam, W. L. (2018). Identification of Tumor Initiating Cells with a Small‐Molecule Fluorescent Probe by Using Vimentin as a Biomarker. Angewandte Chemie, 130(11), 2901-2904.
 Dick, J. (2013). Q&A: John Dick on stem cells and cancer. Cancer discovery, 3(2), 131.