The intestine has a reservoir of stem cells that are resistant to chemotherapy

These comprise a small group of passive stem cells -quiescent- that are activated when needed and have the capacity to produce any kind of intestinal cell. Quiescent cells are relevant for tissue regeneration and for participation in tumor development.

After Chemotherapy, these cells change their behaviour, become active and regenerate all cell types in the intestine (in green). CREDIT Franscisco Barriga, IRB Barcelona

The intestine has a high rate of cellular regeneration due to the wear and tear originated by its function degrading and absorbing nutrients and eliminating waste. The entire cell wall is renewed once a week approximately. This explains why the intestine holds a large number of stem cells in constant division, thereby producing new cell populations of the various types present in this organ.

Researchers at the Institute for Research in Biomedicine (IRB Barcelona) headed by ICREA investigator Eduard Batlle, head of the Colorectal Cancer Laboratory, have discovered a new group of intestinal stem cells with very different characteristics to those of the abundant and active stem cells already known in this organ. Performed in collaboration with the Centro Nacional de Análisis Genómico (CNAG-CRG), the study has been published in Cell Stem Cell. These new group of stem cells are quiescent, that is to say, they do not proliferate and are apparently dormant.

The researchers describe them as a reservoir of stem cells–it is estimated that there is one quiescent cell for every 10 active intestinal stem cells. In healthy conditions, these cells have no apparent relevant function. However, they are important in situations of stress, for example, after chemotherapy, in inflammatory processes, and in tissue infections–all conditions in which the population of “normal/active” stem cells is depleted. These quiescent cells would serve to regenerate the organ by giving rise to the various types of cells present in the intestine, renewing the population of “normal/active” stem cells, and restoring balance to the tissue.

Eduard Batlle explains that the discovery of quiescent stem cells in the intestine reveals that stem cell biology is more complex that previously appreciated and that it does not follow ahierarchical model of cell organisation. “In intestinal cell hierarchy, there are no cells above others, so the two populations are in a continual balance to ensure the proper function of the organ“.

Most drugs against cancer have a secondary effect on the cells that are dividing in our tissues. “Because quiescent stem cells divide infrequently, they are resistant to many types of chemotherapy and they regenerate the tissue that this treatment has damaged,” explains Eduard Batlle, head of one of the labs of international prestige in research into intestinal stem cells and their involvement in colorectal cancer.

Quiescent cells are present in many kinds of tissue. However, in spite of their relevance in tissue regeneration, increasing evidence points to their involvement in tumour development. “It is difficult to study these cells, mainly because they are scarce and there are technical limitations with respect to monitoring, straining and distinguishing them from the others,” explains Francisco Barriga, first author of the study and current postdoctoral fellow at the Memorial Sloan Kettering Cancer Center in New York.

Using advanced techniques, such as genetic tracing of cell lineages and transcriptomic analysis of individual cells, performed by CNAG-CRG and the Bioinformatics and Biostatistics Unit at IRB Barcelona, the group has identified the distinct genetic programme used by quiescent stem cells with respect to normal intestinal ones. This work has been done over six years.

The researchers have labelled this cell population with a specific marker, the Mex3a protein, which has allowed them to track it over time. “We intend to continue studying quiescent stem cells in health and disease and to discover the function of the genes that distinguish them in the colon and in other organs,” says Batlle.

Barriga et al. Mex3a marks a slowly dividing subpopulation of Lgr5+ intestinal stem cells. Cell Stem Cell (2017). doi: 10.1016/j.stem.2017.02.007 [Abstract]


One-two punch catches cancer cells in vulnerable state

Timing may be decisive when it comes to overcoming cancer’s ability to evade treatment. By hitting breast cancer cells with a targeted therapeutic immediately after chemotherapy, researchers from Brigham and Women’s Hospital (BWH) were able to target cancer cells during a transitional stage when they were most vulnerable, killing cells and shrinking tumors in the lab and in pre-clinical models. The team reports its findings in Nature Communications.

We were studying the fundamentals of how resistance develops and looking to understand what drives relapse. What we found is a new paradigm for thinking about chemotherapy,” said senior author Shiladitya Sengupta, PhD, associate bioengineer at BWH.

Previous studies have examined cancer stem cells (CSCs) – small populations of cells within a tumor that are resistant to chemotherapy. Sengupta and his colleagues took breast cancer cells that did not have the markings of CSCs and exposed them to docetaxel, a common chemotherapy drug.

This confocal microscopy image depicts drug-tolerant cancer cells. By hitting breast cancer cells with a targeted therapeutic immediately after chemotherapy, researchers were able to target cancer cells during a transitional stage when they were most vulnerable. Credit: Aaron Goldman

The team found that after exposure to chemotherapy, the cells began developing physical markings usually seen in CSCs, including receptors on the cell surface to which specific proteins can bind. These “markers of stemness” suggested that the cells were transitioning into a different state, during which time they might be vulnerable to other cancer drugs.

To test this, the researchers treated the cells with a variety of targeted therapeutics immediately after chemotherapy. The researchers observed that two drugs each killed a large fraction of the cells that had begun transitioning: dasatinib, a drug that targets the Src Family Kinase (SFK) and RK20449, a new drug in pre-clinical testing that specifically targets one of the SFK proteins called Hck. The researchers confirmed these findings in a mammary carcinoma mouse model – treatment with dasatinib just a few days after administering two high doses of chemotherapy prevented tumor growth and increased survival rates. Treating cells simultaneously with docetaxal and dasatinib or administering dasatinib after a longer period of time did not produce the same effects. The researchers theorize that the cancer cells go through a temporary transition state, which means that administering the drugs in a very specific timeframe and sequence is important.

By treating with chemotherapy, we’re driving cells through a transition state and creating vulnerabilities,” said first author Aaron Goldman, PhD, a postdoctoral fellow in biomedical engineering at BWH. “This opens up the door: we can then try out different combinations and regimens to find the most effective way to kill the cells and inhibit tumor growth.

To make these observations, the researchers developed and leveraged three-dimensional “explants” – tissue derived from a patient’s tumor biopsy and grown in serum from that specific patient for research purposes. This model mimics the tumor’s microenvironment and preserves the tumor’s cellular diversity.

In a continuation of this work, Goldman is also using mathematical modeling to pursue the most effective dose of chemotherapy to induce the vulnerable transition state of the cancer cell demonstrated in this research.

Our goal is to build a regimen that will be efficacious for clinical trials,” said Goldman. “Once we understand specific timing, sequence of drug delivery and dosage better, it will be easier to translate these findings clinically.”

Goldman et al. Temporally sequenced anticancer drugs overcome adaptive resistance by targeting a vulnerable chemotherapy-induced phenotypic transition. 2015; Nature Comm. 6: 6139 doi:10.1038/ncomms7139 [Article]