Body's Own Stem Cells Could Trigger Cancer Spread
Editor's ChoiceMain Category: Cancer / Oncology
Also Included In: Stem Cell Research; Breast Cancer
Article Date: 04 Oct 2007 - 0:00 PDT
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Your body's own stem cells could trigger alterations in cancer cells which facilitate their spreading around the body, say scientist from the Whitehead Institute, USA. They found that human breast cancer in mice have a higher chance of spreading if they are blended with bone marrow stem cells. Fortunately, say the scientists, it is perhaps feasible to reverse the process, undermining the deadliness of the cancer.
You can read about this study in the journal Nature.
When metastasis occurs it is much harder to treat the cancer. Metastasis is when the cancer invades other parts of the body and forms new tumors. In this study, the scientists intended to find out whether it was possible to stop this from happening - they wanted to find a means of isolating the cancer to one part of the body; stopping it from metastasizing (spreading, invading other parts).
The researchers have found an association with a specific type of stem cell, which encourages the breast cancer cells to spread to other parts of the body. They are found in the bone marrow, and are called Mesenchymal stem cells. These stem cells generally turn into cartilage, bone fat and muscle.
Previous studies had indicated that these stem cells generally migrated in huge numbers to where tumors were situated, meaning they were probably involved in the spread of the cancer. The researchers mixed these stem cells with human breast cancer cells in mice and found they spread to the lungs at seven times their normal rate.
The scientists believe the stem cells alter the cancer cells so that they metastasize. However, they add that as soon as they had spread, those cancer cells returned to their original genetic make-up. The bad news here is that as they revert back to their original genetic make up they are hard to identify, the good news, say the researchers, is that it is most likely they can find a way of blocking the whole process.
"Mesenchymal stem cells within tumour stroma promote breast cancer metastasis"
Antoine E. Karnoub, Ajeeta B. Dash, Annie P. Vo, Andrew Sullivan, Mary W. Brooks, George W. Bell, Andrea L. Richardson, Kornelia Polyak, Ross Tubo & Robert A. Weinberg.
Nature 449, 557-563; doi:10.1038/nature06188.
Click here to view abstract online
Written by: Christian Nordqvist
Copyright: Medical News Today
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Some Cancer Cells Mimic Stem Cells To Survive Chemotherapy
posted by Gregory D. Pawelski on 4 Oct 2007 at 1:29 pmAnti-cancer treatments often effectively shrink the size of tumors, but some might have an opposite effect, actually expanding the small population of cancer stem cells believed to drive the disease, according to findings presented in Atlanta, Georgia at the American Association for Cancer Research's second International Conference on Molecular Diagnostics in Cancer Therapeutic Development.
"Our experiments suggest that some treatments could be producing more cancer stem cells that then are capable of metastasizing, because these cells are trying to find a way to survive the therapy," said one of the study's investigators, Vasyl Vasko, M.D. Ph.D., a pathologist at the Uniformed Services University of the Health Sciences in Bethesda, Md.
"This may help explain why the expression of stem cell markers has been associated with resistance to chemotherapy and radiation treatments and poor outcome for patients with cancers including prostate, breast and lung cancers," Dr. Vasko said. "That tells us that understanding how to target these markers and these cells could prove useful in treating these cancers."
The cancer stem cell markers include Nanog and BMI1, both of which contribute to stem cells' defining ability to renew themselves and differentiate into different cell types, Dr. Vasko said. These same molecules are found in embryonic stem cells.
Researchers have recently debated the notion that some therapies are not capable of eradicating cancer because they do not target the cancer stem cells responsible for tumor development. To test this hypothesis, Dr. Vasko, along with scientists from the CRTRC Institute for Drug Development in San Antonio and from the Johns Hopkins University, set out to measure both stem cells markers and tumor volume before and after treatment in a mouse model.
They selected a rare form of cancer, mesenchymal chondrosarcoma (MCS), which has not been well described and for which there is no effective treatment. The researchers first determined that Nanog and BMI1 stem cell markers were more highly expressed in metastatic tumors compared to primary tumors. "This suggests that expression of the marker plays some role in development of metastasis," Dr. Vasko said.
They then applied various therapies -- from VEGF inhibitors such as Avastin to the proteasome inhibitor Velcade -- in mice implanted with human MSC, and analyzed the effects on tumors. Some of the treatments seemed to work, because they led to a dramatic decrease in the size of the tumors, Dr. Vasko said. But analysis of stem cell expression before and after treatment revealed that even as some anti-cancer treatments shrank tumors, they increased expression of Nanog and BMI1. "These treatments were not enough to completely inhibit tumor growth, and the cancer stem cell markers were still present," Dr. Vasko said.
Use of the agents Velcade and Docetaxel led to the most significant increase in stem cell markers within the treated tumor, while ifosfamide and Avastin inhibited expression of the markers in this cancer subtype.
"We hypothesize that the tumor escapes from chemotherapy by induction of stem cell marker expression," he said. "The small number of cells that survive the treatment could then generate another tumor that metastasizes."
Dr. Vasko doesn't know how this happens, but theorizes that "dying cells could secrete a lot of factors that induce expression of stem cell markers in other cancer cells. I think they are trying to survive and they use a mechanism from their experience of embryonic life."
If scientists understood the pathways cancer stem cells use to survive treatment or increase their ranks, then therapeutic targets could be developed, Dr. Vasko said. Some novel therapies are already being tested against cancer stem cells, he added.
Source: American Association for Cancer Research
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