You’d think receiving a cancer diagnosis and then suffering through chemo and/or radiation therapy would be traumatic enough. But as many as 75% of cancer survivors are afflicted by memory and attention problems long after their cancer therapy.
This condition, often called “chemobrain”, shouldn’t be misunderstood as being confined to cancers of the brain. A 2012 analysis of nearly 200 women who had been treated with chemotherapy for breast cancer showed they had ongoing memory and information processing deficits that persisted more than twenty years after their last round of treatment. And young cancer survivors are particularly vulnerable to reduced IQs, nonsocial behavior and an extremely lowered quality of life.
Chemotherapy drugs work by killing off cells that are dividing rapidly, a hallmark of cancer cells. But this brute force method also kills other rapidly dividing cells that are critical for normal bodily functions. In the case of chemobrain, it’s thought that damage to newly formed brain cells in the hippocampus, the memory center of the brain, is the culprit. A UC Irvine study published this week in Cancer Research supports that idea in experiments that test the effect of transplanting human nerve stem cells in rats. The research team leader Charles Limoli, a CIRM grantee and UC Irvine professor of radiation oncology, summarized the groundbreaking results in a press release (note: this study is not funded by CIRM):
“Our findings provide the first solid evidence that transplantation of human neural stem cells can be used to reverse chemotherapeutic-induced damage of healthy tissue in the brain.”
So how the heck do you observe chemotherapy-induced cognitive problems in a rodent let alone show that stem cells can rescue the damage? In the study, the rats undergo a variety of recognition memory tasks after a typical chemotherapy drug treatment. For instance, in the novel place recognition test, an animal is familiarized with two identical objects inside a test “arena”. Later, the animal is returned to the arena but a new object is swapped in for one of the previous objects. Rats given chemotherapy treatment but no stem cell surgery (they’re implanted with a saline solution instead) do not show a preference for the novel object. But rats given chemotherapy and the human nerve stem cell surgery prefer the novel object. This novel seeking behavior is also seen in control rats given no chemotherapy. So these results demonstrate that the transplanted stem cells rescued normal memory recognition in the chemotherapy-treated rats.
The research team also saw differences within the brains of these groups of rats that match up with these behavioral results. First, they confirmed that the transplanted human stem cells had indeed survived and grafted into the rat brains and had matured into the correct type of brain cells. Next they looked at chemotherapy-induced inflammation of brain tissue. The brains of chemotherapy-treated rats with no stem cell transplantation showed increased number of active immune cells compared to the control and stem cell transplanted animals. In another experiment, a detailed analysis of the structure of individual nerve cells showed extensive damage in the chemotherapy treated rats compared to controls. Again, this damage was reversed in chemotherapy treated rats that also received the stem cell transplant.
As many researchers can tell you, these exciting results in animals don’t guarantee a human therapy is around the corner. But still, says Limoli:
“This research suggests that stem cell therapies may one day be implemented in the clinic to provide relief to patients suffering from cognitive impairments incurred as a result of their cancer treatments. While much work remains, a clinical trial analyzing the safety of such approaches may be possible within a few years.”
For a more details about the role of stem cells in chemobrain, watch this recent presentation to the CIRM Governing Board by CIRM grantee and Stanford professor Michelle Monje.