Chemo-Induced Heart Failure: Using Stem Cells to Identify Those at Risk

The good news is you’re cancer free, the bad news is you need a heart transplant.

It almost sounds like the punchline to a joke, but it’s no laugher matter because the scenario is real for some cancer patients.  Chemotherapy is a life saver for many but certain doses can be so toxic that it’s often hard to tell which symptoms are due to the cancer and which are due to the drug. Doxorubicin, used to treat around 50% of people diagnosed with breast cancer, is particularly awful. It’s been estimated that about 8% of those treated with doxorubicin experience side effects to the heart with symptoms ranging from arrhythmias to congestive heart failure severe enough to require heart transplantation.

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doxorubicin, a chemotherapy drug that carries a risk of serious heart damage

Avoiding the fire after jumping out of the frying pan
To avoid this predicament, doctors need a way to screen for an increased risk of heart damage due to doxorubicin before a patient even sets foot in a chemotherapy clinic. A CIRM-funded Stanford research team has made a big step toward that goal. Reporting yesterday in Nature Medicine, the scientists describe a non-invasive laboratory method that could help pinpoint which breast cancer patients are most likely to experience so-called doxorubicin-induced cardiotoxicity, or DIC.

Eight woman with breast cancer who had received doxorubicin treatment were recruited for the study. Four suffered from DIC while the other four did not. Skin samples were obtained from each person as well as four healthy volunteers. In the lab, the skin fibroblasts were reprogrammed into embryonic-like induced pluripotent stem cells (iPS) and then specialized into beating heart muscle cells or cardiomyocytes.

Chemo-induced heart damage in a dish
To find out if these patient-derived heart cells in the lab reflect what happened inside the patients’ hearts, the team compared the effects of doxorubicin on the different groups of cells. Looking at cell survival and the rhythmic beating of the heart cells, differences emerged. Lead author Paul Burridge summarized the results in a university press release:

“We found that cells from the patients who had experienced doxorubicin toxicity responded more negatively to the presence of the drug. They beat more irregularly in response to increased levels of doxorubicin, and we saw a significant increase in cell death after 72 hours of exposure to the drug when we compared those cells to cells from healthy controls or patients who didn’t have heart damage.”

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iPS-derived heart muscle cells from patients without (DOX, first row) and with (DOXTOX, bottom row) doxorubicin toxicity were treated with increasing amounts of the doxorubicin. The regular green stripe patterns indicate normal, intact muscle structures. By 0.1 µM of drug (second column), the DOXTOX structures become disarrayed while the DOX cells remain intact. Image: Burridge et al. Nat Med. 2016 Apr 18.

So how exactly does doxorubicin wreak havoc on the heart and why are some patients more sensitive to the drug?

Feeling the burn of reactive oxygen species (ROS)
The answers, in part, lie inside cellular structures called mitochondria where calories, stored in the form of sugar and fat, are “burned” to generate the body’s energy needs.  A harmful byproduct of this energy metabolism is reactive oxygen species (ROS), a chemically reactive form of oxygen that damages the mitochondria and other cell components. This damage is especially bad for heart cells which are 35% mitochondria by volume due to their intense energy needs as they busily beat for a lifetime.

Now, earlier research studies had pointed to ROS production in mitochondria as a key deliverer of doxorubicin’s destructive effects on the hearts of chemotherapy patients. So the Stanford team investigated the drug’s effects on ROS production and on mitochondria function in context of their patient derived heart cells. In response to doxorubicin, the scientists found that the cells from patients with doxorubicin induced heart damage generated more ROS compared to the cells from patients who had no heart damage. Along with the higher ROS production, mitochondria function was more compromised in the doxorubicin-sensitive heart cells.

And even in the absence of treatment, there was a lower baseline function and quantity of mitochondria in the doxorubicin-sensitive cells. These results suggest some underlying genetic differences in the heart muscle cells of patients with DIC. The team plans to perform DNA comparisons to pinpoint the genes involved and ultimately help patients survive cancer without the fear of swapping it for another life threatening illness.

iPS cells: opening new paths for helping cancers patients
Compared to tools he had previously relied on, Joseph Wu, the team leader and director of the Stanford’s Cardiovascular Institute, is very excited about his lab’s future research possibilities:

“In the past, we’ve tried to model this doxorubicin toxicity in mice by exposing them to the drug and then removing the heart for study. Now we can continue our studies in human cells with iPS-derived heart muscle cells from real patients. One day we may even be able to predict who is likely to get into trouble.”

Combination Cancer Therapy Gives Cells a Knockout Punch

For some forms of cancer, there really is no way to truly eradicate it. Even the most advanced chemotherapy treatments leave behind some straggler cells that can fuel a relapse.

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]

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]

But now, scientists have devised a unique strategy, something they are calling a ‘one-two punch’ that can more effectively wipe out dangerous tumors, and lower the risk of them ever returning for a round two.

Reporting in the latest issue of the journal Nature Communications, bioengineers at Brigham and Women’s Hospital (BWH) in Boston describe how treating breast cancer cells with a targeted drug immediately after chemotherapy was effective at killing the cancer cells and preventing a recurrence. According to lead scientist Shiladitya Sengupta, these findings were wholly unexpected:

“We were studying the fundamentals of how [drug] resistance develops and looking to understand what drives [cancer] relapse. What we found is a new paradigm for thinking about chemotherapy.”

In recent years, many scientists have suggested cancer stem cells are one of the biggest hurdles to curing cancer. Cancer stem cells are proposed to be a subpopulation of cancer cells that are resistant to chemotherapy. As a result, they can propagate the cancer after treatment, leading to a relapse.

In this work, Sengupta and his colleagues treated breast cancer cells with chemotherapy. And here is where things started getting interesting.

After chemotherapy, the breast cancer cells began to morph into cells that bore a close resemblance to cancer stem cells. For a brief period of time after treatment, these cells were neither fully cancer cells, nor fully stem cells. They were in transition.

The team then realized that because these cells were in transition, they may be more vulnerable to attack. Testing this hypothesis in mouse models of breast cancer, the team first zapped the tumors with chemotherapy. And, once the cells began to morph, they then blasted them with a different type of drug. The tumors never grew back, and the mice survived.

Interestingly, the team did not have similar success when they altered the timing of when they administered the therapy. Treating the mice with both types of drugs simultaneously didn’t have the same effect. Neither did increasing the time between treatments. In order to successfully treat the tumor they had a very slim window of opportunity.

“By treating with chemotherapy, we’re driving cells through a transition state and creating vulnerabilities,” said Aaron Goldman, the study’s first author. “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.”

In order to test these combinations, the researchers developed an ‘explant,’ a mini-tumor derived from a patient’s biopsy that can be grown in an environment that closely mimics its natural surroundings. The ultimate goal, says Goldman, is to map the precise order and timing of this treatment regimen in order to move toward clinical trials:

“Our goal is to build a regimen that will be [effective] for clinical trials. Once we’ve understood specific timing, sequence of drug delivery and dosage better, it will be easier to translate these findings clinically.”

Clever Stem Cells Withstand Chemo Drug’s Harmful Side Effects

For some conditions, it seem that the treatment can cause almost as many problems as than the disease itself. That’s often the case with some forms of cancer, such as acute lymphoblastic leukemia.

The most common type of cancer to affect children, treatment usually involves chemotherapy with the drug methotrexate (MTX). And, while effective at destroying the deadly cancer cells circulating in the patients’ blood, it also does significant damage to another part of the body: the bone.

Scientists have long sought a method that helps patients recover more quickly from the harmful effects of chemotherapy.

Scientists have long sought a method that helps patients recover more quickly from the harmful effects of chemotherapy.

But new research from Brown University’s Dr. Eric Darling and his team has found that not all types of bone cells are equally at risk of being damaged by MTX. In fact, one type may actually be impervious to the drug’s negative effects. These findings, published last week in the journal Experimental Cell Research, are especially important as doctors look to ways that help the youngest, most vulnerable cancer patients heal faster after treatment—regaining bone strength that can take them into a healthy adulthood.

As Olivia Beane, a graduate student in the Darling Lab and the lead author of this paper, explained in a news release:

“Kids undergo chemotherapy at such an important time when they should be growing, but instead they are introduced to this very harsh environment where bone cells are damaged with these drugs. If we found a stem cell that was resistant to the chemotherapeutic agent and could promote bone growth by becoming bone itself, then maybe they wouldn’t have these issues.”

The cell type Beane is referring to are called adipose-derived stem cells, or ASCs, which normally mature from this early, stem cell state into several types of mature cells, including bone tissue. Initially, Beane had been researching the basic properties of ASCs. But during her experiments she discovered that ASCs, unlike other stem cell types that mature into bone, appear to survive MTX. Now they just needed to understand why.

Further experiments revealed the underlying strengths of ASCs in resisting MTX’s effects. Normally, MTX works by binding to and shutting down a protein in the cell called dihydrofolate reductase, which is normally involved in synthesizing DNA. With DNA production shut down, cells can’t divide and multiply—which is great for killing harmful cancer cells, but potentially harmful as it can also destroy cells it shouldn’t.

However, ASCs are a little bit different. When coming into contact with MTX, these cells ramp up the DNA-promoting dihydrofolate reductase, producing more than enough to overcome a normal dose of MTX.

This discovery has raised some intriguing possibilities for treating MTX’s side effects. As Darling explained:

“Chemotherapies do a great job of killing cells and killing the cancer, and that’s what you want. But then there is a stage after that where you need to do recovery and regeneration.”

And while the results of this study are preliminary, the researchers are cautiously optimistic that the MTX-resistant properties of ASCs could be the key to fast tracking recovery times.

The first step, Darling adds, is to save a life. And MTX has done that for countless children afflicted by cancer. But the cost of saving that life should also be taken into account—so that these children who have already been through so much may one day not need to worry about long, healthy lives as they mature into adults.

Want to learn more about how CIRM-funded researchers are developing new tools to fight all types of leukemia? Check out our Leukemia Fact Sheet.

Anne Holden

Out with the Old and in with the New: Starvation Sparks Stem Cells to Replenish Immune System

New research from California scientists has revealed a startling side effect to prolonged starvation, or fasting.

In the latest issue of the journal Cell Stem Cell, scientists from the University of Southern California describe how fasting triggers the human immune system to flush out old, damaged cells and replace them with new ones. This marks the first time that this phenomenon has been directly observed, and has major implications for diseases associated with a declining immune system, including a variety of age-related conditions and cancer chemotherapy.

Scientists have discovered how cycles of prolonged fasting can help flush out damaged immune system cells.

Scientists have discovered how cycles of prolonged fasting can help flush out damaged immune system cells.

In lab experiments first in animal models, and then followed by a Phase 1 human clinical trial, the research team found that regular cycles of fasting, each lasting two to four days, triggered the immune system to flush out immune cells. Much to the team’s surprise, however, they also found that these fasting cycles also triggered stem cells—which had been dormant—to spring into action and produce a fresh supply.

While initially unexpected, these findings made sense to the team. As corresponding author Dr. Valter Longo explained in today’s news release:

“When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged. What we started noticing in both our human work and animal work is that the white blood cell count goes down with prolonged fasting. Then when you re-feed, the blood cells come back. So we started thinking, well, where does it come from?”

Scientists have long known that when fasting, your body turns to its reserves for nutrients, using up stores of glucose and fat. At the same time, your body also breaks down white blood cells—the major component of the immune system.

So, Longo and his team mapped precisely how this change takes place. They observed that prolonged fasting also reduced levels of an enzyme called PKA. In a previous study, the team had found a link between reduced PKA levels and increased longevity in simple organisms. Research by other groups also found a connection between PKA and the ability of stem cells to self-renew. In this study, the team further defined that relationship. As Longo continued:

“PKA is the key gene that needs to shut down in order for these stem cells to switch into regenerative mode. And the good news is that the body got rid of the parts of the system that might be damaged or old…during fasting. Now if you start with a system heavily damaged, fasting cycles can generate, literally, a new immune system.”

These findings are particularly encouraging with regards to chemotherapy, which has the unfortunate side effect of often damaging the body’s immune system. But if the patient also participates in cycles of fasting, Longo and his team hypothesize that this could help repair their immune system at a much faster pace, improving their quality of life during treatment.

In order to test this hypothesis, the team then turned to the Phase 1 human clinical trial. They instructed patients currently undergoing chemotherapy to fast for a period of 72 hours. The team found that this fasting did protect against at least some of the toxic effects of chemotherapy treatment.

The next steps, says Longo, are to conduct additional experiments in both animal models and clinical trials. But the team is optimistic that these results could apply beyond chemotherapy.

“We are investigating the possibility that these effects are applicable to many different systems and organs, not just the immune system.”