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.


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.”

Screen Shot 2016-04-19 at 9.27.23 AM

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.”

Stem Cells become Tool to Screen for Drugs; Fight Dangerous Heart Infections.

A Stanford study adds a powerful example to our growing list of diseases that have yielded their secrets to iPS-type stem cells grown in a dish. These “disease-in-a-dish” models have become one of the most rapidly growing areas of stem cell science. But this time they did not start with skin from a patient with a genetic disease and see how that genetic defect manifests in cells in a dish. Instead they started with normal tissue and looked at how the resulting cells reacted to viral infection.

They were looking at a nasty heart infection called viral myocarditis, which can begin to cause damage to heart muscle within hours and often leads to death. Existing antiviral drugs have only a modest impact on reducing these infections. So even though there is an urgent need to find better drugs, animal models have not proven very useful and there is no ready supply of human heart tissue for lab study.

To create a ready supply of human heart tissue Joseph Wu’s CIRM-funded team at Stanford started with skin samples from three healthy donors, reprogrammed them into iPS cells and then matured those into heart muscle tissue. Then they took one of the main culprits of this infection, coxsackievirus, and labeled it with a fluorescent marker so they could track its activity in the heart cells.

They were able to verify that the virus infected the cells in a dish just as they do in normal heart tissue. And when they tried treating the cells with four existing antiviral drugs they saw the same modest decrease in the rate of infected cells seen in patients. For one of the drugs that had been shown to cause some heart toxicity, they also saw some damage to the cells in the dish.

They propose that their model can now be used to screen thousands of compounds for potentially more effective and safer drugs. They published their results in Circulation Research July 15.

What a Difference Differentiation can Make: a Little Change can Reduce the Risk of Rejection

No one likes to be rejected. It hurts. But while rejection is something most of us experience at least a couple of times in our life, researchers at Stanford have found a way to reduce the risk of rejection, at least when it comes to one form of stem cells. Reporting in the latest issue of Nature Communications they have found that turning iPS or induced pluripotent stem cells into other, more specialized kinds of cells, can reduce the risk the immune system will attack them.

Our immune systems are things of beauty. They hunt out invaders like viruses and when they spot something that shouldn’t be there, they attack it. It’s a critical part of our body’s way of fighting off disease and staying healthy.

However, the immune system is not perfect. Researchers have known for some time that when you take skin from an individual and turn it into an iPS cell – one that is capable of turning into any other cell in the body – and then transplant that cell back into the same individual their immune system often attacks it. So far, the only individuals this has been done with are mice, but we assume the same would happen in people.

So Joseph Wu and his CIRM-funded Stanford team decided to see what would happen if they took those same iPS cells and, before transplanting them back into the individual they came from, turned them into a more specialized form of cell. The results were encouraging: the immune system didn’t wage an attack.

Dr. Joseph Wu, Stanford University School of Medicine

Dr. Joseph Wu, Stanford University School of Medicine

Researchers were not sure why the body would attack something that was created from its own tissue, but speculated that turning ordinary skin cells into iPS cells created a kind of cell that the immune system hadn’t seen before, or at least hadn’t seen since it since it was an embryo.

In the Stanford news release, Wu said this finding could be really important in helping avoid rejection in organ or other tissue transplants:

“Induced pluripotent stem cells have tremendous potential as a source for personalized cellular therapeutics for organ repair. This study shows that undifferentiated iPS cells are rejected by the immune system upon transplantation in the same recipient, but that fully differentiating these cells allows for acceptance and tolerance by the immune system without the need for immunosuppression.” 

The team first transplanted some iPS cells into genetically identical recipient mice. The transplants were rejected and within 42 days there were no signs that any cells had survived.

Then they took the same kind of iPS cell and differentiated, or ‘re-programmed,’ them so that they turned into endothelial cells, the kind found in the inner lining of blood vessels. Then they transplanted those cells into the mice. At the same time they took some of the mice’s own endothelial cells out, and transplanted them back into genetically identical mice to see how they would compare. Both sets of cells, the iPS-turned-into endothelial and the endothelial cells, survived for at least 63 days after transplantation.

When the researchers repeated the experiment and examined the areas where the cells had been transplanted, they found much greater signs of immune system activity in the mice that were given iPS cells compared to the mice who got iPS cells that had been turned into endothelial cells, and the mice that just got endothelial cells.

For Wu, the bottom line was simple:

“This study certainly makes us optimistic that differentiation — into any nonpluripotent cell type — will render iPS cells less recognizable to the immune system. We have more confidence that we can move toward clinical use of these cells in humans with less concern than we’ve previously had.” 

 We work closely with Joseph Wu and his team on a number of other different projects, most focusing on heart disease.

kevin mccormack