CIRM funded research could lead to treatment to prevent recurrence of deadly blood cancer

Chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a cancer of the white blood cells. It causes them to increase in number, crowd out other blood cells, leading to anemia, infection or heavy bleeding. Up until the early 2000’s the main weapon against CML was chemotherapy, but the introduction of drugs called tyrosine kinase inhibitors changed that, dramatically improving long term survival rates.

However, these medications are not a cure and do not completely eradicate the leukemia stem cells that can fuel the growth of the cancer, so if people stop taking the medication the cancer can return.

Dr. John Chute: Photo courtesy UCLA

But now Dr. John Chute and a team of researchers at UCLA, in a CIRM-supported study, have found a way to target those leukemia stem cells and possibly eliminate them altogether.

The team knew that mice that had the genetic mutation responsible for around 95 percent of CML cases normally developed the disease and died with a few months. However, mice that had the CML gene but lacked another gene, one that produced a protein called pleiotrophin, had normal white blood cells and lived almost twice as long. Clearly there was something about pleiotrophin that played a key role in the growth of CML.

They tested this by transplanting blood stem cells from mice with the CML gene into healthy mice. The previously healthy mice developed leukemia and died. But when they did the same thing from mice that had the CML gene but lacked the pleiotrophin gene, the mice remained healthy.

So, Chute and his team wanted to know if the same thing happens in human cells. Studying human CML stem cells they found these had not just 100 times more pleiotrophin than ordinary cells, they were also producing their own pleiotrophin.

In a news release Chute, said this was unexpected:

“This provides an example of cancer stem cells that are perpetuating their own disease growth by hijacking a protein that normally supports the growth of the healthy blood system.”

Next Chute and the team developed an antibody that blocked the action of pleiotrophin and when they tested it in human cells the CML stem cells died.

Then they combined this antibody with a drug called imatinib (better known by its brand name, Gleevec) which targets the genetic abnormality that causes most forms of CML. They tested this in mice who had been transplanted with human CML stem cells and the cells died.

“Our results suggest that it may be possible to eradicate CML stem cells by combining this new targeted therapy with a tyrosine kinase inhibitor,” said Chute. “This could lead to a day down the road when people with CML may not need to take a tyrosine kinase inhibitor for the rest of their lives.”

The next step is for the researchers to modify the antibody so that it is better suited for humans and not mice and to see if it is effective not just in cells in the laboratory, but in people.

The study is published in the Journal of Clinical Investigation

Boosting the blood system after life-saving therapy

Following radiation, the bone marrow shows nearly complete loss of blood cells in mice (left). Mice treated with the PTP-sigma inhibitor displayed rapid recovery of blood cells (purple, right): Photo Courtesy UCLA

Chemotherapy and radiation are two of the front-line weapons in treating cancer. They can be effective, even life-saving, but they can also be brutal, taking a toll on the body that lasts for months. Now a team at UCLA has developed a therapy that might enable the body to bounce back faster after chemo and radiation, and even make treatments like bone marrow transplants easier on patients.

First a little background. Some cancer treatments use chemotherapy and radiation to kill the cancer, but they can also damage other cells, including those in the bone marrow responsible for making blood stem cells. Those cells eventually recover but it can take weeks or months, and during that time the patient may feel fatigue and be more susceptible to infections and other problems.

In a CIRM-supported study, UCLA’s Dr. John Chute and his team developed a drug that speeds up the process of regenerating a new blood supply. The research is published in the journal Nature Communications.

They focused their attention on a protein called PTP-sigma that is found in blood stem cells and acts as a kind of brake on the regeneration of those cells. Previous studies by Dr. Chute showed that, after undergoing radiation, mice that have less PTP-sigma were able to regenerate their blood stem cells faster than mice that had normal levels of the protein.

John Chute: Photo courtesy UCLA

So they set out to identify something that could help reduce levels of PTP-sigma without affecting other cells. They first identified an organic compound with the charming name of 6545075 (Chembridge) that was reported to be effective against PTP-sigma. Then they searched a library of 80,000 different small molecules to find something similar to 6545075 (and this is why science takes so long).

From that group they developed more than 100 different drug candidates to see which, if any, were effective against PTP-sigma. Finally, they found a promising candidate, called DJ009. In laboratory tests DJ009 proved itself effective in blocking PTP-sigma in human blood stem cells.

They then tested DJ009 in mice that were given high doses of radiation. In a news release Dr. Chute said the results were very encouraging:

“The potency of this compound in animal models was very high. It accelerated the recovery of blood stem cells, white blood cells and other components of the blood system necessary for survival. If found to be safe in humans, it could lessen infections and allow people to be discharged from the hospital earlier.”

Of the radiated mice, most that were given DJ009 survived. In comparison, those that didn’t get DJ009 died within three weeks.

They saw similar benefits in mice given chemotherapy. Mice with DJ009 saw their white blood cells – key components of the immune system – return to normal within two weeks. The untreated mice had dangerously low levels of those cells at the same point.

It’s encouraging work and the team are already getting ready for more research so they can validate their findings and hopefully take the next step towards testing this in people in clinical trials.