Although we live in an incredible age of research and development and medical discovery, we often take research findings for granted. Yes, we're still a long way from a cure, but we're continuing to discover new treatment regimens that could change the course of a patient's life with cancer, particularly those living with chronic myelogenous leukemia (CML).
CML is a type of cancer that starts in the blood-forming cells of the bone marrow and invades a patient's blood. Currently, there are first-line drug treatments that can successfully induce long-term remission in CML patients, called tyrosine kinase inhibitors (TKIs), but unfortunately, leukemia stem cells—which initiate and maintain the disease—frequently persist, resulting in cancer recurrence.
Earlier this year, Bin Zhang, MD, PhD, Associate Research Professor in the Department of Hematologic Malignancies Translational Science at City of Hope, along with myself, led a study published in Nature Medicine on a more effective, less toxic treatment for patients with CML involving miristen—a new drug developed at the facility—and TKIs (2018;24:450-462). We have reason to believe miristen makes TKIs more effective at killing the leukemia stem cells, so we treated mice with CML with different drug combinations and found those treated with miristen and TKI who had received stem cell transplants went into complete remission.
Miristen targets a type of microRNA that is expressed in leukemia stem cells, known as miR-126. We believe this RNA molecule plays an important role in the self-renewal and persistence of cancer-causing leukemia stem cells. By eliminating this molecule in the blood, there's an opportunity to reduce the chance of cancer recurrence by eradicating the stubborn stem cells altogether.
Transplantation of the bone marrow cells collected from those treated with miristen and TKI resulted in no sign of leukemia in the healthy recipient mice, meaning all leukemia stem cells were eliminated.
Patients Living With CML
With TKIs alone, people living with CML usually have to continue taking the drug for the rest of their lives to reduce the chances of a relapse of the disease. If research continues to demonstrate positive results using miristen combined with TKI, this combination could send CML into permanent remission without the need for ongoing TKI treatments, resulting in a reduction in lifelong medical expenses and the anxiety of living with a cancer that has a high chance of returning.
At City of Hope, we are continuing to work to bring miristen from the laboratory to the clinic for the treatment of patients living with CML.
As part of our CML research, we also discovered that endothelial cells in the blood vessels of a person's bone marrow—where CML begins—contain high levels of miR-126. These endothelial cells transfer miR-126 to leukemia stem cells, essentially feeding the cancer what it needs to survive and persevere. We hypothesized that, in order to eliminate CML, miristen had to lower miR-126 in both the leukemia stem cells and the endothelial cells. So far, our hypothesis is correct.
This discovery demonstrates how the microenvironment surrounding the leukemia stem cells supports them and how we, as physicians, need to target miR-126 in both the leukemia stem cells and the microenvironment to completely eradicate the disease.
Even more meaningful—our current CML research shows these findings may also apply to other types of leukemia.
The miristen mouse study gives us hope that a cure for CML (and other forms of leukemia) is possible. The first step in optimizing physician management of CML is advancing physicians' understanding of stem cells and blood cancer, which will ultimately lead to better patient outcomes.
GUIDO MARCUCCI, MD, is Chair and Professor in the Department of Hematologic Malignancies Translational Science, and Director of the Gehr Family Center for Leukemia Research at City of Hope, Duarte, Calif.