September 12, 2016
As a treatment for acute myeloid leukemia (AML), natural killer (NK) cells show encouraging potential. Because these cells are highly active in killing cancer, researchers have focused on methods of expanding donor cultures to be used in therapy. However, the specific characteristics of NK cells among AML patients have presented barriers to developing effective treatments.
“NK cells in AML patients are known to have reduced cytotoxic activity and be reduced in number,” says David N. Wald, MD, PhD, a clinical pathologist at University Hospitals Seidman Cancer Center and UH Rainbow Babies & Children’s Hospital and Assistant Professor of Pathology and Medicine, Case Western Reserve University School of Medicine.
Now, however, Dr. Wald and a team of colleagues have revealed a reason for this dysfunction, potentially opening up a new treatment avenue for AML patients. In a series of experiments, they’ve shown that NK cell impairment among AML patients can be traced to overexpression of glycogen synthase kinase (GSK) 3 beta protein.
“We’ve found that GSK3 beta protein levels are upregulated in NK cells from AML patients, when compared with cells from normal donors,” Dr. Wald says. “This impairs their ability to kill AML cells. At the same time, we’ve also shown that inhibiting GSK3 expression in NK cells, either genetically or pharmacologically, enhances their cytotoxic activity.” The researchers reported their findings recently in the journal Nature Communications.
Although GSK3 has previously been shown to be a promising target in AML, the protein’s function within NK cells has been less clear, Dr. Wald says.
“This is the first study to identify the important role GSK3 overexpression plays in AML,” he says. “Also, in contrast to previous studies, our findings demonstrate that GSK3 inhibition not only impacts AML cells directly, but also hyperactivates NK cells and leads to AML cell killing.”
“These findings are exciting,” adds Marcos de Lima, MD, Director of the Hematologic Malignancies and Stem Cell Transplant Program at UH Seidman Cancer Center and Professor of Medicine, Case Western Reserve University School of Medicine, a co-author of the study. “Our group is also investigating other cell therapies in cancer involving NK cells, dendritic cells, mesenchymal stromal cells and T lymphocytes.”
Dr. Wald and Dr. de Lima Director collaborated on this work with researchers from the Department of Pathology at Case Western Reserve University School of Medicine, Invenio Therapeutics and MD Anderson Cancer Center.
Importantly, the group’s data show that there are several ways to inhibit GSK3 in NK cells. In vivo strategies do work. Study findings showed that NK cells from patients with high levels of lithium – a known but weak GSK3 inhibitor – had increased cytotoxic activity. Genetic manipulation also was shown to be effective. NK cells in which the GSK3 protein was absent killed 30 to 40 percent of tumor cells, as compared with 10 to 15 percent killed by wild-type NK cells. Experiments in mice also showed that NK cells treated with GSK3 inhibitors were effective in killing leukemia cells.
For now, however, Dr. Wald and the team believe an ex vivo strategy holds the most promise.
“Pretreating NK cells with GSK3 inhibitors resulted in enhanced killing of AML cells,” he says. “Importantly, this enhanced NK cell cytotoxic activity only involves a short ex vivo exposure to GSK3 inhibitors. Therefore, this strategy does not require a patient to be exposed to the high doses of GSK3 inhibitors that are necessary for potent kinase inhibition, as well as NK cell hyperactivation.”
“Our study has revealed the role of GSK3 in NK cell function, but more importantly, it has established a new therapeutic strategy for AML,” Dr. de Lima says. “The hyperactivated NK cells exhibit a significantly improved ability to kill AML cells in both cell and animal systems. Because hyperactivation only requires a short ex vivo treatment with a GSK3 inhibitor, translation of this strategy to the clinic should be rapid.”