Researchers at Cincinnati Children's Hospital Medical Center suggest that blocking the signaling proteins c-Fos and Dusp1, as part of combination therapy, might cure several types of kinase-driven, treatment-resistant leukemia and solid tumor cancers (Nat Med 2017; doi:10.1038/nm.4310).
These include acute myeloid leukemia (AML) fueled by the gene FLT3, lung cancers fueled by genes EGFR and PDGFR, HER2-driven breast cancers, and BCR-ABL-fueled chronic myeloid leukemia (CML), according to Mohammad Azam, PhD, lead investigator and a member of the Division of Experimental Hematology and Cancer Biology.
"We think that within the next 5 years our data will change the way people think about cancer development and targeted therapy," Azam said. "This study identifies a potential Achilles heel of kinase-driven cancers and what we propose is intended to be curative, not just treatment."
The weak spot is a common point of passage in cells (a signaling node) that appears to be required to generate cancer cells in both leukemia and solid tumors. The node is formed by the signaling proteins c-Fos and Dusp1. The researchers identified c-Fos and Dusp1 by conducting global gene expression analysis of mouse leukemia cells and human CML cells donated by patients.
CML is driven by tyrosine kinase, which is formed by the fusion gene BCR-ABL. This fusion gene is the product of translocated chromosomes involving genes BCR (chromosome 22) and ABL (chromosome 9). Analysis of human CML cells revealed extremely high levels of c-FOS and DUSP1 in BCR-ABL-positive chemotherapy resistant cells.
Cancer cells often become addicted to the mutated gene that causes them, such as BCR-ABL in kinase-driven CML. Most chemotherapies work by blocking molecular pathways affected by the gene to shut down the disease process. In the case of CML, imatinib chemotherapy is used to block tyrosine kinase, which initially stops the disease. Unfortunately, the therapeutic benefit is temporary and the leukemia comes back.
Azam and colleagues show in their CML models that signaling from tyrosine kinase-and growth factor proteins that support cell expansion (like interleukins IL3, IL6, etc.)-converge to dramatically elevate c-Fos and Dusp1 levels in the cancer cells.
Working together these molecules maintain the survival of cancer stem cells and minimal residual disease. The dormant cells wait around under the radar screen to rekindle the disease by acquiring additional genetic mutations after initially effective chemotherapy.
Azam noted that Dusp1 and c-Fos support the survival of cancer stem cells by increasing the toxic threshold needed to kill them. This means conventional imatinib chemotherapy will not eliminate the residual disease stem cells. Physicians can't just increase the dose of chemotherapy because it doesn't target the Dusp1 and c-Fos proteins that regulate toxic threshold.
After identifying c-Fos and Dusp1, the authors tested different treatment combinations on mouse models of CML, human CML cells, and mice transplanted with human leukemia cells. They also tested treatments on B-cell acute lymphoblastic leukemia (B-ALL).
The treatment combinations included:
* solo therapy with just imatinib;
* solo treatment with just inhibitors of c-Fos and Dusp1; and
* treatment with all three combined.
As suspected, treatment with imatinib alone initially stopped CML progression, but the leukemia relapsed with the continued presence of residual disease cells. Treatment with c-Fos and Dusp1 inhibitors alone significantly slowed CML progression and prolonged survival in a majority of mice but wasn't curative. Treatment for 1 month with c-Fos/Dusp1 inhibitors and imatinib cured 90 percent of mice with CML, with no signs of residual disease cells.
Azam and his colleagues also point to an interesting finding involving solo treatment with just the deletion of c-Fos and Dusp1. This eliminated expression of the signaling proteins and was sufficient to block B-ALL development, eradicating the disease in mouse models.
The authors stress that, because the study was conducted in laboratory mouse models, additional research is needed before the therapeutic strategy can be tested in clinical trials. They are following up the current study by testing c-Fos and Dusp1 as treatment targets for different kinase-fueled cancers, including lung cancer, breast cancer, and acute forms of leukemia.