PHILADELPHIA—Experiments in mice reinforce the idea that tyrosine kinase inhibitors (TKIs) can treat patients with Ph-like acute lymphoblastic leukemia (ALL).
Investigators recently identified genomic alterations in Ph-like ALL that suggest these patients might respond to TKIs, and tests in a small number of patients supported this theory.
Now, preclinical results show that kinase fusions in Ph-like ALL activate signaling pathways differently, and this affects sensitivity to TKIs.
Kathryn Roberts, PhD, of St Jude Children’s Research Hospital in Memphis, Tennessee, and her colleagues presented these results at the AACR conference Hematologic Malignancies: Translating Discoveries to Novel Therapies.
“We recently described a subtype of B-cell acute lymphoblastic leukemia with very poor outcome that is characterized by genetic alterations involving tyrosine kinases, termed Ph-like ALL,” Dr Roberts said. “We wanted to examine whether these alterations contribute to the development of Ph-like ALL and determine if they could be targeted with tyrosine kinase inhibitors.”
“We showed, for the first time, that the kinase alterations we tested contribute to the development of Ph-like ALL, and that Ph-like ALL can be treated effectively with tyrosine kinase inhibitors in animal models. These findings provide a strong rationale for treating Ph-like ALL patients with targeted therapies to improve their survival.”
Dr Roberts and her colleagues first introduced kinase alterations—RCSD1-ABL2, SSBP2-CSF1R, or PAX5-JAK2—in IL-7-dependent, Arf-/- mouse pre-B cells expressing IK6.
They found that each fusion conferred cytokine-independent growth in vitro. And mice that received transplants of pre-B cells expressing RCSD1-ABL2 or SSBP2-CSF1R developed ALL with a pre-B immunophenotype.
The investigators then assessed the activation of kinase signaling pathways and TKI sensitivity in Arf-/- pre-B cells and human leukemic cells harvested from xenografted mice expressing ETV6-ABL1, RANBP2-ABL1, PAG1-ABL2, RCSD1-ABL2, SSBP2-CSF1R, IGH-EPOR, ATF7IP-JAK2, and PAX5-JAK2.
In both cell types, signaling pathway activation and TKI sensitivity differed according to the kinase fusion.
Cells expressing ABL1-class kinase fusions (ABL1, ABL2, CSF1R, and PDGFRB) exhibited pSTAT5 activation that was inhibited by imatinib or dasatinib. But in cells expressing ATF7IP-JAK2, PAX5-JAK2, or IGH-EPOR, pSTAT5 activation was only inhibited by ruxolitinib.
Finally, the investigators tested dasatinib in xenograft models of ETV6-ABL1, RCSD1-ABL2, PAG1-ABL2, or SSBP2-CSF1R ALL.
They found that treated mice had significantly lower leukemic burdens and splenic weights than control mice. And STAT5 phosphorylation was attenuated in cells from treated mice.
“Our studies show that different FDA-approved TKIs such as imatinib, dasatinib, ruxolitinib, or crizotinib could potentially be used to treat Ph-like ALL patients, depending on the type of kinase alterations their tumors bear,” Dr Roberts said.
“We were able to gain a better understanding of the genetics underlying Ph-like ALL, and our studies could help identify patients who will not respond optimally to current therapy. By knowing the exact genetic alteration upfront, we may be able to implement different therapeutic strategies to improve the survival rate of future patients with ALL.”
