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Neutrophil engulfing bacteria
Image by Volker Brinkmann

Preclinical research suggests ibrutinib could treat G-CSFR-mutant myeloid disorders.

“Mutations in G-CSFR have a harmful effect on the production of neutrophils and are reported in patients with several blood disorders, including severe congenital neutropenia, chronic neutrophilic leukemia, and acute myeloid leukemia,” said Ken Greis, PhD, of the University of Cincinnati in Ohio.

“Unfortunately, despite years of research, the malignant signaling of the mutated G-CSFRs is not well understood.”

With this in mind, Dr Greis and his colleagues created a comprehensive signaling network of normal and mutated G-CSFR. Their goal was to understand how abnormal cellular signaling from the mutant receptors results in disease development.

The researchers described this work in Leukemia.

“We are able to look at . . . phosphorylation that results in phosphate groups being attached to the amino acid tyrosine (Tyr) in proteins,” Dr Greis explained. “These phosphorylation events (pTyr) can act as switches to activate or inactivate proteins and/or specific cellular processes.”

“By evaluating pTyr activity in the normal versus mutant receptor cells, we can produce a network similar to a wiring diagram of cellular regulation. Observed disruptions at any of the nodes in the network for the mutated receptors can then be investigated further to understand and perhaps target the abnormal signaling corresponding to the disease.”

This analysis of pTyr activity revealed that G-CSFR mutants had aberrant activation of BTK, as well as abnormal kinetics of canonical STAT3, STAT5, and MAPK phosphorylation.

“When we first got these results, one of the most exciting things was that BTK was already the target of an FDA-approved drug, ibrutinib . . .,” said study author H. Leighton Grimes, PhD, of the University of Cincinnati.

The researchers tested ibrutinib in cells with mutant and wild-type G-CSFR and found the drug killed the mutant cells but not the wild-type cells. This was the case in myeloid progenitor 32D cell lines and primary human CD34+ umbilical cord blood cells.

“Progenitor cells expressing mutated G-CSFR in animal models and in human blood cells also showed enhanced sensitivity to ibrutinib compared to the normal G-CSFR, thus confirming that the mutated cells could likely be eliminated by treatment with ibrutinib and may represent an effective therapy for these patients,” Dr Grimes said.

Ibrutinib also demonstrated synergy with the JAK1/2 inhibitor ruxolitinib. G-CSFR-mutant CD34+ cells were sensitive to each drug alone, but combining them “dramatically enhanced” the sensitivity, according to the researchers.

“These data demonstrate the strength of global proteomics approaches, like the pTyr profiling used here, in dissecting cancer-forming pathways and points to the possibility that ibrutinib could be an effective therapy for myeloid leukemias with G-CSFR mutations,” Dr Greis said.

“Further studies are needed to determine if these findings will be applicable in patient samples, but the hope is that clinical trials are just around the corner, since we’re investigating a drug that has already been found to be safe by the FDA.”


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