Inhibition Of Inflammation Driven Leukemia Stem Cell Self-Renewal With a Selective JAK2 Antagonist

Chronic myeloid leukemia (CML) represents an important paradigm for identifying the molecular events that promote malignant reprogramming of progenitors into therapeutically recalcitrant leukemia stem cells (LSC) during blast crisis (BC) transformation. To elucidate mechanisms of human BC LSC generation, whole transcriptome RNA sequencing (RNA Seq), lentiviral BCR-ABL and JAK2 transduction, quantitative RT-PCR (qRT-PCR) and serial xenotransplantation studies were performed. In human BC LSC, RNA seq revealed extensive upregulation of inflammation-responsive genes in conjunction with JAK/STAT signaling pathway activation and splice isoform specific qRT-PCR uncovered a predilection for selective STAT5a isoform expression. While lentiviral BCR-ABL1 expression in cord blood progenitors enhanced JAK2 activation and expression of specific STAT5a splice isoforms, lentiviral human JAK2 overexpression globally activated inflammation-response genes and expression of adenosine deaminase RNA associated (ADAR1), a primate specific RNA editase previously shown to activate self-renewal in response to inflammation. Notably, inhibition of BC LSC self-renewal with dasatinib, a BCR-ABL inhibitor, combined with a potent JAK2 inhibitor, SAR302503, was associated with reduced STAT5a isoform expression and phospho-STAT5 activation as well as ADAR1 expression and activity. These results highlight a novel JAK/STAT pathway driven niche-responsive mechanism of human BC LSC generation that can be targeted, at least in part, with a selective JAK2 inhibitor and may be utilized as an RNA editing-based biomarker of cancer stem cell generation and therapeutic resistance.