Ruxolitinib/nilotinib Cotreatment Inhibits Leukemia-propagating Cells in Philadelphia Chromosome-positive ALL

Background: As one of the major treatment obstacles in Philadelphia chromosome-positive acute lymphoblastic leukemia (PhALL), relapse of PhALL may result from the persistence of leukemia-propagating cells (LPCs). Research using a xenograft mouse assay recently determined that LPCs were enriched in the CD34CD38CD58 fraction in human PhALL. Additionally, a cohort study demonstrated that PhALL patients with a LPCs phenotype at diagnosis exhibited a significantly higher cumulative incidence of relapse than those with the other cell phenotypes even with uniform front-line imatinib-based therapy pre- and post-allotransplant, thus highlighting the need for novel LPCs-based therapeutic strategies.

Methods: RNA sequencing (RNA-Seq) and real-time quantitative polymerase chain reaction (qRT-PCR) were performed to analyze the gene expression profiles of the sorted LPCs and other cell fractions from patients with de novo PhALL. In order to assess the effects of the selective BCR-ABL and/or Janus kinase (JAK)2 inhibition therapy by the treatment with single agents or a combination of ruxolitinib and imatinib or nilotinib on PhALL LPCs, drug-induced apoptosis of LPCs was investigated in vitro, as well as in vivo using sublethally irradiated and anti-CD122-conditioned NOD/SCID xenograft mouse assay. Moreover, western blot analyses were performed on the bone marrow cells harvested from the different groups of recipient mice.

Results: RNA-Seq and qRT-PCR demonstrated that JAK2 was more highly expressed in the sorted LPCs than in the other cell fractions in de novo PhALL patients. Combination treatment with a selective JAK1/JAK2 inhibitor (ruxolitinib) and nilotinib more effectively eliminated LPCs than either therapy alone or both in vitro and in humanized PhALL mice by reducing phospho-CrKL and phospho-JAK2 activities at the molecular level.

Conclusions: In summary, this pre-clinical study provides a scientific rationale for simultaneously targeting BCR-ABL and JAK2 activities as a promising anti-LPCs therapeutic approach for patients with de novo PhALL.