JAK2 aberrations in childhood B-cell precursor acute lymphoblastic leukemia

JAK2 abnormalities may serve as target for precision medicines in pediatric B-cell precursor acute lymphoblastic leukemia (BCP-ALL). In the current study we performed a screening for JAK2 mutations and translocations, analyzed the clinical outcome and studied the efficacy of two JAK inhibitors in primary BCP-ALL cells. Importantly, we identify a number of limitations of JAK inhibitor therapy. JAK2 mutations mainly occurred in the poor prognostic subtypes BCR-ABL1-like and non- BCR-ABL1-like B-other (negative for sentinel cytogenetic lesions). JAK2 translocations were restricted to BCR-ABL1-like cases. Momelotinib and ruxolitinib were cytotoxic in both JAK2 translocated and JAK2 mutated cells, although efficacy in JAK2 mutated cells highly depended on cytokine receptor activation by TSLP. However, our data also suggest that the effect of JAK inhibition may be compromised by mutations in alternative survival pathways and microenvironment-induced resistance. Furthermore, inhibitors induced accumulation of phosphorylated JAK2Y1007, which resulted in a profound re-activation of JAK2 signaling upon release of the inhibitors. This preclinical evidence implies that further optimization and evaluation of JAK inhibitor treatment is necessary prior to its clinical integration in pediatric BCP-ALL

Ibrutinib is not an effective drug in primografts of TCF3-PBX1

Aim: The Bruton's tyrosine kinase (BTK) inhibitor Ibrutinib (PCI-32765) is effective in patients with multiple myeloma, non-Hodgkin lymphoma and chronic lymphoblastic leukemia. We previously showed that primary cells of children with TCF3-PBX1 positive B-cell precursor acute lymphoblastic leukemia (BCP-ALL) express BTK and are sensitive to ibrutinib in vitro. However, preclinical studies in mice are lacking that justify clinical implementation. Methods: Immunocompromised NSG mice were engrafted with a luciferase-positive TCF3-PBX1 leukemic cell line or primary leukemic cells and treated with ibrutinib or placebo. Additionally, primary cells were exposed in vitro to 4 main induction drugs as monotherapy and in combination with ibrutinib. Results: Treatment with ibrutinib of mice engrafted with a TCF3-PBX1 cell line, TCF3-PBX1 positive or TCF3-PBX1 negative primary leukemic cells did not result in prolonged life span compared to placebo treated mice. In vitro sensitivity to ibrutinib was unaltered in leukemic cells obtained from engrafted mice compared to the original material. However, ibrutinib treatment did not affect leukemic cell viability and tumor outgrowth, nor could lymphocytosis be detected. Ibrutinib was biologically active, since hCD19+ cells harvested from ibrutinib treated mice had no detectable levels of phospho-BTK at tyrosine 223 (pBTK Y223), whereas pBTK Y223 was still detectable in placebo treated cases. In combination tests, we noticed an antagonistic effect of ibrutinib on vincristine sensitivity, which was not observed for prednisolone, L-asparaginase and daunorubicin. Conclusions: We conclude that ibrutinib is not the precision medicine of choice for TCF3-PBX1 positive BCP-ALL