azd-1480 and Primary-Myelofibrosis

The anti-tumor activity of AZD1480, a potent, selective inhibitor of Janus-associated kinases 1 and 2, was demonstrated in preclinical models of myeloproliferative neoplasms. In a phase I clinical study, 35 patients with myelofibrosis received 2.5-70mg AZD1480 orally once daily (QD) or 10 or 15mg twice daily (BID) continuously during repeated 28-day cycles. Two patients experienced dose-limiting toxicities: one patient in the 2.5mg QD cohort had a grade 3 lung infiltration/acute pneumonia, and one patient receiving 50mg QD had grade 3 presyncope. Dosing was stopped at 70mg QD after the first patient experienced an adverse neurological event (AE) and evidence of low-grade neurological toxicity in patients on lower doses after the initial month of therapy became apparent. The most common AZD1480-related AEs were dizziness and anemia. AZD1480 was absorbed quickly and eliminated from the plasma rapidly, with a mean terminal half-life of 2.45-8.06h; accumulation was not observed after repeated daily dosing for 28 days. Four patients showed evidence of clinical improvement based on IWG-MRT 2006 criteria. AZD1480 was relatively well tolerated, however, low-grade, reversible neurological toxicity was therapy limiting and led to study termination.

Topics: Aged; Aged, 80 and over; Anemia; Dizziness; Female; Humans; Janus Kinase 2; Male; Middle Aged; Primary Myelofibrosis; Pyrazoles; Pyrimidines

Dysregulation of Janus kinase (JAK)-signal transducer and activator of transcription signaling is central to the pathogenesis of myelofibrosis (MF). JAK2 inhibitor therapy in MF patients results in a rapid reduction of the degree of splenomegaly, yet the mechanism underlying this effect remains unknown. The in vitro treatment of splenic and peripheral blood MF CD34(+) cells with the JAK1/2/3 inhibitor, AZD1480, reduced the absolute number of CD34(+), CD34(+)CD90(+), and CD34(+)CXCR4(+) cells as well as assayable hematopoietic progenitor cells (HPCs) irrespective of the JAK2 and calreticulin mutational status. Furthermore, AZD1480 treatment resulted in only a modest reduction in the proportion of HPCs that were JAK2V617F(+) or had a chromosomal abnormality. To study the effect of the drug on MF stem cells (MF-SCs), splenic CD34(+) cells were treated with AZD1480 and transplanted into immunodeficient mice. JAK2 inhibitor therapy did not affect the degree of human cell chimerism or the proportion of malignant donor cells. These data indicate that JAK2 inhibitor treatment affects a subpopulation of MF-HPCs, while sparing another HPC subpopulation as well as MF-SCs. This pattern of activity might account for the reduction in spleen size observed with JAK2 inhibitor therapy as well as the rapid increase in spleen size observed frequently with its discontinuation.

Topics: Adult; Aged; Apoptosis; Cells, Cultured; Female; Humans; Janus Kinase 2; Male; Middle Aged; Polycythemia Vera; Primary Myelofibrosis; Pyrazoles; Pyrimidines; Signal Transduction; Spleen; Stem Cells; Thrombocytosis

In this issue of Blood, Wang et al report on the response of splenic-derived hematopoietic stem and progenitor cells from patients with myelofibrosis (MF) to the Janus kinase (JAK) inhibitor, AZD1480.

Topics: Female; Humans; Janus Kinase 2; Male; Primary Myelofibrosis; Pyrazoles; Pyrimidines; Spleen; Stem Cells