The Clinical Phenotype of Myelofibrosis Encompasses a Chronic Inflammatory State That Is Favorably Altered by INCB018424, a Selective Inhibitor of JAK1/2

Background: Current evidence links some of the disease manifestations in myelofibrosis (MF) to abnormal cytokines, likely produced by clonally involved megakaryocytes and monocytes. Furthermore, the recent discovery of JAK2/MPL mutations in MF suggests the contribution of abnormal JAK-STAT signaling to both clonal myeloproliferation and cytokine-driven debility. In order to gain additional pathogenetic insight regarding cytokine-phenotype correlations in MF, we looked into the plasma cytokine profile of MF before and after treatment with INCB018424, a selective JAK1/2 inhibitor.

Methods: The current study includes subjects with MF enrolled in an ongoing phase 1–2 study of oral INCB018424 (doses ranging from 25 mg/day to 50 mg BID). Plasma samples were obtained prior to treatment and at intervals of 2 weeks, 1 month and 2 months following INCB018424 dosing. Samples were submitted to Rules Based Medicine Human MAP multiplexed immunoassay system to obtain plasma levels on a range of protein analytes.

Results:

• Plasma cytokine levels in MF patients (n=53) vs. normal healthy volunteers (n=15):

  Compared to normal controls, plasma levels of pro-inflammatory cytokines and markers of inflammation were significantly increased in MF patients (Table; mean +/− SD values). Furthermore, the observed inflammatory cytokine levels in MF were often higher than those seen in patients with rheumatoid arthritis or cancer-associated cachexia (data to be presented at the meeting).

• Correlation of plasma cytokine levels in MF withJAK2V617F mutational status, MF subtype and/or constitutional symptoms/cachexia:

  Comparison of JAK2V617F positive (n=40) and negative (n=13) MF cases suggested significantly (p<0.01) higher IL-1RA (mean +/− SD = 5575 +/− 917 vs. 1291 +/− 359 pg/ml) and CRP (17.4 +/− 1.6 vs. 6.7 +/− 1.9 μg/ml) levels for the former whereas the other cytokines were elevated to a similar extent. Plasma cytokine levels in PMF (n=30) vs. post-PV MF (n=15) vs. post-ET MF (n=8) were not significantly different. The presence of prior splenectomy did not appear to alter the specific MF cytokine profile (Table 1); the abnormal cytokine profile in MF is, therefore, not necessarily a consequence of marked splenomegaly. There was a direct correlation between the levels of pro-inflammatory cytokines and the presence or absence of constitutional symptoms/cachexia (Figure). Similarly, increased inflammatory cytokine levels in MF were accompanied with significantly decreased leptin levels, a surrogate for nutritional status (Table).

• Post-INCB018424 treatment cytokine levels: Treatment with INCB018424 induced a rapid decrease in MF-associated inflammatory cytokine levels, in parallel with the observed clinical benefit of both reduced splenomegaly and improvement in constitutional symptoms/cachexia (data to be presented at the meeting).

Conclusion: The plasma cytokine profile of MF is reminiscent of a chronic inflammatory state with levels of pro-inflammatory cytokines that are possibly higher than those seen in other inflammatory/malignant conditions. Furthermore, the current study suggests a fundamental link between these cytokines and MF-associated constitutional symptoms/cachexia. Cytokine modulation through JAK-STAT inhibition appears to be a mechanism of action for INCB018424 in MF.