Bradley, Edward C.

Abstract BACKGROUND: MF is a progressive illness associated with cachexia and weight loss (Mesa et al, Cancer2007;109: 68). These clinical signs, resulting from both hypercatabolism (secondary to increased pro-inflammatory cytokines) and MF associated splenomegaly, are associated with decreased survival (Dupriez et al., Blood1996;88:1013). Currently, there is no therapy that decreases the progressive cachexia of MF. INCB018424 is a selective JAK1/2 inhibitor which has the potential to improve both the aberrant myeloproliferation in MF through decreasing constitutively active JAK-STAT signaling, and nutritional status by decreasing both splenomegaly and the pathologically increased cytokines. METHODS: Symptomatic patients with MF enrolled in a phase I/II trial (www.ClinicalTrials.gov, NCT00509899) with INCB018424, were analyzed for the impact of therapy on nutritional status and cachexia. Specifically, in addition to traditional endpoints of IWG-MRT response (reported elsewhere) patients were assessed for changes in body mass index (BMI), serum cholesterol values, spleen size, and patient reports of early satiety and anorexia. Additionally, leptin, an adipose-derived protein hormone that plays a key role in regulating energy balance and circulates at levels proportional to body fat in health and disease (Mantovani et al, J Mol Med2001; 79:406), was assessed serially. RESULTS: Patients: Thirty four MF patients, treated for at least 2 months with 25 mg twice daily of INCB018424, were included in this analysis. Among this group 85% demonstrated splenomegaly (median 20 cm below left costal margin, range 4 cm to 32 cm; 2 patients had prior splenectomy) and had a median BMI of 24.8 (range 17.9 to 49.7). Although the median BMI at baseline would be considered in the “normal range” (18.5–24.9), loss of lean body mass at enrollment would be underestimated by the contribution of splenomegaly or edema. Appetite: At enrollment, a clearly positive correlation between the presence of anorexia and early satiety (by patient’s report) and significant splenomegaly was observed. Treatment with INCB018424 led to resolution of the symptoms of poor appetite and early satiety, along with the reduction in splenomegaly. Weight: MF patients on therapy initially lost weight, which reflects resolution of excess extravascular water (based on investigators reported decreases in peripheral edema, ascites, or splenomegaly). As the trial progressed MF patients on INCB018424 treatment progressively gained weight (mean increase of 0.40 kg @ 1 month, 2.93 kg @ 2 mo, 3.70 @ 3 mo), and exhibited improved appetite. Importantly, weight gain was more consistent, of greater magnitude and more durable in patients who entered the study in the lowest quartile for BMI. Cholesterol: We previously reported that hypocholesterolemia (total cholesterol <150 or 100 mg/dL; HDL < 60mg/dL) is associated with decreased survival in MF patients (Mesa et al, Blood2007; 2007;110:a2548), potentially from hypercatabolism and splenic consumption of lipids. At enrollment, median total cholesterol was 95 mg/dl (range), with 94% and 55% below 150 mg/dl and 100 mg/dl, respectively. Following treatment with INCB018424, median total cholesterol increased to 145 mg/dl (range 72–289 mg/dL) with 73% increasing to an improved range above their baseline (either to the >100mg/dl or >150 mg/dl range). Leptin: At enrollment, MF patients had very low leptin levels (mean = 2.55 ng/mL with 50% below 1 ng/mL vs. a range of 6–12 ng/mL for normal volunteers). Low plasma levels are associated with shortened survival in cancer patients. The plasma leptin levels increased 176% on average after one month of treatment with INCB018424, and continued to increase to levels matching healthy volunteers with time on study (mean = 7.04 ng/mL (range 0.25 – 35 ng/mL) after 2 months on INCB018424) and correlated to weight increases. CONCLUSIONS: Therapy with INCB018424 improves the nutritional status of MF patients, including improving pathologic weight loss, hypercatabolism associated hypocholesterolemia, and pathologically decreased serum leptin. The improved nutritional status of MF patients treated with INCB018424 may reflect the ability of JAK inhibition to target the underlying pathophysiology of MF cachexia by reducing the organomegaly, levels of pro-inflammatory cytokines, and pro-inflammatory cytokine signaling.

Abstract Background : Myelofibrosis (MF) is characterized by progressive bone marrow dysfunction, extramedullary hematopoiesis, massive splenomegaly, elevated levels of inflammatory cytokines, severe constitutional symptoms, cachexia and premature death. INCB018424 is a potent, selective inhibitor of JAK 1 and 2 which has demonstrated impressive clinical activity in the early portion of a phase 1/2 study in patients with PMF and Post-PV/ET MF. Methods : Following the initial dose escalation phase with a BID schedule (N=11), both twice daily (10 mg BID to 25 mg BID, N=56) and once daily (25 mg QD to 200 mg QD, N= 37) dose regimens were explored. Endpoints included spleen size assessed by manual palpation, constitutional symptoms assessed using the Modified Myelofibrosis Symptom Assessment Form (MFSAF) and JAK2 allele burden. Exercise capacity is being assessed using the Six Minute Walk Test (6MWT), and body mass and composition are being assessed using standard methods. Safety was assessed by collection of adverse events and monitoring of laboratory data. Results : Over 100 patients are currently enrolled in the study, with a mean exposure to drug of > 5 months. Twenty percent of patients have received INCB018424 for > 9 months. INCB018424 is associated with a rapid reduction of splenomegaly in over 93% of patients from a mean baseline spleen size >20 cm, with 50% or greater reduction being observed in 35% of patients dosed with 10 mg BID or 50 mg QD, and 59% of patients dosed with 25mg BID regimens. These declines nearly always occur within the first month of therapy, with further, slower decreases often observed thereafter. In responding patients, spleen size reduction persists for the duration of therapy (currently up to one year follow-up). Constitutional symptoms are reported with high frequency in the study population as assessed by the MFSAF: night sweats, pruritis and fatigue were reported by >60%, >45% and >90% of patients respectively. Improvements in self-assessed symptom scores (mean % improvement of 40% to 60%) occurred by the first assessment at week 2. Activity limitations are also reported by a high proportion of MF patients; 70% of respondents reported impaired ability to exercise or get around, with a mean score >5 on the 11-point MFSAF scale; INCB018424 therapy was associated with rapid (within 2 weeks) and marked (40% or more) improvement in self-assessed score. There was a dose-dependent weight gain, most pronounced in patients with the lowest body mass index (BMI) values at baseline. Profound reductions in inflammatory cytokines were observed by the first evaluation at week 2 in virtually all patients, and were maintained during therapy. INCB018424 is generally well tolerated with the primary toxicity being dose-dependent grade 3 or 4 reversible thrombocytopenia which occurred in 0%, 18% and 32% of patients dosed with 10 mg BID, 50 mg QD or 25 mg BID. Conclusions : INCB18424 shows unprecedented and durable clinical efficacy in reducing spleen size and improving constitutional symptoms in patients with MF. Results from proactive dose modification regimens, assessments of exercise capacity, MRI-based spleen volume assessment and body composition determination will be presented.

Abstract Background: Activating mutations in the pseudokinase domain of JAK2 occur at a high frequency in Philadelphia chromosome-negative myeloproliferative disorders (MPDs). Increasing JAK2 V617F allele burden has been shown to correlate with disease severity (bone marrow dysfunction, organomegaly and constitutional symptoms), which is consistent with exaggerated JAK2 signaling playing a central role in MPDs. INCB018424 is a potent and selective JAK1/2 inhibitor currently being evaluated in the clinic for the treatment of MPDs including primary myelofibrosis (PMF), post-polycythemia vera and essential thrombocythemia myelofibrosis (Post-PV/ET MF). Methods: The percentage of mutant JAK2 V617F relative to wild-type JAK2 was determined in peripheral blood using a quantitative single-nucleotide extension assay. The assay is based on the single nucleotide extension of a DNA primer that anneals adjacent to the V617F mutation. The percentage of JAK2 V617F in bone marrow was determined using pyrosequencing as previously described. The relationship between JAK2 V617F allele burden and clinical phenotype was assessed with samples obtained at study entry. JAK2 V617F allele burden was assessed in nineteen PMF and Post-PV/ET MF patients treated with 25 mg BID INCB018424 for a minimum of three months using peripheral blood and bone marrow. Results: There is an excellent correlation in the JAK2 V617F allele burden between samples obtained from bone marrow and peripheral blood, suggesting that the fraction of cells bearing the mutant clone remains stable during hematopoiesis in this patient group. The mean %V617F values were 59%, 80% and 86% for Post-ET MF (n=2), Post-PV MF (n=8) and PMF (n=9) patients. V617F allele burden correlated with spleen size, absolute neutrophil count (ANC) and Body Mass Index (BMI) in this patient population (R2 values if 0.61, 0.17 and 0.44, respectively), with a higher allele burden predicting larger spleen size, a higher ANC and a lower BMI. Eighteen of the nineteen evaluable JAK2 V617F-positive patients had baseline JAK2 V617F values above 50%, with the mean %V617F value for all evaluable patients being 81%, implying that the majority of hematopoietic stem cells contain the mutant allele in this patient population. During INCB018424 therapy (at least 3 months of treatment) in these patients, profound improvements in clinical endpoints including reduction or resolution of splenomegaly and constitutional symptoms are observed, yet only a modest decrease in JAK2 V617F allele burden is seen in both bone marrow and peripheral blood (13% and 9 % decrease from baseline, respectively, at 3 months). Conclusions: While the patient group is small and heterogeneous in nature, clinical correlates of V617F allele burden observed in myelofibrosis patients in this study are similar to those reported in PV. In addition, despite profound clinical improvements in these patients, V617F allele burdens do not change dramatically suggesting that the clinical activity of INCB018424 might involve inhibition of downstream signaling in cells harboring activating JAK2 mutations rather than changing the allele burden.

Abstract Abstract 756 Background: Myelofibrosis (MF) is the most serious of chronic myeloproliferative neoplasms (MPNs) for which there is no approved therapy. Exaggerated JAK2 signaling, either by gain-of-function mutations (eg, JAK2V617F) or high circulating levels of JAK1/2 activating cytokines (eg, interleukin [IL]-6), is believed to play a key role in MPN pathogenesis. INCB018424 (424), a selective oral inhibitor of JAK1/2, has demonstrated clinical benefits including reduction of splenomegaly and improvement of symptoms in a Phase I/II trial in MF patients. Thrombocytopenia was identified as the dose limiting toxicity occurring in 30% of patients at 25mg BID. Methods: Patients with primary, post-PV or post-ET MF were enrolled in the study. Following the characterization of multiple dosing regimens, an individually optimized dose regimen strategy was developed, based on available efficacy and safety data. In a subset of patients, spleen volume change was measured by MRI at 1, 3 and 6 months of treatment in order to establish an objective measure of spleen response. The impact of 424 on MF associated symptoms was assessed using a validated instrument, MFSAF (Mesa et al., Leukemia Research 2009). As a surrogate marker of functional benefit, exercise capacity was assessed with a standardized 6-minute walk test (6MWT) at baseline, 1, 3 and 6 months of therapy. Results: 155 patients were enrolled in the study, with median duration of treatment of 1+ years and the duration of drug exposure of >150 patient years (76 patients received >1 year of therapy). Clinical responses have been maintained over the entire duration of treatment and most patients remain on therapy (115 of 155 patients; 74%). Progression to AML occurred in 3 patients, which is below the expected frequency based on published data (Barosi et al., Blood 2007). SAEs related to 424 occurred in 12 patients, and are generally related to bone marrow suppression or return of or exacerbation of signs and symptoms of MF when therapy is discontinued. Further optimization of the dosing regimen utilized baseline platelet count to determine the starting dose (10 or 15mg BID) and allowed dose titration after 1 and 2 months of therapy; most patients were optimized to 15 or 20mg BID. This approach significantly reduced the incidence of thrombocytopenia (<5%, N=35), while providing equivalent efficacy to higher dose regimens. With an optimized dosing regimen, spleen volume reduction was evident as early as 1 month, and durable over 6 months, of therapy (33 % median decrease after 6 months, N=23). Eleven of 23 (48%) of patients achieved ≥ 35% reduction (equivalent to IWG clinical improvement criteria of 50% reduction by palpation) from baseline in spleen volume at month 6. MF patients have impaired exercise capacity at baseline (decreased 6MWT performance by 60-90 meters vs. age-matched controls). Treatment with 424 resulted in improved 6MWT performance, with median increase from baseline of 33, 58 and 70 meters after 1,3 or 6 months of therapy, respectively. Rapid and durable reduction of a total symptom score based on key symptoms (fatigue, abdominal discomfort/pain, bone/muscle pain, night sweats and pruritus) was noted (51 % and 58% of patients achieving 50% reduction in the total score following 1 and 6 months of treatment, respectively). Improvement in symptoms coincided with a rapid and sustained reduction in pro-inflammatory cytokines, including IL-1b, IL-1ra, IL-6 and TNFa, without tachyphylaxis to therapy. Finally, spleen response was associated with greater improvements in total symptom score, exercise capacity, and reduced fatigue (see Table). Conclusion: An optimized dosing regimen of INCB018424 resulted in sustained clinical, symptomatic and functional benefits in MF patients with an improved hematological safety profile compared to a 25 mg BID regimen. Safety and efficacy of 424 in MF patients is further supported by the follow-up data of >1 yr of 424 therapy. Disclosures: Verstovsek: Incyte: Research Funding. Bradley:Incyte Corporation: Employment, Equity Ownership. Erickson-Viitanen:Incyte Corporation: Employment, Equity Ownership. Vaddi:Incyte Corporation: Employment, Equity Ownership. Levy:Incyte Corporation: Employment, Equity Ownership.