Citations

Abstract Myeloproliferative diseases (MPDs) are a subset of myeloid malignancies that are characterized by the expansion of a multipotent hematopoietic stem cell. Chronic MPDs can be classified into two categories, those harboring the BCR-ABL oncogene and those that are negative. This later category of neoplasms encompasses polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF). Recent discovery of activating mutations in the tyrosine kinase gene, JAK2 and constitutive activation of JAK2-STAT pathway, in large number of MPD patients has ignited considerable interest in MPD and has highlighted JAK2 as a therapeutic intervention point for drug discovery efforts. However, high-sequence homology with other JAK family members has posed a major challenge to design selective JAK2 inhibitors. Given that other JAK family members are involved in the regulation of immune function, it is important to maintain selectivity for JAK2 over these family members in order to mitigate the risks associated with undesired immunosuppression. Several JAK2 inhibitors with varying selectivity profiles are currently being evaluated in preclinical testing as well as in clinical trials for the treatment of MPD. Additionally, emerging genetic and pharmacologic evidence suggest that inhibition of the JAK2-STAT pathway may be an important therapeutic intervention point in other hematological malignancies as well as in certain solid tumors. We report here the discovery and characterization of BMS-911543, a functionally selective small molecule inhibitor of the Janus kinase family (JAK) member, JAK2. BMS-911543 is a potent and reversible inhibitor of JAK2 with a biochemical Ki of 0.48 nM. It has over 65-, 74- and 350-fold selectivity against the other JAK family members, TYK2, JAK3 and JAK1, respectively. Importantly, examination of > 450 other kinases in competition binding assays and in selected biochemical kinase assays did not reveal significant inhibitory activity for this JAK2 inhibitor, highlighting its high degree of biochemical selectivity for JAK2. Functionally, BMS-911543 displayed potent antiproliferative and pharmacodynamic (PD) effects in mutated JAK2-expressing cell lines dependent upon JAK2-STAT signaling and had little activity in cell types dependent upon other pathways such as JAK1 and JAK3. Further, single agent antiproliferative activity was not observed for BMS-911543 in a variety of solid tumor cell lines dependent upon other signaling pathways. In contrast, BMS-911543 was evaluated in colony growth assays using primary progenitor cells isolated from patients with JAK2V617F-positive myeloproliferative disease (MPD) and resulted in an increased antiproliferative response in MPD cells as compared with those from healthy volunteers. Similar to these in vitro observations, BMS-911543 was also highly active in in vivo models of JAK2-pSTAT signaling in multiple species with durable and potent pathway suppression observed after a single oral dose. Additionally, BMS-911543 was evaluated for effects in a JAK2V617F-expressing SET-2 xenograft model system and displayed a minimally effective dose of <2 mg/kg on pSTAT5 pathway suppression, which lasted up to 8 hours. To test the hypothesis that a JAK2 selective inhibitor would have less effect on immune system function, BMS-911543 was compared to pan-JAK inhibitors in a mouse model of immunosuppression. At low dose levels active in JAK2-dependent PD models, no effects were observed on antigen-induced IgG and IgM production for BMS-911543 whereas a pan-JAK family inhibitor showed pronounced effects at all dose levels tested. The mechanistic selectivity of BMS-911543 to pan-JAK family inhibitors was extended through comparative analysis of these inhibitors in whole genome gene expression profiling experiments performed in sensitive and resistant cell types. In this comparison, BMS-911543 modulated a distinct subset of transcriptional changes as compared to pan-JAK inhibitors in clinical testing, thereby defining a minimal set of transcriptional changes underlying the pharmacologic effects of JAK2 inhibition. Collectively these results define the mechanistic basis for a differential therapeutic index between selective JAK2 and pan-JAK family inhibition pre-clinically and suggest a therapeutic rationale for the further characterization of BMS-911543 in patients with MPD and in other malignancies reliant upon constitutively active JAK2 signaling. References: Levine, R.L., et al. Role of JAK2 in the pathogenesis and therapy of myeloproliferative disorders (2007). Nature Rev. Cancer, 7, 673-683. Atallah, E. and Verstovsek, S. Prospect of JAK2 inhibitor therapy in myeloproliferative neoplasms. (2009). Expert Rev. Anticancer Ther. 9, 663-670. Ghoreschi, K., et al. Janus kinases in immune cell signaling. (2009). Immunol. Rev.,228, 273-287. Mesa, R.A. and Tefferi, A. Emerging drugs for the therapy of primary and post essential thrombocythemia, post polycythemia vera myelofibrosis (2009). Expert Opin. Emerging Drugs, 14, 1-9. Roll, J.D. and Reuther, G.W. CRLF2 and JAK2 in B-progenitor acute lymphoblastic leukemia: a novel association in oncogenesis. (2010) Cancer Res, 70, 7347-7352. Rui et al., Cooperative epigenetic modulation by cancer amplicon genes (2010). Cancer Cell, 18, 590-605. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr DDT01-03. doi:10.1158/1538-7445.AM2011-DDT01-03

Abstract Diagnosis of essential thrombocythemia (ET) has been updated in the last World Health Organization (WHO) classification. We developed a prognostic model to predict survival at diagnosis, named IPSET (International Prognostic Score for ET), studying patients with WHO-defined ET. Age 60 years or older, leukocyte count ≥ 11 × 109/L, and prior thrombosis significantly affected survival, by multivariable Cox regression. On the basis of the hazard ratio, we assigned 2 points to age and 1 each to leukocyte count and thrombosis. So, the IPSET model allocated 867 patients into 3 risk categories with significantly different survival: low (sum of points = 0; median survival not reached), intermediate (sum = 1-2; median survival 24.5 years), and high (sum = 3-4, median survival 13.8 years). The IPSET model was further validated in 2 independent cohorts including 132 WHO-defined ET and 234 Polycythemia Vera Study Group–defined ET patients. The IPSET model was able to predict the occurrence of thrombosis, and not to predict post-ET myelofibrosis. In conclusion, IPSET, based on age ≥ 60 years, leukocyte count ≥ 11 × 109/L, and history of thrombosis allows prognostic assessment of WHO-defined ET and the validation process makes IPSET applicable in all patients phenotypically appearing as ET.

AbstractIn the present study, we investigated disease characteristics and clinical outcome in young patients (< 40 years) with World Health Organization (WHO)–defined essential thrombocythemia (ET) compared with early/prefibrotic primary myelofibrosis (PMF) with presenting thrombocythemia. We recruited 213 young patients (median age, 33.6 years), ncluding 178 patients (84%) with WHO-defined ET and 35 patients (16%) showing early PMF. Median follow-up time was 7.5 years. A trend for more overall thrombotic complications, particularly arterial, was seen in early PMF compared with ET. Progression to overt myelofibrosis was 3% in ET and 9% in early PMF, but no transformation into acute leukemia was observed. Combining all adverse events (thrombosis, bleeding, and myelofibrosis), the rate was significantly different (1.29% vs 3.43% of patients/year, P = .01) in WHO-ET and early PMF, respectively. In multivariate analysis, early PMF and the JAK2V617F mutation emerged as independent factors predicting cumulative adverse events.

Abstract The presence of ≥ 15% bone marrow (BM) ring sideroblasts (RS) and < 5% blasts is required for a diagnosis of refractory anemia with ring sideroblasts. We examined the phenotypic and prognostic relevance of this “15%” RS threshold in 200 patients with myelodysplastic syndromes (MDS) without excess blasts and with ≥ 1% RS. The impact of RS% was assessed both as a continuous and categorical variable: < 5% (n = 56), 5%-14% (n = 32), 15%-50% (n = 79), and > 50% (n = 33). RS% correlated (P < .05) directly with age, platelet count, transfusion dependency, BM cellularity, and mutant SF3B1 and inversely with hemoglobin level, multilineage dysplasia, and high-risk karyotype; but did not correlate with IDH mutations. At a median follow-up of 33 months, 156 (73%) deaths and 24 (12%) leukemic transformations were documented. Neither univariate nor multivariable analysis showed significant effect for RS% on overall or leukemia-free survival, suggesting the limited prognostic value of quantifying BM RS in MDS.

In this issue of Blood, Pascale and colleagues show that biochemical resistance to aspirin in patients with essential thrombocythemia (ET) can be reversed by twice-daily dosing.1

Purpose We hypothesized that surrogate markers of host immune response may predict survival in myeloid malignancies. Because of immediate practical applicability, we chose plasma immunoglobulin free light chain (FLC) concentration as the biomarker of interest. Patients and Methods Two independent cohorts of patients with primary myelofibrosis (PMF) or myelodysplastic syndromes (MDS) were studied. Kappa (κ) and lambda (λ) FLCs were measured by a quantitative nephelometric assay. Patients with monoclonal FLC were excluded. Results Values that were above the upper limit of normal for κ or λ FLC were documented in 33% of 240 patients with PMF and 46% of 74 patients with MDS. Increased FLC was significantly associated with increased creatinine, and advanced age in PMF (P < .001) and hemoglobin less than 10 g/dL in MDS (P = .005). In multivariable analysis, increased FLC predicted shortened survival in both PMF and MDS, independent of age, creatinine, and other conventional risk factors. Cutoff levels based on receiver operating characteristic analysis for κ plus λ total FLCs delineated risk groups with highly significant differences in overall survival; International Prognostic Scoring System–adjusted hazard ratio in PMF was 1.9 (95% CI, 1.3 to 2.7), and was 6.3 (95% CI, 2.7 to 16.6) in MDS. No correlations were seen with leukemia-free survival, karyotype, or JAK2, MPL, or IDH mutations. In patients with PMF who were studied by cytokine profiling, the prognostic value of an increased FLC level was independent of that from circulating interleukin-2 receptor (IL-2R) or IL-8 levels. Conclusion Increased plasma FLC concentration predicts inferior survival in both PMF and MDS. Its lack of correlation with leukemia-free survival and tumor-specific genetic markers suggests a primarily host-driven biologic phenomenon that might be more broadly applicable.

Abstract On November 16, 2011, the Food and Drug Administration approved ruxolitinib (a JAK1 and JAK2 inhibitor) for use in the treatment of high and intermediate risk myelofibrosis. This is welcome news for those patients in whom such therapy is indicated and treatment benefit outweighs attendant risk. The question is who are these patients, what should they expect in terms of both short-term effects and long-term impact, and why would they choose ruxolitinib over other JAK inhibitors that are freely available for use in a research setting. Ruxolitinib and most other JAK inhibitors exert a salutary effect on constitutional symptoms and splenomegaly but have yet to produce histopathologic or cytogenetic remissions, reverse bone marrow fibrosis, or improve survival over best supportive care. Furthermore, the palliative value of JAK inhibitors is diminished by notable side effects, including anemia, thrombocytopenia, gastrointestinal disturbances, metabolic abnormalities, peripheral neuropathy, and hyperacute relapse of symptoms during treatment discontinuation. Therefore, risk-benefit balance favors use of currently available JAK inhibitors in only a select group of patients with myelofibrosis, and their potential value in polycythemia vera, outside of special circumstances (eg, intractable pruritus), is undermined by the absence of evidence for a disease-modifying effect and presence of arguably superior alternatives.