Abstract LB-54: Interferon targets JAK2V617F positive hematopoietic progenitor cells and acts through the p38 MAP kinase pathway

Interferon α (IFNα) has been used for over 20 years to treat patients with MPN, recently it has been reported that IFNα leads to hematological remissions and a reduction of the JAK2V617F allele burden in most PV patients receiving this modality of therapy. In order to evaluate the cellular target by which IFNα affects hematopoietic progenitor cells in PV patients, CD34 + cells were isolated from cord blood, normal bone marrow and the peripheral blood of PV patients and were treated in vitro with each of the three commercially available forms of IFNα: Interferon α 2b (IFNα 2b), pegylated interferon α 2a (Peg-IFNα 2a) and pegylated interferon α 2b (Peg-IFNα 2b). Each form of IFNα was equally potent in suppressing hematopoietic colony formation by normal marrow CD34 + cells in a dose-dependent fashion, the IC50 of each of the three forms of IFNα as showed by inhibition of CFU-GM and BFU-E derived colony formation was 2000 units/ml. Interestedly, Peg-IFNα 2a and IFNα 2b were more effective than Peg-IFNα 2b in inhibiting BFU-E derived colony formation by PV CD34 + cells, at a concentration of 2000 units/ml, IFNα 2b and Peg-IFN 2a diminished CFU-GM derived colony by 80 % and BFU-E derived colony by 90%. The IC50 of IFN 2b and Peg-IFN 2a was 200 units/ml for PV CFU-GM and less than 100 units/ml for PV BFU-E, while the IC50 for Peg-IFN 2b exceeded 2000 units/ml for PV CFU-GM and was 500 units/ml for PV BFU-E. But CD34 + cells from cord blood were less sensitive to the treatment with each of three forms of IFN which was correlated with reduced expression of IFN receptor 1. In addition, exposure of PV CD34 + cells to equal doses of Peg-IFN 2a and IFN 2b resulted in a 38-40% reduction in the proportion of JAK2V617F-positive hematopoietic progenitor cells (HPC), while equivalent doses of Peg-IFN 2b did not reduce the number of malignant HPC. To further assess the cellular target of Peg-IFN 2a on JAK2V617F HPC, we performed similar studies on CD34 + cells from 12 additional PV patients. The numbers of JAK2V617F positive hematopoietic colonies were reduced in 11 of 12 cases treated with Peg-IFN 2a in vitro. Furthermore, in 7 of the 9 cases where JAK2V617F homozygous colonies were observed the addition of Peg-IFN 2a led to either the elimination of such homozygous colonies or a marked reduction in their numbers. In each of the 11 instances where Peg-IFN 2a reduced the number of colonies containing JAK2 mutated cells there was a concomitant increase in the numbers of colonies which contained exclusively WT JAK2. We further explored if IFN induces HPC growth inhibition and apoptosis through activation of the p38 MAP kinase pathway. Treatment with Peg-IFN 2a increased the phosphorylation/activition of p38 MAP kinase in PV CD34 + cells, while the p38-specific inhibitor SB203580 reversed the growth inhibition and apoptosis induced by Peg-IFN 2a. These data suggest that low doses of IFN selectively and directly suppress PV JAK2V617F HPC and that these agents act through the p38 MAP kinase pathway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-54.