In vitro effects of the novel JAK II inhibitor BSK805 in BCR-ABL and JAK II V617F-positive cell lines.

Abstract

e13563 Background: Janus kinases are critical components of cytokine signaling pathways that regulate hematopoiesis, growth, immunity, inflammation, and development. Oncogenic mutations of the nonreceptor tyrosine kinase JAK II can be found in a large part of Philadelphia chromosome negative myeloproliferative neoplasms. The V617F mutation occurs in 95% of patients with polycythemia vera, 55% with essential thrombocythemia and in 65% with primary myelofibrosis. Preclinical results strongly support that JAK II inhibitors could be effectively used in these indications. V617F causes a permanent activation of the JAK-STAT pathway leading to continous proliferation. Therefore, inhibitors of JAK II are under investigation to create new therapy strategies for MPNs. In this project the role of JAK II inhibitors in BCR-ABL positive cells should be investigated. Methods: The in vitro activity of BSK805, a new JAK II inhibitor (Novartis Pharmaceuticals), was analyzed in 10 hematopoietic cell lines, including 5 BCR-ABL positive (K-562, KCL-22, KU812, Lama-87, BV173), 4 JAK II V617F positive (CHRF-288, SET-2, UKE-1, HEL) and the T cell leukemia line Jurkat. Concentration kinetics from 0 up to 25 µM were established using XTT proliferation assay and flow cytometry for measuring apoptosis. Both new drugs were tested in addition together with imatinib and nilotinib. Results: 3 of the 4 tested V617F positive cell lines (CHRF-288, SET-2, UKE-1) showed a significant reduction of proliferation as well as viability compared to the other cell lines. CHRF-288 responded best to BSK805 at IC50 of 0.22 ± 0.04 µM. UKE-1 and SET-2 had similar values of 0.35 ± 0.03 µM and 0.37 ± 0.05 µM. Interestingly, HEL (V617F positive) showed only an IC50 value (1.8 ± 0.17 µM) for BSK805 comparable with the non mutated CML cell lines (1.5 to 2.5 µM). Each cell line responded to concentrations higher than 25 µM with reduced proliferation due to inhibition of various kinases. Combination of the JAK II inhibitors with Imatinib and Nilotinib showed no significant additive or synergistic effects. Conclusions: Here we tested a new JAK II inhibitor for cells carrying the V617F mutation. In cells not harbouring V617F no significant inhibition of proliferation was detected.