Combination of the ABL kinase inhibitor imatinib with the Janus kinase 2 inhibitor TG101348 for targeting residual BCR-ABL-positive cells

Abstract

BackgroundThe ABL kinase inhibitor imatinib is highly effective in treating most, but not all, patients with chronic myeloid leukemia (CML). This is because residual CML cells are generally present in the bone marrow microenvironment and are refractory to imatinib. Hematopoietic cytokine receptor signaling is mediated by Janus kinases (JAKs) and their downstream transcription factor, signal transducer and activator of transcription (STAT). TG101348 (SAR302503) is an oral inhibitor of JAK2.MethodsWe investigated the efficacy of imatinib and TG101348 using the break point cluster region-c-Abelson (BCR-ABL)-positive cell line and primary CML samples wherein leukemia cells were protected by a feeder cell line (HS-5).ResultsImatinib treatment resulted in partial inhibition of cell growth in HS-5-conditioned medium. Furthermore, combined treatment with imatinib and TG101348 abrogated the protective effects of HS-5-conditioned medium on K562 cells. Phosphorylation of Crk-L, a BCR-ABL substrate, decreased considerably, while apoptosis increased. In addition, the combined treatment of CD34-positive primary samples resulted in considerably increased cytotoxicity, decreased Crk-L phosphorylation, and increased apoptosis. We also investigated TG101348 activity against feeder cells and observed that STAT5 phosphorylation, granulocyte macrophage colony-stimulating factor, and interleukin 6 levels decreased, indicating reduced cytokine production in HS-5 cells treated with TG101348.ConclusionsThese results showed that JAK inhibitors may enhance the cytotoxic effect of imatinib against residual CML cells and that a combined approach may be a powerful strategy against the stroma-associated drug resistance of Philadelphia chromosome-positive cells.

Effective Concentration of a Multikinase Inhibitor within Bone Marrow Correlates with In Vitro Cell Killing in Therapy-Resistant Chronic Myeloid Leukemia

“…We have also shown that one of the JAK2 TKIs, ON044580, inhibits both JAK2 and p210 BCR-ABL kinase activities in in vitro assays using their respective peptide substrates (23). Multiple JAK2 TKIs have since then been applied in combination with BCR-ABL TKI for CML treatment (22, 47). Interestingly, the cell killing effect from TG101209 and TG101348 seems to be predominantly from direct inhibition of the p210 BCR-ABL kinase rather than JAK2 (21).…”

Therapeutic targeting of Aurora A kinase in Philadelphia chromosome-positive ABL tyrosine kinase inhibitor-resistant cells

“…Immunoblotting was performed according to a previously described method [ 27 , 28 ]. Briefly, after incubation in indicated concentrations of inhibitor, cells were washed with ice-cold phosphate-buffered saline (PBS) and lysed in radioimmunoprecipitation lysis buffer.…”

Pharmacogenetics and Pharmacogenomics of Targeted Therapeutics in Chronic Myeloid Leukemia

“…Thus, clonal selection of STAT5 expressing cells could be a mechanism of secondary resistance in Ph+ patients who respond to TKIs initially. Multiple recent studies also report that the inhibition of JAK-STAT signaling either via JAK inhibitors [115], or the suppression of STAT5A and STAT5B, significantly enhances responsiveness to imatinib in Ph+ CML cells and to chemotherapy in imatinib-resistant cells [116, 117]. …”