Modulation of Leukotriene Signaling Affecting Cell Growth in Chronic Myeloid Leukemia: A Key Pathway to Cure?

Background: Recent data suggest that tyrosine kinase inhibitor (TKI)-insensitive leukemic stem cells often prevail in chronic myeloid leukemia (CML) patients subjected to long-term TKI treatment. To achieve cure additional aberrant pathways in these patients, such as leukotriene (LT) signaling, may need to be targeted. We have previously shown that human CML cells have an increased capacity to produce LT and that LT can stimulate normal myelopoiesis (Tornhamre ExpHem 2003). Chen later noted a striking up-regulation of ALOX5/5LO (catalyzing an initial step in LT formation) in CML mice, and that inhibition of this enzyme improved survival of these animals by a magnitude similar to that induced by imatinib (Chen NatureGen 2009). Here wexve assessed the effect of LT modulating agents on the growth of human CML cells in vitro.

Materials and methods: Human CML cells, derived from the three cell lines K562, Kcl22 and KU812, were grown in microtitre plate cultures, in the presence of RPMI 1640. The MTT technique was used to evaluate the number of viable cells at 72 hours. Protein expression was assessed by Western blot and immunocytochemistry.

Results: Several specific modulators of LT-signaling were capable of inducing dose-dependent growth inhibitory effects on CML cells. Thus, the cysteinyl-LT receptor antagonist montelukast, a drug with approved clinical use in human asthma, was shown to reduce the growth of all three tested CML cell lines. In Fig. 1 this is examplified by K562 cells, where also additive effects between montelukast and imatinib are indicated. All cell lines expressed the cysLT1-receptor. Furthermore, the LTB₄ receptor antagonist etalocib, as well as the 5-LO activating protein (FLAP) inhibitors licofelone and Bay-X-1005, also executed inhibitory effects at concentrations considered as physiological. As expected, addition of the TKIs imatinib, nilotinib or dasatinib to the cultures also generated dose-dependent inhibitory effects on the growth of all tested CML cell lines. An LD50 of approximately 0.5 µM, 10 nM and 0.1 nM was noted for imatinib, nilotinib and dasatinib, respectively, for K562 cells at 72 hours.

Conclusions: We demonstrate that several compounds, known to specifically inhibit leukotriene signaling by different mechanisms, were at clinically relevant concentrations capable of significantly suppressing the growth of human CML cells. Some of these compounds are already in clinical practice for non-hematological disorders. They could provide an additional therapeutic possibility in the quest to cure CML.

Figure 1.

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Figure 1.

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