Abstract 564: A >50KDa soluble factor from the stroma-derived conditioned media contributes to resistance towards BCR-ABL inhibitors in CML via the JAK-STAT3 pathway

Soluble factors and extracellular matrices from the bone marrow stroma, provides the essential microenvironment that contributes to the persistence of minimal residual disease found in patients with Chronic Myeloid Leukemia (CML), under treatment with tyrosine kinase inhibitors. We previously showed that in CML cells, bone marrow stroma-derived conditioned medium (CM) is sufficient to cause resistance to BCR-ABL inhibitors in a STAT3-dependent manner. In this study, we show that development of resistance in CM correlated with increased STAT3 phosphorylation and increased STAT3 DNA binding in CML cells. The activation of Stat3 in the context of CM was persistent even in the presence of BCR-ABL inhibitors. Moreover, the increase in DNA binding resulted in increased transcriptional activity of STAT3 and increased expression of MCL-1, Bcl-xl and Cyclin D1 in cells exposed to CM. We also found that CM-mediated increase in STAT3 activation requires JAK activity, since use of a pan JAK inhibitor sensitized the cells to BCR-ABL inhibitor in CM. Surprisingly, neutralizing the activity of IL-6, G-CSF and VEGF in the CM did not reverse the protection afforded by CM against BCL-ABL inhibitors. Furthermore, utilizing size exclusion filter columns, we were able to show that CM retentates that were higher than 50 kDa, was sufficient to duplicate the protective effects of CM against BCR-ABL inhibitor. Finally, we could show that CD34⁺ cells from BCR-ABL patients when exposed to CM showed an increase in STAT3 phosphorylation and this correlated with resistance to Nilotinib-mediated cell death. In conclusion, a greater than 50 KDa factor in CM leads to JAK-STAT3 activation, which is necessary and sufficient to confer resistance to CML cells against BCR-ABL inhibitors.

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 564.