Abstract 3604: Investigation of the role of CSF-1 and its receptor in the bone marrow stroma microenvironment in acute myeloid leukemia

Abstract

Abstract Supporting cells in the bone marrow microenvironment are an essential source of growth factors and cytokines that drive both normal hematopoeisis and leukemogenesis. Acute myeloid leukemia (AML) is a heterogeneous and growth factor-dependent disease of the bone marrow. The human macrophage colony stimulating factor (M-CSF, CSF-1) is a cytokine produced by supporting cells in the bone marrow that promotes the differentiation and maturation of monocytes and macrophages from myeloid precursors. Since CSF-1 is an essential factor in myelopoeisis, it has important implications in AML, a disease characterized by the increased proliferation of immature myeloid blast cells. Moreover CSF-1 and CSF-1R are highly expressed in some AML cases, lending further support for their investigation. CSF-1 exists as a full-length secreted (variant 1 or v1) and membrane-bound (variant 3 or v3) isoform. The membrane-bound v3 isoform is the predominant form in the bone marrow. CSF-1 binds to the colony stimulating factor-1 receptor (CSF-1R), a class III receptor tyrosine kinase found on mononuclear phagocytes. CSF-1R activation leads to stimulation of survival, proliferation and differentiation pathways. In this study, the effects of the CSF-1/CSF-1R interaction were investigated in the context of the bone marrow microenvironment in an in-vitro co-culture system. In this model, human leukemic cells (patient samples and cell lines) were grown in co-culture with mouse stromal cells expressing human CSF-1. The cellular and molecular responses arising from the interaction between leukemic cells expressing CSF-1R and stromal cells producing CSF-1 were examined. AML cells cultured with CSF-1-expressing stroma displayed better long-term (2-5 weeks) growth and survival than cells cultured with non-CSF-1-expressing stroma. There was a 2-fold increase in the number of cells on CSF-1 v3 stroma compared to empty vector (ev) control stroma after 5 weeks of co-culture. AML cells were maintained on CSF-1 v3 stroma 1.5-1.75 fold longer than on ev stroma (survival in days). Co-culture of AML cells with CSF-1-expressing stroma led to a decrease in CSF-1R expression on the surface of AML cells, accompanied by an increase in CD34 and decrease in CD38 expression. CSF-1-expressing stroma led to increases in phosphorylation of Akt and p70S6K, effectors of the PI3k/Akt pathway, in AML cells. Analysis of cytokine production in AML-stromal cell co-cultures revealed an increase in the secretion of IL-3 and IL-6 from stromal cells and an increase in IL-8 and vascular endothelial growth factor (VEGF) from AML cells. These findings suggest that CSF-1 presented by stromal cells mediates the growth and survival of AML cells through changes in cell surface markers, molecular signaling effectors and cytokine secretion. This work has helped identify targets of interest that may be exploited for therapeutic purposes in AML-stromal cell interactions. Citation Format: Ayesha Rashid, Mohammed Fateen, Rhe Juan, Rob C. Laister, Mark Minden. Investigation of the role of CSF-1 and its receptor in the bone marrow stroma microenvironment in acute myeloid leukemia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3604. doi:10.1158/1538-7445.AM2014-3604