Abstract 158: Cyclopamine, an inhibitor of hedgehog signaling, induces monocytic differentiation of acute myelogenous leukemia cells

Abstract

Abstract Introduction: Sonic hedgehog homolog (Shh) is known to play a critical role in normal cellular expansion and in the patterning of the early embryo of vertebrates and invertebrates, and is also implicated in some human cancers. While the sonic hedgehog homolog (Shh) pathway has been implicated in hematopoiesis and in maintenance of hematological malignancy, there is little evidence to demonstrate its importance to differentiation therapy. Procedures: We characterized the changes in HL-60 [an acute myelogenous leukemia (AML) cell line] after blocking the Shh pathway by an antagonist of Smoothened, cyclopamine. Findings: The existence of Shh signaling pathway in HL-60 cells was demonstrated by reverse transcription and PCR. Cyclopamine at 20 μM significantly down regulated the mRNA expression of Smo, Gli1 and Gli2. The flow cytometry showed that cyclopamine mediated apoptotic death of HL-60 cells in a dose- and time-dependent manner. After 12 h and 24 h, cyclopamine at 5 μM and 10 μM significantly increased the G0/G1-phase fraction of cells. Furthermore, treatment with cyclopamine increased the expression of monocytic cell markers CD 11b and CD 14, but the expression of CD 13, CD 33 and CD 38 was unchanged in HL-60 cells. The ability of cyclopamine to induce the monocytic differentiation of HL-60 cells was further evidenced by increased Egr-1 expression in a dose-dependent manner. Cyclopamine also down-regulated the phosphorylation of Akt and ERK, but activated AMPK signaling. We also analyzed the effect of cyclopamine on the primary leukemia cells from patients with AML. Conclusions: Blocking the Shh pathway via cyclopamine causes a time- and dose-dependent apoptotic cell death, increases the proportion of cells in G0/G1-phase and induces monocytic differentiation in HL-60 cells. Cyclopamine also down-regulates the mRNA expression of genes in Shh pathways. Further investigations are needed to determine the clinical application of modulating the Shh pathway in the treatment of hematological malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 158. doi:1538-7445.AM2012-158