Abstract 5446: The anti-leukemic efficacy of the decorporation agent ethane-bisphosphonate (EHBP): reversal of epigenetic inactivation of secreted frizzled-related proteins by EHBP
Authors: Miller Alexandra C. , Rivas Rafael , Stewart Michael 
Published: February 2011

Abstract
Bisphosphonates (BP) are a class of synthetic analogues of the endogenous pyrophosphate, which are well established in the treatment of osteoclast-mediated bone diseases. In vivo studies in our laboratory have demonstrated that ethane-1-hydroxy-1-bisphosphonate (EHBP) has anti-leukemia and anti-tumor activity. The anti-neoplastic effects have been linked to protein farnesylation inhibition and pro-apoptotic action in radiation-induced acute myeloid leukemia (AML) mice and malignant cells. BP's are also an attractive chemoprevention strategy for radiation-induced carcinogenic effects not only because of their anti-tumor ability but because of their ability to chelate uranium. Depleted uranium (DU) is used in military munitions and has also been suggested as a possible material for “dirty bombs” which could endanger the public. DU is leukemogenic in vivo. Uranium chelation might be considered a possible treatment approach after DU exposure so a chemoprevention agent that has dual benefits showing activity as a late effects protector and as a chelator would be an attractive candidate to study. Uranium chelation studies in vivo have shown that EHBP can chelate uranium at high doses. The objective of the current was to evaluate additional mechanisms i.e., epigenetic activity of EHBP. A radiation late effects model was also used to study EHBP epigenetic mechanisms. Mice were sub-lethally irradiated (3.5 Gy, 60Co) to induce leukemia. To test the anti-leukemia efficacy of EHBP and epigenetic mechanisms, mice were irradiated and then injected with EHBP (25 uM) or saline daily 3 x weekly (2 weeks) for a total of 6 doses. Secreted Frizzled-related protein genes (SFRPs), which function in the Wnt signaling pathway, have been found to be down-regulated by promoter hypomethylation in human acute myeloid leukemia. Therefore, the methylation status of SFRP genes was analyzed in 20 samples obtained from radiation-induced AML mice. Aberrant CpG island methylation was observed in all four SFRP genes tested by methylation-specific PCR in AML mice. The frequencies of aberrant methylation among the irradiated mice samples were 25% for SFRP1, 20% for SFRP2, 5% for SFRP4, and 12% for SFRP5. In contrast, mice irradiated and treated with EHBP demonstrated aberration frequencies of 8% for SFRP1, 6% for SFRP2, 0% for SFRP4, and 2% for SFRP5 at 120 days post-radiation. At day 120 post-radiation, 50% of irradiated mice had developed leukemia while only 20% of mice treated with EHBP showed leukemia. The results demonstrate 1) that EHBP is an effective countermeasure against radiation-induced leukemia, 2) that epigenetic alterations are associated with radiation-induced leukemia and 3) that EHBP's efficacy may be associated with prevention of epigenetic disturbances involved in leukemogenesis.
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 5446.