Enhancing Targeted Radiotherapy by Copper(II)diacetyl- bis(N-methylthiosemicarbazone) Using 2-Deoxy-D-Glucose

Most cancer deaths are a consequence of resistance to conventional chemotherapy and radiation therapy. This may be attributable to unique phenotypic characteristics of solid tumors. We have exploited two welldescribed characteristics of solid tumors commonly associated with treatment failure, high glucose use and hypoxia, to design a unique therapy based on the selective accumulation of two cytotoxic compounds, 2-deoxyglucose (2-DG) and copper(II)diacetyl-bis(N-methylthiosemicarbazone) (Cu-ATSM). Cu-ATSM localizes to hypoxic regions of tumors and has been used for administering a high local dose of radiation therapy after uptake by cells. 2-DG, a glucose analog, selectively accumulates in cancer cells and interferes with energy metabolism, resulting in cancer cell death. 2-DG has been shown to potentiate the cytotoxic effect of ionizing radiation and certain chemotherapeutic agents. We have tested the effect of 2-DG on tumor response when combined with Cu-ATSM in a mouse breast tumor model using the highly aggressive mouse mammary carcinoma cell line EMT-6. 2-DG administered up to 2 mg/g of body weight daily resulted in no weight loss or systemic symptoms. EMT-6 mammary tumors had similar uptake of [F]fluoro-2-deoxyglucose before and after 2 weeks of 2-DG treatment as determined by microPET imaging, indicating that resistance to 2-DG uptake does not develop. Pretreatment of tumor-bearing mice with 2-DG resulted in increased uptake of CuATSM by tumors compared with nontreated mice. This effect was not observed with the nonhypoxia-specific agent copper(II)pyruvaldehydebis(N-methylthiosemicarbazone. When 2-DG was combined with a single dose of Cu-ATSM (2 mCi), tumor growth was inhibited 60% compared with untreated mice, and animals survived 50% longer than untreated mice or animals treated with each agent alone (32 versus 20 days). The maximum effect on tumor growth and survival was observed when 2-DG was administered daily for the lifetime of the mouse. Our results indicate that 2-DG potentiates the effect of Cu-ATSM on tumoricidal activity and animal survival. We hypothesize that 2-DG alters the metabolic state of the cell, leading to increased uptake of Cu-ATSM by the tumor. This would result in a higher local dose of radiotherapy. The continued presence of 2-DG would then prevent the repair of damaged cells, leading to inhibition of tumor growth. Our data indicate that the strategy of combining tumor-specific cytotoxic agents that function by differing mechanisms can result in an effective, selective, tumor-specific cell death with minimal effect on the host.