64Cu-ATSM Imaging for Cancer Stem Cell-rich Regions: In Vivo and In Vitro characterization

ntroduction: Cancer stem cells are recently noticed to contribute to tumor malignant behaviors, such as resistance to therapy and metastasis ability in tumors. On the other hand, it has been also known that tumor hypoxia is associated with such tumor malignancy. This indicates that tumor hypoxia might be a specific environment to keep up cancer stem cells within tumors. In this study, we examined relationships between existence of cancer stem cells and accumulation of hypoxia imaging agent 64Cu-diacetyl-bis (N4-methylthiosemicarbazone) (64Cu-ATSM) in vivo and conducted in vitro characterization. Methods: Double-tracer autoradiography and immunohistchemistry was performed with mouse colon carcinoma (Colon-26) tumor-bearing mice. In autoradiography, mixture of 74 MBq of 18FDG and 0.37 MBq of 64Cu-ATSM was intravenously injected. The distribution of radio-labeled tracers was compared with the immunohistochemical staining for CD133 expression, which reflected the characteristic of cancer stem cells in Colon-26 cells. Additionally, 64Cu-ATSM uptake and survival of CD133+ cells under hypoxia was also examined with Colon-26 cells in vitro. Results: In Colon-26 tumors, 64Cu-ATSM localizes preferentially in regions with a high density of CD133+ cells. Density of CD133+ cells was highest in regions of high 64Cu-ATSM uptake and lowest in regions of high uptake of 18FDG. In addition, we found that in vitro culturing of Colon-26 cells under hypoxia increased both 64Cu-ATSM uptake and the proportion of CD133+ cells present. Conclusion: Our findings show that, in Colon-26 tumors, 64Cu-ATSM accumulates in CD133+ cell-rich regions and that these cells would be resistant to hypoxic environment. Therefore, 64Cu-ATSM could be a potential imaging agent for cancer stem cell-rich regions within tumors.World Molecular Imaging Congres