Copper-64-diacetyl-bis (N4-methylthiosemicarbazone) accumulates in rich regions of CD133+ highly tumorigenic cells in mouse colon carcinoma

Introduction: 64Cu-diacetyl-bis (N4-methylthiosemicarbazone) (64Cu-ATSM) is a potential imaging agent of hypoxic tumor for use with PET. Recent literature demonstrated that cancer cells expressing CD133, which is a frequently used marker for so-called cancer stem cells or cancer stem cell-like cells (collectively referred to here as CSCs), contribute to tumor's therapeutic resistance and metastasis ability. Culturing under hypoxia is also reported to enlarge the proportion of CD133+ cells, which would indicate survival advantage of CD133+ cells under hypoxia. Here, we investigated the relationships between 64Cu-ATSM accumulation and existence of CD133+ cells using mouse colon carcinoma (colon-26) tumor. Methods: Intratumor distribution of 64Cu-ATSM and 18F-fluorodeoxyglucose (18FDG) was compared with immunohistochemical staining for CD133 with a colon-26 model. In vitro characterization of CD133+ colon-26 cells was also performed. Results: In colon-26 tumors, 64Cu-ATSM localized preferentially in regions with a high density of CD133+ cells. The percentage of CD133+ cells was 11-fold higher in 64Cu-ATSM high-uptake regions compared with 18FDG high- (but 64Cu-ATSM low-) uptake regions. CD133+ colon-26 cells showed characteristics previously linked with CSCs in other cancer cell lines, such as high colony-forming ability, high tumor-initiating ability and enrichment under hypoxic cultivation. The proportion of CD133+ cells was enlarged by culturing under glucose starvation as well as hypoxia, and 64Cu-ATSM uptake was increased under such conditions. Conclusions: Our findings showed that, in colon-26 tumors, 64Cu-ATSM accumulates in rich regions of CD133+ cells with characteristics of CSCs. Therefore 64Cu-ATSM could be a potential imaging agent for rich regions of CD133+ cells, associated with CSCs, within tumors.