PT - JOURNAL ARTICLE AU - Rebekka Hueting AU - Veerle Kersemans AU - Bart Cornelissen AU - Matthew Tredwell AU - Kamila Hussien AU - Martin Christlieb AU - Antony D. Gee AU - Jan Passchier AU - Sean C. Smart AU - Jonathan R. Dilworth AU - Véronique Gouverneur AU - Ruth J. Muschel TI - A Comparison of the Behavior of <sup>64</sup>Cu-Acetate and <sup>64</sup>Cu-ATSM In Vitro and In Vivo AID - 10.2967/jnumed.113.119917 DP - 2014 Jan 01 TA - Journal of Nuclear Medicine PG - 128--134 VI - 55 IP - 1 4099 - http://jnm.snmjournals.org/content/55/1/128.short 4100 - http://jnm.snmjournals.org/content/55/1/128.full SO - J Nucl Med2014 Jan 01; 55 AB - 64Cu-diacetyl-bis(N4-methylthiosemicarbazonate), 64Cu-ATSM, continues to be investigated clinically as a PET agent both for delineation of tumor hypoxia and as an effective indicator of patient prognosis, but there are still aspects of the mechanism of action that are not fully understood. Methods: The retention of radioactivity in tumors after administration of 64Cu-ATSM in vivo is substantially higher for tumors with a significant hypoxic fraction. This hypoxia-dependent retention is believed to involve the reduction of Cu-ATSM, followed by the loss of copper to cellular copper processing. To shed light on a possible role of copper metabolism in hypoxia targeting, we have compared 64Cu retention in vitro and in vivo in CaNT and EMT6 cells or cancers after the administration of 64Cu-ATSM or 64Cu-acetate. Results: In vivo in mice bearing CaNT or EMT6 tumors, biodistributions and dynamic PET data are broadly similar for 64Cu-ATSM and 64Cu-acetate. Copper retention in tumors at 15 min is higher after injection of 64Cu-acetate than 64Cu-ATSM, but similar values result at 2 and 16 h for both. Colocalization with hypoxia as measured by EF5 immunohistochemistry is evident for both at 16 h after administration but not at 15 min or 2 h. Interestingly, at 2 h tumor retention for 64Cu-acetate and 64Cu-ATSM, although not colocalizing with hypoxia, is reduced by similar amounts by increased tumor oxygenation due to inhalation of increased O2. In vitro, substantially less uptake is observed for 64Cu-acetate, although this uptake had some hypoxia selectivity. Although 64Cu-ATSM is stable in mouse serum alone, there is rapid disappearance of intact complex from the blood in vivo and comparable amounts of serum bound activity for both 64Cu-ATSM and 64Cu-acetate. Conclusion: That in vivo, in the EMT6 and CaNT tumors studied, the distribution of radiocopper from 64Cu-ATSM in tumors essentially mirrors that of 64Cu-acetate suggests that copper metabolism may also play a role in the mechanism of selectivity of Cu-ATSM.