The objective of this study was to determine whether (18)F-misonidazole could detect hypoxia in macroscopic and microscopic tumors in mice. In nude mice, subcutaneous xenografts and peritoneal metastases were generated utilizing human non-small cell lung cancer A549 and HTB177 cells. Animals were co-injected with (18)F-misonidazole, pimonidazole and bromodeoxyuridine, and tumor perfusion was assessed by Hoechst 33342 injection. The intratumoral distribution of (18)F-misonidazole was determined by micro-PET scan and autoradiography. Pimonidazole, bromodeoxyuridine and Hoechst 33342 were detected by immunohistochemistry on the autoradiography sections. Submillimeter micrometastases found to be severely hypoxic. In both peritoneal metastases and subcutaneous xenografts models, PET images displayed significant (18)F-misonidazole uptake, and its distribution was non-uniform in these macroscopic subcutaneous tumors. In frozen sections, digital autoradiography and immunohistochemistry revealed similar distributions of (18)F-misonidazole, pimonidazole and glucose transporter-1, in both microscopic and macroscopic tumors. Bromodeoxyuridine stained-positive proliferative regions were well perfused, as judged by Hoechst 33342, and displayed low (18)F-misonidazole accumulation. (18)F-misonidazole uptake was low in tumor stroma and necrotic zones as well. Microscopic non-small cell lung cancer metastases are severely hypoxic. (18)F-misonidazole PET is capable to image hypoxia noninvasively not only in macroscopic tumors but also in micrometastases growing in mice. Accordingly, (18)F-misonidazole may be a promising agent to detect the burden of micrometastatic diseases.
Keywords: 18F-misonidazole; Micrometastasis; PET; autoradiography; hypoxia.