Tumour oxygenation status in individual patients may be assessed using the bioreduction and linkage of
2-nitroimidazole markers to viable hypoxic cells in vivo with subsequent detection by conventional nuclear medicine techniques.
Iodoazomycin arabinoside (
IAZA) was radiolabelled with
Iodine-123 and administered i.v. to 51 patients with newly diagnosed
malignancies whose tumours were subsequently imaged by planar and single-photon emission computed tomographic (SPECT) procedures. Quantitative analyses of radiotracer avidity were performed at 24 h post-injection and tumour-normal tissue ratios of greater than 1.10 were deemed positive for tumour
hypoxia. By this criterion, the frequencies of
hypoxia in
small-cell lung cancer,
squamous cell carcinomas of head and neck and
malignant gliomas were 60% (9/15), 40% (6/15) and 0% (0/11) respectively. The correlation of positive
IAZA scans with tumour control and survival in patients with
lung cancer and head and neck tumours is currently under study. Preliminary observations in neck
metastases from
squamous cell carcinoma of head and neck tumours indicates decreased local control at 3 months post-treatment in tumours with
IAZA avidity. This study concludes that: (1) 123I-IAZA can be administered safely and repeatedly as an outpatient routine imaging procedure in
cancer patients during initial work-up and follow-up; (2) that retained
drug can be detected by conventional nuclear medicine procedures in inaccessible deep-seated tumours; and (3) that this technique could prove useful for identifying those patients for whom
hypoxia-directed
therapy is indicated.