BRU59-21, a second-generation 99mTc-labeled 2-nitroimidazole for imaging hypoxia in tumors.
Hypoxia in tumors is believed to be an important cause of local failure of radiotherapy in certain types of cancer. BRU59-21 (BMS194796) is a second-generation 99mTc-labeled 2-nitroimidazole that has been shown to offer improved characteristics for imaging myocardial ischemia. It has now been evaluated in models of tumor hypoxia.


METHODS
Accumulation of BRU59-21 was compared with that of BMS181321 in Chinese hamster ovary cells incubated under aerobic or hypoxic conditions. The effects of competition with unlabeled nitroimidazoles and oxygen were studied. Biodistribution studies were performed in mice bearing transplanted KHT-C tumors in the leg.


RESULTS
Within 5 min, BRU59-21 partitioned into aerobic cells in vitro at a level 10 times higher than external medium with no further increase over time. In hypoxic cells this initial partitioning was followed by selective accumulation to levels 5 times higher than in aerobic cells by 4 h. Low levels of oxygen (approximately 40 ppm) inhibited the maximal accumulation rate by 50%. Unlabeled misonidazole, a 2-nitroimidazole, inhibited accumulation of radioactivity, whereas tinidazole, a 5-nitroimidazole, enhanced accumulation; similar effects had been reported with BMS181321. Biodistribution studies in mice showed rapid clearance of radioactivity from the blood, resulting in enhanced tumor-to-blood ratios compared with BMS181321. Increasing the hypoxic fraction in the tumor by injection of nitro-L-arginine resulted in increased retention of tracer in the tumor without affecting other tissues.


CONCLUSIONS
These results suggest that BRU59-21 warrants further investigation as an agent for imaging tumor hypoxia in the clinic.
Melo
T
T
Department of Medical Biophysics, University of Toronto, Canada.
Duncan
J
J
Ballinger
J R
JR
Rauth
A M
AM
D000818:Animals; D016466:CHO Cells / Q000000981:diagnostic imaging; D015687:Cell Hypoxia; D006224:Cricetinae; D005260:Female; D007093:Imidazoles; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D009368:Neoplasm Transplantation; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging*; D009593:Nitroimidazoles; D015609:Organotechnetium Compounds; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D014018:Tissue Distribution
C403973:BRU 59-21; D007093:Imidazoles; D009593:Nitroimidazoles; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals; C082027:BMS 181321