TUMOR TARGETING IN-VIVO AND METABOLIC-FATE OF 5-[IODINE-125]IODO-2'-DEOXYURIDINE FOLLOWING INTRATUMORAL INJECTION IN PATIENTS WITH COLORECTAL-CANCER

Previous studies have demonstrated the tumor-targeting potential of ra dioiodinated 5-iodo-2'-deoxyuridine (IUdR) in experimental animal mode ls following direct intratumoral or intracavitary administration. The aim of this study was to measure the tumor uptake and metabolic fate o f 5-[I-125]iodo-2'-deoxyuridine (I-125]IUdR) in humans after a single intratumoral injection. Ten patients with colorectal cancer were injec ted intratumorally with [I-125]IUdR (0.24-3.9 MBq) during endoscopy 24 hr before ablative surgery. Blood and urine samples were collected up to 72 hr after [I-125]IUdR injection. Following resection, the radioa ctivity in the tumor and the surrounding tissues was measured in a gam ma counter, and microautoradiography was performed on semi-thin tissue sections to assess localization of the radiopharmaceutical at the cel lular level. An average of 0.234% of the injected dose was present per gram of tumor (range 0.009-0.918, median value 0.147), and tumor-to-n ontumor radioactivity incorporation ratios were high for colonic mucos a when the nontumor tissue was taken at 1 cm (mean 629, range 27-2391) and 15 cm (mean 2387, range 122-12674) from the injection site. Micro autoradiography confirmed these high tumor-to-nontumor ratios and demo nstrated localization of [I-125]IUdR in the tumor cell nuclei. These r esults suggest that radioiodinated IUdR might have potential as a tumo r-targeting agent in humans, provided homogeneous intratumoral distrib ution of the radiopharmaceutical by a suitable route of loco-regional administration can be achieved.