Absence of preferential uptake of [125I]iododihydrorhodamine 123 by four human tumor xenografts.

The biodistribution of [125I]iododihydrorhodamine 123 has been studied over a 96-h period in four human tumor xenograft models: HT-29 colon adenocarcinoma, PC-3 prostate carcinoma, HT-1080 fibrosarcoma, and PaCa-2 pancreatic carcinoma. Elimination of radioactivity in the tumor-bearing nude mice was rapid during the first 24 h and slow thereafter. The lack of uptake in the thyroid indicated there was little, if any, deiodination of the molecule. Activity was found mainly in the liver and spleen. Accumulation of radioactivity was low in all four tumors examined. At 4 h postinjection, as well as at 24 and 48 h, however, the total radioactive content in each of the four tumors was directly proportional to the weight of the tumor sample. This correlation was independent of tumor type, route of injection (i.v./i.p.) or dose (1.2-6 microCi/mouse). This was not true for any of the normal tissues, suggesting that this accumulation may be governed by certain intrinsic characteristics of the cancers tested.