Binding of misonidazole to V79 spheroids and fragments of Dunning rat prostatic and human colon carcinomas in vitro: diffusion of oxygen and reactive metabolites.

Differences were noted previously in the binding of 14C-Misonidazole (MISO) to V79 and EMT6 spheroids when incubated at low oxygen levels. While binding to the viable cells in EMT6 spheroids was uniform, in V79 spheroids the binding rate increased gradually with distance from the spheroid surface. Further data reported here indicate that the Km for the inhibition of binding by oxygen is lower in V79 than EMT6 spheroids, so that part of the non-uniformity of binding to V79 spheroids can be explained by diffusion of small amounts of oxygen through the entire rim of viable cells. Diffusion of reactive metabolites of MISO out of the spheroid previously was considered an unlikely explanation. Further evidence to support this interpretation is presented here. Patterns of binding of 3H-MISO to Dunning and human colon carcinomas are presented which are consistent with the interpretation that most of the reactive metabolites are confined to the cell in which they are produced. This conclusion is based on a substantial difference in the rate of binding to adjacent stromal and tumor elements.