RELATIONSHIP OF HYPOXIA TO METALLOTHIONEIN EXPRESSION IN MURINE TUMORS

Purpose: To investigate if metallothionein, an endogenous chemo- and r adioprotectant, is expressed in hypoxic cells in mouse C3H mammary car cinomas and if that expression responds to acute changes in tumor hypo xia. Methods and Materials: C3H mammary tumors were established in the hind legs of female CDF, mice. The mice were then subjected to air br eathing (chronic hypoxia), carbogen breathing (acute decrease in hypox ia), or hydralazine injection (acute increase in hypoxia). Ninety nain utes after the start of the experiment, tumors were excised, fixed in formalin, and sectioned, Hypoxic cells and metallothionein-containing cells were quantitated by image analysis. Pimonidazole hydrochloride a nd an IgG, mouse monoclonal antibody were used to detect hypoxia, and a mouse antimetallothionein monoclonal antibody (DAKO) was used to det ect Type I and II metallothionein in sets of contiguous tissue section s. Results: The distribution of immunostaining intensity for metalloth ionein was the same in all three groups-heavy in hypoxic cells and lig ht in other regions of the tumors. The acute increase in hypoxia cause d by hydralazine injection was accompanied by an increase in metalloth ionein expression (p = 0.04), Carbogen breathing largely eliminated pi monidazole binding, but metallothionein expression persisted in the tu mors of carbogen-breathing mice. Conclusions: Hypoxic cells in C3H mam mary carcinomas strongly express metallothionein. Metallothionein expr ession is responsive to acute increases in hypoxia brought about by hy dralazine injection. The effectiveness of hydralazine in enhancing the activation of bioreductive cytotoxins might be offset by the increase d expression of metallothionein, The persistence of metallothionein in tumors of carbogen-breathing mice might contribute to a residual radi oresistance in the tumors, (C) 1998 Elsevier Science Inc.