Variable p-glycoprotein immunoreactivity unrelated to cytotoxic drug-resistance in-vitro of human adrenocortical carcinoma.

Human adrenocortical tissue was immunohistochemically investigated with monoclonal antibodies C219 and JSB-1 for expression of P-glycoprotein (Pgp) associated with resistance to multiple cytotoxic drugs. All normal (n=7) and adenomatous (n=3) glands strongly expressed the protein, while the cancers (n=15) demonstrated variable Pgp reactivity. Cytotoxic drug sensitivity testing in vitro on freshly dispersed cells from one normal adrenal gland and from 6 carcinomas with no to extensive Pgp reactivity demonstrated universally poor sensitivity to 9 standard drugs including those with Pgp mediated resistance. The findings indicate that immunohistochemical staining for Pgp cannot be used to predict cytotoxic drug resistance and that other mechanisms mediate cytotoxic drug resistance in adrenocortical carcinoma.