Immunoperoxidase staining of tumors by an antibody to Xenopus pNiXa

pNiXa, a serpin from oocytes and embryos of Xenopus laevis, was tested as a tumor marker in human and rodent tissues. A peptide corresponding to the histidine-rich domain of pNiXa was conjugated and administered to rabbits to produce a polyclonal antibody, which was purified by antigen-affinity and used for immunoperoxidase staining of formalin-fixed, paraffin-embedded tissue sections. Staining with pNiXa-antibody was positive in 23/187 human tumors (12 percent) and negative in 119 specimens of normal human tissues. Positive reactions were more frequent in liver (38 percent) and colon (34 percent) tumors than breast (18 percent), prostate (9 percent), mesothelioma (20 percent) or lung (0 percent) tumors. Staining was negative in human tumors from other sites. Rodent tumors and preneoplastic foci induced by chemical carcinogens were surveyed for staining with pNiXa-antibody. Staining was positive in 10/10 hepatic lesions (hepatocellular foci, adenomas, carcinomas) induced in hybrid D2B6F1 mice by diethylnitrosamine and phenobarbital, whereas murine mammary tumors and thyroid, pituitary, renal, and colon tumors of F-344/CNr rats were negative. Thus, immunostaining with pNiXa-antibody identifies a subset of human and murine tumors; further studies are needed to determine if reactivity of pNiXa-antibody has diagnostic or prognostic significance.