Immunohistochemical Localization of Cytochrome P450 CYP1B1 in Breast Cancer with Monoclonal Antibodies Specific for CYP1B1

Abstract

SUMMARY Cytochrome P450 CYP1B1 is a recently identified member of the CYP1 P450 family. We have shown that this P450 displays increased expression in several types of human cancer, indicating that CYP1B1 is a potential tumor biomarker. In this study we developed monoclonal antibodies (MAbs) to CYP1B1 that are effective on formalin-fixed, paraffin-embedded tissue sections and investigated the presence of CYP1B1 in a series of primary breast cancers. The MAbs were generated using a synthetic peptide coupled to carrier protein as the immunogen. The MAbs specifically recognized CYP1B1 and did not recognize either CYP1A1 or CYP1A2, related CYP1 forms. The MAbs were tested by immunohistochemistry and were found to be effective on formalin-fixed, paraffin-embedded tissue sections. The majority of breast cancers showed positive immunoreactivity for CYP1B1, and in each case CYP1B1 was specifically localized to tumor cells. The presence of CYP1B1 in breast cancer cells is likely to contribute to their metabolism of estradiol because CYP1B1 is a specific estradiol hydroxylase.

Pharmacogenetics and Regulation of Human CytochromeP450 1B1: Implications in Hormone-Mediated Tumor Metabolism and a Novel Target for Therapeutic Intervention

“…RNA-PCR studies have shown that expression of CYP1B1 is equivalent in normal and tumor tissues, whereas immunohistochemical analysis and activity assays indicate that protein expression is increased in tumors (4,5,63,68). This could suggest that (a) a certain threshold of mRNA expression must be present before the protein can be expressed, (b) cell-specific post-transcriptional modifications must be present before protein expression is achieved, and (c) proteolytic degradation can modulate CYP1B1 protein levels (50,69).…”

“…Since the initial development of antibodies specific to CYP1B1 (4,5), much research has been conducted to investigate the inducibility of CYP1B1. CYP1B1 is overexpressed in several carcinomas and is involved in the premalignant progression of some neoplastic tissue (8).…”

“…CYP1B1 is overexpressed in several carcinomas and is involved in the premalignant progression of some neoplastic tissue (8). Although CYP1B1 is expressed in several normal tissues (6,70,71), it is differentially overexpressed in the tumor microenvironment (4,5). However, it is difficult to assess differences in tumor expression versus normal tissue expression given that different antibodies with differing sensitivities are used to assess expression via immunohistochemistry.…”

“…Before the identification of CYP1B1 as a novel metabolic enzyme, it has been detected in mouse endometrial stromal cells as a polycyclic aromatic hydrocarbon -inducible CYP (2) and was subsequently characterized (3). Since then, much interest has been placed on the inducibility of CYP1B1, especially given that it is differentially expressed within the tumor microenvironment of several human cancers (4)(5)(6). Although CYP1B1 is expressed in normal tissues (6,7), it is expressed at much higher levels in tumor cells compared with the surrounding normal tissue (4,5).…”

“…Since then, much interest has been placed on the inducibility of CYP1B1, especially given that it is differentially expressed within the tumor microenvironment of several human cancers (4)(5)(6). Although CYP1B1 is expressed in normal tissues (6,7), it is expressed at much higher levels in tumor cells compared with the surrounding normal tissue (4,5). The overexpression of CYP1B1 has been implicated in premalignant progression (8), and given its differential expression in tumor tissue, it may be considered a drug and vaccine target for the treatment of several types of cancer (9,10).…”