Expression of Phenotypical Changes by Human Breast Epithelial Cells Treated with Carcinogens in Vitro

Abstract

In order to determine whether human breast epithelial cells undergo malignant transformation when treated with chemical carcinogens in vitro, and how host factors, such as degree of gland development, affect their response to that treatment, twenty-two reduction mammoplasty specimens from women ranging in age from 18 to 63 years and with different parity history were studied in their morphology and in their response to carcinogen treatment in vitro. Fixed tissues were processed for whole mount preparations; it was found that the lobules of the nonpregnant or resting breast tissue could be classified into three types based upon their size and number of alveolar buds composing each one of them, lobules type 1 being the least and lobules type 3 the most differentiated ones. Breast tissues were classified according to the relative proportion of lobules composing it and the reproductive and clinical history of the patient into groups A, B, or C. Fresh tissues from these three groups were digested for obtention of mammary epithelium organoids, which were plated in Dulbecco's minimal essential medium:Ham's F12 (1:1), with 5% horse serum to enhance attachment. When they reached confluence, the cells were replated in serum-free medium; 48 h postplating they were treated with 1.0 µg/ml 7,12-dimethyl-benz(a)anthracene for 24 h, or with 1.0 µg/ml N-methyl-nitrosourea for 3 h. At every passage, the cells were monitored for colony formation efficiency, survival efficiency in agar-methocel, multinucleation assay, karyotyping, immunocytochemical detection of tumor associated antigens, lectin reactivity, and tumorigenic assay by injection into nude mice. By the fourth passage after treatment, both carcinogens induced increased survival, colony formation in agar-methocel, multinucleation, and increased reactivity with the tumor associated antigen B1:1, an epitope of carcinoembryonic antigen, and the lectins concanavalin A, Dolichos biflorus, and soybean agglutinin. This response was observed only in human breast epithelial cells obtained from less differentiated breasts (Groups A and B), whereas human breast epithelial cells from breasts exhibiting good lobular development (Group C) did not exhibit those changes. No karyotypic abnormalities were detected in treated cells, and they failed to induce tumors when injected into nude mice. It was concluded that mammary gland development is independent of age but is strongly influenced by both the reproductive and clinical history of the donor. The observed phenotypic changes were manifested not as a random event, but as specific characteristics of the host, indicating that the developmental stage of the gland with its intrinsic properties modulate the response of the cells to carcinogen exposure.