Abstract A41: Vulnerability of human mammary epithelial cells to oncogenic transformation

Abstract

Abstract Breast cancers display great phenotypic and molecular diversity. Based on these differences, ∼5 breast cancer subtypes have been categorized; importantly, these subtypes show major differences in clinical parameters. Etiology and progression likely differ in subtypes; significant variables may include the type of cell from which the cancer originated, and the specific genomic alterations that subverted normal processes to confer malignancy. However, large gaps exist in our knowledge of target cell identity or molecular events responsible for any breast cancer subtype. Understanding the molecular alterations that lead to the different breast cancer types could facilitate design of clinical interventions in the carcinogenic progression. Our laboratory has addressed this issue with a long-term program to develop an experimentally tractable HMEC culture system for investigating multi-step breast carcinogenesis. Normal finite HMEC have been exposed to pathologically relevant oncogenic agents, generating cells at different stages in transformation with properties consistent with what is known about breast cancer progression in vivo. However, thus far almost all in vitro transformed HMEC lines represent a limited subset of the phenotypes observed in breast cancer cells in vivo. We hypothesized that this limited phenotype could result from targeting cells in culture conditions that restrict most normal HMEC growth, and proposed using HMEC grown in our new media that support growth of cells with luminal, myoepithelial, and progenitor lineage markers. We also hypothesized that unstressed HMEC (without p16INK4a induction) would be more vulnerable to transformation and yield a greater range of transformed phenotypes. Our transformation protocols were based on our model of the tumor-suppressive senescence barriers encountered by cultured HMEC (Garbe et al, Cancer Res 2009). To bypass stasis (stress-induced senescence mediated by Rb/p16) we exposed normal HMEC to shRNA to p16. To bypass telomere dysfunction due to telomere attrition, we used cMyc, an hTERT transactivator. Our data show that p16sh, then cMyc, given to unstressed normal HMEC, produced rapid uniform immortalization. cMyc did not immortalize p16(−) post-stasis HMEC that had high stress exposure prior to epigenetic silencing of p16. HMEC that had become p16(-) post-stasis by different means exhibited additional significant differences, e.g., epigenetic alterations and telomerase activity. Unstressed pre-stasis HMEC were also uniformly immortalized by hTERT, and showed rare clonal immortalization with cMyc alone. Rare clonal immortalization by p16sh alone occurred during the period of genomic instability at telomere dysfunction. Immortalized lines showed many phenotypic differences, but those derived from young women exhibited mainly basal markers. Our recent work showing age-associated changes in lineage markers could be relevant to the observed age-associated increased luminal breast cancer incidence and to generating luminal lines. Applying our p16sh/cMyc protocol to an older woman's HMEC produced an immortal line with luminal properties. Altogether, we have shown that different pathways to transformation are associated with different molecular properties, opening the possibility of individualized therapy for these distinct means of becoming malignant. Future studies will evaluate the effects of specific oncogenic exposures on different normal HMEC types from young and older women. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A41.