Regulation of Genomic Instability in Early Breast Cancer

描述（由申请人提供）：我们最近对人乳腺细胞的研究使我们能够在人乳腺上皮细胞（HMEC）的罕见亚群中鉴定出以前未检测到的表型。如前所述，从健康女性活检组织中生长的大多数上皮细胞在置于培养物中后对约15至20个群体倍增数的增殖屏障有反应。在短暂的停滞（在培养中称为“选择”）之后，一种罕见的细胞亚群（约10-4至10-5）生长超过最初的屏障，并在培养中繁殖数月。这些“选择后”HMEC的典型特征是特定细胞周期控制的丧失和大量染色体异常的积累。当这群细胞在培养物中生长时，它们接近第二个生长平台，其中几乎100%的细胞具有染色体异常。这些观察结果挑战了传统的观点，即细胞如何以及何时获得癌症的基因组变化，提供了一种细胞内在机制，在肿瘤形成过程的早期，产生多种同时发生的遗传变化。这些细胞是在没有强制性暴露于已知的物理、病毒或化学诱变剂的情况下产生的。最后，这些细胞具有通常在癌细胞中发现的定义特征，并可以解释它们的起源。“后选择”HMEC不表达p16，一种重要的细胞周期蛋白依赖性激酶抑制剂，它们缺乏适当的检查点控制，并且它们不保持基因组完整性。如果这些细胞在体内出现，它们可能代表人类乳腺癌发生的最早阶段。这些观察也发现了新的机会。它们可以提供用于评估个体中肿瘤转化的易感性的潜在标记物以及用于预防和治疗的潜在靶点。多种标记物清楚地识别体外不同的细胞状态，并允许在体内识别具有这些特性的细胞。值得注意的是，我们在“选择后”HMEC中检测到的变化模拟了乳腺癌癌前病变中观察到的许多变化。我们假设，上述性质的“后选择”HMEC在体外是至关重要的乳腺上皮细胞在体内的转化过程。本申请的目的是（1）确定p16失活如何促成“选择后”HMEC表型，（2）确定“选择后”HMEC的起源，（3）确定体内检测到的类似细胞是否（a）在乳腺癌高危个体中以增加的频率存在，和（B）表现出干细胞的特征，和（4）检查HMEC中的选择性细胞周期检查点控制。这些研究可能为预防或治疗乳腺癌提供新的靶点。

DESCRIPTION (provided by applicant): Our recent studies on human mammary cells have allowed us to identify a previously undetected phenotype in a rare subpopulation of human mammary epithelial cells (HMEC). As previously reported, the majority of epithelial cells that grow from biopsy tissue from healthy women respond to a proliferation barrier around 15 to 20 population doublings after placement in culture. After a transient arrest (called "selection" in culture), a rare subpopulation of cells (approximately 10-4 to 10-5) grows beyond the initial barrier and propagate for months in culture. These "post-selection" HMEC are typified by loss of specific cell cycle controls and the accumulation of a tremendous number of chromosomal abnormalities. As this population of cells is grown in culture, they approach a second growth plateau in which virtually 100% of the cells have chromosomal abnormalities. These observations challenge traditional views of how and when cells acquire genomic changes in cancer by providing a cell intrinsic mechanism that, early in the neoplastic process, generates multiple simultaneous genetic changes. These cells are generated without obligatory exposure to known physical, viral or chemical mutagenic agents. Finally, these cells possess defined characteristics that are often found in cancer cells and may explain their origin. "Post-selection" HMEC do not express p16, an important cyclin dependent kinase inhibitor, they lack proper checkpoint control and they do not maintain genomic integrity. Should these cells arise in vivo, they could represent the earliest steps in human mammary carcinogenesis. These observations also identify novel opportunities. They may provide potential markers for assessing susceptibility to neoplastic transformation in individuals as well as potential targets for prevention and therapy. Multiple markers clearly identify the different cellular states in vitro and have allowed for the identification of cells with these properties in vivo. Remarkably, the changes we detect in "post-selection" HMEC mimic many of the changes seen in premalignant lesions in breast cancer. We hypothesize that the above-described properties of "post-selection" HMEC in vitro are critically relevant to the transformation processes of mammary epithelial cells in vivo. The goals of this application are to (1) determine how p16 inactivation contributes to the "post-selection" HMEC phenotype, (2) determine the origins of "post-selection" HMEC, 3) determine if similar cells detected in vivo are (a) present in increased frequencies in individuals at high risk for breast cancer, and (b) exhibit characteristics of stem cells, and (4) examine selective cell cycle checkpoint controls in HMEC. These studies may provide novel targets for prevention or treatment of breast cancer.