Functional and phenotypic characterizations of common syngeneic tumor cell lines as estrogen receptor positive breast cancer models

Estrogen receptor positive breast cancers (ER+ BCas) are the most common form of BCa and is increasing in incidence largely due to changes in reproductive practices in recent decades. Tamoxifen is prescribed as a component of standard of care endocrine therapy for treatment and prevention of ER+ BCa. However, it is poorly tolerated leading to low uptake of the drug in the preventative setting. Alternative therapies and preventatives for ER+ BCa are needed but development is hampered due to a paucity of syngeneic ER+ preclinical mouse models that allow pre-clinical experimentation in immunocompetent mice. Two ER positive models, J110 and SSM3, have been reported in addition to other tumor models occasionally shown to express ER (for example 4T1.2, 67NR, EO771, D2.0R and D2A1). Here we have assessed ER expression and protein levels in seven mouse mammary tumor cell lines and their corresponding tumors in addition to their cellular composition, tamoxifen sensitivity and molecular phenotype. By immunohistochemical assessment, SSM3 and to a lesser extent 67NR cells are ER+. Using flow cytometry and transcript expression we show that SSM3 cells are luminal in nature whilst D2.0R and J110 cells are stromal/basal. The remainder are also stromal/basal in nature; displaying a stromal or basal Epcam/CD49f FACS phenotype and stromal and basal gene expression signatures are overrepresented in their transcript profile. Consistent with a luminal identity for SSM3 cells, they also show sensitivity to tamoxifen in vitro and in vivo. In conclusion, the data indicates that the SSM3 syngeneic cell line is the only definitively ER+ mouse mammary tumor cell line widely available for pre-clinical research. Overall design: Gene expression profiling analysis of RNA-seq data for J110 and SSM3 cells

雌激素受体阳性乳腺癌（ER+ BCas）是最常见的乳腺癌亚型，近数十年来其发病率持续上升，主要与生殖行为模式的改变密切相关。他莫昔芬（Tamoxifen）作为标准内分泌治疗的组成部分，被用于ER+乳腺癌的治疗与预防。然而该药物患者耐受性不佳，致使其在预防场景中的药物使用率偏低。目前亟需ER+乳腺癌的替代治疗与预防方案，但由于缺乏可在免疫健全小鼠中开展临床前实验的同源ER+临床前小鼠模型，相关研发工作进展受阻。目前已有两款ER阳性模型J110与SSM3被报道，此外还有部分偶被检测到表达雌激素受体的肿瘤模型（如4T1.2、67NR、EO771、D2.0R及D2A1）。本研究对7株小鼠乳腺肿瘤细胞系及其对应移植瘤的ER表达与蛋白水平进行了评估，同时分析了其细胞组成、他莫昔芬敏感性及分子表型。经免疫组织化学检测，SSM3细胞呈ER阳性，67NR细胞亦呈ER阳性但表达水平较低。通过流式细胞术与转录本表达分析，本研究证实SSM3细胞本质上属于腔型细胞，而D2.0R与J110细胞则属于间质/基底型细胞。其余细胞系同样属于间质/基底型：它们呈现间质或基底型的Epcam/CD49f荧光激活细胞分选表型，且其转录组谱中间质与基底型基因特征显著富集。与SSM3细胞的腔型表型一致，该细胞系在体外与体内实验中均表现出对他莫昔芬的敏感性。综上，本研究数据表明，SSM3同源移植细胞系是目前唯一可广泛用于临床前研究的明确ER阳性小鼠乳腺肿瘤细胞系。实验整体设计：针对J110和SSM3细胞的RNA-seq数据开展基因表达谱分析。