Identification of a Therapeutically Targetable JAK-STAT Enriched Androgen Receptor (AR) and AR Splice Variant Positive Triple Negative Breast Cancer Subtype [project2]. Identification of a Therapeutically Targetable JAK-STAT Enriched Androgen Receptor (AR) and AR Splice Variant Positive Triple Negative Breast Cancer Subtype [project2]

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with no targeted therapeutics. The luminal androgen receptor (LAR), one of the six TNBC subtypes, constitutes 15% of TNBC and is enriched for AR and AR-target genes. Here, we show that a cohort of TNBC not only expresses full-length AR (AR-FL) at a much higher rate (~80%) than previously reported, but also expresses AR splice variants (AR-SVs) (~20%), subclassifying the LAR-TNBC subtype into LAR-FL, LAR-AR-SV, or dual positive. Higher AR and AR-SV expression and corresponding aggressive phenotypes were observed predominantly in specimens obtained from African American women. RNA sequencing of LAR TNBC specimens indicates an enrichment of hallmark interferon, JAK-STAT, and androgen signaling pathways, which were exclusive to AR-expressing epithelial cancer cells as demonstrated by spatial genomics. LAR and LAR-AR-SV TNBC cell proliferation, orthotopic cell line and patient-derived xenograft, and patient-derived tumor explants growth were inhibited by AR N-terminal domain (NTD)-binding selective AR degrader (SARD) that irreversibly inhibits AR or by the JAK inhibitor ruxolitinib. Subsequent biochemical analysis suggests that STAT1 is an AR coactivator, and SARD or ruxolitinib blocks this coactivation. Collectively, our work identifies and characterizes a pharmacologically targetable and previously unreported TNBC subtype predominantly in African American women and identifies a growth-promoting interaction between AR and JAK-STAT signaling. Overall design: To investigate the transcriptome of patient specimens that express androgen receptor (AR), AR splice variants, and specimens that do not express either AR or AR splice variants, RNA was extracted from prospectively collected patient specimens and sequenced.

三阴性乳腺癌（Triple-negative breast cancer, TNBC）是一类侵袭性极强的乳腺癌亚型，目前尚无获批的靶向治疗方案。腔面雄激素受体型（luminal androgen receptor, LAR）作为六大TNBC亚型之一，约占所有TNBC病例的15%，其肿瘤细胞以雄激素受体（androgen receptor, AR）及其靶基因的高富集为特征。本研究发现，一组TNBC样本的全长雄激素受体（full-length AR, AR-FL）表达率高达约80%，远高于此前报道水平；同时约20%的样本表达雄激素受体剪接变体（AR splice variants, AR-SVs），据此可将LAR-TNBC亚型进一步细分为LAR-FL型、LAR-AR-SV型或双阳性型。
高表达AR与AR-SVs的样本及其对应的侵袭性表型，主要富集于非洲裔美国女性的临床标本中。对LAR型TNBC标本的RNA测序结果显示，其标志性干扰素信号、JAK-STAT信号及雄激素信号通路显著富集，空间基因组学分析证实，这些通路仅特异性存在于表达AR的上皮性癌细胞中。
LAR型及LAR-AR-SV型TNBC的细胞增殖、原位细胞系与患者来源异种移植瘤、患者来源肿瘤外植体的生长，均可被结合AR N端结构域（AR N-terminal domain, NTD）的选择性雄激素受体降解剂（selective AR degrader, SARD）——该降解剂可不可逆抑制AR活性——或JAK抑制剂芦可替尼所阻断。后续生化分析表明，信号转导与转录激活因子1（signal transducer and activator of transcription 1, STAT1）是AR的共激活因子，而SARD或芦可替尼可阻断这一共激活过程。
综上，本研究鉴定并表征了一类此前未被报道的、可进行靶向治疗的TNBC亚型，该亚型主要见于非洲裔美国女性；同时本研究还揭示了AR与JAK-STAT信号通路之间的促生长相互作用。
总体实验设计：为探究表达AR、AR-SVs以及不表达上述二者的患者标本的转录组特征，研究人员从前瞻性收集的患者标本中提取总RNA并进行测序。