Hormone receptor-positive, HER2-negative advanced breast cancers exhibit high sensitivity to CDK4/6 inhibitors such as palbociclib. However, most patients inevitably develop resistance, thus identification of new actionable therapeutic targets to overcome the recurrent disease is an urgent need. Immunohistochemical studies of tissue microarray revealed increased activation of non-receptor tyrosine kinase, ACK1 (also known as TNK2) in most of the breast cancer subtypes, independent of their hormone receptor status. Chromatin immunoprecipitation studies demonstrated that the nuclear target of activated ACK1, pY88-H4 epigenetic marks, were deposited at cell cycle genes, CCNB1, CCNB2 and CDC20, which in turn initiated their efficient transcription. Pharmacological inhibition of ACK1 using its inhibitor, (R)-9b dampened CCNB1, CCNB2 and CDC20 expression, caused G2/M arrest, culminating in regression of palbociclib-resistant breast tumor growth. Further, (R)-9b suppressed expression of CXCR4 receptor, which resulted in significant impairment of metastasis of breast cancer cells to lung. Overall, our pre-clinical data identifies activated ACK1 as an oncogene that epigenetically controls the cell cycle genes governing the G2/M transition in breast cancer cells. ACK1 inhibitor, (R)-9b could be a novel therapeutic option for the breast cancer patients that have developed resistance to CDK4/6 inhibitors.

激素受体阳性、HER2 阴性晚期乳腺癌对 CDK4/6 抑制剂（如哌柏西利）表现出高度敏感性。然而，大多数患者不可避免地会产生耐药性，因此迫切需要确定新的可行治疗靶点来克服复发性疾病。组织微阵列的免疫组织化学研究表明，大多数乳腺癌亚型中非受体酪氨酸激酶 ACK1（也称为 TNK2）的激活增加，与激素受体状态无关。染色质免疫沉淀研究表明，激活的 ACK1、pY88-H4 表观遗传标记的核靶标沉积在细胞周期基因CCNB1、CCNB2和CDC20处，这反过来又启动了它们的有效转录。使用其抑制剂 ( R )-9b对ACK1 进行药理学抑制，抑制CCNB1、CCNB2和CDC20表达，导致 G2/M 停滞，最终使帕博西尼耐药的乳腺肿瘤生长消退。此外，( R ) -9b抑制CXCR4受体的表达，从而显着损害乳腺癌细胞向肺的转移。总体而言，我们的临床前数据将激活的 ACK1 确定为一种癌基因，可通过表观遗传学控制控制乳腺癌细胞 G2/M 转变的细胞周期基因。ACK1 抑​​制剂，( R )- 9b对于对 CDK4/6 抑制剂产生耐药性的乳腺癌患者来说，可能是一种新的治疗选择。