Metastases from primary breast cancer result in poor survival. βIII-tubulin (TUBB3) has been established as a therapeutic target for breast cancer metastases specifically to the brain. In this study, we conducted a systematic analysis to determine the regulation of TUBB3 expression in breast cancer metastases to the brain and strategically target these metastases using vinorelbine (VRB), a drug approved by the U.S. Food and Drug Administration (FDA). We found that human epidermal growth factor receptor 2 (HER2) signaling regulates TUBB3 expression in both trastuzumab-sensitive and trastuzumab-resistant neoplastic cells. We further discovered that bromodomain and extra-terminal domain (BET) inhibition increases TUBB3 expression, rendering neoplastic cells more susceptible to apoptosis by VRB. Orthotopic xenograft assays using two different breast cancer cell models revealed a reduction in tumor volume with BET inhibition and VRB treatment. In addition, in vivo studies using a model of multiple brain metastasis (BM) showed improved survival with the combination of radiation + BET inhibitor (iBET-762) + VRB (75% long-term survivors, P < 0.05). Using in silico analysis and BET inhibition, we found that the transcription factor myeloid zinc finger-1 (MZF-1) protein binds to the TUBB3 promoter. BET inhibition decreases MZF-1 expression and subsequently increases TUBB3 expression. Overexpression of MZF-1 decreases TUBB3 expression and reduces BM in vivo, whereas its knockdown increases TUBB3 expression in breast cancer cells. In summary, this study demonstrates a regulatory mechanism of TUBB3 and provides support for an application of BET inhibition to sensitize breast cancer metastases to VRB-mediated therapy.

原发性乳腺癌的转移导致生存率低。βIII-微管蛋白 (TUBB3) 已被确定为乳腺癌脑转移的治疗靶点。在这项研究中，我们进行了一项系统分析，以确定乳腺癌脑转移中TUBB3表达的调节，并使用美国食品和药物管理局 (FDA) 批准的药物长春瑞滨 (VRB) 战略性地靶向这些转移。我们发现人表皮生长因子受体 2 (HER2) 信号调节曲妥珠单抗敏感和曲妥珠单抗耐药的肿瘤细胞中的TUBB3表达。我们进一步发现溴结构域和末端外结构域 (BET) 抑制增加了TUBB3表达，使肿瘤细胞更容易受到 VRB 的凋亡影响。使用两种不同的乳腺癌细胞模型进行的原位异种移植试验揭示了 BET 抑制和 VRB 治疗后肿瘤体积的减少。此外，使用多发性脑转移 (BM) 模型的体内研究表明，放疗 + BET 抑制剂 (iBET-762) + VRB 的组合提高了生存率（75% 的长期生存者，P < 0.05）。使用计算机分析和 BET 抑制，我们发现转录因子髓样锌指-1 (MZF-1) 蛋白与TUBB3启动子结合。BET 抑制降低MZF-1表达，随后增加TUBB3表达。MZF-1 的过度表达减少TUBB3表达并在体内减少 BM，而其敲低会增加TUBB3在乳腺癌细胞中的表达。总之，这项研究证明了TUBB3的调节机制，并为应用 BET 抑制使乳腺癌转移对 VRB 介导的治疗敏感提供支持。