HER2 是一种致癌受体，在许多癌症中过度表达，其中包括20%的乳腺癌。尽管已有HER2靶向治疗方法可用，但患者的疾病在治疗过程中往往仍然进展，这强调了对新型治疗策略的需求。将一种可逆性高选择性HER2酪氨酸激酶抑制剂（TKI）tucatinib 添加到曲妥珠单抗和卡培他滨的治疗中，显著改善了HER2阳性转移性乳腺癌患者的生存结局，包括那些有活动性脑转移的患者。我们认为将tucatinib与其他HER2靶向药物结合，以达到互补作用的机制，能进一步提高抗肿瘤效果。我们在乳腺癌的临床模型中，包括HER2阳性乳腺癌细胞和患者源异种移植模型（PDX），对tucatinib和抗体药物结合物T-DM1的活性进行了研究。我们通过内化和降解研究获得了有关tucatinib活性的机制细节。在联合应用中，tucatinib和T-DM1表现出增强的，往往是协同的细胞毒性反应，并在体内显示出改善的抗肿瘤活性，包括对于T-DM1单一药物活性无效的PDX模型。在机制上，tucatinib通过抑制HER2泛素化介导细胞表面处无活性HER2分子的增加，导致T-DM1的内化和降解增加。这种联合作用与HER2信号通路的抑制增强，细胞增殖的减少以及细胞凋亡的增加相关。在脑转移异种移植模型中，tucatinib能够渗透入颅内肿瘤组织，抑制肿瘤生长并改善生存。这些结果表明，tucatinib可能是HER2靶向治疗的最佳TKI合作伙伴，支持其与T-DM1联合治疗的临床研究，包括脑转移患者。

The oncogenic receptor HER2 is overexpressed in many cancers, including up to 20% of breast cancers. Despite the availability of HER2-targeted treatments, patients' disease often progresses during therapy, underscoring the need for novel treatment strategies. The addition of tucatinib, a reversible, highly selective HER2 tyrosine kinase inhibitor (TKI), to treatment with trastuzumab and capecitabine significantly improved survival outcomes of patients with HER2-positive metastatic breast cancer, including those with active brain metastases. We rationalized that combining tucatinib with other HER2-targeting agents with complementary mechanisms of action would further increase efficacy against tumors. We characterized the activity of tucatinib with the antibody-drug conjugate T-DM1 in preclinical models of breast cancer, including HER2-positive breast cancer cells and patient-derived xenograft (PDX) models. Mechanistic details on tucatinib activity were obtained in internalization and catabolism studies. In combination, tucatinib and T-DM1 showed an enhanced, often synergistic, cytotoxic response and demonstrated improved antitumor activity in vivo, including in PDX models refractory to T-DM1 single agent activity. Mechanistically, tucatinib mediated an increase in inactive HER2 molecules at the cell surface through inhibition of HER2 ubiquitination, resulting in increased internalization and catabolism of T-DM1. The combination was correlated with enhanced HER2 pathway inhibition, decreased proliferation, and increased apoptosis. In a xenograft model of brain metastasis, tucatinib penetrated intracranial tumor tissues, inhibiting tumor growth and improving survival. These results suggest that tucatinib may be the optimal TKI partner for HER2-targeted therapies and support clinical studies of its combination with T-DM1, including in patients with brain metastases.