Potential of overcoming resistance to HER2-targeted therapies through the PI3K/Akt/mTOR pathway

Human epidermal growth factor receptor 2 (HER2) overexpression occurs in up to 30% of breast cancers and is a marker of aggressive disease. While HER2-targeted therapies have improved outcomes in these tumors, resistance to these agents develops in a large proportion of patients. Determining molecular mechanisms underlying resistance might help improve outcomes for patients with HER2-positive disease by allowing development of strategies to overcome resistance. Activation of signaling pathways involving the phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway might contribute to the development of resistance to HER2-targeted therapies. Several inhibitors of this pathway are under investigation in this disease setting and phase 3 data for everolimus in combination with trastuzumab and chemotherapy in trastuzumab-refractory, advanced disease are promising. In this review, molecular mechanisms underlying resistance to HER2-targeted therapies are considered and evidence for strategies to manage resistance is evaluated, including the use of inhibitors of the PI3K/Akt/mTOR pathway.

Current Approaches and Emerging Directions in HER2-resistant Breast Cancer

Human epidermal growth factor receptor-2 (HER2) is overexpressed in up to 30% of breast cancers; HER2 overexpression is indicative of poor prognosis. Trastuzumab, an anti-HER2 monoclonal antibody, has led to improved outcomes in patients with HER2-positive breast cancer, including improved overall survival in adjuvant and first-line settings. However, a large proportion of patients with breast cancer have intrinsic resistance to HER2-targeted therapies, and nearly all become resistant to therapy after initial response. Elucidation of underlying mechanisms contributing to HER2 resistance has led to development of novel therapeutic strategies, including those targeting HER2 and downstream pathways, heat shock protein 90, telomerase, and vascular endothelial growth factor inhibitors. Numerous clinical trials are ongoing or completed, including phase 3 data for the mammalian target of rapamycin inhibitor everolimus in patients with HER2-resistant breast cancer. This review considers the molecular mechanisms associated with HER2 resistance and evaluates the evidence for use of evolving strategies in patients with HER2-resistant breast cancer.

Human epidermal growth factor receptor family-targeted therapies in the treatment of HER2-overexpressing breast cancer

Breast cancer characterized by overexpression of human epidermal growth factor receptor 2 (HER2) has been associated with more aggressive disease progression and a poorer prognosis. Although an improved understanding of breast cancer pathogenesis and the role of HER2 signaling has resulted in significant survival improvements in the past 20 years, resistance to HER2-targeted therapy remains a concern. A number of strategies to prevent or overcome resistance to HER2-targeted therapy in breast cancer are being evaluated. This article provides a comprehensive review of (a) the role of HER2 signaling in breast cancer pathogenesis, (b) potential receptor and downstream therapeutic targets in breast cancer to overcome resistance to HER2-targeted therapy, and (c) clinical trials evaluating agents targeting one or more members of the HER family and/or downstream pathways for the treatment of breast cancer, with a focus on metastatic disease.

Preclinical and clinical development of afatinib: a focus on breast cancer and squamous cell carcinoma of the head and neck

ABSTRACT: Aberrant signaling of the ErbB family of receptors plays an integral role in the tumorigenesis of many cancer types, including head and neck squamous cell carcinoma (HNSCC) and breast cancer (BC). Significant research efforts have focused on developing new treatments that target ErbB family members, with the last decade seeing the approval of small-molecule tyrosine kinase inhibitors and monoclonal antibodies that inhibit ErbB signaling. However, treatment resistance is an ever-growing problem and, therefore, new therapies are being investigated to overcome this hurdle. Afatinib is an irreversible ErbB family blocker that has demonstrated potent anti-tumor activity in preclinical models and has displayed clinical efficacy in patients with non-small-cell lung cancer, and activity in HNSCC and BC. Here, the preclinical and clinical development of afatinib in the treatment of non-small-cell lung cancer, HNSCC and BC is described in the context of currently approved agents.

Emerging approaches for treating HER2-positive metastatic breast cancer beyond trastuzumab

Because metastatic breast cancer (MBC) is incurable in most cases, the goals of treatment are improvement in quality of life, management of symptoms, and prolonged survival. The human epidermal growth factor receptor 2 (HER2) is overexpressed in up to 30% of breast tumors, and before the development of HER-targeted therapy, HER2 positivity was predictive of poorer clinical outcomes. Trastuzumab and pertuzumab (anti-HER2 monoclonal antibodies), lapatinib (a small molecule inhibitor of HER2 and the epidermal growth factor receptor [EGFR]) are approved for treating HER2-positive MBC in the United States. Although trastuzumab plus chemotherapy is currently regarded as the first-line standard of care for HER2-positive MBC, it is not without shortcomings; these include its association with certain adverse events (e.g. cardiotoxic effect) and development of resistance. A number of investigational agents that target HER2 and other members of that receptor family are in clinical development for patients with HER2-positive MBC whose disease has progressed on trastuzumab. In addition, in an effort to overcome treatment resistance, clinical trials are evaluating combination therapy (investigational HER-targeted agents with trastuzumab or lapatinib). This review discusses recently completed and ongoing phase II and III clinical trials of investigational HER-targeted agents in the setting of trastuzumab-progressive, HER2-positive MBC.