Antibody drug conjugates for treatment of breast cancer: Novel targets and diverse approaches in ADC design

Breast cancer is a heterogeneous group of malignancies with a spectrum of molecular subtypes, pathologies and outcomes that together comprise the most common non-cutaneous cancer in women. Currently, over 80% of breast cancer patients are diagnosed at relatively early stages of disease where there are encouraging data on outcomes and long term survival. However, there is currently no curative option for those patients with metastatic disease and there is a substantial medical need to identify effective and safe treatment options for these patients. One approach to improve cancer therapy is by designing therapeutics directed against targets with differential levels of expression on malignant versus normal cells with the goal of improving tumor selectivity and reducing damage to normal tissues. Antibody drug conjugates (ADCs) are a rapidly evolving therapeutic class that exploits the target-selectivity of monoclonal antibodies (MAbs) to deliver cytotoxic drugs to antigen-expressing cells (Lambert & Morris, 2017; Senter, 2009; Thomas, Teicher, & Hassan, 2016; Trail, 2013). The regulatory approval of ADCs for both hematologic malignancies (brentuximab vedotin) (Younes et al., 2010) and solid tumors (ado-trastuzumab emtansine) (Amiri-Kordestani et al., 2014; Verma et al., 2012) clearly demonstrates the clinical potential of ADCs. This review will focus on targets under consideration for breast cancer directed ADCs and on the technology modifications being considered to improve ADC efficacy and safety.