Bispecific Antibodies and Antibody-Drug Conjugates (ADCs) Bridging HER2 and Prolactin Receptor Improve Efficacy of HER2 ADCs

• Published in: Molecular cancer therapeutics Vol. 16; no. 4; pp. 681 - 693
• Main Authors: Andreev, Julian, Thambi, Nithya, Perez Bay, Andres E, Delfino, Frank, Martin, Joel, Kelly, Marcus P, Kirshner, Jessica R, Rafique, Ashique, Kunz, Arthur, Nittoli, Thomas, MacDonald, Douglas, Daly, Christopher, Olson, William, Thurston, Gavin
• Format: Journal Article
• Language: English
• Published: United States American Association for Cancer Research Inc 01.04.2017
• Subjects: Antibodies; Antibodies, Bispecific - pharmacology; Antibodies, Monoclonal, Humanized - pharmacology; Antineoplastic Combined Chemotherapy Protocols - pharmacology; Bispecific antibodies; Breast cancer; Breast Neoplasms - drug therapy; Breast Neoplasms - metabolism; Cancer; Cell Cycle - drug effects; Cell Line, Tumor; Cell Proliferation - drug effects; Cell surface; Cell Survival - drug effects; Conjugates; Crosslinking; Degradation; Drug Synergism; ErbB-2 protein; Female; Humans; Immunoconjugates - pharmacology; Internalization; Intracellular; Lysosomes; Maytansine - analogs & derivatives; Maytansine - pharmacology; Monoclonal antibodies; Prolactin; Protein Transport - drug effects; Proteins; Receptor, ErbB-2 - antagonists & inhibitors; Receptor, ErbB-2 - metabolism; Receptors; Receptors, Prolactin - antagonists & inhibitors; Receptors, Prolactin - metabolism; Targeted cancer therapy; Trastuzumab
• DOI: 10.1158/1535-7163.MCT-16-0658
• ISSN: 1535-7163

The properties of cell surface proteins targeted by antibody-drug conjugates (ADCs) have not been fully exploited; of particular importance are the rate of internalization and the route of intracellular trafficking. In this study, we compared the trafficking of HER2, which is the target of the clinically approved ADC ado-trastuzumab emtansine (T-DM1), with that of prolactin receptor (PRLR), another potential target in breast cancer. In contrast to HER2, we found that PRLR is rapidly and constitutively internalized, and traffics efficiently to lysosomes, where it is degraded. The PRLR cytoplasmic domain is necessary to promote rapid internalization and degradation, and when transferred to HER2, enhances HER2 degradation. In accordance with these findings, low levels of cell surface PRLR (∼30,000 surface receptors per cell) are sufficient to mediate effective killing by PRLR ADC, whereas cell killing by HER2 ADC requires higher levels of cell surface HER2 (∼10 surface receptors per cell). Noncovalently cross-linking HER2 to PRLR at the cell surface, using a bispecific antibody that binds to both receptors, dramatically enhances the degradation of HER2 as well as the cell killing activity of a noncompeting HER2 ADC. Furthermore, in breast cancer cells that coexpress HER2 and PRLR, a HER2xPRLR bispecific ADC kills more effectively than HER2 ADC. These results emphasize that intracellular trafficking of ADC targets is a key property for their activity and, further, that coupling an ADC target to a rapidly internalizing protein may be a useful approach to enhance internalization and cell killing activity of ADCs. .