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

Abstract

The properties of cell surface proteins targeted by antibodydrug 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 6 surface receptors per cell). Noncovalently crosslinking 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.

Manipulation of Cell-Type Selective Antibody Internalization by a Guide-Effector Bispecific Design

“…There are a few recent reports of bispecific ADC with the internalizing arm binding to either a lysosomal protein or an antigen that rapidly traffics to the lysosome (5)(6)(7). In most cases, the observation is empirical and the bispecific effect is rather moderate, suggesting that key parameters affecting bispecific-induced internalization have not been fully delineated.…”

“…For example, through the biparatopic design and the consequent cross-linking effect, HER2 antigen has been targeted for improved ADC internalization (4). In another example, a bispecific composed of a moderately internalizing antibody arm (anti-HER2) and an internalization-inducing antibody arm (anti-CD63, anti-PRLR, or anti-APLP2) was constructed and used to improve ADC uptake (5)(6)(7). However, despite those efforts, the bispecific ADC only showed limited improvement over the parental monospecific anti-HER2 ADC, suggesting that key parameters regarding this design remains to be delineated.…”

Significance of Selective Protein Degradation in the Development of Novel Targeted Drugs and Its Implications in Cancer Therapy

“…[ 76,77 ] For example, the anti‐HER2 antibody has been considered an ideal carrier for trans‐membrane transportation of combination drugs, and studies have indicated that the anti‐HER2 antibody can induce lysosomal trafficking and HER2 degradation. [ 78,79 ]…”

Bispecific Antibodies in the Treatment of Hematologic Malignancies

“…Bispecific ADCs against different targets can also be developed to potentially address heterogeneity of target expression on malignant cells and antigen escape mechanisms. Recently a bispecific ADC targeting human epidermal growth factor receptor 2 and the prolactin receptor was shown to kill more effectively than an ADC targeting HER2 alone …”

“…Recently a bispecific ADC targeting human epidermal growth factor receptor 2 and the prolactin receptor was shown to kill more effectively than an ADC targeting HER2 alone. 40 See Table 2 for a comparison of the properties of various antibody-based approaches that may be used in the treatment of hematologic malignancies.…”