Bystander killing effect of DS‐8201a, a novel anti‐human epidermal growth factor receptor 2 antibody–drug conjugate, in tumors with human epidermal growth factor receptor 2 heterogeneity

Abstract

Antibody–drug conjugates deliver anticancer agents selectively and efficiently to tumor tissue and have significant antitumor efficacy with a wide therapeutic window. DS‐8201a is a human epidermal growth factor receptor 2 (HER2)‐targeting antibody–drug conjugate prepared using a novel linker‐payload system with a potent topoisomerase I inhibitor, exatecan derivative (DX‐8951 derivative, DXd). It was effective against trastuzumab emtansine (T‐DM1)‐insensitive patient‐derived xenograft models with both high and low HER2 expression. In this study, the bystander killing effect of DS‐8201a was evaluated and compared with that of T‐DM1. We confirmed that the payload of DS‐8201a, DXd (1), was highly membrane‐permeable whereas that of T‐DM1, Lys‐SMCC‐DM1, had a low level of permeability. Under a coculture condition of HER2‐positive KPL‐4 cells and negative MDA‐MB‐468 cells in vitro, DS‐8201a killed both cells, whereas T‐DM1 and an antibody–drug conjugate with a low permeable payload, anti‐HER2‐DXd (2), did not. In vivo evaluation was carried out using mice inoculated with a mixture of HER2‐positive NCI‐N87 cells and HER2‐negative MDA‐MB‐468‐Luc cells by using an in vivo imaging system. In vivo, DS‐8201a reduced the luciferase signal of the mice, indicating suppression of the MDA‐MB‐468‐Luc population; however, T‐DM1 and anti‐HER2‐DXd (2) did not. Furthermore, it was confirmed that DS‐8201a was not effective against MDA‐MB‐468‐Luc tumors inoculated at the opposite side of the NCI‐N87 tumor, suggesting that the bystander killing effect of DS‐8201a is observed only in cells neighboring HER2‐positive cells, indicating low concern in terms of systemic toxicity. These results indicated that DS‐8201a has a potent bystander effect due to a highly membrane‐permeable payload and is beneficial in treating tumors with HER2 heterogeneity that are unresponsive to T‐DM1.

[fam‐] trastuzumab deruxtecan, antitumor activity is dependent on HER2 expression level rather than on HER2 amplification

“…This bystander killing effect might be due to the internalization of [fam-] trastuzumab deruxtecan by HER2-positive cells, the release of DXd into the cytoplasm, and the subsequent transfer of DXd into adjacent HER2-negative cells. 11 In conclusion, we have shown that the antitumor effect of [fam-] trastuzumab deruxtecan is determined by the expression level of HER2 protein, not by HER2 amplification per se. Our data also suggest that a bystander killing effect of [fam-] trastuzumab deruxtecan may overcome the heterogeneity of HER2 expression in CRC tumors that limits the efficacy of conventional HER2-targeted therapy.…”

“…In the present study, however, we found that [fam‐] trastuzumab deruxtecan was effective not only against tumor cells positive for HER2 protein expression but also, in the presence of HER2‐positive cells, against those negative for such expression. This bystander killing effect might be due to the internalization of [fam‐] trastuzumab deruxtecan by HER2‐positive cells, the release of DXd into the cytoplasm, and the subsequent transfer of DXd into adjacent HER2‐negative cells …”

“…8,9 [fam-] trastuzumab deruxtecan (DS-8201a) is a new antibody-drug conjugate (ADC) that is stable in plasma and is prepared with a novel linker-payload system 10 that allows conjugation of seven to eight molecules of the topoisomerase I inhibitor (an exatecan derivative, DXd) per molecule of the anti-HER2 monoclonal antibody. In a preclinical study 11 with cell lines positive for HER2 amplification, this agent manifested a pronounced antitumor effect on neighboring HER2-negative cells, a so-called "bystander killing effect". However, the frequency of HER2 amplification in metastatic CRC was found to be only 2.8% in a Japanese cohort 12 and 5.2% in an Italian cohort wild type for KRAS, 13 suggesting that few CRC patients would benefit from treatment strategies that target HER2 amplification.…”

Quantitative characterization of in vitro bystander effect of antibody-drug conjugates

“…The authors showed that increasing fractions of HER2+ cells in a co-culture led to increased bystander effect, however, the extent of bystander killing was much higher with valine-citrulline based conjugates as compared to T-DM1. Thus, all the above mentioned and several other [16,18,19, 25] studies collectively reveal the importance of having a cleavable linker that can yield the cytotoxic drug molecule in its pure form to achieve the bystander effect with an ADC. However, how the relative abundance of Ag+ cells in a tumor microenvironment affect the bystander effect of an ADC is not studied in a detailed quantitative manner yet.…”

Emerging Targeted Therapies for HER2 Positive Gastric Cancer That Can Overcome Trastuzumab Resistance

“…We thus previously showed that trastuzumab deruxtecan is effective not only against tumor cells positive for HER2 protein but also, in the presence of HER2-positive cells, against those negative for such expression [62] (Figure 1). This "bystander killing effect" is likely due to the internalization of trastuzumab deruxtecan by HER2-positive cells ( Figure 1A), the release of DXd into the cytoplasm of these cells ( Figure 1B), and the subsequent transfer of the released DXd into adjacent HER2-negative cells ( Figure 1C) [63]. Given that most anti-HER2 drugs including trastuzumab target only the HER2 signaling pathway, their efficacy is limited to HER2-amplified tumors, which account for ~17% of AGC tumors.…”