Pharmacological and clinical study results of trastuzumab deruxtecan (T-DXd, ENHERTU<sup>®</sup>)

Antibody-drug conjugates (ADCs) combine the specific antibody and cytotoxic agent by a linker and represent a promising drug class with a wider therapeutic window than conventional chemotherapeutic agents by substantiating efficient and specific drug delivery to antigen-expressing tumor cells. However, there are rooms for improvement in terms of efficacy, safety, physicochemical property; therefore, the development of promising ADC drugs across multiple indications are eagerly awaited. In 2015, Daiichi Sankyo initiated the first-in-human study of HER2 ADC, trastuzumab deruxtecan (T-DXd, ENHERTU^®) which possesses DNA topoisomerase I inhibitor, exatecan derivative and proprietary linker, in Japan. Based on the provocative results in phase 1 study, the global development program has been accelerated to show the high and durable efficacy in patients with HER2 positive breast cancer pretreated with trastuzumab emtansine. As a result, T-DXd was approved based on single arm phase 2 study in the US (Dec 2019) and Japan (March 2020) by leveraging the breakthrough designation and conditional early approval system, respectively, at the first time for the HER2 positive breast cancer. In addition, T-DXd was recently approved in gastric cancer through Sakigake designation in Japan based on a randomized phase 2 study. T-DXd is also being developed in the earlier lines or other indications where no anti-HER2 therapies were approved to date. Combination studies with other agents, such as immune checkpoint inhibitors are underway. In the near future, we hope that more patients worldwide can enjoy the therapeutic benefits of T-DXd through our continuous efforts to expand its indications.