Tokyo, Japan – August 27, 2026
Daiichi Sankyo has entered a new phase of oncology development with the first patient dosed in a first-in-human Phase 1 clinical trial of DS1025, an investigational CD25-directed antibody-drug conjugate (ADC) for adults with advanced or metastatic solid tumors. The multicenter study will evaluate DS1025 in patients whose disease has progressed following at least one prior line of standard therapy. The program represents another expansion of Daiichi Sankyo’s ADC pipeline, with DS1025 designed around a novel approach to targeting regulatory T cells (Tregs) within the tumor microenvironment. The company is developing DS1025 as a potential first-in-class CD25-directed ADC, and the candidate contains an immuno-oncology optimized cytotoxic payload discovered by Daiichi Sankyo. Unlike several established ADC approaches that primarily target tumor cells directly, DS1025 is being developed to target CD25, a protein highly expressed on Tregs that can contribute to immune suppression and allow cancer cells to evade immune attack. The clinical entry of DS1025 therefore adds a distinct immuno-oncology strategy to Daiichi Sankyo’s expanding portfolio.
Phase 1 Trial Evaluates Safety and Early Activity
The Phase 1 DS1025 trial is designed primarily to establish the candidate’s safety and tolerability while determining appropriate dose levels for further clinical development. The open-label, dose-escalation study is expected to enroll up to 45 patients across multiple clinical sites in Asia and Europe. Primary endpoints include safety and tolerability, including dose-limiting toxicities and adverse events. Secondary assessments will examine pharmacokinetics and immunogenicity, while exploratory measures will include overall response rate, duration of response and time to response. The study is focused on patients with advanced or metastatic solid tumors who have experienced disease progression after at least one prior standard treatment, providing an initial clinical setting in which investigators can assess DS1025’s therapeutic potential. The first-patient dosing milestone marks the transition of DS1025 from preclinical development into human clinical testing, where its safety profile, pharmacological characteristics and preliminary anti-tumor activity can now be evaluated. Daiichi Sankyo has not yet established the safety or efficacy of DS1025, and the candidate remains investigational.
DS1025 Targets CD25 and Tumor Immune Suppression
The scientific rationale behind DS1025 centers on CD25, a cell-surface protein highly expressed on regulatory T cells, which suppress immune responses and are believed to contribute to an immunosuppressive tumor environment. Daiichi Sankyo has engineered DS1025 to combine a CD25-directed antibody with an immuno-oncology optimized cytotoxic payload intended to deplete immunosuppressive Tregs in the tumor microenvironment. The objective is to potentially reduce immune suppression and enhance the ability of the immune system to recognize and attack cancer cells. This mechanism gives DS1025 a differentiated position within the company’s ADC strategy, particularly as the candidate is intended to influence the tumor microenvironment rather than simply deliver cytotoxic therapy to conventional tumor-associated targets. Daiichi Sankyo’s development of DS1025 builds on its internal ADC technology capabilities while introducing a different payload and target strategy from its DXd ADC platform. The company highlighted the program as part of its continuing effort to develop novel antibody-drug conjugates designed to improve outcomes for people with cancer.
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Daiichi Sankyo Expands Its ADC Oncology Portfolio
The initiation of the DS1025 Phase 1 study further strengthens Daiichi Sankyo’s industry-leading ADC portfolio, which currently includes nine ADCs in clinical development. The company’s established DXd ADC Technology supports multiple clinical-stage programs, including Enhertu and Datroway, while additional investigational ADCs are being developed against diverse biological targets. DS1025 is among the newer approaches in the portfolio, alongside programs such as DS3610, an ADC incorporating a novel STING agonist payload. Daiichi Sankyo’s continued expansion of its ADC pipeline reflects a broader strategy to apply its internally developed antibody, linker and payload technologies across different oncology targets and mechanisms. With the first participant now dosed, DS1025 moves into clinical development, where upcoming safety, pharmacokinetic and preliminary efficacy findings will determine the next steps for the program. For now, the key milestone is the successful transition into human testing and the opportunity to assess whether CD25-targeted ADC therapy can reduce tumor-associated immune suppression and generate meaningful anti-cancer activity in patients with advanced solid tumors.
Source:Daiichi Sankyo, press relese
