DS1025 is designed to recognize and bind CD25, a surface protein found at high levels on regulatory T cells, including those in tumor tissue. Regulatory T cells normally help restrain excessive immune activity, including allergic reactions and excessive inflammation. In tumors, however, these cells can accumulate and suppress immune responses that might otherwise recognize and attack cancer cells. The investigational conjugate is intended to deliver an immuno-oncology optimized cytotoxic payload to CD25-expressing regulatory T cells in the tumor microenvironment, thereby targeting a mechanism that can limit antitumor immunity. Daiichi Sankyo states that DS1025 builds on its DXd ADC technology, but the trial announcement does not provide clinical results for the investigational agent.

The Phase 1 protocol is expected to enroll up to 45 adults with advanced, metastatic, or unresectable solid tumors. Eligible participants must have experienced disease progression after at least one line of standard treatment and must be for whom further standard treatment is not suitable. Clinical sites are located in Japan and elsewhere in Asia and in Europe. As participants are monitored, researchers plan to increase the dose gradually across groups while looking for dose-limiting toxicities and other adverse events. The study will also examine DS1025 pharmacokinetics, pharmacodynamics, biological markers and preliminary signs of antitumor activity. These are planned assessments in an ongoing first-in-human protocol, and the announcement does not report efficacy findings, a selected dose, adverse-event results or a follow-up duration.

The first-dose milestone also reflects the expansion of early-phase trial activity at Kansai Medical University Hospital. The hospital established its Department of New Experimental Therapeutics in November 2024, strengthening its capacity to conduct early-phase clinical trials of new cancer treatments. According to the announcement, the department has conducted multiple international collaborative Phase 1 trials since February 2025, including First-in-Human studies of investigational cancer drugs. Kansai Medical University Hospital said it is actively participating in international early-phase cancer drug development and is contributing to several international trials in a region where access to such studies has been limited. The university and Daiichi Sankyo said they will continue collaborating on early-stage research, but the trial’s eventual results will determine whether DS1025 warrants further clinical development. Until those results are available, the first administered dose marks the start of human testing rather than evidence of clinical benefit.

Subject of Research: An international First-in-Human Phase 1 trial of the investigational CD25-directed antibody drug conjugate DS1025 in adults with advanced solid tumors.

Article Title: Kansai Medical University Hospital administers world’s first dose of DS1025 in an international early phase 1 clinical trial

Article References: Kansai Medical University Hospital administers world’s first dose of DS1025 in an international early phase 1 clinical trial. Original publication (Bibliographic details unavailable.)

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Keywords: DS1025, Phase 1 trial, first-in-human study, CD25, antibody drug conjugate, regulatory T cells, solid tumors, dose escalation, cancer immunotherapy, Kansai Medical University Hospital, Daiichi Sankyo, Kansai