Daiichi Sankyo's DS1025a enters Phase I, protocol suggesting a potential CD25-directed DXd ADC

Daiichi Sankyo has registered a [first-in-human trial](https://app.allsci.com/clinical-trial/ASC-CT-0000001311941-1.0-1782998710) of DS1025a, a previously undisclosed investigational agent, in patients with advanced solid tumors — adding another candidate to the company's expanding oncology pipeline at a time when its antibody-drug conjugate platform has attracted substantial global attention. The molecular target and precise modality of DS1025a have not been publicly confirmed, but specific language embedded in the trial's eligibility criteria provides interpretable signals about both. The Phase I, open-label, dose-escalation study [(NCT07681882) ](https://clinicaltrials.gov/study/NCT07681882)is set to enroll approximately 45 adults with histologically confirmed advanced, metastatic, or unresectable solid tumors who have progressed on at least one prior line of therapy. Sites are located in Japan with enrollment expected to begin in August 2026 and primary data collection running through January 2028. The study will assess safety, tolerability, and pharmacokinetics as primary objectives, with the recommended dose for expansion to be determined based on the totality of safety, efficacy, pharmacokinetic, pharmacodynamic, and biomarker data. Two features of the protocol are particularly informative, though neither constitutes a confirmed disclosure. First, patients who discontinued a DXd-ADC agent due to toxicity and are considered unable to tolerate DS1025a are excluded — a cross-reference that closely mirrors the safety management language used across Daiichi Sankyo's established DXd-based ADC franchise, which includes trastuzumab deruxtecan and datopotamab deruxtecan. Second, the protocol excludes any patient with a history of interstitial lung disease or pneumonitis, a precaution that has become standard practice for DXd-payload ADCs given the class's known pulmonary toxicity profile. Taken together, these exclusions suggest DS1025a is likely an ADC utilizing the DXd exatecan-derivative topoisomerase I inhibitor payload, though this inference has not been confirmed by the company in any public disclosure identified at the time of writing. The eligibility criteria also provide a potential clue to the molecular target, although no public confirmation has been provided. The protocol excludes patients previously treated with anti-CD25 therapies, a criterion consistent with—but not definitive proof of—DS1025a itself targeting CD25 (IL-2Rα). Such exclusions are commonly used in early oncology studies to minimize confounding from prior target-directed therapy, although other explanations are possible. CD25 carries genuine oncological rationale. It is constitutively expressed on regulatory T cells, which suppress antitumor immune responses within the tumor microenvironment, and is also upregulated on malignant cells in certain hematologic cancers, including adult T-cell leukemia/lymphoma and some Hodgkin lymphoma subtypes. Depleting or cytotoxically targeting CD25-positive cells — whether tumor cells directly or immunosuppressive Tregs — represents a strategy that could, in principle, combine direct tumor killing with immune reinvigoration. The secondary endpoint measuring anti-drug antibody formation is consistent with a biologic, further supporting the ADC hypothesis. If DS1025a does target CD25 with a DXd payload, it would enter a competitive space that has seen limited but meaningful clinical activity. [Camidanlumab tesirine ](https://app.allsci.com/article/ASC-PB-0000405956259-1.0-1764675380)(ADCT-301), developed by ADC Therapeutics, is a CD25-targeting ADC using a pyrrolobenzodiazepine dimer payload and has reported clinical data in relapsed or refractory Hodgkin lymphoma and T-cell lymphomas. The mechanistic distinction, if DS1025a's target and payload are confirmed as inferred, would lie in the payload chemistry: DXd operates via topoisomerase I inhibition and has demonstrated a different tolerability and bystander-killing profile compared to pyrrolobenzodiazepine-based payloads. *** This article was generated with AI assistance and reviewed and edited by the AllSci editorial team Explore more at AllSci News: [https://allsci.com/news/](https://allsci.com/news/) --- Spot something wrong? [Report an issue with this article](https://newsgen-prod.reframedata.com/feedback/ds1025a-oncology-trial-daiichi-sankyo-advances)