Corporate Update: Progress on Targeted Immuno‑Oncology Programs in Japan

Phase II Antibody‑Drug Conjugate for Mesothelin‑Positive Tumours

AstraZeneca’s Japanese subsidiary, Daiichi Sankyo Co., Ltd. (DAIICHI SANKYO CO LTD), announced that a phase II trial of a novel antibody‑drug conjugate (ADC) has entered enrolment. The ADC targets the glycoprotein mesothelin, a cell‑surface antigen that is overexpressed in mesothelioma and a spectrum of mesothelin‑positive solid tumours, while exhibiting limited expression on normal tissues.

Mechanistic Rationale The therapeutic construct couples a humanized anti‑mesothelin monoclonal antibody to a microtubule‑disrupting payload (a duocarmycin derivative). Upon binding to mesothelin, the ADC is internalised and trafficked to lysosomes, where intracellular proteases cleave the linker. The released cytotoxin alkylates DNA at guanine residues, inducing apoptosis preferentially in antigen‑bearing cells. This targeted delivery is expected to increase the therapeutic index relative to conventional cytotoxics by sparing mesothelin‑negative cells.

Trial Design and Objectives

  • Population: 90 adult patients with mesothelioma or other mesothelin‑positive solid tumours.
  • Sites: Multi‑institutional, nationwide across Japan.
  • Duration: 12‑month enrolment window.
  • Endpoints: Safety (grade ≥ 3 adverse events), objective response rate (RECIST v1.1), progression‑free survival, and pharmacokinetic/pharmacodynamic correlates.

The phase II study will provide the first clinical evidence of the ADC’s safety profile and preliminary efficacy in a Japanese cohort, complementing ongoing global studies.

Bispecific T‑Cell Engager Targeting DLL3 in Small‑Cell Lung Cancer

Daiichi Sankyo is advancing a DLL3‑directed bispecific T‑cell engager (BiTE) in small‑cell lung cancer (SCLC). DLL3 is a Notch ligand aberrantly expressed on neuroendocrine tumour cells, making it an attractive target for immunotherapy.

Early‑Stage Findings Data from a Japanese phase I expansion cohort demonstrated:

  • Safety: Cytokine release syndrome (CRS) was limited to low‑grade events, with no grade ≥ 3 toxicity observed.
  • Efficacy: 40 % of patients who progressed on standard platinum‑etoposide therapy achieved disease control (partial response or stable disease) at 12 weeks.

These results are encouraging, particularly given the historically refractory nature of extensive‑stage SCLC.

Global Context The same DLL3‑BiTE was evaluated in a global phase III trial in combination with the PD‑L1 inhibitor durvalumab. The combination produced a significant overall survival benefit versus standard chemotherapy. The Japanese data will inform the design of a forthcoming confirmatory study, potentially incorporating biomarker stratification and adaptive randomisation to optimise patient selection.

Next‑Generation Bispecific–Small‑Molecule Combination

In a collaboration with a U.S. partner, Daiichi Sankyo is developing a bispecific antibody that simultaneously engages tumour‑associated antigens and recruits T‑cells, paired with a small‑molecule checkpoint inhibitor (SMCI).

Preclinical Evidence Murine xenograft models of colorectal and pancreatic cancer demonstrated:

  • Tumour Regression: Complete responses in 30‑40 % of treated mice versus 5‑10 % with checkpoint inhibitor alone.
  • Immune Modulation: Increased infiltration of CD8⁺ T‑cells and down‑regulation of myeloid‑derived suppressor cells.

These synergistic effects are attributed to the bispecific antibody’s ability to create a stable immunological synapse while the SMCI alleviates T‑cell exhaustion.

Clinical Trajectory The partnership intends to initiate a first‑in‑human Phase I study within 18 months. Key objectives will include dose‑escalation safety, pharmacodynamics of immune cell activation, and preliminary antitumour activity.

Strategic Implications

Daiichi Sankyo’s focused expansion into mesothelioma, SCLC, and combination immunotherapies aligns with its broader goal of addressing high‑unmet‑needs in solid tumours. The integration of targeted ADCs, bispecific T‑cell engagers, and innovative checkpoint‑modulating combinations reflects a multi‑modal approach that leverages molecular biology, pharmacology, and clinical oncology.

While the phase II ADC and phase I DLL3‑BiTE data remain early, the safety signals and initial efficacy metrics provide a rational basis for progressing these programmes through the regulatory pipeline. The global phase III success of the DLL3‑BiTE plus durvalumab combination further reinforces the therapeutic potential of DLL3 targeting in SCLC.

The next‑generation bispecific–SMCI platform, pending regulatory approval for clinical trials, could open new therapeutic avenues across several tumour types. Overall, these developments reinforce Daiichi Sankyo’s commitment to a diversified, science‑driven oncology portfolio designed to deliver meaningful clinical benefit while maintaining a rigorous safety standard.