Ifinatamab deruxtecan (I-DXd) is a B7-H3 (CD276)-targeting antibody-drug conjugate (ADC) with a topoisomerase I inhibitor payload (DXd, an exatecan derivative). The anti-B7-H3 antibody binds CD276 overexpressed on SCLC tumor cell surfaces. Receptor-mediated internalization delivers the conjugate into the tumor cell, where intracellular cleavage of the tetrapeptide linker releases DXd, which inhibits topoisomerase I and induces DNA single-strand breaks, leading to apoptosis. A bystander killing effect is also implied by DXd's membrane permeability, potentially relevant in heterogeneous SCLC tumors.

DeLLphi-301 studied I-DXd in relapsed/refractory SCLC (patients who had progressed on platinum-based chemotherapy), generating objective response rate (ORR) and duration of response (DOR) data that are referenced in multiple Daiichi Sankyo patent filings. DeLLphi-304 is the pivotal Phase III trial expanding I-DXd into the first-line SCLC setting, where it is being evaluated against the atezolizumab plus carboplatin/etoposide standard of care. The most recent PCT filing (WO2024190871A1, September 2024) expands into first-line SCLC claims consistent with DeLLphi-304 and includes combination data with PD-L1 inhibitors and a chemotherapy backbone.

All 10 retrieved patent records identify B7-H3/CD276 as broadly overexpressed across SCLC tumor cell populations. This expression profile is positioned in the retrieved filings as complementary to or independent of PD-L1 expression — the canonical biomarker driving atezolizumab eligibility in the current first-line standard. Because PD-L1 expression is variable in SCLC and PD-1/PD-L1 response rates are modest, CD276's broad overexpression provides a mechanistically distinct therapeutic rationale: B7-H3-directed cytotoxic payload delivery. Retrieved patents also identify neuroendocrine tumors alongside SCLC as target indications, suggesting high B7-H3 expression may be a shared feature of neuroendocrine differentiation programs active in SCLC.

US20240123076A1 (Daiichi Sankyo, 2024) specifies a dosing regimen of 12 mg/kg administered every three weeks (Q3W), explicitly referencing DeLLphi-301 pharmacokinetics and safety/tolerability observations as the basis for this claim. Retrieved records also address drug-to-antibody ratio (DAR) optimization, converging on a DAR4 configuration as a critical parameter for balancing efficacy and tolerability.

In the retrieved dataset, Daiichi Sankyo Co., Ltd. is the sole assignee across all 10 retrieved patent filings covering I-DXd in SCLC, spanning US, PCT/WIPO, and European Patent Office jurisdictions. Johnson & Johnson is not named as a co-assignee in any retrieved patent record. All IP appears to reside with Daiichi Sankyo, consistent with the commercial collaboration structure in which Daiichi Sankyo retains IP ownership while J&J (Janssen) holds co-commercialization rights.

The current first-line standard of care for SCLC is atezolizumab (a PD-L1 inhibitor) plus carboplatin/etoposide chemotherapy. I-DXd in DeLLphi-304 represents a mechanistically distinct challenge to this standard, employing B7-H3-directed cytotoxic payload delivery rather than PD-L1-mediated immune checkpoint blockade. The investigational arm in DeLLphi-304 integrates I-DXd within or alongside an immunotherapy-chemotherapy platform — a structural parallel to the current atezolizumab plus carboplatin/etoposide standard. No competing biopharma assignees appear in the retrieved records in relation to B7-H3-targeting ADC approaches for SCLC.