Albumin-based DLL3-targeted nano-immunoconjugates of SN38 preserve potency and demonstrate high-affinity DLL3 binding in small cell lung cancer

Background: Small cell lung cancer (SCLC) remains an aggressive malignancy with limited treatment options and a 5-year survival rate under 10%. Delta-like ligand 3 (DLL3), expressed in >85% of SCLC but absent from normal tissue, represents an attractive therapeutic target. Existing DLL3-directed antibody-drug conjugates suffer from poor payload stability and limited tumor penetration. To overcome these limitations, we engineered a DLL3-targeted nano-immunoconjugate (NIC) of SN38, the active metabolite of irinotecan, using an albumin-based nanoscaffold. Methods: SN38 was encapsulated in a human serum albumin (HSA) matrix and non-covalently coated with a recombinant anti-DLL3 monoclonal antibody to yield DLL3-SN38-NIC. Stable conjugation was confirmed by HSA-IgG interactions and zeta-potential shift. Binding kinetics were evaluated using Biacore surface plasmon resonance (SPR) and Octet bio-layer interferometry (BLI) employing AHC biosensors to determine DLL3-antibody affinity and specificity. Cytotoxicity was assessed using IncuCyte live-cell imaging across five SCLC cell lines (DMS454, SHP77, NCI-H82, NCI-H889, and NCI-H211) with varying DLL3 expression. Results: DLL3-SN38-NIC retained high-affinity DLL3 binding (KD ≈ 3 × 10⁻¹⁰ M) and demonstrated potent cytotoxicity in SCLC cell lines. NIC formation did not reduce cytotoxic activity compared with free SN38, confirming preserved potency. Cytotoxicity trends were consistent across lines with variable DLL3 expression, and DLL3 antibody alone exhibited negligible cytotoxicity. These findings confirm that nano-immunoconjugate formation maintains drug activity and DLL3 binding; additional in-vivo studies are underway to evaluate pharmacokinetics and tumor selectivity. Conclusions: Albumin-based DLL3-SN38-NICs represent a novel nano-oncologic platform that preserves SN38 potency and achieves high-affinity DLL3 engagement. Ongoing studies will assess in-vivo selectivity, biodistribution, and therapeutic potential in DLL3-positive SCLC and other neuroendocrine malignancies. Keywords: DLL3, nano-immunoconjugate, SN38, albumin nanocarrier, small cell lung cancer