[Selection and identification of S100B-specific nanobodies for melanoma biomarker]

Objective: A camelid natural nanobody library was screened to target S100 calcium-binding protein B (S100B) for obtaining high-affinity and specific nanobodies (Nbs), which provided a molecular basis for the early diagnosis and prognostic treatment of malignant melanoma. Methods: In this study, affinity panning was employed to isolate S100B-specific nanobodies with unique complementarity-determining region 3 (CDR3) sequences from a camelid natural nanobody library. The selected Nbs were expressed in a prokaryotic system and purified via Ni-NTA affinity chromatography. The affinity, specificity, and diagnostic potential of the Nbs were evaluated using enzyme-linked immunosorbent assay (ELISA), western blot, and bio-layer interferometry (BLI). Results: A camelid natural anti-S100B nanobody library with a capacity of 1.91×10⁸ CFU was successfully constructed. Affinity panning yielded 30 S100B-specific Nbs, among which Nb107, Nb122, Nb212, and Nb324 with distinct CDR3 sequences were selected for expression. Following Ni-NTA purification, all four anti-S100B Nbs exhibited high purity. Western blot analysis confirmed their ability to recognize recombinant S100B. ELISA and BLI analyses revealed that Nb212 demonstrated high affinity (1.96×10^-11 mol). Additionally, Nb107, Nb122, and Nb212 exhibited broad-spectrum recognition capabilities, binding to various tumor cell lines (Hepa1-6, GL261, 4T1, CT26) as well as murine/human melanoma cells. These Nbs also effectively bound to native murine/human antigens in serum samples from melanoma (A375, B16F10) mouse models. Conclusions: Specific anti-S100B Nbs are successfully screened and expressed, demonstrating not only recognition of native conformational antigens but also broad-spectrum binding and high affinity. These findings highlight their significant potential for developing early diagnostic assays and broad-spectrum targeted vaccines or therapeutics against diverse tumor cells.