Tailoring Avidity through Morphology: Structure-Avidity Relationship in CD38-Binding Nanofiber Radiotracers.

The lack of targeted molecular imaging agents for multiple myeloma (MM) hinders precise disease characterization and theranostic development. We address this by engineering a tunable platform of self-assembled peptide nanofibers that target CD38, a key antigen in MM. Simple variation of a conjugated lipid tail length (C4-C12) dictates the supramolecular architecture, as revealed by high-resolution cryo-EM. This structural control directly modulates biological function: avidity for CD38 increases monotonically with tail length, culminating in T12 nanofibers with sub-nanomolar affinity. This optimized morphology also enables unique pH-responsive di-tyrosine cross-linking and, critically, facilitates polyvalent cell-surface engagement that outcompetes high-affinity monomers in vitro. The nanofibers are efficiently radiolabeled with 64Cu, exhibit exceptional serum stability, and show no toxicity at doses 20-fold above projected imaging use. By establishing lipid tail length as a simple, powerful handle for controlling nanofiber structure, avidity, and function, we present a robust, translatable platform for advancing targeted imaging and therapy in CD38-positive malignancies.