Synthesis and Preclinical Development of a Novel 68Ga/89Zr-Labelled α{nu}β6-Integrin Targeting Trimer

The v{beta}6 integrin has emerged as a valuable target for theranostic applications in nuclear medicine with high applicability across a variety of cancers, including head-and-neck, lung, breast, and pancreatic carcinomas. [Ga]Ga-Trivehexin is a prominent example of a diagnostic tracer targeting this integrin. In this work, we aimed to expand on this concept by developing FSC(PEG4-v{beta}6), a novel tracer that retains the Trivehexin design, but features PEGylated spacers and replaces the TRAP chelator with Fusarinine C (FSC), enabling labelling with Zirconium-89 in addition to Gallium-68. Preclinical characterization of [Ga]Ga/[Zr]Zr-FSC(PEG4-v{beta}6) included affinity determination towards the v{beta}6 integrin and cellular uptake studies in v{beta}6-positive H2009 cells. A subcutaneously xenografted H2009 tumor model was used to assess the PET imaging potential and biodistribution at early time points with the Gallium-68-labelled compound, and at later time points (up to 6 days post-injection) with the Zirconium-89-labelled version. While [Ga]Ga-FSC(PEG4-v{beta}6) exhibited moderate binding to v{beta}6, its affinity, cellular internalization, and tumor uptake in vivo were lower compared to [Ga]Ga-Trivehexin. Notably, this decreased target engagement was associated with reduced nonspecific binding, which we primarily attributed to the incorporation of PEGylated linkers. Despite indication of in vivo degradation of [Zr]Zr-FSC(PEG4-v{beta}6), still a meaningful evaluation of pharmacokinetics and biodistribution at extended time points was feasible, indicating its suitability for prolonged imaging studies.