Farnesyltransferase Enables Modular Assembly of Dual-Functional Nanobody Conjugates for in Vivo Imaging of Inflammation.

Non-invasive imaging of inflammation is critical for disease diagnosis, monitoring, and therapeutic evaluation. Nanobodies, due to their many unique properties, are emerging as powerful imaging agents; however, conventional non-specific conjugation strategies often yield heterogeneous products that limit in vivo performance. Here, we report a chemoenzymatic strategy that enables precise and modular assembly of nanobody conjugates using farnesyltransferase (FTase)-mediated site-specific modification. We developed a trifunctional FTase substrate that introduces two orthogonal bioorthogonal handles, an aldehyde and an azide, onto nanobodies in a single enzymatic step. These handles enable independent and controlled conjugation of imaging payloads (fluorophores or radioisotopes) and pharmacokinetic modifiers (i.e. PEG), which enhance in vivo signal-to-noise ratios. Applying this strategy to nanobodies targeting CD45 and CD11b, markers broadly expressed on all immune cells and myeloid subsets, respectively, we generated well-defined, dually modified constructs that enabled high-contrast in vivo visualization of immune organs, including the spleen and lymph nodes. In a mouse model of localized inflammation, these probes robustly delineated inflamed tissue with high sensitivity and specificity. Together, this FTase-enabled dual-labeling approach provides a versatile and generalizable platform for the rapid generation of precisely defined nanobody-based imaging agents, advancing non-invasive detection and monitoring of inflammation across diverse disease contexts.