Affibody and the Case for Antibody Mimetics in Radioligand Therapy

What It Covers

Affibody CEO David Baker explains how the Stockholm-based biotech's engineered proteins — one-twentieth the size of monoclonal antibodies — are designed to expand the radioligand therapy target space beyond the handful of peptide-accessible targets like PSMA and SSTR that currently dominate the entire RLT pipeline.

Key Questions Answered

• •Radioligand target bottleneck: The entire current RLT pipeline is concentrated around just four targets — SSTR, PSMA, FAPI, and DLL3 — all addressed by peptides or small molecules. Antibodies fail in RLT due to bone marrow toxicity from poor biodistribution. Affibody molecules offer a third path: high-affinity binding without the antibody's problematic pharmacokinetic profile.
• •Albumin biodistribution advantage: Serum albumin is not confined to circulation — over 60% resides in interstitial tissue, and it accumulates in tumor lesions and inflammatory sites due to leaky vasculature. Affibody's Albumod technology exploits this by binding albumin, giving therapeutics passive tumor targeting beyond standard EPR effect, particularly relevant for RLT and oncology applications.
• •Manufacturing speed differential: Affibody molecules are produced in E. coli in roughly one day versus several weeks for mammalian cell-derived monoclonal antibodies. The purification process is more robust, tolerating wider pH and temperature ranges. Critically, the same manufacturing process transfers across molecules, enabling near-identical clinical batch production without per-program process redevelopment.
• •Platform-target-modality matching framework: Affibody evaluates every program against three simultaneous criteria: target biology, indication, and modality fit. Programs are deprioritized if the platform offers only marginal improvement over existing antibodies or small molecules. Priority goes to targets where protein-protein interactions resist small molecules and where biodistribution modification — as in inhaled respiratory or RLT settings — creates measurable differentiation.
• •In-house RLT capability as clinical leverage: Affibody retains internal radiochemistry, radiolabeling, and radioligand animal facilities — capabilities held by very few non-service-provider biotechs. This allows full translational work before partnering, justifying later-stage deals. The HER2 imaging probe, produced via chemical synthesis with long shelf life, is under consideration for internal commercialization rather than early out-licensing.