DDDR-55. Engineering and Screening Biologic Conjugates for Target Affinity, Selectivity and Blood Brain Barrier Penetration

Abstract Crossing the blood-brain barrier (BBB) remains an unsolved challenge in neuro-oncology. Despite advances in glioblastoma biology, drug delivery into brain parenchyma is still limited by the inability to efficiently and selectively target tumor tissue. The next generation of therapies will require molecules that not only cross the BBB but do so with precision, persistence, and purpose. Small-format biologics like nanobodies, scFvs, Fabs, and mini-proteins offer distinct advantages in size, modularity, and BBB permeability, especially when conjugated with carrier molecules known to facilitate barrier translocation. But therapeutic success hinges on a narrow kinetic sweet spot: high-affinity binding to promote retention, yet reversible enough to release payloads effectively. With AI accelerating the design phase, experimental validation is now the bottleneck. We close this gap with SPOC (Sensor-integrated Proteome on Chip), a rapid, high-throughput biosensor platform that enables on-chip synthesis and real-time kinetic analysis of thousands of candidate binders. Using cell-free synthesis directly on surface plasmon resonance (SPR) chip, SPOC delivers high-resolution measurements of binding kinetics (on-rate, off-rate, residence time, and affinity) at scale. We applied SPOC to screen a panel of biologics targeting EGFR and HER2. This included engineered HER2-binding nanobody (VHH) variants, scFvs, and de novo AI-designed scaffolds. Resulting kinetic fingerprints allowed us to rapidly triage lead molecules with ideal BBB-targeting profiles. Building on these hits, we are developing BBB-penetrant drug conjugates by fusing the selected binders with chlorotoxin, a glioma-homing peptide from Leiurus quinquestriatus venom. Preliminary data demonstrate strong receptor engagement, promising residence times, and potential for selective tumor targeting in brain. SPOC is a novel and disruptive platform for neuro-oncology drug development—enabling rapid, parallelized optimization of biologics designed to breach the BBB and home in on brain tumors. We present new kinetic and functional data supporting its utility in accelerating the pipeline of next-generation targeted therapies.