Small Organic Carbonic Anhydrase IX Ligands from DNA-Encoded Chemical Libraries for Tumor-Targeted Delivery of Radionuclides

Carbonic anhydrase IX (CAIX) is a membrane protein that is highly expressed in clear cell renal cell carcinoma (ccRCC) and in hypoxic tumors. Being virtually absent in most healthy tissues, CAIX became an attractive target for the selective delivery of diagnostic and therapeutic payloads. Here, we report the discovery and characterization of DNA-encoded chemical library (DEL)-derived CAIX ligands for radionuclide-based imaging applications. Methods: DELs were screened against CAIX and CAII to prioritize hits based on their selectivity and enrichment against CAIX. In vitro characterization of hits was performed by fluorescence polarization (FP), surface plasmon resonance (SPR), and flow cytometry. In vivo biodistribution studies of Lutetium-177 and Gallium-68-radiolabeled compounds were performed in SK-RC-52 tumor-bearing mice. Results: DEL-based CAIX ligands with different affinities and selectivities could be identified. Selectivity and high affinity toward the target correlated with higher tumor-to-organ ratios and improved tumor retention. The best candidate, named OncoCAIX, reached up to ∼55% injected dose per gram in SK-RC-52 lesions at early time points with very low healthy organ uptake (tumor-to-kidney ratio of >23). Conclusion: OncoCAIX demonstrated rapid and selective tumor uptake, which is a key feature for the development of radionuclide-based imaging agents for early and late-stage ccRCC and hypoxic tumors.