Bioengineering of covalent proteins for nuclear medicine applications

/Abstract Targeted radionuclide therapy is resurging as an attractive avenue for cancer treatment, which can potentially be applied to various cancers independent of pathology. However, existing radiopharmaceuticals struggle with balancing safety and efficacy. Radiopharmaceuticals with high molecular weights are effective in tumor uptake yet meanwhile increase radiation exposure of normal tissues, whereas small molecule radiopharmaceuticals reduce undesired systemic radiation but also decrease tumoral absorption. While small molecule radioligands irreversibly bound to target have been shown to improve in vivo imaging, no protein-based radiopharmaceutical has been enabled to bind target irreversibly. To change this paradigm, this project seeks to develop a new class of covalent protein radiopharmaceuticals. New latent bioreactive amino acids will be designed and genetically incorporated into the protein binder of low molecular weight, followed with efficient radionuclide labeling. When administrated in vivo, the low molecular weight of the protein will allow rapid clearance of the radiopharmaceutical from circulation, ensuring low background and safety; Upon recognition of the target by the protein binder, the latent bioreactive amino acid in the binder will react with a natural residue in the target, cross-linking the radiopharmaceutical to the target irreversibly. This covalent and irreversible binding will prolong the radiopharmaceutical’s residence time at the tumoral site and enhance absorbed dose. The pharmacokinetics and biodistribution of the covalent protein radiopharmaceuticals will be assessed in tumor bearing mouse models of human cancer using positron emission tomography, and their antitumor effects will be evaluated in cancer cell xenograft mouse models and clinically relevant patient-derived xenograft mouse models. Mouse studies are critical as only small animal models can recapitulate whole-body radiotracer biodistribution and enable human dosimetry prediction - capabilities that cannot be achieved using cell lines, organoids, or similar in vitro systems. The success of this project will unite an unusual combination of safety with efficacy for protein radiopharmaceuticals, enabling a new class of protein radiopharmaceuticals with expanded therapeutic index for cancer treatment. Project Number: 1R01CA309883-01 | Fiscal Year: 2026 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Michael Evans (+1 co-PI) | Institution: UNIVERSITY OF CALIFORNIA, SAN FRANCISCO, SAN FRANCISCO, CA | Award Amount: $640,466 | Activity Code: R01 | Study Section: Special Emphasis Panel[ZRG1 ISB-T (03)] View on NIH RePORTER: https://reporter.nih.gov/project-details/11314872