Shark Radiotherapy for the Treatment of Triple-Negative Breast Cancer

SUMMARY Triple-negative breast cancer (TNBC), which lacks expression of the estrogen receptor, progesterone receptor, and HER2, is the most aggressive breast cancer subtype with a five-year survival rate of 12% for patients with metastatic disease. Since traditional hormonal therapies are ineffective, few therapeutic options exist for TNBC. Radiopharmaceutical therapies (RPTs) have demonstrated improved survival for several types of cancer, however, there is dearth of RPTs for TNBC. Our goal is to improve outcomes for TNBC patients by developing first-in-class targeted RPTs. One attractive target for the development of RPTs is the receptor tyrosine kinase c-MET. c-MET is overexpressed in nearly two-thirds of all TNBC cases and c-MET signaling results in disease with an aggressive phenotype. Studies have also shown that radiation induces c-MET overexpression suggesting that targeting c-MET with RPTs may result in a feed-forward mechanism where the cancer cells become lethally addicted to RPT. To develop a targeted RPT, we identified a novel Variable New Antigen Receptor (VNAR) binding domain from a nurse shark immunized with the extracellular domain of c-MET. VNARs are the antigen recognition domains of shark antibodies, and at ~11kDa they are the smallest naturally occurring variable fragment. Consisting of a single-chain, VNARs have two complementarity determining regions and two additional variable regions that allow them to adopt multiple unique conformations. Because of their usual geometries, VNARs can engage cryptic epitopes inaccessible to conventional human and camelid antibodies with high affinity. Surprisingly, VNARs also have low to no immunogenicity making them readily translatable. The VNAR we discovered, 2H4, was made into a human Fc fusion protein (2H4-Fc) to increase valency and prolong the in vivo half-life. 2H4-Fc was cross-reactive with c-MET across multiple species, specifically bound c-MET-positive cells lines by flow cytometry and was internalized on receptor binding. In a PET imaging study, [89Zr[Zr-2H4-Fc localized to a TNBC xenograft resulting in high tumor uptake with an exceptionally low background in non-target tissues. The objective of this proposal is to evaluate the ability of our novel targeting vector 2H4-Fc to deliver α- and β-emitting radionuclides (225Ac and 177Lu) for therapeutic benefit in vivo. The first specific aim is to determine the dosimetry of our RPTs and evaluate normal tissue toxicity. In the second aim, we will evaluate their therapeutic efficacy in vivo using multiple TNBC models and investigate the biological effect and mechanism of action of our RPTs. In the third aim, we will conduct studies in non-human primates to determine the immunogenicity of 2H4-Fc in addition to its pharmacokinetic and pharmacodynamic properties by PET imaging. This innovative proposal aims to provide compelling evidence for the further development of c-MET-targeted RPTs for use in TNBC. Project Number: 1R01CA295576-01A1 | Fiscal Year: 2025 | NIH Institute/Center: National Cancer Institute (NCI) | Principal Investigator: Aaron LeBeau | Institution: UNIVERSITY OF WISCONSIN-MADISON, MADISON, WI | Award Amount: $630,171 | Activity Code: R01 | Study Section: Radiation Therapeutics and Biology Study Section[RTB] View on NIH RePORTER: https://reporter.nih.gov/project-details/11224617