CAM-H2 effectively targets and treats HER2 positive brain lesions: A comparative preclinical study with trastuzumab

Background: Despite extensive research in systemic treatments for HER2 positive breast cancer brain metastases (BCBM), only limited benefits have been observed often at the cost of significant toxicities. Treatment failure is attributed to the limited capacity of drugs to cross the blood-tumor-barrier (BTB) or to resistance mechanisms in the brain lesion microenvironment. In this study we evaluate the radiolabeled drug CAM-H2 as a new systemic treatment for the irradiation of HER2 positive BCBM. Single domain antibody fragments (sdAbs) are small (15 kDa) heavy-chain-only antibody fragments. Due to their favorable pharmacokinetics, sdAbs are tested as targeting vehicles for the delivery of cytotoxic irradiation to cancer lesions inside and outside the brain. Here we measure the potential of CAM-H2 (131-Iodine conjugated anti-HER2 sdAb 2Rs15d) for targeting brain lesions with imaging and compare its therapeutic efficacy with Trastuzumab in a preclinical model. Methods: Tumors were inoculated through intracranial injection of HER2+SKOV3.ip1 or MDA-MB-231Br (MDA) cancer cells. Biodistribution of radiolabeled 2Rs15d and Trastuzumab was evaluated through in vivoSPECT/CT imaging at 1h and 72h post injection followed by ex vivotissue radioactivity counting. Five groups of MDA-tumor-bearing mice were treated with either CAM-H2, Trastuzumab plus CAM-H2, unlabeled 2Rs15d, Trastuzumab, or PBS. Results: Mice treated with CAM-H2 and the combination of CAM-H2 plus Trastuzumab showed a significant increase (p < 0.05) in median survival compared to the Trastuzumab only, unlabeled 2Rs15d or PBS. The addition of Trastuzumab did not significantly prolong survival, compared to cold 2Rs15d or PBS. SPECT/CT imaging of CAM-H2 treated animals showed specific uptake in the brain lesions up to 2 days after administration. Conclusions: CAM-H2 crosses the BTB and binds HER2 positive brain lesions. Treatment with therapeutic doses of CAM-H2 significantly increased survival compared to Trastuzumab. Systemically delivered cytotoxic irradiation conjugated to sdAbs has the potential to effectively treat cancer lesions inside the brain, with limited exposure to healthy brain. Clinical translation of CAM-H2 for treatment of BCBM is currently ongoing. Legal entity responsible for the study: Vrije Universiteit Brussel. Funding: Camel-IDS NV/SA. Disclosure: M. D’Huyvetter: Ownership interest, employee: Camel-IDS NV/SA. B. Windhorst: Editor in chief: Nuclear Medicine & Biology; Editor: Journal of Radiolabelled Compounds & Radiopharmaceuticals T. Lahoutte: Holds ownership interest, consultant: Camel-IDS NV/SA; Member of the scientific advisory board: Ion Beam Applications; Member of the strategic committee: IRE; Preclinical contract research: Roche, Telix Pharmaceuticals. N. Devoogdt: Ownership interest, consultant for Camel-IDS NV/SA; Preclinical contract research: Roche, Telix Pharmaceuticals. All other authors have declared no conflicts of interest.