Abstract
BACKGROUND
HER2+ tumors constitute approximately 20% of breast cancer patients and are characterized by overexpression of the growth factor receptor HER2 (ERBB2), a cell proliferation driver. Effective anti-HER2 therapies confer prolonged patient survival necessitating the need for transformative treatments targeting brain metastases, a major cause of mortality in ~30-50% of HER2+ metastatic breast cancer patients. HER2-directed antibody immunotherapy, while efficacious for peripheral disease, has limited central nervous system exposure (CNS). To overcome these challenges, we transduced CNS cells with a novel AAV vector carrying an anti-HER2 antibody payload.
METHODS
We assessed the biochemical equivalence and functional effectiveness of AAV vector-encoded antibodies using in vitro assays. After selecting promising vector-encoded antibody candidates, a novel, blood-brain barrier penetrant AAV capsid was administered via i.v. dosing to an orthotopic xenograft mouse model of HER2+ brain metastases. Bioluminescent imaging provided a longitudinal measure of brain tumor burden. At study termination, we measured antibody biodistribution in cerebrospinal fluid (CSF), serum, and brain homogenates with AlphaLISA assays.
RESULTS
Using HER2+ breast cancer cell lines, we determined that an antibody-dependent cell cytotoxicity (ADCC) enhanced anti-HER2 antibody was most effective and demonstrated that AAV-vector encoded forms of the antibody performed comparably to recombinant reference antibodies. Following i.v. administration of a HER2 antibody encoding AAV vector, we measured >1 ug/mL of the antibody in CSF. Importantly, AAV-mediated expression of the ADCC-enhanced HER2-directed antibody significantly abrogated tumor growth in orthotopic xenograft models.
CONCLUSIONS
Peripheral administration of an AAV vector was able to transduce brain tissue such that efficacious levels of HER2-directed antibodies were produced. This strategy was successful at preventing tumor growth in our physiologically relevant model of breast cancer brain metastases. Such a treatment modality should be further evaluated in patient derived PDX models to validate translational efficacy for human patients.
In Vivo Tumor Growth Rate Measured by US in Preoperative Period and Long Term Disease Outcome in Breast Cancer Patients
