Intrathecal Viral Vector Delivery of Trastuzumab Prevents or Inhibits Tumor Growth of Human HER2-Positive Xenografts in Mice.

Breast cancer brain metastases are a deadly sequela of primary breast tumors that overexpress human epidermal growth factor receptor 2 (HER2); median survival for patients with these tumors is 10 to 13 months from the time of diagnosis. Current treatments for HER2-positive breast cancer brain metastases are invasive, toxic, and largely ineffective. Here, we have developed an adeno-associated virus serotype 9 (AAV9) vector to express the anti-HER2 monoclonal antibody trastuzumab (Herceptin) A single prophylactic intrathecal administration of AAV9.trastuzumab vector in a novel orthotopic murine xenograft model of HER2-positive breast cancer brain metastases significantly increased median survival, attenuated brain tumor growth, and preserved both the HER2 antigen specificity and the natural killer cell-associated mechanism of action of trastuzumab. When administered as a tumor treatment, AAV9.trastuzumab increased median survival. Dose-escalation studies revealed that higher doses of AAV9.trastuzumab resulted in smaller tumor volumes. Our results indicate that intrathecal AAV9.trastuzumab may provide significant antitumor activity in patients with HER2-positive breast cancer brain metastases. Intrathecal delivery of trastuzumab via adeno-associated virus has the potential to become a novel, integral part of adjuvant therapy for patients with HER2-positive breast cancer brain metastases. .