Background: Approximately 20% of patients with Her2+ metastatic breast cancer may be diagnosed with brain metastases. Trastuzumab, has been used successfully to treat peripheral Her2+ breast cancers, but has shown limited efficacy in brain metastases. Human melanotransferrin analog (MTf) is a vector to transport drugs across the blood brain barrier. In the current work, we investigated brain and brain metastases uptake of a MTf-trastuzumab conjugate (BT2111), and determined if the conjugate had efficacy in reducing the number and size of metastatic lesions in a preclinical model of brain metastases of breast cancer.

Methods: Human metastatic brain seeking breast cancer cells (MDA-MB-231-Her2) were injected intracardially in 8 week old female NuNu mice (n=6-12 per group), allowed to circulate, and eventually develop experimental brain metastases. To examine drug uptake, radiolabeled conjugate (BT2111), trastuzumab and MTf was injected intravenously, and allowed to circulate for 30 min, 2 and 8 hours. Serial blood samples were drawn during circulation and terminal brain and blood samples were obtained. Drug uptake (Kin) was analyzed in relation to metastasis size and blood-tumor barrier permeability. To investigate in-vivo activity against brain metastases, we administered equimolar doses of the conjugate, and relevant controls in separate groups, biweekly starting 21 days after intracardiac injection of the metastatic cancer cells. Efficacy was assessed by determining both the number and size of metastases in brain at defined terminal endpoints.

Results: Uptake of trastuzumab in “normal” brain (brain distant to tumor; BDT) was 0.17 + 0.004 x 10-6 mL/s/g and nearly 10 fold higher on average in metastatic lesions (1.1 + 0.04 x 10-6 mL/s/g). MTf uptake into BDT (18.4 + 0.5 x 10-6 mL/s/g) and brain metastases (53.0 + 3.1 x 10-6 mL/s/g) was significantly higher (p<0.01) than that of the antibody alone. BT2111 was nearly 30 fold higher (p<0.01) than that of the antibody alone in BDT (3.91 + 0.3 x 10-6 mL/s/g) and 10 fold higher (p<0.01) in metastases (10.7 + 0.43 x 10-6 mL/s/g). BT2111 reduced the number of preclinical human HER2+ breast cancer metastases in the brain of control animals (85 ± 6.3) by 68% (27.6 ± 3.9; P<0.001). Further, lesions in control animals were 54% larger (1.7 ± 0.7 µm2) than those in the BT2111 treated animals (0.78 ± 0.6 µm2; P<0.001). In contrast, trastuzumab alone had no effect on reducing the number of metastases (74 ± 5.0, P>0.05) and was associated with only a minimal (21%) reduction in metastasis size (1.34 ± 0.04 µm2).

Conclusions: These results provide evidence that the MTf-trastuzumab conjugate, BT2111, has efficacy in treating brain metastasis in preclinical models and validates the role MTf has as a vector for the transport of antibodies across the BBB.

Citation Format: Mohamed Nounou, Chris Adkins, Tori R. Terrell, Afroz Mohamed, Tim Vitalis, Reinhard Gabathuler, Paul R. Lockman. Anti-cancer antibody trastuzumab-melanotransferrin conjugate (BT2111) for the treatment of metastatic HER2+ breast cancer tumors in the brain: An in vivo study. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2653. doi:10.1158/1538-7445.AM2014-2653