Trastuzumab uptake and its relation to efficacy in an animal model of HER2-positive breast cancer brain metastasis

Abstract

Purpose: The extent to which efficacy of the HER2 antibody Trastuzumab in brain metastases is limited by access of antibody to brain lesions remains a question of significant clinical importance. We investigated the uptake and distribution of trastuzumab in brain and mammary fat pad grafts of HER2-positive breast cancer to evaluate the relationship of these parameters to the anti-tumor activity of trastuzumab and trastuzumab emtansine (T-DM1).

Methods: Mouse transgenic breast tumor cells expressing human HER2 (Fo2-1282 or Fo5) were used to establish intracranial and orthotopic tumors. Tumor uptake and tissue distribution of systemically administered ⁸⁹Zr-trastuzumab or muMAb 4D5 (murine parent of trastuzumab) were measured by PET and ELISA. Efficacy of muMAb 4D5, the PI3K/mTOR inhibitor GNE-317, and T-DM1 was also assessed.

Results: ⁸⁹Zr-trastuzumab and muMAb 4D5 exhibited robust uptake into Fo2-1282 brain tumors, but not normal brains. Uptake into brain grafts was similar to mammary grafts. Despite this, muMAb 4D5 was less efficacious in brain grafts. Co-administration of muMAb 4D5 and GNE-317, a brain-penetrant PI3K/mTOR inhibitor, provided longer survival in mice with brain lesions than either agent alone. Moreover, T-DM1 increased survival in the Fo5 brain metastasis model.

Conclusions: In models of HER2-positive breast cancer brain metastasis, trastuzumab efficacy does not appear to be limited by access to intracranial tumors. Anti-tumor activity improved with the addition of a brain-penetrant PI3K/mTOR inhibitor, suggesting that combining targeted therapies is a more effective strategy for treating HER2-positive breast cancer brain metastases. Survival was also extended in mice with Fo5 brain lesions treated with T-DM1.

Keywords: Blood–brain barrier; Brain metastasis; Breast cancer; T-DM1; Trastuzumab.

Fig. 1

Characterization of Fo2-1282 brain metastasis model. a Hematoxylin and eosin (H&E) staining (left) and HER2 protein expression determined by immunohistochemistry (right). b T1-weighted MRI with contrast in separate tumor-bearing mice. Representative data are shown

Fig. 2

Trastuzumab uptake into Fo2-1282 brain grafts following a single systemic dose. PET imaging of ⁸⁹Zr-trastuzumab (left) and ⁸⁹Zr-anti-STEAP1 control antibody (right) uptake

Fig. 3

⁸⁹Zr-trastuzumab uptake in brain lesions, normal brain, liver, and blood following a single systemic dose. Concentrations of ⁸⁹Zr-trastuzumab were measured at 1, 3, and 5 days (n = 2 for each group; each line represents one animal)

Fig. 4

No impact of stereotactic surgery on trastuzumab concentrations in brain following systemic delivery. Mice received sham surgery in one hemisphere and no surgery in the other. Trastuzumab was measured by ELISA in each brain hemisphere and in serum at 1 (n = 4) and 9 (n = 4) days after these procedures

Fig. 5

⁸⁹Zr-trastuzumab uptake in Fo2-1282 brain and mammary tumors following a single systemic dose. Uptake of ⁸⁹Zr-trastuzumab was assessed as  %ID/g (top panels); predicted muMAb4D5 quantification (μg/g) calculated from ⁸⁹Zr-trastuzumab uptake × injected dose (middle panels), and volume (lower panels). N = 10–12 animals per group

Fig. 6

Efficacy of muMAb 4D5 in Fo2-1282 mammary tumors and brain lesions. Antibody treatments were weekly × 3, following a 2× loading dose, at doses of 3, 10, 20, or 30 mg/kg. a Orthotopic mammary tumor volume as determined by caliper measurement; b survival in mice bearing orthotopic mammary tumors; or c, brain lesions, as assessed using Kaplan–Meier analysis. Arrows denote day of antibody administration. d muMAb 4D5 concentrations were assayed in serum, brain graft, normal brain adjacent to graft, un-injected contralateral hemisphere, and normal cerebellum at end of study

Fig. 7

Enhanced survival effect of muMAb 4D5 combined with GNE-317 versus single-agent treatment in mice bearing Fo2-1282 brain lesions. Mice were administered muMAb 4D5 IV weekly (30 mg/kg following a 2× loading dose) and/or 30 mg/kg GNE-317 daily by oral gavage. Treatment was initiated on day 10 and terminated on day 30. Arrows denote antibody treatment; solid line denotes GNE-317 treatment

Fig. 8

Enhanced survival in mice bearing Fo5 brain lesions after treatment with a single dose of 10 mg/kg T-DM1 compared with 10 mg/kg of non-targeted control ADC