Imaging of HER2 with [89Zr]pertuzumab in Response to T-DM1 Therapy

Abstract

Background: The success of human epidermal growth factor receptor 2 (HER2)-targeted therapy depends on accurate characterization of HER2 expression, but current methods available have several limitations. This study aims to investigate the feasibility of [⁸⁹Zr]pertuzumab imaging to monitor early response to Ado-trastuzumab emtansine (T-DM1) therapy in mice bearing xenografts of HER2-positive breast cancer (BCa). Materials and Methods: Pertuzumab was conjugated to DFO-Bz-NCS and labeled with ⁸⁹Zr. Mice bearing BT-474 tumors were imaged with [⁸⁹Zr]pertuzumab and [¹⁸F]FDG before and after T-DM1 therapy. Results: Pertuzumab was successfully labeled with ⁸⁹Zr with a specific activity of 0.740 MBq/μg. Overall [¹⁸F]FDG images showed poor delineation of tumors. Using [¹⁸F]FDG-PET to measure tumor volume, the volume remained unchanged from 107.6 ± 20.7 mm³ before treatment to 89.87 ± 66.55 mm³ after treatment. In contrast, [⁸⁹Zr]pertuzumab images showed good delineation of HER2-positive tumors, allowing accurate detection of changes in tumor volume (from 243.80 ± 40.91 mm³ before treatment to 78.4 ± 40.43 mm³ after treatment). Conclusion: [⁸⁹Zr]pertuzumab may be an imaging probe for monitoring the response of HER2-positive BCa patients to T-DM1 therapy.

Keywords: HER2-positive breast cancer; T-DM1 therapy; [Zr]pertuzumab; molecular imaging; radiolabeled monoclonal antibody.

FIG. 1.

In vivo tumor model development and therapy protocol schema.

FIG. 2.

RCY of pertuzumab conjugated to DFO at different molar ratios and labeled with ⁸⁹Zr at 4 μCi/μg (A); RCY of pertuzumab conjugated to DFO at molar ratio 1:16 and labeled with ⁸⁹Zr at different ratios (B); Radiochromatogram of [⁸⁹Zr]pertuzumab (C). RCY, radiochemical yield. Color images are available online.

FIG. 3.

Stability of [⁸⁹Zr]pertuzumab in NaCl 0.9% at room temperature and 4°C (A). Stability of [⁸⁹Zr]pertuzumab in human serum, mouse serum, and PBS at 37°C (B). PBS, phosphate buffered saline.

FIG. 4.

Uptake of [⁸⁹Zr]pertuzumab in BT-474 and JIMT-1 cells (A). Western blot of BT-474 and JIMT-1. Anti-HER2 antibody (C-18) was used to characterize the HER2 expression, and expression of β-actin was used as the loading control (B). HER2:β-actin ratio for BT-474 and JIMT-1 cells (C). HER2, human epidermal growth factor receptor 2.

FIG. 5.

Effect of T-DM1 therapy in HER2-positive BCa BT-474 xenograft. Athymic nude mice bearing BT-474 tumors were treated (4 mice per group) with saline (control group) or T-DM1 (15 mg/kg, single administration, i.v.). Tumor volume was measured weekly by caliper (A) and by using ROI from PET/CT images before and after therapy using [¹⁸F]FDG and [⁸⁹Zr]pertuzumab as a radiopharmaceutical (B). BCa, breast cancer; CT, computed tomography; PET, positron emission tomography; ROI, region of interest; T-DM1, Ado-trastuzumab emtansine. Color images are available online.

FIG. 6.

Posterior half body PET/CT images of Nu/Nu mice implanted with BT-474 human BCa xenografts (white arrows). Baseline imaging acquired before therapy with T-DM1 using [¹⁸F]FDG (A) and [⁸⁹Zr]pertuzumab (B) and after therapy using [¹⁸F]FDG (C) and [⁸⁹Zr]pertuzumab (D). Color images are available online.