HER2 expression in different cell lines at different inoculation sites assessed by [52Mn]Mn-DOTAGA(anhydride)-trastuzumab

Abstract

Purpose: Positron emission tomography (PET) hybrid imaging targeting HER2 requires antibodies labelled with longer half-life isotopes. With a suitable radiation profile, ⁵²Mn coupled with DOTAGA as a bifunctional chelator is a potential candidate. In this study, we investigated the tumor HER2 specificity and the temporal biodistribution of the [⁵²Mn]Mn-DOTAGA(anhydride)-trastuzumab in preclinical models.

Methods: PET/MRI and PET/CT were performed on SCID mice bearing orthotopic and ectopic HER2-positive and ectopic HER2-negative tumors at 4, 24, 48, 72, and 120 h post-injection with [⁵²Mn]Mn-DOTAGA(anhydride)-trastuzumab. Melanoma xenografts were included for comparison of specificity.

Results: In vivo biodistribution demonstrated strong contrast in HER2-positive tumors, particularly in orthotopic tumors, where uptake was significantly higher than in the blood pool and other organs from 24 h onwards and consistently higher than in ectopic HER2-positive tumors at all time points. Significantly higher tumor-to-blood and tumor-to-muscle ratios were observed in HER2-positive ectopic tumors compared to HER2-negative tumors but only at 4 and 24 h; the differences were likely due to non-specific binding of the tracer. The ratios for orthotopic HER2-positive tumors were significantly higher than those for ectopic HER2-negative tumors and melanoma at all time points. However, the differences between HER2-positive and HER2-negative tumors decreased at later time points.

Conclusion: These results suggest that [⁵²Mn]Mn-DOTAGA(anhydride)-trastuzumab demonstrates efficient tumor-to-background contrast, emphasize the higher tumor uptake observed in orthotopic tumors, and highlight the influence of tumor environment characteristics on uptake.

Keywords: 52Mn; HER2; breast cancer; positron emission tomography; trastuzumab.

FIGURE 1

Line graph shows that in vitro MDA-MB-HER2+ cells exhibited higher [⁵²Mn]Mn-DOTAGA-trastuzumab uptake (counts per minute, cpm) across all time points compared to MDA-MB-468 cells.

FIGURE 2

Bar graphs show mean and standard deviation of the 20-min static PET measurements, which were taken at 4, 24, 48, 72, and 120 h post-injection with [⁵²Mn]Mn-DOTAGA-trastuzumab into MDA-MB-HER2+ tumour- bearing mice (n = 3) scanned with PET/CT.

FIGURE 3

Images of PET/MRI and PET/CT scans were obtained at different time points (4, 24, 48, 72, 120 h) following injection of [⁵²Mn]Mn-DOTAGA-trastuzumab into MDA-MB-468 tumour-bearing mice (upper row) and into the MDA-MB-HER2+ tumour-bearing mice (middle and bottom rows displaying the back and breast tumours, respectively). The upper row displays sagittal planes, with the exception of the 48-hour image in coronal plane. The middle and bottom rows display coronal planes. Red circles were used to highlight the MDA-MB-468 back tumour (upper row), the MDA-MB-HER2+ back tumour (middle row), and the MDA-MB-HER2+ breast tumour (bottom row) at 4 h and 120 h time points. There was a prominent high uptake in the HER2-positive orthotopic xenografts, characterised by a particularly good tumor-to-background. Tumor contrast was also visible in the ectopic HER2-positive xenografts but less markedly, with both HER2-positive tumors showing a stronger peripheral uptake compared to the less avid core. In contrast, the HER2-negative xenografts exhibited less pronounced tumor contrast, but this contrast increased at later time points with relatively homogeneous uptake even in the core of the xenografts.

FIGURE 4

Line graphs represent the mean and standard deviation of the tumor/background ratios of MDA-MB-HER2+ breast (orthotopic) tumors (purple lines), MDA-MB-HER2+ back (ectopic) tumors (blue lines), MDA-MB-468 back tumors (orange lines) in the CB17 SCID mice, and B16F10 tumors (green lines) in the C57BL/6 mice after injection of with [⁵²Mn]Mn-DOTAGA-trastuzumab. * indicates significantly higher ratios of breast HER2-positive tumors than all other tumors, # indicates significantly higher ratios of HER2-positive back tumors than HER2-negative tumors.

FIGURE 5

Histopathological H&E staining (left) and the HER2 staining (right) images of the (A) MDA-MB-HER2+, the (B) MDA-MB-468, and the (C) B16F10 after the tumors were resected and fixed with 10% formalin.