MT1-MMP as a PET Imaging Biomarker for Pancreas Cancer Management

Abstract

Pancreatic ductal adenocarcinoma (PDAC) continues to be one of the deadliest cancers for which optimal diagnostic tools are still greatly needed. Identification of PDAC-specific molecular markers would be extremely useful to improve disease diagnosis and follow-up. MT1-MMP has long been involved in pancreatic cancer, especially in tumour invasion and metastasis. In this study, we aim to ascertain the suitability of MT1-MMP as a biomarker for positron emission tomography (PET) imaging. Two probes were assessed and compared for this purpose, an MT1-MMP-specific binding peptide (MT1-AF7p) and a specific antibody (LEM2/15), labelled, respectively, with ⁶⁸Ga and with ⁸⁹Zr. PET imaging with both probes was conducted in patient-derived xenograft (PDX), subcutaneous and orthotopic, PDAC mouse models, and in a cancer cell line (CAPAN-2)-derived xenograft (CDX) model. Both radiolabelled tracers were successful in identifying, by means of PET imaging techniques, tumour tissues expressing MT1-MMP although they did so at different uptake levels. The ⁸⁹Zr-DFO-LEM2/15 probe showed greater specific activity compared to the ⁶⁸Ga-labelled peptide. The mean value of tumour uptake for the ⁸⁹Zr-DFO-LEM2/15 probe (5.67 ± 1.11%ID/g, n=28) was 25-30 times higher than that of the ⁶⁸Ga-DOTA-AF7p ones. Tumour/blood ratios (1.13 ± 0.51 and 1.44 ± 0.43 at 5 and 7 days of ⁸⁹Zr-DFO-LEM2/15 after injection) were higher than those estimated for ⁶⁸Ga-DOTA-AF7p probes (of approximately tumour/blood ratio = 0.5 at 90 min after injection). Our findings strongly point out that (i) the in vivo detection of MT1-MMP by PET imaging is a promising strategy for PDAC diagnosis and (ii) labelled LEM2/15 antibody is a better candidate than MT1-AF7p for PDAC detection.

Figure 1

(a) Purification of ⁸⁹Zr-DFO-LEM2/15 in a PD-10 column; the antibody elutes between volume fractions 2.5 and 5.0 ml. Inset: ITLC image illustrating RQP of the ⁸⁹Zr-DFO-LEM2/15 peak. 1 corresponds to the radioimmunoconjugate and 2 to the free radionuclide. (b) Percentage of bound radioactivity to LEM2/15 after 7-day incubation of ⁸⁹Zr-DFO-LEM2/15 with human serum at 37°C () and 4°C () and human plasma at 37°C () and 4°C (); data expressed as mean ± SD. (n=4). Representative HPLC chromatogram of ⁶⁸Ga-DOTA-AF7p-1 before (c) or after (d) to Sep-Pak Light C18 cartridge purification. ⁶⁸Ga-DOTA-AF7p-1 is detected at 8.7 min by UV absorbance at 280 nm () and radioactivity detector ().

Figure 2

CAPAN-2-tumour-bearing mice injected with ⁶⁸Ga-DOTA-AF7p probes. (a) PET/CT image of representative mouse with subcutaneous CAPAN-2 xenograft (white arrows) that was injected with ⁶⁸Ga-DOTA-AF7p-1. Image was acquired 90 min after injection. (b) Immunohistochemistry of tumour tissue from xenografted mice. MT1-MMP was detected using LEM2/15 antibody. Scale bar: 1000 µm. Higher magnification of the boxed area is shown at the right corner. Scale bar: 50 µm. (c) Tumour uptake (expressed as %ID/g) of ⁶⁸Ga-DOTA-AF7p-1 and ⁶⁸Ga-DOTA-AF7p-2 probes as quantified by PET imaging. (d) Tumour-to-blood ratio derived from PET images for both radiolabelled probes.

Figure 3

Heterotopic patient-derived xenografted mice injected with ⁶⁸Ga-DOTA-AF7p-1. (a) PET/CT image of representative heterotopic PDX mouse injected with ⁶⁸Ga-DOTA-AF7p-1 acquired 90 min after injection. Tumour locations are indicated by white arrows. (b) Immunohistochemistry of tumour tissue from PDX mice. MT1-MMP was detected using LEM2/15 antibody. Scale bar: 1000 µm. Higher magnification of the boxed area is shown at the right corner. Scale bar: 50 µm. (c) Tumour volume was measured by CT four times after onset of PET imaging study. Each tumour is represented by a different colour line on the graph. (d) Tumour uptake (quantified by PET imaging and expressed as %ID/g) as a function of tumour volume for all scanned mice, showing that there is no relationship between tumour size and ⁶⁸Ga-DOTA-AF7p-1 uptake. (e) Variation of tumour uptake of ⁶⁸Ga-DOTA-AF7p-1 along the PET imaging study. (f) Variation of kidneys and liver uptakes of ⁶⁸Ga-DOTA-AF7p-1 along the PET imaging study.

Figure 4

CAPAN-2-tumour-bearing mice injected with ⁸⁹Zr-DFO-LEM2/15. (a) Representative PET/CT images of a mouse with subcutaneous CAPAN-2 xenograft injected with ⁸⁹Zr-DFO-LEM2/15 acquired at 1 and 7 days after injection. Tumour locations are indicated by white arrows. (b) Immunohistochemistry of tumour tissue from xenografted mice. MT1-MMP was detected using LEM2/15 antibody. Scale bar: 100 µm. (c) Tumour uptake (expressed as %ID/g) of ⁸⁹Zr-DFO-LEM2/15 as quantified by PET imaging. (d) Tumour-to-blood and tumour-to-background ratios derived from PET images. (e) Liver and bone uptake of ⁸⁹Zr-DFO-LEM2/15 as quantified by PET imaging at different times after injection.

Figure 5

Orthotopic patient-derived xenografted mice injected with ⁸⁹Zr-DFO-LEM2/15. (a) Representative PET/CT images of orthotopic PDX and control mice injected with ⁸⁹Zr-DFO-LEM2/15 acquired at 1 and 7 days after injection. Tumour locations are indicated by white arrows. (b) Immunohistochemistry studies of pancreas tissues derived from orthotopic PDX and control mice. MT1-MMP was detected using LEM2/15 antibody. Scale bar: 50 µm. (c) Tumour uptake (expressed as %ID/g) of ⁸⁹Zr-DFO-LEM2/15 as quantified by PET imaging. (d) Tumour-to-blood and tumour-to-background ratios derived from PET images. (e) Liver and bone uptake of ⁸⁹Zr-DFO-LEM2/15 as quantified by PET imaging at different times after injection in PDX and control mice.