Purpose: There is currently no effective noninvasive method for accurate molecular typing of triple negative breast cancer (TNBC) except needle biopsy. Glucoregulated Protein 78 (GRP78) is overexpressed in TNBC cells and tumors which closely related to the invasion, metastasis, and drug resistance of cancer. Meanwhile, it has been verified that VAP peptide bind specifically to GRP78 in vitro and in vivo. In this study, we constructed a GRP78-targeted molecular probe Ga-68-radiolabeled DOTA-VAP conjugate ([68Ga]DOTA-VAP) based on VAP peptide, and evaluated its potential to distinguish TNBC from non-TNBC tumors.
Procedures: DOTA-VAP was synthesized and then radiolabeled with Ga-68 to obtain [68Ga]DOTA-VAP. The expression of GRP78 in TNBC MDA-MB-231 and non-TNBC MCF-7 cells was validated by Western Blot, and cell binding or uptake experiments with both [68Ga]DOTA-VAP and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) were also performed. Biodistribution analysis and positron emission tomography (PET) imaging of [68Ga]DOTA-VAP were carried out in subcutaneous MDA-MB-231 and MCF-7 human breast cancer tumor models with [18F]FDG PET imaging as comparison.
Results: [68Ga]DOTA-VAP was prepared with high radiochemical purity which showed excellent stability in vitro. The MDA-MB-231 tumors were clearly visualized by [68Ga]DOTA-VAP PET imaging with a low background, except for the relatively high liver uptake. Cells and tumors of MDA-MB-231 could be distinguished from MCF-7 by [68Ga]DOTA-VAP instead of [18F]FDG. Biodistribution results were consistent with the imaging results. The blocking study with excess cold peptide showed significantly reduced tumor uptake, which indicated the specificity of [68Ga]DOTA-VAP targeting MDA-MB-231 tumors in vivo.
Conclusions: GRP78-targeted PET imaging with [68Ga]DOTA-VAP provided an effective approach for the noninvasive accurate classification of TNBC from other breast cancer subtypes comparing with [18F]FDG. GRP78 may be a potential target for the diagnosis and treatment of TNBC. For clinical transformation, efforts should be made to overcome deficiencies of [68Ga]DOTA-VAP such as relative high uptake in normal tissues.
Keywords: GRP78; Molecular classification; PET imaging; Triple negative breast cancer; VAP peptide.