Introduction: Distinguishing glioblastoma multiforme (GBM) tumor cells from normal brain remains a significant clinical challenge that limits the efficacy of treatment planning and resection of GBM. Developing agents that specifically target GBM for both non-invasive and intraoperative imaging is an attractive strategy to guide maximal safe resection and other therapy strategies to improve the prognosis for patients with GBM. Matrix metalloproteinase (MMP)-14 is a membrane-bound collagenase that is overexpressed in GBM with negligible expression in normal brain, presenting MMP-14 as an attractive biomarker for imaging GBM. These studies explored the utility of a novel peptide probe containing an MMP-14 binding sequence, an MMP-14-activatable near infrared fluorescence (NIRF) reporter, and a chelate for labeling with positron emission tomography (PET) radionuclides for dual-modality imaging of GBM in preclinical models.
Methods and Results: Immunofluorescence, western blot, and gel zymography studies showed varying in vitro expression and activity of MMP-14 in D54, U87, and U251 GBM cell lines. At 24 h after i.v. injection of the peptide in athymic nude mice bearing s.c. xenografts of the GBM cell lines, NIRF signals in the tumors correlated with the cells’ in vitro expression of MMP-14. At 4 h after i.v. injection of the 64Cu-labeled peptide in mice bearing orthotopic patient derived xenograft (PDX) GBM tumors, PET/CT imaging showed accumulation in the intracranial tumors that was significantly reduced (p<0.05) by co-injecting an excess of the non-labeled peptide as a blocking agent. There was a linear correlation (p<0.05) between in vivo PET and ex vivo NIRF signals in the PDX tumor regions. Microscopic immunohistochemistry showed co-localization of MMP-14 expression and NIRF signal in PDX tumors.
Conclusions: The novel peptide probes successfully targeted MMP-14 for imaging GBM models in mice, warranting continued development of the probes for image-guided resection of GBM in future preclinical studies.