title: Evaluation of prognostic integrin α2β1 PET tracer and concurrent targeting delivery using focused ultrasound for brain glioma detection.
abstract: The ability to early detect and assess the treatment response of recurrent and/or disseminated metastatic glioblastoma is critical for the effective management of this group of patients. Accumulating experimental evidence indicates that integrin α2β1 might be a prognostic biomarker for advanced phenotype of cancers. In this study, a novel (68)Ga-labeled integrin α2β1-targeted PET tracer (68)Ga-NOTA-PEG4-cyclo (GDGEAyK) ((68)Ga-A2B1) was designed and evaluated for the potential prognostic imaging of glioblastoma tumor in preclinical model. To prospectively verify the prognostic value of integrin α2β1, the in vitro Western blot and flow cytometry studies were performed to validate the integrin expression level of human glioblastoma (U87MG) cells. Extremely high expression level of integrin α2β1 justifies its role as a potential targeting marker. Thus, (68)Ga-A2B1 positron emission tomography was performed in subcutaneous U87MG tumor bearing athymic mice at 15 min postinjection after injection of 7-8MBq tracers. The receptor targeting specificity was confirmed in a competition blocking experiment. The tumor uptake of (68)Ga-A2B1 in the control and blockage groups was 1.57 ± 0.13 %ID/g (n = 3) and 0.96 ± 0.23 %ID/g** (n = 3), respectively. However, because of the quick renal washout rate and labile nature of peptide tracers in circulation conditions, the focus ultrasound (FUS) mediated delivery method was adopted to enhance tumor uptake and retention of tracers. To test the FUS delivery efficacy in vivo, three experimental arms were designed as follows: tumor bearing mice were administrated with (68)Ga-A2B1 only or microbubbles (MBs) with FUS treatment ((68)Ga-A2B1 + FUS + MBs) or embedded (68)Ga-A2B1-microbubbles ((68)Ga-A2B1-MBs + FUS) followed with FUS sonication. The average radioactivity accumulation within a tumor was quantified from the multiple region of interest volumes using the %ID/g value and was analyzed in accordance with the ex vivo autoradiographic and pathologic data. The significant tumor uptake in (68)Ga-A2B1 + FUS +MBs group (n = 6) and (68)Ga-A2B1-MBs + FUS group (n = 4) following FUS treatment were calculated as 2.25 ± 0.50 %ID/g* and 2.6 ± 0.49 %ID/g**, comparing with (68)Ga-A2B1 only group 1.48 ± 0.42 %ID/g (n = 10). These results suggest that there is significant difference in (68)Ga-A2B1 tumor uptake by FUS treatment either with or without tracer integration with microbubbles, which demonstrate a promising delivery strategy and critical multimodal setting for phenotyping imaging of aggressive glioma tumor. In conclusion, (68)Ga labeled (68)Ga-A2B1 allows noninvasive imaging of tumor-associated α2β1 expression and can be embedded in MB lipid shell for enhanced delivery and controlled release by sonoporation.
authors.affiliation: Center for Advanced Molecular Imaging and Translation (CAMIT), Chang Gung Memorial Hospital , Taoyuan 333, Taiwan.
authors.forename: Yi-Hsiu
authors.initials: YH
authors.lastname: Chung
authors.forename: Po-Hung
authors.initials: PH
authors.lastname: Hsu
authors.forename: Chiun-Wei
authors.initials: CW
authors.lastname: Huang
authors.forename: Wen-Chuan
authors.initials: WC
authors.lastname: Hsieh
authors.forename: Feng-Ting
authors.initials: FT
authors.lastname: Huang
authors.forename: Wen-Chi
authors.initials: WC
authors.lastname: Chang
authors.forename: Han
authors.initials: H
authors.lastname: Chiu
authors.forename: Shih-Ting
authors.initials: ST
authors.lastname: Hsu
authors.forename: Tzu-Chen
authors.initials: TC
authors.lastname: Yen
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000000981:diagnostic imaging*; D001932:Brain Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology*; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D018450:Disease Progression; D004569:Electroencephalography; D005910:Glioma / Q000000981:diagnostic imaging*; D057809:HEK293 Cells; D006801:Humans; D038982:Integrin alpha2beta1 / Q000737:chemistry*; D008297:Male; D051379:Mice; D009368:Neoplasm Transplantation; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D014018:Tissue Distribution; D014463:Ultrasonography
chemical_list: D038982:Integrin alpha2beta1; D010455:Peptides; D019275:Radiopharmaceuticals
keywords: Glioblastoma; PET imaging; focus ultrasound; integrin α2β1