Small-animal PET imaging of human epidermal growth factor receptor type 2 expression with site-specific 18F-labeled protein scaffold molecules.
ABSTRACT Human epidermal growth factor receptor type 2 (HER2) is a well-established tumor biomarker that is overexpressed in a wide variety of cancers and that serves as a molecular target for therapeutic intervention. HER2 also serves as a prognostic indicator of patient survival and as a predictive marker of the response to antineoplastic therapy. The development of (18)F-labeled biomolecules for PET imaging of HER2 (HER2 PET) is very important because it may provide a powerful tool for the early detection of HER2-positive tumor recurrence and for the monitoring of HER2-based tumor treatment.
In this study, anti-HER2 monomeric and dimeric protein scaffold molecules [Z(HER2:477) and (Z(HER2:477))(2), respectively] were radiofluorinated at a reasonable radiochemical yield (13%-18%) by use of site-specific oxime chemistry. The resulting radiofluorinated protein scaffold molecules were then evaluated as potential molecular probes for small-animal HER2 PET by use of a SKOV3 tumor-bearing mouse model.
The 4-(18)F-fluorobenzaldehyde conjugated aminooxy-protein scaffolds [(18)F-N-(4-fluorobenzylidene)oxime (FBO)-Z(HER2:477) and (18)F-FBO-(Z(HER2:477))(2)] both displayed specific HER2-binding ability in vitro. Biodistribution and small-animal PET imaging studies further revealed that (18)F-FBO-Z(HER2:477) showed rapid and high SKOV3 tumor accumulation and quick clearance from normal tissues, whereas (18)F-FBO-(Z(HER2:477))(2) showed poor in vivo performance (low tumor uptake and tumor-to-normal tissue ratios). The specificity of (18)F-FBO-Z(HER2:477) for SKOV3 tumors was confirmed by its lower uptake on pretreatment of tumor-bearing mice with the HER2-targeting agents Z(HER2) and trastuzumab. Moreover, small-animal PET imaging studies revealed that (18)F-FBO-Z(HER2:477) produced higher-quality tumor imaging than (18)F-FBO-(Z(HER2:477))(2). (18)F-FBO-Z(HER2:477) could clearly identify HER2-positive tumors with good contrast.
Overall, these data demonstrate that (18)F-FBO-Z(HER2:477) is a promising PET probe for imaging HER2 expression in living mice. It has a high potential for translation to clinical applications. The radiofluorination method developed can also be used as a general strategy for the site-specific labeling of other proteins with (18)F. The protein scaffold molecules used here are attractive for the further development of PET probes for other molecular targets.
- [show abstract] [hide abstract]
ABSTRACT: Epidermal growth factor receptor 1 (EGFR) is an attractive target for radionuclide therapy of head and neck carcinomas. Affibody molecules against EGFR (Z(EGFR)) show excellent tumor localizations in imaging studies. However, one major drawback is that radiometal-labeled Affibody molecules display extremely high uptakes in the radiosensitive kidneys which may impact their use as radiotherapeutic agents. The purpose of this study is to further explore whether radiometal-labeled human serum albumin (HSA)-Z(EFGR) bioconjugates display desirable profiles for the use in radionuclide therapy of EGFR-positive head and neck carcinomas. The Z(EFGR) analog, Ac-Cys-Z(EGFR:1907), was site-specifically conjugated with HSA. The resulting bioconjugate 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A)-HSA-Z(EGFR:1907) was then radiolabeled with either (64)Cu or (177)Lu and subjected to in vitro cell uptake and internalization studies using the human oral squamous carcinoma cell line SAS. Positron emission tomography (PET), single photon emission computed tomography (SPECT), and biodistribution studies were conducted using SAS-tumor-bearing mice. Cell studies revealed a high (8.43 ± 0.55 % at 4 h) and specific (0.95 ± 0.09 % at 4 h) uptake of (177)Lu-DO3A-HSA-Z(EGFR:1907) as determined by blocking with nonradioactive Z(EGFR:1907). The internalization of (177)Lu-DO3A-HSA-Z(EGFR:1907) was verified in vitro and found to be significantly higher than that of (177)Lu-labeled Z(EFGR) at 2-24 h of incubation. PET and SPECT studies showed good tumor imaging contrasts. The biodistribution of (177)Lu-DO3A-HSA-Z(EGFR:1907) in SAS-tumor-bearing mice displayed high tumor uptake (5.1 ± 0.44 % ID/g) and liver uptake (31.5 ± 7.66 % ID/g) and moderate kidney uptake (8.5 ± 1.08 % ID/g) at 72 h after injection. (177)Lu-DO3A-HSA-Z(EGFR:1907) shows promising in vivo profiles and may be a potential radiopharmaceutical for radionuclide therapy of EGFR-expressing head and neck carcinomas.European Journal of Biochemistry 03/2012; 17(5):709-18. · 3.42 Impact Factor
- Journal of Nuclear Medicine 07/2013; 50(3):417-425. · 5.77 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Development of reporter genes for multimodality molecular imaging is highly important. In contrast to the conventional strategies which have focused on fusing several reporter genes together to serve as multimodal reporters, human tyrosinase (TYR) - the key enzyme in melanin production - was evaluated in this study as a stand-alone reporter gene for in vitro and in vivo photoacoustic imaging (PAI), magnetic resonance imaging (MRI) and positron emission tomography (PET). Human breast cancer cells MCF-7 transfected with a plasmid that encodes TYR (named as MCF-7-TYR) and non-transfected MCF-7 cells were used as positive and negative controls, respectively. Melanin targeted N-(2-(diethylamino)ethyl)-(18)F-5-fluoropicolinamide was used as a PET reporter probe. In vivo PAI/MRI/PET imaging studies showed that MCF-7-TYR tumors achieved significant higher signals and tumor-to-background contrasts than those of MCF-7 tumor. Our study demonstrates that TYR gene can be utilized as a multifunctional reporter gene for PAI/MRI/PET both in vitro and in vivo.Scientific Reports 03/2013; 3:1490. · 2.93 Impact Factor