Journal: Nuclear medicine and biology
PURPOSE: Development of a heptamethine cyanine based tumor-targeting PET imaging probe for noninvasive detection and diagnosis of breast cancer. METHODS: Tumor-specific heptamethine-cyanine DOTA conjugate complexed with Cu-64 (PC-1001) was synthesized for breast cancer imaging. In vitro cellular uptake studies were performed in the breast cancer MCF-7 and noncancerous breast epithelial MCF-10A cell lines to establish tumor specificity. In vivo time-dependent fluorescence and PET imaging of breast tumor xenografts in mice were performed. Blood clearance, biodistribution, and tumor-specific uptake and plasma binding of PC-1001 were quantified. Tumor histology (H&E staining) and fluorescence imaging were examined. RESULTS: PC-1001 displayed similar fluorescence properties (ε=82,880cm(-1)M(-1), E(x)/E(m)=750/820nm) to the parental dye. Time-dependent cellular accumulation indicated significantly higher probe uptake (>2-fold, 30min) in MCF-7 than MCF-10A cells and the uptake was observed to be mediated by organic anion transport peptides (OATPs) system. In vivo studies revealed that PC-1001 has desirable accumulation profile in tumor tissues, with tumor versus muscle uptake of about 4.3 fold at 24h and 5.8 fold at 48h post probe injections. Blood half-life of PC-1001 was observed to be 4.3±0.2h. Microscopic fluorescence imaging of harvested tumor indicated that the uptake of PC-1001 was restricted to viable rather than necrotic tumor cells. CONCLUSIONS: A highly efficient tumor-targeting PET/fluorescence imaging probe PC-1001 is synthesized and validated in vitro in MCF-7 breast cancer cells and in vivo in mice breast cancer xenograft model.
To improve the synthesis and quality control of carbon-11 labeled radiopharmaceuticals, we report the fully automated loop syntheses of [(11)C]raclopride and [(11)C]DASB using ethanol as the only organic solvent for synthesis module cleaning, carbon-11 methylation, HPLC purification, and reformulation.
INTRODUCTION: Click chemistry, particularly the Huisgen 1,3-dipolar cycloaddition of an alkyne with an azide, has quickly become popular for site-specific radiolabeling. Recently, strain-promoted click chemistries have been developed, eliminating the need for potentially toxic copper catalysts. This study presents radiolabeling of an α(v)β(6) integrin targeting peptide (A20FMDV2) via strain-promoted click using a fluorine-18 prosthetic group, and in vitro and in vivo evaluation. METHODS: The radiotracer was prepared from and N(3)-PEG(7)-A20FMDV2 (ethanol; 10min; 35-45°C). HPLC-purified and formulated radiotracer 1 was evaluated in vitro by cell binding (DX3puroβ6, α(v)β(6)-positive; and DX3puro, α(v)β(6)-negative control) and serum stability, and in vivo using PET/CT imaging and biodistribution studies in mice. RESULTS: The radiotracer 1 was readily prepared and purified (from 2: 40±4min including HPLC, 11.9±3.2% decay corrected isolated radiochemical yield, >99% radiochemical purity, n=4) and displayed good stability (1h: >99%, saline; 94.6%, serum). Strong α(v)β(6)-targeted binding was observed in vitro (DX3puroβ6 cells, 15min: 43.2% binding, >6:1 for DX3puroβ6:DX3puro). In the mouse model DX3puroβ6-tumor binding was low (1h: 0.47±0.28% ID/g, 4h: 0.14±0.09% ID/g) and clearing from the bloodstream was via the renal and hepatobiliary routes (urine: 167±84% ID/g at 1h, 10.3±4.8% ID/g at 4h; gall bladder: 95±33% ID/g at 1h, 63±11% ID/g at 4h). CONCLUSION: Copper-free, strain-promoted click chemistry is an attractive, straightforward approach to radiolabeling. Although the [(18)F]FBA-C(6)-ADBIO-based prosthetic group did not interfere with α(v)β(6)-targeted binding in vitro, it did influence the pharmacokinetics, possibly due to its size and lipophilic nature.
In considering the challenges of approaches to clinical imaging, we are faced with choices that sometimes are impacted by rather dogmatic notions about what is a better or worse technology to achieve the most useful diagnostic image for the patient. For example, is PET or SPECT most useful in imaging any particular disease dissemination? The dictatorial approach would be to choose PET, all other matters being equal. But is such a totalitarian attitude toward imaging selection still valid? In the face of new receptor targeted SPECT agents one must consider the remarkable specificity and sensitivity of these agents. (99m)Tc-Tilmanocept is one of the newest of these agents, now approved for guiding sentinel node biopsy (SLNB) in several solid tumors. Tilmanocept has a Kd of 3×10(-11)M, and it specificity for the CD206 receptor is unlike any other agent to date. This coupled with a number of facts, that specific disease-associated macrophages express this receptor (100 to 150 thousand receptors), that the receptor has multiple binding sites for tilmanocept (>2 sites per receptor) and that these receptors are recycled every 15min to bind more tilmanocept (acting as intracellular “drug compilers” of tilmanocept into non-degraded vesicles), gives serious pause as to how we select our approaches to diagnostic imaging. Clinically, the size of SLNs varies greatly, some, anatomically, below the machine resolution of SPECT. Yet, with tilmanocept targeting, the SLNs are highly visible with macrophages stably accruing adequate (99m)Tc-tilmanocept counting statistics, as high target-to-background ratios can compensate for spatial resolution blurring. Importantly, it may be targeted imaging agents per se, again such as tilmanocept, which may significantly shrink any perceived chasm between the imaging technologies and anchor the diagnostic considerations in the targeting and specificity of the agent rather than any lingering dogma about the hardware as the basis for imaging approaches. Beyond the elements of imaging applications of these agents is their evolution to therapeutic agents as well, and even in the neo-logical realm of theranostics. Characteristics of agents such as tilmanocept that exploit the natural history of diseases with remarkably high specificity are the expectations for the future of patient- and disease-centered diagnosis and therapy.
The goal of this study was to prepare a synthetic peptide derived from breast tumor associated antigen and to evaluate its potential as a breast cancer imaging agent.
[99mTc]duramycin is a SPECT tracer for cell death imaging. We evaluated the impact of kit formulation, purification and species difference on the pharmacokinetic profile and cell death targeting properties of [99mTc]duramycin in order to define the optimal conditions for (pre-)clinical use.
Derived from heavy chain only camelid antibodies, ~15-kDa single-domain antibody fragments (sdAbs) are an attractive platform for developing molecularly specific imaging probes and targeted radiotherapeutics. The rapid tumor accumulation and normal tissue clearance of sdAbs might be ideal for use with 211At, a 7.2-h half-life α-emitter, if appropriate labeling chemistry can be devised to trap 211At in cancer cells after sdAb binding. This study evaluated two reagents, [211At]SAGMB and iso-[211At]SAGMB, for this purpose.
Detection of vulnerable plaques is critically important for the selection of appropriate treatment and/or the prevention of atherosclerosis and ensuing cardiovascular diseases. In order to clarify the utility of [11C]acetate for atherosclerosis imaging, we determined the uptake and metabolism of acetate by in vitro studies using rabbit atherosclerotic arteries and [14C]acetate.
Heat-denatured 99mTc-labeled red blood cells (RBCs) are used for detecting splenic tissues with scintigraphy. The present study aimed to evaluate the feasibility of using heat-denatured [18F]fluorodeoxyglucose ([18F]FDG)-labeled RBCs in detecting splenic tissues using positron emission tomography (PET) in rats.
Gastrin releasing peptide receptors (GRPRs) are significantly over-expressed on a large proportion of prostate cancers making them prime candidates for receptor-mediated nuclear imaging by PET. Recently, we synthesized a novel bifunctional chelator (BFC) bearing hydroxamic acid arms (DOTHA2). Here we investigated the potential of a novel DOTHA2-conjugated, 64Cu-radiolabeled GRPR peptide antagonist, [D-Phe6-Sta13-Leu14-NH2]bombesin(6-14) (DOTHA2-PEG-RM26) to visualize prostate tumors by PET imaging.