Early identification of esophageal cancer patients who are responding or resistant to combined chemoradiotherapy may lead to individualized therapeutic approaches and improved clinical outcomes. We ...assessed the ability of 3'-deoxy-3'-(18)F-fluorothymidine positron emission tomography (FLT-PET) to detect early changes in tumor proliferation after chemoradiotherapy in experimental models of esophageal carcinoma.
The in vitro and ex vivo tumor uptake of (3)HFLT in SEG-1 human esophageal adenocarcinoma cells were studied at various early time points after docetaxel plus irradiation and validated with conventional assessments of cellular proliferation thymidine (Thd) and Ki-67 and (18)FFLT micro-PET imaging. Imaging-histologic correlation was determined by comparing spatial Ki-67 and (18)FFLT distribution in autoradiographs. Comparison with fluorodeoxyglucose (FDG) was done in all experiments.
In vitro (3)HFLT and (3)HThd uptake rapidly decreased in SEG-1 cells 24 hours after docetaxel with a maximal reduction of over 5-fold (P = 0.005). The (3)HFLT tumor-to-muscle uptake ratio in xenografts declined by 75% compared with baseline (P < 0.005) by 2 days after chemoradiotherapy, despite the lack of change in tumor size. In contrast, the decline of (3)HFDG uptake was gradual and less pronounced. Tumor uptake of (3)HFLT was more closely correlated with Ki-67 expression (r = 0.89, P < 0.001) than was (3)HFDG (r = 0.39, P = 0.08). Micro-PET images depicted similar trends in reduction of (18)FFLT and (18)FFDG tumor uptake. Autoradiographs displayed spatial correlations between (18)FFLT uptake and histologic Ki-67 distribution in preliminary studies.
FLT-PET is suitable and more specific than FDG-PET for depicting early reductions in tumor proliferation that precede tumor size changes after chemoradiotherapy.
Drug uptake and anabolism by tumors are prerequisites of response to 5-fluorouracil (5-FU). Positron emission tomography (PET) with 5-(18)FFU (PET/5-(18)FFU) is potentially useful for noninvasive ...measurement of these processes, but is severely hampered by rapid catabolism of 5-(18)FFU in vivo. This study explored the combined use of PET/5-(18)FFU and eniluracil (5-ethynyluracil), a potent inhibitor of 5-FU catabolism, to measure the pharmacokinetics of 5-FU uptake and metabolism in tumors. Rats bearing a s.c. implanted rat colon tumor were given eniluracil and injected i.v. with 5-(18)FFU. Dynamic PET and arterial blood sampling were performed 0-2 h. Tumors (n = 5) were then rapidly excised, frozen, and analyzed for labeled metabolites by high performance liquid chromatography. Tumor TACs were analyzed by compartmental modeling. Compartments were identified with molecular species by comparison with ex vivo assays. Tumor extracellular fluid volume was determined in a separate group of rats. Kinetic analysis indicated partial trapping of (18)F within tumors 0-2 h after injection. Tumor time-activity curves conformed closely to a catenary 3-compartment, 5-parameter model. The model yielded values for 5-FU clearance from plasma into the trap that agreed closely with those reported previously for gastrointestinal tumors from a PET/5-(18)FFU + eniluracil study in humans. Tumor extracellular fluid volume as measured with (99m)Tc DTPA (3.1 +/- 0.2) x 10(-1) ml/g; n = 5 agreed well with the distribution volume for compartment 1 of the 3-compartment, 5-parameter model (3.7 +/- 0.3) x 10(-1) ml/g; n = 5, thus indicating that compartment 1 corresponds to tumor extracellular space. Compartment 3 closely matched the combined magnitudes of (18)F fluoronucleoside (FN) triphosphates and macromolecules in all of the cases, and compartment 2 was quantitatively consistent with the sum of intracellular 5-FU, FNs, and FN mono- and diphosphates. These observations show that PET/5-(18)FFU combined with an inhibitor of 5-FU catabolism and compartmental modeling is capable of quantifying the following for 5-FU in tumors: distribution volume in the extracellular space, cell transport, size and turnover rate of an intermediate intracellular pool, and formation of a long-lived intracellular pool comprising FN triphosphates + macromolecules. Such information could be useful in predicting tumor response to 5-FU, formulating protocols that increase delivery of 5-FU into tumor cells, and modulating 5-FU kinetics to overcome tumor resistance.
Radiolabeling of the MRI contrast agent 1-2-(β-galactopyranosyloxy)propyl-4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane with
111In, and its evaluation is reported. Radiolabeling was ...performed in acetate buffer with 50–78% radiochemical yield.
In vitro studies revealed that the asialoglycoprotein receptor-poor cell line MH1C1 has low uptake, while the receptor-rich cell lines BNL-CL2 and Hep G2 have higher uptake.
In vivo, the uptake of the compound in receptor-rich organ liver was very high. Blocking the receptor in vivo, reduced liver uptake by 90% suggesting that the compound localizes in receptor-enriched tissues by binding to the asialoglycoprotein receptor.
2'-Deoxy-2'-flouro-5-methyl-1-beta-D-arabinofuranosyluracil (FMAU) has been evaluated in HT-29 cells as a potential positron emission tomography (PET) radiotracer for imaging HSV-tk gene expression ...in vivo. In vitro experiments demonstrate that the accumulation of 14C-FMAU in HSV-tk-expressing cells is 2.4-fold (p < .02), 4.0-fold (p < .001), and 5.3-fold (p < .001) higher than the wild-type cells at 1, 3, and 5 hr, respectively. In vivo studies revealed that the tumor uptake in HSV-tk-expressing cells was 2.3-fold (p < .001), 3.0-fold (p < .001), and 5.5-fold (p < .001) higher than the control cells at 1, 2, and 5 hr, respectively. FMAU was found to be more sensitive compared to our earlier studies using 9-(3-18F-fluoro-1-hydroxy-2-propoxy)methyl-guanine (18F-FHPG) and 9-(4-18F-fluoro-3-hydroxy-methylbutyl)guanine (18F-FHBG) in the same cell lines, although, the specificity was less than FHBG. These results suggest that while FMAU labeled with PET isotopes may be useful for imaging HSV-tk-expressing tumors in vivo, multitracer studies across additional tumor models are necessary in order to identify an optimal PET radiotracer.
Recent studies in antibody catabolism have identified residues at the CH2-CH3 interface of the IgG heavy chain critical for serum persistence of immunoglobulins. Amino acid substitutions in the Fc ...region of murine IgG1 were shown to drastically accelerate antibody clearance in mice. Our laboratory has previously described a human-mouse chimeric TNT-3 (chTNT-3) monoclonal antibody directed against a universal nuclear antigen that has potential for the radioimmunotherapy of many solid tumors. In the current study, we engineered a chTNT-3 mutant containing a single amino acid substitution, to determine whether a more rapid clearance profile would make the antibody suitable for diagnostic imaging.
A single amino acid substitution in the CH2 domain of the human gamma1 constant region was made by polymerase chain reaction mutagenesis. High-level expression was achieved using the Glutamine Synthetase Gene Amplification System, and the chTNT-3 mutant was purified by protein A affinity and ion-exchange chromatography. A radioimmunoassay was performed to examine antigen binding, and in vivo studies were undertaken to evaluate clearance and tumor targeting in human tumor xenograft models.
The chTNT-3 mutant retained the high affinity of chTNT-3, with a binding constant of 1.5 x 10(-9) mol/L. The mutant was eliminated rapidly from BALB/c mice, with a beta-phase half-life of 33.8 h, compared to 134.2 h for chTNT-3. Moreover, biodistribution studies in human colon tumor-bearing nude mice reflected this accelerated clearance. Tumor levels of the mutant were, respectively, 65%, 39%, and 36% of the tumor levels achieved with the parental chTNT-3 6, 12, and 24 h postinjection. The rapid clearance of the chTNT-3 mutant from the blood resulted in higher tumor-to-normal organ ratios for many normal tissues. Imaging of tumor-bearing mice with 99mTc-labeled chTNT-3 mutant demonstrated early visualization of tumors in 3 different solid tumor xenograft models.
The accelerated clearance produced by a single amino acid substitution in the Fc region of chTNT-3 leads to improved imaging in tumor-bearing mice. These studies suggest that a rapidly clearing antibody generated by this approach may be useful for the immunoscintigraphy of human tumors.
Abstract Introduction 18 F-Labeled analogues of thymidine have demonstrated efficacy for PET imaging of cellular proliferation. We have synthesized two 18 F-labeled N3 -substituted thymidine ...analogues, N3 -18 Ffluoroethyl thymidine (N3 -18 F-FET) and N3 -18 Ffluoropropyl thymidine (N3 -18 F-FPrT), and performed preliminary PET imaging studies in tumor-bearing mice. Methods Thymidine was converted to its 3′,5′- O -bis-tetrahydropyranyl ether, which was then converted to the N3 -ethyl and propyl-substituted mesylate precursors. Reactions of these mesylate precursors with n-Bu4 N18 F or K18 F/kryptofix followed by acid hydrolysis and HPLC purification yielded N3 -18 F-FET and N3 -18 F-FPrT, respectively. Subcutaneous (sc) xenografts of H441 human non–small cell lung cancer were established in two groups of mice (each n =6). Micro-PET images of the tumor-bearing animals were acquired after intravenous injection of N3 -18 F-FET or N3 -18 F-FPrT (3700 KBq/animal). Results The radiochemical yields were 2–12% (d.c.) for N3 -18 F-FET and 30–38% (d.c.) for N3 -18 F-FPrT. Radiochemical purity was >99% and calculated specific activity was >74 GBq/μmol at the end of synthesis. The accumulation of N3 -18 F-FET and N3 -18 F-FPrT in the tumor tissue at 2 h postinjection was 1.81±0.78 and 2.95±1.14 percent injected dose per gram (%ID/g), respectively; tumor/muscle ratios were 5.57±0.82 and 7.69±2.18, respectively; the unidirectional influx rates ( Ki ) were 0.013 and 0.018 ml/g per minute, respectively. Conclusion Two novel 18 F- N3 -substituted thymidine analogues have been synthesized in good yields, high purity and high specific activity. Preliminary in vivo studies demonstrated the efficacy of these 18 F- N3 -substituted thymidine analogues for PET imaging of tumors.
Positron Emission Tomography (PET) is a nuclear medicine imaging technique that is widely used in early detection and treatment follow up of many diseases, including cancer. This modality requires ...positron-emitting isotope labeled biomolecules, which are synthesized prior to perform imaging studies. Fluorine-18 is one of the several isotopes of fluorine that is routinely used in radiolabeling of biomolecules for PET; because of its positron emitting property and favorable half-life of 109.8 min. The biologically active molecule most commonly used for PET is 2-deoxy-2-(18)F-fluoro-β-D-glucose ((18)F-FDG), an analogue of glucose, for early detection of tumors. The concentrations of tracer accumulation (PET image) demonstrate the metabolic activity of tissues in terms of regional glucose metabolism and accumulation. Other tracers are also used in PET to image the tissue concentration. In this review, information on fluorination and radiofluorination reactions, radiofluorinating agents, and radiolabeling of various compounds and their application in PET imaging is presented.
Positron Emission Tomography (PET) is a nuclear medicine imaging technique that is widely used in early detection and treatment follow up of many diseases, including cancer. This modality requires ...positron-emitting isotope labeled biomolecules, which are synthesized prior to perform imaging studies. Fluorine-18 is one of the several isotopes of fluorine that is routinely used in radiolabeling of biomolecules for PET; because of its positron emitting property and favorable half-life of 109.8 min. The biologically active molecule most commonly used for PET is 2-deoxy-2-
18
F-fluoro-β-D-glucose (
18
F-FDG), an analogue of glucose, for early detection of tumors. The concentrations of tracer accumulation (PET image) demonstrate the metabolic activity of tissues in terms of regional glucose metabolism and accumulation. Other tracers are also used in PET to image the tissue concentration. In this review, information on fluorination and radiofluorination reactions, radiofluorinating agents, and radiolabeling of various compounds and their application in PET imaging is presented.
![Radiosynthesis of 6-([18F]f...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0362-4803/small "Radiosynthesis of 6-([18F]fluoroacetamido)-1-hexanoicanilide ([18F]FAHA) for PET imaging of histone deacetylase (HDAC)")
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