We recently developed the radiotracer 4-(3-iodophenyl)amino-7-(2-2-{2-(2-2-{2-((18)F-fluoroethoxy)-ethoxy}-ethoxy-ethoxy)-ethoxy}-ethoxy-quinazoline-6-yl-acrylamide) ((18)F-PEG(6)-IPQA) for ...noninvasive detection of active mutant epidermal growth factor receptor kinase-expressing non-small cell lung cancer xenografts in rodents. In this study, we determined the pharmacokinetics, biodistribution, metabolism, and radiation dosimetry of (18)F-PEG(6)-IPQA in nonhuman primates.
Six rhesus macaques were injected intravenously with 141 ± 59.2 MBq of (18)F-PEG(6)-IPQA, and dynamic PET/CT images covering the thoracoabdominal area were acquired for 30 min, followed by whole-body static images at 60, 90, 120, and 180 min. Blood samples were obtained from each animal at several time points after radiotracer administration. Radiolabeled metabolites in blood and urine were analyzed using high-performance liquid chromatography. The (18)F-PEG(6)-IPQA pharmacokinetic and radiation dosimetry estimates were determined using volume-of-interest analysis of PET/CT image datasets and blood and urine time-activity data.
(18)F-PEG(6)-IPQA exhibited rapid redistribution and was excreted via the hepatobiliary and urinary systems. (18)F-PEG(6) was the major radioactive metabolite. The critical organ was the gallbladder, with an average radiation-absorbed dose of 0.394 mSv/MBq. The other key organs with high radiation doses were the kidneys (0.0830 mSv/MBq), upper large intestine wall (0.0267 mSv/MBq), small intestine (0.0816 mSv/MBq), and liver (0.0429 mSv/MBq). Lung tissue exhibited low uptake of (18)F-PEG(6)-IPQA due to the low affinity of this radiotracer to wild-type epidermal growth factor receptor kinase. The effective dose was 0.0165 mSv/MBq. No evidence of acute cardiotoxicity or of acute or delayed systemic toxicity was observed. On the basis of our estimates, diagnostic dosages of (18)F-PEG(6)-IPQA up to 128 MBq (3.47 mCi) per injection should be safe for administration in the initial cohort of human patients in phase I clinical PET studies.
The whole-body and individual organ radiation dosimetry characteristics and pharmacologic safety of diagnostic dosages of (18)F-PEG(6)-IPQA in nonhuman primates indicate that this radiotracer should be acceptable for PET/CT studies in human patients.
Abstract Introduction It is important to identify all circulating metabolites, including free fluoride, for accurate pharmacokinetic modeling of 18 F-labeled radiotracers. We sought to determine the ...most efficient method to detect and quantify low levels of free 18 Ffluoride in biological samples. Methods Low levels of 18 Ffluoride were analyzed using two methods: (A) an ion-exchange cartridge and gamma counting, and (B) radio-HPLC, to compare the detection limits of these two analytical methods. Twenty microliters of 18 Ffluoride solution was loaded onto an ion-exchange cartridge, then eluted with 20% MeCN/water (5 ml) and radioactivity trapped in the cartridge counted on a gamma counter. 18 FFluoride was also determined in plasma and urine from mice injected with 18 F-labeled thymidine analogues using Method A. Results The detection sensitivity of Method A was 9.4-fold higher than that of Method B (0.075±0.004 vs. 0.71±0.02 nCi). With Method A, 18 Ffluoride was determined in plasma for 18 FFLT, 18 FFMAU, 18 FFEAU and N3 -18 FFPrT as 1.4±0.31% ( n =4), 0.17±0.49% ( n =3), 4.88±1.62% ( n =3) and 12.94±0.48% ( n =4), respectively. The amount of 18 Ffluoride determined in the urine was 11.49±1.60% ( n =4) from 18 FFLT, 5.36±2.34% ( n =3) from 18 FFMAU, 13.57±1.96% ( n =3) from 18 FFEAU and 11.19±1.98% ( n =4) from N3 -18 FFPrT. Conclusion Low levels of 18 Ffluoride in biological samples can be detected and quantified using an ion-exchange cartridge and gamma counting. This methodology is simple, accurate and superior to the standard use of radio-HPLC on a C18 column for metabolite analysis, and it should be useful in pharmacokinetic modeling for animal imaging studies using an 18 F-labeled radiotracer and PET.
Abstract Introduction Noncatabolized thymidine analogs are being developed for use in imaging DNA synthesis. We sought to relate a labeling index measured by immunohistochemical staining ...bromodeoxyuridine (BUdR) technique to the uptake of11 C 2′-fluoro-5-methyl-1-β- d -arabinofuranosyluracil (FMAU) measured with positron emission tomography (PET) in a brain tumor model. Methods Adult beagles ( n =8) with implanted brain tumors received 11 CFMAU and dynamic imaging with arterial sampling. Six dogs were then infused with BUdR (200 mg/m2 ) and sacrificed. Tumor time–activity curves (TACs) obtained from computed-tomography-defined regions of interest were corrected for partial volume effects and crosstalk from brain tissue. Tissue was analyzed for the percentage of tumor volume occupied by viable cells and by viable cells in S-phase as identified by BUdR staining. PET/11 CFMAU and BUdR were compared by linear regression analysis and analysis of variance, as well as by a nonparametric rank correlation test. Results Tumor standardized uptake values (SUVs) and tumor-to-contralateral-brain uptake ratios at 50 min were 1.6±0.4 and 5.5±1.2 ( n =8; mean±S.E.M.), respectively. No11 C-labeled metabolites were observed in the blood through 60 min. Tumor TACs were well described with a three-compartment/four-parameter model ( k4 =0) and by Patlak analysis. Parametric statistical analysis showed that FMAU clearance from plasma into tumor Compartment 3 ( KFMAU ) was significantly correlated with S-phase percent volume ( P =.03), while tumor SUV was significantly correlated with both S-phase percent volume and cell percent volume ( P =.02 and .03, respectively). Patlak slope, KFMAU and tumor SUV were equivalent with regard to rank correlation analysis, which showed that tumor uptake and trapping of FMAU were correlated with the volume density of dividing cells ( P =.0003) rather than nondividing cells ( P =.3). Conclusions Trapping of 11 CFMAU correlated with tumor growth rate, as measured by direct tissue analysis with BUdR in a canine brain tumor model, suggesting that 11 CFMAU is useful for the imaging of cell proliferation in cancers.
2'-Deoxy-2'-fluoro-5-methyl-1-beta-D-arabinofuranosyluracil (FMAU), 9-(4-fluoro-3-hydroxy-methyl-butyl)guanine (FHBG) and 9-(3-fluoro-1-hydroxy-2-propoxy)methyl-guanine (FHPG) have been evaluated in ...a human breast cancer model as potential radiotracers for PET imaging of HSV1-tk gene expression. In vitro accumulation of 14CFMAU, 18FFHBG, and 18FFHPG in HSV1-tk-expressing cells was 14- to 16-fold (p <.001), 9- to 13-fold (p <.001), and 2- to 3-fold (p <.05) higher than tk-negative control cells, respectively, between 30 and 240 min. Accumulation of FMAU and FHBG in vector-transduced cells was 10- to 14-fold and 6- to 10-fold higher than wild-type cells, respectively. At 2 hr, uptake of (14)CFMAU in tkpositive cells was 6.3-fold and 60-fold higher than 18FFHBG and 18FFHPG, respectively. In vivo, tumor uptake of 14CFMAU in HSV1-tk-expressing cells was 3.7-fold and 5.5-fold (p <.001) higher than tk-negative control cells at 1 and 2 hr, respectively. Tumor uptake of 18FFHBG was 4.2-fold and 12.6-fold higher (p <.001) than tk-negative cells at the same time points. Incorporation of 14CFMAU in tk-positive tumor was 18-fold and 24-fold higher (p <.001) than 18FFHBG at 1 and 2 hr, respectively. Micro-PET images support the biodistribution results and indicate that both 18FFMAU and 18FFHBG are useful for imaging HSV1-tk expression in breast cancer. Although FMAU demonstrates higher total incorporation (%dose/g) in tumor tissue compared with the other tracers, FHBG is superior in terms of specific accumulation in transfected cells at later time points.
Abstract Objective Previous studies have shown that the accumulation level of FMAU in tumor is proportional to its proliferation rate. This study demonstrated that 2′-deoxy-2′-18 Ffluoro-β- d ...-arabinofuranosyluracil (18 FFMAU) is a promising PET probe for noninvasively monitoring the therapeutic efficacy of 6% PEGylated liposomal vinorelbine (lipo-VNB) in a subcutaneous murine NG4TL4 sarcoma mouse model. Methods Female syngenic FVB/N mice were inoculated with NG4TL4 cells in the right flank. After tumor size reached 150 ± 50 mm3 (day 0), lipo-VNB (5 mg/kg) was intravenously administered on days 0, 3 and 6. To monitor the therapeutic efficacy of lipo-VNB, 18 FFMAU PET was employed to evaluate the proliferation rate of tumor, and it was compared with that observed from 18 FFDG/18 Ffluoroacetate PET. The expression of proliferating cell nuclear antigen (PCNA) in tumor during treatment was determined by semiquantitative analysis of immunohistochemical staining. Results A significant inhibition (p < 0.001) in tumor growth was observed on day 3 after a single dose treatment. The tumor-to-muscle ratio ( T/M ) derived from 18 FFMAU-PET images of lipo-VNB-treated group declined from 2.33 ± 0.16 to 1.26 ± 0.03 after three doses of treatment, while that of the control remained steady. The retarded proliferation rate of lipo-VNB-treated sarcoma was confirmed by PCNA immunohistochemistry staining. However, both 18 FFDG and 18 Ffluoroacetate microPET imaging did not show significant difference in T/M between the therapeutic and the control groups throughout the entire experimental period. Conclusion Lipo-VNB can effectively impede the growth of NG4TL4 sarcoma. 18 FFMAU PET is an appropriate modality for early monitoring of the tumor response during the treatment course of lipo-VNB.
Introduction
Epidermal growth factor receptor (EGFR)-targeted therapies with antibodies and small molecular EGFR kinase inhibitors have shown poor efficacy in unselected populations of patients with ...advanced non-small cell lung carcinomas (NSCLC). In contrast, patients with overexpression of EGFR and activating mutations in EGFR kinase domain demonstrated improved responses to EGFR kinase inhibitors. Therefore, we have developed a novel radiotracer,
18
FF-PEG
6
-IPQA for PET imaging of EGFR expression-activity in NSCLC, and have described its radiosynthesis and
in vitro
evaluation in two NSCLC cell lines with wild-type and L858R active mutant EGFR.
Methods
A mesylate precursor was synthesized in multiple steps and radiofluorinated using K
18
F/Kryptofix. The fluorinated intermediate compound was reduced to an amino derivative then treated with acryloyl isobutyl carbonate, followed by purification by HPLC to obtain the desired product.
Results
Decay-corrected radiochemical yields of
18
FF-PEG
6
-IPQA were 3.9–17.6%, with an average of 9.0% (
n
= 11). Radiochemical purity was >97% with specific activity of 34 GBq/μmol (mean value,
n
= 10) at the end of synthesis. The accumulation of
18
FF-PEG
6
-IPQA in H3255 cells was ten-fold higher than in H441 cells, despite a two-fold lower level of activated phospho-EGFR expression in H3255 cells compared with H441 cells. The accumulation of
18
FF-PEG
6
-IPQA in both cell lines was significantly decreased in the presence of a small molecular EGFR kinase inhibitor, Iressa, at 100 μM concentration in culture medium.
Conclusion
We have synthesized
18
FF-PEG
6
-IPQA and demonstrated its highly selective accumulation in active mutant L858R EGFR-expressing NSCLC cells
in vitro
. Further
in vivo
studies are warranted to assess the ability of PET imaging with
18
FF-PEG
6
-IPQA to discriminate the active mutant L858R EGFR-expressing NSCLC that are sensitive to therapy with EGFR kinase inhibitors vs NSCLC that express wild-type EGFR.
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