The discovery and characterization of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor potentiator N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242).

A unique tetrahydrofuran ether class of highly potent α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor potentiators has been identified using rational and structure-based drug design. An acyclic lead compound, containing an ether-linked isopropylsulfonamide and biphenyl group, was pharmacologically augmented by converting it to a conformationally constrained tetrahydrofuran to improve key interactions with the human GluA2 ligand-binding domain. Subsequent replacement of the distal phenyl motif with 2-cyanothiophene to enhance its potency, selectivity, and metabolic stability afforded N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242, 3), whose preclinical characterization suggests an adequate therapeutic index, aided by low projected human oral pharmacokinetic variability, for clinical studies exploring its ability to attenuate cognitive deficits in patients with schizophrenia.

The synthesis and in vivo evaluation of [18F]PF-9811: a novel PET ligand for imaging brain fatty acid amide hydrolase (FAAH).

INTRODUCTION: Fatty acid amide hydrolase (FAAH) is responsible for the enzymatic degradation of the fatty acid amide family of signaling lipids, including the endogenous cannabinoid (endocannabinoid) anandamide. The involvement of the endocannabinoid system in pain and other nervous system disorders has made FAAH an attractive target for drug development. Companion molecular imaging probes are needed, however, to assess FAAH inhibition in the nervous system in vivo. We report here the synthesis and in vivo evaluation of [(18)F]PF-9811, a novel PET ligand for non-invasive imaging of FAAH in the brain. METHODS: The potency and selectivity of unlabeled PF-9811 were determined by activity-based protein profiling (ABPP) both in vitro and in vivo. [(18)F]PF-9811 was synthesized in a 3-step, one-pot reaction sequence, followed by HPLC purification. Biological evaluation was performed by biodistribution and dynamic PET imaging studies in male rats. The specificity of [(18)F]PF-9811 uptake was evaluated by pre-administration of PF-04457845, a potent and selective FAAH inhibitor, 1h prior to radiotracer injection. RESULTS: Biodistribution studies show good uptake (SUV~0.8 at 90 min) of [(18)F]PF-9811 in rat brain, with significant reduction of the radiotracer in all brain regions (37%-73% at 90 min) in blocking experiments. Dynamic PET imaging experiments in rat confirmed the heterogeneous uptake of [(18)F]PF-9811 in brain regions with high FAAH enzymatic activity, as well as statistically significant reductions in signal following pre-administration of the blocking compound PF-04457845. CONCLUSIONS: [(18)F]PF-9811 is a promising PET imaging agent for FAAH. Biodistribution and PET imaging experiments show that the tracer has good uptake in brain, regional heterogeneity, and specific binding as determined by blocking experiments with the highly potent and selective FAAH inhibitor, PF-04457845.

Harderian gland adenectomy: a method to eliminate confounding radio-opacity in the assessment of rat brain metabolism by 18F-fluoro-2-deoxy-D-glucose positron emission tomography.

The 18F isotope of fluoro-2-deoxy-D-glucose (FDG) is a radiotracer commonly used in positron emission tomography (PET) for determining regional metabolic activity in the brain. However, in rats and many other species with nictitating membranes, harderian glands located just behind the eyes aggressively incorporate 18F-FDG to the extent that PET images of the brain become obscured. This radioactive spillover, or 'partial volume error,' combined with the limited spatial resolution of microPET scanners (1.5 to 2 mm) may markedly reduce the ability to quantify neuronal activity in frontal brain structures. Theoretically, surgical removal of the harderian glands before 18F-FDG injection would eliminate the confounding uptake of the radioactive tracer and thereby permit visualization of glucose metabolism in the frontal brain. We conducted a pilot study of unilateral harderian gland adenectomy, leaving the contralateral gland intact for comparison. At 1 wk after surgery, each rat was injected intravenously with 18F-FDG, and 40 min later underwent brain microPET for 20 min. Review of the resulting images showed that the frontal cortex on the surgical side was defined more clearly, with only background 18F-FDG accumulation in the surgical bed. Activity in the frontal cortex on the intact side was obscured by intense accumulation of 18F-FDG in the harderian gland. By reducing partial volume error, this simple surgical procedure may become a valuable tool for visualization of the frontal cortex of rat brain by 18F-FDG microPET imaging.

A positron-emitting internal marker for identification of normal tissue by positron emission tomography: phantom studies and validation in patients.

PURPOSE: This study evaluated in a phantom model and verified in patients with lung cancer whether the use of an internal positron-emitting labeled marker could localize a critical structure by positron emission tomography (PET) imaging and verify multimodality image registration. MATERIALS AND METHODS: An initial device and method were developed to demonstrate by dedicated PET the location of the normal esophagus in a phantom and in three patients using a column of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) solution between proximal and distal gas phases in polyurethane tubing. The device was assessed for possible loss of radioactivity. PET, CT and PET-CT fusion imaging followed. RESULTS: X-rays of the marker device showed a continuous fluid column. No leakage of contents was detected. The internal marker in the phantom and in patients allowed visualization by PET of the esophagus, and verified an image registration algorithm. CONCLUSIONS: A positron-emitting internal marker was constructed, demonstrated to retain tracer, and shown to be capable of verifying an image registration algorithm and identifying a critical structure, the esophagus, by PET in a phantom and in patients.

Update on hybrid conjugate-view SPECT tumor dosimetry and response in 131I-tositumomab therapy of previously untreated lymphoma patients.

UNLABELLED: A study of the use of (131)I-labeled tositumomab, preceded by an unlabeled tositumomab predose, for therapy of 76 previously untreated non-Hodgkin's lymphoma patients has been completed at the University of Michigan. Fifty-two of the 76 treated patients were imaged once during therapy with SPECT to assist in dosimetric estimation. In this article, the patient's average tumor dose, estimated by a hybrid method using that SPECT, is compared with the same statistic estimated by pretherapy conjugate views. METHODS: The SPECT activity-quantification procedure used 3-dimensional CT-to-SPECT image registration. Daily pretherapy conjugate-view images provided the shape of the time-activity curve for the hybrid dose estimation. RESULTS: With the hybrid method, the mean of the patient's average tumor dose over 8 patients using only their axillary tumors (162 cGy) was very significantly lower (P < 0.0001) than the mean over 47 patients using only their evaluated chest, abdominal, and pelvic tumors (624 cGy) for unknown reasons. Excluding axillary tumors as a best case for prediction, there still was considerable overlap in the distribution of a patient's average tumor dose over 38 patients who went on to a complete response (CR) and that from 9 patients who went on to a partial response (PR) using either method. However, a high value of the patient's average tumor dose was correctly associated with a CR for 15 of 16 patients (94%) with hybrid SPECT and for 9 of 12 patients (75%) with conjugate views. Also, the mean of the patient's average tumor dose for the CR patients was larger than the mean for PR patients; the P value was 0.18 with hybrid SPECT and 0.25 with conjugate views. A multiple logistic regression analysis combining the dose, tumor burden, and level of lactate dehydrogenase as explanatory variables for response did not yield statistical significance with either method. CONCLUSION: Patients with evaluated tumors that receive the highest tumor radiation dose are most likely to achieve a CR. Dosimetry based on a combination of pretherapy conjugate views and intratherapy SPECT provides somewhat better correspondence between the patient's average tumor dose and his or her degree of response compared with dosimetry from pretherapy conjugate views alone. Statistical significance for the correspondence is not reached either with the dosimetric method or with either method in combination with the tumor burden and level of lactate dehydrogenase.

FDG metabolism and uptake versus blood flow in women with untreated primary breast cancers.

The aim of this study was to determine the relationship between tumor blood flow and glucose utilization in women with untreated primary breast carcinomas. Noninvasive determinations of blood flow and glucose utilization with positron emission tomography (PET) were performed in 101 regions of tumor from nine women with untreated primary breast carcinoma. [(15)O]H(2)O PET scans of tumor blood flow were compared with fluorine-18 fluoro-2-deoxy- D-glucose (FDG) PET scans of tumor glucose metabolism. Modeling of multiple parameters was undertaken and flow and glucose utilization compared. Mean whole-tumor blood flow was 14.9 ml dl(-1) min(-1), but ranged from 7.6 to 29.2 ml dl(-1) min(-1). Mean whole-tumor standardized uptake value corrected for lean body mass, SUV-lean (50-60 min), was 2.32+/-0.19 while mean K(i) was 1.2 ml dl(-1) min(-1) for FDG. SUV-lean and blood flow were strongly correlated (r=0.82, P=0.007) as were K(1) for FDG and flow (r=0.84, P=0.004). In these women with untreated breast cancers, FDG uptake (SUV-lean) and tumor blood flow are strongly correlated. The slope of FDG uptake versus blood flow appears higher at low flow rates, suggesting the possible presence of areas of tumor hypoxia.

Expression of hexokinase II and Glut-1 in untreated human breast cancer.

Expressions of HKII and Glut-1 were studied in untreated primary human breast cancers by immunohistochemistry. 79% of the breast cancers were HKII-positive and 61% were Glut-1-positive. Average positive malignant cell areas were 66 +/- 41% for HKII and 29 +/- 36% for Glut-1. HKII staining was cytoplasmic, suggesting mitochondrial localization with no variations in staining intensities. Glut-1 staining was heterogeneous, cytoplasmic and membranous and varied with histology and tumor stage. Cells expressing HKII did not always express Glut-1 and vice versa. Increased FDG-uptake appeared to be associated with increased Glut-1 expression (P = 0.021), but not with HKII expression (p = 0.6).FDG uptake in breast cancer tissue appears to be associated with the extent of immunodetectable expression of Glut-1, but not that of HKII, and FDG uptake may differ between individual tumors depending on tumor stage and histology.

Volume reduction versus radiation dose for tumors in previously untreated lymphoma patients who received iodine-131 tositumomab therapy. Conjugate views compared with a hybrid method.

BACKGROUND: A Phase II study of previously untreated patients with malignant low grade follicular lymphoma given a combination of unlabeled tositumomab and tositumomab labeled with iodine-131 has recently been completed. The responses of these patients have been characterized, and for some of them tumor dosimetry during therapy has been estimated not only by pretherapy tracer conjugate views but also by a hybrid method. METHODS: Available patients were studied if they had had a pelvic or abdominal tumor evaluation by single photon emission computed tomography (SPECT) and achieved a partial response. A tumor outlined on the iodine-131 conjugate-view images was called a composite tumor. Its volume estimate came from multiple, not necessarily contiguous, regions of interest (ROI) on the pretherapy computed tomography (CT) scan. Its radiation dose was estimated from the weeklong series of pretherapy images and standard Medical Internal Radiation Dose methods. Computed tomography ROI were also grouped into smaller, contiguous volumes that defined individual tumors. Their radiation doses were estimated by the hybrid method. This method employed the activity measured for each individual tumor by a single intratherapy SPECT scan, as well as the tumor's volume, to individually normalize the composite time-activity curve as appropriate. The individual normalization factors then converted the composite radiation dose to radiation doses for individual tumors. Reduction in tumor volume was calculated for both composite and individual tumors at 12 weeks posttherapy. RESULTS: For 14 composite tumors in 10 patients, the median pretherapy volume was 170 cm(3). Application of a sigmoidal curve function to the plot of volume reduction versus radiation absorbed dose resulted in degeneration of the curve into a straight line with a negative slope. There was no statistical significance in the relationship (P = 0.73). For 43 individual tumors, the median pretherapy tumor volume was 26 cm(3). The plot of volume reduction versus dose was fairly well fit by a sigmoidal curve, and the relationship approached statistical significance (P = 0.06). The representation assigned 56% of the shrinkage to the effects of unlabeled tositumomab. For the subset of individual tumors with a pretherapy volume less than 10 cm(3) from 6 patients (n = 15), the relationship was significant (P = 0.03). The sigmoidal representation assigned only 12% of the shrinkage to unlabeled tositumomab, as contrasted with 72% for tumors with pretherapy volume greater than 10 cm(3). CONCLUSIONS: For patients who attained a partial response, analysis of individual tumors by a hybrid dosimetric method led to a dependence between volume reduction at 12 weeks and radiation dose that tended to be significant. The same was not true with dosimetry of composite tumors based on pretherapy conjugate views alone. It appeared that volume reductions from both unlabeled antibody and radiation dose were important in tositumomab therapy of lymphoma patients, with unlabeled antibody relatively more important for larger tumors.

Comparison of attenuation-corrected and non-corrected FDG-PET images for axillary nodal staging in newly diagnosed breast cancer.

PURPOSE: The aim of this work is to compare the accuracy of non-attenuation-corrected (NAC) and attenuation-corrected (AC) PET images using 2-deoxy-2-[18F]fluoro-D-glucose (FDG) in assessment of the axilla in patients with newly-diagnosed, untreated, primary breast cancers, and to determine the frequency of extra-axillary findings. PATIENTS AND METHODS: FDG-PET was performed in 36 patients with breast cancer one hour following the intravenous injection of approximately 370 MBq of FDG. Patients were imaged prior to axillary dissection to prospectively confirm the presence or absence of axillary metastases. NAC and AC images were separately and independently reviewed in a blinded fashion by two readers. Imaging results were compared with final diagnoses obtained by surgery and pathology. RESULTS: Ninety-six positive axillary lymph nodes in 15 patients were histopathologically confirmed by surgery. The average areas under the ROC curve for NAC and AC image were 0.682 and 0.721, respectively. In patient-based analysis, the sensitivity in interpreting NAC images for the presence of metastases was low (53.3%) and comparable to that of AC images (46.7%). The specificity of NAC image was high (85.7%), but tended to be lower than that in AC (95.2%). The overall diagnostic accuracy for detecting axillary involvement in AC images (75.0%) was comparable to that of NAC images (72.2%). Extra-axillary disease was found in three patients. CONCLUSION: NAC images were comparable to AC images, although there were more false positive results with the NAC images. While AC PET has high specificity in this application, it appears insufficiently sensitive to use these methods to avoid axillary tissue sampling, when negative. Extra-axillary findings, while infrequent, may be quite important. Examination of both NAC and AC images is advised when assessing possible metastatic breast cancer to the axilla using PET.

Reproducibility of common semi-quantitative parameters for evaluating lung cancer glucose metabolism with positron emission tomography using 2-deoxy-2-[18F]fluoro-D-glucose.

PURPOSE: Positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-D-glucose (FDG) has been used for various cancers, but reproducibility of common utilized semi-quantitative parameters, such as the maximal single pixel standardized uptake value (SUV) and effective glycolytic volume (EGV), remains unknown. Knowledge of precision is essential for applying these parameters to treatment monitoring. The purpose of this investigation was to assess the precision of PET results obtained by repeated examinations of patients with untreated lung cancer. PATIENTS AND METHODS: Ten patients with lung cancer underwent two PET examinations within a week with no intervening treatment. The reproducibility of three parameters:((1) maximal SUV of 1 x 1 pixel anywhere in the tumor, calculated on the basis of predicted lean body mass [SULmax]; (2) highest average SUV at 4 x 4 pixels in the tumor adjusted by predicted lean body mass [SULmean]; and (3) EGV calculated by multiplying SUL by tumor volume), using PET images obtained at 50-60 min post-injection, were examined. Plasma glucose, insulin and free fatty acid levels were also monitored. RESULTS: The SULmax, SULmean, and EGV were measured with a mean +/- S.D. difference of 11.3% +/- 8.0, 10.1% +/- 8.2, and 10.1% +/- 8.0%, respectively. By multiplying SUL by plasma glucose concentration, the mean differences were slightly reduced to 7.2% +/- 5.8, 6.7% +/- 6.2, and 9.5% +/- 8.2, respectively. CONCLUSION: These data indicate that commonly used semi-quantitative indices of glucose metabolism on PET show high reproducibly. This supports their use in sequential quantitative analysis in PET, such as in treatment response monitoring.

Diabetes Decreases FDG Accumulation in Primary Lung Cancer.

OBJECTIVE: To compare kinetics and accumulation of 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) in primary lung cancer between diabetic and non-diabetic patients using positron emission tomography (PET).METHODS: Five diabetic patients and 21 non-diabetic patients underwent dynamic FDG-PET to image untreated primary lung cancers. Standardized uptake value normalized for lean body mass (SUL) was determined in tumor, blood, muscle, and lung. A 3-compartment metabolic model was applied to FDG kinetics in tumors in 24 of 26 patients.RESULTS: At the time of PET scans, serum glucose levels were elevated in 5 diabetic patients, while 21 non-diabetic patients showed normal glucose levels. In diabetic patients, tumor SUL, tumor/blood and tumor/muscle SUL ratios were significantly decreased (P < 0.02) and also tumor/lung SUL ratio declined (P = 0.064), as compared to non-diabetic patients. In addition, the rate constant for FDG phosphorylation (k3) and influx constant (Ki) in diabetic patients were significantly lower than those in non-diabetic patients (P < 0.02).CONCLUSION: In diabetic patients, the rate of FDG accumulation in tumors is decreased, and tumor targeting with FDG is impaired. Diabetes may reduce the sensitivity of FDG-PET for lung cancer detection.

FDG-PET Determination of Metabolically Active Tumor Volume and Comparison with CT.

PURPOSE: To determine if tumor volume, in addition to tumor metabolic activity, can be assessed noninvasively from attenuation-corrected fluorodeoxyglucose (FDG)-PET imaging using a semiautomated method.METHODS: CT and FDG-PET scanning was performed in 14 patients, eight with newly diagnosed untreated malignancies, and six patients with progressive non-Hodgkin's lymphoma (NHL). Tumor volume was determined from CT scans by summation of manually drawn regions of interest over tumor. Tumor volume was determined at FDG-PET with a semiautomated method based on quantitation of (18)F uptake and thresholding.RESULTS: Mean tumor volume was 187 +/- 189 cm(3). Tumor volume determined by means of PET and CT was strongly correlated in the patients with untreated tumors. Correlation was weaker for all patients, mainly due to one previously treated patient with a large disparity between CT and metabolically active tumor volumes at FDG-PET, presumably due to tumor necrosis.CONCLUSIONS: Tumor volume determination by FDG-PET was strongly correlated with tumor volumes determined by anatomic imaging with CT. FDG-PET appears comparable to CT in measuring untreated tumor volumes of this size. FDG-PET may be superior to anatomic techniques in assessing metabolically active tumor volume, and warrants further study in this role.