Fluorothymidine Research Articles

Comparison of FLT-PET and FDG-PET for Visualization of Head and Neck Squamous Cell Cancers

We compared 3'[F-18]fluoro-3'-deoxythymidine (FLT) positron emission tomography (PET) and 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) for PET visualization of head and neck squamous cell cancers (HNSCCs) and evaluated which might better reflect proliferative activity as indicated by the Ki-67 index. A total of 43 patients with HNSCCs were examined with FLT-PET and FDG-PET. The PET images were evaluated qualitatively for regions of focally increased metabolism and for semiquantitative analysis the maximum standardized uptake value (SUV) was calculated. For depiction of primary tumours, the sensitivity of both approaches was 100%. The mean (± SD) SUV for FLT (5.65 ± 2.96) was significantly lower than that for FDG (10.9 ± 4.91; p < 0.0001). No significant differences were found for the T category. However, the mean (± SD) FLT SUV was significantly higher in poorly than in well-differentiated tumours (6.49 ± 3.13 vs. 4.2 ± 2.08; p < 0.04). Similarly, FDG SUVs in poorly and moderately differentiated tumours (12.72 ± 4.8 and 11.46 ± 4.64) were significantly higher than in well-differentiated tumours (7.45 ± 3.51; p < 0.004 and p < 0.02). No significant correlation was observed with the Ki-67 index for either. FLT-PET showed as high a sensitivity as FDG-PET for the detection of primary HNSCC lesions, although uptake of FLT was significantly lower than that of FDG.

Investigation of the pharmacokinetics of 3′-deoxy-3′-[18F]fluorothymidine uptake in the bone marrow before and early after initiation of chemoradiation therapy in head and neck cancer

The kinetics of the bone marrow uptake of 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) before and early after initiation of chemoradiation therapy was investigated in patients with head and neck cancer. Fourteen subjects with head and neck cancer underwent FLT positron emission tomography (PET) at baseline and after 10 Gy of radiation therapy. Thirteen subjects also received one cycle of platinum-based chemotherapy before the second FLT PET. Kinetic parameters, including the flux constant based on compartmental analysis (K(FLT)) and the Patlak constant (K(Patlak)) for cervical marrow, were calculated. Standardized uptake values (SUVs) for the cervical marrow (inside the radiation field) and lumbar spine marrow (outside the radiation field) were also determined. There was a significant drop in FLT uptake in the bone marrow inside the radiation field. Mean pretreatment uptake values for the cervical spine were SUV=3.08+/-0.66, K(FLT)=0.045+/-0.016 min(-1) and K(Patlak)=0.039+/-0.013 min(-1). After treatment, these values were SUV=0.74+/-0.19, K(FLT)=0.011+/-0.005 min(-1) and K(Patlak)=0.005+/-0.002 min(-1). Compartmental analysis revealed a significant drop in k(3) in irradiated cervical marrow. FLT uptake in the bone marrow outside the radiation field exhibited a significantly smaller decrease. There is a marked decrease in FLT uptake in irradiated bone marrow after 10 Gy of radiation therapy to the head and neck. The drop in FLT uptake in irradiated marrow is due to a significant decrease in the net phosphorylation rate of FLT.

PET/CT with 18F-FLT Is Unlikely to Cause Significant Hepatorenal or Hematologic Toxicity

TO THE EDITOR: Therapeutic doses of cold fluorothymidine (FLT) used as antiviral therapy have been shown to cause renal, hepatic, and hematologic toxicity within 4 wk of treatment ( [1][1] ). This observed toxicity was of concern when investigational studies using 18F-FLT were initiated in the

Abstract 5220: Early prediction of tumor response to APO866 treatment with 3′-deoxy-3′-[18F]fluorothymidine positron emission tomography in human ovary cancer xenografts in mice

Abstract Introduction: APO866 is a new anti-tumor compound found to inhibit nicotinamide phosphoribosyltransferase (NAMPT), an enzyme involved in the biosynthesis of NAD. The compound has anti-tumor effect in several pre-clinical tumor models and is currently in several clinical phase II studies. 3′-deoxy-3′-[18F]fluorothymidine (FLT) is a tracer used to assess cell proliferation in vivo. The aim of the study was to evaluate if FLT positron emission tomography (PET) may be used to monitor early anti-proliferative effects of APO866. Methods: In vivo uptake of FLT in human ovary cancer xenografts in mice (A2780) was studied at various time points after APO866 treatment (15 mg/kg ip twice daily for 7 days) was initiated. Baseline FLT scans were made before either APO866 (n=10 tumors) or vehicle (n=6 tumors) was injected and repeated after 24 hours (2 treatments), 48 hours (4 treatments) and 7 days (14 treatments). Tumor volume was followed with computed tomography (CT) during the experiment. FLT uptake was quantified using small animal PET/CT. One hour after iv injection of 10 MBq FLT, static PET scans were performed for 10 minutes and region of interests (ROIs) covering whole tumors were defined on PET/CT images for calculation of standard uptake values (SUV). Comparison within treatment groups was performed using paired t-tests and between control and APO866 groups with unpaired t-tests. All p-values were corrected for multiple comparisons using the Bonferroni algorithm. P&amp;lt;0.05 was considered significant. Results: Tumors treated with APO866 had volumes that were 122% (24h), 129 % (48h) and 88% (day 7) relative to baseline volumes day 0. In the control group tumor volumes were 123% (24h), 150% (48h) and 318% (day 7) relative to baseline volumes day 0. Tumor volume between groups were significantly different at day 7 (P=0.006). APO866 treatment caused significant decrease in uptake of FLT at 24 hours (−23%; P&amp;lt;0.001), 48 hours (−29%; P&amp;lt;0.001) and day 7 (−25%; P=0.0013) after treatment start compared to baseline uptake. In the control group uptake of FLT did not change. Conclusions: APO866 treatment caused a significant decrease in FLT uptake 24 and 48 hours after injection of first dose. The early reductions in tumor cell proliferation preceded decrease in tumor volume on day 7. Our data indicate that FLT PET is promising for early non-invasive assessment of APO866 anti-tumor effects. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5220.

Abstract SY20-03: Novel radiotracers for clinical molecular imaging in oncology

Abstract In cancer, molecular imaging (MI) can be thought of as imaging the key molecules and molecular based events that are fundamental to promoting and maintaining the malignant state. Although MI is multimodality, the focus of this discussion will be on the use of positron emitting radiotracers for Positron Emission Tomography (PET), an imaging methodogy that can bridge the divide between discovery in the laboratory and application in clinical medicine. Modern PET incorporates CT into the same gantry and as PET/CT has rapidly penetrated clinical oncology, providing improved tumor staging and the detection of recurrence.. F[18]-2-flouro-2-deoxy-D-glucose (FDG) and PET is being used to imaging more tha 1 million cancer patients per year in the US along. The biologic basis for the successful use of FDG-PET/CT is as follows. Many cancers exhibit a characteristic biochemical phenotype, which is altered in comparison to tissues from which the neoplasm originated. In particular, tumor tissues often exhibit the “Warburg Effect” which is an accelerated aerobic glyolysis. The reasons behind the Warburg effect are thought to relate to a need for carbon backbones for tumor growth, as well as to control.altered REDOX state within the cell. Other metabolic markers useful in functional imaging of cancer include radiolabeled nucleosides like [F-18]-Fluorothymidine (FLT) for proliferation, and radiolabeled amino acids, like [C-11] methionine for imaging amino acid transport. Molecular imaging in oncology is increasingly being applied for evaluation of treatment response,to radiation and chemotherapy, using FDG, FLT, and F-18 misonidazole (FMISO) a nitroimidazole which is taken up in hypoxic tissues. Molecular imaging is also applied clinically for drug discovery, and a large number of targeted agents have been radiolabeled and are being studied in man. At MSKCC our group has used PET imaging to study targeting at both a basic and clinical level with a variety of drugs and monoclonal antibodies, includine antibodyA33, which recognizes the epithelial marker A33, and antibody cG250 which recognizes carbonic anydrase IX, a marker of clear cell lung cancer and hypoxia. Finally, endocrine responsive maligancies form a fascinating group for which specific receptor directed agents, and natural substrates, may open a window on the biology of human disease including lesion by lesion heterogeneity. In this regard, [F-18]FDHT, an agent targeting androgen receptor, in prostate cancer and [I-124] NaI, for sodium iodide symporter in thyroid cancer, are giving new information about the behavior of human tumors studied in situ. Citation Format: Steven M. Larson. Novel radiotracers for clinical molecular imaging in oncology [abstract]. In: Proceedings of the AACR 101st Annual Meeting 2010; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr SY20-03

Increased Cellular Proliferation in Rat Skeletal Muscle and Tendon in Response to Exercise: Use of FLT and PET/CT

The purpose of this study is to investigate exercise-induced cellular proliferation in rat skeletal muscle/tendon with the use of 3'-[F-18]fluoro-3'deoxythymidine (FLT) and to quantitatively study concomitant changes in the proliferation-associated factor, Ki67. Wistar rats (n = 13) performed 3 days of treadmill running. Cellular proliferation was investigated 3 days before and 48 h after the running exercise with the use of FLT and positron emission tomography/computed tomography (PET/CT). Results were compared to a sedentary control group (n = 10). Image-derived standardized uptake values were calculated for Achilles tendons and calf muscles and compared to gene expression and immunohistochemical evaluations of Ki67. Treadmill running induced increased uptake of FLT uptake in calf muscles (30%; p < 0.001) and in Achilles tendon (21%, p < 0.001). The image-derived results were supported by a correlation in calf muscle to Ki67 (protein and mRNA level), while this coherence was not found in tendon. FLT-PET seems to be a promising tool for imaging of exercise-induced cellular proliferation in musculo-tendinous tissue.

Measuring Tumor Cell Proliferation with 18F-FLT PET During Radiotherapy of Esophageal Squamous Cell Carcinoma: A Pilot Clinical Study

The primary aim of this study was to use serial (18)F-3'-deoxy-3'-fluorothymidine (FLT) PET/CT to measure tumor cell proliferation during radiotherapy of squamous cell carcinoma (SCC) of the esophagus. Twenty-one patients with inoperable locally advanced SCC of the esophagus underwent serial (18)F-FLT PET/CT during radiotherapy. Each patient received a pretreatment scan, followed by 1-3 scans after delivery of 2, 6, 10, 20, 30, 40, 50, or 60 Gy to the tumor. Among the 19 patients who completed radiotherapy without interruption, parameters reflecting (18)F-FLT uptake in the tumor (i.e., maximum tumor standardized uptake value [SUVmax] and proliferation target volume) decreased steadily. All patients demonstrated an almost complete absence of proliferating esophageal tumor after 30 Gy and a complete absence after 40 Gy. In the 2 patients whose radiotherapy course was interrupted, (18)F-FLT uptake in the tumor was greater after the interruption than before the interruption. Marked early reduction of (18)F-FLT uptake in irradiated bone marrow was observed in all patients, even after only 2 Gy. All showed a complete absence of proliferating marrow in irradiated regions after 10 Gy. Both patients who underwent scans after completing the entire radiotherapy course showed no tumor uptake on (18)F-FLT PET/CT but high uptake on (18)F-FDG PET/CT. Pathologic examination of these regions revealed inflammatory infiltrates but no residual tumor. (18)F-FLT uptake can be used to monitor the biologic response of esophageal SCC and normal tissue to radiotherapy. Increased uptake of (18)F-FLT after treatment interruptions may reflect accelerated repopulation. (18)F-FLT PET/CT may have an advantage over (18)F-FDG PET/CT in differentiating inflammation from tumor.

3'-Deoxy-3'-[(18)F]fluorothymidine and O-(2-[(18)F]fluoroethyl)-L-tyrosine PET in Patients with Suspicious Recurrence of Glioma after Multimodal Treatment: Initial Results of a Retrospective Comparative Study.

The purpose of this study was to compare the uptakes and diagnostic accuracies between 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) and O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET) PET in patients with a clinical suspicion of having a recurrence of glioma after multimodality treatment. Thirty-two patients who underwent FLT and FET PET due to abnormal enhancement on magnetic resonance (MR) images were included. According to surgical confirmation or follow-up results, patients were divided into those with therapy-related benign changes (TRBCs) and those with recurrence. Recurrences were divided again into initial low-grade glioma (LGG) and high-grade glioma (HGG). The uptakes of FLT and FET were compared with the maximum standardized uptake value (SUVmax) and lesion-to-normal ratio (LNR). The diagnostic accuracies were compared via a receiver-operating-characteristic (ROC) curve analysis. The LNRs of FLT in recurrences with initial HGG (8.26 ± 5.02) were significantly higher than those in recurrences with initial LGG (3.43 ± 2.14) and TRBC (1.81 ± 0.60). The LNRs of FET in recurrence with initial HGG (2.70 ± 0.48) and LGG (3.03 ± 1.32) were significantly higher than those in the TRBC (1.60 ± 0.47). The areas under the ROC curve (AUCs) of FLT and FET for initial LGG were 0.768 and 0.893, respectively. The AUCs of FLT and FET for initial HGG were 1.000 and 0.964. However, there were no statistical significances. The results for comparing with SUVmax were the same as those with LNR. Uptakes of FLT were different according to initial grade in patients with recurrent glioma, but those of FET were not. However, there were no statistical significances in the diagnostic accuracies according to initial grade between the two tracers in this study.

Kinetic filtering of [18F]Fluorothymidine in positron emission tomography studies

[18F]Fluorothymidine (FLT) is a cell proliferation marker that undergoes predominantly hepatic metabolism and therefore shows a high level of accumulation in the liver, as well as in rapidly proliferating tumours. Furthermore, the tracer's uptake is substantial in other organs including the heart. We present a nonlinear kinetic filtering technique which enhances the visualization of tumours imaged with FLT positron emission tomography (FLT-PET). A classification algorithm to isolate cancerous tissue from healthy organs was developed and validated using 29 scan data from patients with locally advanced or metastatic breast cancer. A large reduction in signal from the liver and heart of 80% was observed following application of the kinetic filter, whilst the majority of signal from both primary tumours and metastases was retained. A scan acquisition time of 60 min has been shown to be sufficient to obtain the necessary kinetic data. The algorithm extends utility of FLT-PET imaging in oncology research.

Changes in [18F]Fluorothymidine Pharmacokinetics Following Capecitabine Treatment in Human Breast Cancer Detected by Positron Emission Tomography.

Abstract Background: Pre-clinical models used by our group have demonstrated that thymidylate synthase (TS) inhibition leads to redistribution of the nucleoside transporter, ENT1, to the cell membrane and hence increases the tissue uptake of [18F]fluorothymidine (FLT).Methods: In this study we assessed, for the first time, the altered pharmacokinetics of FLT in patients following TS inhibition. We analyzed 10 lesions from 6 breast cancer patients by positron emission tomography (PET) before and after treatment with capecitabine.Results: Whereas drug treatment did not alter tumor delivery pharmacokinetic variables or blood flow, tumor FLT retention variables increased with drug treatment in all but one patient. The baseline average standardized uptake value (SUV) at 60 min, rate constant for the net irreversible transfer of radiotracer from plasma to tumor (Ki) and unit impulse response function (IRF) at 60 min were 11.11 x 10-5 m2/ml, 4.38 x 10-2 ml plasma/min/ml tissue and 4.93 x 10-2 /min, respectively. At 1 h after capecitabine, the SUV was 13.55 x 10-5 m2/ml (p=0.004), Ki 7.40 x 10-2 ml plasma/min/ml tissue (p=0.004) and IRF 7.40 x 10-2 /min (p= 0.002).Conclusion: FLT pharmacokinetics did not change in normal tissues suggesting that the effect was largely restricted to tumor (p=0.55). In summary, we have identified FLT-PET retention parameters that could be used in future early clinical studies to measure the pharmacodynamics of TS inhibitors, as well as for identifying patients who are unlikely to benefit from TS inhibition. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 5003.

Abstract CN01-02: Detecting tumor responses to treatment using magnetic resonance imaging and spectroscopy

Abstract CN01-02: Detecting tumor responses to treatment using magnetic resonance imaging and spectroscopy

Abstract A109: BMS-754807, an oral, dual IGF-1R / insulin receptor (IR) inhibitor: Early pharmacodynamic (PD) and positron emission tomography (PET) imaging results from a daily-dose study in cancer subjects

Abstract Background: Inhibiting both IGF-1R and IR signaling may be required to disrupt the malignant phenotype regulated by the receptor family. BMS-754807 is a potent and selective reversible inhibitor of IGF-1R/IR family kinases (IGF-1R, IR; Ki &amp;lt;2nM). In non-clinical studies BMS-754807 is an effective inhibitor in a broad range of human tumor types in vitro and in vivo and demonstrates synergies when combined with cytotoxic and targeted agents. Methods: CA191002 is an ascending multiple-dose study to evaluate safety, tolerability, pharmacokinetics, and pharmacodynamics of BMS-754807 in subjects with solid tumors. Dosing occurs daily 2 hours after a light breakfast and is followed by a 4 hour fast. PD effects on IR are studied by assessments of plasma glucose, insulin and C-peptide. 2-deoxy-2-[18F] fluoro-D-glucose (FDG)- and 3′-deoxy-3′-[18F] fluorothymidine (FLT)-PET imaging is performed both as imaging markers for PD and to assess anti-tumor activity. Results: Sixteen subjects have been treated at daily doses of 4, 10, 20, 30 or 50 mg. No dose limiting toxicities have been observed and dose escalation is ongoing. Duration of dosing was between 8 and 197 days. Preliminary analysis shows dose related increases of plasma glucose, insulin and C-peptide at 2 hours post-dose (Table 1). The range [median] of plasma glucose at all time points was 68 –187 [95], 50 – 168 [103] and 54 –333 [124] mg/dL in subjects treated at the 4, 10 and 20, and 30 and 50 mg dose levels, respectively. 65 PET scans have been collected from 14 subjects. Preliminary analysis shows that 1 subject with osteosarcoma and 1 subject with adenoid cystic carcinoma achieved 57 and 28 % reduction of tracer uptake, respectively, on FLT-PET by D12. Both had stable metabolic disease on FDG-PET by D12 and D56. Conclusion: PD effects of IR inhibition differentiate BMS-754807 from IGF-1R specific agents. PET results suggest anti-tumor activity. Future analysis of PD effects, PET imaging data, safety information and response assessments will provide the basis for a rational selection of subjects and a dose or dose range to be further explored. Dose level (number of subjects) Plasma glucose [mg/dL] D1 and 8 2 h post-dose range [median] Insulin [µU/mL] D1 and 8 2 h post-dose range [median] C-peptide [ng/mL] D1 and 8 2 h post-dose range [median] 4 mg (3) 77 – 101 [94] 2 – 82 [12.5] 0.8 – 7 [1.8] 10 and 20 mg (7) 90 – 144 [97] 27 – 251 [58] 3 – 18 [4.6] 30 and 50 mg (6) 110 – 200 [137] 120 – 361 [210] 5 – 17 [12.1] Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A109.

Altered Tissue 3′-Deoxy-3′-[18F]Fluorothymidine Pharmacokinetics in Human Breast Cancer following Capecitabine Treatment Detected by Positron Emission Tomography

We showed in preclinical models that thymidylate synthase (TS) inhibition leads to redistribution of the nucleoside transporter, ENT1, to the cell membrane and hence increases tissue uptake of [(18)F]fluorothymidine (FLT). In this study, we assessed for the first time the altered pharmacokinetics of FLT in patients following administration of capecitabine, a drug whose mode of action has been reported to include TS inhibition. We analyzed 10 lesions from six patients with breast cancer by positron emission tomography before and after treatment with capecitabine. Although drug treatment did not alter tumor delivery pharmacokinetic variables (K1 and permeability product surface area) or blood flow, tumor FLT retention variables increased with drug treatment in all but one patient. The baseline average standardized uptake value at 60 minutes, rate constant for the net irreversible transfer of radiotracer from plasma to tumor (Ki), and unit impulse response function at 60 minutes were 11.11 x 10(-5) m(2)/mL, 4.38 x 10(-2) mL plasma/min/mL tissue, and 4.93 x 10(-2)/min, respectively. One hour after capecitabine administration, the standardized uptake value was 13.55 x 10(-5) m(2)/mL (P = 0.004), Ki 7.40 x 10(-2) mL plasma/min/mL tissue (P = 0.004), and impulse response function was 7.40 x 10(-2)/min (P = 0.002). FLT pharmacokinetics did not change in normal tissues, suggesting that the effect was largely restricted to tumors (P = 0.55). We have identified FLT positron emission tomography retention parameters that could be used in future early clinical studies to measure the pharmacodynamics of TS inhibitors, as well as for identifying patients who are unlikely to benefit from TS inhibition.

USE OF 3′‐DEOXY‐3′‐[18F]FLUOROTHYMIDINE PET/CT FOR EVALUATING RESPONSE TO CYTOTOXIC CHEMOTHERAPY IN DOGS WITH NON‐HODGKIN'S LYMPHOMA

Imaging and measurement of proliferation with computed tomography (CT) and positron emission tomography (PET) provide a noninvasive method for improved staging and monitoring of response to cancer treatment. We evaluated prospectively the proliferation marker 3'-deoxy-3'[18F] fluorothymidine (FLT) in the context of FLT-PET/CT for detection of early response, confirmation of posttreatment response, and prediction of relapse in dogs with non-Hodgkin's lymphoma. Nine dogs with non-Hodgkin's lymphoma who were scheduled to receive five cycles of an investigational cytotoxic chemotherapy agent were included. All dogs received baseline FLT-PET/CT imaging immediately before chemotherapy. Intent was to repeat imaging with FLT-PET/CT at various time points: group 1 (n = 4), 5 days after initiation of chemotherapy and 3 weeks following the last chemotherapy administration; group 2 (n = 5), before the fourth cycle of chemotherapy and 3 weeks following the last administration. Two dogs in group 2 did not undergo repeat PET/CT. Body mass standardized uptake values (SUV) for FLT were calculated for each dog. Eight dogs had initially increased FLT uptake (mean SUVmax = 9.8 [2.6-22.3]). Mean SUV decreased significantly for the seven dogs that underwent follow-up PET/CT following chemotherapy (mean SUVmax = 3.5 [1.1-7.9], P<0.016). Increased uptake preceded clinical and cytological evidence of relapse in two dogs. Ki-67 immunohistochemistry confirmed decreased proliferation corresponding to decreased SUV in three canine lymph node samples. FLT-PET/CT functional and anatomical imaging shows promise for the evaluation of response to cytotoxic chemotherapy in dogs with non-Hodgkin's lymphoma and for predicting relapse before standard clinical and clinicopathologic confirmation.

Predicting gemcitabine transport and toxicity in human pancreatic cancer cell lines with the positron emission tomography tracer 3′-deoxy-3′-fluorothymidine

The abundance of human equilibrative nucleoside transporter 1 (hENT1) has recently been shown to be a predictive marker of benefit from gemcitabine therapy in patients with pancreatic cancer. Since hENT1 is also important for the uptake of positron emission tomography (PET) tracer 3′-deoxy-3′-fluorothymidine (FLT) in various cultured human cell lines, this study was undertaken to determine if FLT uptake predicts gemcitabine uptake and/or toxicity in a panel of human pancreatic cancer cell lines (Capan-2, AsPC-1, BxPC-3, PL45, MIA PaCa-2, and PANC-1). Capan-2 cells displayed the lowest levels of (1) extracellular nitrobenzylmercaptopurine ribonucleoside (NBMPR) binding, which represents cell-surface hENT1, (2) FLT and gemcitabine uptake during short (1–45 s) and prolonged (1 h) periods, and (3) gemcitabine sensitivity. Exposure to NBMPR (inhibits only hENT1) or dilazep (inhibits hENT1 and hENT2) reduced FLT and gemcitabine uptake and gemcitabine sensitivity, with dilazep having greater effects than NBMPR. Gemcitabine permeation was almost completely mediated, primarily by hENT1 and to a lesser extent by hENT2, whereas FLT permeation included a substantial component of passive diffusion. In five of six cell lines, correlations were observed between (1) FLT and gemcitabine initial rates of uptake, (2) gemcitabine uptake and gemcitabine toxicity, (3) FLT uptake and gemcitabine toxicity, and (4) ribonucleotide reductase subunit M1 expression and gemcitabine toxicity. FLT and gemcitabine uptake were comparable for predicting gemcitabine toxicity in the tested pancreatic cancer cell lines suggesting that FLT PET may provide clinically useful information about tumor gemcitabine transport capacity and sensitivity.

7166 Predicting and preventing thrombo-embolic events in patients with germ-cell tumors receiving cisplatin-based chemotherapy

The Aurora kinases play a key role in mitosis and have recently been identified as attractive targets for therapeutic intervention in cancer. The aim of this study was therefore to investigate the utility of 3′-[18F]fluoro-3′-deoxythymidine (FLT) and 2-deoxy-2-[18F]fluoro-D-glucose (FDG) for assessment of tumor response to the multi-targeted Aurora B kinase inhibitor, TAK-901.Balb/c nude mice bearing HCT116 colorectal xenografts were treated with up to 30 mg/kg TAK 901 or vehicle intravenously twice daily for two days on a weekly cycle. Tumor growth was monitored by calliper measurements and PET imaging was performed at baseline, day 4, 8, 11 and 15. Tumors were harvested at time points corresponding to days of PET imaging for analysis of ex vivo markers of cell proliferation and metabolism together with markers of Aurora B kinase inhibition including phospho-histone H3 (pHH3) and senescence associated β-galactosidase.Tumor growth was inhibited by 60% on day 12 of 30 mg/kg TAK-901 therapy. FLT uptake was significantly reduced by day 4 of treatment and this corresponded with reduction in bromodeoxyuridine and pHH3 staining by immunohistochemistry. All biomarkers rebounded towards baseline levels by the commencement of the next treatment cycle, consistent with release of Aurora B kinase suppression. TAK-901 therapy had no impact on glucose metabolism as assessed by FDG uptake and GLUT1 staining by immunohistochemistry.FLT-PET, but not FDG-PET, is a robust non-invasive imaging biomarker of early HCT116 tumor response to the on-target effects of the multi-targeted Aurora B kinase inhibitor, TAK-901.This is the first report to demonstrate the impact of the multi-targeted Aurora B kinase inhibitor, TAK-901 on tumor FLT uptake. The findings provide a strong rationale for the evaluation of FLT-PET as an early biomarker of tumor response in the early phase clinical development of this compound.

149 Validation of bio-imaging methods for radiotherapy

PET imaging with FluoroDesoxyGlucose (FDG) tracer is clinically used for the definition of Biological Target Volumes (BTVs) for radiotherapy. Recently, new tracers, such as FLuoroThymidine (FLT) or FluoroMisonidazol (FMiso), have been proposed. They provide complementary information for the definition of BTVs. Our work is to fuse multi-tracer PET images to obtain a good BTV definition and to help the radiation oncologist in dose painting. Due to the noise and the partial volume effect leading, respectively, to the presence of uncertainty and imprecision in PET images, the segmentation and the fusion of PET images is difficult. In this paper, a framework based on Belief Function Theory (BFT) is proposed for the segmentation of BTV from multi-tracer PET images. The first step is based on an extension of the Evidential C-Means (ECM) algorithm, taking advantage of neighboring voxels for dealing with uncertainty and imprecision in each mono-tracer PET image. Then, imprecision and uncertainty are, respectively, reduced using prior knowledge related to defects in the acquisition system and neighborhood information. Finally, a multi-tracer PET image fusion is performed. The results are represented by a set of parametric maps that provide important information for dose painting. The performances are evaluated on PET phantoms and patient data with lung cancer. Quantitative results show good performance of our method compared with other methods.

Reproducibility of the kinetic analysis of 3′-deoxy-3′-[18F]fluorothymidine positron emission tomography in mouse tumor models

We assessed the reproducibility of the kinetic analysis of 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) positron emission tomography (PET) in A431 human epidermoid carcinoma and murine Lewis lung carcinoma (LLC) tumor models. We injected 7.4 MBq of FLT (n=10 for each group) and acquired 2-h dynamic PET images. A second scan was performed 1 day later. We calculated standardized uptake value (SUV), kinetic rate constants, volume of distribution of phosphorylated FLT (V(dm)), net influx constant (K(FLT-CA)) and influx constant by Patlak graphical analysis (K(FLT-PA)). The percent difference between measurements of a parameter was calculated to compare the reproducibilities of different parameters. FLT phosphorylation was higher in mice with A431 tumors than in mice with LLC tumors (P<.005). Differences in the standard deviations of the percent differences of parameters were statistically significant (P<.001) in each model. In mice with A431 tumors, SUV, V(dm), K(FLT-CA) and K(FLT-PA) had standard deviations of the percent difference of < or = 20%. The most reproducible parameter was K(FLT-PA), although the standard deviation (15.6%) was not statistically different from those of V(dm) (15.8%), K(FLT-CA) (17.5%) and SUV (18.9%). In mice with LLC tumors, K(1), K(1)/k(2) and k(3) had standard deviations of the percent difference of < or = 20%. No macroparameters reflecting a total FLT flux had standard deviations of < or = 20%. Our results show the reproducibility of the kinetic macroparameters of FLT PET in mouse tumors with high FLT phosphorylation.

Molekulare Bildgebung der Proliferation mit [18F]FLT-PET

An increased proliferation fraction is a hallmark of malignant cells and a specific feature of malignant tumors which potentially allows more specific tumor imaging compared to increased glucose consumption (FDG-PET). The majority of therapeutic approaches aim at inhibition of proliferation or induction of apotposis. Accordingly, non-invasive assessment of the proliferation fraction is also of interest for montoring response to treatment and to early detect resistance to a specific kind of therapy. In clinical studies it has been demonstrated that the radiotracer 3′-deoxy-3′-[ 18 F]fluorothymidine (FLT) accumulates specifically in malignant tumors. Regression analysis of tumoral FLT-uptake and immunohistochemically detected proliferation fraction (PCNA, Ki-67) resulted in a significant correlation (e.g., in lung cancer, correlation coefficient r=0.87, p<0.0001). The possibility to non-invasively assess the proliferation fraction with FLT-PET has been shown in a variety of solid cancers. Compared to the standard radiotracer FDG, superior demonstration of the proliferative activity using FLT as the tracer has been demonstrated. On the other hand, accumulation of FLT was significantly lower compared to FDG. Malignant tumors with low proliferation rates did not present with increased FLT-uptake resulting in a reduced sensitivity. In lung cancer for example, the sensitivity was 86% of FLT-PET compared to 100% of FDG-PET. Also, regarding detection of locoregional lymph node metastases or distant metastases, FDG-PET was shown to have a higher sensitivity. Due to the reduced sensitivity, there is no advantage of specific imaging of tumor proliferation regarding tumor staging. In malignant lymphoma, FLT was similar effective for tumor staging as compared to FDG-PET. In a pilot study comprising 34 patients, both tracers showed a similar sensitivity regarding detection of lymphoma. An observed specificity of 100% indicates that FLT-PET represents a diagnostic test for non-invasive assessment of the proliferation fraction in malignant lymphoma which can be used to further guide biopsy of lesions and subsequent tumor grading. This has potential impact on the therapeutic decision making process since all localizations can be evaluated regarding an increased proliferation fraction and transformation to a more aggressive histology. Chemotherapy and radiotherapy induce damage to tumor cells which are passing through the cell cycle at the time point of treatment. Therefore, FLT-PET could be a suitable approach for early response monitoring. Initial in-vitro and in-vivo studies demonstrated a rapid reduction of tumoral FLT-uptake early in the course of cytostatic or cytotoxic treatment. In mouse xenotransplant models, cytostatic drug effects have been demonstrated by a marked reduction of the FLT-uptake as early as 24 h after initiation of therapy. FLT-PET therefore represents a suitable tool to non-invasively assess the increased proliferative activity which is a prerequisite of malignant tumors. Whether the radiotracer FLT offers incremental diagnosis information compared to FDG-PET remains to be determined.

Effect of IGF-1R inhibitor BMS-754807 on tumor glucose metabolism and proliferation in Sal-IGF xenografts by FDG and FLT- PET imaging

e14501 Background: The type 1 insulin-like growth factor receptor (IGF-1R) plays a critical role in mitogenesis and survival in a variety of human tumor cells. IGF-1R is also closely related to the insulin receptor (IR). It is becoming increasingly evident that stimulation of IR or IR/IGF-1R hybrid receptors by insulin or IGF-1/2 may contribute to cancer growth, suggesting that both IGF-1R and IR may be targets for cancer therapy. BMS-754807 (‘807) is an oral IGF-1R tyrosine kinase antagonist under development that also blocks IR activity. This study explores the feasibility of fluorodeoxyglucose (FDG) and fluorothymidine (FLT) positron emission tomography (PET) as pharmacodynamic imaging biomarkers in a xenograft model. Methods: Mice were implanted with fragments of Sal-IGF, a transgenic salivary gland tumor expressing constitutively active IGF-1R. Once tumors reached desired size, the mice were divided into 3 treatment groups (vehicle, 6.25 mg/kg ‘807, &amp; 50 mg/kg ‘807 on days 1–4). FDG-PET scans were performed on day -2 (prior to treatment), days 1 &amp; 2 (max/min concentrations post day 1 dose), and days 4 &amp; 5 (max/min day 4 dose). FLT-PET scans were performed on days -2, 2 (min day 1 dose), &amp; 5 (min day 4 dose). Results: With FDG-PET imaging, a 66% reduction (P&lt;0.05, paired t-test) in tumor SUVmean was observed at the end of the 50 mg/kg therapy (day 4) and sustained for 24h (day 5) with a concomitant reduction of 37% in tumor burden by day 5 (P&lt;0.05). FLT-PET studies demonstrated a 45% reduction (P&lt;0.05) in tumor SUVmean observed 24h after the end of 50 mg/kg therapy (day 5) with a concomitant reduction of 50% in tumor burden (day 5, P&lt;0.05). Conclusions: Correlation with tumor growth inhibition suggests feasibility of FDG- PET despite IR blockade. These results support the use of both FDG and FLT PET imaging in clinical trials with ‘807. [Table: see text]