Fluorothymidine Positron Emission Tomography Imaging Research Articles

STING-driven interferon signaling triggers metabolic alterations in pancreas cancer cells visualized by [18F]FLT PET imaging

Type I interferons (IFNs) are critical effectors of emerging cancer immunotherapies designed to activate pattern recognition receptors (PRRs). A challenge in the clinical translation of these agents is the lack of noninvasive pharmacodynamic biomarkers that indicate increased intratumoral IFN signaling following PRR activation. Positron emission tomography (PET) imaging enables the visualization of tissue metabolic activity, but whether IFN signaling-induced alterations in tumor cell metabolism can be detected using PET has not been investigated. We found that IFN signaling augments pancreatic ductal adenocarcinoma (PDAC) cell nucleotide metabolism via transcriptional induction of metabolism-associated genes including thymidine phosphorylase (TYMP). TYMP catalyzes the first step in the catabolism of thymidine, which competitively inhibits intratumoral accumulation of the nucleoside analog PET probe 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT). Accordingly, IFN treatment up-regulates cancer cell [18F]FLT uptake in the presence of thymidine, and this effect is dependent upon TYMP expression. In vivo, genetic activation of stimulator of interferon genes (STING), a PRR highly expressed in PDAC, enhances the [18F]FLT avidity of xenograft tumors. Additionally, small molecule STING agonists trigger IFN signaling-dependent TYMP expression in PDAC cells and increase tumor [18F]FLT uptake in vivo following systemic treatment. These findings indicate that [18F]FLT accumulation in tumors is sensitive to IFN signaling and that [18F]FLT PET may serve as a pharmacodynamic biomarker for STING agonist-based therapies in PDAC and possibly other malignancies characterized by elevated STING expression.

Abstract P2-01-01: Evaluating the order of treatments to enhance efficacy in a murine model of triple negative breast cancer with quantitative imaging

Abstract Introduction: The purpose of this study is to determine if order of dosing of combination chemotherapies (paclitaxel, doxorubicin) alters response in triple negative breast cancers (TNBCs). TNBC has limited treatment options and primarily relies on chemotherapy in both primary and metastatic disease. There are a number of clinically utilized regimens of combination chemotherapies and the optimal treatment strategy is still unknown. Thus, there is a need to explore how the order of regimens effects tumor response and optimize treatment efficacy in breast cancer population. Currently, one of the most commonly used regimens for locally advanced TNBCs is administration of doxorubicin (DRB) followed by paclitaxel (PTX). DRB, as a topoisomerase inhibitor, targets both cell cycle stage G1 and S, while PTX only targets cell cycle stage S. Our goal is to evaluate and compare tumor response of the order of dosing of PTX and DRB with quantitative molecular imaging. Advanced molecular imaging provides a noninvasive and highly sensitive approach to identify changes in quantify the early signal of drug response prior tumor size changes. Experimental Design: MDA-MB-231-FUCCI (Green fluorescence during S, G2, M phase; Red fluorescence during G1 phase) TNBC cells (2 × 106) were subcutaneously injected into nude mice (n = 12) and randomly assigned into three treatment groups: PTX (10 mg/kg)→DRB (10 mg/kg), DRB→PTX (same drug dosage), and saline control. 3’-Deoxy-3’-[18F]fluorothymidine ([18F]-FLT) positron emission tomography (PET)/computed tomography (CT) (SOFIE preclinical PET/CT) was performed before treatment (day 0), and on days 3 and 6. Treatment occurred on days 0 and 3 post imaging. GFP and RFP fluorescence were measured through in vivo imaging system (IVIS) on baseline and on day 6. In vivo cell proliferation was quantifying the percent change from baseline of normalized [18F]-FLT standard uptake value (SUV) (tumor mean/muscle mean) and normalized GFP signal (tumor/muscle). In vivo cell viability was determined by RFP signal percentage change. Statistical significance was evaluated with a t-test. Results: Cell proliferation and viability assessed through [18F]-FLT PET and fluorescence imaging showed that PTX prior to DRB treatment significantly decreased cancer cell proliferation and viability. From day 0 to 6, overall RFP signal of control increased 14%, while DRB → PTX decreased 36%, and PTX→DRB decreased 50% (p=0.060). Fluorescence imaging showed DRB→PTX treatment GFP signal increase by 3-fold (p=0.029) compared to control, while PTX→DRB treatment is similar to control (p>0.05). 18F-FLT PET SUV revealed from day 0 to 6, control had a 110% increase, DRB→PTX showed 60% increase, while PTX→DRB showed about 10% increase (p=0.010). Conclusion: PTX prior to DRB significantly improved tumor response to chemotherapy in this TNBC model by decreasing tumor cell viability and proliferation. Molecular imaging allows us to visualize and quantitate these cellular changes prior tumor size changes and may help guide clinical decision making for the treatment for TNBC patients. We acknowledge the support of ACS RSG-18-006-01-CCE Citation Format: Yun Lu, Adriana Massicano, Rachel David, Anna Sorace. Evaluating the order of treatments to enhance efficacy in a murine model of triple negative breast cancer with quantitative imaging [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-01-01.

FLT PET/CT imaging of metastatic prostate cancer patients treated with pTVG-HP DNA vaccine and pembrolizumab

BackgroundImmunotherapy has demonstrated remarkable success in treating different cancers. Nonetheless, a large number of patients do not respond, many respond without immediate changes detectable with conventional imaging, and many have unusual immune-related adverse events that cannot be predicted in advance. In this exploratory study, we investigate how 3′-Deoxy-3’-18F-fluorothymidine (FLT) positron emission tomography (PET) measurements of tumor and immune cell proliferation might be utilized as biomarkers in immunotherapy.MethodsSeventeen patients with metastatic castrate resistant prostate cancer were treated with combination pTVG-HP DNA vaccine and pembrolizumab. Patients underwent baseline and 12-week FLT PET/CT scans. FLT PET standardized uptake values (SUVs) were extracted from tumors, non-metastatic lymph nodes, spleen, bone marrow, pancreas, and thyroid to quantify cell proliferation in these tissues. Regional immune cell responses to pTVG-HP DNA vaccine were assessed by comparing FLT uptake changes in vaccine draining and non-draining lymph nodes. Cox proportional hazards regression was utilized to relate FLT uptake and other clinical markers (PSA and tumor size) to progression-free survival. Area under receiver operating characteristic (AUC) curves and concordance indices were used to assess the predictive capabilities of FLT uptake.ResultsChanges in FLT uptake in vaccine draining lymph nodes were significantly greater than changes in non-draining lymph nodes (P = 0.02), suggesting a regional immune response to vaccination. However, the changes in FLT uptake in lymph nodes were not significantly predictive of progression-free survival. Increases in tumor FLT uptake were significantly predictive of shorter progression-free survival (concordance index = 0.83, P < 0.01). Baseline FLT uptake in the thyroid was significantly predictive of whether or not a patient would subsequently experience a thyroid-related adverse event (AUC = 0.97, P < 0.01).ConclusionsFLT PET uptake was significantly predictive of progression-free survival and the occurrence of adverse events relating to thyroid function. The results suggest FLT PET imaging has potential as a biomarker in immunotherapy, providing a marker of tumor and immune responses, and as a possible means of anticipating specific immune-related adverse events.Trial registrationNCT02499835.

18F-3′-Deoxy-3′-Fluorothymidine Positron Emission Tomography Imaging for the Prediction of Acute Graft-Versus-Host Disease in Mouse Hematopoietic Stem Cell Transplant Models

Acute graft-versus-host disease (aGVHD) remains a barrier to the success of allogeneic hematopoietic stem cell transplantation. In mice, studies have demonstrated that donor conventional T cells traffic into host secondary lymphoid tissues early after transplant, and that this process is critical for the development of disease. As a result, the measurement of cellular proliferation within lymphoid sites early after transplant might be a useful approach for predicting aGVHD in humans. 18F-3′-deoxy-3′-fluorothymidine (FLT) positron emission tomography (PET) imaging has recently emerged as a functional imaging modality in oncology patients. FLT, a thymidine analog, is incorporated into replicating DNA and is thus an indirect marker of cellular proliferation. Here we report that FLT PET imaging can differentiate mice receiving alloreactive T cells and destined to develop lethal aGVHD from control mice. Mice receiving allogeneic T cells demonstrated a stronger FLT signal within the peripheral lymph nodes compared with control mice at all time points after transplant. In addition, allogeneic T cell recipients transiently demonstrated stronger FLT uptake within the spleen. Importantly, these differences were apparent before the development of clinical disease. In contrast, the FLT signal within the host bowel, an important aGVHD target organ, was more variable after transplant and was not consistently different between aGVHD mice and control mice. Collectively, these findings suggest that the imaging of patient lymphoid sites using existing FLT PET technology might be useful for predicting aGVHD in the clinical setting.

Whole-Body Distribution of Leukemia and Functional Total Marrow Irradiation Based on FLT-PET and Dual-Energy CT.

This report describes a multimodal whole-body 3′-deoxy-3′[(18)F]-fluorothymidine positron emission tomography (FLT-PET) and dual-energy computed tomography (DECT) method to identify leukemia distribution within the bone marrow environment (BME) and to develop disease- and/or BME-specific radiation strategies. A control participant and a newly diagnosed patient with acute myeloid leukemia prior to induction chemotherapy were scanned with FLT-PET and DECT. The red marrow (RM) and yellow marrow (YM) of the BME were segmented from DECT using a basis material decomposition method. Functional total marrow irradiation (fTMI) treatment planning simulations were performed combining FLT-PET and DECT imaging to differentially target irradiation to the leukemia niche and the rest of the skeleton. Leukemia colonized both RM and YM regions, adheres to the cortical bone in the spine, and has enhanced activity in the proximal/distal femur, suggesting a potential association of leukemia with the BME. The planning target volume was reduced significantly in fTMI compared with conventional TMI. The dose to active disease (standardized uptake value >4) was increased by 2-fold, while maintaining doses to critical organs similar to those in conventional TMI. In conclusion, a hybrid system of functional–anatomical–physiological imaging can identify the spatial distribution of leukemia and will be useful to both help understand the leukemia niche and develop targeted radiation strategies.

Evaluation of Therapeutic Effects of Radiotherapy during Treatment of Lung Adenocarcinoma in Mice with Positron Emission Tomography Imaging of &lt;sup&gt;18&lt;/sup&gt;F-FLT and &lt;sup&gt;18&lt;/sup&gt;F-FDG

Purpose: To assess the role of 3'-deoxy-3'-18F-fluoro-thymidine (18F-FLT) and 2'-deoxy-2'-18F-fluorodeoxy- glucose (18F-FDG) positron emission tomography (PET) imaging in the evaluation of the therapeutic effects of radiotherapy during treatment of lung adenocarcinoma.Methods: Eighteen mice with lung adenocarcinoma were randomly divided into 2 groups; each group was randomly paired and evenly divided into three smaller groups, namely, A, B and C. Group A served as the control group without any treatment; mice in group B were received radiotherapy in sites of tumor. A single dose of 2000 cGy, 6MV x-ray was used in this experiment; mice in group C also received radiotherapy at sites of tumors two days before the experiment using the same procedure and dose as group B. Micro PET imaging was taken after intravenous injection of 18F-FLT and 18F-FDG through the mice’s tail.Results: The intake ratio of 18F-FLT and 18F-FDG was much higher at the tumor sites. After radiotherapy, 18F-FLT uptake was significantly lower than that of the control group (p &lt; 0.05), while there was no obvious change of 18F-FDG uptake. There was a significant decrease in T/NT value of FLT PET imaging group 24 and 48 h after radiotherapy; a significant difference could be seen, compared with that before radiotherapy (p &lt; 0.05).Conclusion: Change in 18F-FLT uptake induced by radiotherapy is more sensitive than that of 18F-FDG. Intake of 18F-FLT is lowered more significantly after radiotherapy than that of 18F-FDG, and this can serve as evidence that 18F-FLT is an effective tracer to monitor the therapeutic effect of radiotherapy on malignant tumors.Keywords: 3'-deoxy-3'-18F-fluoro-thymidine, 2'-deoxy-2'-18F-fluoro-deoxy-glucose, Radiotherapy, Positron Emission Tomography Imaging, Cell Proliferation, Lung Adenocarcinoma

18F]FDG and [18F]FLT positron emission tomography imaging following treatment with belinostat in human ovary cancer xenografts in mice

BackgroundBelinostat is a histone deacetylase inhibitor with anti-tumor effect in several pre-clinical tumor models and clinical trials. The aim of the study was to evaluate changes in cell proliferation and glucose uptake by use of 3’-deoxy-3’-[18F]fluorothymidine ([18F]FLT) and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) following treatment with belinostat in ovarian cancer in vivo models.MethodsIn vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) were studied after treatment with belinostat. Mice were divided in 2 groups receiving either belinostat (40 mg/kg ip twice daily Day 0–4 and 6–10) or vehicle. Baseline [18F]FLT or [18F]FDG scans were made before treatment (Day 0) and repeated at Day 3, 6 and 10. Tracer uptake was quantified using small animal PET/CT.ResultsTumors in the belinostat group had volumes that were 462 ± 62% (640 mm3) at Day 10 relative to baseline which was significantly different (P = 0.011) from the control group 769 ± 74% (926 mm3). [18F]FLT SUVmax increased from baseline to Day 10 (+30 ± 9%; P = 0.048) in the control group. No increase was observed in the treatment group. [18F]FDG SUVmean was significantly different in the treatment group compared to the control group (P = 0.0023) at Day 10. Within treatment groups [18F]FDG uptake and to a lesser extent [18F]FLT uptake at Day 3 were significantly correlated with tumor growth at Day 10.Conclusions[18F]FDG uptake early following treatment initiation predicted tumor sizes at Day 10, suggesting that [18F]FDG may be a valuable biomarker for non-invasive assessment of anti-tumor activity of belinostat.

3′‐deoxy‐3′‐[18F]fluorothymidine positron emission tomography for response assessment in soft tissue sarcoma

This study sought to determine whether [(18)F]fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) imaging allows assessment of tumor viability and proliferation in patients with soft tissue sarcomas who are treated with neoadjuvant therapy. Twenty patients with biopsy-proven, resectable, high-grade soft tissue sarcoma underwent [(18)F]FLT PET/CT imaging before and after neoadjuvant therapy. Histologic subtypes included sarcomas not otherwise specified (n = 5), malignant peripheral nerve sheath tumors (n = 3), gastrointestinal stromal tumors (n = 3), leiomyosarcomas (n = 3), angiosarcomas (n = 2), and others (n = 4). Changes in [(18)F]FLT peak standardized uptake value (SUVpeak) were correlated with percent necrosis in excised tissue, whereas posttreatment [(18)F]FLT tumor uptake was correlated with thymidine kinase 1 (TK1) expression and Ki-67 staining indices in excised tumor tissue. Tumor FLT SUVpeak averaged 7.1 ± 3.7 g/mL (range, 1.9-16.1 g/mL) at baseline and decreased significantly to 2.7 ± 1.6 g/mL (range, 0.8-6.0 g/mL) at follow-up (P < .001); however, marked reductions in SUV were not specific for histopathological response. The posttreatment SUVpeak did not correlate with TK1 (P = .27) or Ki-67 expression (P = .21). Marked reductions in [(18)F]FLT tumor uptake in response to neoadjuvant treatment were observed in most patients with sarcoma. However, these reductions were not specific for histopathologic response to neoadjuvant therapy. Furthermore, posttreatment [(18)F]FLT tumor uptake was unrelated to tumor proliferation by Ki-67 and TK1 staining. These results question the value of [(18)F]FLT PET imaging for treatment response assessments in patients with soft tissue sarcoma.

Early assessment of tumor response to JAC106, an anti-tubulin agent, by 3′-deoxy-3′-[18F]fluorothymidine in preclinical tumor models

We determined whether [(18)F]fluorothymidine (FLT) positron emission tomography (PET) can detect early effects on tumor proliferation of JAC106, a new anti-tubulin agent. Inhibition of tubulin polymerization and [(3)H]colchicine binding were assessed in vitro. The effects of JAC106 on cytotoxicity, mitotic arrest, [(18)F]FLT uptake, and thymidine kinase 1 (TK1) activity were examined in SW620 and KB-V1 cells. Dose-dependent antitumor effects of JAC106 were monitored by measuring tumor growth and by dynamic [(18)F]FLT PET imaging in mice bearing SW620 and KB-V1 tumors. The proliferation status of tumors was examined. JAC106 potently inhibited tubulin polymerization and decreased the viability of SW620 (p < 0.001, half maximal inhibitory concentration, IC(50) = 3.15 ± 1.4) and KB-V1 (p < 0.01, IC(50) = 21.84 ± 24.59) cells. Exposure to JAC106 induced mitotic arrest starting at 18 h and dose-dependently increased [(18)F]FLT uptake/1 × 10(5) cells (p < 0.05) and TK1 activity and expression in vitro. Administration of 30 mg/kg JAC106 to mice inhibited the growth of SW620 and KB-VI tumors (%T/C 3.34 and 20.6%, respectively). The baseline standardized uptake values (SUV) of SW620 and KB-V1 tumors were 0.96 ± 0.31 and 2.29 ± 0.70, respectively, with a significant difference (p < 0.01). After 3 days of treatment with 30 mg/kg JAC106, the [(18)F]FLT SUVs of SW620 and KB-V1 tumors, normalized to those before treatment, were 77.9 ± 22.4% (p = 0.059) and 43.2 ± 14.0% (p < 0.01), respectively. JAC106 significantly decreased the number of Ki-67-positive cells, TK1 activity, cell fraction in G(0)G(1) phase, and tumor expression of cyclins E, A, and B1 on day 3. [(18)F]FLT PET can be used to monitor JAC106 inhibition of tumor growth, beginning 3 days after treatment. Incorporation of [(18)F]FLT PET may be useful in the early clinical development of JAC106.

Compliance with PET acquisition protocols for therapeutic monitoring of erlotinib therapy in an international trial for patients with non-small cell lung cancer

The Response Evaluation Criteria in Solid Tumors (RECIST) are widely used but have recognized limitations. Molecular imaging assessments, including changes in (18)F-deoxyglucose (FDG) or (18)F-deoxythymidine (FLT) uptake by positron emission tomography (PET), may provide earlier, more robust evaluation of treatment efficacy. A prospective trial evaluated on-treatment changes in FDG and FLT PET imaging among patients with relapsed or recurrent non-small cell lung cancer treated with erlotinib to assess the relationship between PET-evaluated response and clinical outcomes. We describe an audit of compliance with the study imaging charter, to establish the feasibility of achieving methodological consistency in a multicentre setting. Patients underwent PET scans at baseline and approximately day 14 and day 56 of treatment (n = 73, 66 and 51 studies, and n = 73, 63 and 50 studies for FDG PET and FLT PET, respectively). Blood glucose levels were within the target range for all FDG PET scans. Charter-specified uptake times were achieved in 86% (63/73) and 89% (65/73) of baseline FDG and FLT scans, respectively. On-treatment scans were less consistent: 72% (84/117) and 68% (77/113), respectively, achieved the target of ±5min of baseline uptake time. However, 96% (112/117) and 94% (106/113) of FDG and FLT PET studies, respectively, were within ±15min. Bland-Altman analysis of intra-individual hepatic average standardized uptake value (SUV(ave)), to assess reproducibility, showed only a small difference in physiological uptake (-0.006 ± 0.224 in 118 follow-up FDG scans and 0.09 ± 0.81 in 111 follow-up FLT scans). It is possible to achieve high reproducibility of scan acquisition methodology, provided that strict imaging compliance guidelines are mandated in the study protocol.

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.

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]

The optimal threshold of 18F-FLT PET and 18F-FDG PET to estimate the length of gross tumor volume in patients with squamous cell carcinoma of the thoracic esophagus verified by pathological examination

e15665 Background: To determine the optimal method of using 3-deoxy-3-18F-fluorothymidine (FLT) positron emission tomography (PET) to estimate gross tumor length in esophageal carcinoma, and compared with that of 18F- fluorodeoxyglucose(FDG) PET. Methods: Twenty patients with esophageal squamous cell carcinoma treated with radical surgery were enrolled and detected by FLT PET, eighteen of them underwent FDG PET scan. Gross tumor volumes (GTVs) were delineated using seven different methods with FLT PET: visual interpretation, standardized uptake value (SUV) 1.3, SUV 1.4, SUV 1.5, and 20% of maximum standard uptake value (SUVmax), 25% SUVmax,30% SUVmax, on FLT PET imaging, and three different methods with FDG PET: visual interpretation, SUV 2.5, and 40%SUVmax on FDG PET imaging. The length of tumors on FLT PET scan were measured and recorded as LFLTvis, LFLT1.3, LFLT1.4, LFLT1.5, LFLT20%, LFLT25%, and LFLT30%, and FDG PET scan were measured and recorded as LFDGvis, LFDG2.5, and LFDG40%, respectively, and compared with the length of gross tumor in the resected specimen measured by pathological examination (LPath). Results: The mean (±SD) LPath was 5.16±2.19cm. The mean LFLTvis, LFLT1.3, LFLT1.4, LFLT1.5, LFLT20%, LFLT25%, and LFLT30%were 5.17±2.40cm, 5.55±2.43cm, 5.17±2.41cm, 4.95±2.44cm, 5.82±2.23cm, 5.32±2.31cm, and 5.04±2.28cm, respectively. Compared with the LPath, the P value were 0.971, 0.045, 0.972, 0.255, 0.066, 0.644, and 0.714, respectively. The correlation coefficients were 0.952, 0.944, 0.959, 0.948, 0.763, 0.783, and 0.800, respectively. The mean LFDGvis, LFDG2.5, and LFDG40% were 5.41±2.27cm, 5.38±2.25cm, and 4.02±1.57cm, respectively. Compared with the LPath, the P value were 0.098, 0.085 and 0.000, respectively. The correlation coefficients were 0.984, 0.990 and 0.932, respectively. On FLT PET, LFLT1.4, and on FDG PET, L FDG2.5 seem more approximate to LPath. The difference between LFLT1.4 and LFDG2.5 was not significantly (P=0.442), the correlation coefficients was 0.960. Conclusions: An SUV cutoff of 1.4 on FLT PET, and an SUV cutoff of 2.5 on FDG PET, provided the closest estimation of GTV length in this study No significant financial relationships to disclose.

Early Detection of Erlotinib Treatment Response in NSCLC by 3′-Deoxy-3′-[18F]-Fluoro-L-Thymidine ([18F]FLT) Positron Emission Tomography (PET)

BackgroundInhibition of the epidermal growth factor receptor (EGFR) has shown clinical success in patients with advanced non-small cell lung cancer (NSCLC). Somatic mutations of EGFR were found in lung adenocarcinoma that lead to exquisite dependency on EGFR signaling; thus patients with EGFR-mutant tumors are at high chance of response to EGFR inhibitors. However, imaging approaches affording early identification of tumor response in EGFR-dependent carcinomas have so far been lacking.Methodology/Principal FindingsWe performed a systematic comparison of 3′-Deoxy-3′-[18F]-fluoro-L-thymidine ([18F]FLT) and 2-[18F]-fluoro-2-deoxy-D-glucose ([18F]FDG) positron emission tomography (PET) for their potential to identify response to EGFR inhibitors in a model of EGFR-dependent lung cancer early after treatment initiation. While erlotinib-sensitive tumors exhibited a striking and reproducible decrease in [18F]FLT uptake after only two days of treatment, [18F]FDG PET based imaging revealed no consistent reduction in tumor glucose uptake. In sensitive tumors, a decrease in [18F]FLT PET but not [18F]FDG PET uptake correlated with cell cycle arrest and induction of apoptosis. The reduction in [18F]FLT PET signal at day 2 translated into dramatic tumor shrinkage four days later. Furthermore, the specificity of our results is confirmed by the complete lack of [18F]FLT PET response of tumors expressing the T790M erlotinib resistance mutation of EGFR.Conclusions[18F]FLT PET enables robust identification of erlotinib response in EGFR-dependent tumors at a very early stage. [18F]FLT PET imaging may represent an appropriate method for early prediction of response to EGFR TKI treatment in patients with NSCLC.

Analysis and Reproducibility of 3′-Deoxy-3′-[18F]Fluorothymidine Positron Emission Tomography Imaging in Patients with Non–Small Cell Lung Cancer

Imaging tumor proliferation with 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) and positron emission tomography is being developed with the goal of monitoring antineoplastic therapy. This study assessed the methods to measure FLT retention in patients with non-small cell lung cancer (NSCLC) to measure the reproducibility of this approach. Nine patients with NSCLC who were untreated or had progressed after previous therapy were imaged twice using FLT and positron emission tomography within 2 to 7 days. Reproducibility (that is, error) was measured as the percent difference between the two patient scans. Dynamic imaging was obtained during the first 60 min after injection. Activity in the blood was assessed from aortic images and the fraction of unmetabolized FLT was measured. Regions of interest were drawn on the plane with the highest activity and the adjacent planes to measure standardized uptake value (SUV(mean)) and kinetic variables of FLT flux. We found that the SUV(mean) obtained from 30 to 60 min had a mean error of 3.6% (range, 0.6-6.9%; SD, 2.3%) and the first and second scans were highly correlated (r(2) = 0.99; P < 0.0001). Using shorter imaging times from 25 to 30 min or from 55 to 60 min postinjection also resulted in small error rates; SUV(mean) mean errors were 8.4% and 5.7%, respectively. Compartmental and graphical kinetic analyses were also fairly reproducible (r(2) = 0.59; P = 0.0152 and r(2) = 0.58; P = 0.0175 respectively). FLT imaging of patients with NSCLC was quite reproducible with a worst case SUV(mean) error of 21% when using a short imaging time.

Quantification of Cellular Proliferation in Tumor and Normal Tissues of Patients with Breast Cancer by [18F]Fluorothymidine-Positron Emission Tomography Imaging: Evaluation of Analytical Methods

There is an unmet need to develop imaging methods for the early and objective assessment of breast tumors to therapy. 3'-Deoxy-3'-[18F]fluorothymidine ([18F]FLT)-positron emission tomography represents a new approach to imaging thymidine kinase activity, and hence, cellular proliferation. We compared graphical, spectral, and semiquantitative analytic methodologies for quantifying [18F]FLT kinetics in tumor and normal tissue of patients with locally advanced and metastatic breast cancer. The resultant kinetic parameters were correlated with the Ki-67 labeling index from tumor biopsies. [18F]FLT accumulation was detected in primary tumor, nodal disease, and lung metastasis. In large tumors, there was substantial heterogeneity in regional radiotracer uptake, reflecting heterogeneity in cellular proliferation; radiotracer uptake in primary tumors also differed from that of metastases. [18F]FLT was metabolized in patients to a single metabolite [18F]FLT-glucuronide. Unmetabolized [18F]FLT accounted for 71.54 +/- 1.50% of plasma radioactivity by 90 minutes. The rate constant for the metabolite-corrected net irreversible uptake of [18F]FLT (Ki) ranged from 0.6 to 10.4 x 10(-4) and from 0 to 0.6 x 10(-4) mL plasma cleared/s/mL tissue in tumor (29 regions, 15 patients) and normal tissues, respectively. Tumor Ki and fractional retention of radiotracer determined by spectral analysis correlated with Ki-67 labeling index (r = 0.92, P < 0.0001 and r = 0.92, P < 0.0001, respectively). These correlations were superior to those determined by semiquantitative methods. We conclude that [18F]FLT-positron emission tomography is a promising clinical tool for imaging cellular proliferation in breast cancer, and is most predictive when analyzed by graphical and spectral methods.