18F-FLT Positron Emission Tomography Research Articles

Evaluation of Hematopoiesis and Disease Status in Patients with Hematologic Malignancies Using Whole-Body Bone Marrow Imaging with 18 F-FLT PET/MRI

Introduction Bone marrow examination is primarily focused on a limited region of the ilium, thereby inadequately assessing systemic hematopoiesis or residual tumor cells after therapy. Magnetic resonance imaging (MRI) of the spine can examine the fat marrow, but does not provide a direct assessment of hematopoietic cells. The use of the radiopharmaceutical 3‘-deoxy-3‘- 18F-fluorothymidine ( 18F-FLT) positron emission tomography (PET), which measures nucleic acid synthesis, can provide a quantifiable means of assessing hematopoietic cell proliferation. The combination of whole-body MRI and 18F-FLT PET may provide a more accurate assessment of whole-body bone marrow hematopoiesis in hematologic malignancies. Methods A prospective, open-label, exploratory study (UMIN000041491) was conducted to evaluate hematopoiesis using 18F-FLT PET/MRI imaging in patients planned for allogeneic hematopoietic stem cell transplantation. Subjects were patients over 20 years of age with hematologic malignancies who underwent 18F-FLT PET/MRI imaging before transplantation and at 50 and 180 days after transplantation. After an intravenous injection of 185 MBq 18F-FLT, patients were transferred to a simultaneous 3.0 T PET/MR scanner (Signa PET/MR; GE Healthcare, Waukesha, WI). The PET acquisition was performed in 3D mode with a 5.5 min/bed position (89 slices/bed) and a 24-slice overlap in 5 to 6 beds. The percentage of fat marrow was determined using MRI proton density fat fraction (PDFF) with a 1 cm 2 region of interest at 26 sites: cervical spine (C2-C7), thoracic spine (Th1-Th12), lumbar spine (L1-L5), and superior posterior iliac spine (two sites on each side). Similarly, the standardized uptake value (SUV) of 18F-FLT was measured. Results Thirteen patients with hematologic malignancies (8 with acute myeloid leukemia, 2 with acute lymphoblastic leukemia, and 3 with malignant lymphoma) were evaluated between August 2020 and April 2023. The median age of the patients was 46 years (range: 23 ~ 65). Seven patients underwent cord blood transplantation, while the remainder received peripheral blood stem cell transplantation. Prior to transplantation, all 13 patients underwent 18F-FLT PET/MRI scans. After transplantation, due to treatment-related death or worsening of the primary disease, 11 patients underwent scans on day 50, while 8 patients underwent scans on day 180, resulting in a total of 32 evaluable scans. In the 28 cases in hematologic remission at imaging, mean PDFF values were higher in the iliac (63.3% ± standard deviation 13.9) and lumbar (60.4% ± 14.9) than in the thoracic (47.2% ± 17.1) and cervical (37.5% ± 14.8) spines. Conversely, mean 18F-FLT SUV was higher in the thoracic (6.98 ± 2.31) and cervical (6.82 ± 2.03) than in the lumbar (5.06 ± 2.39) and iliac (3.95 ± 1.88) spine. This site-specific disparity in PDFF and 18F-FLT SUV was consistent both before and after transplantation. In all 32 cases, the median correlation coefficient between PDFF and 18F-FLT SUV was -0.60 (range: -0.92 ~ 0.17, Pearson's cumulative correlation coefficient), and 25 cases (78.1%) had a negative correlation coefficient below -0.4. Comparing the 12 cases with residual disease (4 cases with hematologic non-remission and 8 cases with hematologic remission but abnormal G-banding or quantitative polymerase chain reaction) with the 20 cases in complete remission, the correlation between PDFF and 18F-FLT SUV was significantly weaker in the residual disease group (-0.37 vs. -0.75, p<0.001, Mann-Whitney U test). When the correlation coefficient threshold was set at -0.57, the ROC curve for determining residual disease had an AUC of 0.86, a sensitivity of 83.3%, and a specificity of 85.0%. Discussion It is important to understand that the fat marrow and hematopoiesis degree in the iliac bone differs from that in the thoracic and cervical spine throughout the transplantation process, thereby influencing the disease status evaluation in hematological malignancies. The correlation between PDFF and 18F-FLT SUV, which is strong in cases of remission, weakens in cases of residual disease, even at the level of minimal residual disease. This discrepancy may reflect aberrant tumorigenic cell proliferation that differs from the norm. Thus, 18F-FLT PET/MRI was useful in understanding the hematopoietic and disease state of the systemic bone marrow in patients with hematologic malignancies.

18F-FDG and 18F-FLT Uptake Profiles for Breast Cancer Cell Lines Treated with Targeted PI3K/Akt/mTOR Therapies.

Background: To evaluate 18F-fluoro-2-deoxy-glucose (18F-FDG) and 18F-fluorothymidine (18F-FLT) as early-response biomarkers for phosphoinositide-3-kinase/Akt/mammalian-target-of-rapamycin (PI3K/Akt/mTOR) inhibition in breast cancer (BC) models. Materials and Methods: Two human epidermal growth factor receptor 2 (HER2)-positive (trastuzumab-sensitive SKBR3; trastuzumab-resistant JIMT1) and one triple-negative BC cell line (MDA-MB-231, trastuzumab, and everolimus resistant) were treated with trastuzumab (HER2 antagonist), PIK90 (PI3K inhibitor), or everolimus (mTOR inhibitor). Radiotracer uptake was measured before, 24, and 72 h after drug exposure and correlated with changes in cell number, glucose transporter 1 (GLUT1), cell cycle phase, and downstream signaling activation. Results: In responsive cells, cell number correlated with 18F-FLT at 24 h and 18F-FDG at 72 h of drug exposure, except in JIMT1 treated with everolimus, where both radiotracers failed to detect response owing to a temporary increase in tracer uptake. This flare can be caused by reflex activation of Akt combined with a hyperactive insulin-like growth factor I receptor (IGF-1R) signaling, resulting in increased trafficking of GLUTs to the cell membrane (18F-FDG) and enhanced DNA repair (18F-FLT). In resistant cells, no major changes were observed, although a nonsignificant flair for both tracers was observed in JIMT1 treated with trastuzumab. Conclusion: 18F-FLT positron emission tomography (PET) detects response to PI3K-targeting therapy earlier than 18F-FDG PET in BC cells. However, therapy response can be underestimated after trastuzumab and everolimus owing to negative feedback loop and crosstalk between pathways.

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.

Posture-motor and posture-ideomotor dual-tasks costs as a putative marker of depressive rumination in patients with major depressive disorder

There is an unmet need to develop noninvasive biomarkers to stratify patients in drug-radiotherapy trials. In this pilot study we investigated lung cancer radiotherapy response and toxicity blood biomarkers and correlated findings with tumor volume and proliferation imaging.Blood samples were collected before and during (day 21) radiotherapy. Twenty-six cell-death, hypoxia, angiogenesis, inflammation, proliferation, invasion, and tumor-burden biomarkers were evaluated. Clinical and laboratory data were collected. Univariate analysis was performed on small-cell and non–small-cell lung cancer (NSCLC) whereas multivariate analysis focused on NSCLC.Blood samples from 78 patients were analyzed. Sixty-one (78.2%) harbored NSCLC, 48 (61.5%) received sequential chemoradiotherapy. Of tested baseline biomarkers, undetectable interleukin (IL)-1b (hazard ratio [HR], 4.02; 95% confidence interval [CI], 2.04-7.93; P < .001) was the only significant survival covariate. Of routinely collected laboratory tests, high baseline neutrophil count was a significant survival covariate (HR, 1.07; 95% CI, 1.02-1.11; P = .017). Baseline IL-1b and neutrophil count were prognostic for survival in a multivariate model. The addition of day-21 cytokeratin-19 antigen modestly improved this model's survival prediction (concordance probability, 0.75-0.78). Chemotherapy (P < .001) and baseline keratinocyte growth factor (P = .019) predicted acute esophagitis, but only chemotherapy remained significant after Bonferroni correction. Baseline angioprotein-1 and hepatocyte growth factor showed a direct correlation with tumor volume whereas changes in vascular cell adhesion molecule 1 showed significant correlations with 18F-fluorothymidine (FLT) positron emission tomography (PET).Select biomarkers are prognostic after radiotherapy in this lung cancer series. The correlation between circulating biomarkers and 18F-FLT PET is shown, to our knowledge for the first time, highlighting their potential role as imaging surrogates.

Optimal transformations leading to normal distributions of positron emission tomography standardized uptake values

The statistical analysis of positron emission tomography (PET) standardized uptake value (SUV) measurements is challenging due to the skewed nature of SUV distributions. This limits utilization of powerful parametric statistical models for analyzing SUV measurements. An ad-hoc approach, which is frequently used in practice, is to blindly use a log transformation, which may or may not result in normal SUV distributions. This study sought to identify optimal transformations leading to normally distributed PET SUVs extracted from tumors and assess the effects of therapy on the optimal transformations. Methods. The optimal transformation for producing normal distributions of tumor SUVs was identified by iterating the Box–Cox transformation parameter (λ) and selecting the parameter that maximized the Shapiro–Wilk P-value. Optimal transformations were identified for tumor SUVmax distributions at both pre and post treatment. This study included 57 patients that underwent 18F-fluorodeoxyglucose (18F-FDG) PET scans (publically available dataset). In addition, to test the generality of our transformation methodology, we included analysis of 27 patients that underwent 18F-Fluorothymidine (18F-FLT) PET scans at our institution. Results. After applying the optimal Box–Cox transformations, neither the pre nor the post treatment 18F-FDG SUV distributions deviated significantly from normality (P > 0.10). Similar results were found for 18F-FLT PET SUV distributions (P > 0.10). For both 18F-FDG and 18F-FLT SUV distributions, the skewness and kurtosis increased from pre to post treatment, leading to a decrease in the optimal Box–Cox transformation parameter from pre to post treatment. There were types of distributions encountered for both 18F-FDG and 18F-FLT where a log transformation was not optimal for providing normal SUV distributions. Conclusion. Optimization of the Box–Cox transformation, offers a solution for identifying normal SUV transformations for when the log transformation is insufficient. The log transformation is not always the appropriate transformation for producing normally distributed PET SUVs.

Prognostic Value of Head and Neck Tumor Proliferative Sphericity From 3’-Deoxy-3’-[18F] Fluorothymidine Positron Emission Tomography

[18F] fluorothymidine (18F-FLT) positron emission tomography (PET) can be used for quantifying tumor proliferation and its changes during chemoradiotherapy (CRT) in head and neck squamous cell carcinoma (HNSCC). We investigated the complementary prognostic value of sphericity (one of several available 3-D shape descriptors) and standard metrics in 18F-FLT PET images before and during CRT regarding 4-year disease-free survival (DFS). Forty-eight HNSCC patients treated with CRT underwent 18F-FLT PET/CT before and during CRT. Median follow-up was 52 months. Primary tumors were automatically delineated and characterized by extracting max and mean standardized uptake value (SUV), proliferative volume and associated sphericity. Prognostic value for DFS of clinical and imaging features was assessed using Kaplan–Meier survival analysis. In univariate analysis after correction for multiple testing, the per-treatment sphericity (HR = 4.2, $p=0.02$ ) and SUVmean (HR = 4.1, $p=0.03$ ) were prognostic factors, whereas none of the pretreatment variables were significant. Reduction in SUV $_{\max }$ (HR = 4, $p=0.04$ ) was also a prognostic factor, but not reduction of proliferative tumor volume. The best stratification of patients for DFS was achieved by combining per-treatment SUVmean and sphericity (HR = 6.7, $p ). High sphericity combined with low mean 18F-FLT uptake during treatment were associated with better DFS. These results suggest the potential prognostic value of tumor characterization from 18F-FLT PET in HNSCC that may be further explored in larger cohorts.

Cell Death, Inflammation, Tumor Burden, and Proliferation Blood Biomarkers Predict Lung Cancer Radiotherapy Response and Correlate With Tumor Volume and Proliferation Imaging

IntroductionThere is an unmet need to develop noninvasive biomarkers to stratify patients in drug-radiotherapy trials. In this pilot study we investigated lung cancer radiotherapy response and toxicity blood biomarkers and correlated findings with tumor volume and proliferation imaging. Patients and MethodsBlood samples were collected before and during (day 21) radiotherapy. Twenty-six cell-death, hypoxia, angiogenesis, inflammation, proliferation, invasion, and tumor-burden biomarkers were evaluated. Clinical and laboratory data were collected. Univariate analysis was performed on small-cell and non–small-cell lung cancer (NSCLC) whereas multivariate analysis focused on NSCLC. ResultsBlood samples from 78 patients were analyzed. Sixty-one (78.2%) harbored NSCLC, 48 (61.5%) received sequential chemoradiotherapy. Of tested baseline biomarkers, undetectable interleukin (IL)-1b (hazard ratio [HR], 4.02; 95% confidence interval [CI], 2.04-7.93; P < .001) was the only significant survival covariate. Of routinely collected laboratory tests, high baseline neutrophil count was a significant survival covariate (HR, 1.07; 95% CI, 1.02-1.11; P = .017). Baseline IL-1b and neutrophil count were prognostic for survival in a multivariate model. The addition of day-21 cytokeratin-19 antigen modestly improved this model's survival prediction (concordance probability, 0.75-0.78). Chemotherapy (P < .001) and baseline keratinocyte growth factor (P = .019) predicted acute esophagitis, but only chemotherapy remained significant after Bonferroni correction. Baseline angioprotein-1 and hepatocyte growth factor showed a direct correlation with tumor volume whereas changes in vascular cell adhesion molecule 1 showed significant correlations with 18F-fluorothymidine (FLT) positron emission tomography (PET). ConclusionSelect biomarkers are prognostic after radiotherapy in this lung cancer series. The correlation between circulating biomarkers and 18F-FLT PET is shown, to our knowledge for the first time, highlighting their potential role as imaging surrogates.

Prospective Study of Serial Imaging Comparing Fluorodeoxyglucose Positron Emission Tomography (PET) and Fluorothymidine PET During Radical Chemoradiation for Non-Small Cell Lung Cancer: Reduction of Detectable Proliferation Associated With Worse Survival

Toinvestigate the associations between interim tumor responses on 18F-fluorodeoxyglucose(18F-FDG) positron emission tomography (PET) and 18F-fluorothymidine (18F-FLT) PET and patient outcomes, especially progression-free survival (PFS) and overall survival (OS), in non-small cell lung cancer (NSCLC) patients. Patients with FDG-PET/computed tomography stage I-III NSCLC were prescribed concurrent chemotherapy and radiation therapy (60Gy in 30 fractions). Scans were acquired at baseline (FDG-PET/computed tomography [FDGBL] for radiation therapy planning and FLT-PET [FLTBL]), week 2 (FDGwk2 and FLTwk2), and week 4 (FDGwk4 and FLTwk4) of chemoradiation therapy. Tumor responses were categorized as complete or partial responses or stable or progressive disease (SD, PD) using European Organization for Research and Treatment of Cancer criteria. Associations between response, OS, and PFS were analyzed with univariate Cox regressions and plotted using Kaplan-Meier curves. Between 2009 and 2013, 60 patients were recruited. Thirty-seven (62%) were male, and the median age was 66years (range, 31-86years). Two-year OS and PFS were 0.51 and 0.26, respectively. Unexpectedly, SD on FLTwk2 compared with complete response/partial response was associated with longer OS (hazard ratio [95% confidence interval] 2.01 [0.87-4.65], P=.082) and PFS (2.01 [0.92-4.36], P=.061). Weeks 2 and 4 FDG PET/CT were not significantly associated with survival. Study scans provided additional information to FDGBL in 21 patients (35%). Distant metastases detected in 3 patients on FLTBL and in 2 patients on FDG/FLTwk2 changed treatment intent from curative to palliative. Locoregional progression during radiation therapy was observed in 5 (8%) patients, prompting larger radiation therapy fields. Stable uptake of 18F-FLT at week 2 was paradoxically associated with longer OS and PFS. This suggests that suppression of tumor cell proliferation may protect against radiation-induced tumor cell killing. Baseline FLT, FLTwk2, and FDGwk2 detected rapid distant and locoregional progression in 10 patients (17%), prompting changes in management.

Current clinical status of 18F-FLT PET or PET/CT in digestive and abdominal organ oncology.

Positron emission tomography (PET) or PET/computed tomography (CT) using 18F-3'-fluoro-3'-deoxythymidine (18F-FLT) offers noninvasive assessment of cell proliferation in human cancers in vivo. The present review discusses the current status on clinical applications of 18F-FLT-PET (or PET/CT) in digestive and abdominal oncology by comparing with 18F-fluorodeoxyglucose (18F-FDG)-PET (or PET/CT). The results of this review show that although 18F-FLT uptake is lower in most cases of digestive and abdominal malignancies compared with 18F-FDG uptake, 18F-FLT-PET can be used to detect primary tumors. 18F-FLT-PET has shown greater specificity for N staging than 18F-FDG-PET which can show false-positive uptake in areas of inflammation. However, because of the high background uptake in the liver and bone marrow, it has a limited role of assessing liver and bone metastases. Instead, 18F-FLT-PET will be a powerful tool for monitoring response to treatment and provide prognostic information in digestive and abdominal oncology.

AKT activation controls cell survival in response to HDAC6 inhibition.

HDAC6 is emerging as an important therapeutic target for cancer. We investigated mechanisms responsible for survival of tumor cells treated with a HDAC6 inhibitor. Expression of the 20 000 genes examined did not change following HDAC6 treatment in vivo. We found that HDAC6 inhibition led to an increase of AKT activation (P-AKT) in vitro, and genetic knockdown of HDAC6 phenocopied drug-induced AKT activation. The activation of AKT was not observed in PTEN null cells; otherwise, PTEN/PIK3CA expression per se did not predict HDAC6 inhibitor sensitivity. Interestingly, HDAC6 inhibitor treatment led to inactivating phosphorylation of PTEN (P-PTEN Ser380), which likely led to the increased P-AKT in cells that express PTEN. Synergy was observed with phosphatidylinositol 3'-kinases (PI3K) inhibitor treatment in vitro, accompanied by increased caspase 3/7 activity. Furthermore, combination of HDAC6 inhibitor with a PI3K inhibitor caused substantial tumor growth inhibition in vivo compared with either treatment alone, also detectable by Ki-67 immunostaining and 18F-FLT positron emission tomography (PET). In aggregate AKT activation appears to be a key survival mechanism for HDAC6 inhibitor treatment. Our findings indicate that dual inhibition of HDAC6 and P-AKT may be necessary to substantially inhibit growth of solid tumors.

(18)F-Fluorothymidine PET-CT for resected malignant gliomas before radiotherapy: tumor extent according to proliferative activity compared with MRI.

ObjectiveTo compare the presence of post-operative residual disease by magnetic resonance imaging (MRI) and [18F]fluorothymidine (FLT)-positron emission tomography (PET)-computer tomography (CT) in patients with malignant glioma and to estimate the impact of 18F-FLT PET on the delineation of post-operative target volumes for radiotherapy (RT) planning.MethodsNineteen patients with post-operative residual malignant gliomas were enrolled in this study. For each patient, 18F- FLT PET-CT and MRI were acquired in the same week, within 4 weeks after surgery but before the initiation of RT. The PET-CT and MRI data were co-registered based on mutual information. The residual tumor volume defined on the 18F-FLT PET (Vol-PET) was compared with that of gadolinium [Gd] enhancement on T1-weighted MRI (Vol-T1) and areas of hyperintensity on T2-weighted MRI (Vol-T2).ResultsThe mean Vol-PET (14.61 cm3) and Vol-T1 (13.60 cm3) were comparable and smaller than the mean Vol-T2 (32.93 cm3). The regions of 18F-FLT uptake exceeded the contrast enhancement and the hyperintense area on the MRI in 14 (73.68%) and 8 patients (42.11%), respectively. In 5 (26.32%) of the 19 patients, Vol-PET extended beyond 25 mm from the margin of Vol-T1; in 2 (10.53%) patients, Vol-PET extended 20 mm from the margin of Vol-T2. Vol-PET was detected up to 35 mm away from the edge of Vol-T1 and 24 mm away from the edge of Vol-T2. In 16 (84.21%) of the 19 patients, the Vol-T1 extended beyond the Vol-PET. In all of the patients, at least some of the Vol-T2 was located outside of the Vol-PET.ConclusionsThe volumes of post-operative residual tumor in patients with malignant glioma defined by 18F-FLT uptake on PET are not always consistent with the abnormalities shown on post-operative MRI. Incorporation of 18F-FLT-PET in tumor delineation may have the potential to improve the definition of target volume in post-operative radiotherapy.

Final Results of a Phase 1 Study of 18F-FLT Positron Emission Tomography (PET)/Computed Tomography Imaging in Myelofibrosis (FLT-MF-2009 Study)

Background: PET with fluorodeoxyglucose combined with computed tomography is a major tool for the diagnosis, staging and monitoring of treatment response in clinical oncology. 3′-18Fluoro-3′-deoxy-L-thymidine (18F-FLT) is a nucleoside analog that quickly accumulates in proliferating cells, evaluated in clinical studies in various cancers as a PET radiotracer offering non invasive assessment of cell proliferation in vivo. Preliminary results of a pilot study suggested that this technique could be useful to assess bone marrow (BM) activity and extramedullary hematopoiesis in patients with myelofibrosis (MF). We present the final analysis of the FLT-MF-2009 study (EudraCT Number: 2009-016804-21) confirming that FLT PET could be a new technique useful for MF management.Methods: Main inclusion criteria were: a diagnosis of MF according to WHO criteria; BM biopsy available for centralized review; written informed consent. 18F-FLT PET was performed 1 hour after injection of 18F-FLT (provided by AAA), and consisted in a whole-body acquisition. Two nuclear physicians interpreted images in a blinded fashion independently, qualitatively and according to a visual scale, and patients were classified according to 3 distinct patterns. 18F-FLT uptake was quantified using maximum standardized uptake value (SUVmax) in several sites of the skeleton (axial skeleton, proximal and distal territories of upper and lower limbs), in the spleen and the liver. Analysis of factors affecting the intensity of 18F-FLT uptake in these sites (using PET pattern and SUVmax as the endpoints) was performed by using non-parametric tests.Results: 15 patients (mean age: 62 years) were included between Apr 2011 and Jul 2012. 8 patients had primary (PMF), 3 post-polycythemia vera (PV), and 4 post-essential thrombocythemia (ET) MF. 13 patients had a palpable splenomegaly. 10 patients had the JAK2V617F mutation with a median mutant allele burden of 59% (interquartile range: 29-80%), 1 had a MPL515 mutation. Therapies at time of PET included hydroxyurea (n=1), androgens (n=1), interferon (n=4) and ruxolitinib (n=5); 4 patients had no specific therapy for MF.Three patterns of 18F-FLT PET images were observed. Pattern A (n=3) showed a normal BM activity in the central skeleton, a mild expansion to distal extremities and normal splenic uptake. Pattern B (n= 9) displayed a rather normal pattern of BM activity in the central skeleton associated with marked expansion of BM activity to distal extremities and intense uptake of the tracer in the spleen. Pattern C (n=3) showed a marked reduced hematopoietic activity in the central skeleton but a high uptake in spleen, suggesting the existence of myeloid metaplasia.Quantitative analyses of 18F-FLT uptake using SUVmax permitted the search for correlations with clinical and biological characteristics. Grade 3 fibrosis in BM biopsy was significantly associated with low SUVmax values measured in axial skeleton (p=0.019), proximal upper limbs (p=0.016) and proximal lower limbs (p=0.019). Significantly higher SUVmax values in proximal upper (p=0.014) and lower limbs (p=0.021) were associated with the diagnosis of post-PV- vs. post-ET- or PMF. SUVmax values in proximal upper limbs also correlated with the hemoglobin level (Spearman correlation coefficient: 0.53; p=0.038). No significant correlation was found between SUVmax values in any territory and platelet values, JAK2V617F positivity or allele burden, disease duration. Significantly lower SUVmax values were measured in proximal upper limbs of patients treated with ruxolitinib (3.9 ± 2) compared to patients treated with interferon (11.2 ± 5) or untreated patients (7.7 ± 3.1) (p=0.043).Conclusion: The results of this pilot study suggests that 18F-FLT PET could be a new, objective, non invasive technique useful for the evaluation of malignant hematopoiesis in MF, in terms of diagnosis, staging and for monitoring response to therapy. SUVmax values may discriminate post-PV MF from other forms of MF, and may distinguish patients with grade 3 fibrosis. If this latter finding is confirmed in a larger study, 18F-FLT PET could become a convenient substitute to sequential biopsies for the staging of BM fibrosis during the course of the disease. In addition, distinct SUVmax values were found in patients treated with ruxolitinib, suggesting that 18F-FLT PET could also be useful to monitor the efficacy of therapies in MF. DisclosuresOff Label Use: 18F-FLT is an investigational isotope not approved for the imaging of myelofibrosis. Patients treated off-label with interferon were included in the study..

Comparison of the diagnostic performance of 18F-fluorothymidine versus 18F-fluorodeoxyglucose positron emission tomography on pulmonary lesions: A meta analysis.

A pulmonary lesion is an extremely common and clinically challenging disorder worldwide, and an accurate diagnosis of lung cancer is crucial for early treatment and management. The aim of the present study was to perform a comprehensive meta analysis to compare the diagnostic performance of 18F-fluorothymidine (18F-FLT) positron emission tomography (PET) with 18F-fluorodeoxyglucose (18F-FDG) PET in evaluating patients with pulmonary lesions. Relevant studies were identified using the PubMed, EMBASE and Cochrane library databases. The pooled estimated sensitivity, specificity, positive-likelihood ratio, negative-likelihood ratio, and diagnostic odds ratio (DOR) for 18F-FLT PET versus 18F-FDG PET were calculated as the main outcome measures. Summary receiver operating characteristic curves were also constructed by Meta-Disk 1.4 software using a Mose's constant of linear model. The meta analysis showed that 18F-FLT PET had a higher specificity (0.70; 95% CI, 0.61-0.77), but lower sensitivity (0.81; 95% CI, 0.74-0.87) compared to 18F-FDG PET (0.50; 95% CI, 0.41-0.58 for specificity; 0.92; 95% CI 0.86-0.95 for sensitivity). For DOR, 18F-FLT PET (12.58; 95% CI, 6.81-23.24) was higher compared to 18F-FDG PET (10.72; 95% CI, 5.51-20.87). The area under the curve was 0.8592 and 0.9240 for 18F-FLT PET and 18F-FDG PET, respectively (Z=0.976, P>0.05). In conclusion, 18F-FLT PET and 18F-FDG PET had good diagnostic performance for the overall assessment of pulmonary lesions, and 18F-FLT PET had a higher specificity compared to 18F-FDG PET, but was less sensitive than 18F-FDG PET. Therefore, 18F-FLT and 18F-FDG together could add diagnostic confidence for pulmonary lesions.

18F-FLT PET/CT imaging in a Wister rabbit inflammation model

The aim of the present study was to determine the tumour specificity of the newly developed nucleoside metabolic positron emission tomography (PET) tracer, 3′-deoxy-3′-18F-fluorothymidine (18F-FLT). Using 18F-FLT PET imaging, DNA synthesis and cell proliferation were detected in Staphylococcus aureus (S. aureus) abscess and calcium sulphate models in Wister rabbits. A total of eight rabbits were implanted with S. aureus in the left tibia to induce an inflammatory process. Calcium sulphate + gentamicin was implanted in the right tibia to induce a physical stimulus without bacterial multiplication. After four weeks, the animals underwent 18F-FLT PET imaging, bacterial culturing and tissue pathology. The uptake of 18F-FLT was significantly higher in the abscess site compared with that in the granuloma, with maximum standardised uptake values of 5.76±0.25 and 1.15±0.32, respectively (P<0.01). This indicates that 18F-FLT is not a specific tumour tracer since active inflammation also results in the uptake of this compound. However, the tumour specificity of this tracer is higher compared with that of 18F-fluorodeoxyglucose. Therefore, 18F-FLT may be useful in the differential diagnosis of benign and malignant tumours.

Combined Injection of 18F-Fluorodeoxyglucose and 3′-Deoxy-3′-[18F]fluorothymidine PET Achieves More Complete Identification of Viable Lung Cancer Cells in Mice and Patients than Individual Radiopharmaceutical: A Proof-of-Concept Study

PURPOSE: The objective is to validate the combination of 3′-deoxy-3′-[18F]fluorothymidine (18F-FLT) and 18F-fluorodeoxyglucose (18F-FDG) as a “novel” positron emission tomography (PET) tracer for better visualization of cancer cell components in solid cancers than individual radiopharmaceutical. METHODS: Nude mice with subcutaneous xenografts of human non-small cell lung cancer A549 and HTB177 cells and patients with lung cancer were included. In ex vivo study, intratumoral radioactivity of 18F-FDG, 18F-FLT, and the cocktail of 18F-FDG and 18F-FLT detected by autoradiography was compared with hypoxia (by pimonidazole) and proliferation (by bromodeoxyuridine) in tumor section. In in vivo study, first, 18F-FDG PET and 18F-FLT PET were conducted in the same subjects (mice and patients) 10 to 14 hours apart. Second, PET scan was also performed 1 hour after one tracer injection; subsequently, the other was administered and followed the second PET scan in the mouse. Finally, 18F-FDG and 18F-FLT cocktail PET scan was also performed in the mouse. RESULTS: When injected individually, 18F-FDG highly accumulated in hypoxic zones and high 18F-FLT in proliferative cancer cells. In case of cocktail injection, high radioactivity correlated with hypoxic regions and highly proliferative and normoxic regions. PET detected that intratumoral distribution of 18F-FDG and 18F-FLT was generally mismatched in both rodents and patients. Combination of 18F-FLT and 18F-FDG appeared to map more cancer tissue than single-tracer PET. CONCLUSIONS: Combination of 18F-FDG and 18F-FLT PET imaging would give a more accurate representation of total viable tumor tissue than either tracer alone and would be a powerful imaging strategy for cancer management.

Non-invasive imaging of glioma vessel size and densities in correlation with tumour cell proliferation by small animal PET and MRI

Angiogenesis is a key event in the progression of glioblastomas (GBM). Our goal was to measure different anatomical and physiological parameters of GBM vessels using steady-state contrast-enhanced magnetic resonance imaging (SSCE-MRI), together with the assessment of biochemical parameters on GBM proliferation and angiogenesis using [(11)C]methyl-L-methionine (MET) and 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) and positron emission tomography (PET). We focused on how these anatomical and biochemical read-outs correlate with one another and with immunohistochemistry. SSCE-MRI together with (11)C-MET and (18)F-FLT PET were performed 3 weeks after intracranial implantation of human GBM spheroids in nude rats (n = 8). Total cerebral blood volume (tCBV), blood volume present in microvessels (μCBV), vessel density and size were calculated. Rats were treated with bevacizumab (n = 4) or vehicle (n = 4) for 3 weeks. Imaging was repeated at week 6, and thereafter immunohistochemistry was performed. Three weeks after implantation, MRI showed an increase of vessel density and μCBV in the tumour compared to the contralateral brain. At week 6, non-treated rats showed a pronounced increase of (11)C-MET and (18)F-FLT tumour uptake. Between weeks 3 and 6, tCBV and vessel size increased, whereas vessel density and μCBV decreased. In rats treated with bevacizumab μCBV values were significantly smaller at week 6 than in non-treated rats, whereas the mean vessel size was higher. Accumulation of both radiotracers was lower for the treated versus the non-treated group. Most importantly, non-invasive measurement of tumour vessel characteristics and tumour proliferation correlated to immunohistochemistry findings. Our study demonstrates that SSCE-MRI enables non-invasive assessment of the anatomy and physiology of the vasculature of experimental gliomas. Combined SSCE-MRI and (11)C-MET/(18)F-FLT PET for monitoring biochemical markers of angiogenesis and proliferation in addition to vessel anatomy could be useful to improve our understanding of therapy response of gliomas.

Pemetrexed Induced Thymidylate Synthase Inhibition in Non-Small Cell Lung Cancer Patients: A Pilot Study with 3′-Deoxy-3′-[18F]fluorothymidine Positron Emission Tomography

ObjectivesPemetrexed is a thymidylate synthase (TS) inhibitor and is effective in non-small cell lung cancer (NSCLC). 3′-deoxy-3′-[18F]fluorothymidine (18F-FLT), a proliferation marker, could potentially identify tumor specific TS-inhibition. The aim of this study was to investigate the effect of pemetrexed-induced TS-inhibition on 18F-FLT uptake 4 hours after pemetrexed administration in metastatic NSCLC patients.MethodsFourteen NSCLC patients underwent dynamic 18F-FLT positron emission tomography (PET) scans at baseline and 4 hours after the first dose of pemetrexed. Volumes of interest were defined with a 41%, 50% and 70% threshold of the maximum pixel. Kinetic analysis and simplified measures were performed. At one, two, four and six hours after pemetrexed, plasma deoxyuridine was measured as systemic indicator of TS-inhibition. Tumor response measured with response evaluation criteria in solid tumors (RECIST), time to progression (TTP) and overall survival (OS) were determined.ResultsEleven patients had evaluable 18F-FLT PET scans at baseline and 4 hours after pemetrexed. Two patients had increased 18F-FLT uptake of 35% and 31% after pemetrexed, whereas two other patients had decreased uptake of 31%. In the remaining seven patients 18F-FLT uptake did not change beyond test-retest borders. In all patients deoxyuridine levels raised after administration of pemetrexed, implicating pemetrexed-induced TS-inhibition. 18F-FLT uptake in bone marrow was significantly increased 4 hours after pemetrexed administration. Six weeks after the start of treatment 5 patients had partial response, 4 stable disease and 2 progressive disease. Median TTP was 4.2 months (range 3.0–7.4 months); median OS was 13.0 months (range 5.1–30.8 months). Changes in 18F-FLT uptake were not predictive for tumor response, TTP or OS.ConclusionsMeasuring TS-inhibition in a clinical setting 4 hours after pemetrexed revealed a non-systematic change in 18F-FLT uptake within the tumor. No significant association with tumor response, TTP or OS was observed.

Multimodal imaging of tumor response to sorafenib combined with radiation therapy: comparison between diffusion‐weighted MRI, choline spectroscopy and 18F‐FLT PET imaging

The purpose of this study was to determine the value of different imaging modalities, that is, magnetic resonance imaging/spectroscopy (MRI/MRS) and positron emission tomography (PET), to assess early tumor response to sorafenib with or without radiotherapy. Diffusion-weighted (DW)-MRI, choline (1)H MRS at 11.7 T, and (18)F-FLT PET imaging were used to image fibrosarcoma (FSaII) tumor-bearing mice over time. The imaging markers were compared with apoptosis cell death and cell proliferation measurements assessed by histology. Anti-proliferative effects of sorafenib were evidenced by (1)H MRS and (18)F-FLT PET after 2 days of treatment with sorafenib, with no additional effect of the combination with radiation therapy, results that are in agreement with Ki67 staining. Apparent diffusion coefficient calculated using DW-MRI was not modified after 2 days of treatment with sorafenib, but showed significant increase 24 h after 2 days of sorafenib treatment combined with consecutive irradiation. The three imaging markers were able to show early tumor response as soon as 24 h after treatment initiation, with choline MRS and (18)F-FLT being sensitive to sorafenib in monotherapy as well as in combined therapy with irradiation, whereas DW-MRI was only sensitive to the combination of sorafenib with radiotherapy.

Evaluation of 3′-deoxy-3′-[18F]-fluorothymidine (18F-FLT) kinetics correlated with thymidine kinase-1 expression and cell proliferation in newly diagnosed gliomas

The thymidine analog 3'-deoxy-3'-[(18)F]fluorothymidine ((18)F-FLT) has been developed as a positron emission tomography (PET) tracer to assess the proliferation activity of tumors in vivo. The present study investigated the relationship between the kinetic parameters of (18)F-FLT in vivo and thymidine kinase-1 (TK-1) expression and cell proliferation rate in vitro, and blood-brain barrier (BBB) breakdown in human brain gliomas. A total of 21 patients with newly diagnosed gliomas were examined by (18)F-FLT PET kinetic analysis. Maximum standardized uptake value (SUVmax) and tumor-to-normal (T/N) ratio of (18)F-FLT in the tumor and (18)F-FLT kinetic parameters in the corresponding contralateral region were determined. The expression levels of TK-1 protein and mRNA were determined by immunohistochemistry (IHC) and real-time polymerase chain reaction (PCR), respectively, using surgical specimens. The cell proliferation rate of the tumor was determined in terms of the Ki-67 labeling index. BBB breakdown was evaluated on MR images with contrast enhancement. (18)F-FLT SUVmax and T/N ratio were significantly correlated with the influx rate constant (K (1); P = 0.001 and P < 0.001, respectively), but not with the phosphorylation rate constant (k (3)). IHC and real-time PCR studies demonstrated a significant correlation between K (1) and TK-1 mRNA expression (P = 0.001), but not between k (3) and TK-1 protein and mRNA expression. Linear regression analysis revealed a significant correlation between K (1) and the Ki-67 index (P = 0.003), but not between k (3) and the Ki-67 index. TK-1 mRNA expression was significantly correlated with the Ki-67 index (P = 0.009). (18)F-FLT SUVmax and T/N ratio were significantly correlated with BBB breakdown evaluated by contrast enhancement in MR images (P = 0.003 and P = 0.011, respectively). These results indicate that (18)F-FLT uptake in the tumor is significantly related to transport through the disrupted BBB, but not through phosphorylation activity. Although the tissue TK-1 expression reflects tumor proliferation activity, the phosphorylation rate constant k (3) determined by (18)F-FLT PET kinetic analysis does not accurately reflect TK-1 expression in the tissue and should not be used as a surrogate biomarker of cell proliferation activity in human brain gliomas.

Imaging proliferation in human leukemia-tumor bearing mice with (18)F-FLT: Comparison with (18)F-FDG PET.

Leukemia threatens human life due to its uncontrolled proliferative malignancy. 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) has been suggested as a new positron emission tomography (PET) tracer for imaging tumor proliferation. The aim of the study was to investigate the usefulness of (18)F-FLT PET for imaging human leukemia-tumor bearing mice, compared with fluorine-18-fluorodesoxyglucose ((18)F-FDG PET). In vitro the experiments of (18)F-FLT and (18)F-FDG uptake were performed in K562 cell lines at various time points and radioactive tracer uptake was measured in a gamma counter. (18)F-FLT and (18)F-FDG PET imaging were performed both in the same mouse when eight tumor-bearing mice models of human chronic myeloid leukemia were established successfully by injecting K562 cells. Regions of interest were drawn over the tumor, the crossed normal tissue was regarded as background and the ratio of tumor to non-tumor counts (T/NT) in tissues was calculated. A higher uptake of (18)F-FLT (15min, 5.73±0.05%; 30min, 5.90±0.06%; 60min, 6.16±0.19%; 120min, 6.32±0.08%) than that of (18)F-FDG (15min, 1.05±0.10%; 30min, 1.11±0.14%; 60min, 1.14±0.37%; 120 min, 1.36±0.25%) was observed in K562 cells in the tracer uptake experiment. Ratios of T/NT of (18)F-FLT PET (0.5h, 5.39±0.42; 1h, 4.88±0.43; 2h, 3.81±0.38) were higher than those of (18)F-FDG PET/CT (0.5h, 0.34±0.12; 1h, 0.21±0.06; 2h, 0.13±0.05) after injection. Both uptake and T/NT differences of (18)F-FLT versus (18)F-FDG were significant (P>0.05). In conclusion, (18)F-FLT and (18)F-FDG quantitative and semi-quantitative uptake measurements resulting from cell lines and PET imaging respectively suggested a promising potential of (18)F-FLT for metabolic imaging of human chronic myeloid leukemia.