Using Dual-Tracer PET to Predict the Biologic Behavior of Human Colorectal Cancer

Exosomal circPOLQ promotes macrophage M2 polarization via activating IL-10/STAT3 axis in a colorectal cancer model

BACKGROUND

Accumulating evidence demonstrates that an increased tumor-associated macrophage abundance is often associated with poor prognosis in colorectal cancer (CRC). The mechanism underlying the effect of tumor-derived exosomes on M2 macrophage polarization remains elusive.

RESULTS

The novel circular RNA circPOLQ exhibited significantly higher expression in CRC tissues than in paired normal tissues. Higher circPOLQ expression was associated with poorer prognosis in patients with CRC. In vitro and in vivo experiments showed that tumor-derived exosomal circPOLQ did not directly regulate CRC cell development but promoted CRC metastatic nodule formation by enhancing M2 macrophage polarization. circPOLQ activated the interleukin-10/signal transducer and activator of transcription 3 axis by targeting miR-379-3 p to promote M2 macrophage polarization.

CONCLUSION

circPOLQ can enter macrophages via CRC cell-derived exosomes and promote CRC metastatic nodule formation by enhancing M2 macrophage polarization. These findings reveal a tumor-derived exosome-mediated tumor-macrophage interaction potentially affecting CRC metastatic nodule formation.

Evaluation of survival of the patients with metastatic rectal cancer by staging 18F-FDG PET/CT radiomic and volumetric parameters

OBJECTIVE

The aim of this study is to predict the prognosis in patients with metastatic rectal cancer (mRC) by obtaining a model with machine learning (ML) algorithms through volumetric and radiomic data obtained from baseline 18-Fluorine Fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) images.

METHODS

Sixty-two patients with mRC who underwent 18F-FDG PET/CT imaging for staging between January 2015 and January 2021 were evaluated using LIFEx software. The volume of interest (VOI) of the primary tumor was generated and volumetric and textural features were obtained from this VOI. In addition, metabolic tumor volume (tMTV) and total lesion glycolysis (tTLG) values of tumor foci in the whole body. Clinical and radiomic data were evaluated with ML algorithms to create a model that predicts survival. Significant associations between these features and 1-year and 2-year survival were investigated.

RESULTS

Random forest algorithm was the most successful algorithm in predicting 2-year survival (AUC: 0.843, PRC: 0.822, and MCC: 0.583). The model obtained with this algorithm was able to predict 49 patients with 79.03% accuracy. While tMTV and tTLG values were successful in predicting 1-year survival (p: 0.002 and 0.007, respectively), texture characteristics from the primary tumor did not show a significant relationship with 1-year survival.

CONCLUSIONS

In addition to the important role of 18F-FDG PET/CT in staging patients with mRC, this study shows that it is possible to predict survival with ML methods, with parameters obtained using texture analysis from the primary tumor and whole body volumetric parameters.

Advances in Imaging Modalities and Contrast Agents for the Early Diagnosis of Colorectal Cancer

Colorectal cancer is one of the most common gastrointestinal cancers worldwide. The mortality rate of colorectal cancer has declined by more than 20% due to the rapid development of early diagnostic techniques and effective treatment. At present, there are many diagnostic modalities available for the evaluation of colorectal cancer, such as the carcinoembryonic antigen test, the fecal occult blood test, endoscopy, X-ray barium meal, computed tomography, magnetic resonance imaging, and radionuclide examination. Sensitive and specific imaging modalities have played an increasingly important role in the diagnosis of colorectal cancer following the rapid development of novel contrast agents. This review discusses the applications and challenges of different imaging techniques and contrast agents applied to detect colorectal cancer, for the purpose of the early diagnosis and treatment of patients with colorectal cancer.

Prognostic value of pretreatment tumor-to-blood standardized uptake ratio (SUR) in rectal cancer

OBJECTIVES

The prognostic value of SUV on pretreatment F-18 FDG PET/CT imaging in patients with rectal cancer is a matter of debate. SUR is of prognostic value for survival in different cancers. In this study, we aimed to examine the potential prognostic value of SUR and other parameters in pretreatment F-18 FDG PET/CT for non-metastatic rectal cancer.

METHODS

One hundred four non-metastatic rectal cancer patients who underwent pretreatment PET/CT between March 2012 and January 2018 were included in the study. Firstly, SUV_max, SUV_mean, MTV, and TLG were calculated semi-automatically at the workstation. SUR was calculated as the ratio of tumor SUV_max to thoracic aorta blood SUV_mean. Univariate Cox regression and Kaplan-Meier analysis were used to evaluate overall survival (OS), progression free survival (PFS), and local recurrence (LR). Then, multivariate Cox regression analysis, which included the parameters that were significant in the univariate analysis, was performed.

RESULTS

Multivariate Cox regression analysis revealed that SUR was a prognostic factor for PFS. Age and T stage were prognostic factors for both OS and PFS. MTV was found to be independent risk factors for OS.

CONCLUSIONS

In our study, SUR was the only F-18 FDG PET/CT parameter found to be significant for PFS. The development of new parameters can increase the prognostic value of F-18 FDG PET/CT.

In vivo imaging of cell proliferation in meningioma using 3'-deoxy-3'-[18F]fluorothymidine PET/MRI

PURPOSE

Positron emission tomography (PET) with 3'-deoxy-3'-[¹⁸F]fluorothymidine ([¹⁸F]FLT) provides a noninvasive assessment of tumour proliferation in vivo and could be a valuable imaging modality for assessing malignancy in meningiomas. We investigated a range of static and dynamic [¹⁸F]FLT metrics by correlating the findings with cellular biomarkers of proliferation and angiogenesis.

METHODS

Seventeen prospectively recruited adult patients with intracranial meningiomas underwent a 60-min dynamic [¹⁸F]FLT PET following surgery. Maximum and mean standardized uptake values (SUV_max, SUV_mean) with and without normalization to healthy brain tissue and blood radioactivity obtained from 40 to 60 min summed dynamic images (PET_40-60) and ~ 60-min blood samples were calculated. Kinetic modelling using a two-tissue reversible compartmental model with a fractioned blood volume (V_B) was performed to determine the total distribution volume (V_T). Expressions of proliferation and angiogenesis with key parameters including Ki-67 index, phosphohistone-H3 (phh3), MKI67, thymidine kinase 1 (TK1), proliferating cell nuclear antigen (PCNA), Kirsten RAt Sarcoma viral oncogene homolog (KRAS), TIMP metallopeptidase inhibitor 3 (TIMP3), and vascular endothelial growth factor A (VEGFA) were determined by immunohistochemistry and/or quantitative polymerase chain reaction.

RESULTS

Immunohistochemistry revealed 13 World Health Organization (WHO) grade I and four WHO grade II meningiomas. SUV_max and SUV_mean normalized to blood radioactivity from PET_40-60 and blood sampling, and V_T were able to significantly differentiate between WHO grades with the best results for maximum and mean tumour-to-whole-blood ratios (sensitivity 100%, specificity 94-95%, accuracy 99%; P = 0.003). Static [¹⁸F]FLT metrics were significantly correlated with proliferative biomarkers, especially Ki-67 index, phh3, and TK1, while no correlations were found with VEGFA or V_B. Using Ki-67 index with a threshold > 4%, the majority of [¹⁸F]FLT metrics showed a high ability to identify aggressive meningiomas with SUV_mean demonstrating the best performance (sensitivity 80%, specificity 81%, accuracy 80%; P = 0.024).

CONCLUSION

[¹⁸F]FLT PET could be a useful imaging modality for assessing cellular proliferation in meningiomas.

Noninvasive evaluation of 18F-FDG/18F-FMISO-based Micro PET in monitoring hepatic metastasis of colorectal cancer

This study aimed to explore the application of two radiotracers (¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-fluoromisonidazole (FMISO)) in monitoring hepatic metastases of human colorectal cancer (CRC). Mouse models of CRC hepatic metastases were established by implantation of the human CRC cell lines LoVo and HT29 by intrasplenic injection. Wound healing and Transwell assays were performed to examine cell migration and invasion abilities. Radiotracer-based cellular uptake in vitro and micro-positron emission tomography imaging of liver metastases in vivo were performed. The incidence of liver metastases in LoVo-xenografted mice was significantly higher than that in HT29-xenografted ones. The SUVmax/mean values of ¹⁸F-FMISO, but not ¹⁸F-FDG, in LoVo xenografts were significantly greater than in HT29 xenografts. In vitro, LoVo cells exhibited stronger metastatic potential and higher radiotracer uptake than HT29 cells. Mechanistically, the expression of HIF-1α and GLUT-1 in LoVo cells and LoVo tumor tissues was remarkably higher than in HT29 cells and tissues. Linear regression analysis demonstrated correlations between cellular ¹⁸F-FDG/¹⁸F-FMISO uptake and HIF-1α/GLUT-1 expression in vitro, as well as between ¹⁸F-FMISO SUVmax and GLUT-1 expression in vivo. ¹⁸F-FMISO uptake may serve as a potential biomarker for the detection of liver metastases in CRC, whereas its clinical use warrants validation.

Validation of Bevacizumab Therapy Effect on Colon Cancer Subtypes by Using Whole Body Imaging in Mice

PURPOSE

Preclinical imaging offers a useful tool for monitoring cancer biological behavior and therapy in vivo without the necessity of animal surgery. The following paper describes our examination of tumor progress and anti-angiogenic therapy with Bevacizumab on colon cancer subtypes (SW480 and SW620) by using different non-invasive real-time in vivo imaging techniques.

PROCEDURES

Color Doppler ultrasound imaging (CDUI) was used to observe the formation of new blood vessels; a homemade fluorescence reflectance imaging (FRI) apparatus was mainly used to test the difference in VEGFR2 expression between the tumor subtypes. Briefly, 15 Balb/c nude mice bearing subcutaneous SW480 and SW620 xenografts were randomly divided into Control and Drug groups. Bevacizumab treatment lasted for 3 weeks. All images were captured pre- and post-treatment. At the end of experiment, all mice were euthanized, and tumor tissue was collected and analyzed by immunohistochemical staining.

RESULTS

Expression of VEGFR2 was found to be slightly (10 %) but significantly higher for the SW620 cells than for SW480 cells. In addition, SW620 has shown to be more vascularized than SW480 subtype. After 3-week Bevacizumab therapy, no blood vessels were found within 83 % of SW620, while it was 67 % in SW480; the increase of SW620 tumor volume post-treatment was only 3.17-fold compared with the tumor volume pre-treatment, and 4.51-fold higher in SW480.

CONCLUSION

Our data suggest that SW480 and SW620 cell lines respond differently to Bevacizumab therapy in vivo. Because of higher vascularization, and subsequently higher reduction by drug of new blood vessels and tumor growth rate, xenografts derived from the metastatic SW620 cell line have a better chance of being successfully treated with Bevacizumab compared with those derived from the primary tumor SW480 cell line.

Advanced Imaging Techniques in Evaluation of Colorectal Cancer

Imaging techniques are clinical decision-making tools in the evaluation of patients with colorectal cancer (CRC). The aim of this article is to discuss the potential of recent advances in imaging for diagnosis, prognosis, therapy planning, and assessment of response to treatment of CRC. Recent developments and new clinical applications of conventional imaging techniques such as virtual colonoscopy, dual-energy spectral computed tomography, elastography, advanced computing techniques (including volumetric rendering techniques and machine learning), magnetic resonance (MR) imaging-based magnetization transfer, and new liver imaging techniques, which may offer additional clinical information in patients with CRC, are summarized. In addition, the clinical value of functional and molecular imaging techniques such as diffusion-weighted MR imaging, dynamic contrast material-enhanced imaging, blood oxygen level-dependent imaging, lymphography with contrast agents, positron emission tomography with different radiotracers, and MR spectroscopy is reviewed, and the advantages and disadvantages of these modalities are evaluated. Finally, the future role of imaging-based analysis of tumor heterogeneity and multiparametric imaging, the development of radiomics and radiogenomics, and future challenges for imaging of patients with CRC are discussed. Online supplemental material is available for this article. ^©RSNA, 2018.

Prediction of tumor biological characteristics in different colorectal cancer liver metastasis animal models using 18F-FDG and 18F-FLT

BACKGROUND

Positron emission tomography (PET) is a noninvasive method to characterize different metabolic activities of tumors, providing information for staging, prognosis, and therapeutic response of patients with cancer. The aim of this study was to evaluate the feasibility of ¹⁸F-fludeoxyglucose (¹⁸F-FDG) and 3'-deoxy-3'-¹⁸F-fluorothymidine (¹⁸F-FLT) PET in predicting tumor biological characteristics of colorectal cancer liver metastasis.

METHODS

The uptake rate of ¹⁸F-FDG and ¹⁸F-FLT in SW480 and SW620 cells was measured via an in vitro cell uptake assay. The region of interest was drawn over the tumor and liver to calculate the maximum standardized uptake value ratio (tumor/liver) from PET images in liver metastasis model. The correlation between tracer uptake in liver metastases and VEGF, Ki67 and CD44 expression was evaluated by linear regression.

RESULTS

Compared to SW620 tumor-bearing mice, SW480 tumor-bearing mice presented a higher rate of liver metastases. The uptake rate of ¹⁸F-FDG in SW480 and SW620 cells was 6.07% ± 1.19% and 2.82% ± 0.15%, respectively (t = 4.69, P = 0.04); that of ¹⁸F-FLT was 24.81% ± 0.45% and 15.57% ± 0.66%, respectively (t = 19.99, P < 0.001). Micro-PET scan showed that all parameters of FLT were significantly higher in SW480 tumors than those in SW620 tumors. A moderate relationship was detected between metastases in the liver and ¹⁸F-FLT uptake in primary tumors (r = 0.73, P = 0.0019). ¹⁸F-FLT uptake was also positively correlated with the expression of CD44 in liver metastases (r = 0.81, P = 0.0049).

CONCLUSIONS

The uptake of ¹⁸F-FLT in metastatic tumor reflects different biological behaviors of colon cancer cells. ¹⁸F-FLT can be used to evaluate the metastatic potential of colorectal cancer in nude mice.

Comparison of Positron Emission Tomography Using 2-[18F]-fluoro-2-deoxy-D-glucose and 3-deoxy-3-[18F]-fluorothymidine in Lung Cancer Imaging

Background:

The detection of solitary pulmonary nodules (SPNs) that may potentially develop into a malignant lesion is essential for early clinical interventions. However, grading classification based on computed tomography (CT) imaging results remains a significant challenge. The 2-[¹⁸F]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) positron emission tomography (PET)/CT imaging produces both false-positive and false-negative findings for the diagnosis of SPNs. In this study, we compared ¹⁸F-FDG and 3-deoxy-3-[¹⁸F]-fluorothymidine (¹⁸F-FLT) in lung cancer PET/CT imaging.

Methods:

The binding ratios of the two tracers to A549 lung cancer cells were calculated. The mouse lung cancer model was established (n = 12), and micro-PET/CT analysis using the two tracers was performed. Images using the two tracers were collected from 55 lung cancer patients with SPNs. The correlation among the cell-tracer binding ratios, standardized uptake values (SUVs), and Ki-67 proliferation marker expression were investigated.

Results:

The cell-tracer binding ratio for the A549 cells using the ¹⁸F-FDG was greater than the ratio using ¹⁸F-FLT (P < 0.05). The Ki-67 expression showed a significant positive correlation with the ¹⁸F-FLT binding ratio (r = 0.824, P < 0.01). The tumor-to-nontumor uptake ratio of ¹⁸F-FDG imaging in xenografts was higher than that of ¹⁸F-FLT imaging. The diagnostic sensitivity, specificity, and the accuracy of ¹⁸F-FDG for lung cancer were 89%, 67%, and 73%, respectively. Moreover, the diagnostic sensitivity, specificity, and the accuracy of ¹⁸F-FLT for lung cancer were 71%, 79%, and 76%, respectively. There was an obvious positive correlation between the lung cancer Ki-67 expression and the mean maximum SUV of ¹⁸F-FDG and ¹⁸F-FLT (r = 0.658, P < 0.05 and r = 0.724, P < 0.01, respectively).

Conclusions:

The ¹⁸F-FDG uptake ratio is higher than that of ¹⁸F-FLT in A549 cells at the cellular level. ¹⁸F-FLT imaging might be superior for the quantitative diagnosis of lung tumor tissue and could distinguish lung cancer nodules from other SPNs.

Establishment of an mKate2-Expressing Cell Line for Non-Invasive Real-Time Breast Cancer In Vivo Imaging

PURPOSE

Non-invasive real-time in vivo imaging experiments using mice as animal models have become crucial for understanding cancer development and treatment. In this study, we have developed and validated a new breast cancer cell line MDA-MB-435s that stably express a far-red fluorescence protein (mKate2) and that could serve as a highly valuable cell model for studying breast cancer detection and therapy using in vivo fluorescence imaging in nude mice.

PROCEDURES

The new cell line (MDA-MB-435s-mKate2) was constructed by plasmid transfection. The stability and sensitivity of mKate2, and the cell biological activities, were tested in vitro using different experimental approaches. For its potential use in tumor growth research and drug therapy in vivo, MDA-MB-435s-mKate2 was validated using the immunocompromised Balb/c nude mice tumor model. In addition, the new cell line has been characterized as a luteinizing hormone-releasing hormone receptor (LHRHR) positive cell line.

RESULTS

Firstly, MDA-MB-435s-mKate2 has shown a stable chromosomal integration of the amplified mKate2 gene and good fluorescence sensitivity for detection using a fluorescence reflectance imaging (FRI) device. Compared to its parental cell line, no significant difference in cell migration, proliferation, and clone formation was observed in vitro. Secondly, using the quantification of tumor-fluorescence surface area in live animals, we were able to monitor and detect the tumor progress or tumor inhibition rate (by Paclitaxel treatment) non-invasively and in real-time. Furthermore, MDA-MB-435s-mKate2 has been positively tested for LHRHR; these findings open the possibility to use this cell line for future studies of breast cancer therapy based on LHRH analogs in vivo.

CONCLUSION

In the present research, we have successfully built the MDA-MB-435s-mKate2 cell line that can be used as a suitable cell model for breast cancer therapy and anti-cancer drug evaluation by non-invasive fluorescence imaging in mice.

Direct Parametric Image Reconstruction in Reduced Parameter Space for Rapid Multi-Tracer PET Imaging

The separation of multiple PET tracers within an overlapping scan based on intrinsic differences of tracer pharmacokinetics is challenging, due to limited signal-to-noise ratio (SNR) of PET measurements and high complexity of fitting models. In this study, we developed a direct parametric image reconstruction (DPIR) method for estimating kinetic parameters and recovering single tracer information from rapid multi-tracer PET measurements. This is achieved by integrating a multi-tracer model in a reduced parameter space (RPS) into dynamic image reconstruction. This new RPS model is reformulated from an existing multi-tracer model and contains fewer parameters for kinetic fitting. Ordered-subsets expectation-maximization (OSEM) was employed to approximate log-likelihood function with respect to kinetic parameters. To incorporate the multi-tracer model, an iterative weighted nonlinear least square (WNLS) method was employed. The proposed multi-tracer DPIR (MT-DPIR) algorithm was evaluated on dual-tracer PET simulations ([18F]FDG and [11C]MET) as well as on preclinical PET measurements ([18F]FLT and [18F]FDG). The performance of the proposed algorithm was compared to the indirect parameter estimation method with the original dual-tracer model. The respective contributions of the RPS technique and the DPIR method to the performance of the new algorithm were analyzed in detail. For the preclinical evaluation, the tracer separation results were compared with single [18F]FDG scans of the same subjects measured two days before the dual-tracer scan. The results of the simulation and preclinical studies demonstrate that the proposed MT-DPIR method can improve the separation of multiple tracers for PET image quantification and kinetic parameter estimations.

Correlations of (18)F-fluorothymidine uptake with pathological tumour size, Ki-67 and thymidine kinase 1 expressions in primary and metastatic lymph node colorectal cancer foci

OBJECTIVE

To examine correlations of (18)F-fluorothymidine (FLT) uptake with pathological tumour size and immunohistochemical Ki-67, and thymidine kinase 1 (TK-1) expressions in primary and metastatic node colorectal cancer foci.

METHODS

Thirty primary cancers (PCs) and 37 metastatic nodes (MNs) were included. FLT uptake was assessed by visual scores (non-visible: 0-1 and visible: 2-4), standardized uptake value (SUV), and correlated with size, Ki-67, and TK-1. SUV was measured in visible lesions. FLT heterogeneity was assessed by visual scores (no heterogeneous uptake: 0 and heterogeneous uptake: 1-4).

RESULTS

Forty-two lesions were visible. The visible group showed significantly higher values than the non-visible group in size, Ki-67, and TK-1 (each p < 0.05). Size correlated significantly with visual score (PC; ρ = 0.74 and MN; ρ = 0.63), SUVmax (PC; ρ = 0.49, and MN; ρ = 0.76), and SUVmean (PC; ρ = 0.40 and MN; ρ = 0.76) (each p < 0.05). Visual score correlated significantly with size (ρ = 0.86), Ki-67max (ρ = 0.35), Ki-67mean (ρ = 0.38), TK-1max (ρ = 0.35) and TK-1mean (ρ = 0.25) (each p < 0.05). No significant correlations were found between FLT uptake and Ki-67 or TK-1 in 42 visible lesions (each p > 0.05). Heterogeneous FLT uptake was noted in 73 % (22/30) of PCs.

CONCLUSION

FLT uptake correlated with size. Heterogeneous FLT distribution in colorectal cancers may be one of the causes of weak or lack of FLT uptake/Ki-67 or TK-1 correlation.

KEY POINTS

FLT uptake correlated well with tumour size in colorectal cancer. Weak or lack of FLT uptake/Ki-67 and TK-1 correlations were observed. Immunohistochemical Ki-67 and TK-1 expressions are not always correlated with FLT uptake.

An integrated quad-modality molecular imaging system for small animals

We developed a novel integrated quad-modality system that included 3 molecular imaging methods (PET, SPECT, and fluorescence molecular imaging [FMI]) and 1 anatomic imaging modality (CT). This system could study various biologic processes in the same animal using multiple molecular tracers. In addition to the technology development, we also discussed the optimization strategy of the imaging protocols. The performance of this system was tested, and the in vivo animal experiment showed its power to trace 3 different molecular probes in living tissues. Our results demonstrated that this system has a great potential for the preclinical study of diseases.

METHODS

A prototype system integrating PET, SPECT, CT, and a charge-coupled device-based free-space FMI system has been developed. Imaging and fusion capabilities of the system were evaluated by a multimodality phantom. In addition, a mouse disease model with both tumor and inflammation was studied by this system to examine the in vivo performance. The 3 types of molecular probes-(18)F-FDG, [(99m)Tc(HYNIC-3PRGD2)(tricine)(TPPTS)] ((99m)Tc-3PRG2) (HYNIC = 6-hydrazinonicotinyl; TPPTS = trisodium triphenylphosphine-3,3',3″-trisulfonate; 3PRGD2 = PEG4-E[PEG4-c(RGDfK)]2), and 3-(triethoxysilyl) propyl-Cy7-entrapped core-cross-linked polymeric micelle (Cy7-entrapped CCPM) nanoparticles-were used to target 3 different biologic processes in the tumor caused by pulmonary adenocarcinoma A549 cells. Moreover, the strategy to optimize multimodal molecular imaging procedure was studied as well, which could significantly reduce the total imaging time.

RESULTS

The imaging performance has been validated by both phantom and in vivo animal experiments. With this system and optimized imaging protocol, we successfully differentiated diseases that cannot be distinguished by a single molecular imaging modality.

CONCLUSION

We developed a novel quad-modality molecular imaging system that integrated PET, SPECT, FMI, and CT imaging methods to obtain whole-body multimodality images of small animals. The imaging results demonstrated that this system provides more comprehensive information for preclinical biomedical research. With optimized imaging protocols, as well as novel molecular tracers, this quad-modality system can help in the study of the physiology mechanism at an unprecedented level.

Evaluation of ¹⁸F-FDG and ¹⁸F-FLT for monitoring therapeutic responses of colorectal cancer cells to radiotherapy

In order to compare the efficacy of (18)F-fluorothymidine (FLT) and (18)F-fluorodeoxyglucose (FDG) for monitoring early responses to irradiation, two human colorectal cancer (CRC) cell lines SW480 and SW620, which were derived from the primary lesions and the metastatic lymph node, underwent X-ray irradiation of 0, 10, or 20 Gy and were examined at 0, 24 and 72 h After irradiation, reduced proliferation of both SW480 and SW620 cells was observed in a dose-dependent manner (P<0.001), G0-G1 arrest was also noted in both cell types after 72 h in the 20 Gy group (P<0.001). Although increased apoptosis was observed in both cell lines after irradiation (P<0.001), a greater percentage of SW480 cells underwent apoptosis in response to irradiation than SW620 cells. Increased Hsp27 and decreased integrin β3, Ki67 and VEGFR2 expression was observed over time via immunocytochemistry and Western blot analysis (P<0.001), however, no significant changes were noted in response to irradiation. Finally, reduced uptake of (18)F-FLT by SW480 or SW620 cells was observed at 24-h post-irradiation, however, reduced (18)F-FDG uptake was only observed after 72 h. Therefore, we conclude that (18)F-FLT is a more suitable positron emission tomography (PET) tracer for monitoring early responses to irradiation in primary and metastatic lymph node CRC cells.

Limits of [18F]-FLT PET as a biomarker of proliferation in oncology

Background

Non-invasive imaging biomarkers of cellular proliferation hold great promise for quantifying response to personalized medicine in oncology. An emerging approach to assess tumor proliferation utilizes the positron emission tomography (PET) tracer 3’-deoxy-3’[¹⁸F]-fluorothymidine, [¹⁸F]-FLT. Though several studies have associated serial changes in [¹⁸F]-FLT-PET with elements of therapeutic response, the degree to which [¹⁸F]-FLT-PET quantitatively reflects proliferative index has been continuously debated for more that a decade. The goal of this study was to elucidate quantitative relationships between [¹⁸F]-FLT-PET and cellular metrics of proliferation in treatment naïve human cell line xenografts commonly employed in cancer research.

Methods and Findings

[¹⁸F]-FLT-PET was conducted in human cancer xenograft-bearing mice. Quantitative relationships between PET, thymidine kinase 1 (TK1) protein levels and immunostaining for proliferation markers (Ki67, TK1, PCNA) were evaluated using imaging-matched tumor specimens. Overall, we determined that [¹⁸F]-FLT-PET reflects TK1 protein levels, yet the cell cycle specificity of TK1 expression and the extent to which tumors utilize thymidine salvage for DNA synthesis decouple [¹⁸F]-FLT-PET data from standard estimates of proliferative index.

Conclusions

Our findings illustrate that [¹⁸F]-FLT-PET reflects tumor proliferation as a function of thymidine salvage pathway utilization. Unlike more general proliferation markers, such as Ki67, [¹⁸F]-FLT PET reflects proliferative indices to variable and potentially unreliable extents. [¹⁸F]-FLT-PET cannot discriminate moderately proliferative, thymidine salvage-driven tumors from those of high proliferative index that rely primarily upon de novo thymidine synthesis. Accordingly, the magnitude of [¹⁸F]-FLT uptake should not be considered a surrogate of proliferative index. These data rationalize the diversity of [¹⁸F]-FLT-PET correlative results previously reported and suggest future best-practices when [¹⁸F]-FLT-PET is employed in oncology.

An evaluation of 2-deoxy-2-[18F]fluoro-D-glucose and 3'-deoxy-3'-[18F]-fluorothymidine uptake in human tumor xenograft models

PURPOSE

The aim of this study is to assess the variability of 2-deoxy-2-[(18)F]fluoro-D: -glucose ([(18)F]-FDG) and 3'-deoxy-3'-[(18)F]-fluorothymidine ([(18)F]-FLT) uptake in pre-clinical tumor models and examine the relationship between imaging data and related histological biomarkers.

PROCEDURES

[(18)F]-FDG and [(18)F]-FLT studies were carried out in nine human tumor xenograft models in mice. A selection of the models underwent histological analysis for endpoints relevant to radiotracer uptake. Comparisons were made between in vitro uptake, in vivo imaging, and ex vivo histopathology data using quantitative and semi-quantitative analysis.

RESULTS

In vitro data revealed that [1-(14)C]-2-deoxy-D: -glucose ([(14)C]-2DG) uptake in the tumor cell lines was variable. In vivo, [(18)F]-FDG and [(18)F]-FLT uptake was highly variable across tumor types and uptake of one tracer was not predictive for the other. [(14)C]-2DG uptake in vitro did not predict for [(18)F]-FDG uptake in vivo. [(18)F]-FDG SUV was inversely proportional to Ki67 and necrosis levels and positively correlated with HKI. [(18)F]-FLT uptake positively correlated with Ki67 and TK1.

CONCLUSION

When evaluating imaging biomarkers in response to therapy, the choice of tumor model should take into account in vivo baseline radiotracer uptake, which can vary significantly between models.

Prognostic value of 18-fluorodeoxyglucose positron emission tomography-computed tomography in resectable colorectal cancer

AIM: To assess the prognostic value of preoperative 18 fluorodeoxyglucose positron emission tomography (FDG-PET)/computed tomography (CT) in patients with resectable colorectal cancer.

METHODS: One hundred sixty-three patients with resectable colorectal cancer who underwent FDG-PET/CT before surgery were included. Patient data including pathologic stage at presentation, histology, treatment, disease-free survival and the maximum standardized uptake value (SUVmax) of the primary tumor on FDG-PET/CT were retrospectively analyzed. Median follow up duration was 756 (range, 419-1355). The primary end point was disease-free survival.

RESULTS: Twenty-five of 163 patients (15.3%) had recurrences. The median SUVmax values of the recurrence and no-recurrence groups were 8.9 (range, 5-24) and 8.2 (range, 0-23, P = 0.998). Receiver operating characteristic (ROC) curve analysis showed no significant association between SUVmax and recurrence (area under the curve = 0.5, P = 0.998, 95% CI: 0.389-0.611). Because a statistically significant value was not found, SUVmax was dichotomized at its median of 8.6. The disease-free survival curve was analyzed using the median SUVmax (8.6) as the cut off. Univariate and multivariate analysis did not provide evidence that disease-free survival rates for the subgroups defined by the median SUVmax were significantly different (P = 0.52, P = 0.25).

CONCLUSION: Our study suggests that the high FDG uptake of primary mass in resectable colorectal cancer doesn’t have a significant relationship with tumor recurrence and disease-free survival.

Simultaneous quantification of multiple magnetic nanoparticles

Distinct magnetic nanoparticle designs can have unique spectral responses to an AC magnetic field in a technique called the magnetic spectroscopy of Brownian motion (MSB). The spectra of the particles have been measured using desktop spectrometers and in vivo measurements. If multiple particle types are present in a region of interest, the unique spectral signatures allow for the simultaneous quantification of the various particles. We demonstrate such a potential experimentally with up to three particle types. This ability to concurrently detect multiple particles will enable new biomedical applications.

[Detection of lymph node involvement and surgical treatment of pulmonary neoplastic processes. Current state of diagnostic and therapeutic procedures]

An analysis is made of different publications associated with the surgical staging and treatment of primary and metastasic pulmonary neoplastic processes. A suitable treatment program is essential to determine lymph node involvement in patients with bronchogenic carcinoma. The indication and sequence of the procedure to use (CT-PET, transbronchial puncture, videomediastinoscopic ultrasound guided transbronchial needle aspiration) is evaluated in accordance to the sensitivity, specificity and positive and negative predictive value of the different methods. Another interesting challenge is to define the criteria for indicating a sublobar resection in certain tumours and patients. Different factors, age, lung function, tumour location and type of sublobar resection, are analysed. Levels of evidence and recommendations of the procedure are also considered. Surgical resection is an accepted therapeutic option in the treatment of colorectal cancer lung metastases. Its indication is based on acceptable survival rates and knowledge of the impact of various factors (interval free of disease, number of metastases, presence of liver metastasis, presence of lymph node involvement, or increased pre-operative levels of carcinoembryonic antigen), is analysed in detail.