Variability of Proliferation and Diffusion in Different Lung Cancer Models as Measured by 3'-Deoxy-3'-¹⁸F-Fluorothymidine PET and Diffusion-Weighted MR Imaging

Evaluation of diffusion-weighted MRI and (18F) fluorothymidine-PET biomarkers for early response assessment in patients with operable non-small cell lung cancer treated with neoadjuvant chemotherapy

Objective:

To correlate changes in the apparent diffusion coefficient (ADC) from diffusion-weighted (DW)-MRI and standardised uptake value (SUV) from fluorothymidine (¹⁸FLT)-PET/CT with histopathological estimates of response in patients with non-small cell lung cancer (NSCLC) treated with neoadjuvant chemotherapy and track longitudinal changes in these biomarkers in a multicentre, multivendor setting.

Methods:

14 patients with operable NSCLC recruited to a prospective, multicentre imaging trial (EORTC-1217) were treated with platinum-based neoadjuvant chemotherapy. 13 patients had DW-MRI and FLT-PET/CT at baseline (10 had both), 12 were re-imaged at Day 14 (eight dual-modality) and nine after completing chemotherapy, immediately before surgery (six dual-modality). Surgical specimens (haematoxylin-eosin and Ki67 stained) estimated the percentage of residual viable tumour/necrosis and proliferation index.

Results:

Despite the small numbers,significant findings were possible. ADC_median increased (p < 0.001) and SUV_mean decreased (p < 0.001) significantly between baseline and Day 14; changes between Day 14 and surgery were less marked. All responding tumours (>30% reduction in unidimensional measurement pre-surgery), showed an increase at Day 14 in ADC75^th centile and reduction in total lesion proliferation (SUV_mean x proliferative volume) greater than established measurement variability. Change in imaging biomarkers did not correlate with histological response (residual viable tumour, necrosis).

Conclusion:

Changes in ADC and FLT-SUV following neoadjuvant chemotherapy in NSCLC were measurable by Day 14 and preceded changes in unidimensional size but did not correlate with histopathological response. However, the magnitude of the changes and their utility in predicting (non-) response (tumour size/clinical outcome) remains to be established.

Advances in knowledge:

During treatment, ADC increase precedes size reductions, but does not reflect histopathological necrosis.

Evaluation of [18F]FDG/[18F]FLT/[18F]FMISO-based micro-positron emission tomography in detection of liver metastasis in human colorectal cancer

INTRODUCTION

Positron emission tomography (PET) is extensively used in clinical oncology for tumor detection. This study aimed to explore the application of the radiotracers [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG), 3'-deoxy-3'- [¹⁸F]fluorothymidine ([¹⁸F]FLT), and [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO) in the diagnosis and monitoring of hepatic metastasis in human colorectal cancer (CRC).

METHODS

A mouse model of human CRC with hepatic metastasis was established by intrasplenic implantation of human CRC cell lines LoVo or HCT8. Metastatic potential of these two cell lines was evaluated by wound healing assay in vitro and survival analysis. Uptake of radiotracers between LoVo and HCT8 cells and uptake of radiotracers in the resulting mouse tumor models were examined by in vivo and in vitro experiments. Uptake of each radiotracer in hepatic metastatic lesions was quantified and expressed as standard uptake value (SUV). Protein expression of multiple tumor biomarkers was determined in metastatic lesions. The correlation between tracer uptake and tumor marker expression was evaluated using linear regression.

RESULTS

LoVo cells exhibited a stronger metastatic potential and a higher radiotracer uptake ability than HCT8 cells, as evidenced by significantly greater wound closure percentage, shorter survival, higher incidence of liver metastases, and higher cellular radiotracer levels in LoVo cells or LoVo cell-xenografted mice. SUV values of [¹⁸F]FLT and [¹⁸F]FMISO, but not [¹⁸F]FDG, in LoVo cell-derived metastatic lesions were significantly greater than those in HCT8 lesions. Mechanistically, the expression of MACC1, HIF-1α, and GLUT-1(metastasis associated in colon cancer 1, MACC1; hypoxia-inducible factor 1-alpha, HIF-1α; and glucose transporter 1, GLUT-1, respectively) in LoVo cell-derived metastatic lesions was more effectively induced than in HCT8-derived ones. A linear regression analysis demonstrated significant positive correlations between [¹⁸F]FLT/[¹⁸F]FMISO uptake and tumor biomarker expression in metastatic tissues.

CONCLUSIONS

[¹⁸F]FLT and [¹⁸F]FMISO-based PET imaging may serve as a promising method for early detection and monitoring of hepatic metastasis in patients with CRC.

Thymidine Metabolism as a Confounding Factor for 3'-Deoxy-3'-18F-Fluorothymidine Uptake After Therapy in a Colorectal Cancer Model

Noninvasive monitoring of tumor therapy response helps in developing personalized treatment strategies. Here, we performed sequential PET and diffusion-weighted MRI to evaluate changes induced by a FOLFOX-like combination chemotherapy in colorectal cancer xenografts, to identify the cellular and molecular determinants of these imaging biomarkers. Methods: Tumor-bearing CD1 nude mice, engrafted with FOLFOX-sensitive Colo205 colorectal cancer xenografts, were treated with FOLFOX (5-fluorouracil, leucovorin, and oxaliplatin) weekly. On days 1, 2, 6, 9, and 13 of therapy, tumors were assessed by in vivo imaging and ex vivo analyses. In addition, HCT116 xenografts, which did not respond to the FOLFOX treatment, were imaged on day 1 of therapy. Results: In Colo205 xenografts, FOLFOX induced a profound increase in uptake of the proliferation PET tracer 3'-deoxy-3'-18F-fluorothymidine (18F-FLT) accompanied by increases in markers for proliferation (Ki-67, thymidine kinase 1) and for activated DNA damage response (γH2AX), whereas the effect on cell death was minimal. Because tracer uptake was unaltered in the HCT116 model, these changes appear to be specific for tumor response. Conclusion: We demonstrated that 18F-FLT PET can noninvasively monitor cancer treatment-induced molecular alterations, including thymidine metabolism and DNA damage response. The cellular or imaging changes may not, however, be directly related to therapy response as assessed by volumetric measurements.

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.

3'-Deoxy-3'-[18F]Fluorothymidine Uptake Is Related to Thymidine Phosphorylase Expression in Various Experimental Tumor Models

PURPOSE

We recently reported that high thymidine phosphorylase (TP) expression is accompanied by low tumor thymidine concentration and high 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) uptake in four untreated lung cancer xenografts. Here, we investigated whether this relationship also holds true for a broader range of tumor models.

PROCEDURES

Lysates from n = 15 different tumor models originating from n = 6 institutions were tested for TP and thymidylate synthase (TS) expression using western blots. Results were correlated to [18F]FLT accumulation in the tumors as determined by positron emission tomography (PET) measurements in the different institutions and to previously published thymidine concentrations.

RESULTS

Expression of TP correlated positively with [18F]FLT SUVmax (ρ = 0.549, P < 0.05). Furthermore, tumors with high TP levels possessed lower levels of thymidine (ρ = - 0.939, P < 0.001).

CONCLUSIONS

In a broad range of tumors, [18F]FLT uptake as measured by PET is substantially influenced by TP expression and tumor thymidine concentrations. These data strengthen the role of TP as factor confounding [18F]FLT uptake.

Multiparametric MR imaging detects therapy efficacy of radioactive seeds brachytherapy in pancreatic ductal adenocarcinoma xenografts

OBJECTIVE

To investigate the therapeutic efficacy of Iodine-125 (¹²⁵I) seeds brachytherapy to pancreatic ductal adenocarcinoma (PDAC) xenografts via multiparametric magnetic resonance imaging (MRI) analysis.

MATERIALS AND METHODS

Twenty mice were implanted subcutaneously with SW-1990 PDAC xenografts. The tumor-bearing mice were randomly divided into ¹²⁵I seeds group (n = 10) and blank control group (n = 10). Treatment response was monitored by diffusion-weighted magnetic resonance imaging (DW-MRI) and dynamic contrast-enhanced MRI (DCE-MRI) obtained 1 day before, 14 and 60 days after treatment. Imaging results were correlated with histopathology.

RESULTS

¹²⁵I seeds brachytherapy resulted in a significant increase in mean tumor apparent diffusion coefficient (ADC) values compared to the control at 14 and 60 days after treatment (p < 0.05). DCE-MRI showed a significant decrease in the perfusion parameters including K^trans and K_ep (p < 0.05). The mean ADCs within the peripheral region of the tumors were linearly proportional to the mean apoptotic cell density (p = 0.015; Spearman's coefficient = 0.945). The K^trans and K_ep were linearly proportional to microvessel density (MVD) (p = 0.043, 0.047; Spearman's coefficient = 0.891, 0.884).

CONCLUSION

¹²⁵I seeds brachytherapy leads to effective inhibition of PDAC cell proliferation, higher degree of necrosis and necroptosis, and lower MVD. Both DW-MRI and DCE-MRI are feasible to monitor a response to ¹²⁵I seeds brachytherapy in the PDAC xenografts. This paper shows an original project concerning about a possible palliative treatment not only in a murine model (preclinical setting) but also in humans.

Response Monitoring with [18F]FLT PET and Diffusion-Weighted MRI After Cytotoxic 5-FU Treatment in an Experimental Rat Model for Colorectal Liver Metastases

PURPOSE

The aim of the study was to investigate the potential of diffusion-weighted magnetic resonance imaging (DW-MRI) and 3'-dexoy-3'-[18F]fluorothymidine ([18F]FLT) positron emission tomography (PET) as early biomarkers of treatment response of 5-fluorouracil (5-FU) in a syngeneic rat model of colorectal cancer liver metastases.

PROCEDURES

Wag/Rij rats with intrahepatic syngeneic CC531 tumors were treated with 5-FU (15, 30, or 60 mg/kg in weekly intervals). Before treatment and at days 1, 3, 7, and 14 after treatment rats underwent DW-MRI and [18F]FLT PET. Tumors were analyzed immunohistochemically for Ki67, TK1, and ENT1 expression.

RESULTS

5-FU inhibited the growth of CC531 tumors in a dose-dependent manner. Immunohistochemical analysis did not show significant changes in Ki67, TK1, and ENT1 expression. However, [18F]FLT SUVmean and SUVmax were significantly increased at days 4 and 7 after treatment with 5-FU (60 mg/kg) and returned to baseline at day 14 (SUVmax at days -1, 4, 7, and 14 was 1.1 ± 0.1, 2.3 ± 0.5, 2.3 ± 0.6, and 1.5 ± 0.4, respectively). No changes in [18F]FLT uptake were observed in the nontreated animals. Furthermore, the apparent diffusion coefficient (ADCmean) did not change in 5-FU-treated rats compared to untreated rats.

CONCLUSION

This study suggests that 5-FU treatment induces a flare in [18F]FLT uptake of responsive CC531 tumors in the liver, while the ADCmean did not change significantly. Future studies in larger groups are warranted to further investigate whether [18F]FLT PET can discriminate between disease progression and treatment response.

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.

Gemcitabine Mechanism of Action Confounds Early Assessment of Treatment Response by 3'-Deoxy-3'-[18F]Fluorothymidine in Preclinical Models of Lung Cancer

3'-Deoxy-3'-[18F]fluorothymidine positron emission tomography ([18F]FLT-PET) and diffusion-weighted MRI (DW-MRI) are promising approaches to monitor tumor therapy response. Here, we employed these two imaging modalities to evaluate the response of lung carcinoma xenografts in mice after gemcitabine therapy. Caliper measurements revealed that H1975 xenografts responded to gemcitabine treatment, whereas A549 growth was not affected. In both tumor models, uptake of [18F]FLT was significantly reduced 6 hours after drug administration. On the basis of the gemcitabine concentration and [18F]FLT excretion measured, this was presumably related to a direct competition of gemcitabine with the radiotracer for cellular uptake. On day 1 after therapy, [18F]FLT uptake was increased in both models, which was correlated with thymidine kinase 1 (TK1) expression. Two and 3 days after drug administration, [18F]FLT uptake as well as TK1 and Ki67 expression were unchanged. A reduction in [18F]FLT in the responsive H1975 xenografts could only be noted on day 5 of therapy. Changes in ADCmean in A549 xenografts 1 or 2 days after gemcitabine did not seem to be of therapy-related biological relevance as they were not related to cell death (assessed by caspase-3 IHC and cellular density) or tumor therapy response. Taken together, in these models, early changes of [18F]FLT uptake in tumors reflected mechanisms, such as competing gemcitabine uptake or gemcitabine-induced thymidylate synthase inhibition, and only reflected growth-inhibitory effects at a later time point. Hence, the time point for [18F]FLT-PET imaging of tumor response to gemcitabine is of crucial importance. Cancer Res; 76(24); 7096-105. ©2016 AACR.

The relationship between endogenous thymidine concentrations and [(18)F]FLT uptake in a range of preclinical tumour models

BACKGROUND

Recent studies have shown that 3'-deoxy-3'-[(18)F] fluorothymidine ([(18)F]FLT)) uptake depends on endogenous tumour thymidine concentration. The purpose of this study was to investigate tumour thymidine concentrations and whether they correlated with [(18)F]FLT uptake across a broad spectrum of murine cancer models. A modified liquid chromatography-mass spectrometry (LC-MS/MS) method was used to determine endogenous thymidine concentrations in plasma and tissues of tumour-bearing and non-tumour bearing mice and rats. Thymidine concentrations were determined in 22 tumour models, including xenografts, syngeneic and spontaneous tumours, from six research centres, and a subset was compared for [(18)F]FLT uptake, described by the maximum and mean tumour-to-liver uptake ratio (TTL) and SUV.

RESULTS

The LC-MS/MS method used to measure thymidine in plasma and tissue was modified to improve sensitivity and reproducibility. Thymidine concentrations determined in the plasma of 7 murine strains and one rat strain were between 0.61 ± 0.12 μM and 2.04 ± 0.64 μM, while the concentrations in 22 tumour models ranged from 0.54 ± 0.17 μM to 20.65 ± 3.65 μM. TTL at 60 min after [(18)F]FLT injection, determined in 14 of the 22 tumour models, ranged from 1.07 ± 0.16 to 5.22 ± 0.83 for the maximum and 0.67 ± 0.17 to 2.10 ± 0.18 for the mean uptake. TTL did not correlate with tumour thymidine concentrations.

CONCLUSIONS

Endogenous tumour thymidine concentrations alone are not predictive of [(18)F]FLT uptake in murine cancer models.

Apparent diffusion coefficient is highly reproducible on preclinical imaging systems: Evidence from a seven-center multivendor study

PURPOSE

To evaluate between-site agreement of apparent diffusion coefficient (ADC) measurements in preclinical magnetic resonance imaging (MRI) systems.

MATERIALS AND METHODS

A miniaturized thermally stable ice-water phantom was devised. ADC (mean and interquartile range) was measured over several days, on 4.7T, 7T, and 9.4T Bruker, Agilent, and Magnex small-animal MRI systems using a common protocol across seven sites. Day-to-day repeatability was expressed as percent variation of mean ADC between acquisitions. Cross-site reproducibility was expressed as 1.96 × standard deviation of percent deviation of ADC values.

RESULTS

ADC measurements were equivalent across all seven sites with a cross-site ADC reproducibility of 6.3%. Mean day-to-day repeatability of ADC measurements was 2.3%, and no site was identified as presenting different measurements than others (analysis of variance [ANOVA] P = 0.02, post-hoc test n.s.). Between-slice ADC variability was negligible and similar between sites (P = 0.15). Mean within-region-of-interest ADC variability was 5.5%, with one site presenting a significantly greater variation than the others (P = 0.0013).

CONCLUSION

Absolute ADC values in preclinical studies are comparable between sites and equipment, provided standardized protocols are employed.

Analysis of NSCLC tumour heterogeneity, proliferative and 18F-FDG PET indices reveals Ki67 prognostic role in adenocarcinomas

AIMS

The role of tumour metabolic and proliferative indices in predicting non-small-cell lung cancer (NSCLC) patients' prognosis is unclear. We correlated fluorine 18 ((18) F)-fluorodeoxyglucose (FDG)-positron emission tomography (PET) value and Ki67 index to patients' survival, taking into account tumour heterogeneity, disease characteristics and genetic aberrations.

METHODS AND RESULTS

A series of 383 NSCLCs was arranged into tissue microarrays and Ki67 staining was analysed by immunohistochemistry. The maximum standardized uptake (SUV(MAX) ) value detected by (18) F-FDG-PET analysis was calculated over a region of interest. Large-cell and squamous cell carcinomas had higher proliferative and metabolic activities than adenocarcinomas, and the two measures were correlated significantly. The hot-spot Ki67 value was correlated with patients' survival and the cut-off to discriminate patients in the survival risk groups was 20%. Ki67 hot-spot values were greater in anaplastic lymphoma kinase (ALK) rearranged tumours. Adenocarcinomas showed the highest intratumour heterogeneity in proliferative activity and the hot-spot Ki67 value predicted only the prognosis of patients in this group. Although tumour metabolic activity was not associated with patients' prognosis, a SUV(MAX) > 2 was related to nodal metastases, tumour size and grade.

CONCLUSIONS

Our results highlight how tumour heterogeneity influences evaluation of prognostic biomarkers. Our data support Ki67 evaluation to estimate NSCLC patients' prognosis, particularly for adenocarcinoma.

Radiopharmaceuticals as probes to characterize tumour tissue

Tumour cells exhibit several properties that allow them to grow and divide. A number of these properties are detectable by nuclear imaging methods. We discuss crucial tumour properties that can be described by current radioprobe technologies, further discuss areas of emerging radioprobe development, and finally articulate need areas that our field should aspire to develop. The review focuses largely on positron emission tomography and draws upon the seminal 'Hallmarks of Cancer' review article by Hanahan and Weinberg in 2011 placing into context the present and future roles of radiotracer imaging in characterizing tumours.