Imaging of cellular proliferation in liver metastasis by [18F]fluorothymidine positron emission tomography: effect of therapy

The Role of 18F-FLT PET/CT in Assessing Early Response to Transarterial Radioembolization and Chemoembolization in Patients with Primary and Metastatic Liver Tumors

Objectives

Metastases and primary malignancies are common in the liver. Local ablative applications such as transarterial chemoembolization (TACE), and transarterial radioembolization (TARE) provide minimally invasive and safe treatment in unresectable liver tumors. Early detection of response to treatment prevents unnecessary toxicity and cost in non-responder patients and provides an earlier use of other options that may be effective. This study aimed to identify the role of ¹⁸F-fluorothymidine (FLT) positron emission tomography/computed tomography (PET/CT) in the assessment of early response to TACE and TARE treatments in patients with unresectable primary and metastatic liver tumors.

Methods

This single-center study included 63 patients who underwent ¹⁸F-FLT PET/CT for response evaluation after TACE and TARE. After excluding 20 patients whose data were missing 43 TARE-receiving patients were analyzed. The compatibility of change in semi-quantitative values obtained from the ¹⁸F-FLT PET/CT images with the treatment responses detected in ¹⁸F-fluorodeoxyglucose PET/CT, CT, and MR images and survival was evaluated.

Results

There was no correlation between early metabolic, morphological response, and ¹⁸F-FLT uptake pattern, and change in standardized uptake values (SUV) which were ΔSUV_max, ΔSUV_mean, ΔSUV_peak., ΔSUV_mean, Δ SUV_peak values. There was no significant correlation between ¹⁸F-FLT uptake pattern, ΔSUV_max, ΔSUV_mean, ΔSUV_peak, and overall survival, progression-free survival (PFS) for the target lobe PFS for the whole-body. The survival distributions for the patients with >30% change in Δ SUV_max and ΔSUV_peak values were statistically significantly longer than the patients with <30% change (p<0.009 and p<0.024, respectively).

Conclusion

There was significant longer PFS for target liver lobe in patients with more than 30% decrease in ¹⁸F-FLT SUV_max and SUV_peak of the liver lesion in primary and metastatic unresectable liver tumors undergoing TARE.

Monitoring Response to Transarterial Chemoembolization in Hepatocellular Carcinoma Using 18F-Fluorothymidine PET

Accurate disease monitoring is essential after transarterial chemoembolization (TACE) in hepatocellular carcinoma (HCC) because of the potential for profound adverse events and large variations in survival outcome. Posttreatment changes on conventional imaging can confound determination of residual or recurrent disease, magnifying the clinical challenge. On the basis of increased expression of thymidylate synthase (TYMS), thymidine kinase 1 (TK-1), and equilibrative nucleoside transporter 1 (SLC29A1) in HCC compared with liver tissue, we conducted a proof-of-concept study evaluating the efficacy of 3'-deoxy-3'-18F-fluorothymidine (18F-FLT) PET to assess response to TACE. Because previous PET studies in HCC have been hampered by high background liver signal, we investigated whether a temporal-intensity voxel clustering (kinetic spatial filtering, or KSF) improved lesion detection. Methods: A tissue microarray was built from 36 HCC samples and from matching surrounding cirrhotic tissue and was stained for TK-1 A prospective study was conducted; 18 patients with a diagnosis of HCC by the criteria of the American Association for the Study of Liver Diseases who were eligible for treatment with TACE were enrolled. The patients underwent baseline conventional imaging and dynamic 18F-FLT PET with KSF followed by TACE. Imaging was repeated 6-8 wk after TACE. The PET parameters were compared with modified enhancement-based RECIST. Results: Cancer Genome Atlas analysis revealed increased RNA expression of TYMS, TK-1, and SLC29A1 in HCC. TK-1 protein expression was significantly higher in HCC (P < 0.05). The sensitivity of 18F-FLT PET for baseline HCC detection was 73% (SUVmax, 9.7 ± 3.0; tumor to liver ratio, 1.2 ± 0.3). Application of KSF did not improve lesion detection. Lesion response after TACE by modified RECIST was 58% (14 patients with 24 lesions). A 30% reduction in mean 18F-FLT PET uptake was observed after TACE, correlating with an observed PET response of 60% (15/25). A significant and profound reduction in the radiotracer delivery parameter K1 after TACE was observed. Conclusion:18F-FLT PET can differentiate HCC from surrounding cirrhotic tissue, with PET parameters correlating with TACE response. KSF did not improve visualization of tumor lesions. These findings warrant further investigation.

FLT-PET for early response evaluation of colorectal cancer patients with liver metastases: a prospective study

BACKGROUND

Fluoro-L-thymidine (FLT) is a positron emission tomography/computed tomography (PET/CT) tracer which reflects proliferative activity in a cancer lesion. The main objective of this prospective explorative study was to evaluate whether FLT-PET can be used for the early evaluation of treatment response in colorectal cancer patients (CRC) with liver metastases. Patients with metastatic CRC having at least one measurable (>1 cm) liver metastasis receiving first-line chemotherapy were included. A FLT-PET/CT scan was performed at baseline and after the first treatment. The maximum and mean standardised uptake values (SUVmax, SUVmean) were measured. After three cycles of chemotherapy, treatment response was assessed by CT scan based on RECIST 1.1.

RESULTS

Thirty-nine consecutive patients were included of which 27 were evaluable. Dropout was mainly due to disease complications. Nineteen patients (70%) had a partial response, seven (26%) had stable disease and one (4%) had progressive disease. A total of 23 patients (85%) had a decrease in FLT uptake following the first treatment. The patient with progressive disease had the highest increase in FLT uptake in SUVmax. There was no correlation between the response according to RECIST and the early changes in FLT uptake measured as SUVmax (p = 0.24).

CONCLUSIONS

No correlation was found between early changes in FLT uptake after the first cycle of treatment and the response evaluated from subsequent CT scans. It seems unlikely that FLT-PET can be used on its own for the early response evaluation of metastatic CRC.

Evaluation of 18F-fluorothymidine positron emission tomography ([18F]FLT-PET/CT) methodology in assessing early response to chemotherapy in patients with gastro-oesophageal cancer

BACKGROUND

3'-Deoxy-3'-[18F]fluorothymidine ([18F]FLT) PET has limited utility in abdominal imaging due to high physiological hepatic uptake of a tracer. We evaluated [18F]FLT-PET/CT combined with a temporal-intensity information-based voxel-clustering approach termed kinetic spatial filtering (KSF) to improve tumour visualisation in patients with locally advanced and metastatic gastro-oesophageal cancer and as a marker of early response to chemotherapy. Dynamic [18F]FLT-PET/CT data were collected before and 3 weeks post first cycle of chemotherapy. Changes in tumour [18F]FLT-PET/CT variables were determined. Response was determined on contrast-enhanced CT after three cycles of therapy using RECIST 1.1.

RESULTS

Ten patients were included. Following application of the KSF, visual distinction of all oesophageal and/or gastric tumours was observed in [18F]FLT-PET images. Among the nine patients available for response evaluation (RECIST 1.1), three patients had responded (partial response) and six patients were non-responders (stable disease). There was a significant association between Ki-67 and all baseline [18F]FLT-PET parameters. Area under the curve (AUC) from 0 to 1 min was associated with treatment response.

CONCLUSIONS

The results of this study indicate that application of the KSF allowed accurate visualisation of both primary and metastatic lesions following imaging with the proliferation marker, [18F]FLT-PET/CT. However, [18F]FLT-PET uptake parameters did not correlate with response. Instead, we observe significant changes in tracer delivery following chemotherapy suggesting that further [18F]FLT-PET/CT studies in this tumour type should be undertaken with caution.

Functional imaging of hepatocellular carcinoma

Imaging plays a key role in the clinical management of hepatocellular carcinoma (HCC), but conventional imaging techniques have limited sensitivity in visualizing small tumors and assessing response to locoregional treatments and sorafenib. Functional imaging techniques allow visualization of organ and tumor physiology. Assessment of functional characteristics of tissue, such as metabolism, proliferation and stiffness, may overcome some of the limitations of structural imaging. In particular, novel molecular imaging agents offer a potential tool for early diagnosis of HCC, and radiomics may aid in response assessment and generate prognostic models. Further prospective research is warranted to evaluate emerging techniques and their cost-effectiveness in the context of HCC in order to improve detection and response assessment.

Molecular imaging of aurora kinase A (AURKA) expression: Synthesis and preclinical evaluation of radiolabeled alisertib (MLN8237)

INTRODUCTION

Survival of patients after resection of colorectal cancer liver metastasis (CRCLM) is 36%-58%. Positron emission tomography (PET) tracers, imaging the expression of prognostic biomarkers, may contribute to assign appropriate management to individual patients. Aurora kinase A (AURKA) expression is associated with survival of patients after CRCLM resection.

METHODS

We synthesized [(3)H]alisertib and [(11)C]alisertib, starting from [(3)H]methyl nosylate and [(11)C]methyl iodide, respectively. We measured in vitro uptake of [(3)H]alisertib in cancer cells with high (Caco2), moderate (A431, HCT116, SW480) and low (MKN45) AURKA expression, before and after siRNA-mediated AURKA downmodulation, as well as after inhibition of P-glycoprotein (P-gp) activity. We measured in vivo uptake and biodistribution of [(11)C]alisertib in nude mice, xenografted with A431, HCT116 or MKN45 cells, or P-gp knockout mice.

RESULTS

[(3)H]Alisertib was synthesized with an overall yield of 42% and [(11)C]alisertib with an overall yield of 23%±9% (radiochemical purity ≥99%). Uptake of [(3)H]alisertib in Caco2 cells was higher than in A431 cells (P=.02) and higher than in SW480, HCT116 and MKN45 cells (P<.01). Uptake in A431 cells was higher than in SW480, HCT116 and MKN45 cells (P<.01). Downmodulation of AURKA expression reduced [(3)H]alisertib uptake in Caco2 cells (P<.01). P-gp inhibition increased [(3)H]alisertib uptake in Caco2 (P<.01) and MKN45 (P<.01) cells. In vivo stability of [(11)C]alisertib 90min post-injection was 94.7%±1.3% and tumor-to-background ratios were 2.3±0.8 (A431), 1.6±0.5 (HCT116) and 1.9±0.5 (MKN45). In brains of P-gp knockout mice [(11)C]alisertib uptake was increased compared to uptake in wild-type mice (P<.01) CONCLUSIONS: Radiolabeled alisertib can be synthesized and may have potential for the imaging of AURKA, particularly when AURKA expression is high. However, the exact mechanisms underlying alisertib accumulation need further investigation.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Radiolabeled alisertib may be used for non-invasively measuring AURKA protein expression and to stratify patients for treatment accordingly.

3'-Deoxy-3'-¹⁸F-fluorothymidine positron emission tomography as an early predictor of disease progression in patients with advanced and metastatic pancreatic cancer

PURPOSE

3'-Deoxy-3'-(18)F-fluorothymidine (FLT) positron emission tomography (PET) has limited utility in abdominal imaging due to high physiological hepatic uptake of tracer. We evaluated FLT PET/CT combined with a temporal-intensity information-based voxel-clustering approach termed kinetic spatial filtering (FLT PET/CTKSF) for early prediction of response and survival outcomes in locally advanced and metastatic pancreatic cancer patients receiving gemcitabine-based chemotherapy.

METHODS

Dynamic FLT PET/CT data were collected before and 3 weeks after the first cycle of chemotherapy. Changes in tumour FLT PET/CT variables were determined. The primary end point was RECIST 1.1 response on contrast-enhanced CT after 3 months of therapy.

RESULTS

Twenty patients were included. Visual distinction between tumours and normal pancreas was seen in FLT PETKSF images. All target lesions (>2 cm), including all primary pancreatic tumours, were visualised. Of the 11 liver metastases, 3 (<2 cm) were not visible after kinetic filtering. Of the 20 patients, 7 progressed (35%). Maximum standardised uptake value at 60 min post-injection (SUV60,max) significantly increased in patients with disease progression (p = 0.04). Receiver-operating characteristic curve analysis indicated that a threshold of SUV60,max increase of ≥ 12% resulted in sensitivity, specificity and positive predictive value (PPV) of 71, 100 and 100%, respectively [area under the curve (AUC) 0.90, p = 0.0001], to predict patients with disease progression. Changes in SUV60,max were not predictive of survival.

CONCLUSION

FLT PET/CT detected changes in proliferation, with early increase in SUV60,max predicting progressive disease with a high specificity and PPV. Therefore, FLT PET/CT could be used as an early response biomarker for gemcitabine-based chemotherapy, to select a poor prognostic group who may benefit from novel therapeutic agents in advanced and metastatic pancreatic cancer.

The value of 18F-FLT PET for detecting second primary cancers and distant metastases in head and neck cancer patients

OBJECTIVE

Diagnostic efficacy of (18)F-FLT PET was compared with that of (18)F-FDG PET regarding second primary cancers and distant metastases of head and neck squamous cell cancers (HNSCCs).

METHODS

A total of 88 patients with HNSCCs were qualitatively examined with FLT PET and FDG PET for regions of focally increased metabolism. Final diagnoses of second primary cancer and distant metastasis were established on the basis of histological findings or clinical follow-up.

RESULTS

FDG PET had 1 false-negative finding with lung metastasis, and FLT PET had 4 false-negative findings with 1 liver metastasis, 1 bone metastasis, and 2 lung metastases. There were no false-positive findings with FLT PET in contrast to 9 with FDG PET (1 in lung, 4 in mediastinum, 1 in rectum, and 3 in stomach). Overall accuracy of FDG PET and FLT PET for pretreatment metastasis staging was 92% and 98%, respectively. Five distant metastases in 3 patients occurred after the initiation of chemoradiotherapy. FLT PET missed 2 metastatic lesions (1 in liver and 1 in lung), whereas FDG PET could not discriminate intracranial metastasis because of FDG uptake in the brain.

CONCLUSIONS

FLT PET does not appear to be recommendable to replace FDG PET for pretreatment metastasis staging in HNSCC cases because of its lower sensitivity and higher background activity in the liver and bone marrow. However, it might provide additional diagnostic specificity and biological information.

Clinical translation of molecular imaging agents used in PET studies of cancer

Over recent years, there has been a rapid expansion in our knowledge of the factors that regulate tumor growth; this has resulted in the identification of new therapeutic targets and improvements in the long-term survival of cancer patients. New noninvasive biomarkers of drug targets and pathway modulation in vivo are needed to guide therapy selection and detect drug resistance early so that alternative, more effective treatments can be offered. The translation of new therapeutics into the clinic is disappointingly slow, expensive, and subject to high rates of attrition often occurring at late stages (phase 3) of development. In an attempt to mitigate these delays and failures, there has been resurgence in the development of new molecular imaging probes for studies with positron emission tomography (PET) to characterize tumor biology. In the assessment of therapeutic effects, PET allows imaging of entire tumor burden in a noninvasive repeatable manner. This chapter focuses on the clinical translation of PET imaging agents from bench to bedside. New probes are being used to study a diverse range of processes such as angiogenesis, apoptosis, fatty acid metabolism, and growth factor receptor expression. In the future, validation of these novel imaging probes could allow more innovative therapies to be adapted earlier in the clinic leading to improved patient outcomes.

Functional imaging biomarkers for assessing response to treatment in liver and lung metastases

Management of patients with metastatic cancer and development of new treatments rely on imaging to provide non-invasive biomarkers of tumour response and progression. The widely used size-based criteria have increasingly become inadequate where early measures of response are required to avoid toxicity of ineffective treatments, as biological, physiologic, and molecular modifications in tumours occur before changes in gross tumour size. A multiparametric approach with the current range of imaging techniques allows functional aspects of tumours to be simultaneously interrogated. Appropriate use of these imaging techniques and their timing in relation to the treatment schedule, particularly in the context of clinical trials, is fundamental. There is a lack of consensus regarding which imaging parameters are most informative for a particular disease site and the best time to image so that, despite an increasing body of literature, open questions on these aspects remain. In addition, standardization of these new parameters is required. This review summarizes the published literature over the last decade on functional and molecular imaging techniques in assessing treatment response in liver and lung metastases.