Monitoring Predominantly Cytostatic Treatment Response with 18F-FDG PET

Baseline and early 18F-FDG PET/CT evaluations as predictors of progression-free survival in metastatic breast cancer patients treated with targeted anti-CDK therapy

BACKGROUND

Exploring the value of baseline and early 18F-FDG PET/CT evaluations in prediction PFS in ER+/HER2- metastatic breast cancer patients treated with a cyclin-dependent kinase inhibitor in combination with an endocrine therapy.

METHODS

Sixty-six consecutive breast cancer patients who underwent a pre-therapeutic 18F-FDG PET/CT and a second PET/CT within the first 6 months of treatment were retrospectively included. Metabolic tumour volume (MTV) and total lesion glycolysis (TLG) and Dmax, which represents tumour dissemination and is defined as the distance between the two most distant lesions, were computed. The variation in these parameters between baseline and early evaluation PET as well as therapeutic evaluation using PERCIST were assessed as prognosticators of PFS at 18 months.

RESULTS

The median follow-up was equal to 22.5 months. Thirty progressions occurred (45.4%). The average time to event was 17.8 ± 10.4 months. At baseline, Dmax was the only predictive metabolic parameter. Patients with a baseline Dmax ≤ 18.10 cm had a significantly better 18 m-PFS survival than the others: 69.2% (7.7%) versus 36.7% (8.8%), p = 0.017. There was no association between PERCIST evaluation and 18 m-PFS status (p = 0.149) and there was no difference in 18 m-PFS status between patients classified as complete, partial metabolic responders or having stable metabolic disease.

CONCLUSION

Disease spread at baseline PET, as assessed by Dmax, is predictive of an event occurring within 18 months. In the absence of early metabolic progression, which occurs in 15% of patients, treatment should be continued regardless of the quality of the initial response to treatment.

Empowering the Battle: Bioenhancers as Allies Against Cancer Drug Resistance

BACKGROUND

Drug resistance has been a great hindrance in the path of counteracting diseases like cancer and is driven by drugs misuse and overuse. In terms of cancer, resistance has been developed due to cellular changes, altered growth activation pathways, increased expression of efflux proteins, and changes in the local physiology of cancer (blood supply, tissue hydrodynamics, increased mutation rate/epigenetics, tumor cell heterogeneity). One of the approaches to address these challenges is the use of bioenhancers, which can overcome drug resistance, thereby improving bioavailability (BA).

CONCLUSION

Bioenhancers when combined with drugs can elicit pharmacological activity. They are generally combined with therapeutic agents at low doses, which increase the BA or therapeutic activity of active pharmaceutical ingredient (API). This review sheds light on the synthesis and classification of bio-enhancers. It also discusses different applications of bio-enhancers like piperine, ginger, quercetin, curcumin, etc. in the treatment of cancer. The review also presents some of the recent advancements in terms of nanocarriers for delivering API combined with bioenhancers.

Advances in PET imaging of cancer

Molecular imaging has experienced enormous advancements in the areas of imaging technology, imaging probe and contrast development, and data quality, as well as machine learning-based data analysis. Positron emission tomography (PET) and its combination with computed tomography (CT) or magnetic resonance imaging (MRI) as a multimodality PET-CT or PET-MRI system offer a wealth of molecular, functional and morphological data with a single patient scan. Despite the recent technical advances and the availability of dozens of disease-specific contrast and imaging probes, only a few parameters, such as tumour size or the mean tracer uptake, are used for the evaluation of images in clinical practice. Multiparametric in vivo imaging data not only are highly quantitative but also can provide invaluable information about pathophysiology, receptor expression, metabolism, or morphological and functional features of tumours, such as pH, oxygenation or tissue density, as well as pharmacodynamic properties of drugs, to measure drug response with a contrast agent. It can further quantitatively map and spatially resolve the intertumoural and intratumoural heterogeneity, providing insights into tumour vulnerabilities for target-specific therapeutic interventions. Failure to exploit and integrate the full potential of such powerful imaging data may lead to a lost opportunity in which patients do not receive the best possible care. With the desire to implement personalized medicine in the cancer clinic, the full comprehensive diagnostic power of multiplexed imaging should be utilized.

18F-fluorodeoxyglucose positron emission tomography correlates with tumor immunometabolic phenotypes in resected lung cancer

Enhanced tumor glycolytic activity is a mechanism by which tumors induce an immunosuppressive environment to resist adoptive T cell therapy; therefore, methods of assessing intratumoral glycolytic activity are of considerable clinical interest. In this study, we characterized the relationships among tumor ¹⁸F-fluorodeoxyglucose (FDG) retention, tumor metabolic and immune phenotypes, and survival in patients with resected non-small cell lung cancer (NSCLC). We retrospectively analyzed tumor preoperative positron emission tomography (PET) ¹⁸F-FDG uptake in 59 resected NSCLCs and investigated correlations between PET parameters (SUV_Max, SUV_Total, SUV_Mean, TLG), tumor expression of glycolysis- and immune-related genes, and tumor-associated immune cell densities that were quantified by immunohistochemistry. Tumor glycolysis-associated immune gene signatures were analyzed for associations with survival outcomes. We found that each ¹⁸F-FDG PET parameter was positively correlated with tumor expression of glycolysis-related genes. Elevated ¹⁸F-FDG SUV_Max was more discriminatory of glycolysis-associated changes in tumor immune phenotypes than other ¹⁸F-FDG PET parameters. Increased SUV_Max was associated with multiple immune factors characteristic of an immunosuppressive and poorly immune infiltrated tumor microenvironment, including elevated PD-L1 expression, reduced CD57⁺ cell density, and increased T cell exhaustion gene signature. Elevated SUV_Max identified immune-related transcriptomic signatures that were associated with enhanced tumor glycolytic gene expression and poor clinical outcomes. Our results suggest that ¹⁸F-FDG SUV_Max has potential value as a noninvasive, clinical indicator of tumor immunometabolic phenotypes in patients with resectable NSCLC and warrants investigation as a potential predictor of therapeutic response to immune-based treatment strategies.

Phase I Study of Rapid Alternation of Sunitinib and Regorafenib for the Treatment of Tyrosine Kinase Inhibitor Refractory Gastrointestinal Stromal Tumors

PURPOSE

Polyclonal emergence of KIT secondary mutations is a main mechanism of imatinib progression in gastrointestinal stromal tumor (GIST). Approved KIT inhibitors sunitinib and regorafenib have complementary activity against KIT resistance mutations. Preclinical evidence suggests that rapid alternation of sunitinib and regorafenib broadens the spectrum of imatinib-resistant subclones targeted.

PATIENTS AND METHODS

Phase Ib study investigating continuous treatment with cycles of sunitinib (3 days) followed by regorafenib (4 days) in patients with tyrosine kinase inhibitor (TKI)-refractory GIST. A 3+3 dosing schema was utilized to determine the recommended phase II dose (RP2D). Plasma samples were analyzed for pharmacokinetics and circulating tumor DNA (ctDNA) studies using targeted error correction sequencing (TEC-seq) and droplet digital PCR (ddPCR).

RESULTS

Of the 14 patients enrolled, 2 experienced dose-limiting toxicities at dose level 2 (asymptomatic grade 3 hypophosphatemia). Sunitinib 37.5 mg/day and regorafenib 120 mg/day was the RP2D. Treatment was well-tolerated and no unexpected toxicities resulted from the combination. Stable disease was the best response in 4 patients, and median progression-free survival was 1.9 months. Combined assessment of ctDNA with TEC-seq and ddPCR detected plasma mutations in 11 of 12 patients (92%). ctDNA studies showed that KIT secondary mutations remain the main mechanism of resistance in TKI-refractory GIST, revealing effective suppression of KIT-mutant subpopulations in patients benefiting from the combination.

CONCLUSIONS

Sunitinib and regorafenib combination is feasible and tolerable. Rapid alternation of TKIs with complementary activity might be effective when combining drugs with favorable pharmacokinetics, potentially allowing active doses while minimizing adverse events. Serial monitoring with ctDNA may guide treatment in patients with GIST.

Response evaluation with 18F-FDG PET/CT in metastatic breast cancer patients treated with Palbociclib: first experience in clinical practice

OBJECTIVE

Palbociclib is a cyclin-dependent kinase 4/6 inhibitor recently approved for treatment in advanced or metastatic breast cancer (BC) patients. The use of ¹⁸F-FDG PET/CT for chemo/endocrine therapy response assessment in BC patients is well reported in the literature, but no studies have evaluated its role for assessing Palbociclib efficacy in clinical practice. Our study aimed to evaluate the potential role of ¹⁸F-FDG PET/CT in this setting.

METHODS

In 12 metastatic BC patients (mean age = 62 ± 10 years) treated with Palbociclib plus endocrine therapy and who underwent a baseline and post-therapy ¹⁸F-FDG PET/CT, we retrospectively compared the Metabolic Response Evaluation (MRE, based on PET/CT) to the Standard Response Evaluation (SRE, based on clinico-laboratory and morphological data); we also assessed the influence of additional PET/CT information on the patients' management.

RESULTS

Compared to SRE, MRE increased the proportion of patients classified with progressive disease from 25 to 50% and differed from SRE in 8/12 patients: 3/8 shifted from stable disease or undetermined response to metabolic progression (more unfavorable category), 4/8 from stable disease to partial or complete metabolic response, and 1/8 from partial response to complete metabolic response (more favorable category). Additional PET/CT information led to a change in patients' management in 3/12 (25%) patients.

CONCLUSION

In BC patients treated with Palbociclib, additional ¹⁸F-FDG PET/CT information seems clinically useful, with respect to personalized management, to early intercept patients who should discontinue Palbociclib because of progressive disease and to select patients requiring a strict monitoring of additional metabolic findings. Further studies are needed to confirm these preliminary results.

Gadofosveset-enhanced MRI as simple surrogate parameter for real-time evaluation of the initial tumour vessel infarction by retargeted tissue factor tTF-NGR

Truncated tissue factor (tTF)-NGR consists of the extracellular domain of the human TF and the binding motif NGR. tTF-NGR activates blood coagulation within the tumour vasculature following binding to CD13, and is overexpressed in the endothelial cells of tumour vessels, resulting in tumour vessel infarction and subsequent retardation/regression of tumour growth. The aim of the present study was to investigate gadofosveset-based real-time dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in evaluating the initial therapeutic effects of the anti-vascular tTF-NGR approach. DCE-MRI (3.0 T) was performed in human U87-glioblastoma tumour-bearing nude mice. During a dynamic T1w GE-sequence, a gadolinium-based blood pool contrast agent (gadofosveset) was injected via a tail vein catheter. Following the maximum contrast intensity inside the tumour being obtained, tTF-NGR was injected (controls received NaCl) and the contrast behaviour of the tumour was monitored by ROI analysis. The slope difference of signal intensities between controls and the tTF-NGR group was investigated, as well as the differences between the average area under the curve (AUC) of the two groups. The association between intensity, group (control vs. tTF-NGR group) and time was analysed by fitting a linear mixed model. Following the injection of tTF-NGR, the signal intensity inside the tumours exhibited a statistically significantly stronger average slope decrease compared with the signal intensity of the tumours in the NaCl group. Furthermore, the initial average AUC values of mice treated with tTF-NGR were 5.7% lower than the average AUC of the control animals (P<0.05). Gadofosveset-enhanced MRI enables the visualization of the initial tumour response to anti-vascular treatment in real-time. Considering the clinical application of tTF-NGR, this method may provide a simple alternative parameter for monitoring the tumour response to vascular disrupting agents and certain vascular targeting agents in humans.

Radioimmunotherapy of pancreatic cancer xenografts in nude mice using 90Y-labeled anti-α6β4 integrin antibody

The contribution of integrin α₆β₄ (α₆β₄) overexpression to the pancreatic cancer invasion and metastasis has been previously shown. We have reported immunotargeting of α₆β₄ for radionuclide-based and near-infrared fluorescence imaging in a pancreatic cancer model. In this study, we prepared yttrium-90 labeled anti-α₆β₄ antibody (⁹⁰Y-ITGA6B4) and evaluated its radioimmunotherapeutic efficacy against pancreatic cancer xenografts in nude mice. Mice bearing xenograft tumors were randomly divided into 5 groups: (1) single administration of ⁹⁰Y-ITGA6B4 (3.7MBq), (2) double administrations of ⁹⁰Y-ITGA6B4 with once-weekly schedule (3.7MBq × 2), (3) single administration of unlabeled ITGA6B4, (4) double administrations of unlabeled ITGA6B4 with once-weekly schedule and (5) the untreated control. Biweekly tumor volume measurements and immunohistochemical analyses of tumors at 2 days post-administration were performed to monitor the response to treatments. To assess the toxicity, body weight was measured biweekly. Additionally, at 27 days post-administration, blood samples were collected through cardiac puncture, and hematological parameters, hepatic and renal functions were analyzed. Both ⁹⁰Y-ITGA6B4 treatment groups showed reduction in tumor volumes (P < 0.04), decreased cell proliferation marker Ki-67-positive cells and increased DNA damage marker p-H2AX-positive cells, compared with the other groups. Mice treated with double administrations of ⁹⁰Y-ITGA6B4, exhibited myelosuppression. There were no significant differences in hepatic and renal functions between the 2 treatment groups and the other groups. Our results suggest that ⁹⁰Y-ITGA6B4 is a promising radioimmunotherapeutic agent against α₆β₄ overexpressing tumors. In the future studies, dose adjustment for fractionated RIT should be considered carefully in order to get the optimal effect while avoiding myelotoxicity.

Molecularly targeted therapies in cancer: a guide for the nuclear medicine physician

Molecular imaging continues to influence every aspect of cancer care including detection, diagnosis, staging and therapy response assessment. Recent advances in the understanding of cancer biology have prompted the introduction of new targeted therapy approaches. Precision medicine in oncology has led to rapid advances and novel approaches optimizing the use of imaging modalities in cancer care, research and development. This article focuses on the concept of targeted therapy in cancer and the challenges that exist for molecular imaging in cancer care.

Effectiveness of FDG-PET/CT for evaluating early response to induction chemotherapy in head and neck squamous cell carcinoma: A systematic review

BACKGROUND

F-Fluoro-Deoxy-Glucose Positron Emission Tomography with Computed Tomography (F-FDG PET/CT) may be a powerful tool to predict treatment outcome. We aimed to review the effectiveness of F-FDG PET/CT in the assessment of early response to induction chemotherapy (IC) in patients with advanced Head and Neck Squamous Cell Cancer (HNSCC) without previous treatment.

METHODS

PubMed, Cochrane Library, Science Direct and Web of Science were searched to May 2016. Reference lists of the included articles and additional studies identified by one nuclear medicine expert were screened for potential relevant studies that investigated the effectiveness of F-FDG PET/CT performed before and after IC. Three authors independently screened all retrieved articles, selected studies that met inclusion criteria and extracted data. The methodology of the selected studies was evaluated by using the risk of bias checklist of the Agency for Healthcare Research and Quality (AHRQ).

RESULTS

Seven out of 170 eligible studies met our inclusion criteria. A total of 207 advanced HNSCC patients were evaluated with F-FDG PET/CT at baseline and after IC in the selected articles. Six from seven studies concluded that F-FDG PET/CT allowed early evaluation response to IC and predicted survival outcomes.

CONCLUSION

The present systematic review confirms the potential value of F-FDG PET/CT as a diagnostic tool for early IV response assessment in HNSCC patients. However, the lack of standard definitions for response criteria and heterogeneous IC protocols indicate the need to further studies in order to better define the role of F-FDG PET/CT in these patients.

Metabolic Imaging to Assess Treatment Response to Cytotoxic and Cytostatic Agents

For several decades, cytotoxic chemotherapeutic agents were considered the basis of anticancer treatment for patients with metastatic tumors. A decrease in tumor burden, assessed by volumetric computed tomography and magnetic resonance imaging, according to the response evaluation criteria in solid tumors (RECIST), was considered as a radiological response to cytotoxic chemotherapies. In addition to RECIST-based dimensional measurements, a metabolic response to cytotoxic drugs can be assessed by positron emission tomography (PET) using (18)F-fluoro-thymidine (FLT) as a radioactive tracer for drug-disrupted DNA synthesis. The decreased (18)FLT-PET uptake is often seen concurrently with increased apparent diffusion coefficients by diffusion-weighted imaging due to chemotherapy-induced changes in tumor cellularity. Recently, the discovery of molecular origins of tumorogenesis led to the introduction of novel signal transduction inhibitors (STIs). STIs are targeted cytostatic agents; their effect is based on a specific biological inhibition with no immediate cell death. As such, tumor size is not anymore a sensitive end point for a treatment response to STIs; novel physiological imaging end points are desirable. For receptor tyrosine kinase inhibitors as well as modulators of the downstream signaling pathways, an almost immediate inhibition in glycolytic activity (the Warburg effect) and phospholipid turnover (the Kennedy pathway) has been seen by metabolic imaging in the first 24 h of treatment. The quantitative imaging end points by magnetic resonance spectroscopy and metabolic PET (including 18F-fluoro-deoxy-glucose, FDG, and total choline) provide an early treatment response to targeted STIs, before a reduction in tumor burden can be seen.

Early 18F-FDG PET/CT Evaluation Shows Heterogeneous Metabolic Responses to Anti-EGFR Therapy in Patients with Metastatic Colorectal Cancer

OBJECTIVE

The aim of this pilot study was to explore intrapatient mixed metabolic response and early 18F-FDG PET response evaluation using predefined quantification strategies in patients with advanced KRAS wild-type colorectal adenocarcinoma (mCRC) treated with cetuximab.

METHODS

A 18F-FDG PET was performed at baseline and after 2 cycles of cetuximab. Metabolic response was categorized using thresholds suggested in PERCIST. Quantitative analysis was done for the sum of all target lesions, ≤ 5 lesions and the metabolically most active lesion per PET. Quantitative data were correlated with clinical benefit, according to RECIST v1.1, after two months of treatment.

RESULTS

In nine evaluable patients the total number of target lesions was 34 (1-8 per patient). Mixed metabolic response was observed in three out of seven patients with multiple target lesions, using TLG. Dichotomised metabolic data of the sum of all or ≤ 5 lesions had a concordance with clinical benefit of 89% using SULmax or SULpeak, and 100% using TLG. Evaluating the metabolically most active lesion, concordance was 89% for all three units. Additionally, the decrease in TLG was significantly correlated with PFS for all three quantification strategies.

CONCLUSION

Mixed metabolic response was observed in nearly half of the patients with advanced KRAS wild-type mCRC treated with cetuximab. If ≤ 5 target lesions were evaluated using TLG clinical benefit was predicted correctly for all patients. Moreover, decrease in TLG is significantly correlated with the duration of PFS. Validation of these promising preliminary results in a larger cohort is currently on-going.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01691391.

PK-PD modeling of individual lesion FDG-PET response to predict overall survival in patients with sunitinib-treated gastrointestinal stromal tumor

Pharmacometric models were developed to characterize the relationships between lesion-level tumor metabolic activity, as assessed by the maximum standardized uptake value (SUVmax) obtained on [(18)F]-fluorodeoxyglucose (FDG) positron emission tomography (PET), tumor size, and overall survival (OS) in 66 patients with gastrointestinal stromal tumor (GIST) treated with intermittent sunitinib. An indirect response model in which sunitinib stimulates tumor loss best described the typically rapid decrease in SUVmax during on-treatment periods and the recovery during off-treatment periods. Substantial interindividual and interlesion variability were identified in SUVmax baseline and drug sensitivity. A parametric time-to-event model identified the relative change in SUVmax at one week for the lesion with the most pronounced response as a better predictor of OS than tumor size. Based on the proposed modeling framework, early changes in FDG-PET response may serve as predictor for long-term outcome in sunitinib-treated GIST.

Positron Emission Tomography Imaging of Tumor Cell Metabolism and Application to Therapy Response Monitoring

Cancer cells do reprogram their energy metabolism to enable several functions, such as generation of biomass including membrane biosynthesis, and overcoming bioenergetic and redox stress. In this article, we review both established and evolving radioprobes developed in association with positron emission tomography (PET) to detect tumor cell metabolism and effect of treatment. Measurement of enhanced tumor cell glycolysis using 2-deoxy-2-[(18)F]fluoro-D-glucose is well established in the clinic. Analogs of choline, including [(11)C]choline and various fluorinated derivatives are being tested in several cancer types clinically with PET. In addition to these, there is an evolving array of metabolic tracers for measuring intracellular transport of glutamine and other amino acids or for measuring glycogenesis, as well as probes used as surrogates for fatty acid synthesis or precursors for fatty acid oxidation. In addition to providing us with opportunities for examining the complex regulation of reprogramed energy metabolism in living subjects, the PET methods open up opportunities for monitoring pharmacological activity of new therapies that directly or indirectly inhibit tumor cell metabolism.

Multimodal imaging with (18)F-FDG-PET/CT and (111)In-Octreotide SPECT in patients with metastatic medullary thyroid carcinoma

OBJECTIVE

The aim of our study was to determine the role of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG-PET/CT) and indium-111 Octreotide single photon emission tomography ((111)In-Octreotide SPECT) in the evaluation of metastatic medullary thyroid carcinoma (MMTC).

METHODS

Twenty-five MMTC patients were retrospectively evaluated. All patients had undergone whole-body (18)F-FDG-PET/CT including 20 who had also undergone (111)In-Octreotide SPECT within a maximum interval of 6 weeks. Diagnostic contrast-enhanced computed tomography (CT) alone or as part of (18)F-FDG-PET/CT examination was performed in all patients.

RESULTS

Contrast-enhanced CT detected a total of 131 lesions including 79 enlarged lymph nodes and 14 bone lesions. (18)F-FDG-PET/CT visualized a total of 92 true positive lesions (SUVmax range 1.1-10.0, mean 4.0 ± 1.7) including 66 lymph nodes, 7 of which were not enlarged on CT, and 8 bone metastases. In the 20 patients studied with both techniques, a total of 64 and 46 true positive lesions were detected by (18)F-FDG-PET/CT and (111)In-Octreotide SPECT, respectively. In particular, (18)F-FDG uptake was found in 43 lymph nodes and in 7 bone metastases whereas (111)In-Octreotide uptake was detected in 27 lymph nodes and in 10 bone metastases.

CONCLUSIONS

In MMTC patients, (18)F-FDG-PET/CT provides a useful contribution mainly in evaluating lymph node involvement whereas (111)In-Octreotide SPECT can contribute to the detection and somatostatin receptor characterization especially of bone lesions.

Monitoring hypoxia and vasculature during bevacizumab treatment in a murine colorectal cancer model

The purpose of this study was to assess the effect of bevacizumab on vasculature and hypoxia in a colorectal tumor model. Nude mice with subcutaneous LS174T tumors were treated with bevacizumab or saline. To assess tumor properties, separate groups of mice were imaged using (18) F-Fluoromisonidazole (FMISO) and (18) F-Fluorodeoxyglucose (FDG) positron emission tomography or magnetic resonance imaging before and 2, 6 and 10 days after the start of treatment. Tumors were harvested after imaging to determine hypoxia and vascular density immunohistochemically. The T2 * time increased significantly less in the bevacizumab group. FMISO uptake increased more over time in the control group. Vessel density significantly decreased in the bevacizumab-treated group. The Carbonic anhydrase 9 (CAIX) and glucose uptake transporter 1 (GLUT1) fractions were higher in bevacizumab-treated tumors. However, the hypoxic fraction showed no significant difference. Bevacizumab led to shorter T2 * times and higher GLUT1 and CAIX expression, suggesting an increase in hypoxia and a higher glycolytic rate. This could be a mechanism of resistance to bevacizumab. The increase in hypoxia, however, could not be demonstrated by pimonidazole/FMISO, possibly because distribution of these tracers is hampered by bevacizumab-induced effects on vascular permeability and perfusion.

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.

Multiparametric monitoring of early response to antiangiogenic therapy: a sequential perfusion CT and PET/CT study in a rabbit VX2 tumor model

OBJECTIVES

To perform dual analysis of tumor perfusion and glucose metabolism using perfusion CT and FDG-PET/CT for the purpose of monitoring the early response to bevacizumab therapy in rabbit VX2 tumor models and to assess added value of FDG-PET to perfusion CT.

METHODS

Twenty-four VX2 carcinoma tumors implanted in bilateral back muscles of 12 rabbits were evaluated. Serial concurrent perfusion CT and FDG-PET/CT were performed before and 3, 7, and 14 days after bevacizumab therapy (treatment group) or saline infusion (control group). Perfusion CT was analyzed to calculate blood flow (BF), blood volume (BV), and permeability surface area product (PS); FDG-PET was analyzed to calculate SUVmax, SUVmean, total lesion glycolysis (TLG), entropy, and homogeneity. The flow-metabolic ratio (FMR) was also calculated and immunohistochemical analysis of microvessel density (MVD) was performed.

RESULTS

On day 14, BF and BV in the treatment group were significantly lower than in the control group. There were no significant differences in all FDG-PET-derived parameters between both groups. In the treatment group, FMR prominently decreased after therapy and was positively correlated with MVD.

CONCLUSIONS

In VX2 tumors, FMR could provide further insight into the early antiangiogenic effect reflecting a mismatch in intratumor blood flow and metabolism.

Positron Emission Tomography (PET) in Oncology

Since its introduction in the early nineties as a promising functional imaging technique in the management of neoplastic disorders, FDG-PET, and subsequently FDG-PET/CT, has become a cornerstone in several oncologic procedures such as tumor staging and restaging, treatment efficacy assessment during or after treatment end and radiotherapy planning. Moreover, the continuous technological progress of image generation and the introduction of sophisticated software to use PET scan as a biomarker paved the way to calculate new prognostic markers such as the metabolic tumor volume (MTV) and the total amount of tumor glycolysis (TLG). FDG-PET/CT proved more sensitive than contrast-enhanced CT scan in staging of several type of lymphoma or in detecting widespread tumor dissemination in several solid cancers, such as breast, lung, colon, ovary and head and neck carcinoma. As a consequence the stage of patients was upgraded, with a change of treatment in 10%-15% of them. One of the most evident advantages of FDG-PET was its ability to detect, very early during treatment, significant changes in glucose metabolism or even complete shutoff of the neoplastic cell metabolism as a surrogate of tumor chemosensitivity assessment. This could enable clinicians to detect much earlier the effectiveness of a given antineoplastic treatment, as compared to the traditional radiological detection of tumor shrinkage, which usually takes time and occurs much later.

CT versus FDG-PET/CT response evaluation in patients with metastatic colorectal cancer treated with irinotecan and cetuximab

We compared morphologic computed tomography (CT)-based to metabolic fluoro-deoxy-glucose (FDG) positron emission tomography (PET)/CT-based response evaluation in patients with metastatic colorectal cancer and correlated the findings with survival and KRAS status. From 2006 to 2009, patients were included in a phase II trial and treated with cetuximab and irinotecan every second week. They underwent FDG-PET/CT examination at baseline and after every fourth treatment cycle. Response evaluation was performed prospectively according to Response Evaluation Criteria in Solid Tumors (RECIST 1.0) and retrospectively according to Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST). Best overall responses were registered. Sixty-one patients were eligible for response evaluation. Partial response (PR) rate was 18%, stable disease (SD) rate 64%, and progressive disease (PD) rate 18%. Partial metabolic response (PMR) rate was 56%, stable metabolic disease rate 33%, and progressive metabolic disease (PMD) rate 11%. Response agreement was poor, κ-coefficient 0.19. Hazard ratio for overall survival for responders (PR/PMR) versus nonresponders (PD/PMD) was higher for CT- than for FDG-PET/CT evaluation. Within patients with KRAS mutations, none had PR but 44% had PMR. In conclusion, morphologic and metabolic response agreement was poor primarily because a large part of the patients shifted from SD with CT evaluation to PMR when evaluated with FDG-PET/CT. Furthermore, a larger fraction of the patients with KRAS mutations had a metabolic treatment response.

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

Molecular imaging allows the noninvasive assessment of cancer progression and response to therapy. The aim of this study was to investigate molecular and cellular determinants of 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) PET and diffusion-weighted (DW) MR imaging in lung carcinoma xenografts.

METHODS

Four lung cancer cell lines (A549, HTB56, EBC1, and H1975) were subcutaneously implanted in nude mice, and growth was followed by caliper measurements. Glucose uptake and tumor proliferation were determined by (18)F-FDG and (18)F-FLT PET, respectively. T2-weighted MR imaging was performed, and the apparent diffusion coefficient (ADC) was determined by DW MR imaging as an indicator of cell death. Imaging findings were correlated to histology with markers for tumor proliferation (Ki67, 5-bromo-2'-deoxyuridine [BrdU]) and cell death (caspase-3, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling). The expression of human equilibrative nucleoside transporter 1 (hENT1), thymidine kinase 1 (TK1), thymidylate synthase, and thymidine phosphorylase (TP) were analyzed by Western blot and immunohistochemistry. Thymidine levels were determined by liquid chromatography-mass spectrometry.

RESULTS

Xenografts varied with respect to in vivo growth rates. MR imaging and PET revealed intratumoral heterogeneities, which were confirmed by histology. (18)F-FLT uptake differed significantly between tumor lines, with A549 and H1975 demonstrating the highest radiotracer accumulation (A549, 8.5 ± 3.2; HTB56, 4.4 ± 0.7; EBC1, 4.4 ± 1.2; and H1975, 12.1 ± 3.5 maximal percentage injected dose per milliliter). In contrast, differences in (18)F-FDG uptake were only marginal. No clear relationship between (18)F-FLT accumulation and immunohistochemical markers for tumor proliferation (Ki67, BrdU) as well as hENT1, TK1, or TS expression was detected. However, TP was highly expressed in A549 and H1975 xenografts, which was accompanied by low tumor thymidine concentrations, suggesting that tumor thymidine levels influence (18)F-FLT uptake in the tumor models investigated. MR imaging revealed higher ADC values within proliferative regions of H1975 and A549 tumors than in HTB56 and EBC1. These ADC values were negatively correlated with cell density but not directly related to cell death.

CONCLUSION

A direct relationship of (18)F-FLT with proliferation or ADC with cell death might be complicated by the interplay of multiple processes at the cellular and physiologic levels in untreated tumors. This issue must be considered when using these imaging modalities in preclinical or clinical settings.

Role of ¹⁸F-FDG PET CT as an independent prognostic indicator in patients with hepatocellular carcinoma

OBJECTIVES

The aim of the study was to evaluate the role of F-fluorodeoxyglucose PET computed tomography (F-FDG PET CT) as an independent prognostic indicator in patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

PET contrast-enhanced CT scans of 100 consecutive patients with HCC were reviewed retrospectively. Patients were asked to fast for 6 h before the study and blood glucose levels were monitored and ensured to be less than 200 mg/dl before injection of F-FDG. After administering the F-FDG injection (370-550 MBq) patients were instructed to rest comfortably for 45-60 min. All images were acquired using a dedicated GE Discovery PET/CT scanner. The PET CT scans of all the patients were reported separately by two nuclear medicine physicians. A stage-wise analysis of the compiled data was carried out. Lesions that showed standardized uptake values greater than background activity (activity in adjacent normal liver tissue) were defined as having increased F-FDG uptake. Pearson's χ -test or the Kruskal-Wallis test was used to assess statistical significance. A P value less than 0.05 was taken as significant.

RESULTS

In this retrospective study of 100 HCC patients, a radiologically higher-stage disease was found more commonly in patients with F-FDG-avid primary tumors (P<0.001), whereas a lower-stage disease was found in patients with non-F-FDG-avid primary tumors. The non-F-FDG-avid tumors also showed lower incidence of metastatic disease and portal vein thrombosis (P<0.001). The histopathological findings of the patients who underwent liver transplantation demonstrated that a higher-grade tumor was more common in the F-FDG-avid tumor group than in the non-F-FDG-avid tumor group (P<0.05).

CONCLUSION

An F-FDG PET CT scan can be used not only for staging but also as a tool for preoperative prediction of cellular differentiation in patients with HCC. The F-FDG uptake seen on a PET scan can serve as a molecular signature for management decisions and can be used as an independent and significant prognostic factor in patients with HCC.

2-Deoxy-2-[18F]fluoro-D-glucose positron emission tomography demonstrates target inhibition with the potential to predict anti-tumour activity following treatment with the AKT inhibitor AZD5363

PURPOSE

The phosphatidyl inositol 3 kinase, AKT and mammalian target of rapamycin are frequently deregulated in human cancer and are among one of the most promising targets for cancer therapy. AZD5363 (AstraZeneca) is an AKT inhibitor in phase 1 clinical trials. Given its utility in assessing glucose metabolism, we investigated the role of 2-Deoxy-2-[18F]fluoro-D-glucose (18F-FDG) positron emission tomography (PET) as a biomarker to demonstrate target inhibition and its potential to predict and demonstrate the anti-tumour activity of AZD5363.

METHODS

18F-FDG PETscans were performed in nude mice in a number of xenograft models (U87-MG glioblastoma, BT474C breast carcinoma and Calu-6 lung). Mice were fasted prior to imaging, and either static or dynamic 18F-FDG PET imaging was performed.

RESULTS

We have shown that 18F-FDG uptake in tumour xenografts was reduced by 39% reduction compared to vehicle after a single dose of AZD5363, demonstrating activation of the AKT pathway after only 4 h of dosing. Multiple doses of AZD5363 showed an anti-tumour volume effect and a reduction in 18F-FDG uptake (28% reduction compared to vehicle), highlighting the potential of 18F-FDG PET as an efficacy biomarker. Furthermore, the degree of inhibition of 18F-FDG uptake corresponded with the sensitivity of the tumour model to AZD5363. The use of dynamic 18F-FDG PET and a two-compartmental analysis identified the mechanism of this change to be due to a change in cellular uptake of 18F-FDG following administration of AZD5363.

CONCLUSIONS

We conclude that 18F-FDG PET is a promising pharmacodynamic biomarker of AKT pathway inhibition, with potential to predict and demonstrate anti-tumour activity. It is a biomarker that may stop ineffective drug schedules, helping to make early stop decisions and identify responding subsets of patients, resulting in improved clinical decision making both during drug development and patient management.

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.

Life history trade-offs in cancer evolution

Somatic evolution during cancer progression and therapy results in tumour cells that show a wide range of phenotypes, which include rapid proliferation and quiescence. Evolutionary life history theory may help us to understand the diversity of these phenotypes. Fast life history organisms reproduce rapidly, whereas those with slow life histories show less fecundity and invest more resources in survival. Life history theory also provides an evolutionary framework for phenotypic plasticity, which has potential implications for understanding 'cancer stem cells'. Life history theory suggests that different therapy dosing schedules might select for fast or slow life history cell phenotypes, with important clinical consequences.

Safety, pharmacokinetics, pharmacodynamics, and antitumor activity of dalantercept, an activin receptor-like kinase-1 ligand trap, in patients with advanced cancer

PURPOSE

The angiogenesis inhibitor dalantercept (formerly ACE-041) is a soluble form of activin receptor-like kinase-1 (ALK1) that prevents activation of endogenous ALK1 by bone morphogenetic protein-9 (BMP9) and BMP10 and exhibits antitumor activity in preclinical models. This first-in-human study of dalantercept evaluated its safety, tolerability, pharmacokinetics, pharmacodynamics, and antitumor activity in adults with advanced solid tumors.

EXPERIMENTAL DESIGN

Patients in dose-escalating cohorts received dalantercept subcutaneously at one of seven dose levels (0.1-4.8 mg/kg) every 3 weeks until disease progression. Patients in an expansion cohort received dalantercept at 0.8 or 1.6 mg/kg every 3 weeks until disease progression.

RESULTS

In 37 patients receiving dalantercept, the most common treatment-related adverse events were peripheral edema, fatigue, and anemia. Edema and fluid retention were dose-limiting toxicities and responded to diuretic therapy. No clinically significant, treatment-related hypertension, proteinuria, gross hemorrhage, or gastrointestinal perforations were observed. One patient with refractory squamous cell cancer of the head and neck had a partial response, and 13 patients had stable disease according to RECISTv1.1, eight of whom had prolonged periods (≥12 weeks) of stable disease. Correlative pharmacodynamic markers included tumor metabolic activity and tumor blood flow, which decreased from baseline in 63% and 82% of evaluable patients, respectively, and telangiectasia in eight patients.

CONCLUSION

Dalantercept was well-tolerated at doses up to 1.6 mg/kg, with a safety profile distinct from inhibitors of the VEGF pathway. Dalantercept displayed promising antitumor activity in patients with advanced refractory cancer, and multiple phase II studies are underway.

(18)F-FDG Is a Surrogate Marker of Therapy Response and Tumor Recovery after Drug Withdrawal during Treatment with a Dual PI3K/mTOR Inhibitor in a Preclinical Model of Cisplatin-Resistant Ovarian Cancer

AIM

Targeting the phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway is a potential means of overcoming chemoresistance in ovarian cancer. We investigated the capability of (18)F-fluororodeoxyglucose ((18)F-FDG) small-animal positron emission tomography (SA-PET) to predict the effects of a dual PI3K/mTOR inhibitor (BEZ-235) in a cisplatin-resistant ovarian cancer model.

METHODS

In a first experiment, nude rats bearing subcutaneous SKOV3 tumors received BEZ-235 for 3 days given alone or after paclitaxel and were compared to controls (either untreated or that were given the excipients of paclitaxel and BEZ-235). SA-PET was performed at baseline, on day 3, and day 7. In a second experiment aiming at further exploring the kinetics of (18)F-FDG tumor uptake during the first 48 hours following drug cessation, untreated controls were compared to rats receiving BEZ-235, which were imaged at baseline, on day 3, on day 4, and on day 5. SA-PET results were compared to cell proliferation assessment (Ki-67), PI3K/mTOR downstream target expression studies (pAKT and phospho-eukaryotic translation initiation factor 4E-binding protein 1), and apoptosis evaluation (cleaved caspase-3).

RESULTS

In the first experiment, BEZ-235, compared to untreated controls, induced a marked decrease in (18)F-FDG uptake on day 3, which was correlated to a significant decrease in cell proliferation and to a significant PI3K/mTOR pathway inhibition. No tumor necrosis or apoptosis occurred. Four days following treatment cessation, tumor recovery (in terms of PI3K/mTOR inhibition and cell proliferation) occurred and was identified by (18)F-FDG SA-PET. Paclitaxel plus BEZ-235 showed results similar to BEZ-235 alone. In the second experiment, PI3K/mTOR pathways exhibited partial recovery as early as 24 hours following treatment cessation, but both (18)F-FDG SA-PET and cell proliferation remained unchanged.

CONCLUSIONS

(18)F-FDG SA-PET is a surrogate marker of target inhibition during treatment with BEZ-235 and predicts tumor recovery 4 days after drug withdrawal, but not during the first 48 hours following drug cessation, when a lag between PI3K/mTOR pathway recovery and metabolic recovery is observed. (18)F-FDG SA-PET could be used for therapy monitoring of PI3K/mTOR inhibitors, but our results also raise questions regarding the potential impact of the delay between PET imaging and the last drug intake on the accuracy of FDG imaging.

A radiologist's guide to treatment response criteria in oncologic imaging: anatomic imaging biomarkers

OBJECTIVE

The purpose of this article is to describe the imaging biomarkers of treatment response and provide an overview of anatomic imaging biomarkers.

CONCLUSION

Imaging biomarkers of treatment response have evolved into the primary endpoint of response in most phase 2 studies. Anatomic imaging biomarkers are applied to depict change in tumor size in response to treatment and are currently the most commonly applied method of treatment response evaluation.

A radiologist's guide to treatment response criteria in oncologic imaging: functional, molecular, and disease-specific imaging biomarkers

OBJECTIVE

This article reviews the functional, molecular, and disease-specific imaging biomarkers of treatment response.

CONCLUSION

Substantial progress has been made in the evolution of drugs directed at specific targets of the tumor lifecycle. These novel agents are predominantly cytostatic, and their efficacy may be optimally evaluated by functional, molecular, and disease-specific imaging biomarkers.

Molecular targeted therapies in non-GIST soft tissue sarcomas: what the radiologist needs to know

Non-gastrointestinal stromal soft tissue sarcomas are uncommon neoplasms that have a dismal prognosis due to a high incidence of metastases and a poor response to conventional chemotherapy. The identification of characteristic genetic alterations in several of these tumors has opened the window for molecular targeted therapies in patients who have failed conventional chemotherapy. Imaging plays a critical role in assessing the response to these novel therapeutic agents. Just like the response of gastrointestinal stromal tumors to imatinib, the response of non-gastrointestinal stromal soft tissue sarcomas to molecular targeted drugs is better evaluated on imaging by alternate tumor response criteria such as the Choi criteria. In addition, these drugs are associated with distinct class-specific drug toxicities that can come to attention for the first time on imaging. The purpose of this article is to provide a primer for the radiologist on the various molecular targeted therapies in advanced/metastatic non-gastrointestinal stromal soft tissue sarcomas with emphasis on the role of imaging in assessing treatment response and complications.

Evaluation of 2-deoxy-2-[18F]fluoro-D-glucose- and 3'-deoxy-3'-[18F]fluorothymidine-positron emission tomography as biomarkers of therapy response in platinum-resistant ovarian cancer

PURPOSE

We evaluated whether 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) and 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) positron emission tomography (PET) could be used as imaging biomarkers of platinum resensitization in ovarian cancer.

PROCEDURES

Paired platinum-sensitive and platinum-resistant ovarian cancer cells from the same patient, PEO1 and PEO4, grown as tumor xenografts in nude mice, were assessed by PET.

RESULTS

The AKT inhibitor, API-2, resensitized platinum-resistant PEO4 tumors to cisplatin, leading to a markedly lower Ki67 labeling index (p ≤ 0.006, n = 6 per group). [(18)F]FDG-PET and [(18)F]FLT-PET imaging variables were lower after combination treatment compared with vehicle treatment (p ≤ 0.006, n = 6 per group). No changes were seen with either drug alone. PRAS40 phosphorylation status was a sensitive biochemical marker of pathway inhibition, whereas reductions thymidine kinase 1 expression defined the [(18)F]FLT response.

CONCLUSIONS

Therapeutic inhibition of AKT activation in acquired platinum-resistant disease can be imaged noninvasively by [(18)F]FDG-PET and [(18)F]FLT-PET warranting further assessment.

Comparison of EORTC criteria and PERCIST for PET/CT response evaluation of patients with metastatic colorectal cancer treated with irinotecan and cetuximab

The study aim was to compare European Organization for Research and Treatment of Cancer (EORTC) criteria with PET Response Criteria in Solid Tumors (PERCIST) for response evaluation of patients with metastatic colorectal cancer treated with a combination of the chemotherapeutic drug irinotecan and the monoclonal antibody cetuximab.

METHODS

From 2006 to 2009, patients with metastatic colorectal cancer were prospectively included in a phase II trial evaluating the combination of irinotecan and cetuximab every second week, as third-line treatment. (18)F-FDG PET/CT was performed between 1 and 14 d before the first treatment and after every fourth treatment cycle until progression was identified by CT with Response Evaluation Criteria in Solid Tumors (RECIST). Response evaluation with (18)F-FDG PET/CT was retrospectively performed according to both EORTC criteria and PERCIST, classifying the patients into 4 response categories: complete metabolic response (CMR), partial metabolic response (PMR), stable metabolic disease (SMD), and progressive metabolic disease (PMD). Individual best overall metabolic response (BOmR) was registered with both sets of criteria, as well as survival within response categories, and compared.

RESULTS

A total of 61 patients and 203 PET/CT scans were eligible for response evaluation. With EORTC criteria, 38 had PMR, 16 had SMD, and 7 had PMD as their BOmR. With PERCIST, 34 had PMR, 20 had SMD, and 7 had PMD as their BOmR. None of the patients had CMR. There was agreement between EORTC criteria and PERCIST in 87% of the patients, and the corresponding κ-coefficient was 0.76. Disagreements were confined to PMR and SMD. Median overall survival (OS) in months with EORTC criteria was 14.2 in the PMR group and 7.2 in the combined SMD + PMD group. With PERCIST, it was 14.5 in the PMR group and 7.9 in the SMD + PMD group.

CONCLUSION

Response evaluation with EORTC criteria and PERCIST gave similar responses and OS outcomes with good agreement on BOmR (κ-coefficient, 0.76) and similar significant differences in median OS between response groups. Compared with EORTC criteria, we find PERCIST unambiguous because of clear definitions and therefore more straightforward to use.

Acute cytotoxic effects of photoimmunotherapy assessed by 18F-FDG PET

We have recently developed a cancer-specific therapy, photoimmunotherapy, which uses an antibody-IR700 (phototoxic phthalocyanine dye) conjugate to bind to the cell membrane and near-infrared light to induce immediate and highly specific tumor killing in vivo. For monitoring the acute cytotoxic effects of photoimmunotherapy before the tumor begins to shrink, we used (18)F-FDG PET before and after this intervention in mice.

METHODS

Photoimmunotherapy was performed by binding panitumumab (anti-HER1)-IR700 to HER1-positive tumor cells (A431), followed by near-infrared light irradiation in vitro and in vivo. The uptake of (18)F-FDG in the tumor after photoimmunotherapy was evaluated in cellular uptake studies and PET imaging studies. Serial histologic analyses were conducted after photoimmunotherapy.

RESULTS

The in vitro cellular uptake of (18)F-FDG was reduced as the dose of light increased, and at high light dose (2 J/cm(2)) the uptake was reduced by more than 99% within 1 h after photoimmunotherapy. In vivo (18)F-FDG PET imaging showed that the accumulation of radioactivity in the treated tumors decreased 76% at 75 min after photoimmunotherapy and did not change for 24 h. In contrast, no significant changes were demonstrated in nontreated tumors. None of tumors changed size within 24 h after photoimmunotherapy, although diffuse necrosis was observed in photoimmunotherapy-treated tumors.

CONCLUSION

Immediate cytotoxic effects induced by photoimmunotherapy were clearly detected by decreased glucose uptake using (18)F-FDG PET even before changes in tumor size became evident. (18)F-FDG allows the clinical assessment of the therapeutic effects of photoimmunotherapy earlier than anatomic methods that rely on tumor size.

Measuring oncogenic signaling pathways in cancer with PET: an emerging paradigm from studies in castration-resistant prostate cancer

As parallel advances in cancer biology and drug development continue to elevate the role of targeted therapies in oncology, the need for imaging biomarkers that systematically measure the biology associated with therapeutic intervention has become more urgent. Although the molecular imaging community has a commitment to develop technologies to this end, few investigational radiotracers directly measure the biology of common oncogenic signaling pathways often addressed by targeted therapies. Visible progress has been achieved with a handful of radiotracers rationally designed to intercalate the pathobiology of prostate cancer, a molecularly heterogeneous disease nevertheless broadly defined by a fairly small repertoire of recurrent oncogenic lesions.

SIGNIFICANCE

That variable treatment responses or emergent resistance phenotypes are often documented in humans argues strongly for diagnostic technologies that can be realistically applied posttherapy to capture the dynamic patterns of disease response. The purpose of this review is to describe a collection of radiotracers developed to measure the pathobiology of prostate cancer for improved treatment monitoring, placing particular emphasis on the biologic rationale for their preparation. A chronologic description of radiotracer development programs is outlined, primarily to stress how an ongoing dialectic between earlier and more contemporary imaging technologies has accelerated discovery.

Novel oncologic drugs: what they do and how they affect images

Targeted therapies are designed to interfere with specific aberrant biologic pathways involved in tumor development. The main classes of novel oncologic drugs include antiangiogenic drugs, antivascular agents, drugs interfering with EGFR-HER2 or KIT receptors, inhibitors of the PI3K/Akt/mTOR pathway, and hormonal therapies. Cancer cells usurp normal signal transduction pathways used by growth factors to stimulate proliferation and sustain viability. The interaction of growth factors with their receptors activates different intracellular pathways affecting key tumor biologic processes such as neoangiogenesis, tumor metabolism, and tumor proliferation. The response of tumors to anticancer therapy can be evaluated with anatomic response assessment, qualitative response assessment, and response assessment with functional and molecular imaging. Angiogenesis can be measured by means of perfusion imaging with computed tomography and magnetic resonance (MR) imaging. Diffusion-weighted MR imaging allows imaging evaluation of tumor cellularity. The main imaging techniques for studying tumor metabolism in vivo are positron emission tomography and MR spectroscopy. Familiarity with imaging findings secondary to tumor response to targeted therapies may help the radiologist better assist the clinician in accurate evaluation of tumor response to these anticancer treatments. Functional and molecular imaging techniques may provide valuable data and augment conventional assessment of tumor response to targeted therapies. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.317115108/-/DC1.

18F-FDG PET as a surrogate biomarker in non-small cell lung cancer treated with erlotinib: newly identified lesions are more informative than standardized uptake value

This study assesses the predictive value of (18)F-FDG PET for overall survival in lung cancer patients treated with a targeted drug.

METHODS

(18)F-FDG PET was performed in 125 second- or third-line non-small cell lung cancer (NSCLC) patients with a baseline Eastern Cooperative Oncology Group performance status less than 3 before treatment with erlotinib (150 mg daily) and 2 wk into treatment. The predictive value of (18)F-FDG PET, clinical parameters, and epithelial growth factor receptor (EGFR) mutation status for survival duration was evaluated by fitting accelerated failure time models.

RESULTS

New lesions on PET at 2 wk, EGFR mutation status, performance status, and baseline tumor burden were independent and significant predictors of overall survival. Reduction of maximum standardized uptake value by at least 35% was predictive of survival only when EGFR mutation status was not accounted for.

CONCLUSION

(18)F-FDG PET in second- or third-line NSCLC patients at 2 wk after starting treatment with erlotinib carries information about overall survival. Parametric survival modeling enables a quantitative assessment of the predictive value of (18)F-FDG PET in the context of clinical and laboratory information. New-lesion status by (18)F-FDG PET at 2 wk is a potential surrogate biomarker for survival in NSCLC.

Development of radiotracers for oncology--the interface with pharmacology

There is an increasing role for positron emission tomography (PET) in oncology, particularly as a component of early phase clinical trials. As a non-invasive functional imaging modality, PET can be used to assess both pharmacokinetics and pharmacodynamics of novel therapeutics by utilizing radiolabelled compounds. These studies can provide crucial information early in the drug development process that may influence the further development of novel therapeutics. PET imaging probes can also be used as early biomarkers of clinical response and to predict clinical outcome prior to the administration of therapeutic agents. We discuss the role of PET imaging particularly as applied to phase 0 studies and discuss the regulations involved in the development and synthesis of novel radioligands. The review also discusses currently available tracers and their role in the assessment of pharmacokinetics and pharmacodynamics as applied to oncology.

Imaging apoptosis with positron emission tomography: 'bench to bedside' development of the caspase-3/7 specific radiotracer [(18)F]ICMT-11

The capacity to evade apoptosis has been defined as one of the hallmarks of cancer and, thus, effective anti-cancer therapy often induces apoptosis. A biomarker for imaging apoptosis could assist in monitoring the efficacy of a wide range of current and future therapeutics. Despite the potential, there are limited clinical examples of the use of positron emission tomography for imaging of apoptosis. [(18)F]ICMT-11 is a novel reagent designed to non-invasively image caspase-3 activation and, hence, drug-induced apoptosis. Radiochemistry development of [(18)F]ICMT-11 has been undertaken to improve specific radioactivity, reduce content of stable impurities, reduce synthesis time and enable automation for manufacture of multi-patient dose. Due to the promising mechanistic and safety profile of [(18)F]ICMT-11, the radiotracer is transitioning to clinical development and has been selected as a candidate radiotracer by the QuIC-ConCePT consortium for further evaluation in preclinical models and humans. A successful outcome will allow use of the radiotracer as qualified method for evaluating the pharmaceutical industry's next generation therapeutics.

Predictive and prognostic molecular markers for cancer medicine

Over the last 10 years there has been an explosion of information about the molecular biology of cancer. A challenge in oncology is to translate this information into advances in patient care. While there are well-formed routes for translating new molecular information into drug therapy, the routes for translating new information into sensitive and specific diagnostic, prognostic and predictive tests are still being developed. Similarly, the science of using tumor molecular profiles to select clinical trial participants or to optimize therapy for individual patients is still in its infancy. This review will summarize the current technologies for predicting treatment response and prognosis in cancer medicine, and outline what the future may hold. It will also highlight the potential importance of methods that can integrate molecular, histopathological and clinical information into a synergistic understanding of tumor progression. While these possibilities are without doubt exciting, significant challenges remain if we are to implement them with a strong evidence base in a widely available and cost-effective manner.

Multimodal imaging with (18)F-FDG PET and Cerenkov luminescence imaging after MLN4924 treatment in a human lymphoma xenograft model

Cerenkov luminescence imaging (CLI) is an emerging imaging technique that combines aspects of both optical and nuclear imaging fields. The ability to fully evaluate the correlation and sensitivity of CLI to PET is critical to progress this technique further for use in high-throughput screening of pharmaceutical compounds. To achieve this milestone, it must first be established that CLI data correlate to PET data in an in vivo preclinical antitumor study. We used MLN4924, a phase 2 oncology therapeutic, which targets and inhibits the NEDD8-activating enzyme pathway involved in the ubiquitin-proteasome system. We compared the efficacious effects of MLN4924 using PET and Cerenkov luminescence image values in the same animals.

METHODS

Imaging of (18)F-FDG uptake was performed at 5 time points after drug treatment in the subcutaneously implanted diffuse large B-cell lymphoma tumor line OCI-Ly10. Data were acquired with both modalities on the same day, with a 15-min delay between CLI and PET. PET data analysis was performed using percentage injected dose per cubic centimeter of tissue (%ID/cm(3)), average standardized uptake values, and total glycolytic volume. CLI measurements were radiance, radiance per injected dose (radiance/ID), and total radiant volume.

RESULTS

A strong correlation was found between PET total glycolytic volume and CLI total radiant volume (r(2) = 0.99) and various PET and CLI analysis methods, with strong correlations found between PET %ID/cm(3) and CLI radiance (r(2) = 0.83) and CLI radiance/ID (r(2) = 0.82). MLN4924 demonstrated a significant reduction in tumor volume after treatment (volume ratio of treated vs. control, 0.114 at day 29).

CONCLUSION

The PET and CLI data presented confirm the correlation and dynamic sensitivity of this new imaging modality. CLI provides a preclinical alternative to expensive PET instrumentation. Future high-throughput studies should provide for quicker turnaround and higher cost-to-return benefits in the drug discovery process.

Response to treatment series: part 2, tumor response assessment--using new and conventional criteria

OBJECTIVE

Conventional anatomic imaging biomarkers, including World Health Organization (WHO) criteria and Response Evaluation Criteria in Solid Tumors (RECIST), although effective, have limitations. This article will discuss the conventional and newer morphologic imaging biomarkers for the assessment of tumor response to therapy.

CONCLUSION

Applying established methods of assessing tumor response to therapy allows consistency in image interpretation and facilitates communication with oncologists. Because of the new methods of treatment, assessment of necrosis and volumetric information will need to be incorporated into size-based criteria.

Approaches using molecular imaging technology -- use of PET in clinical microdose studies

Positron emission tomography (PET) imaging uses minute amounts of radiolabeled drug tracers and thereby meets the criteria for clinical microdose studies. The advantage of PET, when compared to other analytical methods used in microdose studies, is that the pharmacokinetics (PK) of a drug can be determined in the tissue targeted for drug treatment. PET microdosing already offers interesting applications in clinical oncology and in the development of central nervous system pharmaceuticals and is extending its range of application to many other fields of pharmaceutical medicine. Although requirements for preclinical safety testing for microdose studies have been cut down by regulatory authorities, radiopharmaceuticals increasingly need to be produced under good manufacturing practice (GMP) conditions, which increases the costs of PET microdosing studies. Further challenges in PET microdosing include combining PET with other ultrasensitive analytical methods, such as accelerator mass spectrometry (AMS), to gain plasma PK data of drugs, beyond the short PET examination periods. Finally, conducting clinical PET studies with radiolabeled drugs both at micro- and therapeutic doses is encouraged to answer the question of dose linearity in clinical microdosing.