Amarnath Challapalli

Use of [11C]Choline PET-CT as a Noninvasive Method for Detecting Pelvic Lymph Node Status from Prostate Cancer and Relationship with Choline Kinase Expression

Purpose: To evaluate the accuracy and biological basis for [11C]choline-PET-CT in the nodal staging of high risk localized prostate cancer patients. Experimental Design: Twenty-eight patients underwent dynamic [11C]choline-PET-CT of the pelvis and lower abdomen prior to extended laparoscopic pelvic lymph node dissection (eLPL). The sensitivity and specificity of [11C]choline PET, [11C]choline PET-CT, and MRI for nodal detection were calculated. Average and maximal standardized uptake values (SUVave, SUVmax) were compared with choline kinase alpha (CHKα) and Ki67 immunohistochemistry scores. Results: Four hundred and six lymph nodes (LN), in 26 patients, were assessable. Twenty-seven (6.7%) involved pelvic nodes at eLPL were detected in 9 patients. Seventeen of the 27 involved nodes were subcentimeter. The sensitivity and specificity on a per nodal basis were 18.5% and 98.7%, 40.7% and 98.4%, and 51.9% and 98.4% for MRI, [11C]choline PET, and [11C]choline PET-CT, respectively. Sensitivity was higher for [11C]choline PET-CT compared with MRI (P = 0.007). A higher nodal detection rate, including subcentimeter nodes, was seen with [11C]choline PET-CT than MRI. Malignant lesions showed CHKα expression in both cytoplasm and nucleus. SUVave and SUVmax strongly correlated with CHKα staining intensity (r = 0.68, P < 0.0001 and r = 0.63, P = 0.0004, respectively). In contrast, Ki67 expression was generally low in all tumors. Conclusion: This study establishes the relationship between [11C]choline PET-CT uptake with choline kinase expression in prostate cancer and allows it to be used as a noninvasive means of staging pelvic LNs, being highly specific and more sensitive than MRI, including the detection of subcentimeter disease. Clin Cancer Res; 17(24); 7673–83. ©2011 AACR.

[18F]-3′Deoxy-3′-Fluorothymidine Positron Emission Tomography and Breast Cancer Response to Docetaxel

Purpose: To establish biomarkers indicating clinical response to taxanes, we determined whether early changes in [18F]-3′deoxy-3′-fluorothymidine positron emission tomography (FLT-PET) can predict benefit from docetaxel therapy in breast cancer. Experimental Design: This was a prospective unblinded study in 20 patients with American Joint Committee on Cancer (AJCC) stage II–IV breast cancer unresponsive to first-line chemotherapy or progressing on previous therapy. Individuals underwent a baseline dynamic FLT-PET scan followed by a scan 2 weeks after initiating the first or second cycle of docetaxel. PET variables were compared with anatomic response midtherapy (after 3 cycles). Results: Average and maximum tumor standardized uptake values at 60 minutes (SUV60,av and SUV60,max) normalized to body surface area ranged between 1.7 and 17.0 and 5.6 and 26.9 × 10−5 m2/mL, respectively. Docetaxel treatment resulted in a significant decrease in FLT uptake (P = 0.0003 for SUV60,av and P = 0.0002 for SUV60,max). Reduction in tumor SUV60,av was associated with target lesion size changes midtherapy (Pearson R for SUV60,av = 0.64; P = 0.004) and predicted midtherapy target lesion response (0.85 sensitivity and 0.80 specificity). Decreases in SUV60,av in responders were due, at least in part, to reduced net intracellular trapping of FLT (rate constant, Ki). Docetaxel significantly reduced Ki by 51.1% (±28.4%, P = 0.0009). Conclusion: Changes in tumor proliferation assessed by FLT-PET early after initiating docetaxel chemotherapy can predict lesion response midtherapy with good sensitivity warranting prospective trials to assess the ability to stop therapy in the event of non–FLT-PET response. Clin Cancer Res; 17(24); 7664–72. ©2011 AACR.

18F-ICMT-11, a Caspase-3–Specific PET Tracer for Apoptosis: Biodistribution and Radiation Dosimetry

Effective anticancer therapy induces tumor cell death through apoptosis. Noninvasive monitoring of apoptosis during therapy may provide predictive outcome information and help tailor treatment. A caspase-3–specific imaging radiotracer, 18F-(S)-1-((1-(2-fluoroethyl)-1H-[1,2,3]-triazol-4-yl)methyl)-5-(2(2,4-difluorophenoxymethyl)-pyrrolidine-1-sulfonyl)isatin (18F-ICMT-11), has been developed for use in PET studies. We report the safety, biodistribution, and internal radiation dosimetry profiles of 18F-ICMT-11 in 8 healthy human volunteers. Methods: 18F-ICMT-11 was intravenously administered as a bolus injection (mean ± SD, 159 ± 2.75 MBq; range, 154–161 MBq) to 8 healthy volunteers (4 men, 4 women). Whole-body (vertex to mid thigh) PET/CT scans were acquired at 6 time points, up to 4 h after tracer injection. Serial whole blood, plasma, and urine samples were collected for radioactivity measurement and radiotracer stability. In vivo 18F activities were determined from quantitative analysis of the images, and time–activity curves were generated. The total numbers of disintegrations in each organ normalized to injected activity (residence times) were calculated as the area under the curve of the time–activity curve, normalized to injected activities and standard values of organ volumes. Dosimetry calculations were then performed using OLINDA/EXM 1.1. Results: Injection of 18F-ICMT-11 was well tolerated in all subjects, with no serious tracer-related adverse events reported. The mean effective dose averaged over both men and women was estimated to be 0.025 ± 0.004 mSv/MBq (men, 0.022 ± 0.004 mSv/MBq; women, 0.027 ± 0.004 mSv/MBq). The 5 organs receiving the highest absorbed dose (mGy/MBq), averaged over both men and women, were the gallbladder wall (0.59 ± 0.44), small intestine (0.12 ± 0.05), upper large intestinal wall (0.08 ± 0.07), urinary bladder wall (0.08 ± 0.02), and liver (0.07 ± 0.01). Elimination was both renal and via the hepatobiliary system. Conclusion: 18F-ICMT-11 is a safe PET tracer with a dosimetry profile comparable to other common 18F PET tracers. These data support the further development of 18F-ICMT-11 for clinical imaging of apoptosis.

Imaging apoptosis with positron emission tomography: ‘Bench to bedside’ development of the caspase-3/7 specific radiotracer [18F]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 industrys next generation therapeutics.

Biological basis of [11C]choline-positron emission tomography in patients with breast cancer: comparison with [18F]fluorothymidine positron emission tomography

ObjectiveThe biological significance of [11C]choline (CHO) uptake in human tumours is unclear and probably linked to choline kinase-&agr; (CHK&agr;) expression and cell proliferation. We directly compared CHO with [18F]fluorothymidine (FLT), an imaging biomarker of proliferation, by positron emission tomography (PET) in patients with breast cancer to investigate whether cell proliferation is an important determinant of CHO uptake. Furthermore, we evaluated CHK&agr; and the Ki67-labelling index (LIKi67) in tumour biopsies. MethodsSequential CHO-PET and FLT-PET within the same imaging session were performed in 21 patients with oestrogen receptor (ER)-positive breast cancer (28 lesions). Average and maximum CHO standardized uptake values (SUV) at 60 min: SUV60,av, and SUV60,max, and the rate constant of net irreversible uptake, Ki, were compared with FLT uptake at 60 min: SUV60,av and SUV60,max. Biopsies were stained for CHK&agr; and LIKi67 in eight cases. ResultsTumours were equally visible on CHO-PET and FLT-PET imaging. Tumour CHO-PET strongly correlated with FLT imaging variables (Pearson’s r=0.83; P<0.0001 for CHO-SUV60,max vs. FLT-SUV60,max). A statistically significant association was found between CHO-PET variables and categorical scores of cytoplasmic CHK&agr; intensity and between FLT-PET and LIKi67 (P<0.05, one-way analysis of variance). ConclusionCholine metabolism and proliferation as assessed by PET were correlated in ER-positive breast cancer, indicating that high CHO uptake is a measure of cellular proliferation in this setting. CHO uptake was also found to be related to cytoplasmic CHK&agr; expression.

Exploring the potential of [11C]choline-PET/CT as a novel imaging biomarker for predicting early treatment response in prostate cancer.

ObjectivesThe aim of the study was to assess the effects of neoadjuvant androgen deprivation (NAD) and radical prostate radiotherapy with concurrent androgen deprivation (RT-CAD) on prostatic [11C]choline kinetics and thus develop methodology for the use of [11C]choline-PET/computed tomography (CT) as an early imaging biomarker. Materials and methodsTen patients with histologically confirmed prostate cancer underwent three sequential dynamic [11C]choline-PET/CT pelvic scans: at baseline, after NAD and 4 months after RT-CAD. [11C]Choline uptake was quantified using the average and maximum standardized uptake values at 60 min (SUV60,ave and SUV60,max), the tumour-to-muscle ratios (TMR60,max) and net irreversible retention of [11C]choline at steady state (Kimod-pat). ResultsThe combination of NAD and RT-CAD significantly decreased tumour [11C]choline uptake (SUV60,ave, SUV60,max, TMR60,max or Kimod-pat) and prostate-specific antigen (PSA) levels (analysis of variance, P<0.001 for all variables). Although the magnitude of reduction in the variables was larger after NAD, there was a smaller additional reduction after RT-CAD. A wide range of reduction in tumour SUV60,ave (38–83.7%) and SUV60,max (22.2–85.3%) was seen with combined NAD and RT-CAD despite patients universally achieving PSA suppression (narrow range of 93.5–99.7%). There was good association between baseline SUV60,max and initial PSA levels (Pearson’s r=0.7, P=0.04). The reduction in tumour SUV60,ave after NAD was associated with PSA reduction (r=0.7, P=0.04). This association occurred despite the larger reduction in PSA (94%) compared with SUV60,ave (58%). ConclusionThis feasibility study shows that [11C]choline-PET/CT detects metabolic changes within tumours following NAD and RT-CAD to the prostate. A differential reduction in [11C]choline uptake despite a global reduction in PSA following NAD and RT-CAD could provide prognostic information and warrants further evaluation as an imaging biomarker in this setting.

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-[18F]fluoro-D-glucose is well established in the clinic. Analogs of choline, including [11C]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.

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

Although [(18)F]fluorothymidine positron emission tomography (FLT-PET) permits estimation of tumor thymidine kinase-1 expression, and thus, cell proliferation, high physiological uptake of tracer in liver tissue can limit its utility. We evaluated FLT-PET combined with a temporal-intensity information-based voxel-clustering approach termed kinetic spatial filtering (FLT-PET(KSF)) for detecting drug response in liver metastases. FLT-PET and computed tomography data were collected from patients with confirmed breast or colorectal liver metastases before, and two weeks after the first cycle of chemotherapy. Changes in tumor FLT-PET and FLT-PET(KSF) variables were determined. Visual distinction between tumor and normal liver was seen in FLT-PET(KSF) images. Of the 33 metastases from 20 patients studied, 26 were visible after kinetic filtering. The net irreversible retention of the tracer (Ki; from unfiltered data) in the tumor, correlated strongly with tracer uptake when the imaging variable was an unfiltered average or maximal standardized uptake value, 60 min post-injection (SUV(60,av): r = 0.9, SUV(60,max): r = 0.7; p < 0.0001 for both) and occurrence of high intensity voxels derived from FLT-PET(KSF) (r = 0.7, p < 0.0001). Overall, a significant reduction in the imaging variables was seen in responders compared to non-responders; however, the two week time point selected for imaging was too early to allow prediction of long term clinical benefit from chemotherapy. FLT-PET and FLT-PET(KSF) detected changes in proliferation in liver metastases.

Monitoring early response to taxane therapy in advanced breast cancer with circulating tumor cells and [18F] 3´-deoxy-3´-fluorothymidine PET: a pilot study

AIM Early markers of response to chemotherapy, measured by blood markers and imaging, may ultimately lead to tailored therapies that avoid cumulative toxicity. MATERIALS & METHODS We performed a small pilot study to compare early changes in levels of circulatory tumor cells (CTCs) with changes in tumor proliferation, using metabolic imaging with [(18)F] 3´-deoxy-3´-fluorothymidine PET (FLT-PET) in women with advanced breast cancer, before and during docetaxel therapy. RESULTS In those individuals in whom we could detect CTCs, a decrease in CTC count correlated with a decrease in FLT-PET signal, within 2 weeks. CONCLUSION Combined, these two technologies are likely to provide a powerful, albeit expensive, tool to assess immediate responses to therapy.

Molecular mechanisms of hypoxia in cancer

PurposeHypoxia is a condition of insufficient oxygen to support metabolism which occurs when the vascular supply is interrupted, or when a tumour outgrows its vascular supply. It is a negative prognostic factor due to its association with an aggressive tumour phenotype and therapeutic resistance. This review provides an overview of hypoxia imaging with Positron emission tomography (PET), with an emphasis on the biological relevance, mechanism of action, highlighting advantages, and limitations of the currently available hypoxia radiotracers.MethodsA comprehensive PubMed literature search was performed, identifying articles relating to biological significance and measurement of hypoxia, MRI methods, and PET imaging of hypoxia in preclinical and clinical settings, up to December 2016.ResultsA variety of approaches have been explored over the years for detecting and monitoring changes in tumour hypoxia, including regional measurements with oxygen electrodes placed under CT guidance, MRI methods that measure either oxygenation or lactate production consequent to hypoxia, different nuclear medicine approaches that utilise imaging agents the accumulation of which is inversely related to oxygen tension, and optical methods. The advantages and disadvantages of these approaches are reviewed, along with individual strategies for validating different imaging methods. PET is the preferred method for imaging tumour hypoxia due to its high specificity and sensitivity to probe physiological processes in vivo, as well as the ability to provide information about intracellular oxygenation levels.ConclusionEven though hypoxia could have significant prognostic and predictive value in the clinic, the best method for hypoxia assessment has in our opinion not been realised.