Double-tracer autoradiography with Cu-ATSM/FDG and immunohistochemical interpretation in four different mouse implanted tumor models

Feasibility study of multimodal imaging for redox status and glucose metabolism in tumor

Understanding the tumor redox status is important for efficient cancer treatment. Here, we noninvasively detected changes in the redox environment of tumors before and after cancer treatment in the same individuals using a novel compact and portable electron paramagnetic resonance imaging (EPRI) device and compared the results with glycolytic information obtained through autoradiography using 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG). Human colon cancer HCT116 xenografts were used in the mice. We used 3-carbamoyl-PROXYL (3CP) as a paramagnetic and redox status probe for the EPRI of tumors. The first EPRI was followed by the intraperitoneal administration of buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, or X-ray irradiation of the tumor. A second EPRI was performed on the following day. Autoradiography was performed after the second EPRI. After imaging, the tumor sections were evaluated by histological analysis and the amount of reducing substances in the tumor was measured. BSO treatment and X-ray irradiation significantly decreased the rate of 3CP reduction in tumors. Redox maps of tumors obtained from EPRI can be compared with tissue sections of approximately the same cross section. BSO treatment reduced glutathione levels in tumors, whereas X-ray irradiation did not alter the levels of any of the reducing substances. Comparison of the redox map with the autoradiography of [18F]FDG revealed that regions with high reducing power in the tumor were active in glucose metabolism; however, this correlation disappeared after X-ray irradiation. These results suggest that the novel compact and portable EPRI device is suitable for multimodal imaging, which can be used to study tumor redox status and therapeutic efficacy in cancer, and for combined analysis with other imaging modalities.

Feasibility of Renal Blood Flow Measurement Using 64Cu-ATSM PET/MRI: A Quantitative PET and MRI Study

This study aimed to evaluate the renal blood flow (RBF) in patients with chronic kidney disease (CKD) using ⁶⁴Cu(II)-diacetyl-bis(4-methylthiosemicarbazonate) (⁶⁴Cu-ATSM) for positron emission tomography (PET)/magnetic resonance imaging (MRI). We included five healthy controls (HCs) and ten patients with CKD. The estimated glomerular filtration rate (eGFR) was calculated from the serum creatinine (cr) and cystatin C (cys) levels. The estimated RBF (eRBF) was calculated using the eGFR, hematocrit, and filtration fraction. A single dose of ⁶⁴Cu-ATSM (300-400 MBq) was administered for RBF evaluation, and a 40 min dynamic PET scan was performed with simultaneous arterial spin labeling (ASL) imaging. PET-RBF images were obtained from the dynamic PET images at 3 min after injection using the image-derived input function method. The mean eRBF values calculated from various eGFR values differed significantly between the patients and HCs; both groups also differed significantly in terms of the RBF values (mL/min/100 g) measured using PET (151 ± 20 vs. 124 ± 22, p < 0.05) and ASL-MRI (172 ± 38 vs. 125 ± 30, p < 0.001). The ASL-MRI-RBF was positively correlated with the eRBFcr-cys (r = 0.858, p < 0.001). The PET-RBF was positively correlated with the eRBFcr-cys (r = 0.893, p < 0.001). The ASL-RBF was positively correlated with the PET-RBF (r = 0.849, p < 0.001). ⁶⁴Cu-ATSM PET/MRI demonstrated the reliability of PET-RBF and ASL-RBF by comparing them with eRBF. This is the first study to demonstrate that ⁶⁴Cu-ATSM-PET is useful for assessing the RBF and is well correlated with ASL-MRI.

Positron emission tomography imaging of lung cancer: An overview of alternative positron emission tomography tracers beyond F18 fluorodeoxyglucose

Lung cancer has been the leading cause of cancer-related mortality in China in recent decades. Positron emission tomography-computer tomography (PET/CT) has been established in the diagnosis of lung cancer. ¹⁸F-FDG is the most widely used PET tracer in foci diagnosis, tumor staging, treatment planning, and prognosis assessment by monitoring abnormally exuberant glucose metabolism in tumors. However, with the increasing knowledge on tumor heterogeneity and biological characteristics in lung cancer, a variety of novel radiotracers beyond ¹⁸F-FDG for PET imaging have been developed. For example, PET tracers that target cellular proliferation, amino acid metabolism and transportation, tumor hypoxia, angiogenesis, pulmonary NETs and other targets, such as tyrosine kinases and cancer-associated fibroblasts, have been reported, evaluated in animal models or under clinical investigations in recent years and play increasing roles in lung cancer diagnosis. Thus, we perform a comprehensive literature review of the radiopharmaceuticals and recent progress in PET tracers for the study of lung cancer biological characteristics beyond glucose metabolism.

Hypoxia imaging and theranostic potential of [64Cu][Cu(ATSM)] and ionic Cu(II) salts: a review of current evidence and discussion of the retention mechanisms

Background

Tumor hypoxia (low tissue oxygenation) is an adverse condition of the solid tumor environment, associated with malignant progression, radiotherapy resistance, and poor prognosis. One method to detect tumor hypoxia is by positron emission tomography (PET) with the tracer [⁶⁴Cu][Cu-diacetyl-bis(N(4)-methylthiosemicarbazone)] ([⁶⁴Cu][Cu(ATSM)]), as demonstrated in both preclinical and clinical studies. In addition, emerging studies suggest using [⁶⁴Cu][Cu(ATSM)] for molecular radiotherapy, mainly due to the release of therapeutic Auger electrons from copper-64, making [⁶⁴Cu][Cu(ATSM)] a “theranostic” agent. However, the radiocopper retention based on a metal-ligand dissociation mechanism under hypoxia has long been controversial. Recent studies using ionic Cu(II) salts as tracers have raised further questions on the original mechanism and proposed a potential role of copper itself in the tracer uptake. We have reviewed the evidence of using the copper radiopharmaceuticals [^60/61/62/64Cu][Cu(ATSM)]/ionic copper salts for PET imaging of tumor hypoxia, their possible therapeutic applications, issues related to the metal-ligand dissociation mechanism, and possible explanations of copper trapping based on studies of the copper metabolism under hypoxia.

Results

We found that hypoxia selectivity of [⁶⁴Cu][Cu(ATSM)] has been clearly demonstrated in both preclinical and clinical studies. Preclinical therapeutic studies in mice have also demonstrated promising results, recently reporting significant tumor volume reductions and improved survival in a dose-dependent manner. Cu(II)-[Cu(ATSM)] appears to be accumulated in regions with substantially higher CD133⁺ expression, a marker for cancer stem cells. This, combined with the reported requirement of copper for activation of the hypoxia inducible factor 1 (HIF-1), provides a possible explanation for the therapeutic effects of [⁶⁴Cu][Cu(ATSM)]. Comparisons between [⁶⁴Cu][Cu(ATSM)] and ionic Cu(II) salts have showed similar results in both imaging and therapeutic studies, supporting the argument for the central role of copper itself in the retention mechanism.

Conclusions

We found promising evidence of using copper-64 radiopharmaceuticals for both PET imaging and treatment of hypoxic tumors. The Cu(II)-[Cu(ATSM)] retention mechanism remains controversial and future mechanistic studies should be focused on understanding the role of copper itself in the hypoxic tumor metabolism.

Multiple Administrations of 64Cu-ATSM as a Novel Therapeutic Option for Glioblastoma: a Translational Study Using Mice with Xenografts

Glioblastoma is the most aggressive malignant brain tumor in humans and is difficult to cure using current treatment options. Hypoxic regions are frequently found in glioblastoma, and increased levels of hypoxia are associated with poor clinical outcomes of glioblastoma patients. Hypoxia plays important roles in the progression and recurrence of glioblastoma because of drug delivery deficiencies and induction of hypoxia-inducible factor-1α in tumor cells, which lead to poor prognosis. We focused on a promising hypoxia-targeted internal radiotherapy agent, ⁶⁴Cu-diacetyl-bis (N⁴-methylthiosemicarbazone) (⁶⁴Cu-ATSM), to address the need for additional treatment for glioblastoma. This compound can target the overreduced state under hypoxic conditions within tumors. Clinical positron emission tomography studies using radiolabeled Cu-ATSM have shown that Cu-ATSM accumulates in glioblastoma and its uptake is associated with high hypoxia-inducible factor-1α expression. To evaluate the therapeutic potential of this agent for glioblastoma, we examined the efficacy of ⁶⁴Cu-ATSM in mice bearing U87MG glioblastoma tumors. Administration of single dosage (18.5, 37, 74, 111, and 148 MBq) and multiple dosages (37 MBq × 4) of ⁶⁴Cu-ATSM was investigated. Single administration of ⁶⁴Cu-ATSM in high-dose groups dose-dependently inhibited tumor growth and prolonged survival, with slight and reverse signs of adverse events. Multiple dosages of ⁶⁴Cu-ATSM remarkably inhibited tumor growth and prolonged survival. By splitting the dose of ⁶⁴Cu-ATSM, no adverse effects were observed. Our findings indicate that multiple administrations of ⁶⁴Cu-ATSM have effective antitumor effects in glioblastoma without side effects, indicating its potential for treating this fatal disease.

Copper-64 Radiopharmaceuticals for Oncologic Imaging

The positron emitting radionuclide (64)Cu has a radioactive half-life of 12.7 hours. The decay characteristics of (64)Cu allow for PET images that are comparable in quality to those obtained using (18)F. Given the longer radioactive half-life of (64)Cu compared with (18)F and the versatility of copper chemistry, copper is an attractive alternative to the shorter-lived nuclides for PET imaging of peptides, antibodies, and small molecules that may require longer circulation times. This article discusses a number of copper radiopharmaceuticals, such as Cu-ATSM, that have been translated to the clinic and new developments in copper-based radiopharmaceuticals.

Micro Regional Heterogeneity of 64Cu-ATSM and 18F-FDG Uptake in Canine Soft Tissue Sarcomas: Relation to Cell Proliferation, Hypoxia and Glycolysis

OBJECTIVES

Tumour microenvironment heterogeneity is believed to play a key role in cancer progression and therapy resistance. However, little is known about micro regional distribution of hypoxia, glycolysis and proliferation in spontaneous solid tumours. The overall aim was simultaneous investigation of micro regional heterogeneity of 64Cu-ATSM (hypoxia) and 18F-FDG (glycolysis) uptake and correlation to endogenous markers of hypoxia, glycolysis, proliferation and angiogenesis to better therapeutically target aggressive tumour regions and prognosticate outcome.

METHODS

Exploiting the different half-lives of 64Cu-ATSM (13 h) and 18F-FDG (2 h) enabled simultaneous investigation of micro regional distribution of hypoxia and glycolysis in 145 tumour pieces from four spontaneous canine soft tissue sarcomas. Pairwise measurements of radioactivity and gene expression of endogenous markers of hypoxia (HIF-1α, CAIX), glycolysis (HK2, GLUT1 and GLUT3), proliferation (Ki-67) and angiogenesis (VEGFA and TF) were performed. Dual tracer autoradiography was compared with Ki-67 immunohistochemistry.

RESULTS

Micro regional heterogeneity in hypoxia and glycolysis within and between tumour sections of each tumour piece was observed. The spatial distribution of 64Cu-ATSM and 18F-FDG was rather similar within each tumour section as reflected in moderate positive significant correlations between the two tracers (ρ = 0.3920-0.7807; p = 0.0180 -<0.0001) based on pixel-to-pixel comparisons of autoradiographies and gamma counting of tumour pieces. 64Cu-ATSM and 18F-FDG correlated positively with gene expression of GLUT1 and GLUT3, but negatively with HIF-1α and CAIX. Significant positive correlations were seen between Ki-67 gene expression and 64Cu-ATSM (ρ = 0.5578, p = 0.0004) and 18F-FDG (ρ = 0.4629-0.7001, p = 0.0001-0.0151). Ki-67 gene expression more consistently correlated with 18F-FDG than with 64Cu-ATSM.

CONCLUSIONS

Micro regional heterogeneity of hypoxia and glycolysis was documented in spontaneous canine soft tissue sarcomas. 64Cu-ATSM and 18F-FDG uptakes and distributions showed significant moderate correlations at the micro regional level indicating overlapping, yet different information from the tracers.18F-FDG better reflected cell proliferation as measured by Ki-67 gene expression than 64Cu-ATSM.

High-uptake areas on positron emission tomography with the hypoxic radiotracer (18)F-FRP170 in glioblastomas include regions retaining proliferative activity under hypoxia

Objective

The aim was to evaluate the proliferative activity of high-uptake areas on positron emission tomography (PET) with the hypoxic cell radiotracer, 1-(2-[¹⁸F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP170).

Methods

Thirteen patients with glioblastoma underwent FRP170 PET before tumor resection. During surgery, tumor specimens were stereotaxically obtained from regions corresponding to high (high-uptake areas, HUAs) and relatively low (low-uptake areas, LUAs) accumulation of FRP170. We compared immunohistochemical staining for Ki-67 and hypoxia-inducible factor (HIF)-1α between HUA and LUA.

Results

HIF-1α index was significantly higher in HUAs than in LUAs. In contrast, mean Ki-67 indices did not differ significantly between HUAs and LUAs.

Conclusions

Findings for HIF-1α index clearly indicated that HUAs on FRP170 PET represented hypoxic regions in glioblastoma. However, findings of Ki-67 index suggest that HUAs on FRP170 PET include regions retaining proliferative activity regardless of tissue hypoxia.

Comparison of intratumoral FDG and Cu-ATSM distributions in cancer tissue originated spheroid (CTOS) xenografts, a tumor model retaining the original tumor properties

INTRODUCTION

The intratumoral distributions of [(18)F]FDG and [(64)Cu]Cu-ATSM have been reported to be similar in adenocarcinomas but different in squamous cell carcinoma (SCC) in clinical studies. In the present study, we compared the intratumoral distributions of these two tracers in cancer tissue originated spheroid (CTOS) xenografts derived from adenocarcinoma and SCC, which retain the histological characteristics of the original tumors, and in cancer cell line xenografts of corresponding origin, to investigate the underlying mechanism of the distinct FDG and Cu-ATSM distribution patterns in adenocarcinoma and SCC.

METHODS

CTOSs derived from colon adenocarcinoma and lung SCC and cell lines established from colon adenocarcinoma and lung SCC, which were used for comparison, were subcutaneously transplanted into immunodeficient mice. One hour after administering [(14)C]FDG and [(64)Cu]Cu-ATSM, the intratumoral distributions were compared in the xenografts by using dual-tracer autoradiography. Adjacent sections were evaluated for necrosis, vasculature anatomy, Ki-67 antigen, and pimonidazole adducts using hematoxylin and eosin and immunohistochemical staining.

RESULTS

There was a higher regional overlap of high FDG and Cu-ATSM accumulations in the adenocarcinoma CTOS xenografts than in the SCC CTOS xenografts, while the overlap in the adenocarcinoma cell line xenograft was lower than that observed in the SCC cell line. High FDG accumulation occurred primarily in proximity to necrotic or pimonidazole adduct positive regions, while high Cu-ATSM accumulation occurred primarily in live cell regions separate from the necrotic regions. The adenocarcinoma CTOS xenograft had the stereotypical glandular structure, resulting in more intricately mixed regions of live and necrotic cells compared to those observed in the SCC CTOS or the cell line xenografts.

CONCLUSION

Tumor morphological characteristics, specifically the spatial distribution of live and necrotic cell regions, appeared to be one of the most critical factors determining the regional overlap of FDG and Cu-ATSM distributions in adenocarcinoma.

Controlled administration of penicillamine reduces radiation exposure in critical organs during 64Cu-ATSM internal radiotherapy: a novel strategy for liver protection

Purpose

⁶⁴Cu-diacetyl-bis (N⁴-methylthiosemicarbazone) (⁶⁴Cu-ATSM) is a promising theranostic agent that targets hypoxic regions in tumors related to malignant characteristics. Its diagnostic usefulness has been recognized in clinical studies. Internal radiotherapy (IRT) with ⁶⁴Cu-ATSM is reportedly effective in preclinical studies; however, for clinical applications, improvements to reduce radiation exposure in non-target organs, particularly the liver, are required. We developed a strategy to reduce radiation doses to critical organs while preserving tumor radiation doses by controlled administration of copper chelator penicillamine during ⁶⁴Cu-ATSM IRT.

Methods

Biodistribution was evaluated in HT-29 tumor-bearing mice injected with ⁶⁴Cu-ATSM (185 kBq) with or without oral penicillamine administration. The appropriate injection interval between ⁶⁴Cu-ATSM and penicillamine was determined. Then, the optimal penicillamine administration schedule was selected from single (100, 300, and 500 mg/kg) and fractionated doses (100 mg/kg×3 at 1- or 2-h intervals from 1 h after ⁶⁴Cu-ATSM injection). PET imaging was performed to confirm the effect of penicillamine with a therapeutic ⁶⁴Cu-ATSM dose (37 MBq). Dosimetry analysis was performed to estimate human absorbed doses.

Results

Penicillamine reduced ⁶⁴Cu accumulation in the liver and small intestine. Tumor uptake was not affected by penicillamine administration at 1 h after ⁶⁴Cu-ATSM injection, when radioactivity was almost cleared from the blood and tumor uptake had plateaued. Of the single doses, 300 mg/kg was most effective. Fractionated administration at 2-h intervals further decreased liver accumulation at later time points. PET indicated that penicillamine acts similarly with the therapeutic ⁶⁴Cu-ATSM dose. Dosimetry demonstrated that appropriately scheduled penicillamine administration reduced radiation doses to critical organs (liver, ovaries, and red marrow) below tolerance levels. Laxatives reduced radiation doses to the large intestine.

Conclusions

We developed a novel strategy to reduce radiation exposure in critical organs during ⁶⁴Cu-ATSM IRT, thus promoting its clinical applications. This method could be beneficial for other ⁶⁴Cu-labeled compounds.

Development of a new positron emission tomography tracer for targeting tumor angiogenesis: synthesis, small animal imaging, and radiation dosimetry

Angiogenesis plays a key role in cancer progression and correlates with disease aggressiveness and poor clinical outcomes. Affinity ligands discovered by screening phage display random peptide libraries can be engineered to molecularly target tumor blood vessels for noninvasive imaging and early detection of tumor aggressiveness. In this study, we tested the ability of a phage-display-selected peptide sequence recognizing specifically bone marrow- derived pro-angiogenic tumor-homing cells, the QFP-peptide, radiolabeled with 64Cu radioisotope to selectively image tumor vasculature in vivo by positron emission tomography (PET). To prepare the targeted PET tracer we modified QFP-phage with the DOTA chelator and radiolabeled the purified QFP-phage-DOTA intermediate with 64Cu to obtain QFP-targeted radioconjugate with high radiopharmaceutical yield and specific activity. We evaluated the new PET tracer in vivo in a subcutaneous (s.c.) Lewis lung carcinoma (LLC) mouse model and conducted tissue distribution, small animal PET/CT imaging study, autoradiography, histology, fluorescence imaging, and dosimetry assessments. The results from this study show that, in the context of the s.c. LLC immunocompetent mouse model, the QFP-tracer can target tumor blood vessels selectively. However, further optimization of the biodistribution and dosimetry profile of the tracer is necessary to ensure efficient radiopharmaceutical applications enabled by the biological specificity of the QFP-peptide.

Tumor microenvironment-dependent 18F-FDG, 18F-fluorothymidine, and 18F-misonidazole uptake: a pilot study in mouse models of human non-small cell lung cancer

(18)F-FDG, (18)F-fluorothymidine, and (18)F-misonidazole PET scans have emerged as important clinical tools in the management of cancer; however, none of them have demonstrated conclusive superiority. The aim of this study was to compare the intratumoral accumulation of (18)F-FDG, (18)F-fluorothymidine, and (18)F-misonidazole and relate this to specific components of the tumor microenvironment in mouse models of human non-small cell lung cancer (NSCLC).

METHODS

We used NSCLC A549 and HTB177 cells to generate subcutaneous and peritoneal xenografts in nude mice. Animals were coinjected with a PET radiotracer, pimonidazole (hypoxia marker), and bromodeoxyuridine (proliferation marker) intravenously 1 h before animal euthanasia. Tumor perfusion was assessed by Hoechst 33342 injection, given 1 min before sacrifice. The intratumoral distribution of PET radiotracers was visualized by digital autoradiography and related to microscopic visualization of proliferation, hypoxia, perfusion, stroma, and necrosis.

RESULTS

NSCLC xenografts had complex structures with intermingled regions of viable cancer cells, stroma, and necrosis. Cancer cells were either well oxygenated (staining negatively for pimonidazole) and highly proliferative (staining positively for bromodeoxyuridine) or hypoxic (pimonidazole-positive) and noncycling (little bromodeoxyuridine). Hypoxic cancer cells with a low proliferation rate had high(18)F-FDG and (18)F-misonidazole uptake but low (18)F-fluorothymidine accumulation. Well-oxygenated cancer cells with a high proliferation rate accumulated a high level of (18)F-fluorothymidine but low (18)F-FDG and(18)F-misonidazole. Tumor stroma and necrotic zones were always associated with low (18)F-FDG, (18)F-misonidazole, and (18)F-fluorothymidine activity.

CONCLUSION

In NSCLC A549 and HTB177 subcutaneously or intraperitoneally growing xenografts, (18)F-fluorothymidine accumulates in well-oxygenated and proliferative cancer cells, whereas (18)F-misonidazole and (18)F-FDG accumulate mostly in poorly proliferative and hypoxic cancer cells. (18)F-FDG and (18)F-misonidazole display similar intratumoral distribution patterns, and both mutually exclude (18)F-fluorothymidine.

Radiolabeled Cu-ATSM as a novel indicator of overreduced intracellular state due to mitochondrial dysfunction: studies with mitochondrial DNA-less ρ0 cells and cybrids carrying MELAS mitochondrial DNA mutation

OBJECTIVES

Radiolabeled Cu-diacetyl-bis (N(4)-methylthiosemicarbazone) (*Cu-ATSM), including (60/62/64)Cu-ATSM, is a potential imaging agent of hypoxic tumors for positron emission tomography (PET). We have reported that *Cu-ATSM is trapped in tumor cells under intracellular overreduced states, e.g., hypoxia. Here we evaluated *Cu-ATSM as an indicator of intracellular overreduced states in mitochondrial disorders using cell lines with mitochondrial dysfunction.

METHODS

Mitochondrial DNA-less ρ(0)206 cells; the parental 143B human osteosarcoma cells; the cybrids carrying mutated mitochondria from a patient of mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) (2SD); and that carrying wild-type one (2SA) were used. Cells were treated under normoxia or hypoxia, and (64)Cu-ATSM uptake was examined to compare it with levels of biological reductant NADH and NADPH.

RESULTS

ρ(0)206 cells showed higher (64)Cu-ATSM uptake than control 143B cells under normoxia, whereas (64)Cu-ATSM uptake was not significantly increased under hypoxia in ρ(0)206 cells. Additionally, (64)Cu-ATSM uptake showed correlate change to the NADH and NADPH levels, but not oxygenic conditions. 2SD cells showed increased (64)Cu-ATSM uptake under normoxia as compared with the control 2SA, and (64)Cu-ATSM uptake followed NADH and NADPH levels, but not oxygenic conditions.

CONCLUSIONS

(64)Cu-ATSM accumulated in cells with overreduced states due to mitochondrial dysfunction, even under normoxia. We recently reported that (62)Cu-ATSM-PET can visualize stroke-like episodes maintaining oxygen supply in MELAS patients. Taken together, our data indicate that *Cu-ATSM uptake reflects overreduced intracellular states, despite oxygenic conditions; thus, *Cu-ATSM would be a promising marker of intracellular overreduced states for disorders with mitochondrial dysfunction, such as MELAS, Parkinson's disease and Alzheimer's disease.

Copper complexes of bis(thiosemicarbazones): from chemotherapeutics to diagnostic and therapeutic radiopharmaceuticals

The molecules known as bis(thiosemicarbazones) derived from 1,2-diones can act as tetradentate ligands for Cu(II), forming stable, neutral complexes. As a family, these complexes possess fascinating biological activity. This critical review presents an historical perspective of their progression from potential chemotherapeutics through to more recent applications in nuclear medicine. Methods of synthesis are presented followed by studies focusing on their potential application as anti-cancer agents and more recent investigations into their potential as therapeutics for Alzheimer's disease. The Cu(II) complexes are of sufficient stability to be used to coordinate copper radioisotopes for application in diagnostic and therapeutic radiopharmaceuticals. Detailed understanding of the coordination chemistry has allowed careful manipulation of the metal based properties to engineer specific biological activities. Perhaps the most promising complex radiolabelled with copper radioisotopes to date is Cu(II)(atsm), which has progressed to clinical trials in humans (162 references).

High 18F-FDG uptake in microscopic peritoneal tumors requires physiologic hypoxia

The objective of this study was to examine (18)F-FDG uptake in microscopic tumors grown intraperitoneally in nude mice and to relate this to physiologic hypoxia and glucose transporter-1 (GLUT-1) expression.

METHODS

Human colon cancer HT29 and HCT-8 cells were injected intraperitoneally into nude mice to generate disseminated tumors of varying sizes. After overnight fasting, animals, breathing either air or carbogen (95% O(2) + 5% CO(2)), were intravenously administered (18)F-FDG together with the hypoxia marker pimonidazole and cellular proliferation marker bromodeoxyuridine 1 h before sacrifice. Hoechst 33342, a perfusion marker, was administered 1 min before sacrifice. After sacrifice, the intratumoral distribution of (18)F-FDG was assessed by digital autoradiography of frozen tissue sections. Intratumoral distribution was compared with the distributions of pimonidazole, GLUT-1 expression, bromodeoxyuridine, and Hoechst 33342 as visualized by immunofluorescent microscopy.

RESULTS

Small tumors (diameter, <1 mm) had high (18)F-FDG accumulation and were severely hypoxic, with high GLUT-1 expression. Larger tumors (diameter, 1-4 mm) generally had low (18)F-FDG accumulation and were not significantly hypoxic, with low GLUT-1 expression. Carbogen breathing significantly decreased (18)F-FDG accumulation and tumor hypoxia in microscopic tumors but had little effect on GLUT-1 expression.

CONCLUSION

There was high (18)F-FDG uptake in microscopic tumors that was spatially associated with physiologic hypoxia and high GLUT-1 expression. This enhanced uptake was abrogated by carbogen breathing, indicating that in the absence of physiologic hypoxia, high GLUT-1 expression, by itself, was insufficient to ensure high (18)F-FDG uptake.

Semiquantitative assessment of the microdistribution of fluorescence-labeled monoclonal antibody in small peritoneal disseminations of ovarian cancer

Uniform antibody microdistribution throughout tumor nodules is crucial for antibody-targeted therapy, because non-uniform microdistribution leads to suboptimal therapeutic effect, a commonly observed limitation of therapeutic antibodies. Herein, we evaluated the microdistribution of different doses of intraperitoneally injected fluorescence-labeled full-antibody trastuzumab (15, 50, and 150 microg) and its Fab fragment (trastuzumab-Fab: 15 and 50 microg) in a mouse model of ovarian cancer with peritoneal disseminated tumor. A semiquantitative approach (central/peripheral accumulation ratio; C/P ratio) was developed using in situ fluorescence microscopy. Furthermore, we compared the microdistribution of intact trastuzumab with a mixed injection of trastuzumab and trastuzumab-Fab or serial injections of trastuzumab using in situ multicolor fluorescence microscopy. Fluorescence images after the administration of 15 or 50 microg trastuzumab and 15 microg trastuzumab-Fab demonstrated antibody accumulation in the tumor periphery, whereas administration of 150 microg trastuzumab and 50 microg trastuzumab-Fab showed relatively uniform accumulation throughout the tumor nodule. Using serial injections (19-h interval) of trastuzumab-rhodamine green and carboxytetramethylrhodamine (TAMRA), it was observed that the latterly injected trastuzumab-TAMRA was distributed more centrally than trastuzumab-rhodamine green injected first, whereas no difference was observed in the control mixed-injection group. Moreover, the mixed injection of trastuzumab and trastuzumab-Fab showed that trastuzumab-Fab distributed more centrally than the same amount of co-injected trastuzumab. Our results suggest that the strategies of increasing dose and using Fab fragments can be used to achieve a uniform antibody distribution within peritoneal disseminated nodules after intraperitoneal injection. Furthermore, serial-injection and mixed-injection strategies can modify antibody microdistribution within tumors and have the potential for preferential delivery of anticancer drugs to either the tumor periphery or its center.

Copper-64-diacetyl-bis (N4-methylthiosemicarbazone) accumulates in rich regions of CD133+ highly tumorigenic cells in mouse colon carcinoma

INTRODUCTION

(64)Cu-diacetyl-bis (N(4)-methylthiosemicarbazone) ((64)Cu-ATSM) is a potential imaging agent of hypoxic tumor for use with PET. Recent literature demonstrated that cancer cells expressing CD133, which is a frequently used marker for so-called cancer stem cells or cancer stem cell-like cells (collectively referred to here as CSCs), contribute to tumor's therapeutic resistance and metastasis ability. Culturing under hypoxia is also reported to enlarge the proportion of CD133(+) cells, which would indicate survival advantage of CD133(+) cells under hypoxia. Here, we investigated the relationships between (64)Cu-ATSM accumulation and existence of CD133(+) cells using mouse colon carcinoma (colon-26) tumor.

METHODS

Intratumor distribution of (64)Cu-ATSM and (18)F-fluorodeoxyglucose ((18)FDG) was compared with immunohistochemical staining for CD133 with a colon-26 model. In vitro characterization of CD133(+) colon-26 cells was also performed.

RESULTS

In colon-26 tumors, (64)Cu-ATSM localized preferentially in regions with a high density of CD133(+) cells. The percentage of CD133(+) cells was 11-fold higher in (64)Cu-ATSM high-uptake regions compared with (18)FDG high- (but (64)Cu-ATSM low-) uptake regions. CD133(+) colon-26 cells showed characteristics previously linked with CSCs in other cancer cell lines, such as high colony-forming ability, high tumor-initiating ability and enrichment under hypoxic cultivation. The proportion of CD133(+) cells was enlarged by culturing under glucose starvation as well as hypoxia, and (64)Cu-ATSM uptake was increased under such conditions.

CONCLUSIONS

Our findings showed that, in colon-26 tumors, (64)Cu-ATSM accumulates in rich regions of CD133(+) cells with characteristics of CSCs. Therefore (64)Cu-ATSM could be a potential imaging agent for rich regions of CD133(+) cells, associated with CSCs, within tumors.

Radiobiological effects of hypoxia-dependent uptake of 64Cu-ATSM: enhanced DNA damage and cytotoxicity in hypoxic cells

PURPOSE

Hypoxia occurs frequently in cancers and can lead to therapeutic resistance due to poor perfusion and loss of the oxygen enhancement effect. (64)Cu-ATSM has shown promise as a hypoxia diagnostic agent due to its selective uptake and retention in hypoxic cells and its emission of positrons for PET imaging. (64)Cu also emits radiotoxic Auger electrons and beta(-) particles and may therefore exhibit therapeutic potential when concentrated in hypoxic tissue.

METHODS

MCF-7 cells were treated with 0-10 MBq/ml (64)Cu-ATSM under differing oxygen conditions ranging from normoxia to severe hypoxia. Intracellular response to hypoxia was measured using Western blotting for expression of HIF-1alpha, while cellular accumulation of (64)Cu was measured by gamma counting. DNA damage and cytotoxicity were measured with, respectively, the Comet assay and clonogenic survival.

RESULTS

(64)Cu-ATSM uptake in MCF-7 cells increased as atmospheric oxygen decreased (up to 5.6 Bq/cell at 20.9% oxygen, 10.4 Bq/cell at 0.1% oxygen and 26.0 Bq/cell at anoxia). Toxicity of (64)Cu-ATSM in MCF-7 cells also increased as atmospheric oxygen decreased, with survival of 9.8, 1.5 and 0% in cells exposed to 10 MBq/ml at 20.9, 0.1 and 0% oxygen. The Comet assay revealed a statistically significant increase in (64)Cu-ATSM-induced DNA damage under hypoxic conditions.

CONCLUSION

The results support a model in which hypoxia-enhanced uptake of radiotoxic (64)Cu induces sufficient DNA damage and toxicity to overcome the documented radioresistance in hypoxic MCF-7 cells. This suggests that (64)Cu-ATSM and related complexes have potential for targeted radionuclide therapy of hypoxic tumours.

Pathophysiologic correlation between 62Cu-ATSM and 18F-FDG in lung cancer

The purpose of this study was to delineate the differences in intratumoral uptake and tracer distribution of (62)Cu-diacetyl-bis(N(4)-methylthiosemicarbazone) ((62)Cu-ATSM), a well-known hypoxic imaging tracer, and (18)F-FDG in patients with lung cancer of pathohistologically different types.

METHODS

Eight patients with squamous cell carcinoma (SCC) and 5 with adenocarcinoma underwent (62)Cu-ATSM and (18)F-FDG PET within a 1-wk interval. For (62)Cu-ATSM PET, 10-min static data acquisition was started at 10 min after a 370- to 740-MBq tracer injection. After image reconstruction, (62)Cu-ATSM and (18)F-FDG images were coregistered, and multiple small regions of interest were drawn on tumor lesions of the 2 images to obtain standardized uptake values (SUVs). The regression lines were determined between SUVs for (62)Cu-ATSM and (18)F-FDG in each tumor. The slope values were compared between SCC and adenocarcinoma to observe pathohistologic differences in intratumoral distribution of the tracers.

RESULTS

SUVs for (62)Cu-ATSM were lower than those for (18)F-FDG in both SCC and adenocarcinoma. SCC tumors showed high (62)Cu-ATSM and low (18)F-FDG uptakes in the peripheral region of tumors but low (62)Cu-ATSM and high (18)F-FDG uptakes toward the center (spatial mismatching). The relationship of SUVs for the 2 tracers was negatively correlated with a mean regression slope of -0.07 +/- 0.05. On the other hand, adenocarcinoma tumors had a spatially similar distribution of (62)Cu-ATSM and (18)F-FDG, with positive regression slopes averaging 0.24 +/- 0.13. The regression slopes for (62)Cu-ATSM and (18)F-FDG differed significantly between SCC and adenocarcinoma (P < 0.001).

CONCLUSION

The intratumoral distribution patterns of (62)Cu-ATSM and (18)F-FDG were different between SCC and adenocarcinoma in lung cancers, indicating that intratumoral regions of high glucose metabolism and hypoxia could differ with the pathohistologic type of lung cancer. The identification of regional biologic characteristics in tumors such as hypoxia, energy metabolism, and proliferation could play a significant role in the clinical diagnosis and therapy planning for non-small cell lung cancer patients.

Comparison of [18F]FDG uptake and distribution with hypoxia and proliferation in FaDu human squamous cell carcinoma (hSCC) xenografts after single dose irradiation

PURPOSE

This study investigated the uptake of [(18)F]2-fluoro-2-deoxy-glucose ([(18)F]FDG) in the human tumour xenograft FaDu at early time points after single dose irradiation with Positron-Emission-Tomography (PET), autoradiography and functional histology.

MATERIALS AND METHODS

[(18)F]FDG-PET of FaDu hSCC xenografts on nude mice was performed before 25 Gy or 35 Gy single dose irradiation and one, seven or 11 days post irradiation (p.irr.). Before the second PET, mice were injected with pimonidazole (pimo) and bromodeoxyuridine (BrdU). After the PET tumours were excised, sliced and subjected to autoradiography and functional histology staining (pimo, BrdU, Ki67). [(18)F]FDG tumour uptake was quantified in the PET scans by maximal standard uptake value (SUV(max)) and in the autoradiography after co-registration to the histology slices.

RESULTS

No differences in the overall [(18)F]FDG uptake between the two dose groups and time points were found with PET or autoradiography. Comparing autoradiography and histology, the [(18)F]FDG uptake was constant in tumour necrosis over time, while it decreased in vital tumour areas and particularly in hypoxic regions. No differences in the [(18)F]FDG uptake between positive and negative areas of Ki67 and BrdU were found.

CONCLUSIONS

The decline of [(18)F]FDG uptake in vital tumour and in pimopositive areas as seen in autoradiography, was not reflected by evaluation of SUV(max) determined by PET. These findings suggest that the SUV(max) does not necessarily reflect changes in tumour biology after irradiation.

Molecular PET/CT imaging-guided radiation therapy treatment planning

The role of positron emission tomography (PET) during the past decade has evolved rapidly from that of a pure research tool to a methodology of enormous clinical potential. (18)F-fluorodeoxyglucose (FDG)-PET is currently the most widely used probe in the diagnosis, staging, assessment of tumor response to treatment, and radiation therapy planning because metabolic changes generally precede the more conventionally measured parameter of change in tumor size. Data accumulated rapidly during the last decade, thus validating the efficacy of FDG imaging and many other tracers in a wide variety of malignant tumors with sensitivities and specificities often in the high 90 percentile range. As a result, PET/computed tomography (CT) had a significant impact on the management of patients because it obviated the need for further evaluation, guided further diagnostic procedures, and assisted in planning therapy for a considerable number of patients. On the other hand, the progress in radiation therapy technology has been enormous during the last two decades, now offering the possibility to plan highly conformal radiation dose distributions through the use of sophisticated beam targeting techniques such as intensity-modulated radiation therapy (IMRT) using tomotherapy, volumetric modulated arc therapy, and many other promising technologies for sculpted three-dimensional (3D) dose distribution. The foundation of molecular imaging-guided radiation therapy lies in the use of advanced imaging technology for improved definition of tumor target volumes, thus relating the absorbed dose information to image-based patient representations. This review documents technological advancements in the field concentrating on the conceptual role of molecular PET/CT imaging in radiation therapy treatment planning and related image processing issues with special emphasis on segmentation of medical images for the purpose of defining target volumes. There is still much more work to be done and many of the techniques reviewed are themselves not yet widely implemented in clinical settings.

Molecular imaging of hypoxia with radiolabelled agents

Tissue hypoxia results from an inadequate supply of oxygen (O₂) that compromises biological functions. Structural and functional abnormalities of the tumour vasculature together with altered diffusion conditions inside the tumour seem to be the main causes of tumour hypoxia. Evidence from experimental and clinical studies points to a role for tumour hypoxia in tumour propagation, resistance to therapy and malignant progression. This has led to the development of assays for the detection of hypoxia in patients in order to predict outcome and identify patients with a worse prognosis and/or patients that would benefit from appropriate treatments. A variety of invasive and non-invasive approaches have been developed to measure tumour oxygenation including oxygen-sensitive electrodes and hypoxia marker techniques using various labels that can be detected by different methods such as positron emission tomography (PET), single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), autoradiography and immunohistochemistry. This review aims to give a detailed overview of non-invasive molecular imaging modalities with radiolabelled PET and SPECT tracers that are available to measure tumour hypoxia.

Radio-copper-labeled Cu-ATSM: an indicator of quiescent but clonogenic cells under mild hypoxia in a Lewis lung carcinoma model

The purpose of this study is to reveal characteristics of (64)Cu-labeled diacetyl-bis(N(4)-methylthiosemicarbazone) ([(64)Cu]Cu-ATSM) during cell proliferation and hypoxia by autoradiography imaging and immunohistochemical staining.

METHODS

The intratumoral distributions of [(64)Cu]Cu-ATSM and [(18)F]-2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) in mice implanted with Lewis lung carcinoma (LLC1) tumor cells according to dual autoradiography were compared with the immunohistochemical staining patterns of proliferating markers [Ki-67 and 5-bromo-2'-deoxyuridine (BrdU)] and a hypoxic marker (pimonidazole). A clonogenic assay was performed using the cells of LLC1 tumor-implanted mice, and it was compared with the distribution of [(64)Cu]Cu-ATSM.

RESULTS

[(64)Cu]Cu-ATSM mainly accumulated at the edge of tumors, whereas [(18)F]FDG was distributed inside the tumor and inside the [(64)Cu]Cu-ATSM accumulation. The number of Ki-67-positive cells/area tended to increase with [(18)F]FDG accumulation and decrease with [(64)Cu]Cu-ATSM accumulation. On the other hand, the number of BrdU-positive cells/area was negatively correlated with [(18)F]FDG accumulation and positively correlated with [(64)Cu]Cu-ATSM accumulation. High [(64)Cu]Cu-ATSM accumulation was found outside the high-[(18)F]FDG-accumulation and pimonidazole-positive regions. Colony formation ability was significantly higher in the tumor cells obtained from high-[(64)Cu]Cu-ATSM-accumulation regions than the cells from the intermediate- and the low-accumulation regions.

CONCLUSION

[(64)Cu]Cu-ATSM accumulation regions in tumor cells indicate quiescent but clonogenic tumor cells under mild hypoxia. [(64)Cu]Cu-ATSM could play an important role in planning appropriate tumor radiotherapy.

Molecular imaging of cancer: evaluating characters of individual cancer by PET/SPECT imaging

The present status of cancer molecular imaging (MI) with nuclear medicine techniques is reviewed, highlighting the Japanese activities in this field. With the progress in MI research, including significant contributions from Japanese studies, it has become possible to noninvasively evaluate various important characters of cancer in clinical patients, such as metabolism, cellular proliferation, tumor hypoxia, and receptor expression. Tumor metabolic information is used for tumor characterization, treatment response evaluation, and prognosis prediction. Hypoxia imaging is used for treatment planning and predicting treatment response. Receptor imaging can be used for the selection of the candidate for receptor-targeted treatment. Various novel probes that can target cancer-associated antigens, various cellular growth factor receptors, tumor angiogenesis, and so on, are under development, aiming for clinical evaluation. Application of radiolabeled ligands for treatment (targeted internal radiation therapy) is another important field in which MI technique can play a critical role. MI, which can deliver the outcome of basic oncological research to the bedside, is essential translational research for improved individualized patient management, and further advances in MI studies are eagerly awaited.

Autoradiographic and small-animal PET comparisons between (18)F-FMISO, (18)F-FDG, (18)F-FLT and the hypoxic selective (64)Cu-ATSM in a rodent model of cancer

INTRODUCTION

Copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone), or Cu-ATSM, a hypoxia imaging agent, has been shown to be predictive of response to traditional cancer therapies in patients with a wide range of tumors. It is known that the environment of the tumor results in a myriad of physiological consequences, including hypoxia, alterations in metabolism and proliferation. In an effort to better characterize the relationships between Cu-ATSM and other prominent radiopharmaceuticals, this current study was undertaken to compare the regional distribution of (64)Cu-ATSM with [(18)F]fluoromisonidazole ((18)F-FMISO), [(18)F]fluoro-2-deoxy-d-glucose ((18)F-FDG) and [(18)F]fluorothymidine ((18)F-FLT) in 9L tumors.

METHODS

Taking advantage of the different half-life of (18)F (t(1/2)=110 min) in comparison to (64)Cu (t(1/2)=12.7 h), we undertook a dual-tracer autoradiography study in 9L tumors. Four groups were examined: (a) (18)F-FMISO, 2 h postinjection (p.i.) and (64)Cu-ATSM, 10 min p.i.; (b) (18)F-FMISO, 2 h p.i. and (64)Cu-ATSM, 24 h p.i.; (c) (18)F-FDG, 1 h p.i. and (64)Cu-ATSM, 10 min p.i.; and (d) (18)F-FLT, 1 h p.i. and (64)Cu-ATSM, 10 min p.i. Small-animal PET imaging was performed in 9L tumor-bearing rats with imaging on concurrent days comparing (64)Cu-ATSM with (18)F-FMISO and (18)F-FLT.

RESULTS

It was shown that the regional distribution of (18)F-FMISO and (64)Cu-ATSM showed an excellent correlation when the (64)Cu-ATSM had been allowed to distribute for either 10 min (R(2)=.84) or 24 h (R(2)=.86). The regional comparisons between (64)Cu-ATSM (10 min) and (18)F-FDG (1 h) resulted in a very poor correlation (R(2)=.08) between the regional uptake of the two agents. The comparison between (18)F-FLT and (64)Cu-ATSM showed a strong relationship (R(2)=.83) between the two tracers. The small-animal PET images for the distribution comparisons between (64)Cu-ATSM and (18)F-FMISO and (18)F-FLT were in agreement with the data generated from the autoradiography studies.

CONCLUSIONS

The data show that it is important to remember that a number of different metabolic situations can exist when considering the relationship between regions of high glucose uptake, proliferation and hypoxia.

Aerobic glycolysis in cancers: implications for the usability of oxygen-responsive genes and fluorodeoxyglucose-PET as markers of tissue hypoxia

The hypoxia-responsiveness of the glycolytic machinery may allow pretreatment identification of hypoxic tumors from HIF-1 targets (e.g., Glut-1) or [18F]-fluorodeoxyglucose positron emission tomography but results have been mixed. We hypothesized that this discrepancy is an inevitable consequence of elevated aerobic glycolysis in tumors (Warburg effect) as energetics in predominantly glycolytic cells is little affected by hypoxia. Accordingly, we characterized glycolytic and mitochondrial ATP generation in normoxic and anoxic cell lines. Measurements demonstrated that most cancer cells rely largely on aerobic glycolysis as it accounts for 56-63% of their ATP budget, but in the cervical carcinoma SiHa, ATP synthesis was mainly mitochondrial. Moreover, the stimulatory effect of anoxia on glycolytic flux was inversely correlated to the relative reliance on aerobic glycolysis. Next, tumor cells representing a Warburg or a nonglycolytic phenotype were grown in mice and spatial patterns of hypoxia (pimonidazole-stained), Glut-1 expression and (18)F-FDG uptake were analysed on sectioned tumors. Only in SiHa tumors did foci of elevated glucose metabolism consistently colocalize with regions of hypoxia and elevated Glut-1 expression. In contrast, spatial patterns of Glut-1 and pimonidazole staining correlated reasonably well in all tumors. In conclusion, Glut-1's value as a hypoxia marker is not severely restricted by aerobic glycolysis. In contrast, the specificity of (18)F-FDG uptake and Glut-1 expression as markers of regional hypoxia and glucose metabolism, respectively, scales inversely with the intensity of the Warburg effect. This linkage suggests that multi-tracer imaging combining FDG and hypoxia-specific markers may provide therapeutically relevant information on tumor energetic phenotypes.

FDG uptake, a surrogate of tumour hypoxia?

INTRODUCTION

Tumour hyperglycolysis is driven by activation of hypoxia-inducible factor-1 (HIF-1) through tumour hypoxia. Accordingly, the degree of 2-fluro-2-deoxy-D: -glucose (FDG) uptake by tumours might indirectly reflect the level of hypoxia, obviating the need for more specific radiopharmaceuticals for hypoxia imaging.

DISCUSSION

In this paper, available data on the relationship between hypoxia and FDG uptake by tumour tissue in vitro and in vivo are reviewed. In pre-clinical in vitro studies, acute hypoxia was consistently shown to increase FDG uptake by normal and tumour cells within a couple of hours after onset with mobilisation or modification of glucose transporters optimising glucose uptake, followed by a delayed response with increased rates of transcription of GLUT mRNA. In pre-clinical imaging studies on chronic hypoxia that compared FDG uptake by tumours grown in rat or mice to uptake by FMISO, the pattern of normoxic and hypoxic regions within the human tumour xenografts, as imaged by FMISO, largely correlated with glucose metabolism although minor locoregional differences could not be excluded. In the clinical setting, data are limited and discordant.

CONCLUSION

Further evaluation of FDG uptake by various tumour types in relation to intrinsic and bioreductive markers of hypoxia and response to radiotherapy or hypoxia-dependent drugs is needed to fully assess its application as a marker of hypoxia in the clinical setting.

Correlation of [18F]FMISO autoradiography and pimonidazole [corrected] immunohistochemistry in human head and neck carcinoma xenografts

PURPOSE

Tumour cell hypoxia is a common feature in solid tumours adversely affecting radiosensitivity and chemosensitivity in head and neck squamous cell carcinomas. Positron emission tomography (PET) using the tracer [(18)F]fluoromisonidazole ([(18)F]FMISO) is most frequently used for non-invasive evaluation of hypoxia in human tumours. A series of ten human head and neck xenograft tumour lines was used to validate [(18)F]FMISO as hypoxia marker at the microregional level.

METHODS

Autoradiography after injection of [(18)F]FMISO was compared with immunohistochemical staining for the hypoxic cell marker pimonidazole in the same tumour sections of ten different human head and neck xenograft tumour lines. The methods were compared: first, qualitatively considering the microarchitecture; second, by obtaining a pixel-by-pixel correlation of both markers at the microregional level; third, by measuring the signal intensity of both images; and fourth, by calculating the hypoxic fractions by pimonidazole labelling.

RESULTS

The pattern of [(18)F]FMISO signal was dependent on the distribution of hypoxia at the microregional level. The comparison of [(18)F]FMISO autoradiography and pimonidazole immunohistochemistry by pixel-by-pixel analysis revealed moderate correlations. In five tumour lines, a significant correlation between the mean [(18)F]FMISO and pimonidazole signal intensity was found (range, r(2)=0.91 to r(2)=0.99). Comparison of the tumour lines with respect to the microregional distribution pattern of hypoxia revealed that the correlation between the mean signal intensities strongly depended on the microarchitecture. Overall, a weak but significant correlation between hypoxic fractions based on pimonidazole labeling and the mean [(18)F]FMISO signal intensity was observed (r(2)=0.18, p=0.02). For the three tumour models with a ribbon-like microregional distribution pattern of hypoxia, the correlation between the hypoxic fraction and the mean [(18)F]FMISO signal intensity was much stronger and more significant (r(2)=0.73, p<0.001) than for the tumours with a more homogenous, patchy, microregional distribution pattern of hypoxia.

CONCLUSION

Different patterns of [(18)F]FMISO accumulation dependent on the underlying microregional distribution of hypoxia were found in ten head and neck xenograft tumours. A weak albeit significant correlation was found between the mean [(18)F]FMISO signal intensity and the hypoxic fraction of the tumours. In larger clinical tumours, [(18)F]FMISO-PET provides information on the tumour oxygenation status on a global level, facilitating dose painting in radiation treatment planning. However, caution must be taken when studying small tumour subvolumes as accumulation of the tracer depends on the presence of hypoxia and on the tumour microarchitecture.

Assessing tumor hypoxia in cervical cancer by PET with 60Cu-labeled diacetyl-bis(N4-methylthiosemicarbazone)

Tumor hypoxia indicates a poor prognosis. This study was undertaken to confirm our prior pilot results showing that pretreatment tumor hypoxia demonstrated by PET with (60)Cu-labeled diacetyl-bis(N(4)-methylthiosemicarbazone) ((60)Cu-ATSM) is a biomarker of poor prognosis in patients with cervical cancer. Thirty-eight women with biopsy-proved cervical cancer underwent (60)Cu-ATSM PET before the initiation of radiotherapy and chemotherapy. (60)Cu-ATSM uptake was evaluated semiquantitatively as the tumor-to-muscle activity ratio (T/M). A log-rank test was used to determine the cutoff uptake value that was strongly predictive of prognosis. All patients also underwent clinical PET with (18)F-FDG before the institution of therapy. The PET results were correlated with clinical follow-up. Tumor (60)Cu-ATSM uptake was inversely related to progression-free survival and cause-specific survival (P = 0.006 and P = 0.04, respectively, as determined by the log-rank test). We found that a T/M threshold of 3.5 best discriminated patients likely to develop a recurrence from those unlikely to develop a recurrence; the 3-y progression-free survival of patients with normoxic tumors (as defined by T/M of < or = 3.5) was 71%, and that of patients with hypoxic tumors (T/M of > 3.5) was 28% (P = 0.01). Tumor (18)F-FDG uptake did not correlate with (60)Cu-ATSM uptake, and there was no significant difference in tumor (18)F-FDG uptake between patients with hypoxic tumors and those with normoxic tumors (P = 0.9). Pretherapy (60)Cu-ATSM PET provides clinically relevant information about tumor oxygenation that is predictive of outcome in patients with cervical cancer.

Cu-ATSM: a radiopharmaceutical for the PET imaging of hypoxia

Copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone), Cu-ATSM, labeled with a positron emitting isotope of copper ((60)Cu, (61)Cu, (62)Cu or (64)Cu) has been shown, in vitro and in vivo, to be selective for hypoxic tissue. In silico studies have explored the mechanism of its hypoxia selectivity, and clinical studies with this agent have shown non-invasive imaging data that is predictive of a cancer patients' response to conventional therapy. This Perspective discusses the evolution of Cu-ATSM, how its selectivity can be improved upon, and where this metal-ligand platform could be taken in the future.

Time trends in the maximal uptake of FDG on PET scan during thoracic radiotherapy. A prospective study in locally advanced non-small cell lung cancer (NSCLC) patients

BACKGROUND AND PURPOSE

18F-fluoro-2-deoxy-glucose (FDG) uptake on PET scan is a prognostic factor for outcome in NSCLC. We investigated changes in FDG uptake during fractionated radiotherapy in relation to metabolic response with the ultimate aim to adapt treatment according to early response.

METHODS AND MATERIALS

Twenty-three patients, medically inoperable or with advanced NSCLC, underwent four repeated PET-CT scans before, during and after radiotherapy. Changes in maximal standardized uptake value (SUVmax) were described. Patients were treated with accelerated radiotherapy with a total tumour-dose depending on normal tissue dose constraints.

RESULTS

The most striking result was the large intra-individual heterogeneity in the evolution of SUVmax. For the total group a non-significant increase in the first week (p=0.05), and a decrease in the second week (p=0.02) and after radiotherapy (p<0.01) was observed. Different time trends were shown for responders (no change during radiotherapy) and non-responders (48% increase during first week, p=0.02 and 15% decrease in the second week, p=0.04). Non-responders had a higher SUVmax on all time points investigated.

CONCLUSIONS

Time trends in SUVmax showed a large intra-individual heterogeneity and different patterns for metabolic responders and non-responders. These new findings may reflect intrinsic tumour characteristics and might finally be useful to adapt treatment.