Clinical value of 3'-deoxy-3'-[18F]fluorothymidine-positron emission tomography for diagnosis, staging and assessing therapy response in lung cancer.

Lung cancer has the highest mortality rate of any tumour type. The main driver of lung tumour growth and development is uncontrolled cellular proliferation. Poor patient outcomes are partly the result of the limited range of effective anti-cancer therapies available and partly due to the limited accuracy of biomarkers to report on cell proliferation rates in patients. Accordingly, accurate methods of diagnosing, staging and assessing response to therapy are crucial to improve patient outcomes. One effective way of assessing cell proliferation is to employ non-invasive evaluation using 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) positron emission tomography [18F]FLT-PET. [18F]FLT, unlike the most commonly used PET tracer [18F]fluorodeoxyglucose ([18F]FDG), can specifically report on cell proliferation and does not accumulate in inflammatory cells. Therefore, this radiotracer could exhibit higher specificity in diagnosis and staging, along with more accurate monitoring of therapy response at early stages in the treatment cycle. This review summarises and evaluates published studies on the clinical use of [18F]FLT to diagnose, stage and assess response to therapy in lung cancer.

Widespread tissue hypoxia dysregulates cell and metabolic pathways in SMA.

OBJECTIVE: The purpose of the study was to determine the extent and role of systemic hypoxia in the pathogenesis of spinal muscular atrophy (SMA). METHODS: Hypoxia was assayed in vivo in early-symptomatic (postnatal day 5) SMA-model mice by pimonidazole and [18 F]-Fluoroazomycin arabinoside injections, which accumulate in hypoxic cells, followed by immunohistochemistry and tracer biodistribution evaluation. Glucose uptake in hypoxic cells was assayed by [18 F]-Fluorodeoxyglucose labeling. In vitro knockdown of Survival Motor Neuron (SMN) was performed on motor neurons and lactate metabolism measured biochemically, whereas cell cycle progression and cell death were assayed by flow cytometry. RESULTS: All assays found significant levels of hypoxia in multiple organ systems in early symptomatic SMA mouse pups, except aerated tissues such as skin and lungs. This was accompanied by significantly increased glucose uptake in many affected organs, consistent with a metabolic hypoxia response. SMN protein levels were shown to vary widely between motor neuron precursors in vitro, and those with lower levels were most susceptible to cell death. In addition, SMA-model motor neurons were particularly sensitive to hypoxia, with reduced ability to transport lactate out of the cell in hypoxic culture, and a failure in normal cell cycle progression. INTERPRETATION: Not only is there widespread tissue hypoxia and multi-organ cellular hypoxic response in SMA model mice, but SMA-model motor neurons are especially susceptible to that hypoxia. The data support the hypothesis that vascular defects leading to hypoxia are a significant contributor to disease progression in SMA, and offer a route for combinatorial, non-SMN related therapy.

A role for spinal cord hypoxia in neurodegeneration.

The vascular system of the spinal cord is particularly complex and vulnerable. Damage to the main vessels or alterations to the regulation of blood flow will result in a reduction or temporary cessation of blood supply. The resulting tissue hypoxia may be brief: acute, or long lasting: chronic. Damage to the vascular system of the spinal cord will develop after a traumatic event or as a result of pathology. Traumatic events such as road traffic accidents, serious falls and surgical procedures, including aortic cross-clamping, will lead to an immediate cessation of perfusion, the result of which may not be evident for several days, but may have long-term consequences including neurodegeneration. Pathological events such as arterial sclerosis, venous occlusion and spinal cord compression will result in a progressive reduction of blood flow, leading to chronic hypoxia. While in some situations the initial pathology is exclusively vascular, recent research in neurodegenerative disease has drawn attention to concomitant vascular anomalies in disorders, including amyotrophic lateral sclerosis, spinal muscular atrophy and muscular sclerosis. Understanding the role of, and tissue response to, chronic hypoxia is particularly important in these cases, where inherent neural damage exacerbates the vulnerability of the nervous system to stressors including hypoxia.

Enzymatic radiosynthesis of a 18F-Glu-Ureido-Lys ligand for the prostate-specific membrane antigen (PSMA).

Prostate cancer represents a major public health threat as it is one of the most common male cancers worldwide. The prostate-specific membrane antigen (PSMA) is highly over-expressed in prostatic cancer cells in a manner that correlates with both tumour stage and clinical outcome. As such, PSMA has been identified as an attractive target for both imaging and treatment of prostate cancer. In recent years the focus on urea-based peptidomimetic inhibitors of the PSMA (representing low molecular weight/high affinity binders) has intensified as they have found use in the clinical imaging of prostate tumours. Reported herein are the design, synthesis and evaluation of a new fluorinated PSMA targeting small-molecule, FDA-PEG-GUL, which possesses the Glu-NH-CO-NH-Lys pharmacophore conjugated to a 5'-fluorodeoxy-adenosine unit. Inhibition assays were performed with FDA-PEG-GUL which revealed that it inhibits the PSMA in the nanomolar range. Additionally, it has been purposely designed so that it can be produced using the fluorinase enzyme from its chlorinated precursor, allowing for the enzymatic synthesis of radiolabelled [18F]FDA-PEG-GUL via a nucleophilic reaction that takes place in experimentally advantageous conditions (in water at neutral pH and at ambient temperature). Specific binding of [18F]FDA-PEG-GUL to PSMA expressing cancer cells was demonstrated, validating it as a promising PSMA diagnostic tool. This work establishes a successful substrate scope expansion for the fluorinase and demonstrates its first application towards targeting the PSMA.

Binding of αvß3 Integrin-Specific Radiotracers Is Modulated by Both Integrin Expression Level and Activation Status.

PURPOSE: Molecular imaging of αvß3 integrin has exhibited real potential to guide the appropriate use of anti-angiogenic therapies. However, an incomplete understanding of the factors that influence binding of αvß3 integrin-specific radiotracers currently limits their use for assessing response to therapy in cancer patients. This study identifies two fundamental factors that modulate uptake of these radiotracers. Procedures Experiments were performed in prostate cancer (PC3) and glioblastoma (U87MG) cells, which differentially express αvß3 integrin. αvß3 integrin-specific radiotracers were used to investigate the effect of manipulating αvß3 integrin expression or activation in cellular binding assays. ß3 integrin and αvß3 integrin expression were measured by western blotting and flow cytometry, respectively. The effect of select pharmacological inhibitors on αvß3 integrin activation and expression was also determined. RESULTS: Radiotracer binding was proportional to αvß3 integrin expression when it was decreased (ß3 knock-down cells) or increased, either using pharmacological inhibitors of cell signalling or by culturing cells for different times. Studies with both small molecule and arginine-glycine-aspartic acid (RGD)-based radiotracers revealed increased radiotracer binding after activation of αvß3 integrin with Mn2+ or talin head domain. Moreover, inhibition of fundamental signalling pathways (mitogen-activated protein kinase kinase (MEK), Src and VEGFR2) decreased radiotracer binding, reflecting reduced αvß3 integrin activity. CONCLUSION: Binding of small molecule ligands and radiolabelled RGD peptides is modulated by expression and activation status of αvß3 integrin. αvß3 integrin-specific radiotracers can provide otherwise inaccessible information of the effect of signalling pathways on αvß3 integrin. This has significant implications for assessing response to anti-angiogenic therapies in clinical studies.

KEMTUB012-NI2, a novel potent tubulysin analog that selectively targets hypoxic cancer cells and is potentiated by cytochrome p450 reductase downregulation.

PURPOSE: There is an urgent need to develop effective therapies and treatment strategies to treat hypoxic tumors, which have a very poor prognosis and do not respond well to existing therapies. METHODS: A novel hypoxia-targeting agent, KEMTUB012-NI2, was synthesized by conjugating a 2-nitroimidazole hypoxia-targeting moiety to a synthetic tubulysin, a very potent antimitotic. Its hypoxic selectivity and mode of action were studied in breast cancer cell lines. RESULTS: KEMTUB012-NI2 exhibited a similar selectivity for hypoxic cells to that of tirapazamine, a well-established hypoxia-targeting agent, but was >1,000 times more potent in cell cytotoxicity assays. The hypoxia-targeting mechanism for both KEMTUB012-NI2 and tirapazamine was selective and mediated by one-electron reductases. However, while cytochrome p450 reductase (POR) downregulation could inhibit tirapazamine cytotoxicity, it actually sensitized hypoxic cells to KEMTUB012-NI2. CONCLUSION: KEMTUB012-NI2 is a potent new agent that can selectively target hypoxic cancer cells. The hypoxia selectivity of KEMTUB012-NI2 and tirapazamine appears to be differentially activated by reductases. Since reductases are heterogeneously expressed in tumors, the different activation mechanisms will allow these agents to complement each other. Combining POR downregulation with KEMTUB012-NI2 treatment could be a new treatment strategy that maximizes efficacy toward hypoxic tumor cells while limiting systemic toxicity.

High-Affinity "Click" RGD Peptidomimetics as Radiolabeled Probes for Imaging αv ß3 Integrin.

Nonpeptidic Arg-Gly-Asp (RGD)-mimic ligands were designed and synthesized by click chemistry between an arginine-azide mimic and an aspartic acid-alkyne mimic. Some of these molecules combine excellent in vitro properties (high αv ß3 affinity, selectivity, drug-like logD, high metabolic stability) with a variety of radiolabeling options (e.g., tritium and fluorine-18, plus compatibility with radio-iodination), not requiring the use of chelators or prosthetic groups. The binding mode of the resulting triazole RGD mimics to αv ß3 or αIIb ß3 receptors was investigated by molecular modeling simulations. Lead compound 12 was successfully radiofluorinated and used for in vivo positron emission tomography/computed tomography (PET/CT) studies in U87 tumor models, which showed only modest tumor uptake and retention, owing to rapid excretion. These results demonstrate that the novel click RGD mimics are excellent radiolabeled probes for in vitro and cell-based studies on αv ß3 integrin, whereas further optimization of their pharmacokinetic and dynamic profiles is necessary for successful use in in vivo imaging.

Probing the PI3K/Akt/mTor pathway using 31P-NMR spectroscopy: routes to glycogen synthase kinase 3.

Akt is an intracellular signalling pathway that serves as an essential link between cell surface receptors and cellular processes including proliferation, development and survival. The pathway has many downstream targets including glycogen synthase kinase3 which is a major regulatory kinase for cell cycle transit as well as controlling glycogen synthase activity. The Akt pathway is frequently up-regulated in cancer due to overexpression of receptors such as the epidermal growth factor receptor, or mutation of signalling pathway kinases resulting in inappropriate survival and proliferation. Consequently anticancer drugs have been developed that target this pathway. MDA-MB-468 breast and HCT8 colorectal cancer cells were treated with inhibitors including LY294002, MK2206, rapamycin, AZD8055 targeting key kinases in/associated with Akt pathway and the consistency of changes in 31P-NMR-detecatable metabolite content of tumour cells was examined. Treatment with the Akt inhibitor MK2206 reduced phosphocholine levels in MDA-MB-468 cells. Treatment with either the phosphoinositide-3-kinase inhibitor, LY294002 and pan-mTOR inhibitor, AZD8055 but not pan-Akt inhibitor MK2206 increased uridine-5'-diphosphate-hexose cell content which was suppressed by co-treatment with glycogen synthase kinase 3 inhibitor SB216763. This suggests that there is an Akt-independent link between phosphoinositol-3-kinase and glycogen synthase kinase3 and demonstrates the potential of 31P-NMR to probe intracellular signalling pathways.

Last-Step Enzymatic [(18) F]-Fluorination of Cysteine-Tethered RGD Peptides Using Modified Barbas Linkers.

We report a last-step fluorinase-catalyzed [(18) F]-fluorination of a cysteine-containing RGD peptide. The peptide was attached through sulfur to a modified and more hydrophilic variant of the recently disclosed Barbas linker which was itself linked to a chloroadenosine moiety via a PEGylated chain. The fluorinase was able to use this construct as a substrate for a transhalogenation reaction to generate [(18) F]-radiolabeled RGD peptides, which retained high affinity to cancer-cell relevant αv ß3 integrins.

NGR Tumor-Homing Peptides: Structural Requirements for Effective APN (CD13) Targeting.

Cyclic CNGRC (cCNGRC) peptides are very important targeting ligands for Aminopeptidase N (APN or CD13), which is overexpressed on the surface of many cancer cells. In this work we have (1) developed an efficient solid-phase synthesis and (2) tested on purified porcine APN and APN-expressing human cells two different classes of cCNGRC peptides: the first carrying a biotin affinity tag or a fluorescent tag attached to the carboxyl Arg-Cys-COOH terminus and the second with the tags attached to the amino H2N-Cys-Asn terminus. Carboxyl-terminus functionalized cCNGRC peptides 3, 6, and 8 showed good affinity for porcine APN and very good capacity to target and be internalized into APN-expressing cells. In contrast, amino-terminus functionalized cCNGRC peptides 4, 5, and 7 displayed significantly decreased affinity and targeting capacity. These results, which are in agreement with the recently reported X-ray structure of a cCNGRC peptide bound to APN showing important stabilizing interactions between the unprotected cCNGRC amino terminus and the APN active site, indicate that the carboxyl and not the amino-terminus of cCNGRC peptides should be used as a "handle" for the attachment of toxic payloads for therapy or isotopically labeled functions for imaging and nuclear medicine.

Enzymatic transhalogenation of dendritic RGD peptide constructs with the fluorinase.

The substrate scope of fluorinase enzyme mediated transhalogenation reactions is extended. Substrate tolerance allows a peptide cargo to be tethered to a 5'-chloro-5'-deoxynucleoside substrate for transhalogenation by the enzyme to a 5'-fluoro-5'-deoxynucleoside. The reaction is successfully extended from that previously reported for a monomeric cyclic peptide (cRGD) to cargoes of dendritic scaffolds carrying two and four cyclic peptide motifs. The RGD peptide sequence is known to bind upregulated αVß3 integrin motifs on the surface of cancer cells and it is demonstrated that the fluorinated products have a higher affinity to αVß3 integrin than their monomeric counterparts. Extending the strategy to radiolabelling of the peptide cargoes by tagging the peptides with [(18)F]fluoride was only moderately successful due to the poor water solubility of these higher order peptide scaffolds although the strategy holds promise for peptide constructs with improved solubility.

Changes in [18F]Fluoro-2-deoxy-D-glucose incorporation induced by doxorubicin and anti-HER antibodies by breast cancer cells modulated by co-treatment with metformin and its effects on intracellular signalling.

PURPOSES: Metformin, currently undergoing clinical trials as an adjuvant for the treatment of breast cancer, modulates the activity of key intracellular signalling molecules which affect 2-[(18)F]Fluoro-2-deoxy-D-glucose ([(18)F]FDG) incorporation. Here, we investigate the effect of drugs used in the treatment of breast cancer combined with metformin on [(18)F]FDG incorporation in HER2- or HER1-overexpressing breast cancer cells to determine whether or not metformin may obscure changes in [(18)F]FDG incorporation induced by clinically utilised anticancer drugs in the treatment of breast cancer. METHODS: Three breast cancer cell lines expressing HER2 and one HER2 negative but HER1 positive were exposed to metformin, doxorubicin and trastuzumab or cetuximab. Cytotoxicity was measured by the MTT assay. Expression of active (phospho-) AMPK, PKB (Akt) and ERK was determined by Western blotting. [(18)F]FDG incorporation by cells exposed to drug combinations with metformin was determined. Glucose transport was assessed by measuring the initial rate of uptake of [(3)H]O-methyl-D-glucose ([(3)H]OMG). Phosphorylation of [(18)F]FDG was determined in intact cells after exposure to [(18)F]FDG. RESULTS: Phospho-AMPK was increased by metformin in all cell lines whilst phospho-Akt and phospho-ERK expressions were decreased in two. Metformin treatment increased [(18)F]FDG incorporation in all cell lines, and treatment with anti-HER antibodies or doxorubicin only produced minor modulations in the increase induced by metformin alone. Glucose transport was increased in BT474 cells and decreased in SKBr3 and MDA-MB-468 cells after treatment with metformin. The fraction of phosphorylated [(18)F]FDG was increased in metformin-treated cells compared with controls, suggesting that hexokinase efficiency was increased by metformin. CONCLUSION: This is the first study to show that increased [(18)F]FDG incorporation by breast cancer cells induced by metformin overwhelms the effect of doxorubicin and anti-HER treatments on [(18)F]FDG incorporation. Metformin-induced increased [(18)F]FDG incorporation was consistently associated with enhanced [(18)F]FDG phosphorylation.

The tubulysin analogue KEMTUB10 induces apoptosis in breast cancer cells via p53, Bim and Bcl-2.

PURPOSE: Tubulysins are natural tetrapeptides that inhibit tubulin polymerisation. Tubulysins are very potent inhibitors of mammalian cancer cell growth, but restricted availability has limited their characterisation and development as anti-cancer compounds. KEMTUB10 was recently developed as a synthetic analogue of natural tubulysins. METHODS: The cell cytotoxicity of KEMTUB10 was studied in cell lines that represent the main breast cancer sub-types. The KEMTUB10 pro-apoptotic mechanism of action was studied in MCF7 and MDAMB231 cells. RESULTS: KEMTUB10 exerts a potent cytotoxic effect in cells representing the main breast cancer sub-types. KEMTUB10 blocks cells in the G2/M phase of the cell cycle and is a strong stimulator of apoptosis/cell death. KEMTUB10-induced apoptosis involves p53 and Bim, and to some extent Bcl-2 phosphorylation. CONCLUSIONS: KEMTUB10 is a promising new anti-mitotic that exerts a potent cytotoxic effect in breast cancer cells, blocks cells in the G2/M phase of the cell cycle and stimulates apoptosis/cell death. KEMTUB10 has a distinct mode of action to taxol, appears to be sensitive to different molecular factors in cells and is likely subject to different mechanisms of acquired resistance. KEMTUB10 has the potential to be an important addition to the anti-cancer therapeutic armoury.

Early changes in [18F]FDG incorporation by breast cancer cells treated with trastuzumab in normoxic conditions: role of the Akt-pathway, glucose transport and HIF-1α.

HER-2 overexpression does not guarantee response to HER2-targeting drugs such as trastuzumab, which is cardiotoxic and expensive, so early detection of response status is crucial. Factors influencing [(18)F]FDG incorporation in the timeframe of cell signalling down-regulation subsequent to trastuzumab treatment are investigated to provide a better understanding of the relationship between growth response and modulation of [(18)F]FDG incorporation. HER-2-overexpressing breast tumour cell lines, MDA-MB-453, SKBr3 and BT474 and MDA-MB-468 (HER2 non-over-expressor) were treated with trastuzumab (4 h) and probed for AKT, pAKT, ERK1/2, pERK1/2 and HIF-1α to determine early signalling pathway inhibitory effects of trastuzumab. Cells incubated with trastuzumab and/or PI3K inhibitor LY294002 and ERK1/2 inhibitor U0126 and glucose transport and [(18)F]FDG incorporation measured. Cell lines expressed AKT, pAKT, ERK1/2 and pERK1/2 but not HIF-1α. Trastuzumab treatment decreased pAkt but not pERK1/2 levels. Trastuzumab did not further inhibit AKT when maximally inhibited with LY294002. Treatment with LY294002 and trastuzumab for 4 h decreased [(18)F]FDG incorporation in BT474 and MDA-MB-453 but not SKBr3 cells. LY294002 inhibited glucose transport by each cell line, but the glucose transport rate was tenfold higher by SKBr3 cells than BT474 and MDA-MB-453 cells. AKT-induced uptake of [(18)F]FDG was found to be HIF-1α independent in breast cancer cell lines. AKT inhibition level and tumour cell glucose transport rate can influence whether or not PI3K inhibitors affect [(18)F]FDG incorporation which may account for the variation in preclinical and clinical findings associated with [(18)F]FDG-PET in response to trastuzumab and other HER-2 targeting drugs.

Hypoxia stimulates 18F-fluorodeoxyglucose uptake in breast cancer cells via hypoxia inducible factor-1 and AMP-activated protein kinase.

INTRODUCTION: Hypoxia can stimulate (18)F-fluorodeoxyglucose (FDG) uptake in cultured cells. A better understanding of the underlying molecular mechanism is required to determine the value of FDG for studying tumour hypoxia. METHODS: The effect of hypoxia on FDG uptake, and key proteins involved in glucose transport and glycolysis, was studied in MCF7 and MDA231 breast cancer cell lines. RESULTS: Hypoxia induced a dose- and time-dependent increase in FDG uptake. The FDG increase was transient, suggesting that FDG uptake is only likely to be increased by acute hypoxia (<24 h). Molecular analysis indicated that hypoxia upregulated glut1 and 6-phosphofructo-2-kinase, key proteins involved in regulating glucose transport and glycolysis, and that these changes were induced by Hypoxia-Inducible factor 1 (HIF1) upregulation and/or AMP-activated protein kinase activation. CONCLUSIONS: FDG may provide useful information about the oxygenation status of cells in hypoxic regions where HIF1 upregulation is hypoxia-driven.

Efficient bioconjugation of 5-fluoro-5-deoxy-ribose (FDR) to RGD peptides for positron emission tomography (PET) imaging of α(v)ß(3) integrin receptor.

The utility of 5-fluoro-5-deoxyribose (FDR) as an efficient bioconjugation agent for radiolabelling of the RGD peptides c(RGDfK) and c(RGDfC) is demonstrated. The bioconjugation is significantly superior to that achieved with 2-fluoro-2-deoxyglucose (FDG) and benefits from the location of the fluorine at C-5, and that ribose is a 5-membered ring sugar rather than a 6-membered ring. Both features favour ring opening to the aldehydic form of the sugar to promote smooth oxime ligation with aminooxy ether functionalised peptides. [(18)F]FDR was prepared in this study by synthesis from fluoride-18 using an automated synthesis protocol adapting that used routinely for [(18)F]FDG. c(RGDfK) was functionalised with an aminooxyacetyl group (Aoa) via its lysine terminus, while c(RGDfC) was functionalised with an aminooxyhexylmaleimide (Ahm) through a cysteine-maleimide conjugation. Bioconjugation of [(18)F]FDR to c(RGDfC)-Ahm proved to be more efficient than c(RGDfK)-Aoa (92% versus 65%). The unlabelled ((19)F) bioconjugates c(RGDfK)-Aoa-FDR and c(RGDfC)-Ahm-FDR were prepared and their in vitro affinity to purified integrin αvß3 was determined. c(RGDfK)-Aoa-FDR showed the greater affinity. Purified "hot" bioconjugates c(RGDfK)-Aoa-[(18)F]FDR and c(RGDfC)-Ahm-[(18)F]FDR were assayed by incubation with MCF7, LNCaP and PC3 cell lines. In both cases the conjugated RGD peptides showed selectivity for PC3 cells, which express αvß3 integrin, with the c(RGDfK)-Aoa-[(18)F]FDR demonstrating better binding, consistent with its higher in vitro affinity. The study demonstrates that [(18)F]FDR is an efficient bioconjugation ligand for RGD bioactive peptides.

Response to trastuzumab by HER2 expressing breast tumour xenografts is accompanied by decreased Hexokinase II, glut1 and [18F]-FDG incorporation and changes in 31P-NMR-detectable phosphomonoesters.

PURPOSE: Trastuzumab, effective in about 15 % of women with breast cancer, downregulates signalling through the Akt/PI3K and MAPK pathways. These pathways modulate glucose and phospholipid metabolism which can be monitored by [(18)F]FDG-PET and (31)P-NMR spectroscopy, respectively. Here, the relationship between response of HER-2 overexpressing tumours and changes in [(18)F]-FDG incorporation and (31)P-NMR-detectable phosphomonoesters were examined. EXPERIMENTAL: Xenografts derived from HER2-overexpressing MDA-MB-453 human breast tumour cells were grown in SCID mice, treated with trastuzumab for 15 days, then [(18)F]-FDG uptake determined and (31)P-NMR carried out on chemical extracts of the tumours. Western blots were carried out to determine protein expression of Hexokinase II and glut1. RESULTS: [(18)F]-FDG incorporation, Hexokinase II and glut1 protein expression and the concentration of phosphocholine and phosphoethanolamine in chemical extracts subjected to (31)P-NMR were significantly decreased in the xenografts in the trastuzumab-treated mice compared with xenografts from the PBS-injected group. CONCLUSIONS: Changes in FDG incorporation and (31)P-NMR spectral changes can accompany response of HER2-expressing breast cancer xenografts to trastuzumab. This is the first study to show parallel changes in [(18)F]FDG- and (31)P-NMR-detectable metabolites accompany response to targeted anticancer treatment.

Positron emission tomography radiopharmaceutical studies in humans: a guide to regulations for academic researchers.

All clinical trials are covered by a series of regulations that seek to protect the rights, safety and welfare of participating patients. The regulations covering PET studies are especially complex to interpret because of the specialized nature of the language of the regulations and of PET studies themselves. It is often unclear whether the application demands that the radiotracer used be treated as an investigational medical product. This paper is intended to act as a general guide for UK researchers planning to perform PET research in humans by clarifying key aspects of the regulations that may affect the study and/or the radiopharmaceutical manufacturing process, providing links to useful information sources, introducing the concept of a UK Medicines and Healthcare products Regulatory Agency (MHRA) PET expert panel and outlining the value of sharing investigational medical product dossiers.

Recommendations for measurement of tumour vascularity with positron emission tomography in early phase clinical trials.

The evaluation of drug pharmacodynamics and early tumour response are integral to current clinical trials of novel cancer therapeutics to explain or predict long term clinical benefit or to confirm dose selection. Tumour vascularity assessment by positron emission tomography could be viewed as a generic pharmacodynamic endpoint or tool for monitoring response to treatment. This review discusses methods for semi-quantitative and quantitative assessment of tumour vascularity. The radioligands and radiotracers range from direct physiological functional tracers like [(15)O]-water to macromolecular probes targeting integrin receptors expressed on neovasculature. Finally we make recommendations on ways to incorporate such measurements of tumour vascularity into early clinical trials of novel therapeutics. Key Points • [ ( 15 ) O]-water is the gold standard for blood flow/tissue perfusion with PET • In some instances dynamic [ ( 18 ) F]-FDG uptake may be used to estimate perfusion • Radiopharmaceuticals that target integrins are now being evaluated for measuring tumour vascularity.

Positron emission tomography oncology research in the UK: a comparison with USA and Europe.

PET imaging with 18F-fluorodeoxyglucose (FDG) has become a valuable procedure in oncology patient management and drug development. The availability of non-FDG radiotracers to study different aspects of cancer biology presents new opportunities to improve healthcare outcomes and develop new therapeutics. An investigation has been carried out to determine the extent of the use of non-FDG tracers in the UK, assess overall oncology PET research activity and document current UK PET infrastructure. There has been significant recent investment in PET facilities, increasing the UK's capacity to undertake PET research. Nevertheless, the UK still has a lower level of PET equipment compared with Europe and the USA. Despite the increase in PET imaging capacity in UK research centres, there has not been an increase in non-FDG research, with most studies utilizing FDG at multiple sites. Most non-FDG trials are single-centre studies at well established centres. High tracer prices, a limited range of non-FDG tracers and restricted geographical availability make multicentre trials with non-FDG radiotracers difficult. Several solutions have been identified: formation of purchasing consortia for 18F-labelled radiotracers, production of radiotracers with longer half-lives and establishment of production at regional supply centres.