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Biomedical subjects

P M Price

Publications and source records attributed to P M Price.

At least 19 recordsLinked to original sources

Hypoxia-inducible factor-1alpha expression in the gastric carcinogenesis sequence and its prognostic role in gastric and gastro-oesophageal adenocarcinomas.

Hypoxia-inducible factor-1 (HIF-1)alpha expression was studied in the gastric carcinogenesis sequence and as a prognostic factor in surgically resected gastric and gastro-oesophageal junction tumours. Protein expression was examined using immunohistochemistry on formalin-fixed biopsies of normal mucosa (n=20), Helicobacter pylori associated gastritis (n=24), intestinal metaplasia (n=24), dysplasia (n=12) and intestinal (n=19) and diffuse (n=21) adenocarcinoma. The relationship between HIF-1alpha expression and prognosis was assessed in resection specimens from 177 patients with gastric and gastro-oesophageal junction adenocarcinoma. Hypoxia-inducible factor-1alpha expression was not observed in normal gastric mucosa but increased in density (P<0.01) and intensity (P<0.01) with progression from H. pylori-associated gastritis, intestinal metaplasia, dysplasia to adenocarcinoma. The pattern of staining in the resection specimens was focally positive in 49 (28%) and at the invasive tumour edge in 41 (23%). Invasive edge expression was associated with lymph node metastases (P=0.034), advanced TNM stage (P=0.001) and was an adverse prognostic factor for cancer-specific survival (P=0.019). In univariate analysis and in comparison with tumours not expressing HIF-1alpha, invasive edge staining was associated with a hazard ratio of 1.6 (95% CI 1.0-2.5) and focally positive staining a hazard ratio of 0.7 (95% CI 0.5-1.2). Hypoxia-inducible factor-1alpha lost prognostic significance in multivariate analysis. The results suggest HIF-1alpha is involved in gastric carcinogenesis and disease progression, but is only a weak prognostic factor for survival.

Adenocarcinoma↗

Is the hypoxia-inducible factor pathway important in gastric cancer?

Tumour hypoxia is well recognised in oncology to be a key factor resulting in treatment resistance and poor prognosis. Hypoxia leads to the expression of a number of gene products that are involved in tumour progression, invasion and metastasis formation. The most important of these proteins is thought to be hypoxia-inducible factor-1alpha (HIF-1alpha), which appears to be a master regulator of the cellular response to hypoxia. HIF-1alpha expression is associated with a poor prognosis and treatment response in a number of tumour sites. There is some evidence that the HIF-1alpha pathway might be involved in gastric carcinogenesis. Studies have shown reactive oxygen species from Helicobacter pylori, associated with the development of gastric cancer, stabilise HIF-1alpha. Non-steroidal anti-inflammatory drugs, shown to reduce the risk of gastric cancer, can decrease HIF-1alpha expression. Although a large study correlating HIF-1alpha expression with prognosis is lacking in gastric cancer, the immunohistochemical expression of HIF-1alpha target genes (Glut-1, VEGF, CA9, iNOS) is associated with a poor prognosis. In addition, the targeted inhibition of HIF-1alpha has been shown to inhibit the growth of gastric tumours in animals. Increased understanding of the importance of hypoxia and the HIF-1alpha pathways may therefore hold the key to prevention strategies, improved selection of patients for adjuvant therapy and new treatments for the disease.

Anti-Inflammatory Agents, Non-Steroidal↗

Glucose metabolism in brain tumours can be estimated using [18F]2-fluorodeoxyglucose positron emission tomography and a population-derived input function scaled using a single arterialised venous blood sample.

The aim of this study was to assess simplified methods for deriving input functions for estimating glucose metabolism using 18F-FDG-PET. Nine glioma patients underwent paired 18F-FDG-PET scans as part of a phase II study and the data used to estimate the metabolic rate of glucose (MRGlu) using a population-derived input function (arterial data from 14 scans) scaled using a single arterial blood sample taken at 20 min. Paired studies were performed in four further glioma patients with stable disease at least four months following radiotherapy to determine whether scaling the population-derived input function using a 20-min arterialised venous or venous sample further simplified the method. The heated hand method was used to obtain arterialised venous blood that approximated arterial blood. In the 9 phase II glioma patients, there was a good, statistically significant correlation between the MRGlu values estimated using the individual arterial input functions and the single arterial sample scaled population-derived input functions (r(2)=0.88, p<0.001, n=36). Blood samples collected during three scans on two of the stable disease patients showed no significant difference between the arterialised venous and arterial plasma concentrations of 18F (p>0.1, n=15) when the degree of arterialisation of the blood was monitored and maintained using a thermocouple. A significant difference was found between the plasma arterial and venous levels of 18F. There was an excellent correlation between MRGlu estimated using an arterial input function and a population-derived input function scaled using a single arterialised venous blood sample (r(2)=0.98, n=12). The method was reproducible with less than 4.4% variation between repeat tumour scans. Therefore, a population-derived input function scaled using a single arterialised venous blood sample at 20 min can be used for estimating MRGlu using 18F-FDG PET in glioma patients.

Arteries↗

In vivo evaluation of [18F]fluoroetanidazole as a new marker for imaging tumour hypoxia with positron emission tomography.

Development of hypoxia-targeted therapies has stimulated the search for clinically applicable noninvasive markers of tumour hypoxia. Here, we describe the validation of [(18)F]fluoroetanidazole ([(18)F]FETA) as a tumour hypoxia marker by positron emission tomography (PET). Cellular transport and retention of [(18)F]FETA were determined in vitro under air vs nitrogen. Biodistribution and metabolism of the radiotracer were determined in mice bearing MCF-7, RIF-1, EMT6, HT1080/26.6, and HT1080/1-3C xenografts. Dynamic PET imaging was performed on a dedicated small animal scanner. [(18)F]FETA, with an octanol-water partition coefficient of 0.16+/-0.01, was selectively retained by RIF-1 cells under hypoxia compared to air (3.4- to 4.3-fold at 60-120 min). The radiotracer was stable in the plasma and distributed well to all the tissues studied. The 60-min tumour/muscle ratios positively correlated with the percentage of pO(2) values <5 mmHg (r=0.805, P=0.027) and carbogen breathing decreased [(18)F]FETA-derived radioactivity levels (P=0.028). In contrast, nitroreductase activity did not influence accumulation. Tumours were sufficiently visualised by PET imaging within 30-60 min. Higher fractional retention of [(18)F]FETA in HT1080/1-3C vs HT1080/26.6 tumours determined by dynamic PET imaging (P=0.05) reflected higher percentage of pO(2) values <1 mmHg (P=0.023), lower vessel density (P=0.026), and higher radiobiological hypoxic fraction (P=0.008) of the HT1080/1-3C tumours. In conclusion, [(18)F]FETA shows hypoxia-dependent tumour retention and is, thus, a promising PET marker that warrants clinical evaluation.

Animals↗

Positron emission tomography imaging of cell proliferation in oncology.

Tumour-cell proliferation is a hallmark of the malignant phenotype. Positron emission tomography (PET) offers a unique method of imaging biological and biochemical changes in vivo. Radiolabelled thymidine and thymidine analogues are currently in development as PET tracers. By studying the uptake and kinetics of such compounds using PET, a measure of DNA synthesis and hence cell proliferation can be obtained. Molecular imaging of cellular proliferation with PET is now possible, and has the potential to play an important role in the evaluation of efficacy of new anti-cancer agents.

Antiviral Agents↗

Positron emission tomographic imaging of angiogenesis and vascular function.

Surrogate markers of clinical outcome are important in anticancer drug research, since clinical criteria of response develop only slowly and may be confounded by other processes than drug effect. The need for surrogate outcome markers is especially great with newer agents that may act by tumour stabilization as opposed to shrinkage. Neoplastic angiogenesis is associated with a number of detectable changes at molecular and microcirculatory levels. Therefore, direct study of angiogenic molecular biology and tumour circulation before during and after treatment may offer useful surrogate markers for vascular-targeted therapies. The main advantage of radiotracer imaging with positron emission tomography (PET) is its functional specificity. This article will review two main areas: (a) the methodology behind PET imaging of tumour blood supply with 15O-oxygen labelled compounds; and (b) newer tracers in development as markers of angiogenetic biology.

Cell Hypoxia↗

On the development of rational standards for nuclear response evaluation.

AIM: Small variations in test protocols can disproportionately affect the sensitivity and specificity of response evaluation in nuclear medicine. Although use of standardised methods can remedy this, standards must be shown to add value. We think a concept of "societal efficacy" is the benchmark criterion for value of medical interventions. This paper gives an overview of literature on nuclear response evaluation, and promotes a decision-analytic approach to the synthesis of standards. METHODS: A Medline search using the OVID database, 1966-January 2002. Reports were organised in relation to mode of treatment and timing of follow-up evaluation. Protocols of multimodality treatment were classified according to the treatment with the greatest tissue-inflammatory potential. The database will be made available on-line at the Website of the European Organisation for the Research and Treatment of Cancer (EORTC) Functional Imaging Group (http://www.eortc.be). RESULTS: Two hundred and twelve reports could be classified as primary studies in humans. 125 were formal "before-and-after" studies of response to anticancer therapy. More than 60 reported the use of serial positron emission tomography (PET) with fluorodeoxyglucose (FDG). CONCLUSION: Descriptive reports of the accuracy and applications of new diagnostic technologies need to be linked to an expectation of improved research or clinical outcomes. To manage the large volume of information will require a trans-disciplinary perspective and use of advanced decision-analytic METHODS: At stake is the possibility of an "industrial" upscaling of one of nuclear oncology' strongest applications.

Fluorodeoxyglucose F18↗

Assessment of the technology for functional imaging in cancer.

Functional imaging can address hitherto irresolvable questions about cancer biology in both research and practice. In the clinic, by combining features of systemic and local disease markers into reference standards for the diagnosis of new disease entities functional imaging has the potential to literally redefine illness. Clinical assessments can be conducted at two levels: establishment of new reference standards, and evaluation of successor technologies that will substitute for a reference standard in practice. A union of functional imaging with anatomical criteria of disease has shown great promise in the management of numerous cancers. More work is required to use functional imaging to develop 'functional' approaches to diagnosis and therapy. Many methodologies exist for the acquisition of primary data on imaging technology efficacy. A form of economic cost-effectiveness modelling called iterative decision analysis can be used to set research and service priorities. Cancer clinicians need to take an increased role in functional imaging research, as they have primary expertise in the development and use of treatments modifying cell and tissue function.

Decision Making↗

PET for in vivo pharmacokinetic and pharmacodynamic measurements.

Positron emission tomography (PET) scanning is evolving as a unique tool for drug development in oncology for improving both the efficacy of established treatment and in evaluating novel anticancer agents. As a non-invasive functional imaging modality, PET has an unrivalled sensitivity when monitoring the pharmacokinetics and pharmacodynamics of drugs and biochemicals when radiolabelled with short living positron-emitting radioisotopes. This is of particular relevance in assessing newer molecular-targeted therapy where conventional evaluation criteria (maximum tolerated dose and tumour shrinkage for example) may be inappropriate. PET has already been applied to a wide number of drugs to demonstrate activity in vivo from standard chemotherapy such as 5-fluorouracil (5-FU) [J Clin Oncol 17 (1999) 1580], to novel molecular agents such as those involved in tumour angiogenesis [Br J Cancer 83 (2000) P6] and antivascular therapy [Proc Annu Meet Am Soc Clin Oncol 19 (2000) 179a]. This review will evaluate the achievements of PET in the drug development process, an approach that promises to facilitate the rapid translation of scientific research into current clinical practice.

Animals↗

Extraction of 5-fluorouracil by tumor and liver: a noninvasive positron emission tomography study of patients with gastrointestinal cancer.

Tumor and normal tissue pharmacokinetics of 5-Fluorouracil (5-FU) in patients can be determined with positron emission tomography scanning. However, the data obtained are of limited value because of the inability to distinguish catabolites (inactive species) from parent 5-FU and anabolites (cytotoxic species). In this paper, we have blocked 5-FU catabolism in one arm of a paired study with eniluracil, an inactivator of dihydropyrimidine dehydrogenase, enabling catabolite correction and calculation of tissue pharmacokinetic parameters to be achieved. Using this novel approach, we report for the first time that the net clearance of 5-[(18)F]FU from plasma into tumors (liver metastases and pancreatic tumor) of patients is low (K(I) = 0.0033 +/- 0.0005 ml plasma/ml tissue/min). In contrast, the initial (up to 10 min) clearance through catabolism in liver was high (K(I) = 0.7313 +/- 0.092 ml plasma/ml tissue/min). In the absence of eniluracil, catabolites in tumors accounted for 83% of total tumor exposure (range, 66-91%), whereas catabolites in liver accounted for 96% of total liver exposure (range, 94-98%). This study provides definitive evidence that the cytotoxicity of 5-FU in patients with gastrointestinal cancer could be compromised by its intrinsically low uptake by tumors, as well as decreased systemic availability through hepatic catabolism.

Antimetabolites, Antineoplastic↗

Comparative biodistribution and metabolism of carbon-11-labeled N-[2-(dimethylamino)ethyl]acridine-4-carboxamide and DNA-intercalating analogues.

The tricyclic carboxamide N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA) is a DNA-intercalating agent capable of inhibiting both topoisomerases I and II and is currently in Phase II clinical trial. Many related analogues have been developed, but despite their potent in vitro cytotoxicities, they exhibit poor extravascular distribution. As part of an ongoing drug development program to obtain related "minimal intercalators" with lower DNA association constants, we have compared the biodistribution and metabolite profiles of the prototype compound, DACA, with three analogues to aid rational drug selection. All of these compounds share a common structural feature, N-dimethyl side chain, which was radiolabeled with the positron-emitting radioisotope, carbon-11. This strategy was selected because it allows promising candidates emerging from preclinical studies in animals to be evaluated rapidly in humans using positron emission tomography (PET). The acridine DACA, the phenazine SN 23490, the pyridoquinoline SN 23719, and the dibenzodioxin SN 23935 were found to be cytotoxic in in vitro assays with an IC50 of 1.4-1.8 microM, 0.4-0.6 microM, 1.3-1.6 microM, and 24-36 microM, respectively, in HT29, U87MG, and A375M cell lines. Ex vivo biodistribution studies with carbon-11 radiolabeled compounds in mice bearing human tumor xenografts showed rapid clearance of 11C-radioactivity (parent drug and metabolites) from blood and the major organs. Rapid hepatobiliary clearance and renal excretion were also observed. There was low [<5% of injected dose/gram (%ID/g)] and variable uptake of 11C-radioactivity in three tumor types for all of the compounds. Tumor (U87MG) to blood 11C-radioactivity for [11C]DACA, [11C](9-methoxyphenazine-1-carboxamide (SN 23490), [11C]2-(4-pyridyl)quinoline-8-carboxamide (SN 23719), and [11C]dibenzo[1,4]dioxin-1-carboxamide (SN 23935) at 30 min were 2.9 +/- 1.1, 2.3 +/- 0.6, 2.6 +/- 0.6, and 0.7 +/- 0.2, respectively. For SN 23719, the distribution of 11C-radioactivity in normal tissues and tumors determined ex vivo was in broad agreement with that determined in vivo by whole body PET scanning. [11C]DACA was rapidly and extensively metabolized to several plasma metabolites and a major tumor metabolite. In contrast, [11C]SN 23935, [11C]SN 23490, and [11C]SN 23719 showed less extensive metabolism. In the tumor samples, the parent [11C]DACA and [11C]SN 23935 represented between 0.3 and 1.5%ID/g, whereas [11C]SN 23490 and [11C]SN 23719 represented between 1.5 and 2.8%ID/g. In conclusion, by using a strategy with 11C-labeling, we have determined the tissue distribution and metabolic stability of novel tricyclic carboxamides with the view of selecting analogues with potentially better in vivo activity against solid tumors. SN 23490 and SN 23719 had more favorable distribution and metabolic stability compared with DACA and SN 23935 and may warrant further development. The radiolabeling strategy used allows ex vivo and in vivo evaluation of promising anticancer agents in animals and offers the potential of rapid translation to studies in humans using PET.

Acridines↗

Pharmacokinetic evaluation of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide in patients by positron emission tomography.

PURPOSE: To evaluate tumor, normal tissue, and plasma pharmacokinetics of N-[2-(dimethylamino)ethyl]acridine-4-carboxamide (DACA). The study aimed to determine the pharmacokinetics of carbon-11-labeled DACA ([11C]DACA) and evaluate the effect of pharmacologic doses of DACA on radiotracer kinetics. PATIENTS AND METHODS: [11C]DACA (at 1/1,000 phase I starting dose) was administered to 24 patients with advanced cancer (pre-phase I) or during a phase I trial of DACA in five patients. Positron emission tomography (PET) was performed to assess pharmacokinetics and tumor blood flow. Plasma samples were analyzed for metabolite profile of [11C]DACA. RESULTS: There was rapid systemic clearance of [11C]DACA over 60 minutes (1.57 and 1.46 L x min(-1) x m(-2) in pre-phase I and phase I studies, respectively) with the production of several radiolabeled plasma metabolites. Tumor, brain, myocardium, vertebra, spleen, liver, lung, and kidneys showed appreciable uptake of 11C radioactivity. The area under the time-versus-radioactivity curves (AUC) showed the highest variability in tumors. Of interest to potential toxicity, maximum radiotracer concentrations (Cmax) in brain and vertebra were low (0.67 and 0.54 m(2) x mL(-1), respectively) compared with other tissues. A moderate but significant correlation was observed for tumor blood flow with AUC (r = 0.76; P =.02) and standardized uptake value (SUV) at 55 minutes (r = 0.79; P =.01). A decrease in myocardial AUC ( P =.03) and splenic and myocardial SUV ( P =.01 and.004, respectively) was seen in phase I studies. Significantly higher AUC, SUV, and Cmax were observed in tumors in phase I studies. CONCLUSION: The distribution of [11C]DACA and its radiolabeled metabolites was observed in a variety of tumors and normal tissues. In the presence of unlabeled DACA, pharmacokinetics were altered in myocardium, spleen, and tumors. These data have implications for predicting activity and toxicity of DACA and support the use of PET early in drug development.

Acridines↗

Two routes to [11C-carbonyl]organo-isocyanates utilizing [11C]phosgene ([11C]organo-isocyanates from [11C]phosgene).

Two generic radiosynthetic routes for the preparation of [11C-carbonyl]isocyanates have been developed. Reaction of N-organo-sulfinylamines; RNSO, (R = Me, Et, allyl, cyclohexyl and phenyl) with [11C]phosgene gave the corresponding [11C-carbonyl]isocyanates in good radiochemical yield (53-68%) from [11C]phosgene (decay corrected) in ca 16 min from EOB. Alternatively, the reaction of [11C]phosgene with N,N'-organo-ureas; (RNH)(2)CO, (R = Me, Et, Pr and phenyl) also gave the corresponding [11C-carbonyl]isocyanates in moderate radiochemical yield (9-37%) from [11C]phosgene (decay corrected) in ca 16 min from EOB. For identification, the [11C-carbonyl]organo-isocyanates were derivatized with 1-(2-methoxyphenyl)piperazine in situ to [11C-carbonyl]carboxamides and the position of radiolabelling in the carbonyl group confirmed by [11/13C]co-labeling and subsequent carbon-13 NMR spectroscopy.

Carbon Radioisotopes↗

Positive effect of the induction of p21WAF1/CIP1 on the course of ischemic acute renal failure.

BACKGROUND: The p21 protein is found in the nucleus of most cells where it modulates cell cycle activity. At low levels, p21 stabilizes interactions between D cyclins and their cyclin-dependent kinases (cdks), but at high levels after induction by several different stress pathways, it causes cell cycle arrest. The p21 mRNA is induced in murine kidney after several types of acute renal failure, including cisplatin administration, ischemia-reperfusion, and ureteral obstruction. We reported that after cisplatin injection, mice with a p21 gene deletion developed much more severe renal damage than wild-type mice. To dissociate the effects of cisplatin-induced DNA damage and subsequent initiation of DNA damage-dependent cell death pathways from effects of acute renal failure, we have now examined mice after ischemia-reperfusion, a model of renal failure not associated with genotoxin-induced DNA damage early after the injury. METHODS: Wild-type and p21(-/-) mice were made ischemic by clamping both renal hila for 30 or 50 minutes. At various times after reflow, mortality and parameters of renal function and morphology were quantified. Also, the nuclear proteins p21 and proliferating cell nuclear antigen (PCNA) were localized in kidney sections by immunohistochemistry. RESULTS: Kidney function was more impaired and mortality increased significantly in p21(-/-) mice as compared with p21(+/+) mice. We found more cell cycle activity, indicated by increased number of mitotic cells and nuclear PCNA-positive cells, in kidney of p21(-/-) mice. CONCLUSIONS: In this study, p21(-/-) mice were more susceptible to ischemia-induced acute renal failure, with similarly elevated levels of parameters of cell cycle activity. We propose that the increased and inappropriate cell cycle activity in kidney cells is responsible for the increased kidney impairment and mortality.

Acute Kidney Injury↗

Radiolabelled tracers and anticancer drugs for assessment of therapeutic efficacy using PET.

Positron Emission Tomography (PET) has the potential to improve efficacy of established and novel cancer therapies and to assist more rapid and rational progression of promising novel therapies into the clinic. This is due to PET's unrivalled sensitivity and ability to monitor the pharmacokinetics and pharmacodynamics of drugs and biochemicals radiolabelled with short -lived positron emitting radioisotopes. PET is a multidisciplinary science which employs chemists, biologists, mathematical modellers, pharmacologists as well as clinicians. Clinical research questions in oncology determine the methodological challenges faced by these other disciplines. Within this context we focus on the developments of the radiolabelled compounds that have underpinned the clinical work in oncology for monitoring tumour and normal tissue pharmacokinetics, assessment of tumour response, cell proliferation, gene expression, hypoxia, multidrug resistance and status of receptors on tumours.

Animals↗

Modulation of fluorouracil tissue pharmacokinetics by eniluracil: in-vivo imaging of drug action.

BACKGROUND: Fluorouracil is widely used for chemotherapy of gastrointestinal cancer, but response rates are poor. Eniluracil is being developed as an inactivator of dihydropyrimidine dehydrogenase, the enzyme that brings about first-pass degradation of fluorouracil. We studied the mechanism of action of eniluracil by measuring with positron emission tomography (PET) the effect of eniluracil on tumour and normal-tissue pharmacokinetics of fluorine-18-labelled fluorouracil. METHODS: Six patients with advanced gastrointestinal cancers were studied. PET scanning was done after injection of oxygen-15-labelled water to assess tissue blood flow, followed by 1 mg/m2 18F-fluorouracil. We compared the pharmacokinetics of 18F-fluorouracil when the patients had not received eniluracil, during a 4-day course of oral eniluracil, and during a 28-day course of oral fluorouracil plus eniluracil. FINDINGS: In eniluracil-naïve patients, 18F-fluorouracil localised more strongly (mean 0.0234% [SE 0.0019] of injected activity per mL tissue at 11 min) in liver than in tumours (0.0032% [0.0004]). There was substantial inhibition, after eniluracil administration, of radiotracer uptake and retention in normal liver (mean area under the time versus radioactivity curve 0.927 [SE 0.086] vs 1.857 [0.169] m2 mL(-1) s) and kidneys (1.096 [0.048] vs 5.043 [0.915] m2 mL(-1) s). There was also an increase in plasma uracil and unmetabolised 18F-fluorouracil and an increase in the radiotracer half-life in tumours (2.3 h to >4.0 h). INTERPRETATION: Two events strongly suggested increased exposure of 18F-fluorouracil and its anabolites in the tumours, consistent with the inactivation of dihydropyrimidine dehydrogenase: a selective decrease in radiotracer exposure in normal liver and kidneys compared with tumours; and an increase in radiotracer half-life in tumours.

Administration, Oral↗

In vivo monitoring of drugs using radiotracer techniques.

There is an increasing realization of the role of non-invasive monitoring of drug pharmacology. In this review, we discuss the role of positron emission tomography in such monitoring of tumour and normal tissue drug pharmacokinetics as well as assessment of tumour response, drug-receptor interactions and mechanisms of drug action and resistance. These studies represent a multidisciplinary research effort involving radiochemists, imaging scientists, clinicians, pharmacologists and mathematical modellers. This review evaluates achievements in the field from assessment of commonly used therapeutic agents such as 5-fluorouracil to target specific molecules such as markers for gene expression. It is envisaged that application of this technology will facilitate rational drug design and rapid translation of new ideas to the bedside.

Drug Administration Schedule↗