Paul Carnochan

The practical use of thermocouples for temperature measurement in clinical hyperthermia

The use of thermocouples as invasive thermometers in clinical hyperthermia is comprehensively and critically reviewed. The ability to construct thermocouple probes as small-bore, multiple junction assemblies is a major reason for their popularity and full constructional details are given. The potential sources of measurement error when using thermocouples both in temperature gradients and in electromagnetic or ultrasonic heating fields are discussed. Emphasis is placed upon simple practical solutions to these problems and a combination of good measurement practice and electrical filtering can reduce errors to an insignificant level. Techniques are suggested for the assessment of thermocouple performance during clinical measurement. With careful use, thermocouples can be reliable and convenient thermometers.

Evaluation of copper(II)-pyruvaldehyde bis (N-4-methylthiosemicarbazone) for tissue blood flow measurement usina a trapped tracer model

Copper(II)-pyruvaldehyde bis (N-4-methylthiosemicarbazone) (Cu-PTSM) labelled with 62,64Cu is a promising radiotracer for the study of blood flow using positron emission tomography (PET). We have investigated the application of a simple trapped tracer model to measurements of tissue 64Cu-PTSM uptake combined with continuous arterial sampling. A dual-tracer method was used to compare blood flow estimated by 64Cu-PTSM with values derived from measurements using cobalt-57 microspheres in the rat. Prolonged retention of 64Cu-PTSM following intravenous administration was initially confirmed in both normal tissues and tumours. After intraventricular 64Cu-PTSM infusion, cumulative arterial 64Cu activity increased progressively, and after extraction in n-octanol was found to plateau to levels corresponding with those reached following administration of 57CO microspheres. Rapid and species-dependent rates of 64Cu-PTSM decomposition to non-extractable 64Cu complexes were found in rat and human blood in vitro (70%±6% and 43%±5% respectively at 16 min), demonstrating the need for immediate processing of arterial samples. Close agreement was found between blood flow estimated by 64Cu-PTSM and 57CO microsphere methods in tissues of low to moderate flow: muscle (0.01, 0.08, 0.07 ml/min per gram; mean difference, mean 64Cu, mean 57Co), brain (0.09, 0.52, 0.43 ml/min per gram) and kidney (−0.16, 2.29, 2.45 ml/min per gram). Estimates of cardiac output also compared favourably between the two methods (5.7, 59.8, 54.1 ml/min). We conclude that a simple tissue trapping model may be suitable for the derivation of blood flow estimates using 62,64Cu-PTSM, PET imaging and continuous arterial blood sampling.

62Cu-PTSM and PET used for the assessment of angiotensin II-induced blood flow changes in patients with colorectal liver metastases

Abstract. The aim of this study was to establish a quantitative positron emission tomography (PET) method for investigating angiotensin II (AII)-induced changes in blood flow distribution in the liver. This was in order to evaluate the role of vascular manipulation applied to locoregional chemotherapy treatment in patients with colorectal liver metastases. The tracer selected was copper-62 (II) pyruvaldehyde bis-(N4-methyl)thiosemicarbazone (62Cu-PTSM), which exhibits high first-pass extraction and tissue retention following intra-arterial administration. The short half-life of the tracer and its availability from a 62Zn/62Cu generator enabled short-interval repeat PET scans on patients in a single imaging session. Distribution of tracer within the liver was imaged in a single view using a PET camera with rotating large-area detectors. By optimisation of the acquisition protocol, it was possible to acquire sufficient data to produce good-quality images and to quantify tracer uptake with an accuracy of ≤10%. Reproducibility of the imaging method was assessed in a single patient in whom three consecutive 62Cu-PTSM PET scans were obtained, and in whom no vascular manipulation was performed. Sets of scans (before, during and immediately after a 45-min AII infusion) were obtained in nine patients to assess blood flow changes associated with prolonged vascular manipulation. Significant individual responses, varying in both the magnitude and the duration of flow change, were observed in the majority of cases (7/11 lesions; 7/9 patients). These findings illustrate the potential of 62Cu-PTSM and PET for pharmacological studies. The wide range of individual patient responses to AII infusion suggests that PET blood flow assessment would be of value for selecting patients in whom this procedure may be effective.

Copper bis(diphosphine) complexes: radiopharmaceuticals for the detection of multi-drug resistance in tumours by PET.

Abstract.Experience with imaging of the multi-drug resistance (MDR) phenotype in tumours using technetium-99m sestamibi, a substrate of the P-glycoprotein (Pgp) transporter, suggests that better quantification of images and separation of MDR from other variables affecting tracer uptake in tumours are required. One approach to these problems is the development of short half-life positron-emitting tracers which are substrates of Pgp. Several lipophilic cationic copper(I) bis(diphosphine) complexes labelled with copper-64 have been synthesised and evaluated in vitro as substrates for Pgp. The synthesis is rapid and efficient with no need for purification steps. The chemistry is suitable for use with very short half-life radionuclides such as copper-62 (9.7 min) and copper-60 (23.7 min). Incubation of the complexes with human serum in vitro showed that they are sufficiently stable in serum to support clinical imaging, and the more lipophilic members of the series are taken up rapidly by cells (Chinese hamster ovary and human ovarian carcinoma) in vitro with great avidity. Uptake in human ovarian carcinoma cells is significantly reduced after several months of conditioning in the presence of doxorubicin, which induces increased Pgp expression. Uptake in hooded rat sarcoma (HSN) cells, which express Pgp, is significantly increased in the presence of the MDR modulator cyclosporin A. Biodistribution studies in hooded rats show rapid blood clearance, excretion through both kidneys and liver, and low uptake in other tissues. The one complex investigated in HSN tumour-bearing rats showed uptake in tumour increasing up to 30 min p.i. while it was decreasing in other tissues. We conclude that diphosphine ligands offer a good basis for development of radiopharmaceuticals containing copper radionuclides, and that this series of complexes should undergo further evaluation in vivo as positron emission tomography imaging agents for MDR.

Metal complexes of bleomycin: evaluation of [Rh-105]-bleomycin for use in targeted radiotherapy.

Bleomycin has been used as a carrier for several radioisotopes; however, its potential for clinical use has been limited either by the in vivo stability of the complexes or the half-life of the isotope used. The chemical, biological, and radiological properties of 105Rhodium appear to make it an ideal choice for targeted radiotherapy. The synthesis and purification of a hereto unreported 105Rhodium-bleomycin (105Rh-BLM) complex is described. The stability of this complex in plasma is sufficient to allow targeted delivery of the radioisotope. 57Cobalt-bleomycin was studied under identical conditions for comparative purposes. The suitability of 105Rh-BLM for targeted therapy, which appears to be limited by the renal clearance of this agent, is discussed.

Continuous angiotensin II infusion increases tumour: normal blood flow ratio in colo-rectal liver metastases

Insufficient blood flow within colo-rectal hepatic metastases is a factor which may limit drug delivery to, and thus the response of, these tumours to regional chemotherapy. Loco-regional flow may be manipulated pharmacologically to enhance the tumour blood flow relative to that of the normal liver. However, as yet, only transient effects have been studied. Patients receiving regional chemotherapy for unresectable hepatic disease were given a 45 min regional infusion of the vasoconstrictor Angiotensin II. Intrahepatic blood flow distribution was assessed serially by Positron Emission Tomography (PET) imaging together with the trapping tracer copper(II) pyruvaldehyde bis(N-4-methylthiosemicarbazone) (Cu-PTSM) labelled using copper-62. Eleven lesions in nine patients were studied, with no adverse effects. Prior to Angiotensin II administration tumour blood flow was generally found to be greater than that of liver (10/11 lesions; 8/9 patients; median TNR 1.3, iqr 0.9–2.5). A significant increase in relative flow to tumour was seen in response to 10 min Angiotensin II infusion in most cases (7/11 lesions; 7/9 patients; median TNR 2.1, iqr 1.4–4.1; P = 0.008), which appeared to be sustained throughout the 45 min infusion period (median TNR 1.85, iqr 1.3–3.8; P = 0.03). These effects were accompanied by transient elevation of mean arterial pressure, but no change in pulse rate. These observations suggest that prolonged regional vasoconstrictor administration could prove useful in the management of unresectable colo-rectal hepatic metastases, and that further development of vascular manipulation to enhance tumour targeting and drug delivery is warranted.

Nitric oxide inhibition sustains vasopressin-induced vasoconstriction

Hepatic parenchymal vasoconstriction increases cytotoxic drug uptake into hepatic metastases by increasing the tumour to liver blood flow ratio. Prolonged infusion of the vasoconstrictor vasopressin does not result in sustained vasoconstriction, and this may limit the benefit of vasopressin in infusional chemotherapy. We have assessed whether loss of vasopressin-induced vasoconstriction is mediated by nitric oxide. Hepatic and tumour blood flow were continuously monitored, in an animal hepatic tumour model, by laser Doppler flowmetry. The response to regionally infused vasopressin and the nitric oxide inhibitor N-nitro-L-arginine methyl ester (L-NAME) were assessed over a 30 min infusion period. The vasopressin-induced vasoconstrictor effect diminished after 15 min despite continued infusion. Vasoconstriction was significantly prolonged when L-NAME was infused in addition to vasopressin. The increase in tumour to normal blood flow ratio was greater over the infusion period when L-NAME was co-administered with vasopressin. Our results suggest that the loss of vasopressin-induced vasoconstriction seen in liver parenchyma after regional infusion is prevented by the nitric oxide synthase inhibitor L-name and may be mediated by nitric oxide.

Uptake and distribution of L-3-[I-125] Iodo-α-methyl tyrosine in experimental rat tumours: comparison with blood flow and growth rate

Radiolabelled amino acids combined with positron emission tomography (PET) show promise for the accurate delineation of viable tumour extent and may also provide a rapid and sensitive indicator of response to therapy. We have investigated the potential use of the radioiodinated amino acid analogue L-3-iodo-α-methyl tyrosine (IMT) for these purposes using experimental tumours in hooded rats. Preliminary studies using HSN tumours and IMT labelled with iodine-125 demonstrated maximum tumour uptake at 15 min post injection although an improved tumour-to-brain ratio was seen at 24 h due to the relatively poor retention of IMT in normal brain. Brain uptake of IMT was also found to be substantially reduced by competition with another large neutral amino acid phenylalanine; however, relatively less effect was seen in tumour, and in skeletal muscle no change in IMT uptake was observed. Quantitative autoradiography revealed no sign of heterogeneity in tumour IMT uptake: good penetration was seen even in poorly vascularised regions as confirmed by endothelial immunohistochemistry. Similar levels of IMT uptake were found in the OES.HR1 tumour during growth supplemented by exogenous oestrogen. Following arrest of tumour growth by removal of the oestrogen stimulus, IMT uptake was seen to fall from 1.7% to 1.0% of the injected dose per gram: this was matched by a fall in tumour blood flow as estimated by technetium-99m hexamethylpropylene amine oxime distribution. It appears that IMT uptake is more strongly influenced by blood flow than cell proliferation and that intratumoural distribution of IMT is principally determined by diffusion.

Pharmacokinetics and biodistribution of radiolabelled idoxifene: Prospects for the use of PET in the evaluation of a novel antioestrogen for cancer therapy

With a view to evaluating the role of PET imaging in the development of new anticancer drugs, we are investigating the novel antioestrogen pyrrolidino-4-iodotamoxifen (idoxifene). [125I]idoxifene and [131I]idoxifene have been produced in no-carrier-added form using a tributyl stannylated precursor, and the bio-distribution and dynamic behaviour of the compound investigated using syngeneic transplantable mammary tumours in the rat. Our findings support the use of PET imaging with 124I to study the clinical pharmacology of idoxifene. Factors other than hormone receptor levels appear to influence tumour uptake and therefore, possibly the biological effects of this compound.

Basic Fibroblast Growth Factor Infusion Increases Tumour Vascularity, Blood Flow and Chemotherapy Uptake

Tumour response depends on intratumoural cytotoxic concentration, which varies with tumour vascularity. We determined whether basic fibroblast growth factor (bFGF) infusion increased tumour vascularity, blood flow and cytotoxic drug uptake. The effect of interstitial and systemic bFGF infusion was compared with that of saline-infused controls using animal HSN and K12/TR tumour models. Changes in tumour vascularity were assessed by immunohistochemical staining of tumour sections. Blood flow and drug uptake were studied using a radiotracer method. There were significant increases in tumour vascularity, vessel length density and blood flow with both interstitial and systemic bFGF infusions, and a significant increase in tumour fluorouracil uptake after systemic bFGF infusion of liver tumours. The effects were independent of tumour type, and could be produced by bFGF administration after initial tumour growth. bFGF infusion increased tumour fluorouracil uptake. Further studies are required to determine the risks and benefits with this approach to increasing tumour cytotoxic uptake.