Simplified enzymatic synthesis and biodistribution of 11C-S-adenosyl-l-methionine

¹¹C-S-Adenosyl-l-methionine (¹¹C-SAM) was synthesized enzymatically from ¹¹C-l-methionine using ratliver extract [40%–50% saturated (NH₄)₂SO₄ fraction] as the enzyme source. In biodistribution studies in rats, the highest uptake of ¹¹C-SAM was found in the kidneys. ¹¹C-SAM was also accumulated in the small intestine, pancreas, adrenal gland, liver, and spleen. The uptake of ¹¹C-SAM in the brain increased with time, but remained low. At 30 min after injection, about 50%–60% of the ¹¹C radioactivity was present in the acid-insoluble fraction of the kidneys and liver. When a high loading dose of ¹¹C-SAM was administered, the kidney uptake was enhanced, but the proportion of the radioactivity present in the acid-insoluble fraction was lower. In a study of one rabbit, the kidney uptake was of ¹¹-SAM clearly visualized using positronemission tomography.     

Rapid rise in FDG uptake in an irradiated human tumour xenograft

In order to investigate early changes in the glucose metabolism of irradiated tumours, tumour uptake of 2-[¹⁸F]fluoro-2-deoxy-d-glucose (¹⁸FDG) was studied in human tumour xenografts. Three human tumour lines [ependymoblastoma (NNE), small cell lung cancer (GLS), and glioblastoma (KYG)] showing different radiosensitivities and incidences of radiation-induced apoptosis were subcutaneously transplanted into nude mice, and were irradiated at a single dose of 10 Gy. Then 0.5 mCi of¹⁸FDG was intravenously administered 1 h before sacrifice. The animals were sacrificed at 2, 4 and 6 h following irradiation, and¹⁸FDG accumulation in the tumours was examined. Before irradiation, GLS and KYG tumours showed significantly higher rates of¹⁸FDG accumulation compared with NNE tumours (P <0.004 andP <0.001, respectively). NNE (the most radiosensitive tumour with the highest incidence of radiation-induced apoptosis), however, displayed a 2.3-fold higher rate of¹⁸FDG accumulation at 2 h following irradiation compared with a non-irradiated group (P <0.01), and thereafter showed a plateau up to 6 h. The accumulation did not increase significantly in the other tumours with lower radiosensitivity and much less radiation-induced apoptosis. The rapidity of the increase in¹⁸FDG accumulation in the most radiosensitive tumour line, occurring as early as 2 h following irradiation, suggests that the increase was independent of recovery phenomena following radiation damage.     

Crossed cerebellar diaschisis: a positron emission tomography study withl-[methyl-11C]methionine and 2-deoxy-2-[18F]fluoro-d-glucose

OBJECTIVE: Crossed cerebellar diaschisis (CCD) is defined as a depression of blood flow and oxidative metabolism of glucose in the cerebellum contralateral to a supratentorial brain lesion, as detected with positron emission tomography (PET) and single photon emission computed tomography. We examined whether L-[methyl-11C]methionine (MET) uptake is affected in CCD. METHODS: In 12 patients with a unilateral supratentorial brain tumor, we evaluated the uptake of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) and MET in the cerebellar hemispheres by means of PET. Asymmetry index (AI) was defined as a difference in the average count between the ipsilateral and contralateral cerebellar hemispheres divided by the average count in both cerebellar hemispheres. Patients with AI of FDG PET more than 0.1 and those with AI equal to 0.1 or less than 0.1 were classified as CCD-positive and CCD-negative, respectively. RESULTS: Six patients were CCD-positive and others were CCD-negative in the FDG PET study. Between CCD-positive and CCD-negative patients, mean AI of MET was not significantly different (0.017 +/- 0.023 and 0.014 +/- 0.039, respectively). CONCLUSIONS: Different from glucose metabolism, cerebellar MET uptake was not affected in CCD. The present study may indicate that cerebellar MET uptake is independent of suppression of cerebellar neuronal activity.     

Regional 2-[18F]fluoro-2-deoxy-d-glucose uptake varies in normal lung

2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography (FDG-PET) is a promising imaging procedure for detecting primary and metastatic cancer in the lungs. We have, however, failed to detect some small tumors in the lower lobes of the lungs. This study aimed to determine whether increase¹⁸F background activity in the dependent lower lungs is present, which could make lesion detection more difficult. We measured the standardized uptake values (SUVs) for FDG of normal lung remote from the nodular lesion in 16 patients with newly diagnosed untreated lung lesions stronlgy suspected to represent non-small cell lung cancers. In addition, 15 patients with known or suspected primary breast cancers without pulmonary lesions were included as control subjects. After PET transmission images of the thorax were obtained, approximately 370 MBq of FDG was injected intravenously and imaging was immediately begun. Patients were supine throughout the study. SUVs were determined with images obtained 50–70 min after FDG injection. Regions of interest (ROls) of 6×6 pixels were positioned over normal lung in anterior, mid, and posterior portions of upper, middle, and lower lung fields. Thus, as many as 18 ROls were positioned in each patient. The SUVs of the posterior portion were significantly higher than those of the anterior and mid portions in the population of 31 cases (P <0.001). Also, the mean SUV of the lower lung field was significantly higher than the SUVs of the upper and middle lung fields in this population (P <0.01). This pattern was seen among the two groups of 16 patients suspected of having lung cancer and 15 control subjects. Background¹⁸F activity was highest in posterior and lower lung in these patients. The maximum value of mean SUV observed in normal posterior lower lung was 0.804±0.230 (41% greater than the mean SUV in the anterior upper lung), which is in the range of the apparent SUV for a 5-mm lung lesion, with higher SUV, due to recovery coefficient issues. Thus this phenomenon could contribute to occasional false-negative lesions in those areas. Increased blood flow and FDG delivery and also scatter from heart and liver may contribute to the increased lower lung background activity. Regional differences in normal lung FDG uptake are significant and should be considered when interpreting pulmonary PET studies in patients with suspected primary or metastatic lung cancer.     

Synthesis of optically active dodecaborate-containing l-amino acids for BNCT

A convenient and simple synthetic method of dodecaboratethio-l-amino acid, a new class of tumor-seeking boron carrier for BNCT, was accomplished from S-cyanoethylthioundecahydro-closo-dodecaborate (S-cyanoethyl-¹⁰BSH, [¹⁰B₁₂H₁₁]²⁻SCH₂CH₂CN) and bromo-l-α-amino acids by nearly one step S-alkylation. An improved synthesis of S-cyanoethyl-¹⁰BSH, a key starting compound for S-alkylation, was also performed by Michael addition of ¹⁰BSH with acryronitrile in high yield. Four kinds of new dodecaboratethio-l-amino acids were obtained in optically pure form without the need for any optical resolution.     

Value of 123I-IMT SPECT for diagnosis of recurrent non-astrocytic intracranial tumours

The value of single-photon emission tomography (SPECT) using iodine-123-alpha-methyl-tyrosine (IMT) for the diagnosis of recurrent or residual gliomas is well established. In the current study we investigated whether IMT-SPECT could also be useful in the follow-up of brain metastases and other intracranial tumours of non-astrocytic origin. The study included 22 patients with suspected recurrent intracranial tumours of non-astrocytic origin (12 brain metastases, one supratentorial primitive neuroendocrine tumour (PNET), one rhabdoid tumour, two clivus chordomas, three ependymomas, two pituitary tumours, one anaplastic meningioma) who had previously been treated by surgery and/or radio/chemotherapy. SPECT results were correlated with clinical and MRI follow-up data. The study was true positive in 13 patients, true negative in five, false positive in one and false negative in three patients. Notably, all false negative findings were <13 mm. The resulting sensitivity of the IMT-SPECT was 81%. We concluded that the IMT-SPECT is a promising complementary imaging tool for the detection of recurrences of non-astrocytic intracranial tumours and their distinguishing from treatment-induced changes. The limitation of the IMT-SPECT is its low sensitivity for the detection of small lesions.     

O-[18F]fluoromethyl-L-tyrosine is a potential tracer for monitoring tumour response to chemotherapy using PET: an initial comparative in vivo study with deoxyglucose and thymidine

Purpose To compare the utility of a new artificial amino acid, O-[¹⁸F]fluoromethyl-L-tyrosine ([¹⁸F]FMT), for monitoring cancer chemotherapy with deoxyglucose and thymidine.Methods [¹⁸F]FMT, [¹⁴C]deoxyglucose ([¹⁴C]DG) and [6-³H]thymidine ([³H]Thd) were applied in this study. A 2.5 mg/kg dose of mitomycin (MMC) was administered to AH272 rat hepatoma-bearing Donryu rats. Tumour uptake of each tracer was measured just before (baseline) and on days 1, 3, 5 and 7 after the MMC administration, 1 h after a mixture of [¹⁸F]FMT, [¹⁴C]DG and [³H]Thd had been injected, and was shown as DURs (% injected dose/gram tissue normalised for the rat body weight). Dual-tracer macroautoradiographs with [¹⁸F]FMT and [¹⁴C]DG were also prepared.Results The tumour uptake for each tracer decreased earlier than did the tumour size. DURs (mean±SD) at baseline and on days 1, 3, 5 and 7 were as follows: [¹⁸F]FMT: 4.68±0.72, 3.34±0.66, 3.13±0.72, 3.42±0.45, 3.01±0.32; [¹⁴C]DG: 3.26±0.40, 3.09±0.55, 3.01±0.97, 2.28±0.35, 1.70±0.72; and [³H]Thd: 2.23±0.46, 1.54±0.45, 1.28±0.37, 1.35±0.20, 0.94±0.12. Decrease in [¹⁸F]FMT uptake compared with baseline was significant from day 1 (p<0.01), and the decrease in [³H]Thd uptake was also significant on day 1 (p<0.05) and days 3–7 (p<0.01). However, decrease in [¹⁴C]DG uptake was only significant from day 5 (p<0.01). Macroautoradiography suggested that the influence of inflammatory cells on the accumulation of [¹⁸F]FMT in tumours is smaller than that on the accumulation of [¹⁴C]DG.Conclusion [¹⁸F]FMT uptake shows a rapid and sensitive response to chemotherapy, comparable to that of [³H]Thd, suggesting that it may be applied as a powerful tracer for monitoring of proliferative activity after cancer chemotherapy using PET.     

Positron detection for the intraoperative localisation of cancer deposits

Purpose The study investigated the feasibility of a positron-sensitive hand-held detector system for the intraoperative localisation of tumour deposits resulting from intravenous [¹⁸F]FDG administration. Methods A total of 17 patients (12 receiving preoperative [¹⁸F]FDG PET imaging) with various histologically proven malignancies were included. Radioactivity from tumours and surrounding normal tissue was measured on average 3 h after administration of 36–110 MBq [¹⁸F]FDG and the tumour-to-background (T/B) ratio was calculated. In addition, phantom studies were performed to evaluate the spatial resolution and sensitivity of the probe. Results All known targeted tumour sites were identified by the positron probe. T/B ratios were generally high, with a mean T/B ratio of 6.6, allowing easy identification of most tumour sites. In one case of a hepatic metastasis, the T/B ratio of 1.34 was below expectations, since the preoperative [¹⁸F]FDG PET scan was positive. The probe was instrumental in the localisation of three additional tumour lesions (two lymph nodes, one anastomotic ring) that were not immediately apparent at surgery. Phantom studies revealed that [¹⁸F]FDG-containing gel (simulating tumour tissue), having 10 times more [¹⁸F]FDG than surrounding “normal” background gel, was clearly detectable in quantities as low as 15 mg. As measured in two cases, the absorbed radiation doses ranged from 2.5 to 8.6 μSv/h for the surgical team to 0.8 μSv/h for the aesthetician. Conclusion [¹⁸F]FDG-accumulating tumour tissues can be localised with positron probes intraoperatively with a low radiation burden to the patient and medical personnel. The methodology holds promise for further clinical testing.     

In vitro and in vivo studies of three radiolabelled somatostatin analogues:123I-Octreotide (OCT),123I-Tyr-3-OCT and111In-TIRA-d-Phe-1-OCT

Scintigraphy with long-acting somatostatin (SST) analogues may be useful for the localization of tumours expressing receptors (R) for SST. In this study we have analysed the in vitro and in vivo binding properties of three SST analogues,¹²³I-octreotide (OCT),¹²³I-Tyr-3-OCT and¹¹¹In-DTPA-d-Phe-l-OCT. In vitro binding studies performed with a variety of primary tumours (n=48) as well as with several tumour cell lines (A431, HT29, PANC1, COLO320, HMC1, KU812) indicated significant in vitro binding of these three radiolabelled SST analogues to two subpopulations of SSTR, high (K _d 0.2–2.0 nM) and low (K _d 5–15 nM) affinity ones. The number of SSTR on tumour cells was at least a 1000-fold higher as compared with normal peripheral blood cells. Comparative scintigraphic studies using¹²³I-OCT and/or¹²³I-Tyr-3-OCT and/or¹¹¹In-DTPA-d-Phe-1-OCT were performed in 21 patients with histologically verified intestinal carcinoid tumours. Corresponding scintigraphic results were obtained in 18 of 21 patients investigated with two different SSTR ligands, either¹²³I-OCT/¹²³I-Tyr-3-OCT (four of five),¹²³I-OCT/¹¹¹In-DTPA-d-Phe-1-OCT (eight of nine), or¹²³I-Tyr-3-OCT/¹¹¹In-DTPA-d-Phe-1-OCT (six of seven). We conclude that various tumours express high amounts of SSTR which are recognized by three radiolabelled SST analogues:¹²³I-OCT,¹²³I-Tyr-3-OCT and¹¹¹In-DTPA-d-Phe-1-OCT. Differences between these SST analogues in their in vitro binding and/or in vivo scanning properties are observed in a minority of patients. Thus, the labelling of OCT with iodine may be an alternative approach for those nuclear medicine departments for which¹¹¹In-DTPA-d-Phe-1-OCT is not easily available, or is too expensive.     

Central neurocytoma with unusually intense FDG uptake: Case report

Central neurocytoma is a benign neuronal tumor with a favorable prognosis. This tumor is typically characterized by decreased uptake of 18F-fluorodeoxy glucose (FDG) and any increased uptake of FDG in patients suffering from this tumor would be highly unusual. A case of central neurocytoma with an intense FDG uptake, combined with atypical histopathological features and a high proliferation index is reported in this paper. A 45-year-old male had a two months' history of right hemiweakness. Magnetic resonance (MR) imaging showed a large tumor in the right lateral ventricle. Positron emission tomography (PET) with FDG revealed high glucose metabolism in the tumor. The histological diagnosis was central neurocytoma with atypical features characterized by microvascular proliferation. The MIB-1 labeling index, ordinarily smaller than 2.0%, was 7.0%. Conventional radiotherapy, with a total dose of 50 Gy, was administered after the surgical treatment. The patient returned to his normal daily activities after the cessation of radiation therapy.     

The added value of [<Superscript>18</Superscript>F]fluoro-<Emphasis Type="SmallCaps">L</Emphasis>-DOPA PET in the diagnosis of hyperinsulinism of infancy: a retrospective study involving 49 children

Purpose Neuroendocrine diseases are a heterogeneous group of entities with the ability to take up amine precursors, such as L-DOPA, and convert them into biogenic amines, such as dopamine. Congenital hyperinsulinism of infancy (HI) is a neuroendocrine disease secondary to either focal adenomatous hyperplasia or a diffuse abnormal pancreatic insulin secretion. While focal hyperinsulinism may be reversed by selective surgical resection, diffuse forms require near-total pancreatectomy when resistant to medical treatment. Here, we report the diagnostic value of PET with [¹⁸F]fluoro-L-DOPA in distinguishing focal from diffuse HI. Methods Forty-nine children were studied with [¹⁸F]fluoro-L-DOPA. A thoraco-abdominal scan was acquired 45–65 min after the injection of 4.2 ± 1.0 MBq/kg of [¹⁸F]fluoro-L-DOPA. Additionally, 12 of the 49 children were submitted to pancreatic venous catheterisation for blood samples (PVS) and 31 were also investigated using MRI. Results We identified abnormal focal pancreatic uptake of [¹⁸F]fluoro-L-DOPA in 15 children, whereas diffuse radiotracer uptake was observed in the pancreatic area in the other 34 patients. In children studied with both PET and PVS, the results were concordant in 11/12 cases. All patients with focal radiotracer uptake and nine of the patients with diffuse pancreatic radiotracer accumulation, unresponsive to medical treatment, were submitted to surgery. In 21 of these 24 patients, the histopathological results confirmed the PET findings. In focal forms, selective surgery was followed by clinical remission without carbohydrate intolerance. Conclusion These data demonstrate that PET with [¹⁸F]fluoro-L-DOPA is an accurate non-invasive technique allowing differential diagnosis between focal and diffuse forms of HI.     

Diagnosis of maxillofacial tumor withl-3-[18F]-fluoro-α-methyltyrosine (FMT) PET: a comparative study with FDG-PET

OBJECTIVES: To compare L-3-[18F]-fluoro-a-methyltyrosine (FMT)-positron emission tomography (PET) and 2-[18F]-fluoro-2-deoxy-D-glucose (FDG)-PET in the differential diagnosis of maxillofacial tumors. METHODS: This study included 36 patients (16 males, 20 females; 31-90 years old) with untreated malignant tumors (34 squamous cell carcinoma, one mucoepidermoid carcinoma, one rhabdomyosarcoma) and seven patients (five males, two females; 32-81 years old) with benign lesions. In all patients, both FMT-PET and FDG-PET were performed within two weeks before biopsy or treatment of the lesions. To evaluate the diagnostic usefulness of FMT-PET and FDG-PET, visual interpretation and semiquantitative analysis were performed. PET images were rated according to the contrast of tumor uptake as compared with background, and were statistically analyzed. As a semiquantitative analysis, standardized uptake values (SUV) of the primary tumors were measured, and the SUV data were analyzed using receiver operating characteristic (ROC) curves. Results: The mean SUV of the malignant lesions were significantly higher than those of the benign lesions in both FMT-PET (2.62 +/- 1.58 vs. 1.20 +/- 0.30, p < 0.01) and FDG-PET (9.17 +/- 5.06 vs. 3.14 +/- 1.34, p < 0.01). A positive correlation (r = 0.567, p < 0.0001, n = 46) was noted between FMT and FDG. ROC analysis revealed that there was no statistically significant difference in SUVs between FMT and FDG for differentiating malignant tumors. In 27 of 36 patients, FMT-PET had better contrast of malignant tumor visualization to the surrounding normal structures by visual assessment (p < 0.005, binomial proportion test). CONCLUSIONS: Differential diagnosis of FMT-PET based on the uptake in maxillofacial tumors is equivalent to FDG-PET. However, the contrast of FMT uptake between maxillofacial tumors and the surrounding normal structures is higher than that of FDG, indicating the possibility of accurate diagnosis of maxillofacial tumors by FMT-PET.     

High- and moderately high-methionine uptake demonstrated by PET in a patient with a subacute cerebral infarction

In patients with cerebral tumors, high accumulations of L-methyl-11C-methionine (11C-Met) have been reported in some cases of cerebral ischemic disease, but no high accumulations of 11C-Met in areas where only transient arterial occlusions are most likely to occur have been reported. Herein we present a case of a high accumulation of 11C-Met in an area of frontal interhemispheric cerebral infarction and a moderately high accumulation with an unclear margin in a distant frontal convexity area. A craniotomy revealed a subacute stage of cerebral infarction in the interhemispheric lesion, and an ischemic change in the distant convexity area. Sixteen months after onset, CT scans demonstrated an infarction area in the interhemispheric lesion only, and no atrophic changes were observed in the distant convexity area indicating that no serious tissue damage had occurred.     

The Bücherer-Strecker synthesis of d- and l-(1-11C)tyrosine and the in vivo study of l-(1-11C)tyrosine in human brain using positron emission tomography

The synthesis of d-and l-(1-¹¹C)tyrosine, starting with ¹¹C-cyanide, is reported. dl-(1-¹¹C)Tyrosine was prepared by the Bücherer-Strecker reaction, from carrier added ¹¹C-cyanide with an incorporation of 80% in 20 min. The isolation of the pure d- and l-amino acid isomers from the enantiomeric mixture was accomplished within 15 min by preparative HPLC using a chiral stationary phase and a phosphate buffer as the mobile phase. Typically, the total synthesis time was 50 min (including purification) from end of trapping of ¹¹C-cyanide, with a radiochemical yield of d- and l-amino acid of 40%–60%. The d- and l-(1-¹¹C)tyrosine were both obtained optically pure, with a carrier added specific activity of 0.3–0.5 Ci/mmol and a radiochemical purity better than 99%. The ¹¹C labelled l-tyrosine was used in an in vivo study in the human brain using positron emission tomography (PET).     

Yttrium-90 and indium-111 labelling, receptor binding and biodistribution of [DOTA0,d-Phe1,Tyr3]octreotide, a promising somatostatin analogue for radionuclide therapy

In vitro octreotide receptor binding of [¹¹¹In-DOTA⁰,d-Phe¹,Tyr³]octreotide (¹¹¹In-DOTATOC) and the in vivo metabolism of⁹⁰Y or¹¹¹In-labelled DOTATOC were investigated in rats in comparison with [¹¹¹In-DTPA⁰]octreotide [¹¹¹In-DTPAOC).¹¹¹In-DOTATOC was found to have an affinity similar to octreotide itself for the octreotide receptor in rat cerebral cortex microsomes. Twenty-four hours after injection of⁹⁰Y or¹¹¹In-labelled DOTATOC, uptake of radioactivity in the octreotide receptor-expressing tissues pancreas, pituitary, adrenals and tumour was a factor of 2–6 that after injection of¹¹¹In-DTPAOC. Uptake of labelled DOTATOC in pituitary, pancreas, adrenals and tumour was almost completely blocked by pretreatment with 0.5 mg unlabelled octreotide, indicating specific binding to the octreotide receptors. These findings strongly indicate that⁹⁰Y-DOTATOC is a promising radiopharmaceutical for radiotherapy and that¹¹¹In-DOTATOC is of potential value for diagnosis of patients with octreotide receptor-positive lesions, such as most neuroendocrine tumours.     

Repair of type-2 SLAP lesions using Corkscrew anchors

The aim of the study was to perform a clinical assessment of patients who had undergone arthroscopic repair of a type-2 SLAP lesion using one double-looped Corkscrew anchor. Fifteen consecutive patients who agreed to fill in a pre- and post-operative questionnaire were included in the study. The aetiology was traumatic in 10/15 patients and non-traumatic in 5/15. At the index operation four patients underwent a concomitant acromioplasty, while four patients underwent supplementary anterior labrum fixation using suture anchors. Thirteen/15 (87%) of the patients were physically re-examined by independent observers after a follow-up period of 25 months (11–32). The questionnaire involved a patient-administered assessment of ten common activities of daily living. At follow-up, the Rowe score was 84 points (51–98) and the Constant score was 83 points (35–100). The external rotation in abduction was 85° (60–110) on the operated side and 90° (80–110) on the non-operated side (p<0.05). The isometric strength in abduction was 8.3 kg (0.8–14.4) on the operated side and 8.9 kg (2.7–15.5) on the non-operated side (p=0.006). Significant improvements (p<0.05) compared with the pre-operative assessments were found in 2/10 activities of daily living. Another 4/10 activities seemed to improve but did not reach statistical significance (p<0.08). Eleven of 15 patients returned to their pre-injury activity level. In conclusion, the majority of patients returned to their pre-injury activity level and the subjective patient-administered evaluations appeared to improve after arthroscopic repair of type-2 SLAP lesions using one double-looped Corkscrew anchor. We feel encouraged to continue using this technique.     

DOTATOC: A powerful new tool for receptor-mediated radionuclide therapy

This study presents the first successful use of a peptidic vector, DOTATOC, labelled with the -emitting radioisotope yttrium-90, for the treatment of a patient with somatostatin receptor-positive abdominal metastases of a neuroendocrine carcinoma of unknown localization. Tumour response and symptomatic relief were achieved. In addition, the new substance DOTA-TOC was labelled with the diagnostic chemical analogue indium-111 and studied in three patients with histopathologically verified neuroendocrine abdominal tumours for its diagnostic sensitivity and compared with the commercially available OctreoScan. In all patients the kidney-to-tumour uptake ratio (in counts per pixel) was on average 1.9-fold lower with¹¹¹In-DOTATOC than with OctreoScan. DOTATOC could be a potential new diagnostic and therapeutic agent in the management of neuroendocrine tumours.     

Uptake kinetics and biodistribution of <Superscript>14</Superscript>C-<Emphasis Type="SmallCaps">d</Emphasis>-luciferin—a radiolabeled substrate for the firefly luciferase catalyzed bioluminescence reaction: impact on bioluminescence based reporter gene imaging

Purpose  Firefly luciferase catalyzes the oxidative decarboxylation of d-luciferin to oxyluciferin in the presence of cofactors, producing bioluminescence. This reaction is used in optical bioluminescence-based molecular imaging approaches to detect the expression of the firefly luciferase reporter gene. Biokinetics and distribution of the substrate most likely have a significant impact on levels of light signal and therefore need to be investigated. Methods  Benzene ring ¹⁴C(U)-labeled d-luciferin was utilized. Cell uptake and efflux assays, murine biodistribution, autoradiography and CCD-camera based optical bioluminescence imaging were carried out to examine the in vitro and in vivo characteristics of the tracer in cell culture and in living mice respectively. Results  Radiolabeled and unlabeled d-luciferin revealed comparable levels of light emission when incubated with equivalent amounts of the firefly luciferase enzyme. Cell uptake assays in pCMV-luciferase-transfected cells showed slow trapping of the tracer and relatively low uptake values (up to 22.9-fold higher in firefly luciferase gene-transfected vs. nontransfected cells, p = 0.0002). Biodistribution studies in living mice after tail-vein injection of ¹⁴C-d-luciferin demonstrated inhomogeneous tracer distribution with early predominant high radioactivity levels in kidneys (10.6% injected dose [ID]/g) and liver (11.9% ID/g), followed at later time points by the bladder (up to 81.3% ID/g) and small intestine (6.5% ID/g), reflecting the elimination routes of the tracer. Kinetics and uptake levels profoundly differed when using alternate injection routes (intravenous versus intraperitoneal). No clear trapping of ¹⁴C-d-luciferin in firefly luciferase-expressing tissues could be observed in vivo. Conclusions  The data obtained with ¹⁴C-d-luciferin provide insights into the dynamics of d-luciferin cell uptake, intracellular accumulation, and efflux. Results of the biodistribution and autoradiographic studies should be useful for optimizing and adapting optical imaging protocols to specific experimental settings when utilizing the firefly luciferase and d-luciferin system. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Experimental studies on myocardial glucose metabolism of rats with 18F-2-fluoro-2-deoxy-d-glucose

The myocardial uptake of ¹⁸F-FDG was investigated under various conditions, and compared with brain and tumor uptake as a function of blood glucose level. The uptake by the heart of normal feeding rats was rapid and remained essentially unchanged up to 2 h after ¹⁸F-FDG injection, approximately 3%–4% dose/g tissue. On the other hand, the myocardial uptake of fasted rats was significantly lower than that of control rats throughout the course of the study, and it was about 0.3%–0.4% dose/g tissue. Myocardial uptake of ¹⁸F-FDG was relatively constant at glucose levels under about 120 mg/100 ml and increased steeply at higher blood glucose levels. In contrast, brain uptake decreased linearly with increasing levels of blood glucose, revealing a strong negative correlation between brain uptake of ¹⁸F-FDG and blood glucose levels. The tumor uptake pattern remained relatively unchanged, irrespective of blood glucose levels. It was revealed that the glucose demands of brain, heart, and tumor were entirely different. After a glucose load, the myocardial uptake of fasted rats increased only slightly from 0.4% to 0.6% dose/g tissue, in spite of transitional hyperglycemia. In contrast, insulin caused myocardial uptake to increase extraordinarily, although it caused a decrease in blood glucose levels.     

FDG-PET imaging in HIV-infected subjects: relation with therapy and immunovirological variables

Purpose

To characterise tissue sites of immune activation and HIV replication we performed FDG-PET in ART-treated and ART-naive HIV-infected individuals. Specific aims were to establish whether HIV-infected patients can be differentiated on the basis of the detection of specific locations of viral replication, even in the presence of an apparently optimal immunovirological response to ART, and whether these FDG-PET findings can be related to immunovirological variables and AIDS history status.

Patients and methods

Patients were divided into five groups as follows: subgroup A1 (full responders, n?=?8): current ART treatment, CD4+ T lymphocytes >500/mL, viral load <50 copies/mL; subgroup A2 (full responders, n?=?5): same criteria as A-1, but with a previous history of AIDS; subgroup A3 (immunological non responders, n?=?5): current ART treatment, viral load <50 copies/mL, low CD4+ T lymphocytes (<200/mL); group B (virological non responders, n?=?2): current ART treatment, CD4+ T lymphocytes around 500/mL, viral load >50,000 copies/mL; group C (ART-naïve, n?=?5): no current or previous ART treatment, increased viral load.

Results

PET images revealed different patterns of FDG uptake. All ART-treated patients with either suppressed (<50 copies/mL; Group A) or high viremia (group B) showed a normal pattern of FDG uptake. On the contrary, the ART-naïve subjects with high viraemia (group C) displayed multiple foci of increased glucose metabolism in the lymph nodes. In the ART-naïve subjects, FDG uptake, apparently related to viraemia level, was observed in the upper torso mainly in the axillary nodes bilaterally in patients with viraemia below 100,000 copies/mL; in those with viraemia higher than 100,000 copies/mL, FDG uptake was also observed in the inguinal lymph nodes.

Conclusions

The emergence, in our study, of a correlation between the percentage of CD8+/CD38+/RO+ T cells (well established markers of progression to AIDS independently of CD4+ T lymphocytes) and positive FDG-PET in ART-naive patients is a novel finding that seems to confer prognostic value on FDG uptake. FDG uptake is strongly associated with response to ART independently of a previous AIDS diagnosis. Notably, no differences were observed between ART-treated subjects classed as immunological responders and those classed as non responders. Data herewith indicate that FDG uptake and immunological variables are unrelated when ART is being administered. This is evidence of the complementarity of immunological and FDG measures. FDG uptake is a sensitive marker of disease state and its relation with CD8+/CD38+/CD45RO+ T cells indicates that it can be considered a marker of disease status. The lack of a correlation between FDG uptake and immunological variables in patients under ART warrants further investigation.