Single-photon emission computed tomography and positron-emission tomography assays for tissue oxygenation.

Radiotherapy prescription can now be customized to target the major mechanism(s) of resistance of individual tumors. In that regard, functional imaging techniques should be exploited to identify the dominant mechanism(s). Tumor biology research has identified several mechanisms of tumor resistance that may be unique to radiation treatments. These fall into 3 broad areas associated with (1) tumor hypoxic fraction, (2) tumor growth rate, (3) and the intrinsic radiosensitivity of tumor clonogens. Imaging research has markers in various stages of development for quantifying relevant information about each of these mechanisms, and those that measure tumor oxygenation and predict for radioresistance are the most advanced. Positron-emission tomography (PET) measurement of oxygen 15 has yielded important information, particularly about brain tissue perfusion, metabolism, and function. Indirect markers of tumor hypoxia have exploited the covalent binding of bioreductive intermediates of azomycin-containing compounds whose uptakes are inversely proportional to intracellular oxygen concentrations. Pilot clinical studies with single-photon emission computed tomography (SPECT) and PET detection of radiolabeled markers to tumor hypoxia have been reported. Recently, other studies have attempted to exploit the reduction properties of both technetium and copper chelates for the selective deposition of radioactive metals in hypoxic tissues. A growing number of potentially useful isotopes are now available for labeling several novel chemicals that could have the appropriate specificity and sensitivity. Preclinical studies with "microSPECT" and "microPET" will be important to define the optimal radiodiagnostic(s) for measuring tissue oxygenation and for determining the time after their administration for optimal hypoxic signal acquisition. Radiolabeled markers of growth kinetics and intrinsic radiosensitivity of cells in solid tumors are also being developed. We conclude that radiation oncology is uniquely positioned to benefit from functional imaging markers that identify important mechanisms of tumor radioresistance, since several strategies for overcoming these individual mechanisms have already been identified.

Defining a future role for radiogenic therapy.

The goal of cancer therapy is to eliminate the cancer and/or to arrest further growth while decreasing normal tissue toxicity, i.e. to increase the therapeutic ratio. This review focuses on a group of therapeutics that are either (1) directly stimulated by radiation to produce either directly or indirectly cytotoxic agents (i.e. genes under the control of a radiation inducible promoter that produce a cytotoxic protein or an enzyme that converts a prodrug to an active form, respectively); (2) auger-electron emitting radiolabelled oligonucleotides, antibodies, nucleotide analogues, or other small molecules that are internalized; (3) radiation inducible genes that produce a ligand or transporter (or the like) which then can be targeted by cytotoxic agents (e.g. radiolabelled substance). We have termed this group of therapeutics radiogenic therapy.

Quantitation of regional ventilation during the washout phase of lung scintigraphy: measurement in patients with severe COPD before and after bilateral lung volume reduction surgery.

STUDY OBJECTIVES: We sought to investigate the effect of lung volume reduction surgery (LVRS) on regional lung ventilation. DESIGN: Retrospective analysis of routinely acquired data before and after LVRS. SETTING: Large, urban, university medical center. PATIENTS: Twenty-nine patients with severe emphysema. INTERVENTION: Bilateral LVRS. MEASUREMENTS AND RESULTS: (133)Xe washout curves during lung scintigraphy exhibit a biphasic pattern (the first component of the washout curve [m(r)] corresponds to an initial rapid phase in washout that reflects larger airways emptying, and the second component [m(s)] reflects a slower phase of washout that is attributed to gas elimination via smaller airways). We analyzed six standardized regions of the lung (upper, mid, and lower zones of the right and left lung), and calculated m(r) and m(s) for each lung region. The mean (+/- SE) baseline FEV(1) was 0.69+/-0.04 L, total lung capacity (TLC) was 139 +/-4% predicted, and the residual volume (RV)/TLC ratio was 65+/-2%. The mean improvement in FEV(1) 3 months post-LVRS was 38%. Post-LVRS, m(r) and m(s) increased in 79 and 74 lung regions, respectively, and there was no relationship with respect to lung regions that had or had not been operated on. The increase in m(s), however, significantly correlated with the increase in FEV(1) (r = 0.66; p<0.0001) and the decrease in RV/TLC (r = -0.67; p<0.0001). An increase in m(s) also correlated with a decrease in PaCO(2) (r = -0.39; p = 0.03), but m(r) showed no relationship with any parameter. CONCLUSIONS: Small airways ventilation in lung regions that had and had not been operated on is associated with a greater improvement in lung mechanics following LVRS.

Oncogenes, cancer and imaging.

At the dawn of the 21st century, nuclear oncology is undergoing a formidable and rapid mutagenesis. The progress in radiochemistry, radiopharmacy and, foremost, the advances in molecular oncology are the determinant mutagenic factors. Mutation, amplification, deletion or translocation of deoxyribonucleic acid segments in proto-oncogenes and tumor suppressor genes also called anti-oncogenes account for the uncontrolled cell growth and proliferation resulting in cancer. The astonishing developments in peptide and nucleic acid chemistry have opened the door for the development of new, highly specific probes such as antisense, aptamer and peptidomimetic molecules to image the oncogenes and anti-oncogenes transcriptional (messenger ribonucleic acid) and translational (protein) products involved in carcinogenesis. In this article, I shall review the basic molecular mechanisms of carcinogenesis and describe the molecular probes that are currently being developed.

In vitro measurement of beta-lactamase-catalyzed ampicillin hydrolysis by recombinant Escherichia coli extracts using quantitative high-performance liquid chromatography.

We report a rapid and simple protocol for measuring the beta-lactamase activity from recombinant Escherichia coli cells transformed with any of the common plasmid vectors that provide ampicillin resistance through constitutive expression and periplasmic localization of the beta-lactamase TEM-1. The hydrolytic enzyme was extracted from the E. coli periplasm and the beta-lactamase activity determined by measuring conversion of ampicillin to aminobenzyl-penicilloic acid using quantitative high-performance liquid chromatography. Under saturating conditions the in vitro assay was linear as a function of both incubation time and enzyme concentration. Application of this assay to investigate TEM-1 expression, from two different protein expression vector systems, demonstrated the potential importance of this assay in studies of recombinant protein expression and translocation.

Effects of in vitro versus in vivo red cell labeling on image quality in gastrointestinal bleeding studies.

OBJECTIVE: Both in vivo and in vitro red cell labeling methods are available for performing gastrointestinal bleeding studies. While in vitro labeling has been shown to result in higher binding efficiency, no comparison of clinical image quality has been reported between those techniques. This study compares in vivo and in vitro methods using both subjective and objective measurements of image quality. METHODS: A consecutive series of gastrointestinal bleeding studies performed on 23 patients using in vivo labeling was compared to a series of 23 studies using in vitro labeling. Images at 30 min postinjection were randomized and analyzed by two observers. Subjective evaluation of image quality, as well as renal activity, was based on a comparison of femoral vein and inferior vena cava activity to adjacent background using numerical scores with a scale of 0-3. Image quality using the subjective scores was further classified as acceptable and poor. Target-to-background measurements of femoral vein to adjacent soft tissue in the thigh and inferior vena cava to adjacent abdominal background also were made. RESULTS: In vitro label subjective image quality was acceptable in 87% and 91% of cases for vascular and renal activity, respectively, but only 35% and 52% for in vivo labeling. In vitro label target-to-background ratios were significantly better than in vivo label for the femoral vein and inferior vena cava, as well as for the subjective assessment of vascular image quality, but not for renal activity. CONCLUSION: In vitro red cell labeling improves clinical image quality as compared with in vivo labeling. Both subjective and objective measurements of image quality are useful for comparing the results of labeling methods.

Effect of gastric acid suppressants on human gastric motility.

BACKGROUND: The effect of histamine H2 receptor antagonists on gastric emptying is controversial. AIMS: To determine the effects of ranitidine, famotidine, and omeprazole on gastric motility and emptying. PATIENTS AND METHODS: Fifteen normal subjects underwent simultaneous antroduodenal manometry, electrogastrography (EGG), and gastric emptying with dynamic antral scintigraphy (DAS). After 30 minutes of fasting manometry and EGG recording, subjects received either intravenous saline, ranitidine, or famotidine, followed by another 30 minutes recording and then three hours of postprandial recording after ingestion of a radiolabelled meal. Images were obtained every 10-15 minutes for three hours to measure gastric emptying and assess antral contractility. Similar testing was performed after omeprazole 20 mg daily for one week. RESULTS: Fasting antral phase III migrating motor complexes (MMCs) were more common after ranitidine (9/15 subjects, 60%), famotidine (12/15, 80%), and omeprazole (8/12, 67%) compared with placebo (4/14, 29%; p < 0.05). Postprandially, ranitidine, famotidine, and omeprazole slowed gastric emptying, increased the amplitude of DAS contractions, increased the EGG power, and increased the antral manometric motility index. CONCLUSIONS: Suppression of gastric acid secretion with therapeutic doses of gastric acid suppressants is associated with delayed gastric emptying but increased antral motility.

Electrogastrography and gastric emptying scintigraphy are complementary for assessment of dyspepsia.

We have tried to correlate abnormalities in electrogastrography (EGG) and gastric emptying (GE) with symptom severity in patients with functional dyspepsia. Seventy-two patients with functional dyspepsia underwent EGG, GE, and symptom severity quantitation. EGGs were assessed for dominant frequency (DF), percentage of time of DF in the 2 to 4 cpm range, and postprandial-fasting DF power ratio. Solid-phase GE scintigraphy was assessed for 2-hour percentage retention. Symptoms of upper abdominal discomfort, early satiety, postprandial abdominal distension, nausea, vomiting, and anorexia were graded as none (0), mild (1), moderate (2), and severe (3); the sum represented a total symptom score. The EGG was abnormal in 11 of 22 (50%) patients with delayed GE compared with 11 of 50 (22%) with normal GE (p < 0.025). The total symptom scores were higher in patients with both delayed GE and abnormal EGG compared with patients with normal GE and EGG, normal GE and abnormal EGG, and delayed GE and normal EGG. We conclude that EGG abnormalities are more common in dyspeptic patients with delayed GE. Patients with both delayed GE and abnormal EGG have more severe symptoms. Our results suggest that EGG and GE complement each other in correlating symptoms to gastric dysmotility.

Regional differences in gastric acidity and antacid distribution: is a single pH electrode sufficient?

UNLABELLED: Accurate measurement of intragastric acidity has both clinical and investigational importance in studying gastric pathophysiology. OBJECTIVES: The aims of this study were fourfold: (1) to investigate whether regional differences in intragastric acidity exist; (2) to determine intragastric acidity after a standard antacid was administered in both the fasting and fed states; (3) to monitor gastric emptying of and anatomic distribution of radiolabeled antacid during fasting and postprandial periods; and (4) to determine whether the regional effects of ingested antacid correlated with the anatomic distribution of the antacid. METHODS: Eight normal male volunteers were studied after fluoroscopically guided nasogastric placement of a tube assembly containing four pH electrodes, with one electrode in each quartile of the stomach. Simultaneous pH readings were made from the four electrodes while fasting, after administration of fasting antacid (30 ml, 79 mEq buffering capacity), postprandially, and after postprandial antacid ingestion. All subjects repeated the protocol on a separate day, five of them using radiolabeled antacid. Gastric emptying and gastric distribution over time of radiolabeled antacid were determined for comparison to regional intragastric acidity. RESULTS: Intragastric acidity varied regionally over time in response to meals and to fasting and postprandial antacid. In the fasting state, intragastric acidity returned to baseline after antacid ingestion in a proximal to distal (cardia to antrum) sequence, while postprandial antacid resulted in a return to baseline acidity in a distal to proximal (antrum to cardia) sequence. Radiolabeled antacid distribution paralleled intragastric pH and hydrogen ion concentration in the fasting state, with 82% of the antacid localizing in the distal half of the stomach within the first minute after antacid ingestion. Postprandially, the greatest initial and most prolonged antacid buffering effect occurred proximally, correlating with the presence of radiolabeled antacid. Postprandial antacid remained in the stomach for a longer time (T1/2 = 93.1 +/- 23.4 min) compared with fasting antacid (T1/2 = 23.6 +/- 11.1 min). CONCLUSIONS: Measurement of acidity in the four quartiles of the stomach demonstrated regional variation in response to both food and a standard antacid. A single pH electrode does not detect regional intragastric pH differences.

Comparison of scintigraphy and lactulose breath hydrogen test for assessment of orocecal transit: lactulose accelerates small bowel transit.

UNLABELLED: The lactulose breath test (LBT) and gastroenterocolonic scintigraphy (GECS) can both be used to measure orocecal transit time (OCTT). The aims of this study were (1) to measure OCTT by LBT and GECS and (2) to determine whether lactulose alters orocecal transit. METHODS: Eight normal subjects underwent simultaneous breath hydrogen testing, GECS, and duodenal manometry while receiving either 10 g lactulose or placebo with a radiolabeled solid/liquid test meal during two studies. There was a good correlation between OCTT by LBT and GECS when performed simultaneously (r = 0.95; P < 0.001). OCTT by GECS with lactulose was significantly faster (P = 0.004) than by GECS without lactulose, despite no change in gastric emptying of liquids and slowing of gastric emptying of solids (P = 0.02). The postprandial duodenal motility index was greater with lactulose than with placebo (P = 0.031). This study demonstrates that LBT and GECS (without lactulose) are not equivalent measures of OCTT. The standard LBT accelerates OCTT and slows gastric emptying. Therefore, lactulose has a direct accelerating effect on small intestinal transit.

Nuclear oncology and the Imagene concept.

Over the past 2 decades we have witnessed an explosion of new radioisotopic tracers aimed at detecting, staging and eventually treating tumors. In fact, nuclear oncology has evolved into a field on its own. Aside from aspecific radioisotopic tracers such as thallium 201 or gallium 67, clinicians and oncologists can now use specific radiolabeled monoclonal antibodies and metabolic tracers. In the near future, molecular probes based on the sequencing of the human genome with an exquisite specificity should also become available. In this article, we shall review the most recent developments in this new field.

Evidence for a circadian rhythm of insulin secretion.

Insulin secretion was studied in healthy volunteers at three different levels of glycemia. Plasma glucose was clamped at approximately 5, approximately 8.8 and approximately 12.6 mM for 68 h. Measured were serum insulin concentration and insulin secretion rates (ISR), the latter by deconvolution of plasma C-peptide concentration. Rhythmic patterns of ISR were identified (with a refined first-order Fourier transform) at all three glucose concentrations tested but were most clearly seen at 12.6 mM. ISR and serum insulin concentration changed in a circadian (approximately 24 h) rhythm, increasing from a nadir between midnight and 6 A.M. and reaching a peak between noon and 6 P.M. At 12.6 mM hyperglycemia, the amplitude of the insulin concentration cycles was greater than that of the ISR cycles (+/- 13.0 vs. +/- 8.7%) due to a decrease in insulin clearance (from 1.55 to 0.5 l/min, P < 0.01). Plasma melatonin levels (a marker of light-dark rhythmicity) changed in the opposite direction, i.e., they peaked when ISR bottomed and bottomed when ISR peaked. We concluded that normal human subjects have a circadian rhythm of insulin secretion, which becomes more apparent with rising ISR, and that circadian changes in ISR, rising during the day and falling during the night, may be one explanation for the well-established observation that glucose tolerance and insulin responses to glucose and meals are higher in the morning than at night.

Evidence for a circadian rhythm of insulin sensitivity in patients with NIDDM caused by cyclic changes in hepatic glucose production.

Diurnal variation in insulin sensitivity in patients with NIDDM has long been suspected but has been difficult to document mainly because of the interdependence of changes in glucose and insulin. Stable serum insulin levels during hyperglycemic clamping in patients with NIDDM in the present study provided the opportunity to examine changes in insulin sensitivity unaffected by changes in blood glucose and insulin concentrations. Six patients with NIDDM (four men and two women, BMI 33.9 +/- 2.5) underwent hyperglycemic (11.1 mmol/l, approximately 200 mg/dl) clamping for 72 h. Measured were serum insulin, free fatty acid (FFA), cortisol, and growth hormone concentrations and rates of insulin secretion, insulin clearance, and glucose infusion rate (GIR) needed to maintain hyperglycemia. In addition, five patients (three men and two women, BMI 32.6 +/- 0.6) underwent hyperglycemic clamping for 24 h with hourly determinations of hepatic glucose production (HGP) and glucose disappearance rates (GRd). GIR, reflecting insulin sensitivity, changed rhythmically with a cycle duration of 22.9 +/- 1.4 h and an amplitude of 47.8 +/- 11.2%. GIR was lowest at 8:31 a.m. (+/- 52 min) and highest at 7:04 p.m. (+/- 58 min). Circadian changes in GIR were completely accounted for by changes in HGP, while GRd remained unchanged. Plasma levels of FFAs and cortisol also exhibited circadian fluctuations, and their blood levels correlated negatively with GIR (r = -0.72 and -0.64, respectively). We concluded that insulin sensitivity in patients with NIDDM changed with circadian (approximately 24 h) rhythmicity (decreasing during the night and increasing during the day). These changes were unrelated to blood levels of glucose and insulin, insulin clearance, exercise, food intake, and sleep. They were caused by circadian changes in HGP, which in turn were closely correlated with circadian changes in blood FFA and cortisol levels. We believe that recognition of these circadian changes has implications for the diagnosis and the treatment of patients with NIDDM.

Recent advances in gastric emptying scintigraphy.

Gastric emptying scintigraphy was introduced more than 25 years ago by Griffith and still remains the gold standard to assess gastric emptying. Test meals, radiopharmaceutical and acquisition procedures have been refined and optimized over the years and the test procedure is now well standardized. However, in its most common use, gastric emptying scintigraphy provides little information on gastric physiology and pathophysiology. Over the last decade, modeling of the liquid- and solid-emptying curves has provided some insight into the complex gastric physiology. Compartmental analysis of the stomach has also provided information on the pathophysiological mechanisms of delayed gastric emptying. Over the past 5 years, the most dramatic development in gastric emptying scintigraphy has been the introduction of digital antral scintigraphy. Digital antral scintigraphy consists primarily of dynamic imaging of the stomach and a refined Fourier transform processing method. This new procedure allows for the visualization of antral contractions and, like manometry, permits quantitative characterization of the frequency and amplitude of these contractions. Overall, this new procedure provides a unique, noninvasive tool to characterize gastric motility, to define the pathophysiological mechanisms of gastric motor disorders, and to evaluate the effect of new gastrokinetic compounds.

Dynamic antral scintigraphy to characterize gastric antral motility in functional dyspepsia.

UNLABELLED: We evaluated intragastric food distribution and antral motor activity in patients with functional dyspepsia. METHODS: A standard gastric emptying test and dynamic imaging of the antrum were used to characterize gastric antral motility disturbances and to correlate them with total and compartmental gastric emptying in 25 dyspeptic patients. RESULTS: We found a 40% prevalence of gastroparesis in functional dyspepsia. Solid gastric emptying delay is indicated by a prolonged lag phase and an increase in frequency and amplitude of gastric contractions, resulting in nonexpulsive antral contractions and/or antropyloric dyscoordination. Food retention in the distal stomach and antral distention appears to account for patients' dyspeptic symptoms. CONCLUSION: This study demonstrates that scintigraphy not only detects abnormalities of food distribution in the stomach but also provides information on antral motor activity noninvasively. Dynamic antral scintigraphy and compartmental gastric emptying are useful tools to define the pathophysiology of dyspeptic patients with or without gastroparesis.

Scintigraphic imaging of oncogenes with antisense probes: does it make sense?

Based on the specificity of the Watson-Crick base pairing formation, antisense deoxyoligonucleotides have been used to inhibit the expression of oncogenes in various cancer cells. Activation of an oncogene by means of amplification leads to an increased, detectable amount of the mRNA transcript in the cytoplasm. The aim of this study was to demonstrate that cells which are expressing a particular mRNA transcript do preferentially and specifically retain the antisense probe targeting that mRNA. Using a mouse plasmacytoma cell line (MOPC315) which produces high levels of IgA heavy chain mRNA, a control mouse pre B cell line (7OZ/3B), a human mammary cell line (MCF7) which expresses the erbB2 or neu oncogene, MOPC315 cells as neu-negative controls, and antisense DNA oligonucleotides complementary to the 5' region of the mRNAs and the sense sequence, we have shown that there is a preferential, specific retention of the IgA and neu antisense sequence in MOPC315 and MCF7 cells, respectively. We have further demonstrated that this retention is time and concentration dependent with a maximum at 24 h. We conclude that cancer cells which express a particular oncogene are suitable targets for radiolabeled antisense deoxyoligonucleotides directed toward the oncogene transcript. This work and recent developments in the antisense field lead to the expectation of a new class of radiopharmaceuticals with unique specificity.