A Radiolabeled Self-assembled Nanoparticle Probe for Diagnosis of Lung-Metastatic Melanoma.

Melanoma is a highly malignant skin cancer that frequently metastasizes to the lung, bone, and brain at an early phase. Therefore, noninvasive detection of metastasized melanoma could be beneficial to determine suitable therapeutic strategies. We previously reported a biocompatible ternary anionic complex composed of plasmid DNA (pDNA), polyethyleneimine (PEI), and γ-polyglutamic acid (γ-PGA) based on an electrostatic interaction, which was highly taken up by melanoma cells (B16-F10), even if it was negatively charged. Here, we developed a radiolabeled γ-PGA complex by using indium-111 (111In)-labeled polyamidoamine dendrimer (4th generation; G4) instead of pDNA and iodine-125 (125I)-labeled PEI instead of native PEI, and evaluated its effectiveness as a melanoma-targeted imaging probe. This ternary complex was synthesized at a theoretical charge ratio; carboxyl groups of 111In-diethylenetriaminepentaacetic acid (DTPA)-G4 : amino groups of 125I-PEI : carboxyl groups of γ-PGA was 1 : 8 : 16, and the size and zeta potential were approximately 29 nm and -33 mV, respectively. This complex was taken up by B16-F10 cells with time. Furthermore, a biodistribution study, using normal mice, demonstrated its accumulation in the liver, spleen, and lung, where macrophage cells are abundant. Almost the same level of radioactivity derived from both 111In and 125I was observed in these organs at an early phase after probe injection. Compared with the normal mice, significantly higher lung-to-blood ratios of radioactivity were observed in the B16-F10-lung metastatic cancer model. In conclusion, the radiolabeled γ-PGA complex would hold potentialities for nuclear medical imaging of lung metastatic melanoma.

Bismuth chelate as a contrast agent for X-ray computed tomography.

BACKGROUNDS: Due to the unexpected side effects of the iodinated contrast agents, novel contrast agents for X-ray computed tomography (CT) imaging are urgently needed. Nanoparticles made by heavy metal elements are often employed, such as gold and bismuth. These nanoparticles have the advantages of long in vivo circulation time and tumor targeted ability. However, due to the long residence time in vivo, these nanoparticles may bring unexpected toxicity and, the preparation methods of these nanoparticles are complicated and time-consuming. METHODS: In this investigation, a small molecular bismuth chelate using diethylenetriaminepentaacetic acid (DPTA) as the chelating agent was proposed to be an ideal CT contrast agent. RESULTS: The preparation method is easy and cost-effective. Moreover, the bismuth agent show better CT imaging for kidney than iohexol in the aspect of improved CT values. Up to 500 µM, the bismuth agent show negligible toxicity to L02 cells and negligible hemolysis. And, the bismuth agent did not induce detectable morphology changes to the main organs of the mice after intravenously repeated administration at a high dose of 250 mg/kg. The pharmacokinetics of the bismuth agent follows the first-order elimination kinetics and, it has a short half-life time of 0.602 h. The rapid clearance from the body promised its excellent biocompatibility. CONCLUSIONS: This bismuth agent may serve as a potential candidate for developing novel contrast agent for CT imaging in clinical applications.

COMPARATIVE RENAL DISPOSITION OF CREATINE, AND TECHNETIUM DIAGNOSTIC CONTRAST AGENTS IN THE PIGEON (COLUMBA LIVIA).

Clinical assessment of renal function in avian species often involves the measurement of plasma uric acid and blood urea nitrogen, relatively insensitive markers of renal dysfunction and dehydration. In mammals, endogenous creatinine is widely used as an indicator of renal glomerular dysfunction. However, avian species produce primarily creatine. Here, renal creatine, 99mTc99-DTPA (diethylenepentaacetic acid, DTPA) and 99mTc-MAG3 (mercaptoacetyl triglycine, MAG3) renal clearances are characterized in the pigeon avian model by infusing DTPA with inulin and creatine with each tracer and examining the slope of their blood disappearance curves. Clearance curves for inulin and DTPA were parallel, suggesting DTPA is cleared by renal filtration. MAG3 clearance (slope: -2.74 × 105, r2 = 0.97) had a slope almost 10-fold steeper than for DTPA (slope: -6.29 × 104, r2 = 0.90), and orders of magnitude steeper than for creatine (slope: -1.4, r2 = 1.0). These results suggest that DTPA is cleared by glomerular filtration like inulin, while MAG3 is filtered and actively excreted in a manner similar to mammals. In contrast, creatine is filtered and resorbed, has a larger volume of distribution (Vd), or exhibits a greater blood protein binding, making it more complex as a renal marker, when compared with creatinine handling in mammals. The two radiotracers can be readily adapted for use in birds, inviting both qualitative and semiquantitative functional evaluation of avian renal function for research and clinical purposes. The elimination of creatine appears to be more complex requiring further study.

Radiosynthesis, radiochemical, and biological characterization of 177 Lu-labeled diethylenetriamine penta-acetic acid.

Diethylenetriamine penta-acetic acid (DTPA), when complexed with a gamma (γ)-emitter radioisotope like 99m Tc, is used for renal function diagnosis and many other diagnostic applications. The main aim of this study was to develop a novel and versatile single-step methodology for the synthesis of a new 177 Lu-labeled radiopharmaceutical with high radiochemical yield, which can be used for diagnostic purposes and therapeutic purposes also. The single and well-defined 177 Lu-DTPA complex was radiochemically characterized by paper chromatography, thin-layer chromatography, high-performance liquid chromatography, and electrophoresis techniques. Dependence of the labeling yield of 177 Lu-DTPA complex on different factors was studied in detail. Biological evaluation was also performed in a normal rabbit by developing images under a γ camera at various time intervals. More than 99% labeling yield was obtained by reacting DTPA with 177 Lu at specific conditions (pH 7.0, 15 minutes reaction time at 100 °C). 177 Lu-DTPA complex showed high stability both at room temperature and in vitro. Biodistribution studies in normal mice indicated the fractional renal uptake of intravenously administered 177 Lu-DTPA complex, which reached in the kidneys within 2-3 minutes. Scintigraphy showed rapid clearance from the body. Based on these results, we propose that 177 Lu-DTPA complex might be used as an ideal candidate for functional evaluation of kidneys and the urinary tract, especially when needed to be transported to long-range consumer sites, because of its suitable half-life.

A physiologically-motivated model of cystic fibrosis liquid and solute transport dynamics across primary human nasal epithelia.

Cystic fibrosis (CF) disease is caused by mutations affecting the gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR), an anion channel expressed in the mucosal side of epithelial tissue. In the airway, dysfunctional CFTR results in a transepithelial osmotic imbalance leading to hyperabsorption of airway surface liquid mucostasis, chronic inflammation, and eventual respiratory failure. Human nasal epithelial cell cultures from healthy and CF donors were used to perform studies of liquid and solute transport dynamics at an air/liquid interface in order to emulate the in vivo airway. Then, these results were used to inform a quantitative systems pharmacology model of airway epithelium describing electrically and chemically driven transcellular ionic transport, contributions of both convective and diffusive paracellular solute transport, and osmotically driven transepithelial water dynamics. Model predictions showed CF cultures, relative to non-CF ones, have increased apical and basolateral water permeabilities, and increase paracellular permeability and transepithelial chemical driving force for a radiolabeled tracer used to track small molecule absorption. These results provide a computational platform to better understand and probe the mechanisms behind the liquid hyperabsorption and small molecule retention profiles observed in the CF airway.

68Ga labeled fatty acids for cardiac metabolic imaging: Influence of different bifunctional chelators.

Development of 68Ga labeled fatty acids is of immense interest due to the availability of 68Ga through a generator and its superiority over SPECT based tracers in carrying out dynamic imaging on a PET scanner. Our present work explores the influence of different chelators on the cardiac uptake and pharmacokinetics of the 68Ga-labeled fatty acids. Two new 68Ga labeled fatty acids were synthesized by conjugation of 11-aminoundecanoic acid with the bifunctional chelators (BFCs) viz. p-SCN-Bn-DTPA (S-2-(4-isothiocyanatobenzyl)-diethylenetriaminepentaacetic acid) and p-SCN-Bn-NODAGA (S-2-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1-glutaric acid-4,7-acetic acid) and their comparison was carried out with the previously reported 68Ga-NOTA-undecanoic acid. Both the conjugates were radiolabeled with 68Ga in high yields and purities (>95%). Their formation was established by preparation and characterization of their inactive analogs with natGa at macroscopic levels. Biodistribution studies of the complexes in Swiss mice showed lower initial myocardial uptake for 68Ga-NODAGA-undecanoic acid (3.8±0.6%ID/g) and 68Ga-DTPA-undecanoic acid (1.3±0.5%ID/g) complexes in comparison to previously reported 68Ga-NOTA-undecanoic acid complex (7.4±2.8%ID/g) at 2min p.i. However, significant retention of the tracer in the myocardium was observed in the case of 68Ga-NODAGA-undecanoic complex, which led to improved heart/non-target ratios of the complex over time in comparison to the other 68Ga complexes. Similarly, the DTPA complex exhibited increased washout from the liver in comparison to other 68Ga derivatives. The ß oxidation mechanism in myocytes was investigated by isolating the myocardial extract post intravenous injection of the respective 68Ga complexes and analyzing them by radio-HPLC, which showed metabolic transformation of the parent fatty acid complex peak in all the three complexes. This study has provided an insight into the design characteristics of 68Ga labeled fatty acids to achieve the desired myocardial imaging characteristics.

Development and Characterization of the Recombinant Human VEGF-EGF Dual-Targeting Fusion Protein as a Drug Delivery System.

The design, preparation, as well as structural and functional characterizations of the recombinant fusion protein hVEGF-EGF as a dual-functional agent that may target both EGFR (R: receptor) and angiogenesis are reported. hVEGF-EGF was found to bind to EGFR more strongly than did EGF, and to bind to VEGFR similarly to VEGF. Mass spectrometry measurements showed that the sites of DTPA (diethylenetriaminepentaacetic acid) conjugated hVEGF-EGF (for radiolabeling) were the same as those of its parent hEGF and hVEGF proteins. All DTPA-conjugated proteins retained similar binding capacities to their respective receptors as compared to their respective parent proteins. In vitro cell binding studies using BAEC (a bovine aortic endothelial cell) and MDA-MB-231 (a human breast cancer) cells expressing both EGFR and VEGFR confirmed similar results. Treating BAEC cells with hVEGF-EGF induced remarkable phosphorylation of EGFR, VEGFR, and their downstream targets ERK1/2. Nevertheless, the radiolabeled (111)In-DTPA-hVEGF-EGF showed cytotoxicity against MDA-MB-231 cells. Pharmacokinetic studies using (111)In-DTPA-hVEGF-EGF in BALB/c nude mice showed that appreciable tracer activities were accumulated in liver and spleen. In all, this study demonstrated that the fusion protein hVEGF-EGF maintained the biological specificity toward both EGFR and VEGFR and may be a potential candidate as a dual-targeting moiety in developing anticancer drugs.

Metal-Chelating Polymers (MCPs) with Zwitterionic Pendant Groups Complexed to Trastuzumab Exhibit Decreased Liver Accumulation Compared to Polyanionic MCP Immunoconjugates.

Metal-chelating polymers (MCPs) can amplify the radioactivity delivered to cancer cells by monoclonal antibodies or their Fab fragments. We focus on trastuzumab (tmAb), which is used to target cancer cells that overexpress human epidermal growth factor receptor 2 (HER2). We report the synthesis and characterization of a biotin (Bi) end-capped MCP, Bi-PAm(DET-DTPA)36, a polyacrylamide with diethylenetriaminepentaacetic acid (DTPA) groups attached as monoamides to the polymer backbone by diethylenetriamine (DET) pendant groups. We compared its behavior in vivo and in vitro to a similar MCP with ethylenediamine (EDA) pendant groups (Bi-PAm(EDA-DTPA)40). These polymers were complexed to a streptavidin-modified Fab fragment of tmAb, then labeled with (111)In to specifically deliver multiple copies of (111)In to HER2+ cancer cells. Upon decay, (111)In emits γ-rays that can be used in single-photon emission computed tomography radioimaging, as well as Auger electrons that cause lethal double strand breakage of DNA. Our previous studies in Balb/c mice showed that radioimmunoconjugates (RICs) containing the Bi-PAm(EDA-DTPA)40 polymer had extremely short blood circulation time and high liver uptake and were, thus, unsuitable for in vivo studies. The polymer Bi-PAm(EDA-DTPA)40 carries negative charges on each pendant group at neutral pH and a net charge of (-1) on each pendant group when saturated with stable In(3+). To test our hypothesis that charge associated with the polymer repeat unit is a key factor affecting its biodistribution profile, we examined the biodistribution of RICs containing Bi-PAm(DET-DTPA)36. While this polymer is also negatively charged at neutral pH, it becomes a zwitterionic MCP upon saturation of the DTPA groups with stable In(3+) ions. In both nontumor bearing Balb/c mice and athymic mice implanted with HER2+ SKOV-3 human ovarian cancer tumors, we show that the zwitterionic MCP has improved biodistribution, higher blood levels of radioactivity, lower levels of normal tissue uptake, and higher tumor uptake. Surface plasmon resonance experiments employing the extracellular domain of HER2 show that the MCP immunoconjugates retain high affinity antigen recognition, with dissociation constants in the low nM range. In vitro studies with SKOV-3 cells for both MCP immunoconjugates show a combination of specific binding that can be completed in the presence of excess tmAb IgG and nonspecific binding (NSB) that persists in the presence of tmAb IgG. We conclude that zwitterionic MCPs represent a much better choice than polymers with charges along the backbone for in vivo delivery of RICs to HER2+ cancer cells.

Renal perfusional cortex volume for arterial input function measured by semiautomatic segmentation technique using MDCT angiographic data with 0.5-mm collimation.

OBJECTIVE: The purpose of this study was to evaluate the usefulness of renal perfusional cortex volume for arterial input function. MATERIALS AND METHODS: This retrospective study included 45 potential kidney donors--33 patients with aortic dissection and 12 patients with renovascular hypertension--who underwent both MDCT angiography with 0.5-mm collimation and renal (99m)Tc-diethylenetriamine pentaacetic acid (DTPA) scanning using the modified Gates method. Each perfusional cortex volume for the arterial input function and parenchymal volume was measured by semiautomatic segmentation using the region-growing technique. Linear regression analysis and correlation coefficients were used to assess the impact of the cortical volume, parenchymal volume, and renal scanning glomerular filtration rate (GFR) on estimated GFR (eGFR) using a modified Modification of Diet in Renal Disease (MDRD) equation. RESULTS: The correlation coefficient was higher for the total renal DTPA GFR adjusted for body surface area, weight-adjusted perfusion cortex volume, and adjusted total parenchyma volume in rank (r = 0.712, 0.642, 0.510, respectively, p< 0.0001 for each). The coefficient of the right renal perfusional cortex volume percent with a mean value of 52.1% ± 10.1% was 0.826 (p < 0.0001) for the right renal DTPA GFR percent with a mean value of 51.0% ± 12.1% (range, 22.0-89.5%), although the value for the right renal parenchymal volume percent with a mean value of 49.5% ± 5.5% was 0.764 (p < 0.0001). CONCLUSION: Weight-adjusted perfusional cortex volume for arterial input function can be measured clinically and may replace renal DTPA scanning using the modified Gates method.

Multimodality imaging probe for positron emission tomography and fluorescence imaging studies.

Our goal is to develop multimodality imaging agents for use in cell tracking studies by positron emission tomography (PET) and optical imaging (OI). For this purpose, bovine serum albumin (BSA) was complexed with biotin (histologic studies), 5(6)-carboxyfluorescein, succinimidyl ester (FAM SE) (OI studies), and diethylenetriamine pentaacetic acid (DTPA) for chelating gallium 68 (PET studies). For synthesis of BSA-biotin-FAM-DTPA, BSA was coupled to (+)-biotin N-hydroxysuccinimide ester (biotin-NHSI). BSA-biotin was treated with DTPA-anhydride and biotin-BSA-DTPA was reacted with FAM. The biotin-BSA-DTPA-FAM was reacted with gallium chloride 3 to 5 mCi eluted from the generator using 0.1 N HCl and was passed through basic resin (AG 11 A8) and 150 µCi (100 µL, pH 7-8) was incubated with 0.1 mg of FAM conjugate (100 µL) at room temperature for 15 minutes to give 68Ga-BSA-biotin-DTPA-FAM. A shaved C57 black mouse was injected with FAM conjugate (50 µL) at one flank and FAM-68Ga (50 µL, 30 µCi) at the other. Immediately after injection, the mouse was placed in a fluorescence imaging system (Kodak In-Vivo F, Bruker Biospin Co., Woodbridge, CT) and imaged (λex: 465 nm, λem: 535 nm, time: 8 seconds, Xenon Light Source, Kodak). The same mouse was then placed under an Inveon microPET scanner (Siemens Medical Solutions, Knoxville, TN) injected (intravenously) with 25 µCi of 18F and after a half-hour (to allow sufficient bone uptake) was imaged for 30 minutes. Molecular weight determined using matrix-associated laser desorption ionization (MALDI) for the BSA sample was 66,485 Da and for biotin-BSA was 67,116 Da, indicating two biotin moieties per BSA molecule; for biotin-BSA-DTPA was 81,584 Da, indicating an average of 30 DTPA moieties per BSA molecule; and for FAM conjugate was 82,383 Da, indicating an average of 1.7 fluorescent moieties per BSA molecule. Fluorescence imaging clearly showed localization of FAM conjugate and FAM-68Ga at respective flanks of the mouse, whereas only a hot spot at the expected flank (FAM-68Ga injection site) was observed in microPET imaging. Our results suggest that BSA-biotin-DTPA-FAM may function as a multiprobe for PET and fluorescence imaging. Experiments are currently in progress to demonstrate cell tracking using both optical and nuclear imaging.

H4octapa: an acyclic chelator for 111In radiopharmaceuticals.

This preliminary investigation of the octadentate acyclic chelator H(4)octapa (N(4)O(4)) with (111)In/(115)In(3+) has demonstrated it to be an improvement on the shortcomings of the current industry "gold standards" DOTA (N(4)O(4)) and DTPA (N(3)O(5)). The ability of H(4)octapa to radiolabel quantitatively (111)InCl(3) at ambient temperature in 10 min with specific activities as high as 2.3 mCi/nmol (97.5% radiochemical yield) is presented. In vitro mouse serum stability assays have demonstrated the (111)In complex of H(4)octapa to have improved stability when compared to DOTA and DTPA over 24 h. Mouse biodistribution studies have shown that the radiometal complex [(111)In(octapa)](-) has exceptionally high in vivo stability over 24 h with improved clearance and stability compared to [(111)In(DOTA)](-), demonstrated by lower uptake in the kidneys, liver, and spleen at 24 h. (1)H/(13)C NMR studies of the [In(octapa)](-) complex revealed a 7-coordinate solution structure, which forms a single isomer and exhibits no observable fluxional behavior at ambient temperature, an improvement to the multiple isomers formed by [In(DTPA)](2-) and [In(DOTA)](-) under the same conditions. Potentiometric titrations have determined the thermodynamic formation constant of the [In(octapa)](-) complex to be log K(ML) = 26.8(1). Through the same set of analyses, the [(111/115)In(decapa)](2-) complex was found to have nonoptimal stability, with H(5)decapa (N(5)O(5)) being more suitable for larger metal ions due to its higher potential denticity (e.g., lanthanides and actinides). Our initial investigations have revealed the acyclic chelator H(4)octapa to be a valuable alternative to the macrocycle DOTA for use with (111)In, and a significant improvement to the acyclic chelator DTPA.

A novel paramagnetic substrate for detecting myeloperoxidase activity in vivo.

Bis-phenylamides and bis-hydroxyindolamides of diethylenetriaminepentaacetic acid-gadolinium (DTPA(Gd)) are paramagnetic reducing substrates of peroxidases that enable molecular imaging of peroxidase activity in vivo. Specifically, gadolinium chelates of bis-5-hydroxytryptamide-DTPA (bis-5HT-DTPA(Gd)) have been used to image localized inflammation in animal models by detecting neutrophil-derived myeloperoxidase (MPO) activity at the inflammation site. However, in other preclinical disease models, bis-5HT-DTPA(Gd) presents technical challenges due to its limited solubility in vivo. Here we report a novel MPO-sensing probe obtained by replacing the reducing substrate serotonin (5-HT) with 5-hydroxytryptophan (HTrp). Characterization of the resulting probe (bis-HTrp-DTPA(Gd)) in vitro using nuclear magnetic resonance spectroscopy and enzyme kinetic analysis showed that bis-HTrp-DTPA(Gd) (1) improves solubility in water; (2) acts as a substrate for both horseradish peroxidase and MPO enzymes; (3) induces cross-linking of proteins in the presence of MPO; (4) produces oxidation products, which bind to plasma proteins; and (5) unlike bis-5HT-DTPA(Gd), does not follow first-order reaction kinetics. In vivo magnetic resonance imaging (MRI) in mice demonstrated that bis-HTrp-DTPA(Gd) was retained for up to 5 days in MPO-containing sites and cleared faster than bis-5HT-DTPA(Gd) from MPO-negative sites. Bis-HTrp-DTPA(Gd) should offer improvements for MRI of MPO-mediated inflammation in vivo, especially in high-field MRI, which requires a higher dose of contrast agent.

Biokinetics and dosimetry of 111In-DOTA-NOC-ATE compared with 111In-DTPA-octreotide.

PURPOSE: The biokinetics and dosimetry of (111)In-DOTA-NOC-ATE (NOCATE), a high-affinity ligand of SSTR-2 and SSTR-5, and (111)In-DTPA-octreotide (Octreoscan™, OCTREO) were compared in the same patients. METHODS: Seventeen patients (10 men, 7 women; mean age 60 years), referred for an OCTREO scan for imaging of a neuroendocrine tumour (15), thymoma (1) or medullary thyroid carcinoma (1), agreed to undergo a second study with NOCATE. Whole-body anterior-posterior scans were recorded 0.5 (100 % reference scan), 4, 24 and 48 h (17 patients) and 120 h (5 patients) after injection. In 16 patients the OCTREO scan (178 ± 15 MBq) was performed 16 ± 5 days before the NOCATE scan (108 ± 14 MBq) with identical timing; 1 patient had the NOCATE scan before the OCTREO scan. Blood samples were obtained from 14 patients 5 min to 48 h after injection. Activities expressed as percent of the initial (reference) activity in the whole body, lung, kidney, liver, spleen and blood were fitted to biexponential or single exponential functions. Dosimetry was performed using OLINDA/EXM. RESULTS: Initial whole-body, lung and kidney activities were similar, but retention of NOCATE was higher than that of OCTREO. Liver and spleen uptakes of NOCATE were higher from the start (p < 0.001) and remained so over time. Whole-body activity showed similar α and ß half-lives, but the ß fraction of NOCATE was double that of OCTREO. Blood T (1/2)ß for NOCATE was longer (19 vs. 6 h). As a result, the effective dose of NOCATE (105 µSv/MBq) exceeded that of OCTREO (52 µSv/MBq), and the latter result was similar to the ICRP 106 value of 54 µSv/MBq. Differential activity measurement in blood cells and plasma showed an average of <5 % of NOCATE and OCTREO attached to globular blood components. CONCLUSION: NOCATE showed a slower clearance from normal tissues and its effective dose was roughly double that of OCTREO.

Quantification of the spatial distribution of rectally applied surrogates for microbicide and semen in colon with SPECT and magnetic resonance imaging.

AIMS: We sought to describe quantitatively the distribution of rectally administered gels and seminal fluid surrogates using novel concentration-distance parameters that could be repeated over time. These methods are needed to develop rationally rectal microbicides to target and prevent HIV infection. METHODS: Eight subjects were dosed rectally with radiolabelled and gadolinium-labelled gels to simulate microbicide gel and seminal fluid. Rectal doses were given with and without simulated receptive anal intercourse. Twenty-four hour distribution was assessed with indirect single photon emission computed tomography (SPECT)/computed tomography (CT) and magnetic resonance imaging (MRI), and direct assessment via sigmoidoscopic brushes. Concentration-distance curves were generated using an algorithm for fitting SPECT data in three dimensions. Three novel concentration-distance parameters were defined to describe quantitatively the distribution of radiolabels: maximal distance (D(max) ), distance at maximal concentration (D(Cmax) ) and mean residence distance (D(ave) ). RESULTS: The SPECT/CT distribution of microbicide and semen surrogates was similar. Between 1 h and 24 h post dose, the surrogates migrated retrograde in all three parameters (relative to coccygeal level; geometric mean [95% confidence interval]): maximal distance (D(max) ), 10 cm (8.6-12) to 18 cm (13-26), distance at maximal concentration (D(Cmax) ), 3.8 cm (2.7-5.3) to 4.2 cm (2.8-6.3) and mean residence distance (D(ave) ), 4.3 cm (3.5-5.1) to 7.6 cm (5.3-11). Sigmoidoscopy and MRI correlated only roughly with SPECT/CT. CONCLUSIONS: Rectal microbicide surrogates migrated retrograde during the 24 h following dosing. Spatial kinetic parameters estimated using three dimensional curve fitting of distribution data should prove useful for evaluating rectal formulations of drugs for HIV prevention and other indications.

Differences in predicted and actually absorbed doses in peptide receptor radionuclide therapy.

PURPOSE: An important assumption in dosimetry prior to radionuclide therapy is the equivalence of pretherapeutic and therapeutic biodistribution. In this study the authors investigate if this assumption is justified in sst2-receptor targeting peptide therapy, as unequal amounts of peptide and different peptides for pretherapeutic measurements and therapy are commonly used. METHODS: Physiologically based pharmacokinetic models were developed. Gamma camera and serum measurements of ten patients with metastasizing neuroendocrine tumors were conducted using (111)In-DTPAOC. The most suitable model was selected using the corrected Akaike information criterion. Based on that model and the estimated individual parameters, predicted and measured (90)Y-DOTATATE excretions during therapy were compared. The residence times for the pretherapeutic (measured) and therapeutic scenarios (simulated) were calculated. RESULTS: Predicted and measured therapeutic excretion differed in three patients by 10%, 31%, and 7%. The measured pretherapeutic and therapeutic excretion differed by 53%, 56%, and 52%. The simulated therapeutic residence times of kidney and tumor were 3.1 ± 0.6 and 2.5 ± 1.2 fold higher than the measured pretherapeutic ones. CONCLUSIONS: To avoid the introduction of unnecessary inaccuracy in dosimetry, using the same substance along with the same amount for pretherapeutic measurements and therapy is recommended.

Immunohistochemical localization and quantitative expression of somatostatin receptors in normal human spleen and thymus: Implications for the in vivo visualization during somatostatin receptor scintigraphy.

BACKGROUND: [111In-DTPA-D-Phe1]-octreotide scintigraphy allows the visualization of SRIF receptor (SSR)-expressing tumors, including thymic tumors, and normal tissues. While the spleen is clearly visualized, the thymus is not depicted, although both contain SSR. AIM: We evaluated whether the heterogeneity, the type, and the amount of SSR might explain this contrasting finding. MATERIALS, METHODS, AND RESULTS: By ligand-binding the number of [125I-Tyr11]-SRIF- 14 binding sites resulted comparable between the two tissues, whereas the number of [125I-Tyr3]-octreotide sites was significantly higher in the spleen (p<0.001). Quantitative RTPCR showed a significantly higher expression of sst2A mRNA in the spleen, whereas a significantly higher expression of SRIF and sst3 in the thymus. The highest density of sst2A in the spleen is in line with the in vivo uptake of [111In-DTPA-D-Phe1]- octreotide, which is considered a sst2-preferring ligand. The specificity is confirmed by the evidence that in vivo [111In-DTPA- D-Phe1]-octreotide uptake can be abolished during chronic administration of "cold" octreotide. Immunohistochemistry confirmed a preferential expression of sst2A on microenvironmental cells and of sst3 on lymphoid cells. CONCLUSIONS: The heterogeneity of SSR expression and the higher SRIF content explain the lack of thymus visualization during scintigraphy, whereas thymic tumors, which do not express SRIF, are visualized. Apart from the affinity of the radioligand, also the efficacy of the internalization is crucial for the in vivo uptake, and both heterogeneity and SRIF content affect this process. These observations might have an important impact when interpretating in vivo visualization of SSR-positive lesions, and when treatment with novel SRIF analogs is considered.

PET imaging of tumor angiogenesis in mice with VEGF-A-targeted (86)Y-CHX-A″-DTPA-bevacizumab.

Bevacizumab is a humanized monoclonal antibody that binds to tumor-secreted vascular endothelial growth factor (VEGF)-A and inhibits tumor angiogenesis. In 2004, the antibody was approved by the US Food and Drug Administration (FDA) for the treatment of metastatic colorectal carcinoma in combination with chemotherapy. This report describes the preclinical evaluation of a radioimmunoconjugate, (86)Y-CHX-A″-DTPA-bevacizumab, for potential use in Positron Emission Tomography (PET) imaging of VEGF-A tumor angiogenesis and as a surrogate marker for (90)Y-based radioimmunotherapy. Bevacizumab was conjugated to CHX-A″-DTPA and radiolabeled with (86)Y. In vivo biodistribution and PET imaging studies were performed on mice bearing VEGF-A-secreting human colorectal (LS-174T), human ovarian (SKOV-3) and VEGF-A-negative human mesothelioma (MSTO-211H) xenografts. Biodistribution and PET imaging studies demonstrated highly specific tumor uptake of the radioimmunoconjugate. In mice bearing VEGF-A-secreting LS-174T, SKOV-3 and VEGF-A-negative MSTO-211H tumors, the tumor uptake at 3 days postinjection was 13.6 ± 1.5, 17.4 ± 1.7 and 6.8 ± 0.7 % ID/g, respectively. The corresponding tumor uptake in mice coinjected with 0.05 mg cold bevacizumab were 5.8 ± 1.3, 8.9 ± 1.9 and 7.4 ± 1.0 % ID/g, respectively at the same time point, demonstrating specific blockage of the target in VEGF-A-secreting tumors. The LS-174T and SKOV3 tumors were clearly visualized by PET imaging after injecting 1.8-2.0 MBq (86)Y-CHX-A″-DTPA-bevacizumab. Organ uptake quantified by PET closely correlated (r(2) = 0.87, p = 0.64, n = 18) to values determined by biodistribution studies. This preclinical study demonstrates the potential of the radioimmunoconjugate, (86)Y-CHX-A″-DTPA-bevacizumab, for noninvasive assessment of the VEGF-A tumor angiogenesis status and as a surrogate marker for (90)Y-CHX-A″-DTPA-bevacizumab radioimmunotherapy.

Radiolabeled cetuximab: dose optimization for epidermal growth factor receptor imaging in a head-and-neck squamous cell carcinoma model.

Noninvasive imaging of the epidermal growth factor receptor (EGFR) in head-and-neck squamous cell carcinoma could be of value to select patients for EGFR-targeted therapy. We assessed dose optimization of (111) Indium-DTPA-cetuximab ((111) In-cetuximab) for EGFR imaging in a head-and-neck squamous cell carcinoma xenograft model. (111) In-cetuximab slowly internalized into FaDu cells in vitro, amounting to 1.0 × 10(4) molecules cetuximab per cell after 24 hr (15.8% of added activity). In nude mice with subcutaneous FaDu xenograft tumors, a protein dose escalation study with (111) In-cetuximab showed highest specific accumulation in tumors at protein doses between 1 and 30 µg per mouse (mean tumor uptake 33.1 ± 3.1%ID/g, 3 days postinjection (p.i.)). The biodistribution of (111) In-cetuximab and (125) I-cetuximab was determined at 1, 3 and 7 days p.i. at optimal protein dose. Tumor uptake was favorable for (111) In-cetuximab compared to (125) I-cetuximab. With pixel-by-pixel analysis, good correlations were found between intratumoral distribution of (111) In-cetuximab as determined by autoradiography and EGFR expression in the same tumor sections as determined immunohistochemically (mean r = 0.74 ± 0.14; all correlations p < 0.0001). Micro Single Photon Emission Computed Tomography (MicroSPECT) scans clearly visualized FaDu tumors from 1 day p.i. onward and tumor-to-background contrast increased until 7 days p.i. (tumor-to-liver ratios 0.58 ± 0.24, 3.42 ± 0.66, 8.99 ± 4.66 and 16.33 ± 11.56, at day 0, day 1, day 3 and day 7 p.i., respectively). Our study suggests that, at optimal cetuximab imaging dose, (111) In-cetuximab can be used for visualization of EGFR expression in head-and-neck squamous cell carcinoma using SPECT.

High-resolution in vivo imaging of breast cancer by targeting the pro-invasive integrin alphavbeta6.

The integrin alphavbeta6 is expressed only on epithelia and then usually only during processes of tissue remodelling including cancer, where its high expression correlates with reduced survival. Thus, alphavbeta6 represents an important target for imaging and therapy of cancer and new molecular-specific targeting agents are required. We have developed A20FMDV2, a peptide derived from the VP1 coat protein of foot-and-mouth-disease virus that binds specifically and stably to alphavbeta6. Using a newly generated pair of isogenic human cell lines that differ only in alphavbeta6 expression, it was shown, using biodistribution and SPECT imaging, that indium-111-labelled A20FMDV2 locates specifically to alphavbeta6-expressing tissues in vivo, achieving at least seven-times higher retention in alphavbeta6-positive than in alphavbeta6-negative tumours. In further studies with MCF10.DCIS.COM and MCF10A.CA1a breast carcinoma cell lines, which express alphavbeta6 endogenously, the radiopeptide achieved similar levels of tumour retention and permitted excellent discriminatory imaging of tumours. Thus, A20FMDV2 can be used for molecular-specific targeting of alphavbeta6 for imaging in vivo the often more aggressive, alphavbeta6-positive cancers. In the future, A20FMDV2 could serve also to deliver therapy to these same cancers.

Inaccuracies in estimated glomerular filtration rate in one Australian renal centre.

BACKGROUND: Early identification of true renal disease (glomerular filtration rate (GFR) < 60 mL/min) results in better patient outcomes. There is now routine reporting in Australia of estimated GFR (eGFR) in all patients over age 18 who have serum creatinine measured, calculated by the Modification of Diet in Renal Disease (MDRD) formula, which was validated in an American Caucasian cohort. Significant clinical decisions and prognosis are often made on the basis of this calculation. AIM: To assess the accuracy of three estimates of GFR in an Australian population by comparing eGFR obtained by the abbreviated MDRD (aMDRD), Cockcroft-Gault corrected for body surface area (BSA) (CG) and Chronic Kidney Disease Epidemiology (CKD-Epi) formulae with a gold standard, isotopic (51) Cr-ethylenediaminetetra-acetic acid ((51) Cr-EDTA) GFR. METHODS: Patients referred with an eGFR of <60 mL/min reported by the aMDRD formula underwent isotopic measurement of GFR (over 4 h) and had eGFR calculated using CG corrected for BSA, aMDRD and CKD-Epi formulae. Data were analysed using Bland-Altman plots and regression analysis to compare methods; bias, precision and the proportion of patients correctly stratified by stage of chronic kidney disease (CKD) were also compared according to the three estimates of GFR, using (51) Cr-EDTA GFR as the gold standard. RESULTS: A total of 139 patients were recruited (female 45%), mean age 64 years and mean serum creatinine 212 µmol/L. The mean GFR (SD) (mL/min per m(2) ) for isotopic, CG, aMDRD and CKD-Epi were 47 (28), 37 (20), 32 (17) and 33 (18) (P = 0.001). CG (57%) was more likely to correctly stage CKD than aMDRD (37%) or CKD-Epi (37%), and absolute bias was significantly lower using CG than either other method (P = 0.001). CONCLUSION: In this small Australian population the CG formula corrected for BSA agreed more closely with isotopic GFR and correctly staged patients with CKD more often than the aMDRD or CKD-Epi formulae. It is important that each renal Unit considers the accuracy of estimates of GFR according to their population demographics.