Fate of intravenously administered rat lymphokine-activated killer cells labeled with different markers

Summary Rat lymphokine-activated killer (LAK) cells, generated by adhering rat splenocytes isolated from the 52% Percoll density fraction to plastic flasks, demonstrate restricted in vivo tissue distribution, localizing in the lungs and liver after 2 h, but redistributing into the liver and spleen 24 h after i.v. administration. However, a different pattern of distribution was observed when this population of LAK cells was labeled with one of four commonly used radioisotopes. For example, LAK cells showed a high distribution into the lungs 30 min after administration when labeled with⁵¹Cr,¹²⁵I-dUrd or¹¹¹In-oxine, whereas¹¹¹InCl-labeled LAK cells showed an equal distribution into the blood, lungs and liver at this time. Two hours after administration, cells labeled with¹¹¹In-oxine showed an equivalent distribution into the lungs and liver, those labeled with¹²⁵I-dUrd or⁵¹Cr showed a high accumulation in the lungs, whereas those labeled with¹¹¹In-Cl entered more into the liver and blood. The pattern of distribution of¹¹¹In-Cl- or¹¹¹In-oxine-labeled cells was confirmed using gamma camera imaging analysis. By 24 h, LAK cells labeled with¹¹¹InCl,¹¹¹In-oxine or⁵¹Cr distributed in the liver and spleen in variable concentrations. In contrast, cells labeled with¹²⁵I-dUrd were not detected in any organ tested.This study was paralleled by monitoring the distribution of LAK cells labeled with Hoechst 33342 (H33342) and analyzed for the presence of fluoresceinated cells in different organs either by flow cytometry analysis, or in frozen section. The data indicate that the distribution pattern of LAK cells labeled with¹¹¹In-oxine is the closest to the distribution of H33342-labeled cells. Of all the radioisotopes used,¹²⁵I-dUrd has the most disadvantages and is not recommended for monitoring the in vivo distribution of leukocytes.     

Rapid miniaturized chromatography for 111In labeled monoclonal antibodies: Comparison to size exclusion high performance liquid chromatography

Our laboratory investigated the use of a rapid miniaturized chromatography system, ITLC-SG with 0.9% NaCl, to assess the radiochemical purity of ¹¹¹In labeled monoclonal antibodies (MoAbs). Radiochemical analysis was performed on numerous ¹¹¹In labeled antibody preparations with labeling efficiencies ranging from 40 to greater than 95% and the results compared to those obtained with size exclusion high performance liquid chromatography (HPLC). The chromatographic procedure involved challenging radiolabeled antibodies with 0.05 M DTPA to chelate unbound and/or non-specific bound ¹¹¹In, spotting on miniaturized instant thin layer-silica gel chromatography strips, developing in 0.9% NaCl, and counting appropriate segments for radioactivity. Results of the study demonstrated that the miniaturized chromatography procedure was rapid, taking less than 4 min to complete, and accurate in assessing the amount of unbound or non-specific bound ¹¹¹In in ¹¹¹In labeled monoclonal antibodies, when compared to size exclusion HPLC.     

Comparative studies using 125I- and 111In-labeled monoclonal antibodies

HDP-1 monoclonal antibody was labeled with ¹¹¹In using deferoxamine, diethylenetriaminepentaacetic acid or 1-(para-bromoacetamidobenzyl)-EDTA as chelating agents or with ¹²⁵I. The in vitro binding capacity and stability of the labeled molecules were evaluated using affinity chromatography. The biodistribution and imaging capabilities were compared using an animal model system that does not involve the use of tumors. Similar studies were done using the corresponding labeled F(ab′)₂ and Fab′ fragments. All labeled molecules, except those treated with deferoxamine, were stable in vitro. When tested in vivo, all retained their capacity to localize in the target tissue (lung). The lung %ID/g levels for the ¹¹¹In-labeled molecules were, however, slightly lower than those observed for the corresponding ¹²⁵I-labeled molecules. High uptake was also observed in the liver or kidneys when the ¹¹¹In-labeled molecules were used; no such results were obtained with the ¹²⁵I-labeled molecules. More work appears to be necessary before the use of bifunctional chelates becomes the optimal method for radiolabeling monoclonal antibodies for use in tumor imaging.     

Efficient conjugation of DTPA to an IgM monoclonal antibody in ascites fluid

We have developed a simple, rapid, and reproducible method for conjugating the bifunctional metal chelator diethylenetriaminepentaacetic acid (DTPA) to an IgM monoclonal antibody (MoAb) without first isolating the MoAb from the ascites fluid. Treatment of the protein mixture in the ascites fluid with cyclic DTPA anhydride (cDTPAA) followed by HPLC purification on a size exclusion column allowed isolation of the DTPA-IgM conjugate which could then be labeled with ¹¹¹ In ⩾80% yield. Over the range of total protein concentrations used (11–44 mg/mL), the number of DTPA molecules per molecule of IgM was approximately one-half the molar ratio of cDTPAA to total protein. We have used this method to prepare an ¹¹¹In labeled anti-Thy 1.2 IgM, a MoAb with specificity for a murine cell-surface antigen found on normal and malignant T cells and neuroectodertmal tissues. Analysis of the DTPA-IgM conjugate prior to and after ¹¹¹In labeling using indirect immunofluorescence flow cytometry and a target-cell binding assay showed that the antigen specificity of this anti-Thy 1.2 MoAb is not substantially altered by the presence of up to 8 DTPA molecules per IgM molecule.     

New 111In labeling of IgG: 111In-oxine mediated chelation

Current methods of ¹¹¹In chelate conjugation labeling of antibodies expose the protein to pH 5–6 during ¹¹¹In chelation. These conditions could be detrimental if the antibody is acid labile. We have successfully labeled human IgG via the cyclic anhydride of DPTA and ¹¹¹In-oxyquinoline(oxine). Chelation was achieved at pH 6.9–8.4 and was complete within 1 min at room temperature. The chelation was sensitive to trace metal contamination on labware and in some reagents (including commercial ¹¹¹In-oxine).     

Evaluation of two new bifunctional chelates for radiolabeling a parathyroid-specific monoclonal antibody with In-111

BB5-G1, a monoclonal antibody specific for human parathyroid cell membrane antigen was conjugated with two new ligands, BrMe₂HBED and BrφHBED and radiolabeled with ¹¹¹In. We have compared the biodistribution of ¹¹¹In-labeled BBS using the new ligands to conventionally labeled (¹²⁵I-labeled and ¹¹¹In-DTPA-labeled) BBS in a nude mouse model. Both ¹¹¹In-BrMe₂HBED-BB5 and ¹¹¹In-BrφHBED-BB5 attained high parathyroid-to-blood and parathyroid-to-muscle ratios by 72–96 h. ¹¹¹In-BrφHBED-BB5 showed lower %ID/g than ¹¹¹In-BrMe₂HBED-BB5 in the clearance organs, the liver and kidney; renal activity had cleared significantly by 120 h. This work suggests that ¹¹¹In-BrφHBED-BB5 offers improved in vivo behavior and may be useful as a radiopharmaceutical for localizing parathyroid tissue.     

Radiolabeled products in rat liver and serum after administration of antibody—amide—DTPA—indium-111

Anti-human serum albumin antibody (Ab) was used as a model antibody. Ab was conjugated with DTPA using cyclic DTPA dianhydride reaction and radiolabeled with ¹¹¹In. The labeled Ab was purified by affinity chromatography. Size exclusion HPLC of this product showed 62% of ¹¹¹In bound to monomeric Ab and 38% of the activity bound to antibody oligomers with molecular weights ranging from 300,000 to 450,000. The labeled antibody preparation was injected into the tail vein of rats. The radioactive substances in serum and the supernatant from liver homogenates were analyzed for molecular weight and immunoreactivity. Size exclusion HPLC of the serum samples indicated that the monomeric and dimeric Abs disappeared from the serum at a similar rate over a 48 h period. In addition, a new radioactive substance with an estimated molecular weight of 35,000 appeared in the serum. The immunoreactive fraction of the circulating ¹¹¹In substances decreased slowly, somewhat proportional to the appearance of the metabolite. On the other hand, the immunoreactivity of the ¹¹¹In substances in the supernatant from the liver homogenate decreased rapidly and no appreciable immunoreactivity was observed after 48 h. The labeled antibody was catabolized very rapidly in the liver and the major activity in the supernatant was associated with a small molecular weight metabolite which had a HPLC retention time identical to that of DTPA-¹¹¹In. The second metabolite had an estimated molecular weight of 35,000. No radioactivity was associated with transferrin.     

Studies on the metabolic fate of 111In-labeled antibodies

Indium-111-labeled antibodies, though providing superior photon flux to iodine-labeled antibodies, can exhibit high levels of accumulation in some non-target organs. In an effort to understand the nature of this non-target uptake we have evaluated the molecular weight of ¹¹¹In species retained in several tissues by radio-FPLC (sizing chromatography) following injection of [¹¹¹In]DTPA 5G6.4, a murine monoclonal antibody, into normal mice. Blood, liver and kidneys were removed, and liver and kidneys were homogenized at several time points after antibody injection. The proportion of ¹¹¹In-containing species was found to vary with the tissue and with time. Analysis of blood showed only radiolabeled antibody. In the liver, several ¹¹¹In species were identified with molecular weights compatible with intact antibody, [¹¹¹In]transferrin, and low molecular weight complexes, with an increase in the proportion of [¹¹¹In]transferrin and low molecular weight species occurring over time. While the same molecular weight species were also identified in the kidneys, the kidneys contained the largest percentage of low molecular weight species which increased over time. When ¹²⁵I-labeled 5G6.4 was injected and the tissues similarly analyzed, only radioactive material with the molecular weight of intact antibody was detected. Comparison of two methods of purification of [¹¹¹In]labeled antibody after labeling revealed a significant difference in the organ uptake of radiolabeled products for ¹¹¹In. Although dialysis was sufficient for the removal of labile ¹¹¹In, as determined by TLC, subsequent sizing chromatography on Bio-Gel P-60 dramatically dropped the hepatic and renal uptake of ¹¹¹In relative to blood and diminished the proportion of the low molecular weight species present on sizing FPLC of extracts from tissues. These data indicate that low and intermediate molecular weight ¹¹¹In compounds are accreted in the liver and kidneys following the i.p. injection of ¹¹¹In-labeled monoclonal antibodies and that their uptake can be diminished by more stringent radioantibody purification. This knowledge may be valuable in developing methods for reducing non-target ¹¹¹In uptake.     

Serum stability of 67Cu chelates: Comparison with 111In and 57Co

Simple chelates and chelate conjugated monoclonal antibodies labeled with ¹¹¹In, ⁵⁷Co and ⁶⁷Cu demonstrate marked differences in stability when exposed to a serum environment. Among these radiometals, on DTPA, the order of stability is ¹¹¹In ⁵⁷Co ⪢ ⁶⁷Cu. On benzyl-EDTA, the order of stability is ¹¹¹In ⋍ ⁵⁷Co ⪢ ⁶⁷Cu. Among those investigated, the only serum stable ⁶⁷Cu chelate found was ⁶⁷Cu-TETA. The order of stability observed for ⁵⁷Co vs ⁶⁷Cu is contrary to published equilibrium constants. These in vitro studies suggest that the in vivo behavior of metal chelates exposed to a complex molecular environment may not be predicted by classically determined equilibrium constants.     

Clumping of labeled leukocyte suspension. A simple measure for avoiding it

Leukocytes in “mixed” suspensions can clump together, resulting in cell clusters which are responsible for false positive hot spots in lungs of patients, in the case of abscess localization studies using ¹¹¹In labeled leukocytes.Addition of extra ACD (acid-citrate-dextrose) in those labeled leukocyte suspensions prevented cell clumping and avoided occurrence of focal radioactivity accumulation in lungs. The acidification did not interfere in leukocyte migration under agar.     

90Y Labeling of monoclonal antibody MOv18 and preclinical validation for radioimmunotherapy of human ovarian carcinomas

The monoclonal antibody (mAb) MOv18 binds the membrane alpha isoform of the folate receptor (FR) which is overexpressed in human ovarian carcinoma cells. Exploiting the targeting capacity of this mAb, we developed and preclinically validated a protocol for the stable labeling of the mAb with ⁹⁰Y, an isotope which has shown promise in cancer radioimmunotherapy. MOv18 was derivatized with the stable macrocyclic ligand p-isothiocyanatobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10- tetraacetic acid (Bz-DOTA). MOv18-Bz-DOTA conjugates were labeled with ⁹⁰Y or ¹¹¹In under metal-free and good laboratory practice conditions. At the optimal Bz-DOTA/mAb derivatization ratio of 4–5, conjugates maintained binding activity up to 6 months, were efficiently labeled with ⁹⁰Y or ¹¹¹In (mean labeling yield 85 and 64%, associated to a final mean specific activity of 74 and 37 MBq/mg) and displayed a mean immunoreactivity of 60 and 58%, respectively. The radiolabeled preparations were stable in human serum, with >97% radioactivity associated to mAb at 48 h after labeling. The ability of ⁹⁰Y- and ¹¹¹In-MOv18 to localize FR on tumors in vivo was analyzed in nude mice bearing tumors induced by isogenic cell lines differing only in the presence or absence of the relevant antigen [A431FR (FR-positive) and A431tMock (FR-negative)]. In vivo biodistribution in organs other than tumor was comparable in non-tumor-, A431tMock- and A431FR-bearing mice, whereas the median tumor uptake of the radiolabeled reagents, expressed as area under the curve (AUC) and maximum uptake (U_max), was significantly higher (sixfold to sevenfold) in A431FR than in A431tMock tumors (P=0.0465 and P=0.0332, respectively). Mean maximum uptake (% ID/g) for ⁹⁰Y-MOv18 was 53.7 and 7.4 in A431FR and A431tMock respectively; corresponding values for ¹¹¹In-Mov18 were 45.0 and 11.3. These data demonstrate the feasibility of ⁹⁰Y-labeling of MOv18 without compromising antibody binding ability and the immunoreagent-specific localization in vivo on FR-expressing tumors, suggesting the suitability of ⁹⁰Y-MOv18 for clinical studies.Angela Coliva and Alberto Zacchetti contributed equally to this work.     

Hepatocyte-specific distribution of catalase and its inhibitory effect on hepatic ischemia/reperfusion injury in mice

To explore the possibility of using catalase for the treatment of reactive oxygen species (ROS)-mediated injuries, the pharmacokinetics of bovine liver catalase (CAT) labeled with ¹¹¹In was investigated in mice. At a dose of 0.1 mg/kg, more than 70% of ¹¹¹In-CAT was recovered in the liver within 10 min after intravenous injection. In addition, ¹¹¹In-CAT was predominantly recovered from the parenchymal cells (PC) in the liver. Increasing the dose retarded the hepatic uptake of ¹¹¹In-CAT, suggesting saturation of the uptake process. This cell-specific uptake could not be inhibited by coadministration of various compounds which are known to be taken up by liver PC, indicating that the uptake mechanism of CAT by PC is very specific to this compound. The preventive effect of CAT on a hepatic ischemia/reperfusion injury was examined in mice by measuring the GOT and GPT levels in plasma. A bolus injection of CAT at 5 min prior to the reperfusion attenuated the increase in the levels of these indicators in a dose-dependent manner. These results suggest that catalase can be used for various hepatic injuries caused by ROS.     

Methods to label monoclonal antibodies for use in tumor imaging

The use of radiolabeled monoclonal antibodies as a diagnostic tool in nuclear medicine has grown rapidly over the past several years. Early studies utilized antibodies labeled with radionuclides of iodine (i.e. ¹²⁵I and ¹³¹I) although these radionuclides are not ideal for use in tumor imaging. Recent advances and the development of new chemical methods has made it possible to label antibodies with other radionuclides (i.e. ⁷⁷Br, ¹¹¹In and ^99mTc). The advantages and disadvantages associated with all of the different radionuclides and labeling methods will be discussed.     

Facile synthesis and evaluation of C-functionalized benzyl-1-oxa-4,7,10-triazacyclododecane-N,N',N″-triacetic acid as chelating agent for ¹¹¹In-labeled polypeptides

A 12-membered polyazamacrocycle, 1-oxa-4,7,10-triazacyclododecane-N,N′,N″-triacetic acid (ODTA), has been reported to provide an indium chelate of net neutral charge with thermodynamic stability higher than 1,4,7,10-tetraazacyclododecane-N,N′,N″,N?-tetraacetic acid (DOTA). However, neither synthetic procedure for a C-functionalized ODTA (C-ODTA) nor its chelating ability with a trace amount of radioactive indium-111 (¹¹¹In) has been elucidated. We herein present a facile synthetic procedure for C-ODTA, and estimated its ability as a chelating agent for radiolabeling peptides and proteins with ¹¹¹In. The synthetic procedure involves the synthesis of a linear precursor using a para-substituted phenylalanine derivative as a starting material. The following intramolecular cyclization reaction was best performed (>73% yield) when Boc-protected linear compound and the condensation reagent, HATU, were simultaneously added to the reaction vessel at the same flow rate. The cyclic compound was then reduced with BH₃ and alkylated with tert-butyl bromoacetate. The synthetic procedure was straightforward and some optimization would be required. However, most of the intermediate compounds were obtained easily in good yields, suggesting that the present synthetic procedure would be useful to synthesize C-ODTA derivatives. The intramolecular cyclization reaction might also be applicable to synthesize polyazamacrocycles of different ring sizes and cyclic peptides. In ¹¹¹In radiolabeling reactions, C-ODTA provided ¹¹¹In chelates in higher radiochemical yields at low ligand concentrations when compared with C-DOTA. The ¹¹¹In-labeled C-ODTA remained unchanged in the presence of apo-transferrin. The biodistribution studies also showed that the ¹¹¹In-labeled compound was mainly excreted into urine as intact. These findings indicate that C-ODTA would be useful to prepare ¹¹¹In-labeled peptides of high specific activities in high radiochemical yields.     

Investigations of N-linked macrocycles for 111in and 90Y labeling of proteins

To simplify the synthesis of macrocyclic chelators, commercially available macrocyclic amines were condensed with halogenated acetic acid to prepare the five chelators 12N4 (DOTA), 14N4 (TETA), 15N4, 9N3 and 12N3. Only 12N4 and 9N3 showed efficient labeling of the free chelator with ¹¹¹In and ⁹⁰Y. Serum stability studies at 37 °C with In-labeled DTPA, 12N4 and 9N3 showed no loss of label over 2 days whereas, with ⁹⁰Y, only 12N4 showed stabilities comparable to DTPA. The 12N4 chelator was derivatized by attaching biotin on one N-acetate group to simulate the attachment to protein. The serum stability for both ¹¹¹In and ⁹⁰Y was identical to that of biotin derivatized DTPA and lower than that of the free chelators. Biodistribution studies in normal mice of a model protein (avidin) labeled with ⁹⁰Y via biotinylated 12N4 and biotinylated DTPA showed identical distribution at 1 day except in bone where the %ID/g for the macrocyclic-conjugated protein (3.4 ± 0.5, N = 8) was significantly (P < 0.001) lower than that of the DTPA-conjugated protein (9.4 ± 0.9, N = 7). In conclusion, macrocycles may be readily synthesized from the macrocyclic amines and several show useful stabilities with In and Y. When N-linked to a protein, the Y biodistribution was found to be superior to that of the corresponding DTPA-coupled protein.     

Comparison of two methods of labeling proteins with 111In

DTPA N-hydroxysuccinimide pentaester (DHSE) can be used as an alternative to bicyclic anhydride for coupling proteins with DTPA.⁽¹⁾ However, in-vitro analysis of labeled proteins coupled with DHSE compared to bicyclic anhydride showed more high molecular weight product and less serum stability. We studied the magnitude of these differences in vivo by coupling HSA and IgG with DTPA using both methods, labeling with ¹¹¹In, and analyzing the biodistribution in mice. The results of this analysis showed comparable activity in the liver, kidneys and blood.     

An optimized antibody-chelator conjugate for imaging of carcinoembryonic antigen with indium-111

A monoclonal antibody to carcinoembryonic antigen showing minimal cross-reactivity with blood cells and normal tissues was derivatized with benzylisothiocyanate derivatives of EDTA and DTPA. Seven chelators per immunoglobulin could be incorporated without loss of immunoreactivity. The resulting conjugates, labeled with indium-111, showed low liver uptake in animals. A cold kit, comprising the DTPA conjugate at a molarity of antibody bound chelator exceeding 1 x 10⁻⁴M, gave radiochemical yields of indium labeled antibody of ⩾95% and was stable for 1 yr.     

Activated platelets in carotid artery thrombosis in mice can be selectively targeted with a radiolabeled single-chain antibody

Background

Activated platelets can be found on the surface of inflamed, rupture-prone and ruptured plaques as well as in intravascular thrombosis. They are key players in thrombosis and atherosclerosis. In this study we describe the construction of a radiolabeled single-chain antibody targeting the LIBS-epitope of activated platelets to selectively depict platelet activation and wall-adherent non-occlusive thrombosis in a mouse model with nuclear imaging using in vitro and ex vivo autoradiography as well as small animal SPECT-CT for in vivo analysis.

Methodology/Principal Findings

LIBS as well as an unspecific control single-chain antibody were labeled with ¹¹¹Indium (¹¹¹In) via bifunctional DTPA ( = ¹¹¹In-LIBS/¹¹¹In-control). Autoradiography after incubation with ¹¹¹In-LIBS on activated platelets in vitro (mean 3866±28 DLU/mm², 4010±630 DLU/mm² and 4520±293 DLU/mm²) produced a significantly higher ligand uptake compared to ¹¹¹In-control (2101±76 DLU/mm², 1181±96 DLU/mm² and 1866±246 DLU/mm²) indicating a specific binding to activated platelets; P<0.05. Applying these findings to an ex vivo mouse model of carotid artery thrombosis revealed a significant increase in ligand uptake after injection of ¹¹¹In-LIBS in the presence of small thrombi compared to the non-injured side, as confirmed by histology (49630±10650 DLU/mm² vs. 17390±7470 DLU/mm²; P<0.05). These findings could also be reproduced in vivo. SPECT-CT analysis of the injured carotid artery with ¹¹¹In-LIBS resulted in a significant increase of the target-to-background ratio compared to ¹¹¹In-control (1.99±0.36 vs. 1.1±0.24; P<0.01).

Conclusions/Significance

Nuclear imaging with ¹¹¹In-LIBS allows the detection of platelet activation in vitro and ex vivo with high sensitivity. Using SPECT-CT, wall-adherent activated platelets in carotid arteries could be depicted in vivo. These results encourage further studies elucidating the role of activated platelets in plaque pathology and atherosclerosis and might be of interest for further developments towards clinical application.     

(R)-NODAGA-PSMA: A Versatile Precursor for Radiometal Labeling and Nuclear Imaging of PSMA-Positive Tumors

Purpose

The present study aims at developing and evaluating an urea-based prostate specific membrane antigen (PSMA) inhibitor suitable for labeling with ¹¹¹In for SPECT and intraoperative applications as well as ⁶⁸Ga and ⁶⁴Cu for PET imaging.

Methods

The PSMA-based inhibitor-lysine-urea-glutamate-coupled to the spacer Phe-Phe-D-Lys(suberoyl) and functionalized with the enantiomerically pure prochelator (R)-1-(1-carboxy-3-carbotertbutoxypropyl)-4,7-carbotartbutoxymethyl)-1,4,7-triazacyclononane ((R)-NODAGA(tBu)₃), to obtain (R)-NODAGA-Phe-Phe-D-Lys(suberoyl)-Lys-urea-Glu (CC34). CC34 was labeled with ¹¹¹In, ⁶⁸Ga and ⁶⁴Cu. The radioconjugates were further evaluated in vitro and in vivo in LNCaP xenografts by biodistribution and PET studies. Biodistribution studies were also performed with ⁶⁸Ga-HBED-CC-PSMA (HBED-CC: N,N′-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylenediamine-N,N′-diacetic acid) and ¹¹¹In-PSMA-617 for comparison.

Results

⁶⁸Ga-CC34, ⁶⁴Cu-CC34, and ¹¹¹In-CC34 were prepared in radiochemical purity >95%. ^68/natGa-CC34, ^64/natCu-CC34, ^111/natIn-CC34, ^68/natGa-HBED-CC-PSMA, and ^111/natIn-PSMA-617 exhibited high affinity for the LNCaP cells, with K_d values of 19.3±2.5 nM, 27.5±2.7 nM, 5.5±0.9 nM, 2.9±0.6 nM and 5.4±0.8 nM, respectively. They revealed comparable internalization profiles with approximately 75% of the total cell associated activity internalized after 3 h of incubation. ⁶⁸Ga-CC34 showed very high stability after its administration in mice. Tumor uptake of ⁶⁸Ga-CC34 (14.5±2.9% IA/g) in LNCaP xenografts at 1 h p.i. was comparable to ⁶⁸Ga-HBED-CC-PSMA (15.8±1.4% IA/g) (P = 0.67). The tumor-to-normal tissue ratios at 1 and 2 h p.i of ⁶⁸Ga-CC34 were also comparable to ⁶⁸Ga-HBED-CC-PSMA (P>0.05). Tumor uptake of ¹¹¹In-CC34 (28.5±2.6% IA/g) at 1 h p.i. was lower than ¹¹¹In-PSMA-617 (52.1±6.5% IA/g) (P = 0.02). The acquisition of PET-images with ⁶⁴Cu-CC34 at later time points showed wash-out from the kidneys, while tumor uptake still remained relatively high. This resulted in an increased tumor-to-kidney ratio over time.

Conclusions

⁶⁸Ga-CC34 is comparable to ⁶⁸Ga-HBED-CC-PSMA in terms of tumor uptake and tumor to normal tissue ratios. ⁶⁴Cu-CC34 could enable high contrast imaging of PSMA positive tissues characterized by elevated expression of PSMA or when delayed imaging is required. ⁶⁴Cu-CC34 is currently being prepared for clinical translation.     

Sucralfate delays gastric emptying of liquids and solids in duodenal ulcer patients

Gastric emptying studies were performed on nine healthy volunteers and ten duodenal ulcer (DU) patients utilizing a dual radionuclide technique to assess simultaneously emptying rates of liquid (¹¹¹In labeled water) and solid (^99mTc sulfur colloid labeled chicken liver) components of a meal. One gram of sucralfate was compared to placebo in separate days in a randomized double-blind crossover fashion. Subjects ingested the radiolabeled test meal 1 h after receiving medication, and gastric emptying was monitored for 3 h using a γ camera interfaced with a computer. We found that DU patients had significantly faster gastric emptying of solids (P < 0.05) compared to normals on the placebo days, while liquid emptying rates were similar. Sucralfate, in the DU patients, significantly (P < 0.05) slowed gastric emptying of water from 20 to 40 min and emptying of the solid component from 100–160 min after the meal compared to placebo. In normal subjects, gastric emptying of liquids and solids was not significantly affected by sucralfate.We conclude that slowing of gastric emptying, possibly mediated through aluminum ions, occurs in DU patients on sucralfate. This may be one mechanism by which sucralfate enhances healing and decreases recurrence of duodenal ulcer.