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124I-huA33 antibody uptake is driven by A33 antigen concentration in tissues from colorectal cancer patients imaged by immuno-PET.

ABSTRACT: The primary aim of this analysis was to examine the quantitative features of antibody-antigen interactions in tumors and normal tissue after parenteral administration of antitumor antibodies to human patients.Humanized anti-A33 antibody (10 mg) labeled with the positron-emitting radionuclide (124)I ((124)I-huA33) was injected intravenously in 15 patients with colorectal cancer. Clinical PET/CT was performed approximately 1 wk later, followed by a detailed assay of surgically removed tissue specimens including radioactivity counting, autoradiography, immunohistochemistry, and antigen density determination.PET/CT showed high levels of antibody targeting in tumors and normal bowel. In tissue specimens, the spatial distribution of (124)I-huA33 conformed to that of A33 antigen, and there was a linear relationship between the amount of bound antibody and antigen concentration. Antibody uptake was high in 1- to 2-mm regions of antigen-positive tumor cells (mean, ~0.05 percentage injected dose per gram) and in antigen-positive normal colonic mucosa (mean, ~0.03 percentage injected dose per gram). The estimated binding site occupancy for tumor and normal colon was 20%-50%.The in vivo biodistribution of (124)I-huA33 in human patients 1 wk after antibody administration was determined by A33 antigen expression. Our data imply that the optimal strategy for A33-based radioimmunotherapy of colon cancer will consist of a multistep treatment using a radionuclide with short-range (?- or ?-particle) emissions.

SUBMITTER: O'Donoghue JA

PROVIDER: S-EPMC3394180 | biostudies-literature | 2011 Dec

REPOSITORIES: biostudies-literature

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124I-huA33 antibody uptake is driven by A33 antigen concentration in tissues from colorectal cancer patients imaged by immuno-PET.

O'Donoghue Joseph A JA Smith-Jones Peter M PM Humm John L JL Ruan Shutian S Pryma Daniel A DA Jungbluth Achim A AA Divgi Chaitanya R CR Carrasquillo Jorge A JA Pandit-Taskar Neeta N Fong Yuman Y Strong Vivian E VE Kemeny Nancy E NE Old Lloyd J LJ Larson Steven M SM

Journal of nuclear medicine : official publication, Society of Nuclear Medicine 20111108 12

<h4>Unlabelled</h4>The primary aim of this analysis was to examine the quantitative features of antibody-antigen interactions in tumors and normal tissue after parenteral administration of antitumor antibodies to human patients.<h4>Methods</h4>Humanized anti-A33 antibody (10 mg) labeled with the positron-emitting radionuclide (124)I ((124)I-huA33) was injected intravenously in 15 patients with colorectal cancer. Clinical PET/CT was performed approximately 1 wk later, followed by a detailed assay ...[more]

PMID: 22068895

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Project description:UNLABELLED:Tumor endothelial marker 1 (TEM1/endosialin) is a tumor vascular marker highly overexpressed in multiple human cancers with minimal expression in normal adult tissue. In this study, we report the preparation and evaluation of (124)I-MORAb-004, a humanized monoclonal antibody targeting an extracellular epitope of human TEM1 (hTEM1), for its ability to specifically and sensitively detect vascular cells expressing hTEM1 in vivo. METHODS:MORAb-004 was directly iodinated with (125)I and (124)I, and in vitro binding and internalization parameters were characterized. The in vivo behavior of radioiodinated MORAb-004 was characterized in mice bearing subcutaneous ID8 tumors enriched with mouse endothelial cells expressing hTEM1 and by biodistribution and small-animal immuno-PET studies. RESULTS:MORAb-004 was radiolabeled with high efficiency and isolated in high purity. In vitro studies demonstrated specific and sensitive binding of MORAb-004 to MS1 mouse endothelial cells expressing hTEM1, with no binding to control MS1 cells. (125)I-MORAb-004 and (124)I-MORAb-004 both had an immunoreactivity of approximately 90%. In vivo biodistribution experiments revealed rapid, highly specific and sensitive uptake of MORAb-004 in MS1-TEM1 tumors at 4 h (153.2 ± 22.2 percentage injected dose per gram [%ID/g]), 24 h (127.1 ± 42.9 %ID/g), 48 h (130.3 ± 32.4 %ID/g), 72 h (160.9 ± 32.1 %ID/g), and 6 d (10.7 ± 1.8 %ID/g). Excellent image contrast was observed with (124)I-immuno-PET. MORAb-004 uptake was statistically higher in TEM1-positive tumors than in control tumors. Binding specificity was confirmed by blocking studies using excess nonlabeled MORAb-004. CONCLUSION:In our preclinical model, with hTEM1 exclusively expressed on engineered murine endothelial cells that integrate into the tumor vasculature, (124)I-MORAb-004 displays high tumor-to-background tissue contrast for detection of hTEM1 in easily accessible tumor vascular compartments. These studies strongly suggest the clinical utility of (124)I-MORAb-004 immuno-PET in assessing TEM1 tumor-status.

Project description:Unlabelled5B1 is a fully human, monoclonal antibody that has shown promise for the PET imaging of cancers expressing carbohydrate antigen 19.9 (CA19.9)--a carbohydrate prevalent in cells with aberrant glycosylation and an established effector of metastasis. The long physiologic half-life of the antibody and interference from circulating CA19.9 may increase the time required to generate quality images as well as the risk of radiation exposure to healthy tissues during repeated PET imaging. Pretargeting methodologies are an effective approach to expeditiously acquire PET images, but in this case, the pretargeting approach is complicated by the internalization of 5B1 by CA19.9-expressing cells. We sought to adapt and optimize a pretargeting strategy that exploits the bioorthogonal reaction between transcyclooctene (TCO) and tetrazine (Tz) to overcome these complications.Methods5B1 was modified with TCO, and a novel NOTA-PEG7-Tz radioligand was synthesized with the goal of improving on a previously reported analog. BxPC3 and Capan-2 cells were evaluated for their ability to internalize anti-CA19.9 antibodies using a fluorometric assay, and xenografts of the same lines were used for in vivo studies. The pretargeting approach was optimized, and the 2 radioligands were compared using biodistribution and PET imaging in murine models of pancreatic cancer.ResultsBxPC3 and Capan-2 cells were shown to rapidly internalize anti-CA19.9 monoclonal antibodies, including 5B1. (64)Cu-NOTA-PEG7-Tz showed improved in vivo pharmacokinetics relative to (64)Cu-NOTA-Tz using 5B1-TCO as the targeting vector. PET imaging and biodistribution studies showed that injecting the radioligand 72 h after the administration of 5B1-TCO resulted in the best uptake (8.2 ± 1.7 percentage injected dose per gram at 20 h after injection) and tumor-to-background activity concentration ratios. Dosimetry calculations revealed that the pretargeting system produced a greater than 25-fold reduction in total body radiation exposure relative to (89)Zr-desferrioxamine-5B1. PET/CT imaging in an orthotopic Capan-2 xenograft model--which secretes large amounts of CA19.9 and more rapidly internalizes anti-CA19.9 antibodies--showed that this approach is viable even in the difficult circumstances presented by a circulating antigen and internalized targeting vector.ConclusionThe 5B1-TCO and (64)Cu-NOTA-PEG7-Tz system evaluated in these studies can delineate CA19.9-positive xenografts in murine models of pancreatic cancer despite the challenges posed by the combination of circulating antigen and internalization of the 5B1-TCO.

Project description:The purpose of this study was to establish a practical method to estimate the absolute boron concentrations in the tissues based on the standardized uptake values (SUVs) after administration of 4-borono-phenylalanine (BPA) using 4-borono-2-18F-fluoro-phenylalanine (18F-FBPA) PET.Rat xenograft models of C6 glioma (n = 7, body weight 241 ± 28.0 g) were used for the study. PET was performed 60 min after intravenous injection of 18F-FBPA (30.5 ± 0.7 MBq). After the PET scanning, BPA-fructose (167.3 ± 18.65 mg/kg) was administered by slow intravenous injection to the same subjects. The rats were killed 60 min after the BPA injection and tissue samples were collected from the major organs and tumors. The absolute boron concentrations (unit: ppm) in the samples were measured by inductively coupled plasma optical emission spectrometry (ICP-OES). The boron concentrations in the tissues/tumors were also estimated from the 18F-FBPA PET images using the following formula: estimated absolute boron concentration (ppm) = 0.0478 × [BPA dose (mg/kg)] × SUV. The measured absolute boron concentrations (mBC) by ICP-OES and the estimated boron concentrations (eBC) from the PET images were compared.The percent difference between the mBC and eBC calculated based on the SUVmax was -5.2 ± 21.1% for the blood, -9.4 ± 22.3% for the brain, 1.6 ± 21.3% for the liver, -14.3 ± 16.8% for the spleen, -9.5 ± 27.5% for the pancreas, and 3.4 ± 43.2% for the tumor. Relatively large underestimation was observed for the lung (-48.4 ± 16.2%), small intestine (-37.8 ± 19.3%) and large intestine (-33.9 ± 11.0%), due to the partial volume effect arising from the air or feces contained in these organs. In contrast, relatively large overestimation was observed for the kidney (34.3 ± 29.3%), due to the influence of the high uptake in urine.The absolute boron concentrations in tissues/tumors can be estimated from the SUVs on 18F-FBPA PET using a practical formula. Caution must be exercised in interpreting the estimated boron concentrations in the lung, small intestine and large intestine, to prevent the adverse effects of overexposure, which could occur due to underestimation by partial volume effect using PET.

Project description:Antibody-based PET tracers are exceptionally well-suited for determination of the in vivo biodistribution and quantification of therapeutic antibodies. The continued expansion in antibody-based therapeutics has accordingly driven the development towards more robust conjugation strategies in order to reliably predict the performance of such agents. We therefore aimed to evaluate the effect of site-specific labeling by enzymatic remodeling on the stability, immuno-reactivity and tumor-targeting properties of the monoclonal antibody (mAb) trastuzumab and compare it to conventional, random labeling in a HER2-positive xenograft mouse model. Methods: Trastuzumab was conjugated with the p-SCN-Bn-Desferrioxamine (SCN-Bn-DFO) chelator randomly on lysine residues or site-specifically on enzymatically modified glycans using either β-galactosidase or endoglycosidase S2 prior to 89Zr radiolabeling. 89Zr-DFO-trastuzumab was injected into SK-OV-3 tumor-bearing NMRI nude mice. The antibody dose was titrated with either 100 µg or 500 µg of unlabeled trastuzumab. Mice underwent small animal PET/CT imaging 24, 70 and 120 hours post-injection for longitudinal assessment. Parallel experiments were conducted with an isotype control matched antibody. In vivo imaging was supported by conventional ex vivo biodistribution and HER2 immuno-histochemistry. Furthermore, site-specifically labeled 89Zr-DFO-trastuzumab was evaluated in a panel of subcutaneous patient-derived xenograft (PDX) models. Additionally, the affinity, in vitro stability and immuno-reactivity were assessed for all tracers. Results: Site-specific labeling significantly increased PET tumor uptake (One-way ANOVA, p<0.0001) at all time-points when compared to random labeling. Mean tumor uptakes were 6.7 ± 1.7, 13.9 ± 3.3 and 15.3 ± 3.8 % injected dose per gram tissue (%ID/g) at 70 hours post-injection, for random, β-galactosidase or endoglycosidase S2 labeled probes, respectively. Co-injection with unlabeled trastuzumab increased the circulation time of tracers but did not alter tumor uptake notably. Site-specific probes presented with a superior in vitro stability and immuno-reactivity compared to the randomly labeled probe. Ex vivo biodistribution confirmed the data obtained by in vivo PET imaging, and site-specific 89Zr-DFO-trastuzumab successfully detected HER2-positive tumors in PDX mouse models. Conclusion: 89Zr-DFO-trastuzumab is well-matched for specific immuno-PET imaging of HER2-positive tumors and site-specific labeling of trastuzumab by the SiteClickTM technology minimizes the impact of the DFO chelator on immuno-reactivity, stability and biodistribution. These findings support further development of site-specifically radiolabeled mAbs for immuno-PET.

Dataset Information

124I-huA33 antibody uptake is driven by A33 antigen concentration in tissues from colorectal cancer patients imaged by immuno-PET.

Publications

124I-huA33 antibody uptake is driven by A33 antigen concentration in tissues from colorectal cancer patients imaged by immuno-PET.

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