Shutian Ruan

Preoperative characterisation of clear-cell renal carcinoma using iodine-124-labelled antibody chimeric G250 (124I-cG250) and PET in patients with renal masses: a phase I trial

BACKGROUND Preoperative identification of tumour type could have important implications for the choice of treatment for renal cancers. Antibody cG250 reacts against carbonic anhydrase-IX, which is over-expressed in clear-cell renal carcinomas. We aimed to assess whether iodine-124-labelled antibody chimeric G250 ((124)I-cG250) PET predicts clear-cell renal carcinoma, the most common and aggressive renal tumour. METHODS 26 patients with renal masses who were scheduled to undergo surgical resection by laparotomy received a single intravenous infusion of 185 MBq/10 mg of (124)I-cG250 over 20 min in this open-label pilot study. Surgery was scheduled 1 week after (124)I-cG250 infusion. PET and CT scanning of the abdomen, including the kidneys, within 3 h before surgery was planned for all patients. The obtained images were graded as positive (defined as a tumour-to-healthy-kidney ratio >3 to 1) or negative for antibody uptake, and the surgeon was informed of the scan results before surgery. After surgery, resected tumours were histopathologically classified as clear-cell renal carcinoma or otherwise. The trial is registered on the clinical trials site of the National Cancer Institute website http://clinicaltrials.gov/ct/show/NCT00199888. FINDINGS One patient received inactive antibody and was excluded from analysis. 15 of 16 clear-cell carcinomas were identified accurately by antibody PET, and all nine non-clear-cell renal masses were negative for the tracer. The sensitivity of (124)I-cG250 PET for clear-cell kidney carcinoma in this trial was 94% (95% CI 70-100%); the negative predictive value was 90% (55-100%), and specificity and positive predictive accuracy were both 100% (66-100% and 78-100%, respectively). INTERPRETATION PET with (124)I-cG250 can identify accurately clear-cell renal carcinoma; a negative scan is highly predictive of a less aggressive phenotype. Stratification of patients with renal masses by (124)I-cG250 PET can identify aggressive tumours and help decide treatment.

Ga-66 labeled somatostatin analogue DOTA-DPhe1-Tyr3-octreotide as a potential agent for positron emission tomography imaging and receptor mediated internal radiotherapy of somatostatin receptor positive tumors.

Radionuclide labeled somatostatin analogues selectively target somatostatin receptor (SSTR)-expressing tumors as a basis for diagnosis and treatment of these tumors. Recently, a DOTA-functionalized somatostatin analogue, DOTATOC (DOTA-DPhe1-Tyr3-octreotide) has been developed. This compound has been shown to be superior to the other somatostatin analogues as indicated by its uniquely high tumor-to-non-target tissue ratio. DOTATOC can be labeled with a variety of radiometals including gallium radioisotopes. Gallium-66 is a positron emitting radionuclide (T(1/2) =9.5 hr; beta+=56%), that can be produced in carrier free form by a low-beam energy cyclotron. In this study we investigated SSTR targeting characteristics of 66Ga-DOTATOC in AR42J rat pancreas tumor implanted nude mice as a potential agent for diagnosis and receptor-mediated internal radiotherapy of SSTR-expressing tumors. We compared our results with 67Ga- and 68Ga- labeled DOTATOC. The radiolabeling procedure gave labeling yield ranged from 85-95% and radiochemical and chemical purity was > 95%. In-vitro competitive binding curves and in-vivo competitive displacement studies with an excess of unlabeled peptide indicates that there is specific binding of the radioligand to SSTR. Animal biodistribution data and serial microPET images demonstrated rapid tumor uptake and rapid clearance from the blood and all tissues except kidney. Maximum % ID/g values for tumor were 10.0 +/- 0.7, 13.2 +/- 2.1 and 9.8 +/- 1.5 for 66Ga-, 67Ga-, and 68Ga-DOTATOC, respectively. Calculated tumor, kidney and bone marrow doses for 66Ga-DOTATOC based on biodistribution data were 178, 109 and 1.2 cGy/MBq, respectively. We conclude that 66Ga labeled DOTATOC can be used for PET diagnosis and quantitative imaging-based dosimetry of SSTR positive tumors. 66Ga-DOTATOC may also be used in higher doses for ablation of these tumors. However, kidney is the critical organ for toxicity (tumor/kidney ratio = 1.64), and high kidney uptake must be eliminated before devising a therapy protocol.

124 I-huA33 Antibody PET of Colorectal Cancer

Humanized A33 (huA33) is a promising monoclonal antibody that recognizes A33 antigen, which is present in more than 95% of colorectal cancers and in normal bowel. In this study, we took advantage of quantitative PET to evaluate 124I huA33 targeting, biodistribution, and safety in patients with colorectal cancer. We also determined the biodistribution of 124I-huA33 when a large dose of human intravenous IgG (IVIG) was administered to manipulate the Fc receptor or when 124I-huA33 was given via hepatic arterial infusion (HAI). Methods: We studied 25 patients with primary or metastatic colorectal cancer; 19 patients had surgical exploration or resection. Patients received a median of 343 MBq (44.4–396 MBq) and 10 mg of 124I-huA33. Nineteen patients received the antibody intravenously and 6 patients via HAI, and 5 patients also received IVIG. Results: Ten of 12 primary tumors were visualized in 11 patients. The median concentration in primary colon tumors was 0.016% injected dose per gram, compared with 0.004% in normal colon. The PET-based median ratio of hepatic tumor uptake to normal-liver uptake was 3.9 (range, 1.8–22.2). Quantitation using PET, compared with well counting of serum and tissue, showed little difference. Prominent uptake in bowel hindered tumor identification in some patients. Pharmacokinetics showed that patients receiving IVIG had a significantly shorter serum half-time (41.6 ± 14.0 h) than those without (65.2 ± 9.8 h). There were no differences in clearance rates among the intravenous group, IVIG group, and HAI group, nor was there any difference in serum area under the curve, maximum serum concentration, or volume of distribution. Weak titers of human–antihuman antibodies were observed in 6 of 25 patients. No acute side effects or significant toxicities were associated with huA33. Conclusion: Good localization of 124I-huA33 in colorectal cancer with no significant toxicity has been observed. PET-derived 124I concentrations agreed well with those obtained by well counting of surgically resected tissue and blood, confirming the quantitative accuracy of 124I-huA33 PET. The HAI route had no advantage over the intravenous route. No clinically significant changes in blood clearance were induced by IVIG.

A stereotactic method for the three-dimensional registration of multi-modality biologic images in animals: NMR, PET, histology, and autoradiography.

The objective of this work was to develop and then validate a stereotactic fiduciary marker system for tumor xenografts in rodents which could be used to co-register magnetic resonance imaging (MRI), PET, tissue histology, autoradiography, and measurements from physiologic probes. A Teflon fiduciary template has been designed which allows the precise insertion of small hollow Teflon rods (0.71 mm diameter) into a tumor. These rods can be visualized by MRI and PET as well as by histology and autoradiography on tissue sections. The methodology has been applied and tested on a rigid phantom, on tissue phantom material, and finally on tumor bearing mice. Image registration has been performed between the MRI and PET images for the rigid Teflon phantom and among MRI, digitized microscopy images of tissue histology, and autoradiograms for both tissue phantom and tumor-bearing mice. A registration accuracy, expressed as the average Euclidean distance between the centers of three fiduciary markers among the registered image sets, of 0.2 +/- 0.06 mm was achieved between MRI and microPET image sets of a rigid Teflon phantom. The fiduciary template allows digitized tissue sections to be co-registered with three-dimensional MRI images with an average accuracy of 0.21 and 0.25 mm for the tissue phantoms and tumor xenografts, respectively. Between histology and autoradiograms, it was 0.19 and 0.21 mm for tissue phantoms and tumor xenografts, respectively. The fiduciary marker system provides a coordinate system with which to correlate information from multiple image types, on a voxel-by-voxel basis, with sub-millimeter accuracy--even among imaging modalities with widely disparate spatial resolution and in the absence of identifiable anatomic landmarks.

124I-huA33 Antibody Uptake Is Driven by A33 Antigen Concentration in Tissues from Colorectal Cancer Patients Imaged by Immuno-PET

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. Methods: Humanized anti-A33 antibody (10 mg) labeled with the positron-emitting radionuclide 124I (124I-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. Results: PET/CT showed high levels of antibody targeting in tumors and normal bowel. In tissue specimens, the spatial distribution of 124I-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%. Conclusion: The in vivo biodistribution of 124I-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 (α- or β-particle) emissions.

Renal uptake of bismuth-213 and its contribution to kidney radiation dose following administration of actinium-225-labeled antibody

Clinical therapeutic studies using (225)Ac-labeled antibodies have begun. Of major concern is renal toxicity that may result from the three alpha-emitting progeny generated following the decay of (225)Ac. The purpose of this study was to determine the amount of (225)Ac and non-equilibrium progeny in the mouse kidney after the injection of (225)Ac-huM195 antibody and examine the dosimetric consequences. Groups of mice were sacrificed at 24, 96 and 144 h after injection with (225)Ac-huM195 antibody and kidneys excised. One kidney was used for gamma ray spectroscopic measurements by a high-purity germanium (HPGe) detector. The second kidney was used to generate frozen tissue sections which were examined by digital autoradiography (DAR). Two measurements were performed on each kidney specimen: (1) immediately post-resection and (2) after sufficient time for any non-equilibrium excess (213)Bi to decay completely. Comparison of these measurements enabled estimation of the amount of excess (213)Bi reaching the kidney (γ-ray spectroscopy) and its sub-regional distribution (DAR). The average absorbed dose to whole kidney, determined by spectroscopy, was 0.77 (SD 0.21) Gy kBq(-1), of which 0.46 (SD 0.16) Gy kBq(-1) (i.e. 60%) was due to non-equilibrium excess (213)Bi. The relative contributions to renal cortex and medulla were determined by DAR. The estimated dose to the cortex from non-equilibrium excess (213)Bi (0.31 (SD 0.11) Gy kBq(-1)) represented ∼46% of the total. For the medulla the dose contribution from excess (213)Bi (0.81 (SD 0.28) Gy kBq(-1)) was ∼80% of the total. Based on these estimates, for human patients we project a kidney-absorbed dose of 0.28 Gy MBq(-1) following administration of (225)Ac-huM195 with non-equilibrium excess (213)Bi responsible for approximately 60% of the total. Methods to reduce renal accumulation of radioactive progeny appear to be necessary for the success of (225)Ac radioimmunotherapy.

First-in-Human Imaging with 89Zr-Df-IAB2M Anti-PSMA Minibody in Patients with Metastatic Prostate Cancer: Pharmacokinetics, Biodistribution, Dosimetry, and Lesion Uptake

We conducted a phase I dose-escalation study with 89Zr-desferrioxamine-IAB2M (89Zr-IAB2M), an anti–prostate-specific membrane antigen minibody, in patients with metastatic prostate cancer. Methods: Patients received 185 MBq (5 mCi) of 89Zr-IAB2M and Df-IAB2M at total mass doses of 10 (n = 6), 20 (n = 6), and 50 mg (n = 6). Whole-body and serum clearance, normal-organ and lesion uptake, and radiation absorbed dose were estimated, and the effect of mass escalation was analyzed. Results: Eighteen patients were injected and scanned without side effects. Whole-body clearance was monoexponential, with a median biologic half-life of 215 h, whereas serum clearance showed biexponential kinetics, with a median biologic half-life of 3.7 (12.3%/L) and 33.8 h (17.9%/L). The radiation absorbed dose estimates were 1.67, 1.36, and 0.32 mGy/MBq to liver, kidney, and marrow, respectively, with an effective dose of 0.41 mSv/MBq (1.5 rem/mCi). Both skeletal and nodal lesions were detected with 89Zr-IAB2M, most visualized by 48-h imaging. Conclusion: 89Zr-IAB2M is safe and demonstrates favorable biodistribution and kinetics for targeting metastatic prostate cancer. Imaging with 10 mg of minibody mass provides optimal biodistribution, and imaging at 48 h after injection provides good lesion visualization. Assessment of lesion targeting is being studied in detail in an expansion cohort.

Changes in FDG Tumor Uptake during and after Fractionated Radiation Therapy in a Rodent Tumor Xenograft

OBJECTIVE: The uptake of FDG was measured before, during, and after fractionated radiation in order to evaluate the potential of FDG-PET imaging as an indicator of tumor response.METHODS: The study was performed with nude rats bearing the human neuroblastoma BE(2)C tumor xenografts. Tumors were irradiated with 10 fractions of 2 Gy using a 320 kV(p) X-ray unit. Following a baseline FDG-PET scan, repeat scans were performed weekly until animal sacrifice. The rodents were given up to 10 FDG-PET scans, over a period of up to 75 days posttreatment.RESULTS AND CONCLUSIONS: Neither, the average and maximum activity/cc of FDG tumor uptake, nor the respective standardized uptake values (SUV), correlated with tumor response. Instead, the total FDG uptake (defined as the product of the average FDG activity/cc with the tumor volume) correlated better with tumor response.

PET-based compartmental modeling of (124)I-A33 antibody: quantitative characterization of patient-specific tumor targeting in colorectal cancer.

PurposeThe molecular specificity of monoclonal antibodies (mAbs) directed against tumor antigens has proven effective for targeted therapy of human cancers, as shown by a growing list of successful antibody-based drug products. We describe a novel, nonlinear compartmental model using PET-derived data to determine the “best-fit” parameters and model-derived quantities for optimizing biodistribution of intravenously injected 124I-labeled antitumor antibodies.MethodsAs an example of this paradigm, quantitative image and kinetic analyses of anti-A33 humanized mAb (also known as “A33”) were performed in 11 colorectal cancer patients. Serial whole-body PET scans of 124I-labeled A33 and blood samples were acquired and the resulting tissue time–activity data for each patient were fit to a nonlinear compartmental model using the SAAM II computer code.ResultsExcellent agreement was observed between fitted and measured parameters of tumor uptake, “off-target” uptake in bowel mucosa, blood clearance, tumor antigen levels, and percent antigen occupancy.ConclusionThis approach should be generally applicable to antibody–antigen systems in human tumors for which the masses of antigen-expressing tumor and of normal tissues can be estimated and for which antibody kinetics can be measured with PET. Ultimately, based on each patient’s resulting “best-fit” nonlinear model, a patient-specific optimum mAb dose (in micromoles, for example) may be derived.

First-in-human HER2-targeted imaging using 89Zr-pertuzumab PET/CT: Dosimetry and clinical application in patients with breast cancer

In what we believe to be a first-in-human study, we evaluated the safety and dosimetry of 89Zr-pertuzumab PET/CT for human epidermal growth factor receptor 2 (HER2)–targeted imaging in patients with HER2-positive breast cancer. Methods: Patients with HER2-positive breast cancer and evidence of distant metastases were enrolled in an institutional review board–approved prospective clinical trial. Pertuzumab was conjugated with deferoxamine and radiolabeled with 89Zr. Patients underwent PET/CT with 74 MBq of 89Zr-pertuzumab in a total antibody mass of 20–50 mg of pertuzumab. PET/CT, whole-body probe counts, and blood drawing were performed over 8 d to assess pharmacokinetics, biodistribution, and dosimetry. PET/CT images were evaluated for the ability to visualize HER2-positive metastases. Results: Six patients with HER2-positive metastatic breast cancer were enrolled and administered 89Zr-pertuzumab. No toxicities occurred. Dosimetry estimates from OLINDA demonstrated that the organs receiving the highest doses (mean ± SD) were the liver (1.75 ± 0.21 mGy/MBq), the kidneys (1.27 ± 0.28 mGy/MBq), and the heart wall (1.22 ± 0.16 mGy/MBq), with an average effective dose of 0.54 ± 0.07 mSv/MBq. PET/CT demonstrated optimal imaging 5–8 d after administration. 89Zr-pertuzumab was able to image multiple sites of malignancy and suggested that they were HER2-positive. In 2 patients with both known HER2-positive and HER2-negative primary breast cancers and brain metastases, 89Zr-pertuzumab PET/CT suggested that the brain metastases were HER2-positive. In 1 of the 2 patients, subsequent resection of a brain metastasis proved HER2-positive disease, confirming that the 89Zr-pertuzumab avidity was a true-positive result for HER2-positive malignancy. Conclusion: This first-in-human study demonstrated safety, dosimetry, biodistribution, and successful HER2-targeted imaging with 89Zr-pertuzumab PET/CT. Potential clinical applications include assessment of the HER2 status of lesions that may not be accessible to biopsy and assessment of HER2 heterogeneity.