Copper-64 trastuzumab PET imaging: a reproducibility study.

BACKGROUND: The current study aims to assess the safety, pharmacokinetics, feasibility, and reproducibility of immunoPET imaging with copper-64 (64Cu) trastuzumab. METHODS: An IV injection of 296-370 MBq/5 mg 64Cu-trastuzumab was administered between 1 to 4 hours after routine trastuzumab treatment. Whole-body PET scans were performed immediately post-injection and at 24 hours post-injection. Serial pharmacokinetics were performed. Of 11 patients (median age of 52; range of 31-61), 8 underwent a repeat study with 64Cu-trastuzumab to assess image and pharmacokinetic reproducibility. Patients were monitored for toxicity. RESULTS: Patients experienced no allergic reactions or significant adverse effects from 64Cu-trastuzumab. Eight patients successfully completed a repeat 64Cu-trastuzumab study, with acceptable reproducibility of both the biodistribution and pharmacokinetic clearance. Study 1 versus study 2 showed similar serum concentration post-injection (mean 42.4±7.8 %ID/L vs. 44.7±12.6 %ID/L) and similar T1/2 (single exponential 46.1 vs. 44.2 hours), P>0.5. The volume of distribution (median 2.50 L) was in the range reported for trastuzumab and close to the estimated plasma volume of 2.60 L. Of 11 patients, two had 64Cu-trastuzumab localization corresponding to known tumor sites - one in liver and one in breast. CONCLUSIONS: Preliminary results suggest that scanning with 64Cu-trastuzumab is feasible, safe, and reproducible. Tumor uptake of 64Cu-trastuzumab was observed, but tumor detection exhibited low sensitivity in this study in which imaging was performed in the presence of trastuzumab therapy.

Utility of positron emission tomography for drug development for heart failure.

Only about 1 in 5,000 investigational agents in a preclinical stage acquires Food and Drug Administration approval. Among many reasons for this includes an inefficient transition from preclinical to clinical phases, which exponentially increase the cost and the delays the process of drug development. Positron emission tomography (PET) is a nuclear imaging technique that has been used for the diagnosis, risk stratification, and guidance of therapy. However, lately with the advance of radiochemistry and of molecular imaging technology, it became evident that PET could help novel drug development process. By using a PET radioligand to report on receptor occupancy during novel agent therapy, it may help assess the effectiveness, efficacy, and safety of such a new medication in an early preclinical stage and help design successful clinical trials even at a later phase. In this article, we explore the potential implications of PET in the development of new heart failure therapies and review PET's application in the respective pathophysiologic pathways such as myocardial perfusion, metabolism, innervation, inflammation, apoptosis, and cardiac remodeling.

Theranostic pretargeted radioimmunotherapy of colorectal cancer xenografts in mice using picomolar affinity 86Y- or ¹77Lu-DOTA-Bn binding scFv C825/GPA33 IgG bispecific immunoconjugates.

PURPOSE: GPA33 is a colorectal cancer (CRC) antigen with unique retention properties after huA33-mediated tumor targeting. We tested a pretargeted radioimmunotherapy (PRIT) approach for CRC using a tetravalent bispecific antibody with dual specificity for GPA33 tumor antigen and DOTA-Bn-(radiolanthanide metal) complex. METHODS: PRIT was optimized in vivo by titrating sequential intravenous doses of huA33-C825, the dextran-based clearing agent, and the C825 haptens (177)Lu-or (86)Y-DOTA-Bn in mice bearing the SW1222 subcutaneous (s.c.) CRC xenograft model. RESULTS: Using optimized PRIT, therapeutic indices (TIs) for tumor radiation-absorbed dose of 73 (tumor/blood) and 12 (tumor/kidney) were achieved. Estimated absorbed doses (cGy/MBq) to tumor, blood, liver, spleen, and kidney for single-cycle PRIT were 65.8, 0.9 (TI 73), 6.3 (TI 10), 6.6 (TI 10), and 5.3 (TI 12), respectively. Two cycles of PRIT (66.6 or 111 MBq (177)Lu-DOTA-Bn) were safe and effective, with a complete response of established s.c. tumors (100 - 700 mm(3)) in nine of nine mice, with two mice alive without recurrence at >140 days. Tumor log kill in this model was estimated to be 2.1 - 3.0 based on time to 500-mm(3) tumor recurrence. In addition, PRIT dosimetry/diagnosis was performed by PET imaging of the positron-emitting DOTA hapten (86)Y-DOTA-Bn. CONCLUSION: We have developed anti-GPA33 PRIT as a triple-step theranostic strategy for preclinical detection, dosimetry, and safe targeted radiotherapy of established human colorectal mouse xenografts.

89Zr-huJ591 immuno-PET imaging in patients with advanced metastatic prostate cancer.

PURPOSE: Given the bone tropism of prostate cancer, conventional imaging modalities poorly identify or quantify metastatic disease. (89)Zr-huJ591 positron emission tomography (PET) imaging was performed in patients with metastatic prostate cancer to analyze and validate this as an imaging biomarker for metastatic disease. The purpose of this initial study was to assess safety, biodistribution, normal organ dosimetry, and optimal imaging time post-injection for lesion detection. METHODS: Ten patients with metastatic prostate cancer received 5 mCi of (89)Zr-huJ591. Four whole-body scans with multiple whole-body count rate measurements and serum activity concentration measurements were obtained in all patients. Biodistribution, clearance, and lesion uptake by (89)Zr-huJ591 immuno-PET imaging was analyzed and dosimetry was estimated using MIRD techniques. Initial assessment of lesion targeting of (89)Zr-huJ591 was done. Optimal time for imaging post-injection was determined. RESULTS: The dose was well tolerated with mild chills and rigors seen in two patients. The clearance of (89)Zr-huJ591 from serum was bi-exponential with biological half-lives of 7 ± 4.5 h (range 1.1-14 h) and 62 ± 13 h (range 51-89 h) for initial rapid and later slow phase. Whole-body biological clearance was 219 ± 48 h (range 153-317 h). The mean whole-body and liver residence time was 78.7 and 25.6 h, respectively. Dosimetric estimates to critical organs included liver 7.7 ± 1.5 cGy/mCi, renal cortex 3.5 ± 0.4 cGy/mCi, and bone marrow 1.2 ± 0.2 cGy/mCi. Optimal time for patient imaging after injection was 7 ± 1 days. Lesion targeting of bone or soft tissue was seen in all patients. Biopsies were performed in 8 patients for a total 12 lesions, all of which were histologically confirmed as metastatic prostate cancer. One biopsy-proven lesion was not positive on (89)Zr-huJ591, while the remaining 11 lesions were (89)Zr-huJ591 positive. Two biopsy-positive nodal lesions were noted only on (89)Zr-huJ591 study, while the conventional imaging modality was negative. CONCLUSION: (89)Zr-huJ591 PET imaging of prostate-specific membrane antigen expression is safe and shows good localization of disease in prostate cancer patients. Liver is the critical organ for dosimetry, and 7 ± 1 days is the optimal imaging time. A larger study is underway to determine lesion detection in an expanded cohort of patients with metastatic prostate cancer.

Noninvasive measurement of androgen receptor signaling with a positron-emitting radiopharmaceutical that targets prostate-specific membrane antigen.

Despite encouraging clinical results with next generation drugs (MDV3100 and abiraterone) that inhibit androgen receptor (AR) signaling in patients with castration-resistant prostate cancer (CRPC), responses are variable and short-lived. There is an urgent need to understand the basis of resistance to optimize their future use. We reasoned that a radiopharmaceutical that measures intratumoral changes in AR signaling could substantially improve our understanding of AR pathway directed therapies. Expanding on previous observations, we first show that prostate-specific membrane antigen (PSMA) is repressed by androgen treatment in multiple models of AR-positive prostate cancer in an AR-dependent manner. Conversely, antiandrogens up-regulate PSMA expression. These expression changes, including increased PSMA expression in response to treatment with the antiandrogen MDV3100, can be quantitatively measured in vivo in human prostate cancer xenograft models through PET imaging with a fully humanized, radiolabeled antibody to PSMA, (64)Cu-J591. Collectively, these results establish that relative changes in PSMA expression levels can be quantitatively measured using a human-ready imaging reagent and could serve as a biomarker of AR signaling to noninvasively evaluate AR activity in patients with CRPC.

Positron Emission Tomography Imaging of Staphylococcus aureus Infection Using a Nitro-Prodrug Analogue of 2-[18F]F-p-Aminobenzoic Acid.

Deep-seated bacterial infections caused by pathogens such as Staphylococcus aureus are difficult to diagnose and treat and are thus a major threat to human health. In previous work we demonstrated that positron emission tomography (PET) imaging with 2-[18F]F-p-aminobenzoic acid (2-[18F]F-PABA) could noninvasively identify, localize, and monitor S. aureus infection with excellent sensitivity and specificity in a rodent soft tissue infection model. However, 2-[18F]F-PABA is rapidly N-acetylated and eliminated, and in an attempt to improve radiotracer accumulation in bacteria we adopted a prodrug strategy in which the acid was protected by an ester and the amine was replaced with a nitro group. Metabolite analysis indicated that the nitro group of ethyl 2-[18F]fluoro-4-nitrobenzoate (2-[18F]F-ENB) is converted to the corresponding amine by bacteria-specific nitroreductases while the ester is hydrolyzed in vivo into the acid. PET/CT imaging of 2-[18F]F-ENB and the corresponding acid 2-[18F]F-NB in a rat soft tissue infection model demonstrated colocalization of the radiotracer with the bioluminescent signal arising from S. aureus Xen29, and demonstrated that the tracer could differentiate S. aureus infection from sterile inflammation. Significantly, the accumulation of both 2-[18F]F-ENB and 2-[18F]F-NB at the site of infection was 17-fold higher than at the site of sterile inflammation compared to 8-fold difference observed for 2-[18F]F-PABA, supporting the proposal that the active radiotracer in vivo is 2-[18F]F-NB. Collectively, these data suggest that 2-[18F]F-ENB and 2-[18F]F-NB have the potential for translation to humans as a rapid, noninvasive diagnostic tool to identify and localize S. aureus infections.

Complement factor H-deficient mice develop spontaneous hepatic tumors.

Hepatocellular carcinoma (HCC) is difficult to detect, carries a poor prognosis, and is one of few cancers with an increasing yearly incidence. Molecular defects in complement factor H (CFH), a critical regulatory protein of the complement alternative pathway (AP), are typically associated with inflammatory diseases of the eye and kidney. Little is known regarding the role of CFH in controlling complement activation within the liver. While studying aging CFH-deficient (fH-/-) mice, we observed spontaneous hepatic tumor formation in more than 50% of aged fH-/- males. Examination of fH-/- livers (3-24 months) for evidence of complement-mediated inflammation revealed widespread deposition of complement-activation fragments throughout the sinusoids, elevated transaminase levels, increased hepatic CD8+ and F4/80+ cells, overexpression of hepatic mRNA associated with inflammatory signaling pathways, steatosis, and increased collagen deposition. Immunostaining of human HCC biopsies revealed extensive deposition of complement fragments within the tumors. Investigating the Cancer Genome Atlas also revealed that increased CFH mRNA expression is associated with improved survival in patients with HCC, whereas mutations are associated with worse survival. These results indicate that CFH is critical for controlling complement activation in the liver, and in its absence, AP activation leads to chronic inflammation and promotes hepatic carcinogenesis.

Preclinical radioimmunotargeting of folate receptor alpha using the monoclonal antibody conjugate DOTA-MORAb-003.

INTRODUCTION: The in vitro and in vivo behavior of the radiolabeled monoclonal antibody MORAb-003 was investigated as a prelude to a clinical trial. METHODS: The cellular retention of 111In- and 131I-labeled MORAb-003 was investigated using IGROV1 and SW620 cells. Biodistribution studies in tumor-bearing mice were performed with the more favorable agent. RESULTS: Five 1,4,7,10-tetraazacyclododecane-N,N',N",N'"-tetraacetic acid (DOTA) molecules were conjugated to MORAb-003 with no apparent loss of immunoreactivity. Radiolabeled MORAb-003 had a high affinity for the folate receptor alpha (FRA) expressed by both IGROV1 and SW620 cells and was found to bind to around 8 x 10(5) and 7 x 10(5) sites/cell, respectively. Both cancer cell lines were found to internalize both 131I- and 111In-labeled MORAb-003, but 111In was retained and 131I was released as iodide. In athymic mice, 111In-DOTA-MORAb-003 was cleared from the blood with a single exponential biological clearance rate of 110 h. The uptake in SW620 tumors was 32+/-5%ID/g after 4 days. The clearance rate of activity from normal organs such as liver, kidney and spleen was similar to the blood clearance and was 5.36%ID/g, 4.03%ID/g and 4.36%ID/g at 1 day postinjection and 2.14%ID/g, 1.65%ID/g and 3.74%ID/g after 8 days, respectively. In a pilot clinical study, the biodistribution and tumor targeting of 111In-MORAb-003 was assessed in three patients undergoing treatment with cold MORAb-003. CONCLUSION: MORAb-003 is an attractive antibody for radioimmunoscintigraphy and possibly radioimmunotherapy of FRA-expressing cancers in addition to its potential direct therapeutic effects.

GABAA Receptor Availability Changes Underlie Symptoms in Isolated Cervical Dystonia.

GABAA receptor availability changes within sensorimotor regions have been reported in some isolated forms of dystonia. Whether similar abnormalities underlie symptoms in cervical dystonia is not known. In the present study, a total of 15 cervical dystonia patients and 15 age- and sex-matched controls underwent 11C-flumazenil PET/CT scanning. The density of available GABAA receptors was estimated using a Simplified Reference Tissue Model 2. Group differences were evaluated using a two-sample T-test, and correlations with dystonia severity, as measured by the Toronto Western Spasmodic Torticollis Rating Scale, and disease duration were evaluated using a regression analysis. Voxel-based analyses revealed increased GABAA availability within the right precentral gyrus in brain motor regions previously associated with head turning and the left parahippocampal gyrus. GABAA availability within the bilateral cerebellum was negatively correlated with dystonia severity, and GABAA availability within the right thalamus and a variety of cerebellar and cortical regions were negatively correlated with disease duration. While GABAA availability changes within primary motor areas could represent a partial compensatory response to loss of inhibition within sensorimotor network, GABAergic signaling impairment within the cerebellum may be a key contributor to dystonia severity.

I-124 codrituzumab imaging and biodistribution in patients with hepatocellular carcinoma.

BACKGROUND: I-124 codrituzumab (aka GC33), an antibody directed at Glypican 3, was evaluated in patients with hepatocellular carcinoma (HCC). Fourteen patients with HCC underwent baseline imaging with I-124 codrituzumab (~ 185 MBq, 10 mg). Seven of these patients undergoing sorafenib/immunotherapy with 2.5 or 5 mg/kg of cold codrituzumab had repeat imaging, with co-infusion of I-124 codrituzumab, as part of their immunotherapy treatment. Three patients who progressed while on sorafenib/immunotherapy were re-imaged after a 4-week washout period to assess for the presence of antigen. Serial positron emission tomography (PET) imaging and pharmacokinetics were performed following I-124 codrituzumab. An ELISA assay was used to determine "cold" codrituzumab serum pharmacokinetics and compare it to that of I-124 codrituzumab. Correlation of imaging results was performed with IHC. Short-term safety assessment was also evaluated. RESULTS: Thirteen patients had tumor localization on baseline I-124 codrituzumab; heterogeneity in tumor uptake was noted. In three patients undergoing repeat imaging while on immunotherapy/sorafenib, evidence of decreased I-124 codrituzumab uptake was noted. All three patients who underwent imaging after progression while on immunotherapy continued to have I-124 codrituzumab tumor uptake. Pharmacokinetics of I-124 codrituzumab was similar to that of other intact IgG. No significant adverse events were observed related to the I-124 codrituzumab. CONCLUSIONS: I-124 codrituzumab detected tumor localization in most patients with HCC. Pharmacokinetics was similar to that of other intact iodinated humanized IgG. No visible cross-reactivity with normal organs was observed.

Positron Emission Tomography Imaging with 2-[18F]F- p-Aminobenzoic Acid Detects Staphylococcus aureus Infections and Monitors Drug Response.

Staphylococcus aureus is the leading cause of life-threatening infections, frequently originating from unknown or deep-seated foci. Source control and institution of appropriate antibiotics remain challenges, especially with infections due to methicillin-resistant S. aureus (MRSA). In this study, we developed a radiofluorinated analog of para-aminobenzoic acid (2-[18F]F-PABA) and demonstrate that it is an efficient alternative substrate for the S. aureus dihydropteroate synthase (DHPS). 2-[18F]F-PABA rapidly accumulated in vitro within laboratory and clinical (including MRSA) strains of S. aureus but not in mammalian cells. Biodistribution in murine and rat models demonstrated localization at infection sites and rapid renal elimination. In a rat model, 2-[18F]F-PABA positron emission tomography (PET) rapidly differentiated S. aureus infection from sterile inflammation and could also detect therapeutic failures associated with MRSA. These data suggest that 2-[18F]F-PABA has the potential for translation to humans as a rapid, noninvasive diagnostic tool to identify, localize, and monitor S. aureus infections.

Synthesis and biological evaluation of a fluorine-18 derivative of dasatinib.

Tyrosine kinases often play pivotal roles in the pathogenesis of cancer and are good candidates for therapeutic intervention and targeted molecular imaging. The precursor synthesis, radiosynthesis, and biological characterization of a fluorine-18 analog of dasatinib, a multitargeted kinase inhibitor, are reported. Compound 5 potently inhibits Abl, Src, and Kit kinases and inhibits K562 and M07e/p210bcr-abl human leukemic cell growth. Using positron emission tomography, we visualized K562 tumor xenografts in mice with [18F]-5.

Imaging the pharmacodynamics of HER2 degradation in response to Hsp90 inhibitors.

The development of therapeutic inhibitors of key signaling pathways has been hampered by the inability to assess the effect of a drug on its target in the patient. 17-allylaminogeldanamycin (17-AAG) is the first Hsp90 inhibitor to be tested in a clinical trial. It causes the degradation of HER2 and other Hsp90 targets, and has antitumor activity in preclinical models. We have developed a method for imaging the inhibition of Hsp90 by 17-AAG. We labeled an F(ab')2 fragment of the anti-HER2 antibody Herceptin with 68Ga, a positron emitter, which allows the sequential positron-emission tomographic imaging of HER2 expression. We have used this method to quantify as a function of time the loss and recovery of HER2 induced by 17-AAG in animal tumors. This approach allows noninvasive imaging of the pharmacodynamics of a targeted drug and will facilitate the rational design of combination therapy based on target inhibition.

Phase Ib study of codrituzumab in combination with sorafenib in patients with non-curable advanced hepatocellular carcinoma (HCC).

PURPOSE: Codrituzumab, a humanized antibody against glypican-3, is highly expressed in HCC. A phase I study evaluated the combination with sorafenib in HCC. PATIENTS AND METHODS: In a 3 + 3 design, codrituzumab was given intravenously in various doses with sorafenib 400 mg twice daily to patients with advanced HCC, age ≥18, ECOG 0-1, Child-Pugh A and B7, adequate organ functions, and no prior systemic therapy, with tumor assessment by RECIST 1.0 and safety by CTCAE 3.0. PK and pre, during, and post-therapy 124I radiolabeled codrituzumab PET scan imaging were performed. RESULTS: 41 patients were enrolled: 2.5 mg/kg weekly (qw) (12), 5 mg/kg qw (12), 10 mg/kg qw (3), 1600 mg every 2 weeks (q2w) (6), and 1600 mg qw (7). Two drug limiting toxicities occurred: grade 3 hyponatremia at 5 mg/kg and grade 3 hyponatremia and hyperglycemia at 1600 mg q2w. Adverse events occurred in 80% of patients, including at least one ≥grade 3: ten (25%) increased AST, three (7.5%) increased ALT, and ten (25%) increased lipase. There were no responses and nine (25.7%) had stable disease. PK C max and AUCt of codrituzumab and sorafenib were comparable to single-agent data. Thirteen out of 14 patients showed 124I radiolabeled codrituzumab uptake in tumor. In all three patients who underwent a post-progression PET, glypican-3 remained expressed. CONCLUSION: Codrituzumab plus sorafenib were tolerated at 1600 mg q2w and 400 mg bid, respectively, with no responses. Codrituzumab exerts selective distribution to HCC cells, and GPC3 does not show any down-regulation post-progression (NCT00976170).

Pretargeted radioimmunotherapy with a single-chain antibody/streptavidin construct and radiolabeled DOTA-biotin: strategies for reduction of the renal dose.

UNLABELLED: Multistep immune targeting holds great promise for radioimmunodiagnosis and therapy of cancer. Pretargeting of the tetrameric single-chain, variable-fragment streptavidin construct of the tetrameric monoclonal antibody CC49 with subsequent administration of radiolabeled 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid (DOTA)-biotin has yielded promising results in TAG-72-expressing tumor xenograft models. A potential limitation of this approach, however, has been high and prolonged renal uptake of radioactivity. The objective of the current study, therefore, was to evaluate the reduction of kidney uptake of radiolabeled DOTA-biotin achieved by each of 4 different methods. METHODS: A human pancreatic adenocarcinoma xenograft model (HPAC) in nude mice was used. The animals were intravenously injected with the antibody-streptavidin construct and a synthetic clearing agent (biotinylated N-acetyl-galactosamine) 24 and 4 h, respectively, before the administration of (67)Ga-DOTA-biotin. For reduction of the renal uptake, different groups of mice were treated with streptavidin saturated with biotin, with several administrations of lysine or colchicine or with a succinylated antibody-streptavidin construct (resulting in a decreased electrical charge). All animals were sacrificed 24 h after injection of the (67)Ga-DOTA-biotin for biodistribution and quantitative autoradiography (QAR) studies and selected animals underwent microSPECT/microCT studies. RESULTS: There was marked targeting of the radiolabeled DOTA-biotin to tumor in all groups except in negative-control animals. Only succinylation of the scFv-CC49-streptavidin fusion protein significantly reduced ( approximately 30%) kidney uptake without affecting tumor activity. QAR corroborated these results and demonstrated that radiolabeled DOTA-biotin localized selectively in the renal cortex. Among the other experimental groups, there was no change in kidney uptake of the radiolabeled biotin. CONCLUSION: In contrast to directly labeled antibodies and antibody fragments, administration of the negatively charged amino acid lysine was largely ineffective in pretargeting strategies with a single-chain-immuno-streptavidin fusion protein. Succinylation of the scFv-CC49-streptavidin construct, on the other hand, reduces kidney uptake of subsequently administered radiolabeled biotin, presumably by inhibiting reuptake of the fusion protein in the proximal renal tubules, and, therefore, could significantly reduce renal doses and improve therapeutic indices associated with multistep immune targeting approaches to radioimmunotherapy.

Early tumor response to Hsp90 therapy using HER2 PET: comparison with 18F-FDG PET.

UNLABELLED: We compared (68)Ga-DOTA-F(ab')(2)-herceptin (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid [HER2 PET]) and (18)F-FDG PET for imaging of tumor response to the heat shock protein 90 (Hsp90) inhibitor 17-allylamino-17-demethoxygeldanamycin (17AAG). METHODS: Mice bearing BT474 breast tumor xenografts were scanned with (18)F-FDG PET and HER2 PET before and after 17AAG treatment and then biweekly for up to 3 wk. RESULTS: Within 24 h after treatment, a significant decrease in HER2 was measured by HER2 PET, whereas (18)F-FDG PET uptake, a measure of glycolysis, was unchanged. Marked growth inhibition occurred in treated tumors but became evident only by 11 d after treatment. Thus, Her2 downregulation occurs independently of changes in glycolysis after 17AAG therapy, and Her2 reduction more accurately predicts subsequent tumor growth inhibition. CONCLUSION: HER2 PET is an earlier predictor of tumor response to 17AAG therapy than (18)F-FDG PET.

Radioimmunotargeting of human rhabdomyosarcoma using monoclonal antibody 8H9.

Although metastatic rhabdomyosarcoma (RMS) is chemotherapy and radiotherapy responsive, few patients are cured. 8H9, a murine IgG(1) monoclonal antibody, recognizes a unique cell surface tumor antigen broadly distributed on neuroectodermal, epithelial, and mesenchymal tumors, including RMS. We now report on the in vitro characterization of radiolabeled 8H9 and its in vivo immunotargeting potential in mice with subcutaneous human RMS. Saturation-binding studies carried out to determine (125)I-8H9 affinity to the RMS cell line HTB82 demonstrated that (125)I-8H9 had a K(d) of 10.3nM with an estimated 115,000 binding sites on every HTB82 cell. (125)I-8H9 was retained on the cell surface without significant internalization. Biodistribution of (125)I-8H9 was studied in athymic mice bearing HTB82 xenografts. Following intravenous injection of 4.44MBq of (125)I-8H9, selective tumor uptake was evident 4 to 172 hours after injection. Average tumor uptake was 7.0 +/- 1.8, 11.5 +/- 3.9, 15.1 +/- 3.7, and 5.4 +/- 1.2% injected dose per gram at 4, 24, 48, and 172 hours, respectively. Mean tumor: tissue ratios were maximal at 172 hours (for lung, 4, kidney, 6, liver, 7, spleen, 11, femur, 14, muscle, 18, and brain, 48). Established RMS xenografts treated with a single injection of 18.5 MBq (131)I-8H9 were significantly suppressed compared to controls. Radiolabeled 8H9 effectively targeted RMS xenografts and may have a potential clinical role in radioimmunotherapy.

Radiolabeled monoclonal antibodies specific to the extracellular domain of prostate-specific membrane antigen: preclinical studies in nude mice bearing LNCaP human prostate tumor.

UNLABELLED: Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein, is highly expressed by virtually all prostate cancers. PSMA is also expressed on the tumor vascular endothelium of virtually all solid carcinomas and sarcomas but not on normal vascular endothelium. PSMA is currently the focus of several diagnostic and therapeutic strategies. We have previously reported on the radiolabeling and in vitro binding properties of monoclonal antibodies (mAbs) (J415, J533, and J591) that recognize and bind with high affinity to the extracellular domain of PSMA (PSMA(ext)). This article reports on the in vivo behavior and tumor uptake of (131)I- and (111)In-labeled antiPSMA(ext) mAbs (J415, J533, and J591) and their potential utility for radioimmunotherapy. METHODS: In nude mice bearing PSMA-positive human LNCaP tumors, the pharmacokinetics, biodistribution, and tumor uptake of these antibodies was compared with (111)In-7E11 mAb, specific to the intracellular domain of PSMA (PSMA(int)). Autoradiographic studies were done to identify intratumoral distribution of radiolabeled mAbs. RESULTS: With (131)I-labeled antibodies, the net tumor retention of radioactivity by day 6 was significantly higher with J415 (15.4% +/- 1.1%) and 7E11 (14.5% +/- 1.7%) than with J591 (9.58% +/- 1.1%). By contrast, the tumor uptake of (111)In-1,4,7,10-tetraazacyclododecane-N,N',N", N"'-tetraacetic acid-labeled J415 and J591 gradually increased with time and was quite similar to that of 7E11. In addition, the blood clearance of (111)In-labeled J415 and J591 antibodies was relatively faster than that of radiolabeled 7E11. As a consequence, the tumor-to-blood ratios with J415 and J591 were higher than that of 7E11. The localization of radiolabeled anti-PSMA(ext) antibodies in PSMA-positive LNCaP tumors was highly specific because the tumor uptake of (131)I-labeled J415 and J591 was more than twice that of a nonspecific antibody. Furthermore, the tumor uptake of (131)I-J591 was almost 20 times higher in PSMA-positive LNCaP tumors than in PSMA-negative PC3 and DU145 tumor xenografts. Autoradiographic studies suggested that 7E11 (anti-PSMA(int)) distinctly favors localization to areas of necrosis whereas J415 and J591 (anti-PSMA(ext)) demonstrated a distinct preferential accumulation in areas of viable tumor. CONCLUSION: These results clearly demonstrate that PSMA-specific internalizing antibodies such as J415 and J591 may be the ideal mAbs for the development of novel therapeutic methods to target the delivery of beta-emitting radionuclides ((131)I, (90)Y, and (177)Lu) for the treatment of PSMA-positive tumors. In addition, because J591 and J415 mAbs are specific to PSMA(ext), thus targeting viable tumor, these immunoconjugates are better candidates for targeted radioimmunotherapy than are antibodies targeting PSMA(int).

Efficient 1-step radiolabeling of monoclonal antibodies to high specific activity with 225Ac for α-particle radioimmunotherapy of cancer.

UNLABELLED: Targeted α-particle radiation using the radioisotope (225)Ac is a promising form of therapy for various types of cancer. Historic obstacles to the use of (225)Ac have been the difficulty in finding suitable chelators to stably attach it to targeting vehicles such as peptides and monoclonal antibodies, the low specific activities of the products, and the lack of cost-effective radiolabeling procedures. We initially solved the first problem with a procedure involving 2 chemical steps that has been used as a standard in preclinical and clinical studies. However, this procedure involves the loss of 90% of the input (225)Ac. A more efficient, economical process is needed to facilitate the more widespread use of (225)Ac. METHODS: We conjugated representative antibodies with 2 forms of DOTA as well as other chelators as controls. We developed conditions to radiolabel these constructs in 1 chemical step and characterized their stability, immunoreactivity, biodistribution, and therapeutic efficacy in healthy and tumor-bearing mice. RESULTS: DOTA-antibody constructs were labeled to a wide range of specific activities in 1 chemical step at 37°C. Radiochemical yields were approximately 10-fold higher, and specific activities were up to 30-fold higher than with the previous approach. The products retained immunoreactivity and were stable to serum challenge in vitro and in mice. Labeling kinetics of DOTA-antibody constructs linked through a benzyl isothiocyanate linkage were more favorable than those linked through an N-hydroxysuccinimide linkage. Tissue distribution was similar but not identical between the constructs. The constructs produced specific therapeutic responses in a mouse model of acute myeloid leukemia. CONCLUSION: We have characterized an efficient, 1-step radiolabeling method that produces stable, therapeutically active conjugates of antibodies with (225)Ac at high specific activity. We propose that this technology greatly expands the possible clinical applications of (225)Ac monoclonal antibodies.

Phase 1 radioimmunotherapy study with lutetium 177-labeled anti-carbonic anhydrase IX monoclonal antibody girentuximab in patients with advanced renal cell carcinoma.

BACKGROUND: Patients with metastatic clear cell renal cell carcinoma (ccRCC) have a dismal prognosis. Therefore, new and less toxic treatments are needed. OBJECTIVE: We determined the maximum tolerated dose (MTD) and potential therapeutic efficacy of multiple infusions of lutetium 177 ((177)Lu)-girentuximab (cG250) on various dose levels in a phase 1 trial in patients with progressive metastasized ccRCC. DESIGN, SETTING, AND PARTICIPANTS: In this uncontrolled case series in 23 patients with progressive ccRCC metastases, cG250 accumulation was verified by diagnostic indium 111-cG250 imaging. Patients then received a high-activity dose of (177)Lu-cG250. INTERVENTION: Groups of three patients received (177)Lu-cG250, starting at a dose level of 1110 MBq/m(2)(177)Lu-cG250, with dose increments of 370 MBq/m(2) per group. In the absence of persistent toxicity, progressive disease, and accelerated blood clearance, patients were eligible for retreatment after 3 mo with 75% of the previous activity dose. Patients could receive a total of three treatment cycles. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Determination of the MTD was the primary and therapeutic efficacy was the secondary outcome measurement of the study. RESULTS AND LIMITATIONS: The MTD was 2405 MBq/m(2) because higher doses resulted in dose-limiting myelotoxicity. Some patients received second (13 of 23 [56%]) and third (4 of 23 [17%]) treatment cycles. Most patients (17 of 23 [74%]) demonstrated stable disease 3 mo after the first treatment, and one patient showed a partial response that lasted for 9 mo. Mean growth of target tumor lesions was reduced from 40.4% (95% confidence interval [CI], ± 17.0) during the last 3 mo before study entry to 5.5% (95% CI, ± 5.3; p<0.001) at 3 mo after the first treatment cycle. No major nonhematologic side effects were observed. CONCLUSIONS: (177)Lu-cG250 radioimmunotherapy in metastatic ccRCC patients is well tolerated at an activity dose level as high as 2405 MBq/m(2) (MTD). Radioimmunotherapy with (177)Lu-cG250 may stabilize previously progressive metastatic ccRCC.