Towards tailored radiopeptide therapy.

PURPOSE: Somatostatin receptor-targeted radiopeptide therapy is commonly performed using single radioisotopes. We evaluated the benefits and harms of combining radioisotopes in radiopeptide therapy in patients with neuroendocrine tumor. METHODS: Using multivariable-adjusted survival analyses and competing risk analyses we evaluated outcomes in patients with neuroendocrine tumor receiving (90)Y-DOTATOC, (177)Lu-DOTATOC or their combination. RESULTS: (90)Y-DOTATOC plus (177)Lu-DOTATOC treatment was associated with longer survival than (90)Y-DOTATOC (66.1 vs. 47.5 months; n = 1,358; p < 0.001) or (177)Lu-DOTATOC alone (66.1 vs. 45.5 months; n = 390; p < 0.001). (177)Lu-DOTATOC was associated with longer survival than (90)Y-DOTATOC in patients with solitary lesions (HR 0.3, range 0.1 - 0.7; n = 153; p = 0.005), extrahepatic metastases (HR 0.5, range 0.3 - 0.9; n = 256; p = 0.029) and metastases with low uptake (HR 0.1, range 0.05 - 0.4; n = 113; p = 0.001). (90)Y-DOTATOC induced higher hematotoxicity rates than combined treatment (9.5% vs. 4.0%, p = 0.005) or (177)Lu-DOTATOC (9.5 vs. 1.4%, p = 0.002). Renal toxicity was similar among the treatments. CONCLUSIONS: Using (90)Y and (177)Lu might facilitate tailoring radiopeptide therapy and improve survival in patients with neuroendocrine tumors.

Synergism of peptide receptor-targeted Auger electron radiation therapy with anti-angiogenic compounds in a mouse model of neuroendocrine tumors.

BACKGROUND: Neuroendocrine tumors are well vascularized and express specific cell surface markers, such as somatostatin receptors and the glucagon-like peptide-1 receptor (GLP-1R). Using the Rip1Tag2 transgenic mouse model of pancreatic neuroendocrine tumors (pNET), we have investigated the potential benefit of a combination of anti-angiogenic treatment with targeted internal radiotherapy. METHODS: [Lys40(Ahx-DTPA-111In)NH2]-exendin-4, a radiopeptide that selectively binds to GLP-1R expressed on insulinoma and other neuroendocrine tumor cells, was co-administered with oral vatalanib (an inhibitor of vascular endothelial growth factor receptors (VEGFR)) or imatinib (a c-kit/PDGFR inhibitor). The control groups included single-agent kinase inhibitor treatments and [Lys40(Ahx-DTPA-natIn)NH2]-exendin-4 monotherapy. For biodistribution, Rip1Tag2 mice were pre-treated with oral vatalanib or imatinib for 0, 3, 5, or 7 days at a dose of 100 mg/kg. Subsequently, [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 was administered i.v., and the biodistribution was assessed after 4 h. For therapy, the mice were injected with 1.1 MBq [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 and treated with vatalanib or imatinib 100 mg/kg orally for another 7 days. Tumor volume, tumor cell apoptosis and proliferation, and microvessel density were quantified. RESULTS: Combination of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 and vatalanib was significantly more effective than single treatments (p < 0.05) and reduced the tumor volume by 97% in the absence of organ damage. The pre-treatment of mice with vatalanib led to a reduction in the tumor uptake of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4, indicating that concomitant administration of vatalanib and the radiopeptide was the best approach. Imatinib did not show a synergistic effect with [Lys40(Ahx-DTPA-111In)NH2]-exendin-4. CONCLUSION: The combination of 1.1 MBq of [Lys40(Ahx-DTPA-111In)NH2]-exendin-4 with 100 mg/kg vatalanib had the same effect on a neuroendocrine tumor as the injection of 28 MBq of the radiopeptide alone but without any apparent side effects, such as radiation damage of the kidneys.

Targeting GRPR in urological cancers--from basic research to clinical application.

Gastrin releasing peptide (GRP) is a regulatory peptide that acts through its receptor (GRPR) to regulate physiological functions in various organs. GRPR is overexpressed in neoplastic cells of most prostate cancers and some renal cell cancers and in the tumoral vessels of urinary tract cancers. Thus, targeting these tumours with specifically designed GRP analogues has potential clinical application. Potent and specific radioactive, cytotoxic or nonradioactive GRP analogues have been designed and tested in various animal tumour models with the aim of receptor targeting for tumour diagnosis or therapy. All three categories of compound were found suitable for tumour targeting in animal models. The cytotoxic and nonradioactive GRP analogues have not yet shown convincing tumour-reducing effects in human trials; however, the first clinical studies of radioactive GRP analogues--both agonists and antagonists--suggest promising opportunities for both diagnostic tumour imaging and radiotherapy of prostate and other GRPR-expressing cancers.

Cohort study of somatostatin-based radiopeptide therapy with [(90)Y-DOTA]-TOC versus [(90)Y-DOTA]-TOC plus [(177)Lu-DOTA]-TOC in neuroendocrine cancers.

PURPOSE: Radiopeptide therapy is commonly performed with a single radioisotope. We aimed to compare the effectiveness of somatostatin-based radiopeptide therapy with a single versus a combination of radioisotopes. PATIENTS AND METHODS: In a cohort study, patients with metastasized neuroendocrine cancer were treated with repeated cycles of (90)yttrium-labeled tetraazacyclododecane-tetraacetic acid modified Tyr-octreotide ([(90)Y-DOTA]-TOC) or with cycles alternating between [(90)Y-DOTA]-TOC and (177)lutetium-labeled DOTA-TOC ([(177)Lu-DOTA]-TOC) until tumor progression or permanent toxicity. Multivariable Cox regression and competing risk regression were used to study predictors of survival and renal toxicity in patients completing three or more treatment cycles. RESULTS: A total of 486 patients completed three or more treatment cycles; 237 patients received [(90)Y-DOTA]-TOC and 249 patients received [(90)Y-DOTA]-TOC + [(177)Lu-DOTA]-TOC. Patients receiving [(90)Y-DOTA]-TOC + [(177)Lu-DOTA]-TOC had a significantly longer survival than patients receiving [(90)Y-DOTA]-TOC alone (5.51 v 3.96 years; hazard ratio, 0.64; 95% CI, 0.47 to 0.88; P = .006). The rates of severe hematologic toxicities (6.3% v 4.4%; P = .25) and severe renal toxicity (8.9% v 11.2%; P = .47) were comparable in both groups. CONCLUSION: [(90)Y-DOTA]-TOC + [(177)Lu-DOTA]-TOC was associated with improved overall survival compared with [(90)Y-DOTA]-TOC alone in patients completing three or more cycles of treatment. Contrary to the current practice in radiopeptide therapy, our results suggest an advantage of using a combination of radioisotopes.

Response, survival, and long-term toxicity after therapy with the radiolabeled somatostatin analogue [90Y-DOTA]-TOC in metastasized neuroendocrine cancers.

PURPOSE: To investigate response, survival, and safety profile of the somatostatin-based radiopeptide (90)yttrium-labeled tetraazacyclododecane-tetraacetic acid modified Tyr-octreotide ([(90)Y-DOTA]-TOC) in neuroendocrine cancers. PATIENTS AND METHODS: In a clinical phase II single-center open-label trial, patients with neuroendocrine cancers were treated with repeated cycles of [(90)Y-DOTA]-TOC. Each cycle consisted of a single intravenous injection of 3.7GBq/m(2) body-surface [(90)Y-DOTA]-TOC. Additional cycles were withheld in case of tumor progression and/or permanent toxicity. RESULTS: Overall, 1,109 patients received 2,472 cycles of [(90)Y-DOTA]-TOC (median, two; range, one to 10 cycles per patient). Of the 1,109 patients, 378 (34.1%) experienced morphologic response; 172 (15.5%), biochemical response; and 329 (29.7%), clinical response. During a median follow-up of 23 months, 491 patients (44.3%) died. Longer survival was correlated with each: morphologic (hazard ratio [HR], 0.46; 95% CI, 0.38 to 0.56; median survival, 44.7 v 18.3 months; P < .001), biochemical (HR, 0.75; 95% CI, 0.59 to 0.96; 35.3 v 25.7 months; P = .023), and clinical response (HR, 0.68; 95% CI, 0.56 to 0.82; 36.8 v 23.5 months; P < .001). Overall, 142 patients (12.8%) developed grade 3 to 4 transient hematologic toxicities, and 103 patients (9.2%) experienced grade 4 to 5 permanent renal toxicity. Multivariable regression revealed that tumoral uptake in the initial imaging study was predictive for overall survival (HR, 0.45; 95% CI, 0.29 to 0.69; P < .001), whereas the initial kidney uptake was predictive for severe renal toxicity (HR, 1.59; 95% CI, 1.17 to 2.17; P = .003). CONCLUSION: This study documents the long-term outcome of [(90)Y-DOTA]-TOC treatment in a large cohort. Response to [(90)Y-DOTA]-TOC is associated with longer survival. Somatostatin receptor imaging is predictive for both survival after [(90)Y-DOTA]-TOC treatment and occurrence of renal toxicity.

Exendin-4-based radiopharmaceuticals for glucagonlike peptide-1 receptor PET/CT and SPECT/CT.

UNLABELLED: Strong overexpression of glucagonlike peptide-1 (GLP-1) receptors in human insulinoma provides an attractive target for imaging. The first clinical trials demonstrated that GLP-1 receptor SPECT/CT using [Lys(40)(Ahx [6-aminohexanoic acid]-DOTA-(111)In)NH(2)]-exendin-4 can localize hardly detectable insulinomas. However, [Lys(40)(Ahx-DOTA-(111)In)NH(2)]-exendin-4 imaging has drawbacks related to the use of (111)In in that it is costly and carries a relatively high radiation burden for the patient. The aim of this study was the preclinical evaluation of [Lys(40)(Ahx-DOTA-(68)Ga)NH(2)]-exendin-4 for PET/CT and [Lys(40)(Ahx-hydrazinonicotinamide [HYNIC]-(99m)Tc)NH(2)]-exendin-4 for SPECT/CT. METHODS: Internalization, biodistribution, dosimetry, and imaging studies were performed in the Rip1Tag2 mouse model of pancreatic beta-cell carcinogenesis and compared with our gold standard [Lys(40)(Ahx-DOTA-(111)In)NH(2)]-exendin-4. Poly-glutamic acid and Gelofusine, a gelatin-based plasma expander, were used for renal uptake reduction studies. RESULTS: The tumor uptake of [Lys(40)(Ahx-DOTA-(68)Ga)NH(2)]-exendin-4 was 205 +/- 59 percentage injected activity per gram of tissue at 4 h. Other GLP-1 receptor-positive organs showed more than 4.8 times lower radioactivity uptake. [Lys(40)(Ahx-HYNIC-(99m)Tc/ethylenediaminediacetic acid [EDDA])NH(2)]-exendin-4, compared with its (111)In- and (68)Ga-labeled sister compounds, showed significantly less tumor and organ uptake. The significantly lower tumor and organ uptake of [Lys(40)(Ahx-HYNIC-(99m)Tc/EDDA)NH(2)]-exendin-4 did not result in inferior tumor-to-organ ratios or reduced image quality. All radiopeptides tested showed a high tumor-to-background ratio, resulting in the visualization of small tumors (maximum diameter between 1.0 and 3.2 mm) by SPECT and PET. The only exception was the kidneys, which also showed high uptake. This uptake could be reduced by 49%-78% using poly-glutamic acid, Gelofusine, or a combination of the 2. The estimated effective radiation dose was 3.7 muSv/MBq for [Lys(40)(Ahx-HYNIC-(99m)Tc/EDDA)NH(2)]-exendin-4, which was 8 times less than that for [Lys(40)(Ahx-DOTA-(68)Ga)NH(2)]-exendin-4 and 43 times less than that for [Lys(40)(Ahx-DOTA-(111)In)NH(2)]-exendin-4. CONCLUSION: These promising pharmacokinetic and imaging data show that [Lys(40)(Ahx-DOTA-(68)Ga)NH(2)]-exendin-4 and [Lys(40)(Ahx-HYNIC-(99m)Tc/EDDA)NH(2)]-exendin-4 are suitable candidates for clinical GLP-1 receptor imaging studies.

Agonist-biased signaling at the sst2A receptor: the multi-somatostatin analogs KE108 and SOM230 activate and antagonize distinct signaling pathways.

Somatostatin analogs that activate the somatostatin subtype 2A (sst2A) receptor are used to treat neuroendocrine cancers because they inhibit tumor secretion and growth. Recently, new analogs capable of activating multiple somatostatin receptor subtypes have been developed to increase tumor responsiveness. We tested two such multi-somatostatin analogs for functional selectivity at the sst2A receptor: SOM230, which activates sst1, sst2, sst3, and sst5 receptors, and KE108, which activates all sst receptor subtypes. Both compounds are reported to act as full agonists at their target sst receptors. In sst2A-expressing HEK293 cells, somatostatin inhibited cAMP production, stimulated intracellular calcium accumulation, and increased ERK phosphorylation. SOM230 and KE108 were also potent inhibitors of cAMP accumulation, as expected. However, they antagonized somatostatin stimulation of intracellular calcium and behaved as partial agonists/antagonists for ERK phosphorylation. In pancreatic AR42J cells, which express sst2A receptors endogenously, SOM230 and KE108 were both full agonists for cAMP inhibition. However, although somatostatin increased intracellular calcium and ERK phosphorylation, SOM230 and KE108 again antagonized these effects. Distinct mechanisms were involved in sst2A receptor signaling in AR42J cells; pertussis toxin pretreatment blocked somatostatin inhibition of cAMP accumulation but not the stimulation of intracellular calcium and ERK phosphorylation. Our results demonstrate that SOM230 and KE108 behave as agonists for inhibition of adenylyl cyclase but antagonize somatostatin's actions on intracellular calcium and ERK phosphorylation. Thus, SOM230 and KE108 are not somatostatin mimics, and their functional selectivity at sst2A receptors must be considered in clinical applications where it may have important consequences for therapy.

Response to [90Yttrium-DOTA]-TOC treatment is associated with long-term survival benefit in metastasized medullary thyroid cancer: a phase II clinical trial.

PURPOSE: We aimed to explore the efficacy of (90)Yttrium-1,4,7,10-tetra-azacyclododecane N,N',N'',N-'''-tetraacetic acid ((90)Y-DOTA)-Tyr(3)-octreotide (TOC) therapy in advanced medullary thyroid cancer. EXPERIMENTAL DESIGN: In a phase II trial, we investigated the response, survival, and long-term safety profile of systemic [(90)Y-DOTA]-TOC treatment in metastasized medullary thyroid cancer. Adverse events were assessed according to the criteria of the National Cancer Institute. Survival analyses were done using multiple regression models. RESULTS: Thirty-one patients were enrolled. A median cumulative activity of 12.6 GBq (range, 1.7-29.6 GBq) of [(90)Y-DOTA]-TOC was administered. Response was found in nine patients (29.0%). Four patients (12.9%) developed hematologic toxicities and seven patients (22.6%) developed renal toxicities. Response to treatment was associated with longer survival from time of diagnosis (hazard ratio, 0.20; 95% confidence interval, 0.05-0.81; P = 0.02) and from time of first [(90)Y-DOTA]-TOC therapy (hazard ratio, 0.16; 95% confidence interval, 0.04-0.63; P = 0.009). The visual grade of scintigraphic tumor uptake was not associated with treatment response or survival. CONCLUSIONS: Response to [(90)Y-DOTA]-TOC therapy in metastasized medullary thyroid cancer is associated with a long-term survival benefit. Treatment should be considered independently from the result of the pretherapeutic scintigraphy.

Dosimetry for (90)Y-DOTATOC therapies in patients with neuroendocrine tumors.

The aim of this study was to determine the inter- and intrapatient variability of absorbed dose to the whole body, kidneys, and tumor, as well as the question of whether the first therapy could serve as a guide for future therapies. Fifty (50) (90)Y-DOTATOC therapies were given to 30 patients diagnosed with refractory stage IV neuroendocrine tumors (20 patients received two therapies, 10 patients received one therapy). The first and second therapies were delivered at standard intervals. (90)Y-activity was prescribed by surface area (3.7 GBq/m(2)), and approximately 100 MBq (111)In-DOTATOC was administered concurrently for imaging purposes. Amino acid coadministration for renal protection was performed. Measurements of activity in whole-body and single-photon emission computed tomography images were acquired at various time points after the administration of the radiopharmaceutical. The dosimetry for whole body, kidneys, and tumor was based on these data. The interpatient variability (the ratio of the maximum absorbed dose per injected activity for all patients) was larger than the intrapatient variability (the ratio of absorbed dose per injected activity for subsequent therapies in the same patient for whole body, kidneys, and tumor. These results imply that the first therapy could serve as a guide for future therapies. This approach might allow for targeted radionuclide therapy to be delivered by prescribed absorbed dose, rather than by administered activity.

68Ga-labeled bombesin studies in patients with gastrointestinal stromal tumors: comparison with 18F-FDG.

UNLABELLED: Dynamic PET studies with a 68Ga-bombesin analog, DOTA-PEG2-[d-Tyr6, beta-Ala11,Thi13,Nle14] BN(6-14) amide (68Ga-BZH3; DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid, and PEG is ethylene glycol [2-aminoethyl-carboxymethyl ether]), were performed on patients with gastrointestinal stromal tumors (GIST) to investigate the impact of complementary receptor scintigraphy on diagnosis and the potential of a radionuclide treatment. Furthermore, dynamic 18F-FDG studies were performed on the same patients. METHODS: This study comprised 17 patients with GIST. All patients were scheduled for therapy with imatinib because of unresectable primary or recurrent GIST or because of metastatic disease. Dynamic PET scans using 68Ga-BZH3 and 18F-FDG were obtained on 2 consecutive days. Multivariate analysis was used to evaluate the kinetic data. Standardized uptake values (SUVs) were calculated, and a compartmental model (2-tissue) and noncompartmental model were used for data evaluation of both tracers. RESULTS: Fourteen of 17 patients (25/30 lesions) were positive for uptake on 18F-FDG imaging, whereas 68Ga-BZH3 demonstrated an enhanced accumulation in 7 of 17 patients (8/30 lesions). Thirteen lesions were confirmed by histologic examination, and the remaining 17 were confirmed by follow-up. One recurrent tumor in the stomach could not be delineated on 18F-FDG imaging but showed enhanced 68Ga-BZH3 uptake. The median SUV for 68Ga-BZH3 was 3.3, in comparison with 7.9 for 18F-FDG. Best-subset analysis demonstrated that the global SUV (55-60 min after injection) for 18F-FDG was primarily dependent on k3, followed by k1. Multivariate analysis did not show a significant correlation between the kinetic parameters (k1-k4, fractional blood volume, and SUV) for 18F-FDG and bombesin. CONCLUSION: 68Ga-BZH3 may be helpful for diagnostic reasons in a subgroup of patients with GIST, as in the case of negative 18F-FDG findings and suspicion of viable tumor tissue. The meaning of the enhanced 68Ga-BZH3 uptake is open at the moment.

[Lys40(Ahx-DTPA-111In)NH2]-Exendin-4 is a highly efficient radiotherapeutic for glucagon-like peptide-1 receptor-targeted therapy for insulinoma.

PURPOSE: Although metabolic changes make diagnosis of insulinoma relatively easy, surgical removal is hampered by difficulties in locating it, and there is no efficient treatment for malignant insulinoma. We have previously shown that the high density of glucagon-like peptide-1 receptors (GLP-1R) in human insulinoma cells provides an attractive target for molecular imaging and internal radiotherapy. In this study, we investigated the therapeutic potential of [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4, an (111)In-labeled agonist of GLP-1, in a transgenic mouse model of human insulinoma. EXPERIMENTAL DESIGN: [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4 was assessed in the Rip1Tag2 mouse model of pancreatic beta-cell carcinogenesis, which exhibits a GLP-1R expression comparable with human insulinoma. Mice were injected with 1.1, 5.6, or 28 MBq of the radiopeptide and sacrificed 7 days after injection. Tumor uptake and response, the mechanism of action of the radiopeptide, and therapy toxicity were investigated. RESULTS: Tumor uptake was >200% injected activity per gram, with a dose deposition of 3 Gy/MBq at 40 pmol [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4. Other GLP-1R-positive organs showed > or =30 times lower dose deposition. A single injection of [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4 resulted in a reduction of the tumor volume by up to 94% in a dose-dependent manner without significant acute organ toxicity. The therapeutic effect was due to increased tumor cell apoptosis and necrosis and decreased proliferation. CONCLUSIONS: The results suggest that [Lys(40)(Ahx-DTPA-(111)In)NH(2)]-Exendin-4 is a promising radiopeptide capable of selectively targeting insulinoma. Furthermore, Auger-emitting radiopharmaceuticals such as (111)In are able to produce a marked therapeutic effect if a high tumor uptake is achieved.

[Lys40(Ahx-DTPA-111In)NH2]exendin-4, a very promising ligand for glucagon-like peptide-1 (GLP-1) receptor targeting.

UNLABELLED: High levels of glucagon-like peptide-1 (GLP-1) receptor expression in human insulinomas and gastrinomas provide an attractive target for imaging, therapy, and intraoperative tumor localization, using receptor-avid radioligands. The goal of this study was to establish a tumor model for GLP-1 receptor targeting and to use a newly designed exendin-4-DTPA (DTPA is diethylenetriaminepentaacetic acid) conjugate for GLP-1 receptor targeting. METHODS: Exendin-4 was modified C-terminally with Lys(40)-NH(2), whereby the lysine side chain was conjugated with Ahx-DTPA (Ahx is aminohexanoic acid). The GLP-1 receptor affinity (50% inhibitory concentration [IC(50)] value) of [Lys(40)(Ahx-DTPA)NH(2)]exendin-4 as well as the GLP-1 receptor density in tumors and different organs of Rip1Tag2 mice were determined. Rip1Tag2 mice are transgenic mice that develop insulinomas in a well-defined multistage tumorigenesis pathway. This animal model was used for biodistribution studies, pinhole SPECT/MRI, and SPECT/CT. Peptide stability, internalization, and efflux studies were performed in cultured beta-tumor cells established from tumors of Rip1Tag2 mice. RESULTS: The GLP-1 receptor affinity of [Lys(40)(Ahx-DTPA)NH(2)]exendin-4 was found to be 2.1 +/- 1.1 nmol/L (mean +/- SEM). Because the GLP-1 receptor density in tumors of Rip1Tag2 mice was very high, a remarkably high tumor uptake of 287 +/- 62 %IA/g (% injected activity per gram tissue) was found 4 h after injection. This resulted in excellent tumor visualization by pinhole SPECT/MRI and SPECT/CT. In accordance with in vitro data, [Lys(40)(Ahx-DTPA-(111)In)NH(2)]exendin-4 uptake in Rip1Tag2 mice was also found in nonneoplastic tissues such as pancreas and lung. However, lung and pancreas uptake was distinctly lower compared with that of tumors, resulting in a tumor-to-pancreas ratio of 13.6 and in a tumor-to-lung ratio of 4.4 at 4 h after injection. Furthermore, in vitro studies in cultured beta-tumor cells demonstrated a specific internalization of [Lys(40)(Ahx-DTPA-(111)In)NH(2)]exendin-4, whereas peptide stability studies indicated a high metabolic stability of the radiopeptide in beta-tumor cells and human blood serum. CONCLUSION: The high density of GLP-1 receptors in insulinomas as well as the high specific uptake of [Lys(40)(Ahx-DTPA-(111)In)NH(2)]exendin-4 in the tumor of Rip1Tag2 mice indicate that targeting of GLP-1 receptors in insulinomas may become a useful imaging method to localize insulinomas in patients, either preoperatively or intraoperatively. In addition, Rip1Tag2 transgenic mice represent a suitable animal tumor model for GLP-1 receptor targeting.

Radiolabeled somatostatin receptor antagonists are preferable to agonists for in vivo peptide receptor targeting of tumors.

Targeting neuroendocrine tumors expressing somatostatin receptor subtypes (sst) with radiolabeled somatostatin agonists is an established diagnostic and therapeutic approach in oncology. While agonists readily internalize into tumor cells, permitting accumulation of radioactivity, radiolabeled antagonists do not, and they have not been considered for tumor targeting. The macrocyclic chelator 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was coupled to two potent somatostatin receptor-selective peptide antagonists [NH(2)-CO-c(DCys-Phe-Tyr-DAgl(8)(Me,2-naphthoyl)-Lys-Thr-Phe-Cys)-OH (sst(3)-ODN-8) and a sst(2)-selective antagonist (sst(2)-ANT)], for labeling with (111/nat)In. (111/nat)In-DOTA-sst(3)-ODN-8 and (111/nat)In-DOTA-[4-NO(2)-Phe-c(DCys-Tyr-DTrp-Lys-Thr-Cys)-DTyr-NH(2)] ((111/nat)In-DOTA-sst(2)-ANT) showed high sst(3)- and sst(2)-binding affinity, respectively. They did not trigger sst(3) or sst(2) internalization but prevented agonist-stimulated internalization. (111)In-DOTA-sst(3)-ODN-8 and (111)In-DOTA-sst(2)-ANT were injected intravenously into mice bearing sst(3)- and sst(2)-expressing tumors, and their biodistribution was monitored. In the sst(3)-expressing tumors, strong accumulation of (111)In-DOTA-sst(3)-ODN-8 was observed, peaking at 1 h with 60% injected radioactivity per gram of tissue and remaining at a high level for >72 h. Excess of sst(3)-ODN-8 blocked uptake. As a control, the potent agonist (111)In-DOTA-[1-Nal(3)]-octreotide, with strong sst(3)-binding and internalization properties showed a much lower and shorter-lasting uptake in sst(3)-expressing tumors. Similarly, (111)In-DOTA-sst(2)-ANT was injected into mice bearing sst(2)-expressing tumors. Tumor uptake was considerably higher than with the highly potent sst(2)-selective agonist (111)In-diethylenetriaminepentaacetic acid-[Tyr(3),Thr(8)]-octreotide ((111)In-DTPA-TATE). Scatchard plots showed that antagonists labeled many more sites than agonists. Somatostatin antagonist radiotracers therefore are preferable over agonists for the in vivo targeting of sst(3)- or sst(2)-expressing tumors. Antagonist radioligands for other peptide receptors need to be evaluated in nuclear oncology as a result of this paradigm shift.

Quantitative assessment of SSTR2 expression in patients with non-small cell lung cancer using(68)Ga-DOTATOC PET and comparison with (18)F-FDG PET.

PURPOSE: Dynamic PET studies with(68)Ga-DOTATOC were performed in patients with non-small cell lung cancer (NSCLC) to assess the somatostatin receptor 2 (SSTR2) expression. Furthermore, dynamic(18)F-fluorodeoxyglucose (FDG) studies were performed in the same patients to compare the SSTR2 expression with the tumour viability. METHODS: The study population comprised nine patients, examined with both tracers on two different days within 1 week. Standardised uptake values (SUVs) were calculated and a two-tissue compartment model was applied to the data. Furthermore, a non-compartment model based on the fractal dimension (FD) was applied to the data. RESULTS: The DOTATOC uptake was generally lower than the FDG uptake. Moderately enhanced DOTATOC uptake was noted in seven of the nine tumours. All kinetic parameters except k (4) were lower for DOTATOC than for FDG. The mean SUV was 2.018 for DOTATOC, in comparison to 5.683 for FDG. In particular, k (3) was highly variable for DOTATOC and showed an overlap with the normal lung tissue. The fractional blood volume V (B) was relatively low for both tracers, not exceeding 0.3. The highest significant logarithmic correlation was found for the FD of the two tracers (r=0.764, p=0.017). The logarithmic correlation for SUVs was also significant (r=0.646, p=0.060), as was that forV (B) (r=0.629, p=0.069). In contrast, none of the eight metastases which were positive on FDG PET showed any DOTATOC uptake. CONCLUSION: The results demonstrated moderate (68)Ga-DOTATOC uptake in primary NSCLC but did not provide any evidence for SSTR2 expression in metastases. This may be caused by loss of the gene expression in metastases as compared with the primary tumours.

CCK-2/gastrin receptor-targeted tumor imaging with (99m)Tc-labeled minigastrin analogs.

UNLABELLED: The aim of this study was to evaluate 3 new (99m)Tc-labeled minigastrin analogs modified with open chain tetraamines at the N-terminus for their suitability in the CCK-2/gastrin-R-targeted imaging of tumors (CCK-2/gastrin-R = cholecystokinin subtype 2/gastrin receptor). METHODS: The [(D)Glu(1)]minigastrin sequence was assembled on the solid support and the respective tetraamine precursors coupled at the N-terminus. Purified peptide conjugates were labeled with (99m)Tc under alkaline conditions. Saturation binding experiments were performed for (radio)metallated peptides [(99m)Tc/(99g)Tc]Demogastrin 1-3 in rat acinar pancreatic AR4-2J cell membranes. Internalization was studied in AR4-2J cells at 37 degrees C. Radiopeptide stability was tested in murine plasma, urine, and kidney homogenates. Tissue distribution of the peptides was compared in healthy mice and athymic mice bearing AR4-2J tumors. RESULTS: Peptide conjugates were obtained in 10%-30% overall yields by solid-phase techniques. Radiolabeling afforded >98% pure [(99m)Tc]Demogastrin 1-3 species in specific activities of approximately 37 GBq/mumol. Radiopeptides retained a high affinity for the CCK-2/gastrin-R in vitro (50% inhibitory concentration values of approximately 1 nmol/L) and internalized rapidly in CCK-2/gastrin-R-positive cells. After injection in mice they displayed rapid, high, and specific localization in the CCK-2/gastrin-R-expressing tissues (stomach and AR4-2J tumor) and were excreted from the body via the kidneys in the form of hydrophilic metabolites. CONCLUSION: The promising characteristics of [(99m)Tc]Demogastrin 1-3 both in vitro and in animal models illustrate their suitability for CCK-2/gastrin-R-targeted tumor imaging. These qualities could be confirmed for [(99m)Tc]Demogastrin 2, which provided excellent delineation of tumor deposits in a first patient with metastatic medullary thyroid cancer.

Evaluation of [99mTc/EDDA/HYNIC0]octreotide derivatives compared with [111In-DOTA0,Tyr3, Thr8]octreotide and [111In-DTPA0]octreotide: does tumor or pancreas uptake correlate with the rate of internalization?

UNLABELLED: Radiolabeled somatostatin analogs are important tools for the in vivo localization and targeted radionuclide therapy of somatostatin receptor-positive tumors. The aim of this study was to compare 3 somatostatin analogs designed for the labeling with (99m)Tc (where HYNIC is 6-hydrazinopyridine-3-carboxylic acid): 6-hydrazinopyridine-3-carboxylic acid(0)-octreotide (HYNIC-OC/(99m)Tc-(1)), [HYNIC(0),Tyr(3)]octreotide (HYNIC-TOC/(99m)Tc-(2)), and [HYNIC(0),Tyr(3),Thr(8)]octreotide (HYNIC-TATE/(99m)Tc-(3)), using ethylenediamine-N,N'-diacetic acid (EDDA) as a coligand. In addition, we compared the (99m)Tc-labeled peptides [(111)In-diethylenetriaminepentaacetic acid(0)]octreotide ([(111)In-DTPA]-OC) and [(111)In-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid(0),Tyr(3),Thr(8)]octreotide ([(111)In-DOTA]-TATE) with regard to the rate of internalization and the biodistribution in AR4-2J (expressing the somatostatin receptor subtype 2) tumor-bearing rats. The main attention was directed toward a potential correlation between the rate of internalization and the tumor or pancreas uptake. METHODS: Synthesis was performed on solid phase using a standard Fmoc strategy. Internalization was studied in cell culture (AR4-2J) and biodistribution was studied using a Lewis rat tumor model (AR4-2J). RESULTS: The 5 radiopeptides showed a specific internalization into AR4-2J cells in culture (as shown by blocking experiments). The rate of internalization of the 5 radiopeptides differed significantly according to the following order: (99m)Tc-(1) approximately = [(111)In-DTPA]-OC < (99m)Tc-(2) < (99m)Tc-(3) approximately = [(111)In-DOTA]-TATE. All radiopeptides displayed a rapid blood clearance and a fast clearance from all somatostatin receptor-negative tissues predominantly via the kidneys. A receptor-specific uptake of radioactivity was observed for all compounds in somatostatin receptor-positive organs such as the pancreas, the adrenals, and the stomach. After 4 h, the uptake in the AR4-2J tumor was comparable for (99m)Tc-(2) (3.85 +/- 1.0 injected dose per gram tissue (%ID/g)), (99m)Tc-(3) (3.99 +/- 0.58%ID/g), and [(111)In-DOTA]-TATE (4.12 +/- 0.74%ID/g) but much lower for [(111)In-DTPA]-OC (0.99 +/- 0.08%ID/g) and (99m)Tc-(1) (0.70 +/- 0.13%ID/g). The specificity was determined by blocking experiments using a large excess of [Tyr(3)]octreotide. (99m)Tc-(3) displayed the highest tumor-to-kidney ratio (2.5:1), followed by (99m)Tc(2) (1.9:1) and [(111)In-DOTA]-TATE (1.7:1). CONCLUSION: These data show that the 5 radiopeptides are specific radioligands for the somatostatin receptor subtype 2. The rate of internalization correlates with the uptake in the tumor (R(2) = 0.75; P = 0.026) and pancreas (R(2) = 0.98; P = 7.4.10(-5)). [Tyr(3),Thr(8)]octreotide derivatives show superiority over the corresponding octreotide and [Tyr(3)]octreotide derivatives, indicating that [(111)In-DOTA]-TATE and [(99m)Tc/EDDA/HYNIC]-TATE are suitable candidates for clinical studies.

Characterization of 68Ga-DOTA-D-Phe1-Tyr3-octreotide kinetics in patients with meningiomas.

UNLABELLED: Because biopsy has a high risk of hemorrhage and the findings of CT and MRI are often ambiguous, especially at the base of the skull, additional methods for the characterization of intracranial tumors are needed. Meningiomas show high expression of the somatostatin receptor subtype 2 and thus offer the possibility of receptor-targeted imaging. We used the somatostatin analog (68)Ga-DOTA-d-Phe(1)-Tyr(3)-octreotide (DOTA-TOC) labeled with the positron emitter (68)Ga (half-life, 68 min), obtained from a (68)Ge/(68)Ga generator, for PET of these tumors. In contrast to (18)F-FDG, this ligand shows high meningioma-to-background ratios. The aim was to evaluate kinetic parameters in meningiomas before radiotherapy. METHODS: Dynamic PET scans (3-dimensional mode; 28 frames; ordered-subsets expectation maximization reconstruction) were acquired for 21 patients (mean age +/- SD, 51 +/- 13 y) before radiotherapy during the 60 min after intravenous injection of 156 +/- 29 MBq of (68)Ga-DOTA-TOC. We analyzed 28 meningiomas (median grade [I] according to the system of the World Health Organization) with volumes of at least 0.5 mL (mean volume, 13.1 mL) and nasal mucosa as reference tissue, showing a slight to moderate physiologic uptake. For evaluation of the (68)Ga-DOTA-TOC kinetics, the vascular fraction (vB) and the rate constants (k1, k2, k3, and k4 [1/min]) were computed using a 2-tissue-compartment model. Furthermore, receptor binding (RB) (k1 - k1 x k2) and the ratios k1/k2 and k3/k4 were calculated. RESULTS: Significant differences (P < 0.05; t test) between meningiomas and the reference tissue were found for the mean standardized uptake value (10.5 vs.1.3), vB (0.42 vs. 0.11), k2 (0.12 vs. 0.56), k3 (0.024 vs. 0.060), k4 (0.004 vs. 0.080), and RB (0.49 vs. 0.13). Although there was no significant difference for k1 (0.54 vs. 0.40), the ratios k1/k2 (4.50 vs. 0.71) and k3/k4 (6.00 vs. 0.75) were markedly greater in meningiomas than in reference tissue. CONCLUSION: The high uptake of (68)Ga-DOTA-TOC in meningiomas can be explained by the high values for vB and by the remarkably low values for k2 and k4, leading to significantly greater k1/k2 and k3/k4 ratios and RB in meningiomas than in reference tissue. Thus, pharmacokinetic modeling offers a more detailed analysis of biologic properties of meningiomas. In further studies, these data might serve as a basis for monitoring the somatostatin receptors of meningiomas after radiotherapy.

GRP receptor-targeted PET of a rat pancreas carcinoma xenograft in nude mice with a 68Ga-labeled bombesin(6-14) analog.

UNLABELLED: Bombesin (BN), a 14-amino-acid peptide, shows high affinity for the human gastrin-releasing peptide receptor (GRP-r), which is overexpressed on several types of cancer, including prostate, breast, gastrointestinal, and small cell lung cancer. Thus, radiolabeled BN or BN analogs may prove to be specific tracers for diagnostic and therapeutic targeting of GRP-r-positive tumors in nuclear medicine. This study evaluated a novel BN analog labeled with the positron emitter 68Ga for receptor imaging with PET. METHODS: DOTA-PEG2-[D-Tyr6,beta-Ala11,Thi13,Nle14] BN(6-14) amide (BZH3) (DOTA is 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid; PEG is ethyleneglycol (2-aminoethyl)carboxymethyl ether) was synthetized using the Fmoc strategy and radiolabeled with either 67Ga or 177Lu for in vitro and biodistribution experiments. 68Ga for PET was obtained from a 68Ge/68Ga generator. In vitro binding, internalization, and efflux were determined using the pancreatic tumor cell line AR42J. Biodistribution of the peptide as a function of time and dose was studied in AR42J tumor-bearing mice. RESULTS: In vitro assays demonstrated a high affinity of 67Ga-BZH3 (dissociation constant = 0.46 nmol/L), a rapid internalization (70% of total cell-associated activity was endocytosed after a 15-min incubation), and an intracellular retention half-life (t1/2) of the 67Ga activity of 16.5 +/- 2.4 h. Biodistribution indicated a dose-dependent uptake in the tumor and a prolonged tumor residence time (t1/2 approximately 16 h). Clearance from GRP-r-negative tissues was fast, resulting in high tumor-to-tissue ratios as early as 1 h after injection. Replacing 67Ga by 177Lu, a therapeutic radionuclide, for peptide labeling resulted in a slightly reduced (approximately 20%) tumor uptake and tumor residence time of 177Lu-BZH3. In contrast, 177Lu decline in the pancreas was significantly accelerated by a factor of 3 compared with that of 67Ga. PET of mice with 68Ga-BZH3 clearly delineated tumors in the mediastinal area. CONCLUSION: The promising in vivo data of 68Ga-BZH3 indicate its potential for an improved localization of GRP-r-positive tumors and also suggest its application in patients. PET may also be favorably used for GRP-r density determination, a prerequisite for therapeutic applications.

Three-year recurrence-free survival in a patient with recurrent medulloblastoma after resection, high-dose chemotherapy, and intrathecal Yttrium-90-labeled DOTA0-D-Phe1-Tyr3-octreotide radiopeptide brachytherapy.

BACKGROUND: Most medulloblastomas express high levels of somatostatin type 2 receptors (sst2). DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC) specifically binds sst2 in the low nanomolar range. The cytotoxic effect is mediated by the chelated, beta-emitting, metallic radionuclide Yttrium 90 (90Y). The authors applied this innovative treatment option in a boy age 8 years who presented with a recurrent medulloblastoma of the cauda equina: a prognostically poor condition. Targeted radiotherapy was administered to treat minimal sst2-expressing tumor remnants, which persisted despite conventional and high-dose chemotherapy and intercurrent resection of the lesion. METHODS: A medulloblastoma arising from the floor of the fourth ventricle had been removed surgically; then, the patient was treated with standard adjuvant chemotherapy and craniospinal irradiation according to the prospective HIT '91 protocol. Complete remission was achieved for 20 months, when a drop metastasis of the cauda equina manifested with sensorimotor lumbosacral deficits and urinary incontinence. After four cycles of neoadjuvant chemotherapy (which consisted of combined ifosfamide, carboplatinum and etoposide), two cycles of high-dose chemotherapy and autologous stem cell transplantation were performed; in between, the responding residual tumor within the lumbosacral nerve fibers was microscopically removed. Thereafter, an Indium-111-DOTATOC test injection indicated sst2-expressing tumor remnants within the cauda equina. Consequently, 4 cycles of [90Y]-DOTATOC (4x562.5 megabecquerels) were injected directly into the cerebrospinal fluid in monthly intervals. RESULTS: The consolidating intrathecal brachytherapy using [90Y]-DOTATOC was tolerated well. A complete remission was achieved for a 3-year period. The only remaining deficit was urinary incontinence. CONCLUSIONS: Intrathecal administration of targeted radiopeptide brachytherapy in combination with conventional and high-dose chemotherapy and surgical removal represents a promising new option to treat recurrent medulloblastoma and should be explored further.

Candidates for peptide receptor radiotherapy today and in the future.

Regulatory peptide receptors are overexpressed in numerous human cancers. These receptors have been used as molecular targets by which radiolabeled peptides can localize cancers in vivo and, more recently, to treat cancers with peptide receptor radiation therapy (PRRT). This review describes the candidate tumors eligible for such radiotherapy on the basis of their peptide receptor content and discusses factors in PRRT eligibility. At the present time, PRRT is performed primarily with somatostatin receptor- and cholecystokinin-2 (CCK2)-receptor-expressing neuroendocrine tumors with radiolabeled octreotide analogs or with radiolabeled CCK2-selective analogs. In the future, PRRT may be extended to many other tumor types, including breast, prostate, gut, pancreas, and brain tumors, that have recently been shown to overexpress several other peptide receptors, such as gastrin-releasing peptide-, neurotensin-, substance P-, glucagon-like peptide 1-, neuropeptide Y-, or corticotropin-releasing factor-receptors. A wide range of radiolabeled peptides is being developed for clinical use. Improved somatostatin or CCK(2) analogs as well as newly designed bombesin, neurotensin, substance P, neuropeptide Y, and glucagon-like peptide-1 analogs offer promise for future PRRT.