Therapeutic potentials of terbium hydroxide nanorods for amelioration of hypoxia-reperfusion injury in cardiomyocytes.

Myocardial hypoxia reperfusion (H/R) injury is the paradoxical exacerbation of myocardial damage, caused by the sudden restoration of blood flow to hypoxia affected myocardium. It is a critical contributor of acute myocardial infarction, which can lead to cardiac failure. Despite the current pharmacological advancements, clinical translation of cardioprotective therapies have proven challenging. As a result, researchers are looking for alternative approaches to counter the disease. In this regard, nanotechnology, with its versatile applications in biology and medicine, can confer broad prospects for treatment of myocardial H/R injury. Herein, we attempted to explore whether a well-established pro-angiogenic nanoparticle, terbium hydroxide nanorods (THNR) can ameliorate myocardial H/R injury. For this study, in vitro H/R-injury model was established in rat cardiomyocytes (H9c2 cells). Our investigations demonstrated that THNR enhance cardiomyocyte survival against H/R-induced cell death. This pro-survival effect of THNR is associated with reduction of oxidative stress, lipid peroxidation, calcium overload, restoration of cytoskeletal integrity and mitochondrial membrane potential as well as augmentation of cellular anti-oxidant enzymes such as glutathione-s-transferase (GST) and superoxide dismutase (SOD) to counter H/R injury. Molecular analysis revealed that the above observations are traceable to the predominant activation of PI3K-AKT-mTOR and ERK-MEK signalling pathways by THNR. Concurrently, THNR also exhibit apoptosis inhibitory effects mainly by suppression of pro-apoptotic proteins like Cytochrome C, Caspase 3, Bax and p53 with simultaneous restoration of anti-apoptotic protein, Bcl-2 and Survivin. Thus, considering the above attributes, we firmly believe that THNR have the potential to be developed as an alternative approach for amelioration of H/R injury in cardiomyocytes.

Terbium-Rose Bengal Coordination Nanocrystals-Induced ROS Production under Low-Dose X-rays in Cultured Cancer Cells for Photodynamic Therapy.

X-ray-triggered scintillators (Sc) and photosensitizers (Ps) have been developed for X-ray-induced photodynamic therapy (X-PDT) to selectively destruct deep tissue tumors with a low X-ray dose. This study designed terbium (Tb)-rose bengal (RB) coordination nanocrystals (T-RBNs) by a solvothermal treatment, aiming to reduce photon energy dissipation between Tb3+ and RB and thus increase the reactive oxygen species (ROS) production efficiency. T-RBNs synthesized at a molar ratio of [RB]/[Tb] = 3 exhibited a size of 6.8 ± 1.2 nm with a crystalline property. Fourier transform infrared analyses of T-RBNs indicated successful coordination between RB and Tb3+. T-RBNs generated singlet oxygen (1O2) and hydroxyl radicals (•OH) under low-dose X-ray irradiation (0.5 Gy) via scintillating and radiosensitizing pathways. T-RBNs produced ∼8-fold higher ROS amounts than bare RB and ∼3.6-fold higher ROS amounts than inorganic nanoparticle-based controls. T-RBNs did not exhibit severe cytotoxicity up to 2 mg/mL concentration in cultured luciferase-expressing murine epithelial breast cancer (4T1-luc) cells. Furthermore, T-RBNs were efficiently internalized into cultured 4T1-luc cells and induced DNA double strand damage, as evidenced by an immunofluorescence staining assay with phosphorylated γ-H2AX. Ultimately, under 0.5 Gy X-ray irradiation, T-RBNs induced >70% 4T1-luc cell death via simultaneous apoptosis/necrosis pathways. Overall, T-RBNs provided a promising Sc/Ps platform under low-dose X-PDT for advanced cancer therapy.

Combination of terbium-161 with somatostatin receptor antagonists-a potential paradigm shift for the treatment of neuroendocrine neoplasms.

PURPOSE: The ߯-emitting terbium-161 also emits conversion and Auger electrons, which are believed to be effective in killing single cancer cells. Terbium-161 was applied with somatostatin receptor (SSTR) agonists that localize in the cytoplasm (DOTATOC) and cellular nucleus (DOTATOC-NLS) or with a SSTR antagonist that localizes at the cell membrane (DOTA-LM3). The aim was to identify the most favorable peptide/terbium-161 combination for the treatment of neuroendocrine neoplasms (NENs). METHODS: The capability of the 161Tb- and 177Lu-labeled somatostatin (SST) analogues to reduce viability and survival of SSTR-positive AR42J tumor cells was investigated in vitro. The radiopeptides' tissue distribution profiles were assessed in tumor-bearing mice. The efficacy of terbium-161 compared to lutetium-177 was investigated in therapy studies in mice using DOTATOC or DOTA-LM3, respectively. RESULTS: In vitro, [161Tb]Tb-DOTA-LM3 was 102-fold more potent than [177Lu]Lu-DOTA-LM3; however, 161Tb-labeled DOTATOC and DOTATOC-NLS were only 4- to fivefold more effective inhibiting tumor cell viability than their 177Lu-labeled counterparts. This result was confirmed in vivo and demonstrated that [161Tb]Tb-DOTA-LM3 was significantly more effective in delaying tumor growth than [177Lu]Lu-DOTA-LM3, thereby, prolonging survival of the mice. A therapeutic advantage of terbium-161 over lutetium-177 was also manifest when applied with DOTATOC. Since the nuclear localizing sequence (NLS) compromised the in vivo tissue distribution of DOTATOC-NLS, it was not used for therapy. CONCLUSION: The use of membrane-localizing DOTA-LM3 was beneficial and profited from the short-ranged electrons emitted by terbium-161. Based on these preclinical data, [161Tb]Tb-DOTA-LM3 may outperform the clinically employed [177Lu]Lu-DOTATOC for the treatment of patients with NENs.

Terbium-161 for PSMA-targeted radionuclide therapy of prostate cancer.

PURPOSE: The prostate-specific membrane antigen (PSMA) has emerged as an interesting target for radionuclide therapy of metastasized castration-resistant prostate cancer (mCRPC). The aim of this study was to investigate 161Tb (T1/2 = 6.89 days; Eß͞av = 154 keV) in combination with PSMA-617 as a potentially more effective therapeutic alternative to 177Lu-PSMA-617, due to the abundant co-emission of conversion and Auger electrons, resulting in an improved absorbed dose profile. METHODS: 161Tb was used for the radiolabeling of PSMA-617 at high specific activities up to 100 MBq/nmol. 161Tb-PSMA-617 was tested in vitro and in tumor-bearing mice to confirm equal properties, as previously determined for 177Lu-PSMA-617. The effects of 161Tb-PSMA-617 and 177Lu-PSMA-617 on cell viability (MTT assay) and survival (clonogenic assay) were compared in vitro using PSMA-positive PC-3 PIP tumor cells. 161Tb-PSMA-617 was further investigated in therapy studies using PC-3 PIP tumor-bearing mice. RESULTS: 161Tb-PSMA-617 and 177Lu-PSMA-617 displayed equal in-vitro properties and tissue distribution profiles in tumor-bearing mice. The viability and survival of PC-3 PIP tumor cells were more reduced when exposed to 161Tb-PSMA-617 as compared to the effect obtained with the same activities of 177Lu-PSMA-617 over the whole investigated concentration range. Treatment of mice with 161Tb-PSMA-617 (5.0 MBq/mouse and 10 MBq/mouse, respectively) resulted in an activity-dependent increase of the median survival (36 vs 65 days) compared to untreated control animals (19 days). Therapy studies to compare the effects of 161Tb-PSMA-617 and 177Lu-PSMA-617 indicated the anticipated superiority of 161Tb over 177Lu. CONCLUSION: 161Tb-PSMA-617 showed superior in-vitro and in-vivo results as compared to 177Lu-PSMA-617, confirming theoretical dose calculations that indicate an additive therapeutic effect of conversion and Auger electrons in the case of 161Tb. These data warrant more preclinical research for in-depth investigations of the proposed concept, and present a basis for future clinical translation of 161Tb-PSMA-617 for the treatment of mCRPC.

Deuteron induced Tb-155 production, a theranostic isotope for SPECT imaging and auger therapy.

Several terbium isotopes are suited for diagnosis or therapy in nuclear medicine. Tb-155 is of interest for SPECT imaging and/or Auger therapy. High radionuclide purity is mandatory for many applications in medicine. The quantification of the activity of the produced contaminants is therefore as important as that of the radionuclide of interest. The experiments performed at the ARRONAX cyclotron (Nantes, France), using the deuteron beam delivered up to 34MeV, provide an additional measurement of the excitation function of the Gd-nat(d,x)Tb-155 reaction and of the produced terbium and gadolinium contaminants. In this study, we investigate the achievable yield for each radionuclide produced in natural gadolinium as a function of the deuteron energy. Other reactions are discussed in order to define the production route that could provide Tb-155 with a high yield and a high radionuclide purity. This article aims to improve data for the Gd-nat(d,x) reaction and to optimize the irradiation conditions required to produce Tb-155.

Dose Deposits from 90Y, 177Lu, 111In, and 161Tb in Micrometastases of Various Sizes: Implications for Radiopharmaceutical Therapy.

UNLABELLED: Radiopharmaceutical therapy, traditionally limited to refractory metastatic cancer, is being increasingly used at earlier stages, such as for treating minimal residual disease. The aim of this study was to compare the effectiveness of (90)Y, (177)Lu, (111)In, and (161)Tb at irradiating micrometastases. (90)Y and (177)Lu are widely used ß(-)-emitting radionuclides. (161)Tb is a medium-energy ß(-) radionuclide that is similar to (177)Lu but emits a higher percentage of conversion and Auger electrons. (111)In emits γ-photons and conversion and Auger electrons. METHODS: We used the Monte Carlo code CELLDOSE to assess electron doses from a uniform distribution of (90)Y, (177)Lu, (111)In, or (161)Tb in spheres with diameters ranging from 10 mm to 10 µm. Because these isotopes differ in electron energy per decay, the doses were compared assuming that 1 MeV was released per µm(3), which would result in 160 Gy if totally absorbed. RESULTS: In a 10-mm sphere, the doses delivered by (90)Y, (177)Lu, (111)In, and (161)Tb were 96.5, 152, 153, and 152 Gy, respectively. The doses decreased along with the decrease in sphere size, and more abruptly so for (90)Y. In a 100-µm metastasis, the dose delivered by (90)Y was only 1.36 Gy, compared with 24.5 Gy for (177)Lu, 38.9 Gy for (111)In, and 44.5 Gy for (161)Tb. In cell-sized spheres, the dose delivered by (111)In and (161)Tb was higher than that of (177)Lu. For instance, in a 10-µm cell, (177)Lu delivered 3.92 Gy, compared with 22.8 Gy for (111)In and 14.1 Gy for (161)Tb. CONCLUSION: (177)Lu, (111)In, and (161)Tb might be more appropriate than (90)Y for treating minimal residual disease. (161)Tb is a promising radionuclide because it combines the advantages of a medium-energy ß(-) emission with those of Auger electrons and emits fewer photons than (111)In.

Highly Efficient FRET System Capable of Deep Photodynamic Therapy Established on X-ray Excited Mesoporous LaF3:Tb Scintillating Nanoparticles.

Photodynamic therapy (PDT) for deep-seated tumor is largely impeded by the limited penetration depth of excitation light in tissue. X-ray is considered as an ideal energy source to activate photosensitizers (PSs) located deep within the body with the assistance of scintillating nanoparticles (ScNPs). However, the efficacy under this concept is not satisfying due to the low scintillating luminescence and weak energy transfer from ScNPs to PSs. Here, mesoporous LaF3:Tb ScNPs were successfully synthesized by a facile hydrothermal process to act as PS carriers and X-ray energy transducers, owing to their good ionizing radiation stopping power and high luminescence efficiency. The formation mechanism of porous structure was elucidated in detail with classical crystallization theory. After a systematic investigation, LaF3:Tb ScNPs with optimized scintillating luminescence were obtained for loading Rose Bengal (RB) to establish an efficient FRET system, owing to their excellent spectral match. The FRET efficiency between ScNPs and RB was calculated to be as high as 85%. Under irradiation, enhanced (1)O2 generation induced by LaF3:Tb-RB nanocomposites via FRET process was detected. This LaF3:Tb-RB FRET system shows great potential to be applied in X-ray stimulated PDT for deep-seated tumors in the future.

Anti-L1CAM radioimmunotherapy is more effective with the radiolanthanide terbium-161 compared to lutetium-177 in an ovarian cancer model.

PURPOSE: The L1 cell adhesion molecule (L1CAM) is considered a valuable target for therapeutic intervention in different types of cancer. Recent studies have shown that anti-L1CAM radioimmunotherapy (RIT) with (67)Cu- and (177)Lu-labelled internalising monoclonal antibody (mAb) chCE7 was effective in the treatment of human ovarian cancer xenografts. In this study, we directly compared the therapeutic efficacy of anti-L1CAM RIT against human ovarian cancer under equitoxic conditions with the radiolanthanide (177)Lu and the potential alternative (161)Tb in an ovarian cancer therapy model. METHODS: Tb was produced by neutron bombardment of enriched (160)Gd targets. (161)Tb and (177)Lu were used for radiolabelling of DOTA-conjugated antibodies. The in vivo behaviour of the radioimmunoconjugates (RICs) was assessed in IGROV1 tumour-bearing nude mice using biodistribution experiments and SPECT/CT imaging. After ascertaining the maximal tolerated doses (MTD) the therapeutic impact of 50 % MTD of (177)Lu- and (161)Tb-DOTA-chCE7 was evaluated in groups of ten mice by monitoring the tumour size of subcutaneous IGROV1 tumours. RESULTS: The average number of DOTA ligands per antibody was 2.5 and maximum specific activities of 600 MBq/mg were achieved under identical radiolabelling conditions. RICs were stable in human plasma for at least 48 h. (177)Lu- and (161)Tb-DOTA-chCE7 showed high tumour uptake (37.8-39.0 %IA/g, 144 h p.i.) with low levels in off-target organs. SPECT/CT images confirmed the biodistribution data. (161)Tb-labelled chCE7 revealed a higher radiotoxicity in nude mice (MTD: 10 MBq) than the (177)Lu-labelled counterpart (MTD: 12 MBq). In a comparative therapy study with equitoxic doses, tumour growth inhibition was better by 82.6 % for the (161)Tb-DOTA-chCE7 than the (177)Lu-DOTA-chCE7 RIT. CONCLUSIONS: Our study is the first to show that anti-L1CAM (161)Tb RIT is more effective compared to (177)Lu RIT in ovarian cancer xenografts. These results suggest that (161)Tb is a promising candidate for future clinical applications in combination with internalising antibodies.

Direct in vitro and in vivo comparison of (161)Tb and (177)Lu using a tumour-targeting folate conjugate.

PURPOSE: The radiolanthanide (161)Tb (T 1/2 = 6.90 days, Eß(-) av = 154 keV) was recently proposed as a potential alternative to (177)Lu (T 1/2 = 6.71 days, Eß(-) av = 134 keV) due to similar physical decay characteristics but additional conversion and Auger electrons that may enhance the therapeutic efficacy. The goal of this study was to compare (161)Tb and (177)Lu in vitro and in vivo using a tumour-targeted DOTA-folate conjugate (cm09). METHODS: (161)Tb-cm09 and (177)Lu-cm09 were tested in vitro on folate receptor (FR)-positive KB and IGROV-1 cancer cells using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) viability assay. In vivo (161)Tb-cm09 and (177)Lu-cm09 (10 MBq, 0.5 nmol) were investigated in two different tumour mouse models with regard to the biodistribution, the possibility for single photon emission computed tomography (SPECT) imaging and the antitumour efficacy. Potentially undesired side effects were monitored over 6 months by determination of plasma parameters and examination of kidney function with quantitative SPECT using (99m)Tc-dimercaptosuccinic acid (DMSA). RESULTS: To obtain half-maximal inhibition of tumour cell viability a 4.5-fold (KB) and 1.7-fold (IGROV-1) lower radioactivity concentration was required for (161)Tb-cm09 (IC50 ~0.014 MBq/ml and ~2.53 MBq/ml) compared to (177)Lu-cm09 (IC50 ~0.063 MBq/ml and ~4.52 MBq/ml). SPECT imaging visualized tumours of mice with both radioconjugates. However, in therapy studies (161)Tb-cm09 reduced tumour growth more efficiently than (177)Lu-cm09. These findings were in line with the higher absorbed tumour dose for (161)Tb-cm09 (3.3 Gy/MBq) compared to (177)Lu-cm09 (2.4 Gy/MBq). None of the monitored parameters indicated signs of impaired kidney function over the whole time period of investigation after injection of the radiofolates. CONCLUSION: Compared to (177)Lu-cm09 we demonstrated equal imaging features for (161)Tb-cm09 but an increased therapeutic efficacy for (161)Tb-cm09 in both tumour cell lines in vitro and in vivo. Further preclinical studies using other tumour-targeting radioconjugates are clearly necessary to draw final conclusions about the future clinical perspectives of (161)Tb.

A unique matched quadruplet of terbium radioisotopes for PET and SPECT and for α- and ß- radionuclide therapy: an in vivo proof-of-concept study with a new receptor-targeted folate derivative.

UNLABELLED: Terbium offers 4 clinically interesting radioisotopes with complementary physical decay characteristics: (149)Tb, (152)Tb, (155)Tb, and (161)Tb. The identical chemical characteristics of these radioisotopes allow the preparation of radiopharmaceuticals with identical pharmacokinetics useful for PET ((152)Tb) and SPECT diagnosis ((155)Tb) and for α- ((149)Tb) and ß(-)-particle ((161)Tb) therapy. The goal of this proof-of-concept study was to produce all 4 terbium radioisotopes and assess their diagnostic and therapeutic features in vivo when labeled with a folate-based targeting agent. METHODS: (161)Tb was produced by irradiation of (160)Gd targets with neutrons at Paul Scherrer Institute or Institut Laue-Langevin. After neutron capture, the short-lived (161)Gd decays to (161)Tb. (149)Tb, (152)Tb, and (155)Tb were produced by proton-induced spallation of tantalum targets, followed by an online isotope separation process at ISOLDE/CERN. The isotopes were purified by means of cation exchange chromatography. For the in vivo studies, we used the DOTA-folate conjugate cm09, which binds to folate receptor (FR)-positive KB tumor cells. Therapy experiments with (149)Tb-cm09 and (161)Tb-cm09 were performed in KB tumor-bearing nude mice. Diagnostic PET/CT ((152)Tb-cm09) and SPECT/CT ((155)Tb-cm09 and (161)Tb-cm09) studies were performed in the same tumor mouse model. RESULTS: Carrier-free terbium radioisotopes were obtained after purification, with activities ranging from approximately 6 MBq (for (149)Tb) to approximately 15 MBq (for (161)Tb). The radiolabeling of cm09 was achieved in a greater than 96% radiochemical yield for all terbium radioisotopes. Biodistribution studies showed high and specific uptake in FR-positive tumor xenografts (23.8% ± 2.5% at 4 h after injection, 22.0% ± 4.4% at 24 h after injection, and 18.4% ± 1.8% at 48 h after injection). Excellent tumor-to-background ratios at 24 h after injection (tumor to blood, ≈ 15; tumor to liver, ≈ 5.9; and tumor to kidney, ≈ 0.8) allowed the visualization of tumors in mice using PET ((152)Tb-cm09) and SPECT ((155)Tb-cm09 and (161)Tb-cm09). Compared with no therapy, α- ((149)Tb-cm09) and ß(-)-particle therapy ((161)Tb-cm09) resulted in a marked delay in tumor growth or even complete remission (33% for (149)Tb-cm09 and 80% for (161)Tb-cm09) and a significantly increased survival. CONCLUSION: For the first time, to our knowledge, 4 terbium radionuclides have been tested in parallel with tumor-bearing mice using an FR targeting agent. Along with excellent tumor visualization enabled by (152)Tb PET and (155)Tb SPECT, we demonstrated the therapeutic efficacy of the α-emitter (149)Tb and ß(-)-emitter (161)Tb.

The low-energy ß(-) and electron emitter (161)Tb as an alternative to (177)Lu for targeted radionuclide therapy.

INTRODUCTION: The low-energy ß(-) emitter (161)Tb is very similar to (177)Lu with respect to half-life, beta energy and chemical properties. However, (161)Tb also emits a significant amount of conversion and Auger electrons. Greater therapeutic effect can therefore be expected in comparison to (177)Lu. It also emits low-energy photons that are useful for gamma camera imaging. METHODS: The (160)Gd(n,γ)(161)Gd→(161)Tb production route was used to produce (161)Tb by neutron irradiation of massive (160)Gd targets (up to 40 mg) in nuclear reactors. A semiautomated procedure based on cation exchange chromatography was developed and applied to isolate no carrier added (n.c.a.) (161)Tb from the bulk of the (160)Gd target and from its stable decay product (161)Dy. (161)Tb was used for radiolabeling DOTA-Tyr3-octreotate; the radiolabeling profile was compared to the commercially available n.c.a. (177)Lu. A (161)Tb Derenzo phantom was imaged using a small-animal single-photon emission computed tomography camera. RESULTS: Up to 15 GBq of (161)Tb was produced by long-term irradiation of Gd targets. Using a cation exchange resin, we obtained 80%-90% of the available (161)Tb with high specific activity, radionuclide and chemical purity and in quantities sufficient for therapeutic applications. The (161)Tb obtained was of the quality required to prepare (161)Tb-DOTA-Tyr3-octreotate. CONCLUSIONS: We were able to produce (161)Tb in n.c.a. form by irradiating highly enriched (160)Gd targets; it can be obtained in the quantity and quality required for the preparation of (161)Tb-labeled therapeutic agents.

Electron- and positron-emitting radiolanthanides for therapy: aspects of dosimetry and production.

UNLABELLED: All lanthanides have similar chemical properties regarding labeling. Therefore, radiolanthanides that have been used for therapy, such as (153)Sm and (177)Lu, might easily be replaced with other radiolanthanides. The aim of this work was to investigate the suitability of electron- and positron-emitting radiolanthanides for radionuclide therapy with reference to dosimetry and production possibilities. METHODS: Radiolanthanides with half-lives of 1 h to 15 d, stable or long-lived daughters, and limited photon emission were selected. The ratio of the absorbed dose rate to the tumors and the normal tissue (TND) was calculated for different tumor sizes and compared with the TND values for (90)Y and (131)I. The normal tissue and tumors were simulated as an ellipsoid and spheres, respectively. The TND values depend on the physical parameters of the radionuclides, the tumor size, and the ratio between the activity concentrations in the tumor and normal tissue (TNC). RESULTS: (153)Sm, (161)Tb, (169)Er, (175)Yb, and (177)Lu had the highest TND values for most of the tumor sizes studied. Among these radiolanthanides, (161)Tb and (177)Lu are the only ones that can be produced no-carrier-added (nca) and with high specific activities. The Auger-electron emitters (161)Ho and (167)Tm had high TND values for tumors weighing less than 1 mg and can be produced nca and with high specific activities. (142)Pr, (145)Pr, and (166)Ho showed TND values similar to those of (90)Y. (166)Ho is generator produced and can be obtained nca and at high specific activities. (143)Pr, (149)Pm, (150)Eu, (159)Gd, (165)Dy, (176m)Lu, and (179)Lu had higher TND values than did (90)Y for all tumor sizes studied, but only (149)Pm can be produced nca and at high specific activities. The other electron-emitting radiolanthanides and the positron-emitting radiolanthanides showed low TND values for all tumor sizes because of the high photon contribution. CONCLUSION: The low-energy electron emitters (161)Tb, (177)Lu, and (167)Tm might be suitable for radionuclide therapy. The Auger-electron emitter (161)Ho might not be suitable for systemic radionuclide therapy (intravenous injection) because of its short half-life but might be suitable for local therapy (e.g., in body cavities). If higher electron energy is needed, (149)Pm or (166)Ho might be suitable for radionuclide therapy.

Comparison of the radiotoxicity of two alpha-particle-emitting immunoconjugates, terbium-149 and bismuth-213, directed against a tumor-specific, exon 9 deleted (d9) E-cadherin adhesion protein.

We investigated the effects of the alpha-particle emitters (149)Tb and (213)Bi coupled to a tumor-specific antibody targeting the mutated delta 9 E-cadherin (d9 E-Cad) on single cells and cell pellets. The d9 mutation of the adhesion molecule E-cadherin is found in 10% of diffuse-type gastric cancers and is not expressed in normal tissue. Human breast cancer cells (MDA-MB-435S) transfected with d9 E-Cad or the wild-type E-cadherin gene were used to study the effects of anti-d9 E-Cad MAb coupled to (149)Tb and (213)Bi ((149)Tb-d9 MAb and (213)Bi-d9 MAb). The density of binding sites determined on transfected MDA tumor cells by Scatchard analysis and flow cytometry varied from 4 x 10(4) to 6 x 10(4) antigens per cell. Internalization of radioimmunoconjugates by cells expressing d9 E-Cad was less than 10% of bound antibody within 240 min. The effect of the radioimmunoconjugates on cell suspensions and cell pellets was quantified by [(3)H]thymidine incorporation, and the dose to the cell nuclei was determined using microdosimetric calculations. (149)Tb and (213)Bi immunoconjugates affected cells in suspension similarly. Significant differences in the proliferation capacity of d9 E-cadherin- and wild-type E-cadherin-expressing cells were observed at activity concentrations around 185 kBq/ml, corresponding to antibody concentrations between 200 ng/ml and 1000 ng/ml. Proliferation after incubation with (213)Bi-d9 MAb was 50% greater in pelleted wild-type E-Cad-expressing cells compared to wild-type E-Cad cells in suspension. In contrast, the proliferation of pelleted d9 E-Cad cells was similar to that of d9 E-Cad cells in suspension. For (149)Tb-d9 MAb, no significant difference was found between pelleted cells and cells in suspension for low activity concentrations. However, at high activity concentrations, (149)Tb-d9 MAb had only a small effect on pelleted cells. These in vitro studies demonstrate different effects of (149)Tb and (213)Bi conjugated to a tumor-specific antibody toward single cells and tumor cell pellets. Microdosimetric simulation of single cell survival after alpha-particle irradiation modeled the experimental results with reasonable accuracy.

Advancements in cancer therapy with alpha-emitters: a review.

PURPOSE: This synopsis attempts to shed light on the progresses made in the field of cancer therapy using alpha-particles. HURDLES AND PROGRESSES: The rationale of selection of radionuclides focusing on comparison of alpha- and beta-emitters, the hurdles and their solutions, and recent developments are addressed. The efforts made in the field of alpha-radioimmunotherapy of hematologic malignancies are emphasized. A good deal of progress has been achieved in the past decade, and preclinical studies with a variety of radioimmunoconjugates with astatine and bismuth radioisotopes (At-211, Bi-212, and Bi-213) have generated encouraging results, providing an impetus for future clinical trials. CONCLUSION: The onset of early clinical trials with alpha-emitters will hopefully enable the cancer researchers to come up with extremely effective and highly specific "smart bombs" to target cancer cells.

Radioimmunoconjugates for targeted alpha therapy of malignant melanoma.

Effective targeted cancer therapy requires high selectivity and cytotoxicity. To this end we have prepared and tested a new alpha-emitting radioimmunoconjugate (RIC) against malignant melanoma. The melanoma antibody 9.2.27 is specific for most melanoma cell lines. This antibody was labelled with an a emitter, bismuth-213 (213Bi), and a positron emitter, terbium-152 (152Tb), which is an analogue of the alpha-emitting radioisotope terbium-149. The chelators cDTPAa (a cyclic anhydride of diethylenetriamine pentacetic acid) and CHX-A" (a 2-(p-SCN-Bz)-cyclohexyl-DTPA ligand) were used in order to obtain high labelling yields for both isotopes with either chelator. The labelling efficiency with 213Bi was found to be 96% and 92% with cDTPAa and CHX-A", respectively. With 152Tb it was 93% and 89%, respectively. Serum stability studies showed 20% leaching with 213Bi over a period of 2.5 half-lives. For 152Tb the leaching was 13%. There was no difference in the melanoma cell binding of the labelled and unlabelled antibodies. DNA synthesis data were compared for both isotopes with either chelator. Based on these results, the therapeutic activity ratio for 213Bi a particles and 152Tb positrons for the same endpoint was calculated to be 120. The stability of the bismuth and terbium RICs, together with the outstanding cytotoxicity of the alpha emitter, provides the basis for a new approach to the potential control of micrometastatic melanoma.

Targeted alpha therapy: evidence for potential efficacy of alpha-immunoconjugates in the management of micrometastatic cancer.

There can be little doubt that one of the most important problems in the management of cancer is control of metastatic disease. This objective must be achieved ideally with a systemic therapeutic modality that targets cancer cells and gives minimal collateral damage to critical normal cells. The efficacy of targeted cancer therapy relies on the ability of a toxin to be located in the target cancer cell. The ideal toxin is one that is active only in the cancer cell, and not in critical normal cells. Failing this, the next best approach is a toxin with a short effective lifetime to target early stage micrometastatic disease. This rules out chemical toxins, given that they remain effective until excreted from the body, and localization of dose to the cancer cell rules out beta-emitting radio-isotopes (RI). Alpha-emitting RI, however, are much more appropriate toxins because they are short-lived and because their cytotoxicity is the result of their high rate of energy loss and short range of the alpha particles. These radionuclides have properties that are particularly suited for the elimination of single cells in transit or small nests of cancer cells. In vitro and in vivo experiments with alpha RI show dramatic superiority over beta RI. Only a few nuclear hits are needed to kill cells, and the formation of metastatic lung lesions and subcutaneous lesions in mice can be inhibited by systemic administration of alpha emitters. But alpha RI have not been able to control solid tumours, for which beta RI are better suited. A small number of alpha-emitting radionuclides are currently under investigation. These are terbium (Tb)-149, astatine (At)-211, bismuth (Bi)-212 and Bi-213. Terbium-149 and At-211 both require accelerators in close proximity to the place of application. The Bi isotopes are produced by long-lived parents and, as such, can be obtained from generators. The first phase-1 dose escalation trial with Bi-213 radioimmunoconjugate (RIC) commenced in New York in 1997, and other trials are planned with At-211 RIC and At-211 methylene blue for melanoma. Actinium (Ac)-225 is obtained from the decay of thorium (Th)-229, which is a waste product in the enrichment of fissile Th-233. Alternative accelerator production routes are being investigated, beginning with the European Centre for Nuclear Research (CERN) GeV proton spallation source. The ready and low-cost availability of the Ac:Bi generator is an important element in the implementation of clinical trials for patients with poor prognoses but without evidence of metastatic disease.

Alpha- and beta-emitting radiolanthanides in targeted cancer therapy: the potential role of terbium-149.

The efficacy of systemic cancer therapy rests on the ability of a toxin to be preferentially located in cancer cells, so that cancer cell kill is maximized and normal tissue spared. This requires that the lifetime of the toxin be less than the lifetime of the carrier in the body, effectively ruling out chemical toxins, as they remain effective until excreted from the body. The requirement of localization of dose to the cancer cell makes radioactive beta-emitting radionuclides unattractive. Alpha-emitting radionuclides are much more appropriate toxins, as their efficacy depends on the high energy and short range of the alpha particles, and terbium-149 is shown to be the most efficacious of these. However, the merit of various alpha- and beta-emitting radionuclides depends on the stage and type of cancer. Recommendations are made with respect to the matching of the target cancer with required properties of the radiolabel and carrier.

Evaluation in vitro and in rats of 161Tb-DTPA-octreotide, a somatostatin analogue with potential for intraoperative scanning and radiotherapy.

The characteristics of terbium-161 diethylene triamine penta-acetic acid (DTPA) labelled octreotide with respect to specific binding to somatostatin (octreotide) receptors on rat brain cortex membranes, biological activity, uptake and excretion by isolated perfused rat livers and metabolism in vivo in normal and tumour-bearing rats were determined and compared to those of indium-111 DTPA-octreotide. The results of the binding studies demonstrate that 161Tb-DTPA-octreotide is a high-affinity radioligand for somatostatin receptors, with an affinity comparable to that of 111In-DTPA-octreotide. Rat growth hormone secretion inhibition experiments showed that 161Tb-DTPA-octreotide has a similar potency to 111In-DTPA-octreotide. 161Tb-DTPA-octreotide appeared to be taken up even less by the isolated perfused rat liver than 111In-DTPA-octreotide, as almost no tracer disappeared from the perfusion medium. Furthermore, hardly any radioactivity was found in the liver, and excretion into the bile was negligible. The biodistribution studies showed that for octreotide receptor-positive organs, such as pancreas and adrenals, uptake of 161Tb-DTPA-octreotide is lower then that of 111In-DTPA-octreotide. However, as the clearance from the blood of the former compound is faster than that of the latter, the tissue/blood ratio is higher in the case of 161Tb-DTPA-octreotide than with 111In-DTPA-octreotide. Furthermore, these studies demonstrated that the uptake of 161Tb-DTPA-octreotide by the renal tubular cells after glomerular filtration can be reduced by administration of lysine or sodium maleate. Increase in urine production before and during the experiment had no effect on the kidney uptake of 161Tb-DTPA-octreotide.(ABSTRACT TRUNCATED AT 250 WORDS)