Preclinical Characterization of the 177Lu-Labeled Prostate Stem Cell Antigen (PSCA)-Specific Monoclonal Antibody 7F5.

Prostate specific membrane antigen (PSMA) is an excellent target for imaging and treatment of prostate carcinoma (PCa). Unfortunately, not all PCa cells express PSMA. Therefore, alternative theranostic targets are required. The membrane protein prostate stem cell antigen (PSCA) is highly overexpressed in most primary prostate carcinoma (PCa) cells and in metastatic and hormone refractory tumor cells. Moreover, PSCA expression positively correlates with tumor progression. Therefore, it represents a potential alternative theranostic target suitable for imaging and/or radioimmunotherapy. In order to support this working hypothesis, we conjugated our previously described anti-PSCA monoclonal antibody (mAb) 7F5 with the bifunctional chelator CHX-A″-DTPA and subsequently radiolabeled it with the theranostic radionuclide 177Lu. The resulting radiolabeled mAb ([177Lu]Lu-CHX-A″-DTPA-7F5) was characterized both in vitro and in vivo. It showed a high radiochemical purity (>95%) and stability. The labelling did not affect its binding capability. Biodistribution studies showed a high specific tumor uptake compared to most non-targeted tissues in mice bearing PSCA-positive tumors. Accordingly, SPECT/CT images revealed a high tumor-to-background ratios from 16 h to 7 days after administration of [177Lu]Lu-CHX-A″-DTPA-7F5. Consequently, [177Lu]Lu-CHX-A″-DTPA-7F5 represents a promising candidate for imaging and in the future also for radioimmunotherapy.

Development of 177Lu-Cetuximab-PAMAM dendrimeric nanosystem: a novel theranostic radioimmunoconjugate.

PURPOSE: Epidermal growth factor receptors (EGFRs) are overexpressed in a wide range of tumors and are attractive candidates to target in targeted therapies. This study aimed to introduce a novel radiolabeled compound, 177Lu-cetuximab-PAMAM G4, for the treatment of EGFR-expressing tumors. METHODS: In this study, the cetuximab mAb was bound to PAMAM G4 and labeled with 177Lu via DTPA-CHX chelator. The synthesized nanosystem was confirmed by different analyses such as DLS, FT-IR, TEM, and RT-LC. Cell viability of the radioimmunoconjugate was assessed over the EGFR-expressing cell line of SW480. The biodistribution of 177Lu-Cetuximab-PAMAMG4 was determined in different intervals after injection of the radiolabeled compound in normal and tumoral nude mice via scarification and SPECT images. RESULTS: The average size of PAMAM G4 and PAMAM-Cetuximab-DTPA-CHX nanoparticles were 2 and 70 nm, respectively. 177Lu-Cetuximab-PAMAMG4 was prepared with radiochemical purity of more than 98%. The survival rates of SW480 cells at 24, 48, and 72 h post-treatment with177Lu-Cetuximab-PAMAMG4 (500 nM) were 18%, 15%, and 14%, respectively. The biodistribution studies showed a significant accumulation of 177Lu-Cetuximab-PAMAM in the EGFR-expressing tumor. CONCLUSION: According to the results, this new agent can be considered as an efficient therapeutic complex for tumors expressing EGFR receptors.

Leveraging a Dual Variable Domain Immunoglobulin to Create a Site-Specifically Modified Radioimmunoconjugate.

Site-specifically modified radioimmunoconjugates exhibit superior in vitro and in vivo behavior compared to analogues synthesized via traditional stochastic methods. However, the development of approaches to site-specific bioconjugation that combine high levels of selectivity, simple reaction conditions, and clinical translatability remains a challenge. Herein, we describe a novel solution to this problem: the use of dual-variable domain immunoglobulins (DVD-IgG). More specifically, we report the synthesis, in vitro evaluation, and in vivo validation of a 177Lu-labeled radioimmunoconjugate based on HER2DVD, a DVD-IgG containing the HER2-targeting variable domains of trastuzumab and the catalytic variable domains of IgG h38C2. To this end, we first modified HER2DVD with a phenyloxadiazolyl methlysulfone-modified variant of the chelator CHX-A″-DTPA (PODS-CHX-A''-DTPA) and verified the site-specificity of the conjugation for the reactive lysines within the catalytic domains via chemical assay, MALDI-ToF mass spectrometry, and SDS-PAGE. The chelator-bearing immunoconjugate was subsequently labeled with [177Lu]Lu3+ to produce the completed radioimmunoconjugate, [177Lu]Lu-CHX-A″-DTPAPODS-HER2DVD, in >80% radiochemical conversion and a specific activity of 29.5 ± 7.1 GBq/µmol. [177Lu]Lu-CHX-A″-DTPAPODS-HER2DVD did not form aggregates upon prolonged incubation in human serum, displayed 87% stability to demetalation over a 7 days of incubation in serum, and exhibited an immunoreactive fraction of 0.95 with HER2-coated beads. Finally, we compared the pharmacokinetic profile of [177Lu]Lu-CHX-A″-DTPAPODS-HER2DVD to that of a 177Lu-labeled variant of trastuzumab in mice bearing subcutaneous HER2-expressing BT-474 human breast cancer xenografts. The in vivo performance of [177Lu]Lu-CHX-A″-DTPAPODS-HER2DVD matched that of 177Lu-labeled trastuzumab, with the former producing a tumoral activity concentration of 34.1 ± 12.1 %ID/g at 168 h and tumor-to-blood, tumor-to-liver, and tumor-to-kidney activity concentration ratios of 10.5, 9.6, and 21.8, respectively, at the same time point. Importantly, the DVD-IgG did not exhibit a substantially longer serum half-life than the traditional IgG despite its significantly larger size (202 kDa for the former vs 148 kDa for the latter). Taken together, these data suggest that DVD-IgGs represent a viable platform for the future development of highly effective site-specifically labeled radioimmunoconjugates for diagnostic imaging, theranostic imaging, and radioimmunotherapy.

Delta-like ligand 3-targeted radioimmunotherapy for neuroendocrine prostate cancer.

Neuroendocrine prostate cancer (NEPC) is a lethal subtype of prostate cancer with limited meaningful treatment options. NEPC lesions uniquely express delta-like ligand 3 (DLL3) on their cell surface. Taking advantage of DLL3 overexpression, we developed and evaluated lutetium-177 (177Lu)-labeled DLL3-targeting antibody SC16 (177Lu-DTPA-SC16) as a treatment for NEPC. SC16 was functionalized with DTPA-CHX-A" chelator and radiolabeled with 177Lu to produce 177Lu-DTPA-SC16. Specificity and selectivity of 177Lu-DTPA-SC16 were evaluated in vitro and in vivo using NCI-H660 (NEPC, DLL3-positive) and DU145 (adenocarcinoma, DLL3-negative) cells and xenografts. Dose-dependent treatment efficacy and specificity of 177Lu-DTPA-SC16 radionuclide therapy were evaluated in H660 and DU145 xenograft-bearing mice. Safety of the agent was assessed by monitoring hematologic parameters. 177Lu-DTPA-SC16 showed high tumor uptake and specificity in H660 xenografts, with minimal uptake in DU145 xenografts. At all three tested doses of 177Lu-DTPA-SC16 (4.63, 9.25, and 27.75 MBq/mouse), complete responses were observed in H660-bearing mice; 9.25 and 27.75 MBq/mouse doses were curative. Even the lowest tested dose proved curative in five (63%) of eight mice, and recurring tumors could be successfully re-treated at the same dose to achieve complete responses. In DU145 xenografts, 177Lu-DTPA-SC16 therapy did not inhibit tumor growth. Platelets and hematocrit transiently dropped, reaching nadir at 2 to 3 wk. This was out of range only in the highest-dose cohort and quickly recovered to normal range by week 4. Weight loss was observed only in the highest-dose cohort. Therefore, our data demonstrate that 177Lu-DTPA-SC16 is a potent and safe radioimmunotherapeutic agent for testing in humans with NEPC.

Development of Novel 191Pt-Labeled Hoechst33258: 191Pt Is More Suitable than 111In for Targeting DNA.

This study aims to establish new labeling methods for no-carrier-added radio-Pt (191Pt) and to evaluate the in vitro properties of 191Pt-labeled agents compared with those of agents labeled with the common emitter 111In. 191Pt was complexed with the DNA-targeting dye Hoechst33258 via diethylenetriaminepentaacetic acid (DTPA) or the sulfur-containing amino acid cysteine (Cys). The intranuclear fractions of 191Pt- and 111In-labeled Hoechst33258 were comparable, indicating that the labeling for 191Pt via DTPA or Cys and the labeling for 111In via DTPA worked equally well. 191Pt showed a DNA-binding/cellular uptake ratio of more than 1 order of magnitude greater than that of 111In. [191Pt]Pt-Hoechst33258 labeled via Cys showed a higher cellular uptake than that labeled via DTPA, resulting in a very high DNA-binding fraction of [191Pt]Pt-Cys-Hoechst33258 and extensive DNA damage. Our labeling methods of radio-Pt, especially via Cys, promote the development of radio-Pt-based agents for use in Auger electron therapy targeting DNA.

Gram-scale synthesis of a neodymium chelate as a spectral CT and second near-infrared window imaging agent for visualizing the gastrointestinal tract in vivo.

The diagnosis of gastrointestinal (GI) tract diseases is frequently performed in the clinic, so it is crucial to develop high-performance contrast agents for real-time and non-invasive imaging examination of the GI tract. Herein, we show a novel method to synthesize a neodymium (Nd) chelate, Nd-diethylenetriaminepentaacetic acid (Nd-DTPA), on a large scale without byproducts for spectral computed tomography (CT) and second near-infrared window imaging of the GI tract in vivo. The Nd-DTPA was simply generated by heating the mixture of Nd2O3 and DTPA in water at 85 °C for 2 h. This dual-modal imaging agent has the advantages of a simple and green synthesis route, no need of purification process, high yield (86.24%), large-scale production capability (>10 g in lab synthesis), good chemical stability and excellent water solubility (≈2 g mL-1). Moreover, the Nd-DTPA emitted strong near-infrared fluorescence at 1308 nm, and exhibited superior X-ray attenuation ability compared to clinical iohexol. The proposed Nd-DTPA can integrate the complementary merits of dual-modal imaging to realize spatial-temporal and highly sensitive imaging of the GI tract in vivo, and accurate diagnosis of the location of intestinal obstruction and monitor its recovery after surgery. The developed highly efficient method for the gram-scale synthesis of Nd-DTPA and the proposed spectral CT and second near-infrared window dual-modal imaging strategy provide a promising route for accurate visualization of the GI tract in vivo.

Evidence for a differential translocation of actinides across human lung epithelial cell monolayer in vitro according to their physicochemical properties and the presence of a chelating agent.

The epithelial cell plays a key role in the transfer of radionuclides from lungs to blood following pulmonary exposure. The present study was designed to evaluate the transfer across human lung epithelial cells of various actinides (plutonium, americium and uranium), the influence of the physicochemical properties of plutonium compounds and of the chelating agent diethylene triamine pentaacetic acid (DTPA). To address this question, Calu-3 cells grown in a bicameral culture system were used. The integrity of the epithelial barrier was evaluated by measuring transepithelial electrical resistance (TEER) and the passage of a fluorescent marker, lucifer yellow. Activity measurement in basal compartment following periodic collection of culture medium was made from 2 h to seven days. To facilitate data handling and analysis, the statistical tool STATBIODIS was used. The results indicate differences in transfer for the different elements, and according to Pu physicochemical properties. Though to various extents, the chelating agent DTPA always increased the transfer of Pu and Am across the epithelial cells, without altering the integrity of the epithelial barrier. This in vitro cell culture model, by mimicking translocation of actinides from lungs to blood, can represent a valuable tool to further understand the underlying mechanisms and properties controlling this process.

Effect of Iron Source and Medium pH on Growth and Development of Sorbus commixta In Vitro.

Sorbus commixta is a valuable hardwood plant with a high economical value for its medicinal and ornamental qualities. The aim of this work was to investigate the effects of the iron (Fe) source and medium pH on the growth and development of S. commixta in vitro. The Fe sources used, including non-chelated iron sulfate (FeSO4), iron ethylenediaminetetraacetic acid (Fe-EDTA), and iron diethylenetriaminepentaacetic acid (Fe-DTPA), were supplemented to the Multipurpose medium with a final Fe concentration of 2.78 mg·L-1. The medium without any supplementary Fe was used as the control. The pH of the agar-solidified medium was adjusted to either 4.70, 5.70, or 6.70. The experiment was conducted in a culture room for six weeks with 25 °C day and night temperatures, and a 16-h photoperiod with a light intensity of 50 mmol·m-2·s-1 photosynthetic photon flux density (PPFD). Both the Fe source and pH affected the growth and development of the micropropagated plants in vitro. The leaves were greener in the pH 4.70 and 5.70 treatments. The tissue Fe content decreased with the increase of the medium pH. The leaf chlorophyll content was similar between plants treated with FeSO4 and those with Fe-EDTA. The numbers of the shoots and roots of plantlets treated with FeSO4 were 2.5 and 2 times greater than those of the control, respectively. The fresh and dry weights of the shoot and the root were the greatest for plants treated with Fe-EDTA combined with pH 5.70. The calcium, magnesium, and manganese contents in the plantlets increased in the pH 5.70 treatments regardless of the Fe source. Supplementary Fe decreased the activity of ferric chelate reductase. Overall, although the plantlets absorbed more Fe at pH 4.70, Fe-EDTA combined with pH 5.70 was found to be the best for the growth and development of S. commixta in vitro.

Peptide Ligands Specifically Targeting HER2 Receptor and the Role Played by a Synthetic Model System of the Receptor Extracellular Domain: Hypothesized Future Perspectives.

A short (Fab)trastuzumab-derived peptide specific for HER2 receptor was identified. Its affinity for the model system HER2-DIVMP was found in a nanomolar range. The structural determinants responsible for the interaction between this ligand (A9) and HER2-DIVMP were investigated by both computational and NMR analysis. Next, the possibility of using A9 as HER2- specific probe for the nuclear medicine imaging was evaluated by conjugating A9 with the DTPA chelator and radiolabeling it with 111In. The developed probe retained a nanomolar affinity to HER2-overexpressing cancer cells, however, some unspecific binding also occurred. The peptide internalization into cells by receptor-mediated endocytosis was also studied. Future perspectives are aimed at using A9 as a probe for molecular imaging diagnostics as well as active targeting of anticancer drugs. Lead structure optimization is needed to minimize the percentage of A9 unspecific binding and to increase the binding affinity to the receptor.

Bismuth chelate as a contrast agent for X-ray computed tomography.

BACKGROUNDS: Due to the unexpected side effects of the iodinated contrast agents, novel contrast agents for X-ray computed tomography (CT) imaging are urgently needed. Nanoparticles made by heavy metal elements are often employed, such as gold and bismuth. These nanoparticles have the advantages of long in vivo circulation time and tumor targeted ability. However, due to the long residence time in vivo, these nanoparticles may bring unexpected toxicity and, the preparation methods of these nanoparticles are complicated and time-consuming. METHODS: In this investigation, a small molecular bismuth chelate using diethylenetriaminepentaacetic acid (DPTA) as the chelating agent was proposed to be an ideal CT contrast agent. RESULTS: The preparation method is easy and cost-effective. Moreover, the bismuth agent show better CT imaging for kidney than iohexol in the aspect of improved CT values. Up to 500 µM, the bismuth agent show negligible toxicity to L02 cells and negligible hemolysis. And, the bismuth agent did not induce detectable morphology changes to the main organs of the mice after intravenously repeated administration at a high dose of 250 mg/kg. The pharmacokinetics of the bismuth agent follows the first-order elimination kinetics and, it has a short half-life time of 0.602 h. The rapid clearance from the body promised its excellent biocompatibility. CONCLUSIONS: This bismuth agent may serve as a potential candidate for developing novel contrast agent for CT imaging in clinical applications.

Perturbed Angular Correlation as a Tool to Study Precursors for Radiopharmaceuticals.

One of the key components of radiopharmaceuticals for targeting imaging and therapy is a stable bifunctional chelating system to attach radionuclides to selective delivery systems. After-effects of radioactive decay can cause the release of a radioactive isotope from its chelation agent. Perturbed angular correlation (PAC) of γ-rays has become a unique technique to study the behavior of complexes formed between a chelating agent and radionuclide in vivo (in real time) over a relevant range of concentrations (10-12 M). In the present work, four radionuclides, 111In, 111mCd, and 152, 154Eu, were investigated with diethylenetriaminepentaacetic acid (DTPA) at different pH values to determine the stability constants of the complexes as well as the effects of post-decay processes, which play a major role in determining the suitability of these complexes for application as radiopharmaceuticals (e.g., in vivo generators). The study provides a convenient parameter for the characterization of radionuclide-chelator systems using the PAC method. PAC is proven to be a suitable tool to study novel chelators and radiopharmaceutical precursors attached to radiometals.

Evaluation of [131I]I- and [177Lu]Lu-DTPA-A11 Minibody for Radioimmunotherapy in a Preclinical Model of PSCA-Expressing Prostate Cancer.

PURPOSE: Radioimmunotherapy uses tumor-specific antibodies to deliver therapeutic radionuclides, but hematological toxicity due to the long serum half-life of intact antibodies remains a challenge. We evaluated a smaller antibody fragment, the minibody, with faster kinetics and a potentially improved therapeutic index. PROCEDURES: The anti-prostate stem cell antigen (PSCA) minibody (A11 Mb) was radiolabeled with iodine-124 ([124I]I-A11 Mb) or conjugated with deferoxamine (DFO) and labeled with zirconium-89 ([89Zr]Zr-DFO-A11 Mb) for surrogate immunoPET to profile pharmacokinetics in a human prostate cancer xenograft model. Subsequently, minibodies labeled with two therapeutic beta emitters, directly iodinated [131I]I-A11 Mb (non-residualizing) and 177Lu chelated using DTPA ([177Lu]Lu-DTPA-A11 Mb) (residualizing), were compared for in vitro antigen-specific cytotoxicity. Full biodistribution studies (in 22Rv1-PSCA tumor bearing and hPSCA knock-in mice) were conducted for dosimetry calculations. Finally, the lead candidate [131I]I-A11 Mb was evaluated in a radioimmunotherapy experiment. Escalating single doses (3.7, 11, or 37 MBq) and saline control were administered to 22Rv1-PSCA tumor bearing mice and anti-tumor effects (tumor volume) and toxicity (body weight) were monitored. RESULTS: Minibodies radiolabeled with therapeutic beta emitters [131I]I-A11 Mb and [177Lu]Lu-DTPA-A11 Mb exhibited comparable tumor cell growth inhibition in vitro. In vivo surrogate immunoPET imaging using [89Zr]Zr-DFO-A11 Mb showed activity retention in liver and kidney up to 72 h, while [124I]I-A11 Mb cleared from liver, kidney, and blood by 48 h. Based on full biodistribution and dosimetry calculations, administering 37 MBq [131I]I-A11 Mb was predicted to deliver a favorable dose to the tumor (35 Gy), with a therapeutic index of 22 (tumor:bone marrow). For [177Lu]Lu-DTPA-A11 Mb, the kidneys would be dose-limiting, and the maximum tolerated activity (7.4 MBq) was not predicted to deliver an effective radiation dose to tumor. Radioimmunotherapy with a single dose of [131I]I-A11 Mb showed dose-dependent tumor inhibition with minimal off-target toxicity and improved median survival (19 and 24 days, P < 0.001) compared with untreated mice (12 days). CONCLUSIONS: These findings show the potential of the anti-PSCA minibody for targeted radioimmunotherapy with minimal toxicity, and the application of immunoPET and dosimetry for personalized treatment.

Genetic Engineering-Facilitated Coassembly of Synthetic Bacterial Cells and Magnetic Nanoparticles for Efficient Heavy Metal Removal.

Heavy-metal pollution is becoming a worldwide problem severely threatening our health and ecosystem. In this study, we constructed a genetic-engineering-driven coassembly of synthetic bacterial cells and magnetic nanoparticles (MNPs) for capturing heavy metals. The Escherichia coli cells were genetically engineered by introducing a de novo synthetic heavy-metal-capturing gene (encoding a protein SynHMB containing a six-histidine tag, two cystine-rich peptides, and a metallothionein sequence) and a synthetic type VI secretory system (T6SS) cluster of Pseudomonas putida, endowing the synthetic cells (SynEc2) with high ability of displaying the heavy-metal-capturing SynHMB on cell surface. MNPs were synthesized by a coprecipitation method and further modified by polyethylenimine (PEI) and diethylenetriaminepentaacetic acid (DTPA). Owing to the surface exposure of six-histidine tag on the synthetic bacteria and carboxyl groups on the modified MNPs (MNP@SiO2-PEI-DTPA), the synthetic bacterial cells and MNPs coassembled to form biotic/abiotic complex exhibiting a self-developing characteristic. In the culture medium containing both Cd2+ and Pb2+, the coassemblies captured these heavy metals with high removal efficiency (>90% even at 50 mg/L of Cd2+ and 50 mg/L of Pb2+) and were conveniently recycled by artificial magnetic fields. Moreover, the coassemblies realized coremoval of organic carbon pollutants with the removal efficiency of >80%. This study builds a novel biotic/abiotic coassembling platform facilitated by genetic engineering and sheds light on development of artificial magnetic biological systems for efficient treatment of environmental pollution.

DTPAA-Gd Functionalized Ultrasmall Au15NCs Nanohybrids for Multimodal Imaging.

INTRODUCTION: Multimodal imaging agent has the potential to overcome the shortage and incorporate the advantages of different imaging tools for extremely sensitive diagnosis. To achieve multimodal imaging, combining multiple contrast agents into a special nanostructure has become a main strategy; However, the combination of all of these functions into one nanoplatform usually requires a complicated synthetic procedure that results in heterogeneous nanostructure. METHODS: In this study, we develop ultrasmall gold nanoclusters with 15 gold atoms (Au15NCs) functionalized with diethylenetriamine-pentaacetic acid dianhydride (DTPAA-Gd) as an optimized multimodal imaging agent to enhance imaging ability. RESULTS: The Au15NCs-DTPAA-Gd nanohybrids possess the ultra-small size and are capable of enhancing the contrast in near-infrared fluorescence (NIRF), magnetic resonance (MR) and X-ray computed tomography (CT) imaging. Meanwhile, the integrated DTPAA-Gd component not only endow the nanohybrids to produce higher T1 relaxivity (r1 = 21.4 mM-1 s-1) than Omnipaque (r1 = 3.973 mM-1s-1) but also further enhance X-ray attenuation property of Au15NCs. Importantly, the fluorescence intensity of Au15NCs-DTPAA-Gd did not decrease compared with Au15NCs. Ultimately, in vivo imaging experiments have demonstrated that Au15NCs-DTPAA-Gd nanohybrids can be quickly eliminated from the body through the urinary system and has great potential for anatomical imaging. CONCLUSION: These data manifest Au15NCs-DTPAA-Gd present great potential as a multimodal contrast agent for disease diagnosis, especially for early accurate detection of tumors.

Effectiveness and normal tissue toxicity of Auger electron (AE) radioimmunotherapy (RIT) with [111In]In-Bn-DTPA-nimotuzumab in mice with triple-negative or trastuzumab-resistant human breast cancer xenografts that overexpress EGFR.

INTRODUCTION: Our objective was to evaluate the effectiveness and normal tissue toxicity of nimotuzumab labeled with the Auger electron (AE)-emitter, 111In ([111In]In-Bn-DTPA-nimotuzumab) for radioimmunotherapy (RIT) of human triple-negative breast cancer (TNBC) or trastuzumab-resistant HER2-positive BC tumors overexpressing epidermal growth factor receptors (EGFR) in athymic mice. METHODS: Normal tissue toxicity was studied in non-tumor-bearing Balb/c mice i.v. administered 9.0 or 28.6 MBq (3 mg/kg) of [111In]In-Bn-DTPA-nimotuzumab, unlabeled nimotuzumab (3 mg/kg) or normal saline. A complete blood cell count (CBC) and serum alanine aminotransferase (ALT) and creatinine (Cr) were measured at 14 days. Body weight was monitored. RIT studies were performed in CD-1 athymic mice engrafted s.c. with MDA-MB-468 human TNBC tumors or TrR1 HER2-positive but trastuzumab-resistant BC tumors. Mice were i.v. administered two amounts (15.5 MBq; 3 mg/kg) of [111In]In-Bn-DTPA-nimotuzumab separated by 14 days. Control mice received unlabeled Bn-DTPA-nimotuzumab (3 mg/kg) or anti-HER2 [111In]In-Bn-DTPA-trastuzumab or normal saline. Tumor growth and body weight were measured for 6 weeks. A tumor growth index (TGI) and body weight index (BWI) were calculated to compare the tumor size and body weight post-treatment with the pre-treatment values. A tumor doubling ratio (TDR) was calculated for each treatment group compared to control mice receiving normal saline. RESULTS: There was no loss of body weight or decreased red blood cells (RBC) or platelets (PLT) or increased serum ALT or Cr in Balb/c mice administered 9.0 or 28.6 MBq (3 mg/kg) of [111In]In-Bn-DTPA-nimotuzumab compared to mice treated with unlabeled Bn-DTPA-nimotuzumab (3 mg/kg) or normal saline. There was a significant decrease in white blood cell (WBC) counts in Balb/c mice receiving 28.6 MBq but not 9.0 MBq of [111In]In-Bn-DTPA-nimotuzumab. Based on these results, an administered amount of 15.5 MBq (3 mg/kg) was selected for RIT studies. Administration of two amounts (15.5 MBq; 3 mg/kg) separated by 14 days to CD-1 athymic mice with s.c. MDA-MB-468 xenografts strongly inhibited tumor growth. The TDR for mice treated with [111In]In-Bn-DTPA-nimotuzumab was 2.15 compared to control mice receiving normal saline. In contrast, treatment with unlabeled Bn-DTPA-nimotuzumab or [111In]In-Bn-DTPA-trastuzumab had no significant effect on tumor growth (TDR = 0.96 and 1.08, respectively). RIT with [111In]In-Bn-DTPA-nimotuzumab also strongly inhibited the growth of TrR1 tumors in athymic mice (TDR = 2.13) compared to unlabeled Bn-DTPA-nimotuzumab (TDR = 0.91). There were no losses in body weight over 6 weeks in tumor bearing mice receiving [111In]In-Bn-DTPA-nimotuzumab, unlabeled Bn-DTPA-nimotuzumab, [111In]In-Bn-DTPA-trastuzumab or normal saline. CONCLUSIONS: [111In]In-Bn-DTPA-nimotuzumab was effective for treatment of TNBC or trastuzumab-resistant HER2-positive human BC tumors in mice that overexpress EGFR at administered amounts that caused no decrease in body weight or normal tissue toxicity in non-tumor-bearing Balb/c mice. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: Our results suggest that Auger electron RIT with [111In]In-Bn-DTPA-nimotuzumab may provide a novel therapeutic option for patients with TNBC or trastuzumab-resistant HER2-positive BC that overexpresses EGFR. The low normal tissue toxicity of this approach may allow combination with other targeted therapies such as antibody-drug conjugates (ADCs).

Uptake and excretion dynamics of gold nanoparticles in cancer cells and fibroblasts.

Radiotherapy is one of the main treatments used to fight cancer. A major limitation of this modality is the lack of selectivity between cancerous and healthy tissues. One of the most promising strategies proposed in this last decade is the addition of nanoparticles with high-atomic number to enhance radiation effects in tumors. Gold nanoparticles (AuNPs) are considered as one of the best candidates because of their high radioenhancing property, simple synthesis and low toxicity. Ultra small AuNPs (core size of 2.4 nm and hydrodynamic diameter of 4.5 nm) covered with dithiolated diethylenetriaminepentaacetic acid (Au@DTDTPA) are of high interest because of their properties to bind MRI active or PET active compounds at their surface, to concentrate in some tumors and be eliminated via renal clearance thanks to their small size. These key figures make Au@DTDTPA the best candidate to develop image-guided radiotherapy. Surprisingly the capacity of the nanoparticles to penetrate cells, an important issue to predict radioenhancement, has not been established yet. Here, we report the uptake dynamics, internalization routes and excretion dynamics of Au@DTDTPA nanoparticles in various cancer cell lines including glioblastoma (U87-MG), chordoma (UM-Chor1), cervix (HeLa), prostate (PC3), and pancreatic (BxPC-3) cell lines as well as fibroblasts (Dermal fibroblasts). This study demonstrates a strong cell line dependence of the nanoparticle uptake and excretion dynamics. Different pathways of cell internalization evidenced here explain this dependence. As a major finding, the retention of Au@DTDTPA nanoparticles was found to be higher in cancer cells than in fibroblasts. This result strengthens the strategy of using nanoagents to improve tumor selectivity of radiation treatments. In particular Au@DTDTPA nanoparticles are good candidates to improve the treatment of radioresitant gliobastoma, pancreatic and prostate cancer in particular. In conclusion, the variability of cell-to-nanoparticle interaction is a new parameter to consider in the choice of nanoagents in a combined treatment.

Optimization of the radiolabelling method for improved in vitro and in vivo stability of 90Y-albumin microspheres.

Biologically stable 90Y-labelled albumin microspheres (AMS) were developed by optimizing the process of their preparation. Three formulations of 90Y-AMS were initially prepared with high radiolabelling yield but depending on the step when the radionuclide 90Y and DTPA chelator were added, radiolabelled microspheres with different in vitro and in vivo stability were obtained. DTPA was proved as a useful chelating agent that tightly links radionuclide 90Y to albumin. Also, AMS radiolabelled via DTPA during preparation and before microspheres stabilization, showed significant in vitro and in vivo stability ready for the potential use in selective internal radiation therapy.

Metal-based antibody drug conjugates. Potential and challenges in their application as targeted therapies in cancer.

Antibody drug conjugates have emerged as a very attractive type of targeted therapy in cancer. They combine the antigen-targeting specificity of monoclonal antibodies (mAbs) with the cytotoxic potency of chemotherapeutics. This review focuses on antibody drug conjugates based on metal-containing cytotoxic payloads. We will also describe antibody drug conjugates (ADCs) in which a metal-based component (mostly metallic nanoparticles) exerts a relevant function in the ADC (for photodynamic or photothermal therapy, as air-plasma-enhancer or chemo-sensitizer, as carrier of other cytotoxic payloads or as an integral part of the linker structure). Challenges and opportunities to increase the translational potential of these ADCs will be discussed.

Measuring the Pancreatic ß Cell Mass in Vivo with Exendin SPECT during Hyperglycemia and Severe Insulitis.

OBJECTIVE: Targeting the glucagon-like peptide-1 receptor with radiolabeled exendin is a very promising method to noninvasively determine the ß cell mass in the pancreas, which is needed to unravel the pathophysiology of type 1 and type 2 diabetes. The present study aimed to explore the effects of both hyperglycemia and insulitis on the uptake of exendin in a spontaneous type 1 diabetes mouse model, nonobese diabetic (NOD) mice. METHODS: NOD mice (n = 75, 7-21 weeks old) were injected intravenously with [111In]In-DTPA-exendin-3, and single-photon emission computed tomography (SPECT) images were acquired 1 h pi. The pancreatic accumulation of [111In]In-DTPA-exendin-3 was quantified in vivo using SPECT and by ex vivo counting and correlated to the ß cell mass (BCM). The influence of insulitis and hyperglycemia on the exendin uptake was assessed. RESULTS: The pancreas could be visualized longitudinally using SPECT. A linear correlation was found between the BCM (%) and pancreatic uptake (%ID/g) as measured by ex vivo counting (Pearson r = 0.64, p < 0.001), which was not affected by either insulitis (Pearson r = 0.66, p = 0.83) or hyperglycemia (Pearson r = 0.57, p = 0.51). Biodistribution and ex vivo autoradiography revealed remaining [111In]In-DTPA-exendin-3 uptake in the pancreas despite total ablation of BCM. CONCLUSIONS: Despite hyperglycemia and severe insulitis, we have found a good correlation between BCM and pancreatic exendin uptake, even in a suboptimal model with relatively high background activity.

Redox potential changes during ATP-dependent corrinoid reduction determined by redox titrations with europium(II)-DTPA.

Corrinoids are essential cofactors of enzymes involved in the C1 metabolism of anaerobes. The active, super-reduced [CoI ] state of the corrinoid cofactor is highly sensitive to autoxidation. In O-demethylases, the oxidation to inactive [CoII ] is reversed by an ATP-dependent electron transfer catalyzed by the activating enzyme (AE). The redox potential changes of the corrinoid cofactor, which occur during this reaction, were studied by potentiometric titration coupled to UV/visible spectroscopy. By applying europium(II)-diethylenetriaminepentaacetic acid (DTPA) as a reductant, we were able to determine the midpoint potential of the [CoII ]/[CoI ] couple of the protein-bound corrinoid cofactor in the absence and presence of AE and/or ATP. The data revealed that the transfer of electrons from a physiological donor to the corrinoid as the electron-accepting site is achieved by increasing the potential of the corrinoid cofactor from -530 ± 15 mV to -250 ± 10 mV (ESHE , pH 7.5). The first 50 to 100 mV of the shift of the redox potential seem to be caused by the interaction of nucleotide-bound AE with the corrinoid protein or its cofactor. The remaining 150-200 mV had to be overcome by the chemical energy of ATP hydrolysis. The experiments revealed that Eu(II)-DTPA, which was already known as a powerful reducing agent, is a suitable electron donor for titration experiments of low-potential redox centers. Furthermore, the results of this study will contribute to the understanding of thermodynamically unfavorable electron transfer processes driven by the power of ATP hydrolysis.