Auger Electron Emission Research Articles

Relativistic multiconfiguration Dirac–Fock calculations of photoionization, electron-impact ionization, Auger decay, and relaxed-orbital oscillations of Cu ions

Core-hole creation and decay are of tremendous importance in both theory and applications. However, different ionization approaches and decay channels, especially at L-shell, bring many challenges to accurate simulation. In order to understand the ionization state effects on the creation and decay at L-shell hole, we performed a theoretical study of photon/electron-impact L-shell ionization of differently charged copper ions and the subsequent Auger electron and fluorescence emission by using the relativistic multiconfiguration Dirac–Fock approach. It was found that photoionization has much larger cross sections than electron-impact ionization near the ionization threshold, but smaller ones at higher impact energies. The ionization cross sections for 2s-sublevels are negligibly small compared with those for 2p-sublevels for both photon and electron impact ionizations. Additionally, the ionization cross sections decrease with the ionization state for both electron- and photon- impact L-shell ionizations. Similar to radiative (fluorescence) decay, Auger kinetic energy and yield decrease with ionization state, and the energy gaps and rate ratios between major Auger transitions change with ionization state. Furthermore, Auger rates from the L-shell decay are much larger than fluorescence rates, and the Auger-to-fluoresce decay ratio slightly decreases with increase in the ionization state of Cu ion.

Monte Carlo dosimetry of a realistic multicellular model of follicular lymphoma in a context of radioimmunotherapy.

Small-scale dosimetry studies generally consider an artificial environment where the tumors are spherical and the radionuclides are homogeneously biodistributed. However, tumor shapes are irregular and radiopharmaceutical biodistributions are heterogeneous, impacting the energy deposition in targeted radionuclide therapy. To bring realism, we developed a dosimetric methodology based on a three-dimensional in vitro model of follicular lymphoma incubated with rituximab, an anti-CD20 monoclonal antibody used in the treatment of non-Hodgkin lymphomas, which might be combined with a radionuclide. The effects of the realistic geometry and biodistribution on the absorbed dose were highlighted by comparison with literature data. Additionally, to illustrate the possibilities of this methodology, the effect of different radionuclides on the absorbed dose distribution delivered to the in vitro tumor were compared. The starting point was a model named multicellular aggregates of lymphoma cells (MALC). Three MALCs of different dimensions and their rituximab biodistribution were considered. Geometry, antibody location and concentration were extracted from selective plane illumination microscopy. Assuming antibody radiolabeling with Auger electron (125 I and 111 In) and β- particle emitters (177 Lu, 131 I and 90 Y), we simulated energy deposition in MALCs using two Monte Carlo codes: Geant4-DNA with "CPA100" physics models for Auger electron emitters and Geant4 with "Livermore" physics models for β- particle emitters. MALCs had ellipsoid-like shapes with major radii, r, of ~0.25, ~0.5 and ~1.3mm. Rituximab was concentrated in the periphery of the MALCs. The absorbed doses delivered by 177 Lu, 131 I and 90 Y in MALCs were compared with literature data for spheres with two types of homogeneous biodistributions (on the surface or throughout the volume). Compared to the MALCs, the mean absorbed doses delivered in spheres with surface biodistributions were between 18% and 38% lower, while with volume biodistribution they were between 15% and 29% higher. Regarding the radionuclides comparison, the relationship between MALC dimensions, rituximab biodistribution and energy released per decay impacted the absorbed doses. Despite releasing less energy, 125 I delivered a greater absorbed dose per decay than 111 In in the r~0.25mm MALC (6.78·10-2 vs 6.26·10-2 µGy·Bq-1 ·s-1 ). Similarly, the absorbed doses per decay in the r~0.5mm MALC for 177 Lu (2.41·10-2 µGy·Bq-1 ·s-1 ) and 131 I (2.46·10-2 µGy·Bq-1 ·s-1 ) are higher than for 90 Y (1.98·10-2 µGy·Bq-1 ·s-1 ). Furthermore, radionuclides releasing more energy per decay delivered absorbed dose more uniformly through the MALCs. Finally, when considering the radiopharmaceutical effective half-life, due to the biological half-life of rituximab being best matched by the physical half-life of 177 Lu and 131 I compared to 90 Y, the first two radionuclides delivered higher absorbed doses. In the simulated configurations, β- emitters delivered higher and more uniform absorbed dose than Auger electron emitters. When considering radiopharmaceutical half-lives, 177 Lu and 131 I delivered absorbed doses higher than 90 Y. In view of real irradiation of MALCs, such a work may be useful to select suited radionuclides and to help explain the biological effects.

Radiobiological and dosimetric assessment of DNA-intercalated 99mTc-complexes bearing acridine orange derivatives

BackgroundRecently, a new family of 99mTc(I)-tricarbonyl complexes bearing an acridine orange (AO) DNA targeting unit and different linkers between the Auger emitter (99mTc) and the AO moiety was evaluated for Auger therapy. Among them, 99mTc-C3 places the corresponding radionuclide at a shortest distance to DNA and produces important double strand breaks (DSB) yields in plasmid DNA providing the first evidence that 99mTc can efficiently induce DNA damage when well positioned to the double helix. Here in, we have extended the studies to human prostate cancer PC3 cells using the 99mTc-C3 and 99mTc-C5 complexes, aiming to assess how the distance to DNA influences the radiation-induced biological effects in this tumoral cell line, namely, in which concerns early and late damage effects.ResultsOur results highlight the limited biological effectiveness of Auger electrons, as short path length radiation, with increasing distances to DNA. The evaluation of the radiation-induced biological effects was complemented with a comparative microdosimetric study based on intracellular dose values. The comparative study, between MIRD and Monte Carlo (MC) methods used to assess the cellular doses, revealed that efforts should be made in order to standardize the bioeffects modeling for DNA-incorporated Auger electron emitters.Conclusions99mTc might not be the ideal radionuclide for Auger therapy but can be useful to validate the design of new classes of Auger-electron emitting radioconjugates. In this context, our results highlight the crucial importance of the distance of Auger electron emitters to the target DNA and encourage the development of strategies for the fine tuning of the distance to DNA for other medical radionuclides (e.g., 111In or 161Tb) in order to enhance their radiotherapeutic effects within the Auger therapy of cancer.

Occupational and ambient radiation exposures from Lu-177 DOTATATE during targeted therapy

Lutetium-177 (DOTATATE) (177Lu; T1/2 6.7 days), a labelled β− and Auger-electron emitter, is widely used in treatment of neuroendocrine tumours. During performance of the procedure, staff and other patients can potentially receive significant doses in interception of the gamma emissions [113 keV (6.4%) and 208 keV (11%)] that are associated with the particle decays. While radiation protection and safety assessment are required in seeking to ensure practices comply with international guidelines, only limited published studies are available. The objectives of present study are to evaluate patient and occupational exposures, measuring ambient doses and estimating the radiation risk. The results, obtained from studies carried out in Riyadh over an 11 month period, at King Faisal Specialist Hospital and Research Center, concerned a total of 33 177Lu therapy patients. Patient exposures were estimated using a calibrated Victoreen 451P survey meter (Fluke Biomedical), for separations of 30 cm, 100 cm and 300 cm, also behind a bed shield that was used during hospitalization of the therapy patients. Occupational and ambient doses were also measured through use of calibrated thermoluminescent dosimeters and an automatic TLD reader (Harshaw 6600). The mean and range of administered activity (in MBq)) was 7115.2 ± 917.2 (4329–7955). The ambient dose at corridors outside of therapy isolation rooms was 1.2 mSv over the 11 month period, that at the nursing station was below the limit of detection and annual occupational doses were below the annual dose limit of 20 mSv. Special concern needs to be paid to comforters (carers) and family members during the early stage of radioisotope administration.

Radiation doses from 161Tb and 177Lu in single tumour cells and micrometastases

BackgroundTargeted radionuclide therapy (TRT) is gaining importance. For TRT to be also used as adjuvant therapy or for treating minimal residual disease, there is a need to increase the radiation dose to small tumours. The aim of this in silico study was to compare the performances of 161Tb (a medium-energy β− emitter with additional Auger and conversion electron emissions) and 177Lu for irradiating single tumour cells and micrometastases, with various distributions of the radionuclide.MethodsWe used the Monte Carlo track-structure (MCTS) code CELLDOSE to compute the radiation doses delivered by 161Tb and 177Lu to single cells (14 μm cell diameter with 10 μm nucleus diameter) and to a tumour cluster consisting of a central cell surrounded by two layers of cells (18 neighbours). We focused the analysis on the absorbed dose to the nucleus of the single tumoral cell and to the nuclei of the cells in the cluster. For both radionuclides, the simulations were run assuming that 1 MeV was released per μm3 (1436 MeV/cell). We considered various distributions of the radionuclides: either at the cell surface, intracytoplasmic or intranuclear.ResultsFor the single cell, the dose to the nucleus was substantially higher with 161Tb compared to 177Lu, regardless of the radionuclide distribution: 5.0 Gy vs. 1.9 Gy in the case of cell surface distribution; 8.3 Gy vs. 3.0 Gy for intracytoplasmic distribution; and 38.6 Gy vs. 10.7 Gy for intranuclear location. With the addition of the neighbouring cells, the radiation doses increased, but remained consistently higher for 161Tb compared to 177Lu. For example, the dose to the nucleus of the central cell of the cluster was 15.1 Gy for 161Tb and 7.2 Gy for 177Lu in the case of cell surface distribution of the radionuclide, 17.9 Gy for 161Tb and 8.3 Gy for 177Lu for intracytoplasmic distribution and 47.8 Gy for 161Tb and 15.7 Gy for 177Lu in the case of intranuclear location.Conclusion161Tb should be a better candidate than 177Lu for irradiating single tumour cells and micrometastases, regardless of the radionuclide distribution.

Multiple Auger decays of core-excited states in N2.

Multi-electron coincidence measurements have been performed at the photon energies for the core-to-valence (1s → π*) and core-to-Rydberg (1s → 3sσ and 3pπ) resonant excitations in N2 in order to investigate the dynamics of multiple Auger-electron emissions from these core-excited states in detail. Peaks due to slow electrons from superexcited atomic fragments are observed in the decay processes by emission of two or three Auger electrons, indicating stepwise (cascade) multiple Auger decays that involve faster dissociations than electronic relaxations. Energy partitions between the emitted electrons enable us to reveal the detailed decay mechanisms for these processes. Branching ratios among the decays by emission of one, two, or three Auger electrons and those between the simultaneous (direct) and stepwise (cascade) processes have been determined for each of the core-excited states. Branching ratios of decay channels resulting in molecular or fragment ions have also been substantiated.

Targeted Delivery of 111In Into the Nuclei of EGFR Overexpressing Cells via Modular Nanotransporters With Anti-EGFR Affibody.

Since cell nucleus is one of the most vulnerable compartments, the maximum therapeutic effect from a variety of locally acting agents, such as photosensitizers, alfa-emitters, Auger electron emitters, will be expected when they get there. Therefore, the targeted delivery of these agents into the nuclei of target tumor cells is necessary for their anticancer effects and minimization of side effects. Modular nanotransporters (MNT) are artificial polypeptides comprising several predefined modules that recognize target cell, launching their subsequent internalization, escape from endosomes, and transport the drug load to the nucleus. This technology significantly enhances the cytotoxicity of locally acting drugs in vitro and in vivo. Epidermal growth factor receptors (EGFR) are useful molecular targets as they are overexpressed in glioblastoma, head-and-neck cancer, bladder cancer, and other malignancies. Here, we examined the possibility of using internalizable anti-EGFR affibody as an EGFR-targeting MNT module for drug transport into the cancer cell nuclei. It binds to both murine and human EGFR facilitating preclinical studies. We showed that MNT with affibody on the N-terminus (MNTN-affibody) effectively delivered the Auger electron emitter 111In to target cell nuclei and had pronounced cytotoxic efficacy against EGFR-overexpressing human A431 epidermoid carcinoma cells. Using EGFR-expressing human adenocarcinoma MCF-7 cells, we demonstrated that in contrast to MNT with N-terminal epidermal growth factor (EGF), MNTN-affibody and MNT with EGF on the C-terminus did not stimulate cancer cell proliferation.

Design, synthesis, and biological evaluation of a multifunctional neuropeptide-Y conjugate for selective nuclear delivery of radiolanthanides

BackgroundTargeting G protein-coupled receptors on the surface of cancer cells with peptide ligands is a promising concept for the selective tumor delivery of therapeutically active cargos, including radiometals for targeted radionuclide therapy (TRT). Recently, the radiolanthanide terbium-161 (161Tb) gained significant interest for TRT application, since it decays with medium-energy β-radiation but also emits a significant amount of conversion and Auger electrons with short tissue penetration range. The therapeutic efficiency of radiometals emitting Auger electrons, like 161Tb, can therefore be highly boosted by an additional subcellular delivery into the nucleus, in order to facilitate maximum dose deposition to the DNA. In this study, we describe the design of a multifunctional, radiolabeled neuropeptide-Y (NPY) conjugate, to address radiolanthanides to the nucleus of cells naturally overexpressing the human Y1 receptor (hY1R).By using solid-phase peptide synthesis, the hY1R-preferring [F7,P34]-NPY was modified with a fatty acid, a cathepsin B-cleavable linker, followed by a nuclear localization sequence (NLS), and a DOTA chelator (compound pb12). In this proof-of-concept study, labeling was performed with either native terbium-159 (natTb), as surrogate for 161Tb, or with indium-111 (111In).Results[natTb]Tb-pb12 showed a preserved high binding affinity to endogenous hY1R on MCF-7 cells and was able to induce receptor activation and internalization similar to the hY1R-preferring [F7,P34]-NPY. Specific internalization of the 111In-labeled conjugate into MCF-7 cells was observed, and importantly, time-dependent nuclear uptake of 111In was demonstrated. Study of metabolic stability showed that the peptide is insufficiently stable in human plasma. This was confirmed by injection of [111In]In-pb12 in nude mice bearing MCF-7 xenograft which showed specific uptake only at very early time point.ConclusionThe multifunctional NPY conjugate with a releasable DOTA-NLS unit represents a promising concept for enhanced TRT with Auger electron-emitting radiolanthanides. Our research is now focusing on improving the reported concept with respect to the poor plasmatic stability of this promising radiopeptide.

Core-hole spectator Auger decay

For an atomic state with two electrons missing from different core orbitals one may assume that the deeper hole decays first. However, it is quite probable that the double core-hole state will decay by emission of a slow Auger electron where the deeper core hole remains a spectator, especially if the outer core hole can be filled by Coster-Kronig transition, while the deeper cannot. We study here the competition of both Auger decay channels in a model system, the $1s2s2{p}^{6}(3s/3p)$ states of $\mathrm{N}{\mathrm{e}}^{+}$ ions. As the phenomenon can take place in any decay chain involving multiple core-excited states it can be critical to understand the ion yields, the electron and x-ray emission spectra, and the molecular fragmentation.

Determination of 161Tb half-life by three measurement methods

The radiolanthanide 161Tb is being studied as an alternative to 177Lu for targeted radionuclide tumor therapy. Both β--particle emitters show similar chemical behavior and decay characteristics, but 161Tb delivers additional conversion and Auger electron emissions that may enhance the therapeutic efficacy. In this study, the half-life of 161Tb was determined by a combination of three independent measurement systems: reference ionization chamber (CIR, chambre d'ionization de référence), portable ionization chamber (TCIR) and a CeBr3 γ-emission detector with digital electronics. The half-life determined for 161Tb is 6.953(2) days, showing a significant improvement in the uncertainty, which is one order of magnitude lower, with a deviation of 0.91% from the last nuclear data reference value. The previous large uncertainty of the half-life had a direct impact on activity measurements. Now it is no more an obstacle to a primary standardization.

165Er: A new candidate for Auger electron therapy and its possible cyclotron production from natural holmium targets

165Er, a pure Auger-electron emitter, could be an attractive candidate for targeted radionuclide therapy. Auger electrons possess short penetration paths with high linear energy transfer. In this study, experimental cross-sections of the 165Ho(p, n)165Er nuclear reaction were measured and targets irradiated with protons using Injector II cyclotron at Paul Scherrer Institute (Switzerland) and the 18 MeV medical cyclotron laboratory at the University Hospital in Bern. A purification method was developed in order to obtain 165Er suitable for in vivo applications.

Radioimmunotherapy of human pancreatic cancer xenografts in NOD-scid mice with [64Cu]Cu-NOTA-panitumumab F(ab′)2 alone or combined with radiosensitizing gemcitabine and the PARP inhibitor, rucaparib

IntroductionOur objective was to determine the feasibility of extending our previously reported PET imaging study of pancreatic cancer (PnCa) with [64Cu]Cu-NOTA-panitumumab F(ab′)2 to radioimmunotherapy (RIT) by exploiting the β-particle and Auger electron emissions of 64Cu (PET theranostic concept). To enhance the effectiveness of [64Cu]Cu-NOTA-panitumumab F(ab′)2, we further combined RIT with radiosensitizing gemcitabine (GEM) and the poly(ADP)ribose polymerase inhibitor (PARPi), rucaparib. MethodsNormal tissue toxicity was assessed in non-tumor-bearing NOD-scid mice injected i.v. with [64Cu]Cu-NOTA-panitumumab F(ab′)2 (1.85–9.25 MBq; 10 μg) or [64Cu]Cu-NOTA-anti-mouse EGFR Ab30 F(ab′)2 (12.95 MBq). Body weight was monitored, and hematopoietic (CBC), liver (ALT) and kidney [creatinine (SCr)] toxicity were assessed. RIT studies were performed in NOD-scid mice with s.c. OCIP23 human PnCa patient-derived xenografts (PDX) administered [64Cu]Cu-NOTA-panitumumab F(ab′)2 (3.7 MBq; 10 μg), unlabeled panitumumab F(ab′)2 (10 μg) or normal saline every two weeks. Subsequent studies evaluated RIT with [64Cu]Cu-NOTA-panitumumab F(ab′)2 (12.95 MBq; 10 μg) administered alone or combined with GEM and the PARPi, rucaparib administered on a 14-day treatment cycle for up to 6 cycles in NOD-scid mice with s.c. PANC-1 human PnCa xenografts. The radiation absorbed dose in PANC-1 tumors and normal organs in mice after a single i.v. injection of [64Cu]Cu-NOTA-panitumumab F(ab′)2 (12.95 MBq; 10 μg) was estimated based on previously reported biodistribution studies of [64Cu]Cu-NOTA-panitumumab F(ab′)2. ResultsNo normal tissue toxicity was observed in non-tumor-bearing NOD-scid mice administered up to 3.7 MBq (10 μg) of [64Cu]Cu-NOTA-panitumumab F(ab′)2 but slightly increased ALT was noted at 9.25 MBq. Administration of [64Cu]Cu-NOTA-anti-mouse EGFR Ab30 F(ab′)2 (12.95 MBq; 10 μg) caused some hematopoietic toxicity but no increase in ALT or SCr or decreased body weight. A slight tumor growth delay and increased survival was noted in NOD-scid mice with s.c. OCIP23 PDX treated with [64Cu]Cu-NOTA-panitumumab F(ab′)2 (3.7 MBq; 10 μg) or unlabeled panitumumab F(ab′)2 (10 μg) compared to normal saline treated mice. RIT with [64Cu]Cu-NOTA-panitumumab F(ab′)2 (12.95 MBq; 10 μg) combined with GEM + PARPi for up to 6 cycles was most effective for the treatment of PANC-1 tumors. Tumor doubling time increased to 13.3 ± 0.9 days vs. 7.8 ± 3.7 days for RIT alone and 9.3 ± 2.2 days for normal saline treatment. Median survival was significantly longer (P < 0.05) than in mice treated with normal saline (35 days) for RIT + GEM + PARPi (71 days), GEM + PARPi (44 days) and RIT + GEM (43 days) but not for RIT alone (25 days). RIT + GEM + PARPi provided a longer median survival than RIT (P < 0.01), GEM + PARPi (P = 0.01) but not RIT + GEM (P = 0.23). Nonetheless, PANC-1 tumors grew exponentially in all treatment groups. The absorbed dose in PANC-1 tumors after a single i.v. injection of [64Cu]Cu-NOTA-panitumumab F(ab′)2 (12.85 MBq; 10 μg) was 0.8 Gy, while the dose in normal organs ranged from 0.6–1.2 Gy. ConclusionsWe conclude that RIT with [64Cu]Cu-NOTA-panitumumab F(ab′)2 did not cause significant normal tissue toxicity but was not effective when administered alone for treatment of PnCa xenografts in NOD-scid mice. Combining RIT with GEM and the PARPi, rucaparib enhanced its effectiveness but tumors continued to grow exponentially. Our results suggest that 64Cu is not feasible for RIT of PnCa due to low tumor absorbed doses. 177Lu which has a higher abundance of moderate energy β-particle emissions may be more effective than 64Cu. The hematopoietic toxicity of [64Cu]Cu-NOTA-anti-mouse EGFR Ab30 F(ab′)2 may be mediated by binding to mouse EGFR expressed on some hematopoietic stem cells. Advances in knowledge and implications for patient careDirect extension of PET with 64Cu(Cu)-NOTA-panitumumab F(ab′)2 to RIT exploiting the β-particle and Auger electron emissions of 64Cu is not feasible. Theranostic approaches that combine PET with RIT employing 177Lu may be more promising and should be explored.

Simulations of X-ray conversion into primary electrons in GEM-based detector

The paper presents the results of simulations of the interaction of X-rays of different discrete energies (1–25 keV) with the structure of the GEM chamber. The simulations were performed using Geant4 software. This program allowed taking into account phenomena such as the emission of photoelectrons, Auger electrons and fluorescence X-rays. As a result, the energy distributions of primary electrons formed in the absorption region of the detector (drift gap) were obtained. The distributions of primary electrons, which are the source of electron avalanches in the detector under study, are directly responsible for the distribution of pulses on the detector reading anode. Some measurements were also performed, confirming the compatibility of simulated spectra and experimental ones. The main conclusion from the simulation is the need to eliminate copper from the detector structure, especially from GEM foils and from the reading electrode, if there is an intension to record X-rays with energies above 9 keV . An observable parasitic contribution to the spectrum recorded by the detector is also given by several other materials.

Establishing Radiolanthanum Chemistry for Targeted Nuclear Medicine Applications.

We report the first targeted nuclear medicine application of the lanthanum radionuclides 132/135 La. These isotopes represent a matched pair for diagnosis via the positron emissions of 132 La and therapy mediated by the Auger electron emissions of 135 La. We identify two effective chelators, known as DO3Apic and macropa, for these radionuclides. The 18-membered macrocycle, macropa, bound 132/135 La with better molar activity than DO3Apic under similar conditions. These chelators were conjugated to the prostate-specific membrane antigen (PSMA)-targeting agent DUPA to assess the use of radiolanthanum for in vivo imaging. The 132/135 La-labeled targeted constructs showed high uptake in tumor xenografts expressing PSMA. This study validates the use of these radioactive lanthanum isotopes for imaging applications and motivates future work to assess the therapeutic effects of the Auger electron emissions of 135 La.

An 111In-labelled bis-ruthenium(ii) dipyridophenazine theranostic complex: mismatch DNA binding and selective radiotoxicity towards MMR-deficient cancer cells.

Theranostic radionuclides that emit Auger electrons (AE) can generate highly localised DNA damage and the accompanying gamma ray emission can be used for single-photon emission computed tomography (SPECT) imaging. Mismatched DNA base pairs (mismatches) are DNA lesions that are abundant in cells deficient in MMR (mismatch mediated repair) proteins. This form of genetic instability is prevalent in the MMR-deficient subset of colorectal cancers and is a potential target for AE radiotherapeutics. Herein we report the synthesis of a mismatch DNA binding bis-ruthenium(ii) dipyridophenazine (dppz) complex that can be radiolabelled with the Auger electron emitting radionuclide indium-111 (111In). Greater stabilisation accompanied by enhanced MLCT (metal to ligand charge-transfer) luminescence of both the bis-Ru(dppz) chelator and non-radioactive indium-loaded complex was observed in the presence of a TT mismatch-containing duplex compared to matched DNA. The radioactive construct [111In]In-bisRu(dppz) ([111In][In-2]4+) targets cell nuclei and is radiotoxic towards MMR-deficient human colorectal cancer cells showing substantially less detrimental effects in a paired cell line with restored MMR function. Additional cell line studies revealed that [111In][In-2]4+ is preferentially radiotoxic towards MMR-deficient colorectal cancer cells accompanied by increased DNA damage due to 111In decay. The biodistribution of [111In][In-2]4+ in live mice was demonstrated using SPECT. These results illustrate how a Ru(ii) polypyridyl complex can incorporate mismatch DNA binding and radiometal chelation in a single molecule, generating a DNA-targeting AE radiopharmaceutical that displays selective radiotoxicity towards MMR-deficient cancer cells and is compatible with whole organism SPECT imaging.

New Recombinant Carriers Binding Specifically to the Epidermal Growth Factor Receptor.

New recombinant carriers-modular nanotransporters (MNTs)-with N-terminal ligand module to the epidermal growth factor receptor (EGFR) were developed and characterized. Human epidermal growth factor (hEGF) and antibody-like protein Z1907 were used as a ligand module. We demonstrated that MNTs are able to internalize in a receptor-specific manner into the target cancer cells and to accumulate in the target cell nuclei. Conjugation of MNTs with the Auger electron emitter 111In significantly enhanced the cytotoxic effect of 111In on the target cells. It was found that the transfer of EGF from the C-terminus to the N-terminus of the MNT enhanced the proliferation of target cells, whereas the use of Z1907 did not have a similar effect.

Auger radiopharmaceutical therapy targeting prostate-specific membrane antigen in a micrometastatic model of prostate cancer

Auger radiopharmaceutical therapy is a promising strategy for micrometastatic disease given high linear energy transfer and short range in tissues, potentially limiting normal tissue toxicities. We previously demonstrated anti-tumor efficacy of a small-molecule Auger electron emitter targeting the prostate-specific membrane antigen (PSMA), 2-[3-[1-carboxy-5-(4-[125I]iodo-benzoylamino)-pentyl]-ureido]-pentanedioic acid), or 125I-DCIBzL, in a mouse xenograft model. Here, we investigated the therapeutic efficacy, long-term toxicity, and biodistribution of 125I-DCIBzL in a micrometastatic model of prostate cancer (PC).Methods: To test the therapeutic efficacy of 125I-DCIBzL in micrometastatic PC, we used a murine model of human metastatic PC in which PSMA+ PC3-ML cells expressing firefly luciferase were injected intravenously in NSG mice to form micrometastatic deposits. One week later, 0, 0.37, 1.85, 3.7, 18.5, 37, or 111 MBq of 125I-DCIBzL was administered (intravenously). Metastatic tumor burden was assessed using bioluminescence imaging (BLI). Long-term toxicity was evaluated via serial weights and urinalysis of non-tumor-bearing mice over a 12-month period, as well as final necropsy.Results: In the micrometastatic PC model, activities of 18.5 MBq 125I-DCIBzL and above significantly delayed development of detectable metastatic disease by BLI and prolonged survival in mice. Gross metastases were detectable in control mice and those treated with 0.37-3.7 MBq 125I-DCIBzL at a median of 2 weeks post-treatment, versus 4 weeks for those treated with 18.5-111 MBq 125I-DCIBzL (P<0.0001 by log-rank test). Similarly, treatment with ≥18.5 MBq 125I-DCIBzL yielded a median survival of 11 weeks, compared with 6 weeks for control mice (P<0.0001). At 12 months, there was no appreciable toxicity via weight, urinalysis, or necropsy evaluation in mice treated with any activity of 125I-DCIBzL, which represents markedly less toxicity than the analogous PSMA-targeted α-particle emitter. Macro-to-microscale dosimetry modeling demonstrated lower absorbed dose in renal cell nuclei versus tumor cell nuclei due to lower levels of drug uptake and cellular internalization in combination with the short range of Auger emissions.Conclusion: PSMA-targeted radiopharmaceutical therapy with the Auger emitter 125I-DCIBzL significantly delayed development of detectable metastatic disease and improved survival in a micrometastatic model of PC, with no long-term toxicities noted at 12 months, suggesting a favorable therapeutic ratio for treatment of micrometastatic PC.

Assessment of Single-and Double-Strand Breaks in DNA Induced by Auger Electrons of Radioisotopes Used in Diagnostic and Therapeutic Applications.

Introduction:Most of the radionuclides that are used for diagnostic purposes emit Auger electrons and can thus cause damage to the DNA molecule on a nanometer scale. Therefore, the nanodosimetric calculation of these radioisotopes is necessary to achieve better understanding on their effects.Aim:The aim of this study was to calculate the mean number of DNA strand breaks (single-strand breaks and double-strand breaks) caused by direct and indirect effects for six widely used Auger electron-emitting diagnostic radioisotopes, including 123I, 125I, 99mTc, 67Ga, 201Tl, 111In and two therapeutic radioisotopes of 131I(beta + Auger + CK emitter) and 211At(alpha + Auger + CK emitter).Materials and Methods:Geant4-DNA simulation tool was used to evaluate the effects of Auger electrons, beta and alpha particles of these radioisotopes on DNA molecules. Two different DNA molecule geometric models were simulated and the results of these two models were compared with each other as well as with the results of previous studies.Results and Conclusion:The results showed that the geometric shape of the sugar-phosphate groups may have a significant effect on the number of single-strand breaks (SSBs) and double-strand breaks (DSBs) of the DNA molecule. Among the most widely used diagnostic radioisotopes, 201Tl and 125I, had the greatest impact on the number of SSBs and DSBs, respectively, while therapeutic radioisotope of 131I almost had no effect, therapeutic radioisotope of 211At had the moderate effect on the number of breaks in the DNA chain.

The effect of hypoxia on the induction of strand breaks in plasmid DNA by alpha-, beta- and Auger electron-emitters 223Ra, 188Re, 99mTc and DNA-binding 99mTc-labeled pyrene

IntroductionRadiation-induced DNA damage occurs from direct and indirect effects. The induction is influenced by the physical characteristics of the radionuclide, especially its linear energy transfer. Hypoxia reduces the effect of irradiation treatment in tumor cells and leads to poor patient outcomes. High linear energy transfer emitters can overcome this obstacle. Our aim is to demonstrate the influence of hypoxia on the interaction of different radiation qualities with isolated DNA. MethodsPuC19 Plasmid DNA was irradiated with 223Ra, 188Re, 99mTc and 99mTc-labeled pyrene with and without DMSO under hypoxia or normoxic conditions. DNA damages in form of single-(SSB) and double-strand breaks (DSB) were analyzed by gel electrophoresis. ResultsRadiation doses up to 200 Gy of 223Ra, 188Re and 99mTc led to maximal yields of 80% SSB and 30%, 28% and 32% DSB, respectively. Hypoxia had minor effects on damages from 223Ra, but caused a small enhancement in DSB for 188Re and 99mTc. DMSO prevented DSB completely and reduced SSB from the “free” radionuclides to comparable levels. DNA-binding 99mTc-labeled pyrene induced less SSB and DSB compared to [99mTc]TcO4−. However, the incubation with DMSO could prevent the SSB and DSB induction only to a minor extent. ConclusionsHypoxia does not limit DNA damage induced by 223Ra, 188Re, 99mTc and 99mTc-labeled pyrene. Dose-dependent radiation effects were comparable for alpha-emitters and both high- and low-energy electron emitters. The radioprotection by DMSO was not influenced by hypoxia. The results indicate the contribution of mainly indirect radiation effects for 99mTc, 188Re and 223Ra. 99mTc-labeled pyrene caused direct DNA damages and Auger-electrons from 99mTc-labeled pyrene are more effective than high-energy electrons or alpha particles. Advances in knowledgeWithout the consideration of DNA repair mechanisms, oxygen has no direct influence in radiation-induced DNA damages by different radiation qualities. Implications for patient careThe short-time stimulation with oxygen during patient radiation could have minor influence compared to constant oxygen flooding to overcome hypoxic barriers.

In vitro cytotoxicity of Auger electron-emitting [67Ga]Ga-trastuzumab

IntroductionMolecular radiotherapy exploiting short-range Auger electron-emitting radionuclides has potential for targeted cancer treatment and, in particular, is an attractive option for managing micrometastatic disease. Here, an approach using chelator-trastuzumab conjugates to target radioactivity to breast cancer cells was evaluated as a proof-of-concept to assess the suitability of 67Ga as a therapeutic radionuclide. MethodsTHP-trastuzumab and DOTA-trastuzumab were synthesised and radiolabelled with Auger electron-emitters 67Ga and 111In, respectively. Radiopharmaceuticals were tested for HER2-specific binding and internalisation, and their effects on viability (dye exclusion) and clonogenicity of HER2-positive HCC1954 and HER2–negative MDA-MB-231 cell lines was measured. Labelled cell populations were studied by microautoradiography. ResultsLabelling efficiencies for [67Ga]Ga-THP-trastuzumab and [111In]In-DOTA-trastuzumab were 90% and 98%, respectively, giving specific activities 0.52 ± 0.16 and 0.61 ± 0.11 MBq/μg (78–92 GBq/μmol). At 4 nM total antibody concentration and 200 × 103 cells/mL, [67Ga]Ga-THP-trastuzumab showed higher percentage of cell association (10.7 ± 1.3%) than [111In]In-DOTA-trastuzumab (6.2 ± 1.6%; p = 0.01). The proportion of bound activity that was internalised did not differ significantly for the two tracers (62.1 ± 1.4% and 60.8 ± 15.5%, respectively). At 100 nM, percentage cell binding of both radiopharmaceuticals was greatly reduced compared to 4 nM and did not differ significantly between the two (1.2 ± 1.0% [67Ga]Ga-THP-trastuzumab and 0.8 ± 0.9% for [111In]In-DOTA-trastuzumab). Viability and clonogenicity of HER2-positive cells decreased when each radionuclide was incorporated into cells by conjugation with trastuzumab, but not when the same level of radioactivity was confined to the medium by omitting the antibody conjugation, suggesting that 67Ga needs to be cell-bound or internalised for a therapeutic effect. Microautoradiography showed that radioactivity bound to individual cells varied considerably within the population. Conclusions[67Ga]Ga-THP-trastuzumab reduced cell viability and clonogenicity only when cell-bound, suggesting 67Ga holds promise as a therapeutic radionuclide as part of a targeted radiopharmaceutical. The causes and consequences of non-homogeneous uptake among the cell population should be explored.