A non-internalised CD38-binding radiolabelled single-domain antibody fragment to monitor and treat multiple myeloma.

BACKGROUND: Antibody-based therapies targeting CD38 are currently used as single agents as well as in combination regimens for multiple myeloma, a malignant plasma cell disorder. In this study, we aimed to develop anti-CD38 single-domain antibodies (sdAbs) that can be used to trace CD38+ tumour cells and subsequently used for targeted radionuclide therapy. SdAbs are derived from Camelidae heavy-chain antibodies and have emerged as promising theranostic agents due to their favourable pharmacological properties. METHODS: Four different anti-CD38 sdAbs were produced, and their binding affinities and potential competition with the monoclonal antibody daratumumab were tested using biolayer interferometry. Their binding kinetics and potential cell internalisation were further studied after radiolabelling with the diagnostic radioisotope Indium-111. The resulting radiotracers were evaluated in vivo for their tumour-targeting potential and biodistribution through single-photon emission computed tomography (SPECT/CT) imaging and serial dissections. Finally, therapeutic efficacy of a lead anti-CD38 sdAb, radiolabelled with the therapeutic radioisotope Lutetium-177, was evaluated in a CD38+ MM xenograft model. RESULTS : We retained anti-CD38 sdAb #2F8 as lead based on its excellent affinity and superior stability, the absence of competition with daratumumab and the lack of receptor-mediated internalisation. When intravenously administered to tumour-xenografted mice, radiolabelled sdAb #2F8 revealed specific and sustained tumour retention with low accumulation in other tissues, except kidneys, resulting in high tumour-to-normal tissue ratios. In a therapeutic setting, myeloma-bearing mice received three consecutive intravenous administrations of a high (18.5 MBq) or a low radioactive dose (9.3 MBq) of 177Lu-DTPA-2F8 or an equal volume of vehicle solution. A dose-dependent tumour regression was observed, which translated into a prolonged median survival from 43 days for vehicle-treated mice, to 62 days (p = 0.027) in mice receiving the low and 65 days in mice receiving the high (p = 0.0007) radioactive dose regimen, respectively. CONCLUSIONS: These results highlight the theranostic potential of radiolabelled anti-CD38 sdAbs for the monitoring and treatment of multiple myeloma.

Comparison between 177Lu-iPSMA and 225Ac-iPSMA dosimetry at a cellular level in an animal bone metastasis model.

The recent use of prostate-specific membrane antigen as a biological target have improved the theragnostic approach to prostate and other types of cancer. Radiopharmaceuticals based on PSMA inhibitors radiolabeled with beta emitters as Lutetium-177 have demonstrated remarkable efficacy and safety, however, their clinical evaluation have also shown that therapeutic response of bone located metastases is poorer than that presented by soft tissue lesions. These observations conducted to the development and study at different levels of PSMA-targeting alpha-particle therapy exhibiting effective and promising antitumor activity. However, some aspects of the use of alpha emitters such as cellular dosimetry should be considered before applying them safely. The aim of the present work was to compare and calculate the absorbed dose of 177Lu-iPSMA and 225Ac-iPSMA using an animal bone metastasis model and experimental data obtained from cellular fractionation. The number of disintegrations and the dose factors for the theragnostic iPSMA pair, molecule that can be radiolabeled with 177Lu or 225Ac, were determined based on MIRD methodology, and used to calculate the absorbed dose to cell nucleus. A five times difference between 225Ac-iPSMA and 177Lu-iPSMA average dose rate to the tumor was calculated, being 2.3 ± 0.037 for the first and 0.5 ± 0.018 Gy for the second, both for each activity unit (MBq) administered.

In Vivo Biokinetics of 177Lu-OPS201 in Mice and Pigs as a Model for Predicting Human Dosimetry.

Introduction: 177Lu-OPS201 is a high-affinity somatostatin receptor subtype 2 antagonist for PRRT in patients with neuroendocrine tumors. The aim is to find the optimal scaling for dosimetry and to compare the biokinetics of 177Lu-OPS201 in animals and humans. Methods: Data on biokinetics of 177Lu-OPS201 were analyzed in athymic nude Foxn1 nu mice (28 F, weight: 26 ± 1 g), Danish Landrace pigs (3 F-1 M, weight: 28 ± 2 kg), and patients (3 F-1 M, weight: 61 ± 17 kg) with administered activities of 0.19-0.27 MBq (mice), 97-113 MBq (pigs), and 850-1086 MBq (patients). After euthanizing mice (up to 168 h), the organ-specific activity contents (including blood) were measured. Multiple planar and SPECT/CT scans were performed until 250 h (pigs) and 72 h (patients) to quantify the uptake in the kidneys and liver. Blood samples were taken up to 23 h (patients) and 300 h (pigs). In pigs and patients, kidney protection was applied. Time-dependent uptake data sets were created for each species and organ/tissue. Biexponential fits were applied to compare the biokinetics in the kidneys, liver, and blood of each species. The time-integrated activity coefficients (TIACs) were calculated by using NUKFIT. To determine the optimal scaling, several methods (relative mass scaling, time scaling, combined mass and time scaling, and allometric scaling) were compared. Results: A fast blood clearance of the compound was observed in the first phase (<56 h) for all species. In comparison with patients, pigs showed higher liver retention. Based on the direct comparison of the TIACs, an underestimation in mice (liver and kidneys) and an overestimation in pigs' kidneys compared to the patient data (kidney TIAC: mice = 1.4 h, pigs = 7.7 h, and patients = 5.8 h; liver TIAC: mice = 0.7 h, pigs = 4.1 h, and patients = 5.3 h) were observed. Most similar TIACs were obtained by applying time scaling (mice) and combined scaling (pigs) (kidney TIAC: mice = 3.9 h, pigs = 4.8 h, and patients = 5.8 h; liver TIAC: mice = 0.9 h, pigs = 4.7 h, and patients = 5.3 h). Conclusion: If the organ mass ratios between the species are high, the combined mass and time scaling method is optimal to minimize the interspecies differences. The analysis of the fit functions and the TIACs shows that pigs are better mimicking human biokinetics.

Value of post-therapy 177Lu-PSMA images for accurate interpretation of therapy response with 68Ga-PSMA PET/CT. / Valor de las imágenes de 177Lu-PSMA post-terapia para una interpretación precisa de la respuesta a la terapia con PET/TC con 68Ga-PSMA.

A 54-year-old man with progressive prostate cancer underwent a 68Ga-PSMA PET/CT, which showed lymph node and bone metastases. After 2-cycles of 177Lu-PSMA therapy, the repeated 68Ga-PSMA PET/CT showed decreased radiotracer uptake in lymph node and bones metastases, but there were new lesions which may be compatible with progression or tumour sink-effect. A review of 177Lu-PSMA-therapy images revealed that new lesions in the second PET/CT were the metastatic lesions that progressed after the first PET/CT, and subsequently showed a good response. The patient received additional cycles of 177Lu-PSMA therapy, and the disease regressed further, with a PSA of 0.06ng/ml. Response evaluation of new therapeutic diagnostics (theranostic) agents needs a review of not only diagnostic PET/CT images, but also post-therapy images and laboratory results.

(177)Lu: DDEP Evaluation of the decay scheme for an emerging radiopharmaceutical.

A new decay scheme evaluation using the DDEP methodology for (177)Lu is presented. Recently measured half-life measurements have been incorporated, as well as newly available γ-ray emission probabilities. For the first time, a thorough investigation has been made of the γ-ray multipolarities. The complete data tables and detailed evaluator comments are available through the DDEP website.

Turn-on fluorescent chemosensor for determination of lutetium ion.

A turn-on fluorescent chemosensor is introduced for the detection of Lu(3+) ion using N-[3-methyl]-2-[pyridine-2-amido] phenyl] pyridine-2-carboxamide (L) molecule. Fluorescent emission intensity of L enhances after binding to Lu(3+) ions in ethanol-water solution (1:9, v/v). The observed enhancement is the result of a strong covalent binding between Lu(3+) ion and L (the binding constant value is 2.0×10(6) mol(-1) L). The proposed optical chemosensor can be applied for the analysis of Lu(3+) ion in a linear range of 3.3×10(-7) to 1.0×10(-5) mol L(-1). The limit of detection was obtained 8.6×10(-7) mol L(-1). The probe exhibits high selectivity toward Lu(3+) ion in comparison with common metal ions. The proposed fluorescent chemosensor was successfully used in the determination of Lu(3+) ion in some water samples.

Comparison of 9°Y and ¹77Lu measurement capability in UK and European hospitals.

Comparison exercises involving (90)Y and (177)Lu were performed during 2009 and 2012, respectively, to assess the measurement capability of hospitals in the UK and Europe. The results from the measurement of a typical liquid solution of (90)Y show that only 40% of participants could measure the solution to within 5% of the certificated value and that a significant -6% bias was present due to the use of non-standard geometries for the calibration of equipment. The results from the measurement of a standard liquid solution of (177)Lu show that 81% of participants could measure to within 5% of the certificated value and in fact 65% of these results were within 2% of the certificated value, showing administered activities can be far more accurately measured for (177)Lu than for (90)Y and that (177)Lu has a far smaller geometry dependence. These studies were performed to identify specific measurement issues in the user community and to identify areas where future research should be focused. In addition to this the work allows the participants to adjust measurement practice and identify key measurement issues.

Large Pt anomaly in the Greenland ice core points to a cataclysm at the onset of Younger Dryas.

One explanation of the abrupt cooling episode known as the Younger Dryas (YD) is a cosmic impact or airburst at the YD boundary (YDB) that triggered cooling and resulted in other calamities, including the disappearance of the Clovis culture and the extinction of many large mammal species. We tested the YDB impact hypothesis by analyzing ice samples from the Greenland Ice Sheet Project 2 (GISP2) ice core across the Bølling-Allerød/YD boundary for major and trace elements. We found a large Pt anomaly at the YDB, not accompanied by a prominent Ir anomaly, with the Pt/Ir ratios at the Pt peak exceeding those in known terrestrial and extraterrestrial materials. Whereas the highly fractionated Pt/Ir ratio rules out mantle or chondritic sources of the Pt anomaly, it does not allow positive identification of the source. Circumstantial evidence such as very high, superchondritic Pt/Al ratios associated with the Pt anomaly and its timing, different from other major events recorded on the GISP2 ice core such as well-understood sulfate spikes caused by volcanic activity and the ammonium and nitrate spike due to the biomass destruction, hints for an extraterrestrial source of Pt. Such a source could have been a highly differentiated object like an Ir-poor iron meteorite that is unlikely to result in an airburst or trigger wide wildfires proposed by the YDB impact hypothesis.

Experimental half-life determination of ¹76Lu.

The half-life of the naturally occurring long-lived rare earth isotope (176)Lu was determined by a combination of highly sophisticated experimental procedures in order to further improve the reliability and the precision of literature data. The amount of lutetium in the samples was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using a NIST reference standard. The isotopic ratio N((176)Lu)/N(Lu) in the samples was measured by means of inductively coupled plasma high resolution mass spectrometry (ICP-HRMS). The activity divided by the mass of Lu was determined by applying liquid scintillation (LS) counting. The LS counting efficiency of the beta/gamma emitter (176)Lu was determined with the CIEMAT/NIST efficiency tracing technique with low uncertainty. The influences of colour quenching and background effects are discussed in this paper. The half-life was found to be 3.640(35)×10(10)y. The result is in good agreement with other evaluations and the relative standard uncertainty of 0.95% is among the lowest of previously published data.

Mass transfer resistance in a liquid-phase microextraction employing a single hollow fiber under unsteady-state conditions.

In this study, the mass transport resistance in liquid-phase microextraction (LPME) in a single hollow fiber was investigated. A mathematical model has been developed for the determination of the overall mass transfer coefficient based on the acceptor phase in an unsteady state. The overall mass transfer coefficient in LPME in a single hollow fiber has been estimated from time-dependent concentration of extracted analyte in the acceptor phase while maintaining a constant analyte concentration in the donor phase. It can be achieved either using a high volume of donor to acceptor phase ratio or tuning the extraction conditions to obtain a low-enrichment factor, so that the analyte concentration in the sample is not significantly influenced by the mass transfer. Two extraction systems have been used to test experimentally the developed model: the extraction of Lu(III) from a buffer solution and the extraction of three local anesthetics from a buffer or plasma solution. The mass transfer resistance, defined as a reciprocal values of the mass transfer coefficient, was found to be 1.2 × 10(3) cm(-1) min for Lu(III) under optimal conditions and from 1.96 to 3.3 × 10(3) cm(-1) min for the local anesthetics depending on the acceptor pH and the hydrophobicity of the drug.

Dose point kernel simulation for monoenergetic electrons and radionuclides using Monte Carlo techniques.

Monte Carlo (MC) simulation has been commonly used in the dose evaluation of radiation accidents and for medical purposes. The accuracy of simulated results is affected by the particle-tracking algorithm, cross-sectional database, random number generator and statistical error. The differences among MC simulation software packages must be validated. This study simulated the dose point kernel (DPK) and the cellular S-values of monoenergetic electrons ranging from 0.01 to 2 MeV and the radionuclides of (90)Y, (177)Lu and (103 m)Rh, using Fluktuierende Kaskade (FLUKA) and MC N-Particle Transport Code Version 5 (MCNP5). A 6-µm-radius cell model consisting of the cell surface, cytoplasm and cell nucleus was constructed for cellular S-value calculation. The mean absolute percentage errors (MAPEs) of the scaled DPKs, simulated using FLUKA and MCNP5, were 7.92, 9.64, 4.62, 3.71 and 3.84 % for 0.01, 0.1, 0.5, 1 and 2 MeV, respectively. For the three radionuclides, the MAPEs of the scaled DPKs were within 5 %. The maximum deviations of S(N←N), S(N←Cy) and S(N←CS) for the electron energy larger than 10 keV were 6.63, 6.77 and 5.24 %, respectively. The deviations for the self-absorbed S-values and cross-dose S-values of the three radionuclides were within 4 %. On the basis of the results of this study, it was concluded that the simulation results are consistent between FLUKA and MCNP5. However, there is a minor inconsistency for low energy range. The DPK and the cellular S-value should be used as the quality assurance tools before the MC simulation results are adopted as the gold standard.

Comparison between two absolute methods used for 177Lu activity measurements and its standardization.

A (177)Lu primary standard was developed at the ENEA-INMRI in the frame of an international comparison organized by BIPM and piloted by NIST (USA). The CIEMAT/NIST method with (3)H standard source as tracer was used for standardizing a solution of (177)Lu. The activity value was compared also with the measurements of the same mother solution carried out by the 4πγ integral counting method. Particular efforts were made to identify and quantify the long-lived (177m)Lu impurity in the mother solution. The results obtained by the two methods are in good agreement within their standard uncertainties. The arithmetic mean of the two values is in good agreement with the Comparison Reference Value (CRV). By the new primary standard two well-type ionization chambers (ICs), one fixed and the other one portable, were calibrated with an uncertainty lower than 2%. These ICs are used for routinely applications in the activity measurements of short-lived radionuclides particularly useful for medical applications.

Gamma-ray emission probabilities in the decay of (177m)Lu.

γ-Ray emission probabilities from the decay of the long-lived (T(1/2)=160.44d) isomeric state in (177m)Lu were measured with planar (LEPS) and coaxial Ge detectors. The isomer γ-ray and ß(-)-decay branching intensities were also determined. Measurements were carried out at low absolute efficiencies in order to minimize coincidence summing losses. The results are compared with the previous measurements.

Activity determination and nuclear decay data of 177Lu.

The activity concentration of a (177)Lu solution was measured within the scope of the international comparison CCRI(II)-K2.Lu-177, starting in 2009. At PTB, the solution was measured by means of 4πß-γ coincidence counting using a proportional counter and a NaI detector. In addition, liquid scintillation counting using the CIEMAT/NIST efficiency tracing method as well as the triple-to-double coincidence ratio (TDCR) method was applied. The efficiency computation for the TDCR method was realized by means of the MICELLE2 program, applying a stochastic model for the computation of electron emission spectra. The activity concentrations derived from the three methods were found to be in good agreement and the relative standard uncertainty of the combined result was found to be 0.19%. At PTB, the combined result was used to calibrate a 4π ionization chamber for future calibrations of this isotope which is frequently used in nuclear medicine. In addition, activity standardizations were combined with gamma-ray spectrometry to determine photon emission probabilities. To this end, the comparison solution as well as another (177)Lu solution was used. The results are in good agreement with previous measurements at PTB but show a considerable discrepancy to recently published values from Deepa et al. (2011). The decay curve of a third solution was followed by liquid scintillation counting for about 66 days to determine the half-life of (177)Lu, which was found to be T(1/2)=6.639(9) d.

Accurate activity measurement of Lu-177 by the liquid scintillation 4πß-γ coincidence counting technique.

This paper reports on absolute measurements made at the NMISA by the 4π[LS]ß-γ coincidence extrapolation technique, which formed part of a key comparison of activity measurements of the radionuclide lutetium-177, a beta-gamma emitter. A detection efficiency analysis based on the decay scheme indicated that the coincidence extrapolation method is feasible for extracting the source disintegration rate of (177)Lu. A simulation was undertaken utilizing the efficiency equations to give an indication of the expected variation of the source count rate with efficiency for different gamma-ray windows. Both the simulation and experiment indicated that the window giving the highest counting efficiency was centered about the 208.4 keV photopeak, with the data showing linear variation in the upper efficiency range. The extracted activity concentration of the (177)Lu solution proved to be highly accurate, being higher than the proposed comparison reference value by 0.15%, well within one standard uncertainty (σ=0.26%) as specified by the NMISA.

Results of an international comparison for the activity measurement of 177Lu.

An international Key Comparison of (177)Lu has recently been carried out. Twelve laboratories performed assays for radioactivity content on aliquots of a common master solution of (177)Lu, leading to eleven results submitted for entry into the Key Comparison Database of the Mutual Recognition Arrangement. A proposed Comparison Reference Value (CRV) was calculated to be 3.288(4)MBq/g using all eleven results. Degrees of equivalence and their uncertainties were calculated for each laboratory based on the CRV. Most of the values reported by the participating laboratories were within 0.6% of the CRV.

Photon emission probabilities of 176Lu.

An aqueous solution containing dissolved lutetium nitrate with a natural isotopic composition was measured by means of gamma-ray spectrometry to determine emission probabilities of photons which are emitted as a consequence of the decay of the primordial isotope (176)Lu. The geometry and matrix of the sample were taken into account in terms of efficiency transfer factors computed with the aid of the upgraded Monte Carlo simulation software GESPECOR. A combination of these results, with the activity determination via liquid scintillation counting using the CIEMAT/NIST efficiency tracing method, yields absolute values of P(X)(54.61 keV)=0.095(4), P(X)(55.79 keV)=0.168(5), P(γ)(88.36 keV)=0.149(5), P(γ)(201.83 keV)=0.777(9) and P(γ)(306.84 keV)=0.929(9). In addition, the upper limit of the probability for a potential electron-capture decay of (176)Lu was improved using additional high resolution gamma-ray spectra taken with a planar HPGe detector.

Precision electron-gamma spectroscopic measurements in the decay of 177Lu.

Complete precision electron and gamma spectroscopy measurements were undertaken for the 6.647 day decay of (177)Lu. Precision measurements of the K, L, and M internal conversion coefficients (ICCs) were made using a high transmission Mini Orange Electron Spectrometer coupled to a Si(Li) detector. We also report energies and intensities of the 6 gamma rays measured with a large volume 60 cc HPGe detector and 9 X-rays with better precision. The energies and intensities of the beta transitions from (177)Lu leading to the levels in the daughter (177)Hf were calculated by transition intensity balance at the levels.

Examination of competitive lanthanide sorption onto smectites and its significance in the management of radioactive waste.

The competitive effect of La and Lu (analogues of radionuclides appearing in radioactive waste) in the sorption in four smectites was examined. Sorption and desorption distribution coefficients (K(d); K(d,des)), and desorption rates (R(des)) were determined from batch tests in two media: deionized water and, to consider the influence of cement leachates, 0.02 mol L(-1) Ca. The competitive effect was lower when high-affinity sites were available, as in the water medium at the lowest range of initial lanthanide concentration, with high K(d) for La and for Lu (5-63×10(4) L kg(-1)). Lower K(d) was measured at higher initial concentrations and in the Ca medium, where Lu showed a stronger competitive effect. This was confirmed by fitting the sorption data to a two-solute Langmuir isotherm. The desorption data indicated that sorption was virtually irreversible for the scenarios with high sorption, with an excellent correlation between K(d) and K(d,des) (R(2) around 0.9 for the two lanthanides). Assuming that radioactive waste is a mixture of radionuclides, and that Ca ions will be provided by the cement leachates, this would reduce the retention capacity of clay engineered barriers.

Standardization and measurement of gamma-ray probability per decay of 177Lu.

The procedure followed by the Nuclear Metrology Laboratory (LMN), at the Nuclear and Energy Research Institute (IPEN), for the primary standardization of (177)Lu is described. This radionuclide is widely used in radiopharmacy due to its convenient half-life and emitted beta ray energies. The (177)Lu solution was supplied during an international comparison sponsored by BIPM in 2009 and the primary standardization has been accomplished by the 4pibeta-gamma coincidence method using a proportional counter in 4pi geometry coupled with two NaI(Tl) scintillation counters. The beta efficiency was varied by placing Collodion and aluminum absorbers over and under the radioactive source. The (177)Lu calibrated sources were also measured in a previously calibrated HPGe spectrometer, in order to obtain the emission probability per decay for the selected gamma-ray transitions. The experimental extrapolation curves were also compared with Monte Carlo simulations by means of code ESQUEMA developed at the LMN.