The ROS-generating photosensitizer-free NaYF4:Yb,Tm@SiO2upconverting nanoparticles for photodynamic therapy application

In this work we adapt rare-earth-ion-doped NaYF₄nanoparticles coated with a silicon oxide shell (NaYF₄:20%Yb,0.2%Tm@SiO₂) for biological and medical applications (for example, imaging of cancer cells and therapy at the nano level). The wide upconversion emission range under 980 nm excitation allows one to use the nanoparticles for cancer cell (4T1) photodynamic therapy (PDT) without a photosensitizer. The reactive oxygen species (ROS) are generated by Tm/Yb ion upconversion emission (blue and UV light). Thein vitroPDT was tested on 4T1 cells incubated with NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and irradiated with NIR light. After 24 h, cell viability decreased to below 10%, demonstrating very good treatment efficiency. High modification susceptibility of the SiO₂shell allows for attachment of biological molecules (specific antibodies). In this work we attached the anti-human IgG antibody to silane-PEG-NHS-modified NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and a specifically marked membrane model by bio-conjugation. Thus, it was possible to perform a selective search (a high-quality optical method with a very low-level organic background) and eventually damage the targeted cancer cells. The study focuses on therapeutic properties of NaYF₄:20%Yb,0.2%Tm@SiO₂nanoparticles and demonstrates, upon biological functionalization, their potential for targeted therapy.

Ultrasmall, water dispersible, TWEEN80 modified Yb:Er:NaGd(WO4)2 nanoparticles with record upconversion ratiometric thermal sensitivity and their internalization by mesenchymal stem cells

This work presents the synthesis by coprecipitation of diamond shaped Yb:Er:NaGd(WO₄)₂ crystalline nanoparticles (NPs) with diagonal dimensions in the 5-7 nm × 10-12 nm range which have been modified with TWEEN80 for their dispersion in water, and their interaction with mesenchymal stem cells (MSCs) proposed as cellular NP vehicles. These NPs belong to a large family of tetragonal Yb:Er:NaT(XO₄)₂ (T = Y, La, Gd, Lu; X = Mo, W) compounds with green (²H_11/2 + ⁴S_3/2 → ⁴I_15/2) Er-related upconversion (UC) efficiency comparable to that of Yb:Er:β-NaYF₄ reference compound, but with a ratiometric thermal sensitivity (S) 2.5-3.5 times larger than that of the fluoride. At the temperature range of interest for biomedical applications (∼293-317 K/20-44 °C) S = 108-118 × 10^-4 K^-1 for 20 at%Yb:5 at%Er:NaGd(WO₄)₂ NPs, being the largest values so far reported using the ²H_11/2/⁴S_3/2 Er intensity ratiometric method. Cultured MSCs, incubated with these water NP emulsions, internalize and accumulate the NPs enclosed in endosomes/lysosomes. Incubations with up to 10 μg of NPs per ml of culture medium maintain cellular metabolism at 72 h. A thermal assisted excitation path is discussed as responsible for the UC behavior of Yb:Er:NaT(XO₄)₂ compounds.

Development of Dendrimer Encapsulated Radio-Ytterbium and Biodistributionin Tumor Bearing Mice

The aim of this study is preparation of dendrimer encapsulated ytterbium-175 radio-nanoparticles and investigation of the compound chemical characteristic before and after the neutron irradiation and also study the in vivo biodistribution for targeted radiopharmaceutical dose delivery to solid tumors. For preparation of dendrimer-metal nanocomposite, a dendrimer compound containing an average of 55 Yb⁺³ ions per dendrimer was prepared. The synthesized encapsulated ytterbium irradiated by neutron for 2 h at 3×10¹¹ n.cm [Formula: see text] neutron flux. The resulting mixture was injected into 2 separate groups of tumor bearing mice. One group were injected intravenously and the other group were injected directly in tumor and were excised, weighed and counted at certain times to study the biodistribution and to compare the tumor treatment and the leakage of the radiopharmaceutical to non-target organs. The formation of dendrimer-Yb³⁺complex was confirmed by UV-vis spectrometer. High-resolution transmission electron microscopy (HRTEM) and Dynamic Light Scattering (DLS) results showed a particle size of less than 10 nm. The specific activity and radio-ytterbium purity of the irradiated nano-composite were as follows: 7 MBq/mg and >95%. The measured radiochemical purity by Instant Thin Layer Chromatography (ITLC) was more than 99%. In intravenous injection the complex showed rapid up take in liver, spleen, and lung, while accumulation in other organs was insignificant. In tumor direct injection the average size of the tumor mass in mice was reduced by 30%.

Biodistribution of sub-10 nm PEG-modified radioactive/upconversion nanoparticles

The biodistribution of lanthanide-based upconversion nanophosphors (UCNPs) has attracted increasing attention, and all of the reported UCNPs display metabolism in the liver and spleen mainly. Herein, ∼8 nm poly(ethylene glycol) (PEG)-coated NaYF4 nanoparticles codoped with Yb(3+), Er(3+), and (or) radioactive (153)Sm(3+) ions were synthesized, through a hydrothermal synthetic system assisted by binary cooperative ligands with oleic acid and PEG dicarboxylic acids. The as-prepared PEG-coating NaYF4:Yb,Er and NaYF4:Yb,Er,(153)Sm are denoted as PEG-UCNPs and PEG-UCNPs((153)Sm), respectively. PEG-UCNPs were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD) analysis, and Fourier-transform infrared (FTIR) spectroscopy. The PEG-UCNPs showed excellent water solubility with a hydrodynamic diameter of ∼10 nm and displayed upconversion luminescence (UCL) under continuous-wave excitation at 980 nm. At the same time, the (153)Sm-doped nanoparticles PEG-UCNPs((153)Sm) displayed radioactivity, and time-dependent biodistribution of PEG-UCNPs((153)Sm) was investigated, through single-photon emission computed tomography (SPECT) imaging and γ-counter analysis. Interestingly, PEG-UCNPs((153)Sm) had a long blood retention time and were partly eliminated through urinary pathways in vivo. Therefore, the concept of fabricating PEG-coated, small nanosize (sub-10 nm) nanoparticles with radioactive property is a useful strategy for providing a potential method to monitor lanthanide nanoparticles renal clearable.

PEGylated hybrid ytterbia nanoparticles as high-performance diagnostic probes for in vivo magnetic resonance and X-ray computed tomography imaging with low systemic toxicity

Novel nanoparticulate contrast agents with low systemic toxicity and inexpensive character have exhibited more advantages over routinely used small molecular contrast agents for the diagnosis and prognosis of disease. Herein, we designed and synthesized PEGylated hybrid ytterbia nanoparticles as high-performance nanoprobes for X-ray computed tomography (CT) imaging and magnetic resonance (MR) imaging both in vitro and in vivo. These well-defined nanoparticles were facile to prepare and cost-effective, meeting the criteria as a biomedical material. Compared with routinely used Iobitridol in clinic, our PEG-Yb2O3:Gd nanoparticles could provide much significantly enhanced contrast upon various clinical voltages ranging from 80 kVp to 140 kVp owing to the high atomic number and well-positioned K-edge energy of ytterbium. By the doping of gadolinium, our nanoparticulate contrast agent could perform perfect MR imaging simultaneously, revealing similar organ enrichment and bio-distribution with the CT imaging results. The super improvement in imaging efficiency was mainly attributed to the high content of Yb and Gd in a single nanoparticle, thus making these nanoparticles suitable for dual-modal diagnostic imaging with a low single-injection dose. In addition, detailed toxicological study in vitro and in vivo indicated that uniformly sized PEG-Yb2O3:Gd nanoparticles possessed excellent biocompatibility and revealed overall safety.

A facile synthesis of strong near infrared fluorescent layered double hydroxide nanovehicles with an anticancer drug for tumor optical imaging and therapy

In this work, a new multifunctional nanovehicle for tumor optical imaging and therapy was developed using Y2O3:Er(3+),Yb(3+) nanoparticles as near infrared fluorescent nanophosphors, and MgAl-layered double hydroxide (LDH) nanosheets as anticancer drug nanovehicles. Monodispersed Y2O3:Er(3+),Yb(3+) nanophosphors were readily synthesized by the urea assisted homogenous precipitation method. Hierarchically structured LDH nanosheets intercalated with an anticancer drug, fluorouracil (5FU), were deposited on the surface of Y2O3:Er(3+),Yb(3+)@SiO2 by a simple precipitation method followed by hydrothermal treatment. The resultant Y2O3:Er(3+),Yb(3+)@SiO2@LDH-5FU nanovehicles exhibit strong red upconversion fluorescence under the excitation of a 980 nm laser, which allows tracking of the nanovehicles after localization in cancer cells. A better anticancer efficiency was obtained over the nanovehicles than the free drug which can be attributed to their positively charged surfaces for favorable interaction with the negatively charged cell membranes. The multifunctional nanovehicles designed in this work are expected to be promising material candidates for simultaneous tumor optical imaging and therapy.

In vitro and in vivo investigations of upconversion and NIR emitting Gd₂O₃:Er³⁺,Yb³⁺ nanostructures for biomedical applications

The use of an "over 1000-nm near-infrared (NIR) in vivo fluorescence bioimaging" system based on lanthanide containing inorganic nanostructures emitting in the visible and NIR range under 980-nm excitation is proposed. It may overcome problems of currently used biomarkers including color fading, phototoxicity and scattering. Gd(2)O(3):Er(3+),Yb(3+) nanoparticles and nanorods showing upconversion and NIR emission are synthesized and their cytotoxic behavior is investigated by incubation with B-cell hybridomas and macrophages. Surface modification with PEG-b-PAAc provides the necessary chemical durability reducing the release of toxic Gd(3+) ions. NIR fluorescence microscopy is used to investigate the suitability of the nanostructures as NIR-NIR biomarkers. The in vitro uptake of bare and modified nanostructures by macrophages is investigated by confocal laser scanning microscopy. In vivo investigations revealed nanostructures in liver, lung, kidneys and spleen a few hours after injection into mice, while most of the nanostructures have been removed from the body after 24 h.

An early investigation of ytterbium nanocolloids for selective and quantitative "multicolor" spectral CT imaging

We report a novel molecular imaging agent based on ytterbium designed for use with spectral "multicolor" computed tomography (CT). Spectral CT or multicolored CT provides all of the benefits of traditional CT, such as rapid tomographic X-ray imaging, but in addition, it simultaneously discriminates metal-rich contrast agents based on the element's unique X-ray K-edge energy signature. Our synthetic approach involved the use of organically soluble Yb(III) complex to produce nanocolloids of Yb of noncrystalline nature incorporating a high density of Yb (>500K/nanoparticle) into a stable metal particle. The resultant particles are constrained to vasculature (∼200 nm) and are highly selective for binding fibrin in the ruptured atherosclerotic plaque. Nanoparticles exhibited excellent signal sensitivity, and the spectral CT technique uniquely discriminates the K-edge signal (60 keV) of Yb from calcium (bones). Bioelimination and preliminary biodistribution reflected the overall safety and defined clearance of these particles in a rodent model.

Comparative toxicity of nanoparticulate/bulk Yb₂O₃ and YbCl₃ to cucumber (Cucumis sativus)

With the increasing utilization of nanomaterials, there is a growing concern for the potential environmental and health effects of them. To assess the environmental risks of nanomaterials, better knowledge about their fate and toxicity in plants are required. In this work, we compared the phytotoxicity of nanoparticulate Yb(2)O(3), bulk Yb(2)O(3), and YbCl(3)·6H(2)O to cucumber plants. The distribution and biotransformation of the three materials in plant roots were investigated in situ by TEM, EDS, as well as synchrotron radiation based methods: STXM and NEXAFS. The decrease of biomass was evident at the lowest concentration (0.32 mg/L) when exposed to nano-Yb(2)O(3), while at the highest concentration, the most severe inhibition was from YbCl(3). The inhibition was dependent on the actual amount of toxic Yb uptake by the cucumber plants. In the intercellular regions of the roots, Yb(2)O(3) particles and YbCl(3) were all transformed to YbPO(4). We speculate that the dissolution of Yb(2)O(3) particles induced by the organic acids exuded from roots played an important role in the phytotoxicity. Only under the nano-Yb(2)O(3) treatment, YbPO(4) deposits were found in the cytoplasm of root cells, so the phytotoxicity might also be attributed to the Yb internalized into the cells.

[Development of a new photosensitizer on the basis of ytterbium porphyrazine complex]

The tetraphenyltetracyanoporphyrazine complex of ytterbium has been studied as a potential photosensitizer for fluorescence diagnostics and photodynamic therapy (PDT) of cancer. It has been shown that the new compound has an intensive absorption and fluorescence in the "tissue optical window". In particular, the absorption maximum of the complex is at the wavelength of 590 nm, and the fluorescence emission maximum is at 640 nm. A strong fluorescence enhancement with a 50-fold increase in the quantum yield has been revealed in blood serum. The experiments on human cancer cells line have demonstrated that the complex penetrates the cells in vitro and is located around the nuclei. The biodistribution and pharmacokinetics of the complex in animals have been investigated in vivo by a new method of transillumination fluorescence imaging using a peculiar setup. It has been found that the period of maximum uptake of the complex in mouse cervical carcinoma is from 3 to 6 h after i.v. injection, with the half-life in the tumor being 24 h. However, the selectivity of the complex in the tumor is not high enough. The time of clearance from the body is about 48 h. The area of the strongest fluorescence in the abdominal cavity in in vivo images is anatomically recognized as the intestine. This indicates that the new compounds undergo mainly the hepatic clearance mainly. The conventional methods ex vivo (confocal microscopy and point spectroscopic measurements) have detected the largest content of the complex in the intestine, liver, skin and tumor tissue. In general, the optical characteristics of the ytterbium porphyrazine complex as well as the features of its interaction with biological objects make it promising drug candidate for the photodynamic therapy and/or fluorescence diagnostics of cancer. However, a search for other novel formulations possessing a higher tumor selectivity remains an urgent problem.

175Yb-labeled hydroxyapatite: a potential agent for use in radiation synovectomy of small joints

The preparation of 175Yb-labeled hydroxyapatite (HA) particle is described for possible use as an agent for radiation synovectomy (RS) of small-sized joints. 175Yb was produced by thermal neutron irradiation of enriched (98.6% in 174Yb) ytterbium target at a flux of approximately 3 x 10(13) n/cm(2)/s for 7 days. Specific activity of 5.5-6.0 GBq/mg and a very high radionuclidic purity to the extent of approximately 100% were obtained. In the work reported herein, HA could be labeled with 175Yb in very high radiochemical purity (>99%) using 10 mg of HA particle at pH approximately 7. The radiolabeled particulates showed excellent in vitro stability at room temperature. Serial scintigraphic images of normal as well as arthritis-bearing Wistar rats following intra-articular injection of 175Yb-HA particles in the knee joint showed complete retention of activity within the synovial cavity with no measurable activity leaching out from the joint till 144 h post-injection.

Distribution of ytterbium-169 in rat brain after intravenous injection

It is well known that lanthanides have come into extensive and rapid use in a number of fields. As a result, more and more lanthanides are getting into the environment and food chains. However, the distributions of lanthanides in brain are not yet very clear. In this study, adult Sprague-Dawley male rats were intravenously injected with 0.5 ml of 169YbCl3 solution (containing 10 microg Yb). The brains were perfused with saline to minimize the blood influence. The radioactivities of 169Yb in the five brain regions (hypothalamus, cerebellum, hippocampus, corpus striatum and cerebral cortex) were counted. The results suggested that Yb did enter into the brain. Though only about 0.005% of the given dose was accumulated in the brain, Yb seemed to remain in the brain for long time. The highest specific activities were observed in the hypothalamus, hippocampus and cerebellum.

175Yb labeled polyaminophosphonates as potential agents for bone pain palliation

Ytterbium-175 (T1/2 = 4.2 d, Ebeta(max) = 480 keV) has radionuclidic properties suitable to be used in palliative therapy of bone metastases. 175Yb can be produced in moderate specific activity and good radionuclidic purity by thermal neutron bombardment of natural Yb target. The analysis of the neutron irradiated sample exhibited the presence of 96.2% 175Yb along with 2.1% 169Yb and 1.7% 177Lu at 6 h post-EOB. Four polyaminomethylene phosphonic acid ligands, ethylenediamine tetramethylene phosphonic acid, propylenediamine tetramethylene phosphonic acid, triethylenetetramine hexamethylene phosphonic acid and diethylenetriamine pentamethylene phosphonic acid were synthesized and radiolabeled with 175Yb. Complexation parameters were optimized to achieve maximum yields (92-99%). All complexes were found to retain their stability at room temperature even after 10d of preparation. Biodistribution studies of the complexes carried out in Wistar rats showed significant bone uptake (3-4.4%/g in tibia at 3h post-injection) with rapid clearance from blood and minimum uptake in soft tissues for all the complexes (bone/blood ratio approximately 40-150 and bone/muscles ratio approximately 40-400 at 3 h post-injection). These studies suggest that 175Yb complexes with the phosphonate ligands have potential for use in palliative treatment of painful bone metastases.

Synthesis and luminescence properties of a kinetically stable dinuclear ytterbium complex with differentiated binding sites

The complex Yb2L contains two DO3A units separated by a phenol bridging group and gives time-resolved luminescence spectra in solution consistent with the presence of two types of binding site.

Ytterbium-169: a promising new radionuclide for intravascular brachytherapy

PURPOSE

To explore the feasibility of 169Yb (gamma, 93 keV) as a new radionuclide for intravascular brachytherapy (IVBT) in terms of dose distribution, penetration power, and radiation safety features as compared with 125I and 192Ir.

METHODS

The dose distributions for catheter-based sources, 169Yb, 125I, and 192Ir, in homogeneous water and in the presence of calcium and a steel stent have been determined and compared using the Monte Carlo method (MCNP4B2 code). The dose rates of the sources were evaluated from 0.02 to 100 cm.

RESULTS

In the short distance range (0.02<r<1.0 cm), the dose distributions in homogeneous water are very similar for the three radionuclides when the dose rates are normalized at 2 mm. Between 1 and 20 cm, the relative dose rates fall off similarly for 169Yb and 192Ir, whereas for 125I, it decreases much more rapidly. At a distance further away (r approximately 100 cm), the dose rate of 169Yb is about 10 times lower than that of 192Ir, indicating the cathlab radiation shielding requirement for 169Yb is substantially reduced as compared with 192Ir. Calcified plaques and stents cause a drastic dose reduction in the arterial wall for 125I, but have no effect for 192Ir gamma-rays. Only slight dose reductions were detected for 169Yb beyond a layer of 1.0-mm calcium (2-3%), and behind a steel stent strut (5%).

CONCLUSION

169Yb is a promising new radionuclide for IVBT. It has a much better penetrating power through calcified plaques and stents compared with the low-energy source 125I. It also provides easier radiation protection measures for cardiac cathlab personnel than the high-energy source 192Ir, while preserving a favorable dose distribution in tissues surrounding an arterial vessel.

[Synthesis of tumor affinity label Yb-169- and Y-90- porphyrin complexes and animal experimental investigations with various Yb-169-porphyrins]

AIM

It should be shown, that it is possible to insert radioactive isotopes of Yb and Y into some selected porphyrins. Besides, first informations about the biodistribution of Yb-169-por-phyrin-complexes should be obtained.

METHODS

Carrier added radioactive isotopes were used for the synthesis of the metal porphyrin complexes. The animal experiments were done with mamma carcinoma bearing mice. The activity of the organs was determined 5 and 24 h after i.v. injection in a well counter.

RESULTS

Four Yb-169-porphyrin complexes and Y-90-porphyrin complexes could be synthesized in non-carrier-free form. This was verified by absorption spectra, TLC and HPLC. Depending on the complex, the average tumour/background ratios were between 2 and 20.

CONCLUSION

The synthesized radioactive metal-porphyrin complexes showed a clear tumour-affinity which could be used for tumour scintigraphy or perhaps therapy if the synthesis is improved (goal: reduction of carrier, other radionuclides).

Phase I study of 90Y-labeled B72.3 intraperitoneal administration in patients with ovarian cancer: effect of dose and EDTA coadministration on pharmacokinetics and toxicity

The tumor-associated glycoprotein 72 (TAG-72) antigen is present on a high percentage of tumor types including ovarian carcinomas. Antibody B72.3 is a murine monoclonal recognizing the surface domain of the TAG-72 antigen and has been widely used in human clinical trials. After our initial encouraging studies (M. G. Rosenblum et al., J. Natl. Cancer Inst., 83: 1629-1636, 1991) of tissue disposition, metabolism, and pharmacokinetics in 9 patients with ovarian cancer, we designed an escalating dose, multi-arm Phase I study of 90Y-labeled B72.3 i.p. administration. In the first arm of the study, patients (3 pts/dose level) received an i.p. infusion of either 2 or 10 mg of B72.3 labeled with either 1, 10, 15, or 25 mCi of 90Y. Pharmacokinetic studies demonstrated that concentrations of 90Y-labeled B72.3 persist in peritoneal fluid with half-lives >24 h after i.p. administration. In addition, 90Y-labeled B72.3 was absorbed rapidly into the plasma with peak levels achieved within 48 h, and levels declined slowly thereafter. Cumulative urinary excretion of the 90Y label was 10-20% of the administered dose which suggests significant whole-body retention of the radiolabel. Biopsy specimens of bone and marrow obtained at 72 h after administration demonstrated significant content of the label in bone (0.015% of the dose/g) with relatively little in marrow (0.005% of the dose/g). The maximal tolerated dose was determined to be 10 mCi because of hematological toxicity and platelet suppression. This typically occurred on the 29th day after administration and was thought to be a consequence of the irradiation of the marrow from the bony deposition of the radiolabel. In an effort to suppress the bone uptake of 90Y, patients were treated with a continuous i.v. infusion of EDTA (25 mg/kg/12 h x 6) infused immediately before i.p. administration of the radiolabeled antibody. Patients (3 pts/dose level) were treated with doses of 10, 15, 20, 25, 30, 35, 40, or 45 mCi of 90Y-labeled B72.3 for a total of 38 patients. EDTA administration resulted in significant myeloprotection, which allowed escalation to the maximal tolerated dose of 40 mCi. Dose-limiting toxicity was thrombocytopenia and neutropenia. Studies of plasma and peritoneal fluid pharmacokinetics demonstrate no changes compared with patients without EDTA pretreatment. Cumulative urinary excretion of the radiolabel was not increased in patients pretreated with EDTA compared with the untreated group. However, analysis of biopsy specimens of bone and marrow demonstrated that bone and marrow content of the 90Y label was 15-fold lower (<0.001% injected dose/g) than a companion group without EDTA. Four responses were noted in patients who received 15-30 mCi of 90Y-labeled B72.3 with response durations of 1-12 months. These results demonstrate the myeloprotective ability of EDTA, which allows safe i.p. administration of higher doses of 90Y-labeled B72.3 and, therefore, clearly warrant an expanded Phase II trial in patients with minimal residual disease after standard chemotherapy or for the palliation of refractory ascites.

Locoregional regulatory peptide receptor targeting with the diffusible somatostatin analogue 90Y-labeled DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC): a pilot study in human gliomas

Human gliomas, especially of low-grade type, have been shown to express high-affinity somatostatin receptor type 2 (J-C. Reubi et al., Am. J. Pathol, 134: 337-344, 1989). We enrolled seven low-grade and four anaplastic glioma patients in a pilot study using the diffusible peptidic vector 90Y-labeled DOTA0-D-Phe1-Tyr3-octreotide (DOTATOC) for receptor targeting. The radiopharmakon was locoregionally injected into a stereotactically inserted Port-a-cath. DOTATOC competes specifically with somatostatin binding to somatostatin receptor type 2 in the low nanomolar range as shown by a displacement curve of 125I-[Tyr3]-octreotide in tumor tissue sections. Diagnostic (111)In-labeled DOTATOC-scintigraphy following local injection displayed homogeneous to nodular intratumoral vector distribution. The cumulative activity of regionally injected peptide-bound 90Y amounted to 370-3300 MBq, which is equivalent to an effective dose range between 60 +/- 15 and 550 +/- 110 Gy. Activity was injected in one to four fractions according to tumor volumes; 1110 MBq of 90Y-labeled DOTATOC was the maximum activity per single injection. We obtained six disease stabilizations and shrinking of a cystic low-grade astrocytoma component. The only toxicity observed was secondary perifocal edema. The activity:dose ratio (MBq:Gy) represents a measure for the stability of peptide retention in receptor-positive tissue and might predict the clinical course. We conclude that SR-positive human gliomas, especially of low-grade type, can be successfully targeted by intratumoral injection of the metabolically stable small regulatory peptide DOTATOC.

Uptake of 169Yb complexes in normal and tumour cells: influence of ligand and metabolic cell activity and stability of cellular association

For better understanding of the accumulation of trivalent radiometal tracers in tumours, studies of uptake of different 169Yb complexes into cultured normal (V79/4) and tumour (KTCTL-2) cells were performed. Cellular uptake of 169Yb3+ is dependent on both the metabolic activity of the cells and the nature of the ligand used. Uptake of 169Yb3+ from the citrate complex is an active cellular transport process but not tumour-specific. The 169Yb-aminopolycarboxylic acid complexes are taken up via a different, unknown mechanism, and in higher amounts by the tumour cells than by the V79/4 cell line, but the general features of uptake were principally the same with the normal and the tumour cells. Uptake of the complexes studied leads to a stable association of cellular components, which is a good premise for the therapeutic use of trivalent radiometals.

Ytterbium- and dysprosium-EOB-DTPA. A new prototype of liver-specific contrast agents for computed tomography

RATIONALE AND OBJECTIVES

A series of studies was conducted to determine whether metal complexes of the EOB-DTPA type are useful as contrast agents for computed tomography (CT).

METHODS

Metal complexes using EOB-DTPA as ligand were synthesized with lanthanide metal ions (lanthanum [La], cerium [Ce], praseodyme [Pr], gadolinium [Gd], dysprosium [Dy], ytterbium [Yb], and lutetium [Lu]) and with nonlanthanides (lead [Pb] and bismuth [Bi]). Complex stability was assessed by measuring binding to bone meal. The physicochemical parameters partition coefficient, osmolality, viscosity, and protein binding were determined in vitro. Tolerability was tested both in vitro (thromboplastin time, effect on erythrocytes) and in vivo (acute, neural, and cardiovascular toxicities). Biliary excretion and tissue distribution, especially liver, kidney, and bone concentrations, were measured in rats after intravenous doses of 0.5 mmol/kg. Imaging performance using CT was investigated in vitro in a phantom model and, for Gd-EOB-DTPA, in vivo by injecting doses of 0.5 mmol/kg into healthy or tumor-bearing rats and rabbits.

RESULTS

The kinetic stability of M-EOB-DTPA complexes differed widely. Nonlanthanide metals, especially Pb-EOB-DTPA, provided less stable complexes than lanthanides with an optimum of stability for the metals Gd, Dy, Yb, and Lu. Tolerability was good for all compounds, best results were obtained for Gd and Yb. Concentrations in rat liver after administration of Gd-EOB-DTPA, 0.5 mmol/kg intravenous, were approximately 1 mumol/g, resulting in CT enhancement of 16 Hounsfield units (HU). Tumor tissue was not enhanced. In rabbits, at the same dose level 30 HU was found.

CONCLUSIONS

Metal complexes of the EOB-DTPA type, especially those of Gd and Yb seem to be useful as iodine-free liver-specific contrast agents for CT.

[Long term biokinetics of 169Yb following injection as citrate, hydroxyethylethylenediaminetetraacetate and nitrilotriacetate]

169Yb complexes with known biokinetics in tumour-bearing mice up to 48 h p.i. were injected into healthy mice to study the radionuclide biodistribution in various organs and tissues for 672 h after injection, in order to obtain reliable biokinetic data in an animal model, not affected by tumour-growth, as a basis for the calculation of biological half-life and dose distribution. The results demonstrated the existence of at least two components with different biological half-lives in the organs and tissues investigated. The effective half-lives of these components decreased with increasing stability of the complexes administered. The effective half-life of the fast component was a few hours and that of the slow one between about 200 and 800 h.

[CT contrast administration of iodine, gadolinium and ytterbium. In-vitro studies and animal experiments]

The absorption of the elements iodine, gadolinium and ytterbium in various dilutions was studied in relation to CT. Regression analysis and specific CT density measurements showed that absorption decreases from gadolinium to ytterbium and iodine. These results were confirmed by experiments using ten dogs. Boli of 0.5 molar gadolinium used for angio-CT without table movement showed the largest increase in density in the aorta and liver with an average of 190HU and 21HU respectively compared with iodine which gave 157HU and 12HU respectively. The animal experimental studies suggest that gadolinium and ytterbium are suitable contrast media for dynamic CT investigations.

[The effect of ethylenediaminetetramethylenephosphonate on the biodistribution of tumor-seeking radionuclides]

It is well known that after application of radioactive complexes for tumour diagnosis or therapy, such as 67Ga-citrate or radiolanthanide complexes (167Tm- or 169Yb-nitrilotriacetate, -citrate, -alpha-hydroxyisobutyrate, 90Y-citrate, etc.) activity is accumulated not only in the tumour but also in other organs, above all liver and bone. This is the main obstacle to their medical use. Recently published results encouraged us to use ethylenediaminetetramethylene phosphonate (EDTMP) for the reduction of extratumoural liver activity. The results show that even small amounts of EDTMP (1-2 mg/kg BW) reduce the activity deposition in the liver by about one order of magnitude. EDTMP provoked elimination of activity from tumour, skeleton and other tissues but not to the same extent as from the liver. Tumor/liver activity ratios > 5 are achievable in this manner.

[The effect of bone-seeking metal salts on the biodistribution of tumor-seeking heavy metal complexes]

This work attempted to overcome the problem of unwanted bone radioactivity after injection of tumour-affine heavy-metal compounds (prototype 169Yb-citrate) by pre-application of stable yttrium- and calcium-compounds into tumour-bearing mice in doses of 1 mg metal/kg body weight. The pre-application of stable yttrium and calcium resulted in a smaller bone radioactivity. The most favourable results were achieved by injecting the metal salts simultaneously at or within 5 h before the 169Yb-citrate. On the other hand a strong radioactivity increase in the RES (liver and spleen) by a factor of 2 to 4 was observed after yttrium-preapplication.

[The effect of Ca-diethylenetriamine pentaacetate on the bio-behavior of tumor-affine metal complexes]

The complexon CaDTPA was injected into tumour-bearing mice in concentrations of 0.05, 0.1, 0.3, and 0.6 mole/l (pH:6) 30 min after the 169Yb-injection. 100 microliters of a 0.3 M CaDTPA solution were injected at different time points (simultaneously, 2, 5, 10, 20, 30, 40 and 50 min, 1, 1.25, 1.5, 2.5 and 10 h) after 169Yb-citrate injection. The animals were killed 24 h after radionuclide administration. A strong radioactivity decrease was observable 24 h p.i. not only in blood, liver, spleen, muscle and bone but also in the tumour if CaDTPA was administered within the first 2 h after ytterbium injection. Thereafter no change in radioactivity could be achieved by DTPA. A time phase in which the Yb could be eliminated from the tissues by means of DTPA (time intervals < 2 h) was distinguishable from a time phase in which it was not attainable for DTPA (time intervals > 5 h). This indicates that the incorporation of Yb into the cells is completed after 5 h and that the metals are intracellularly bound, probably to the lysosomes. Improvements of the scintigraphic tumour detection cannot be expected from the use of complexons.

Studies on the incorporation of lanthanides in dental hard tissues

Rare earth elements (lanthanides)--known from chrystal-chemistry for the rehardening effect on apatites--have been tested previously for the possibility of their incorporation in dental enamel. From the non-toxic lanthanides cerium was incorporated under in vitro conditions in human dental enamel. In the present study, the incorporation of lanthanum (La), europium (Eu), samarium (Sa), ytterbium (Yb) and neodymium (Nd) in human permanent enamel, dentine and deciduous enamel has been investigated by neutron activation analysis. The lanthanides were incorporated--following the above sequence--in an increasing ratio into enamel and dentine, by forming new, more resistant rare earth elements containing apatite structures.

Yb-DTPA, a novel contrast agent in magnetic resonance imaging: application to rat kidney

We have developed a novel contrast agent, ytterbium-diethylenetriamine pentaacetic acid (Yb-DTPA), for magnetic resonance imaging (MRI) and its mechanism of action is predominantly by the susceptibility mechanism. We have applied this contrast agent for renal MRI studies. We also demonstrate that Yb-DTPA has a renal clearance similar to that of inulin in rats and may therefore be useful for the estimation of glomerular filtration rate.

Relationship between left ventricular systolic function and plasma clearance of 169Yb-DTPA in normal and ischemic dogs

Plasma clearance of 169Yb-DTPA, a heavy chelate metal excreted only by glomerular filtration, was measured serially in a canine model to determine whether the clearance of this substance correlates with left ventricular systolic function. Fourteen anesthetized open-chest dogs were studied. Six dogs (group I) were used to estimate the clearance of 169Yb-DTPA in the setting of normal left ventricular function. Eight dogs (group II) were used to estimate clearance of 169Yb-DTPA in the presence of ischemic left ventricular dysfunction. Cardiac output, mean arterial pressure, and plasma levels of 169Yb-DTPA were measured serially. In group II dogs, area at risk for necrosis was defined using myocardial contrast echocardiography. The change in clearance of 169Yb-DTPA in group II dogs correlated well with change in cardiac output and area at risk (r = 0.80 and -0.93, respectively) and was significantly different from group I dogs (p less than 0.01). However, changes in clearance of 169Yb-DTPA in the group II dogs did not correlate well with change in mean arterial pressure (r = 0.26).

IN CONCLUSION

(1) clearance of 169Yb-DTPA is constant over time in the absence of ischemic left ventricular dysfunction and derangement of other hemodynamic parameters; (2) changes in clearance of 169Yb-DTPA correlate well with changes in systolic pump function and left ventricular area at risk in the setting of ischemic left ventricular dysfunction, and (3) clearance of 169Yb-DTPA is not related to mean arterial pressure.