In vivo evaluation of PEGylated-liposome encapsulating gadolinium complexes for gadolinium neutron capture therapy.

Gadolinium neutron capture therapy (GdNCT) is a form of binary radiotherapy. It utilizes nuclear reactions that occur when gadolinium-157 is irradiated with thermal neutrons, producing high-energy γ-rays and Auger electrons. Herein, we evaluate the potential of GdNCT for cancer treatment using PEGylated liposome incorporated with an FDA-approved MRI contrast agent. The clinical gadolinium complex (Gadovist®) was successfully encapsulated inside the aqueous core of PEGylated liposomes by repeated freeze and thaw cycling. At a concentration of 152 µM Gd, the Gd-liposome showed high cytotoxicity upon thermal-neutron irradiation. In animal experiments, when a CT26 tumor model was administered with Gd-liposomes (19 mg 157Gd per kg) followed by 20-min irradiation of thermal neutron at a flux of 1.94 × 104 cm-2 s-1, tumor growth was suppressed by 43%, compared to that in the control group, on the 23rd day of post-irradiation. After two-cycle GdNCT treatment at a 10-day interval, tumor growth was more efficiently retarded. On the 31st day after irradiation, the weight of the excised tumor in the GdNCT group (38 mg 157Gd per kg per injection) was only 30% of that of the control group. These results demonstrate the potential of GdNCT using PEGylated liposomes containing MRI contrast agents in cancer treatment.

Neutron Capture Enhances Dose and Reduces Cancer Cell Viability in and out of Beam During Helium and Carbon Ion Therapy.

PURPOSE: Neutron capture enhanced particle therapy (NCEPT) is a proposed augmentation of charged particle therapy that exploits thermal neutrons generated internally, within the treatment volume via nuclear fragmentation, to deliver a biochemically targeted radiation dose to cancer cells. This work is the first experimental demonstration of NCEPT, performed using both carbon and helium ion beams with 2 different targeted neutron capture agents (NCAs). METHODS AND MATERIALS: Human glioblastoma cells (T98G) were irradiated by carbon and helium ion beams in the presence of NCAs [10B]-BPA and [157Gd]-DOTA-TPP. Cells were positioned within a polymethyl methacrylate phantom either laterally adjacent to or within a 100 × 100 × 60 mm spread out Bragg peak (SOBP). The effect of NCAs and location relative to the SOBP on the cells was measured by cell growth and survival assays in 6 independent experiments. Neutron fluence within the phantom was characterized by quantifying the neutron activation of gold foil. RESULTS: Cells placed inside the treatment volume reached 10% survival by 2 Gy of carbon or 2 to 3 Gy of helium in the presence of NCAs compared with 5 Gy of carbon and 7 Gy of helium with no NCA. Cells placed adjacent to the treatment volume showed a dose-dependent decrease in cell growth when treated with NCAs, reaching 10% survival by 6 Gy of carbon or helium (to the treatment volume), compared with no detectable effect on cells without NCA. The mean thermal neutron fluence at the center of the SOBP was approximately 2.2 × 109 n/cm2/Gy (relative biological effectiveness) for the carbon beam and 5.8 × 109 n/cm2/Gy (relative biological effectiveness) for the helium beam and gradually decreased in all directions. CONCLUSIONS: The addition of NCAs to cancer cells during carbon and helium beam irradiation has a measurable effect on cell survival and growth in vitro. Through the capture of internally generated neutrons, NCEPT introduces the concept of a biochemically targeted radiation dose to charged particle therapy. NCEPT enables the established pharmaceuticals and concepts of neutron capture therapy to be applied to a wider range of deeply situated and diffuse tumors, by targeting this dose to microinfiltrates and cells outside of defined treatment regions. These results also demonstrate the potential for NCEPT to provide an increased dose to tumor tissue within the treatment volume, with a reduction in radiation doses to off-target tissue.

In vivo evaluation of the effects of combined boron and gadolinium neutron capture therapy in mouse models.

While boron neutron capture therapy (BNCT) depends primarily on the short flight range of the alpha particles emitted by the boron neutron capture reaction, gadolinium neutron capture therapy (GdNCT) mainly relies on gamma rays and Auger electrons released by the gadolinium neutron capture reaction. BNCT and GdNCT can be complementary in tumor therapy. Here, we studied the combined effects of BNCT and GdNCT when boron and gadolinium compounds were co-injected, followed by thermal neutron irradiation, and compared these effects with those of the single therapies. In cytotoxicity studies, some additive effects (32‒43%) were observed when CT26 cells were treated with both boron- and gadolinium-encapsulated PEGylated liposomes (B- and Gd-liposomes) compared to the single treatments. The tumor-suppressive effect was greater when BNCT was followed by GdNCT at an interval of 10 days rather than vice versa. However, tumor suppression with co-injection of B- and Gd-liposomes into tumor-bearing mice followed by neutron beam irradiation was comparable to that observed with Gd-liposome-only treatment but lower than B-liposome-only injection. No additive effect was observed with the combination of BNCT and GdNCT, which could be due to the shielding effect of gadolinium against thermal neutrons because of its overwhelmingly large thermal neutron cross section.

Rational surface modification of gadolinium borate nanoparticles enhancing colloidal stability in physiological media for potential neutron capture therapy and magnetic resonance imaging.

Colloidal stability of nanomaterials in physiological media is an indispensable property for their biomedical applications. However, gadolinium borate (GdBO3) nanoparticles that hold promise as a theranostic agent for neutron capture therapy (NCT) and magnetic resonance imaging (MRI) of cancer tend to precipitate in phosphate buffered saline (PBS) owing to formation of insoluble gadolinium phosphate. To address this issue, in this work 10B-enriched GdBO3 nanoparticles were prepared and coated with mesoporous silica (mSiO2) of ~ 40 nm in thickness and subsequently grafted with hydrophilic polyglycerol (PG). The resulting GdBO3 @mSiO2-PG nanoparticles showed excellent colloidal stability in PBS due to the protection of the mSiO2 coating as well as superior dispersibility because of the high hydrophilicity of the PG layer. In vitro experiments revealed that GdBO3 @mSiO2-PG possessed low cytotoxicity and could be taken up by cancer cells in a concentration-dependent manner. In vivo studies indicated that GdBO3 @mSiO2-PG can circulate in mouse body for a considerably long time without obvious acute toxicity. In addition, GdBO3 @mSiO2-PG also showed promise as a T1-weighted MRI contrast agent with a proton longitudinal relaxivity of 0.67 mM-1 s-1. Our results indicate that GdBO3 @mSiO2-PG with enhanced colloidal stability in physiological media could serve as a promising multifunctional agent for cancer theranostics.

Formulation considerations of gadolinium lipid nanoemulsion for intravenous delivery to tumors in neutron-capture therapy.

The effects of the formulation and particle composition of gadolinium (Gd)-containing lipid nanoemulsion (Gd-nanoLE) on the biodistribution of Gd after its intravenous (IV) injection in D(1)-179 melanoma-bearing hamsters were evaluated for its application in cancer neutron-capture therapy. Gd-nanoLEs whose particles had an oily core (soybean oil, ethyl oleate, lipiodol, or triolein) and a surface layer of hydrogenated phosphatidylcholine, gadolinium-diethyl-enetriaminepentaacetic acid-distearylamide, and a cosurfactant (Myrj 53, Brij 700, or HCO-60) were prepared by a thin-layer hydration-sonication method. Biodistribution data revealed that Brij 700 and HCO-60 prolonged the retention of Gd in the blood and enhanced its accumulation in tumors. Among the core components employed, soybean oil yielded the highest Gd concentration in the blood and tumor and the lowest in the liver and spleen. Gd-nanoLEs with a Gd content of 1.5-4.5 mg/ml could be formulated by using HCO-60 and soybean oil at a constant oil-to-water ratio, and by enriching Gd in the surface layer with the particle size maintained below 100 nm. When each Gd-nanoLE was IV injected once or twice at a 24-h interval, the Gd concentration in the tumor correlated well with the total dose of Gd, and it reached a maximum of 189 microg/g wet tumor. This maximum Gd level was greater than the limit required for significantly suppressing tumor growth in neutron-capture therapy.

Theranostic Nanoparticles Loaded with Imaging Probes and Rubrocurcumin for Combined Cancer Therapy by Folate Receptor Targeting.

The combination of different therapeutic modalities is a promising option to combat the recurrence of tumors. In this study, polylactic and polyglycolic acid nanoparticles were used for the simultaneous delivery of a boron-curcumin complex (RbCur) and an amphiphilic gadolinium complex into tumor cells with the aim of performing boron and gadolinium neutron capture therapy (NCT) in conjunction with the additional antiproliferative effects of curcumin. Furthermore, the use of Gd complexes allows magnetic resonance imaging (MRI) assessment of the amount of B and Gd internalized by tumor cells. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles were targeted to ovarian cancer (IGROV-1) cells through folate receptors, by including in the formulation a PEGylated phospholipid functionalized with the folate moiety. NCT was performed on IGROV-1 cells internalizing 6.4 and 78.6 µg g-1 of 10 B and 157 Gd, respectively. The synergic action of neutron treatment and curcumin cytotoxicity was shown to result in a significant therapeutic improvement.

Biodistribution and tumor-accumulation of gadolinium (Gd) encapsulated in long-circulating liposomes in tumor-bearing mice for potential neutron capture therapy.

To deliver and maintain a sufficient amount of Gd into tumors is required for a successful Gd neutron capture therapy (Gd-NCT), but it has been proven to be rather challenging to achieve. Previously, we have reported a Gd-encapsulated liposome formulation that has the potential to overcome this challenge. In the present study, we sought to systemically evaluate the biodistribution and the tumor-accumulation of the Gd in model tumor-bearing mice. The Gd-encapsulated liposomes were injected into mice pre-grafted with two different model tumors. The Gd content in the tumors and other organs were determined at various time after the injection. A sufficient amount of Gd was readily delivered into those two different model tumors. Increasing the dose of Gd by injecting the Gd-encapsulated liposomes multiple times tended to increase the uptake of the Gd by the tumors. Finally, the uptake of Gd by tumors was inversely correlated with the size of the tumors. The Gd-encapsulated liposomes hold great potentials as a Gd delivery system for NCT of small- and medium-size tumors. Alternative strategies may have to be adopted in order to use NCT to treat large, advanced solid tumors, although for which, Gd-NCT might be advantageous over boron-NCT.

Long-circulating gadolinium-encapsulated liposomes for potential application in tumor neutron capture therapy.

Gadolinium neutron capture therapy (Gd-NCT) is a promising cancer therapy modality. One of the key factors for a successful Gd-NCT is to deliver and maintain a sufficient amount of Gd in tumor tissues during neutron irradiation. We proposed to prepare a Gd delivery system by complexing a Gd-containing compound, diethylenetriaminepentaacetic acid (Gd-DTPA), with a polycationic peptide, poly-L-lysine (pLL), and then encapsulate the complexed Gd-DTPA into PEGylated liposomes. Complexation of Gd-DTPA with pLL not only enhanced the encapsulation efficiency of Gd-DTPA in liposomes, but also significantly limited the release of Gd-DTPA from the liposomes. A Gd-DTPA-encapsulated liposome formulation that contained 6.8+/-0.3 mg/mL of pure encapsulated Gd was prepared. The blood half-life of the Gd encapsulated into the liposome formulation was estimated to be about 24 h in healthy tumor-free mice. About 12 h after the Gd-encapsulated liposomes were intravenously injected into mice with pre-established model tumors, the Gd content in the tumors reached an average of 159 microg/g of wet tumor tissue. This Gd-DTPA encapsulated liposome may be used to deliver Gd into solid tumors for NCT and tumor imaging.

RBE of the MIT epithermal neutron beam for crypt cell regeneration in mice.

The RBE of the new MIT fission converter epithermal neutron capture therapy (NCT) beam has been determined using intestinal crypt regeneration in mice as the reference biological system. Female BALB/c mice were positioned separately at depths of 2.5 and 9.7 cm in a Lucite phantom where the measured total absorbed dose rates were 0.45 and 0.17 Gy/ min, respectively, and irradiated to the whole body with no boron present. The gamma-ray (low-LET) contributions to the total absorbed dose (low- + high-LET dose components) were 77% (2.5 cm) and 90% (9.7 cm), respectively. Control irradiations were performed with the same batch of animals using 6 MV photons at a dose rate of 0.83 Gy/min as the reference radiation. The data were consistent with there being a single RBE for each NCT beam relative to the reference 6 MV photon beam. Fitting the data according to the LQ model, the RBEs of the NCT beams were estimated as 1.50 +/- 0.04 and 1.03 +/- 0.03 at depths of 2.5 and 9.7 cm, respectively. An alternative parameterization of the LQ model considering the proportion of the high- and low-LET dose components yielded RBE values at a survival level corresponding to 20 crypts (16.7%) of 5.2 +/- 0.6 and 4.0 +/- 0.7 for the high-LET component (neutrons) at 2.5 and 9.7 cm, respectively. The two estimates are significantly different (P = 0.016). There was also some evidence to suggest that the shapes of the curves do differ somewhat for the different radiation sources. These discrepancies could be ascribed to differences in the mechanism of action, to dose-rate effects, or, more likely, to differential sampling of a more complex dose-response relationship.

Hybrid Calcium Phosphate-Polymeric Micelles Incorporating Gadolinium Chelates for Imaging-Guided Gadolinium Neutron Capture Tumor Therapy.

Gadolinium (Gd) chelates-loaded nanocarriers have high potential for achieving magnetic resonance imaging (MRI)-guided Gd neutron capture therapy (GdNCT) of tumors. Herein, we developed calcium phosphate micelles hybridized with PEG-polyanion block copolymers, and incorporated with the clinical MRI contrast agent Gd-diethylenetriaminepentaacetic acid (Gd-DTPA/CaP). The Gd-DTPA/CaP were nontoxic to cancer cells at the concentration of 100 µM based on Gd-DTPA, while over 50% of the cancer cells were killed by thermal neutron irradiation at this concentration. Moreover, the Gd-DTPA/CaP showed a dramatically increased accumulation of Gd-DTPA in tumors, leading to the selective contrast enhancement of tumor tissues for precise tumor location by MRI. The enhanced tumor-to-blood distribution ratio of Gd-DTPA/CaP resulted in the effective suppression of tumor growth without loss of body weight, indicating the potential of Gd-DTPA/CaP for safe cancer treatment.

Cellular uptake and in vitro antitumor efficacy of composite liposomes for neutron capture therapy.

BACKGROUND: Neutron capture therapy for glioblastoma has focused mainly on the use of (10)B as neutron capture isotope. However, (157)Gd offers several advantages over boron, such as higher cross section for thermal neutrons and the possibility to perform magnetic resonance imaging during neutron irradiation, thereby combining therapy and diagnostics. We have developed different liposomal formulations of gadolinium-DTPA (Magnevist®) for application in neutron capture therapy of glioblastoma. The formulations were characterized physicochemically and tested in vitro in a glioma cell model for their effectiveness. METHODS: Liposomes entrapping gadolinium-DTPA as neutron capture agent were manufactured via lipid/film-extrusion method and characterized with regard to size, entrapment efficiency and in vitro release. For neutron irradiation, F98 and LN229 glioma cells were incubated with the newly developed liposomes and subsequently irradiated at the thermal column of the TRIGA reactor in Mainz. The dose rate derived from neutron irradiation with (157)Gd as neutron capturing agent was calculated via Monte Carlo simulations and set in relation to the respective cell survival. RESULTS: The liposomal Gd-DTPA reduced cell survival of F98 and LN229 cells significantly. Differences in liposomal composition of the formulations led to distinctly different outcome in cell survival. The amount of cellular Gd was not at all times proportional to cell survival, indicating that intracellular deposition of formulated Gd has a major influence on cell survival. The majority of the dose contribution arises from photon cross irradiation compared to a very small Gd-related dose. CONCLUSIONS: Liposomal gadolinium formulations represent a promising approach for neutron capture therapy of glioblastoma cells. The liposome composition determines the uptake and the survival of cells following radiation, presumably due to different uptake pathways of liposomes and intracellular deposition of gadolinium-DTPA. Due to the small range of the Auger and conversion electrons produced in (157)Gd capture, the proximity of Gd-atoms to cellular DNA is a crucial factor for infliction of lethal damage. Furthermore, Gd-containing liposomes may be used as MRI contrast agents for diagnostic purposes and surveillance of tumor targeting, thus enabling a theranostic approach for tumor therapy.

Radiation-guided drug delivery to tumor blood vessels results in improved tumor growth delay.

Tumor blood vessels are biological targets for cancer therapy. In this study, a tumor vasculature targeting system that consisted of liposomes and lectin (WGA) was built. Liposomes were used to carry a number of liposome-friendly anti-tumoral agents along with WGA, a lectin which posseses a specific affinity for binding to inflamed endothelial cells. In order to target tumor vasculature, inflammation of endothelial cells was induced by radiation. Because ionizing radiation induces an inflammatory response in tumor vasculature, lectin-conjugates were utilized to determine whether radiation can be used to target drug delivery to tumor vessels. Wheat germ agglutinin (WGA) is one such lectin that binds to inflamed microvasculature. WGA was conjugated to liposomes containing cisplatin and administered to tumor bearing mice. Tumor growth delay was used to analyze the efficacy of cytotoxicity. FITC-conjugated WGA accumulated within irradiated tumor microvasculature. WGA was conjugated to liposomes and labeled with 111In. This demonstrated radiation-inducible tumor-selective binding. WGA-liposome-conjugates were loaded with Cisplatin and administered to mice bearing irradiated tumors. Tumors treated with a combination of liposome encapsulated cisplatin together with radiation showed a significant increase in tumor growth delay as compared to radiation alone. These findings demonstrate that ionizing radiation can be used to guide drug delivery to tumor microvasculature.

Measurements and calculations of thermal neutron fluence rate and neutron energy spectra resulting from moderation of 252Cf fast neutrons: applications for neutron capture therapy.

252Cf is a neutron emitting radioisotope which has promise for both standard brachytherapy and neutron capture enhanced brachytherapy. In this study, experimental measurements and calculations were used to determine the thermal neutron fluence rate, phi(th) [n cm(-2) s(-1) mg(-1)], in the vicinity of 252Cf applicator tube (AT) type sources. Results of these measurements were confirmed with Monte Carlo calculations performed in a distributed manner on multiple workstations using MCNP. Three studies were executed: (1) relative phi(th) as a function of distance from a 252Cf AT source in an A-150 tissue equivalent plastic phantom using thermoluminescent dosimeters (TLDs) of varying 6Li/Li enrichment, (2) phi(th) measured with gold foils in a 114 liter water phantom 5 cm from two 252Cf AT sources, and (3) calculations of the impact of phantom material composition (e.g., A-150, water, brain, muscle) on phi(th) from moderated 252Cf fast neutrons. TLD results and Monte Carlo calculations in A-150 of relative phi(th) typically agreed within 1% and at most differed by 3% for distances from 1 to 6 cm. Foil measurements followed the ASTM E 262-86e protocol, and the ratio of activated plain and Cd encased gold foils (7.31) agreed well with the calculated ratio (7.26). Measured phi(th) at 5 cm (1.70+/-0.10 x 10(7) n cm(-2) s(-1) mg(-1)) was 10% greater than that determined using MCNP (1.55+/-0.12 x 10(7) n cm(-2) s(-1) mg(-1)), but was within the combined uncertainties. Compared with A-150 at a distance of 1 cm, phi(th) was 20%, 22%, and 32% less for water, brain, and muscle, respectively; these ratios decreased to 16%, 16%, and 24% less, respectively, at a distance of 5 cm from the source in a 15 cm diameter phantom. Comparisons of these results generally agreed with those in the literature for a value of 2 x 10(7) n cm(-2) s(-1) mg(-1) in water at 3 cm.

The evaluation of nylon and polyethylene as build-up material in a neutron therapy beam.

In high-energy neutron beams a substantial amount of build-up material is required to irradiate biological samples under conditions of charged particle equilibrium. Ideally A-150 tissue-equivalent plastic is used for this purpose. This material is however not always readily available and hence the need for a substitute compound. The selected hydrocarbon should satisfy two requirements: the quality of the radiation on the distal side needs to be the same as that measured for A-150 plastic and the absorbed dose should remain consistent. A tissue-equivalent proportional counter operating at reduced pressure not only measures the absorbed dose accurately but provides a means for assessing the nature of a radiation field in terms of a secondary charged particle spectrum. Using build-up caps manufactured from nylon (type 6) and polyethylene, it is shown that the former is an acceptable substitute for A-150 plastic. The data further demonstrate that both the absorbed dose and the spectral character of the measured single-event distribution are altered when polyethylene is used and that these discrepancies are attributable to the higher hydrogen content of polyethylene.

Direct determination of kerma for a d(48.5) + Be therapy beam.

An experimental determination of the neutron kerma ratio between muscle tissue and A-150 plastic was performed at the newly commissioned d(48.5)+ Be therapy facility in Detroit. Low-pressure proportional counters with separate walls made from A-150 plastic, graphite, zirconium oxide and zirconium served to measure ionization yield spectra. The absorbed dose in the wall of each counter was determined and rendered the A-150 and carbon kerma directly, whilst that for oxygen was deduced from differences between the matched metal oxide and metal pair. This enabled the evaluation of an effective kerma ratio as a function of radiation field size and hydrogenous filtration. Although filtration was observed to harden the beam, the application of a single kerma ratio for the various irradiation conditions investigated was found to be appropriate. A neutron kerma ratio of 0.90+/-0.03 was assessed for the Detroit facility, which is lower at the 1sigma level than the 0.95 currently recommended in the dosimetry protocol for high-energy neutron beams.

In vitro cellular accumulation of gadolinium incorporated into chitosan nanoparticles designed for neutron-capture therapy of cancer.

The accumulation of gadolinium loaded as gadopentetic acid (Gd-DTPA) in chitosan nanoparticles (Gd-nanoCPs), which were designed for gadolinium neutron-capture therapy (Gd-NCT) for cancer, was evaluated in vitro in cultured cells. Using L929 fibroblast cells, the Gd accumulation for 12 h at 37 degrees C was investigated at Gd concentrations lower than 40 ppm. The accumulation leveled above 20 ppm and reached 18.0+/-2.7 (mean+/-S.D.) microg Gd/10(6) cells at 40 ppm. Furthermore, the corresponding accumulations in B16F10 melanoma cells and SCC-VII squamous cell carcinoma, which were used in the previous Gd-NCT trials in vivo, were 27.1+/-2.9 and 59.8+/-9.8 microg Gd/10(6) cells, respectively, hence explaining the superior growth-suppression in the in vivo trials using SCC-VII cells. The accumulation of Gd-nanoCPs in these cells was 100-200 times higher in comparison to dimeglumine gadopentetate aqueous solution (Magnevist), a magnetic resonance imaging contrast agent. The endocytic uptake of Gd-nanoCPs, strongly holding Gd-DTPA, was suggested from transmission electron microscopy and comparative studies at 4 degrees C and with the solution system. These findings indicated that Gd-nanoCPs had a high affinity to the cells, probably contributing to the long retention of Gd in tumor tissue and leading to the significant suppression of tumor growth in the in vivo studies that were previously reported.

Tumor growth suppression by gadolinium-neutron capture therapy using gadolinium-entrapped liposome as gadolinium delivery agent.

Neutron capture therapy (NCT) is a promising non-invasive cancer therapy approach and some recent NCT research has focused on using compounds containing gadolinium as an alternative to currently used boron-10 considering several advantages that gadolinium offers compared to those of boron. In this study, we evaluated gadolinium-entrapped liposome compound as neutron capture therapy agent by in vivo experiment on colon-26 tumor-bearing mice. Gadolinium compound were injected intravenously via tail vein and allowed to accumulate into tumor site. Tumor samples were taken for quantitative analysis by ICP-MS at 2, 12, and 24 h after gadolinium compound injection. Highest gadolinium concentration was observed at about 2 h after gadolinium compound injection with an average of 40.3 µg/g of wet tumor tissue. We performed neutron irradiation at JRR-4 reactor facility of Japan Atomic Energy Research Institute in Tokaimura with average neutron fluence of 2×10¹² n/cm². The experimental results showed that the tumor growth suppression of gadolinium-injected irradiated group was revealed until about four times higher compared to the control group, and no significant weight loss were observed after treatment suggesting low systemic toxicity of this compound. The gadolinium-entrapped liposome will become one of the candidates for Gd delivery system on NCT.

A thermo-sensitive polymeric gel containing a gadolinium (Gd) compound encapsulated into liposomes significantly extended the retention of the Gd in tumors.

Gadolinium neutron capture therapy (Gd-NCT) is a promising approach to fight cancer. One key factor for the success of Gd-NCT is to deliver and maintain a sufficient amount of Gd inside tumors. A large amount of Gd can be readily introduced into tumors by direct intratumor injection. However, an innovative approach is needed to maintain the Gd in the tumors. We encapsulated a Gd compound into a liposome formulation and then dispersed the liposomes into a thermo-sensitive polymeric gel. In murine tumor models, we showed that this liposome-in-thermo-sensitive gel system significantly extended the retention of the Gd compound in tumors. This similar concept may be applied to prolong the retention of other cytotoxic chemicals in tumors, and thus, improve their anti-tumor efficacy.

Design and preparation of ethyl cellulose microcapsules of gadopentetate dimeglumine for neutron-capture therapy using the Wurster process.

Microcapsules of hygroscopic, highly water-soluble gadopentetate dimeglumine (Gd-DTPA-DM) for use in preliminary in vivo experiments for neutron-capture therapy were designed. They were prepared with such properties as a particle size small enough to be suspended and injected through a syringe, a negligible release of Gd-DTPA-DM, and a high drug content by means of the Wurster process, a spray coating method using a spouted bed with a draft tube. They were composed of lactose cores of 53-63 microm, an undercoat of ethyl cellulose (EC) and polyvinylpyrrolidone (PVP), a drug-layer of Gd-DTPA-DM, EC and PVP, a waterproof coat and a release-sustaining overcoat of EC and cholesterol (1:1), and a surface treated with hydrogenated egg lecithin. By curing at 110 degrees C for 30 min after mixing with 20% pulverized mannitol powder, the 20% overcoating suppressed the release of Gd-DTPA-DM from 75-106 microm microcapsules to less than 10% for the first 20 min, which was the period required to prepare a suspension, inject it and irradiate the neutron. The microcapsules could be used to confirm that the intracellular presence of Gd is not critical in gadolinium neutron-capture therapy.

Folate receptor-mediated liposomal delivery of a lipophilic boron agent to tumor cells in vitro for neutron capture therapy.

PURPOSE: This study was aimed at the in vitro evaluations of folate receptor (FR)-targeted liposomes as carriers for a lipophilic boron agent, K[nido-7-CH3(CH2)15-7,8-C2B9H11, in FR-overexpressing tumor cells for neutron capture therapy. METHODS: Large unilamellar vesicles (-200 nm in diameter) were prepared with the composition of egg PC/chol/K[nido-7-CH3(CH2)15-7,8-C2B9H11] (2:2:1, mol/mol), with an additional 0.5 mol % of folate-PEG-DSPE or PEG-DSPE added for the FR-targeted or nontargeted liposomal formulations, respectively. RESULTS: Boron-containing, FR-targeted liposomes readily bound to KB cells, an FR-overexpressing cell line, and were internalized via FR-mediated endocytosis. The boron uptake in cells treated with these liposomes was approximately 10 times greater compared with those treated with control liposomes. In contrast, FR-targeted and nontargeted liposomes showed no difference in boron delivery efficiency in F98 cells, which do not express the FR. The subcellular distribution of the boron compound in KB cells treated with the FR-targeted liposomes was investigated by cellular fractionation experiments, which showed that most of the boron compound was found in either the cytosol/endosomal or cell membrane fractions, indicating efficient internalization of the liposomal boron. CONCLUSION: FR-targeted liposomes incorporating the lipophilic boron agent, K[nido-7-CH3(CH2)15-7,8-C2B9H11], into its bilayer were capable of specific receptor binding and receptor-mediated endocytosis in cultured KB cells. Such liposomes warrant further investigations for use in neutron capture therapy.