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PubMed2002

Molecular targeting of the epidermal growth factor receptor for neutron capture therapy of gliomas.

Success of boron neutron capture therapy (BNCT) is dependent on cellular and molecular targeting of sufficient amounts of boron-10 to sustain a lethal (10)B (n, alpha) (7)Li capture reaction. The purpose of the present study was to determine the efficacy of boronated epidermal growth factor (EGF) either alone or in combination with boronophenylalanine (BPA) as delivery agents for an epidermal growth factor receptor (EGFR) -positive glioma, designated F98(EGFR). A heavily boronated precision macromolecule [boronated starburst dendrimer (BSD)] was chemically linked to EGF by heterobifunctional reagents. Either F98 wild-type (F98(WT)) receptor (-) or EGFR gene-transfected F98(EGFR) cells, which expressed 5 x 10(5) receptor sites/cell, were stereotactically implanted into the brains of Fischer rats, and 2 weeks later biodistribution studies were initiated. For biodistribution studies rats received an intratumoral (i.t.) injection of (125)I-labeled BSD-EGF and were euthanized either 6 or 24 h later. At 6 h, equivalent amounts of BSD-EGF were detected in F98(EGFR) and F98(WT) tumors. Persistence of the bioconjugate in F98(EGFR) tumors was specifically determined by EGFR expression. By 24 h 33.2% of injected dose/g of EGF-BSD was retained by F98(EGFR) gliomas compared with 9.4% % of injected dose/g in F98(WT) gliomas, and the corresponding boron concentrations were 21.1 microg/g and 9.2 microg/g, respectively. Boron concentrations in normal brain, blood, liver, kidneys, and spleen all were at nondetectable levels (<0.5 microg/g). On the basis of these results, BNCT was initiated at the Brookhaven National Laboratory Medical Research Reactor. Two weeks after implantation of 10(3) F98(EGFR) or F98(WT) tumor cells, rats received an i.t. injection of BSD-EGF (approximately 60 microg (10)B/approximately 15 microg EGF) either alone or in combination with i.v. BPA (500 mg/kg). Rats were irradiated at the Brookhaven Medical Research Reactor 24 h after i.t. injection, which was timed to coincide with 2.5 h after i.v. injection of BPA for those animals that received both capture agents. Untreated control rats had a mean survival time (MST) +/- SE of 27 +/- 1 day, and irradiated controls had a MST of 31 +/- 1 day. Animals bearing F98(EGFR) gliomas, which had received i.t. BSD-EGF and BNCT, had a MST of 45 +/- 5 days compared with 33 +/- 2 days for animals bearing F98(WT) tumors (P = 0.0032), and rats that received i.t. BSD-EGF in combination with i.v. BPA had a MST of 57 +/- 8 days compared with 39 +/- 2 days for i.v. BPA alone (P = 0.016). Our data are the first to show in vivo efficacy of BNCT using a high molecular weight boronated bioconjugate to target amplified EGFR expressed on gliomas, and they provide a platform for the future development of combinations of high and low molecular weight agents for BNCT.

Animals↗
PubMedDate not supplied

Boron delivery to a murine lung carcinoma using folate receptor-targeted liposomes.

BACKGROUND: Folate receptor (FR) is amplified in a variety of human tumors. Folate-derived liposomes have been shown to selectively deliver entrapped agents into tumor cells via receptor-mediated endocytosis. In this preliminary study, the biodistribution of FR-targeted liposomes were evaluated as a potential delivery agent for Na3 (B20H17NH3) for boron neutron capture therapy (BNCT) of FR(+) tumors. MATERIALS AND METHODS: Na3 (B20H17NH3) was incorporated into liposomes by passive entrapment, following which they were administered intravenously into BALB/c mice bearing subcutaneous implants of FR(+) M109 murine lung carcinoma. Tumor and normal tissue boron content was measured by direct current plasma atomic emission spectroscopy. RESULTS: Mice that received FR-targeted and non-targeted control liposomes showed indistinguishable levels of tumor boron uptake (up to 85 microg/g tumor), which reached a maximum at the 24 hour time-point, while the tumor-to-blood (T/B) ratio continued to rise until the 72 hour time-point. CONCLUSION: High-level boron delivery is possible using liposomes as a delivery agent. FR targeting does not significantly enhance overall tumor localization but may improve boron delivery at the cellular and subcellular levels, which warrant further investigation.

Animals↗
PubMed2003

Introductory experiments on ligand liposomes as delivery agents for boron neutron capture therapy.

Liposomes are, when coupled to receptor ligands, candidates for receptor mediated delivery of boron for tumour therapy since they have capacity to deliver large amounts of boron per receptor interaction. With EGF-liposomes we present a pegylated ligand liposome delivery vehicle, containing water soluble boronated phenanthridine, WSP1, or water soluble boronated acridine, WSA1, for EGFR targeting. In the case of WSA1 a ligand dependent uptake was obtained and the boron uptake was as good as if free WSA1 was given. No ligand dependent boron uptake was seen for WSP1 containing liposomes. Thus, WSA1 is a candidate for further studies. Approximately 10(5) boron atoms were in each liposome. A critical assessment indicates that after optimization up to 10(6) boron atoms can be loaded. Since it is known that, for therapeutic effect, approximately 10(8)-10(9) boron atoms are needed in a single tumour cell it is realized that 10(2)-10(3) receptor interactions are needed to meet the demand. Tests applying cultured glioma cells indicate, without optimization of the delivery conditions, a boron uptake in the ppm range, which is necessary for successful BNCT. Thus, it seems possible to kill micro-invasive tumour cells with targeted liposomes if the delivery conditions are optimal.

Acridines↗
PubMed2003

Prognostic and therapeutic indicator of fluoroboronophenylalanine positron emission tomography in patients with gliomas.

PURPOSE: Boron neutron capture therapy (BNCT) for the treatment of brain tumors has attracted attention recently, and its clinical application has been progressing. We have focused on the use of BNCT with 10B-boronophenylalanine, which preferentially delivers boron-10 atoms to malignant cells through the amino acid transport system. In the present study, we evaluated the long-term outcomes of treatments using 18F-10B-fluoroboronophenylalanine (FBPA), which is an analogue of 10B-boronophenylalanine, by investigating the prognostic significance of the metabolic values and ratios of FBPA as determined by positron emission tomography (PET) in patients with gliomas. EXPERIMENTAL DESIGN: Our subjects were 22 patients who underwent an FBPA-PET study and were followed for at least 4 months thereafter. PET parameters, such as the rate constants K1, k2, k3, and k4, were measured before treatment. Data regarding the tumors, the contralateral normal region, and the uptake ratio of FBPA between the tumor and normal tissue 40 min after injection of the tracer were compared with survival rates after the PET treatment. The survival time and the prognostic factors were tested using a Kaplan-Meier survival curve and Cox regression analysis, respectively. RESULTS: Among the clinical parameters, the histological grade of a tumor influences survival significantly. When the survival of patients with PET parameters or ratios above the median was compared with that of patients with parameters or ratios below the median, the most significant PET parameter was the K1 value of the tumor. Median survival in patients with a tumor K1 value of 0.033 ml/min (median value) or higher was 11 months, which was significantly shorter than the 77 months in patients with a K1 value below the median (P=0.0006 by generalized Wilcoxon test). CONCLUSIONS: The kinetic constants of FBPA metabolism as determined by PET can be of ancillary significance in predicting the prognosis and indicating the feasibility of BNCT in patients with gliomas. The mean survival time was significantly shorter in patients with high uptakes of FBPA. A contributing factor is the K1 value, which reflects amino acid transport activity. FBPA-PET images can allow clinicians to develop treatment plans that are better tailored to the clinical features of their patients.

Adult↗
PubMed2004

Evaluation of 4-borono-2-18F-fluoro-L-phenylalanine-fructose as a probe for boron neutron capture therapy in a glioma-bearing rat model.

UNLABELLED: L-p-Boronophenylalanine (BPA) has been applied as a potential boron carrier for the treatment of malignant glioma in clinical boron neutron capture therapy (BNCT) since 1994. To provide the pharmacokinetics of BPA for clinical use of BNCT in Taiwan, 4-borono-2-(18)F-fluoro-L-phenylalanine-fructose ((18)F-FBPA-Fr) was synthesized and the biologic characteristics of this radiotracer in glioma-bearing rats were investigated. METHODS: Radiolabeled (18)F-F(2) was produced via the (20)Ne(d,alpha)(18)F reaction, and (18)F-acetyl hypofluorite ((18)F-AcOF) was generated by passing (18)F-F(2) through a column filled with tightly packed KOAc/HOAc powder. The effluent containing (18)F-AcOF was bubbled into BPA in trifluoroacetic acid, then purified by high-performance liquid chromatography, and further composited with fructose to afford (18)F-FBPA-Fr. Male Fischer 344 rats bearing F98 glioma in the left brain were used for biologic studies. The biodistribution of BPA-Fr and (18)F-FBPA-Fr was determined, and the microautoradiography and PET imaging of (18)F-FBPA-Fr were performed, on the 13th day after tumor inoculation. RESULTS: The radiochemical purity of (18)F-FBPA-Fr was >97% and the radiochemical yield of (18)F-FBPA-Fr was 20%-25%. In glioma-bearing rats, the accumulation ratios of B-10 for glioma-to-normal brain were 2.05, 1.86, 1.24, and 1.10 at 0.5, 1, 2, and 4 h, respectively, after administration of 43 mg BPA-Fr via the tail vein. The accumulation ratios of (18)F-FBPA-Fr for glioma-to-normal brain were 3.45, 3.13, 2.61, and 2.02, whereas the tumor-to-heart blood ratios were 1.72, 2.61, 2.00, and 1.93, respectively, for the same time points. The uptake characteristics of BPA-Fr and (18)F-FBPA-Fr in F98 glioma were similar with a maximum at 1 h after the drugs' administration. The results obtained from the biodistribution studies indicated that 0.5-1 h after BPA-Fr injection would be the optimal time for BNCT. Biodistribution, PET images, and brain microautoradiography of (18)F-FBPA-Fr all confirmed this finding. CONCLUSION: (18)F-FBPA-Fr showed specific tumor uptake in F98 glioma-bearing rats and could be used as a probe for BPA-Fr in BNCT. This study provides useful information for the future clinical application of BNCT in brain tumor therapy.

Animals↗
PubMed2005

Effect of filler loading on resin cement bonding to silanized buildup composites.

PURPOSE: To determine the effects of silanation for core buildup composites on bond strength of resin cement. METHODS: Three core buildup composites including FluoroCore LV, Core Restore, and Clearfil Photo Core, of which filler loadings were 65 wt%, 74 wt%, and 83 wt% respectively, were used. All composite specimens were randomly divided into four surface treatment groups of eight each as following; 1) 600-grit ground only, 2) 600-grit ground plus silanation, 3) 600-grit ground plus air-particle abrasion, 4) air-particle abrasion plus silanation. Following these treatments, 4-META/MMA-TBB resin (C&B Metabond) was bonded to the specimen surfaces. Completed specimens were stored in 37 degree C water for 24 hours, and then thermocycled 20,000 times (4 degree C - 60 degree C) before shear bond strengths were tested. Data were analyzed by two-way ANOVA and Scheffé's test for statistical significance (P < 0.05). RESULTS: Clearfil Photo Core, of which filler loading was the highest among the resin composites tested, treated with air-particle abrasion plus silanation obtained the highest bond strength. However, silanation alone was not effective for improving the bond strength.

Air Abrasion, Dental↗
PubMed1967

[Boron in nutrition].

Explore the source record for details and available documents.

Animal Nutritional Physiological Phenomena↗
PubMed1995

Effect of L-10B-p-boronophenylalanine-fructose and the boron neutron capture reaction on mouse brain dopaminergic neurons.

Radiation damage to the dopamine tracts caused by enriched L-10B-p-boronophenylalanine (L-10BPA)-fructose and the boron neutron capture reaction was investigated using the mouse model. Following various treatments with L-10BPA and neutron irradiation of the head, the brain was perfusion fixed and removed; 50-microns frozen sections were cut. Dopaminergic neurons were visualized using immunohistochemistry for tyrosine hydroxylase. The administration of L-10BPA had no permanent effect on dopaminergic tracts. Neutron capture therapy with L-10BPA caused a reduction in tyrosine hydroxylase immunohistochemical activity within 4 h of irradiation, but by 48 h, this reduction reversed. No damage was observed at 120 h postirradiation.

Animals↗
PubMed1994

Subcellular localization of p-boronophenylalanine-delivered boron-10 in the rat 9L gliosarcoma: cryogenic preparation in vitro and in vivo.

A well-characterized in vitro cryogenic preparation for ion microscopic isotope imaging, which minimizes redistribution of diffusible species, was used to determine the distribution of boron in GS-9L gliosarcoma cells incubated with the boron neutron capture therapy agent, p-boronophenylalanine (BPA). At the subcellular level, boron from BPA distributes relatively homogeneously within the glioma cell. Boron from BPA was eliminated rapidly, indicating that most is unbound. Thus a large pool of boron is susceptible to diffusion artifact. Removal of this artifact increases the degree of confidence in microdosimetric results inferred from the homogeneous subcellular distribution. The ion microscopic imaging of boron in subcutaneous tumors cryofixed in situ was achieved in rats treated with BPA. Boron signals from BPA were adequate to image microdistributions at the 1-micron resolution level. As in the in vitro case, boron did not localize discretely at the subcellular level. However, boron heterogeneity was seen at the tissue level. Physiologically valid cellular potassium and sodium levels were seen, which demonstrates minimized redistribution artifact. Future tissue studies designed to correlate ion microscopic boron images to microscopic structure are feasible using cryogenic sample preparation and ion microscopy.

Animals↗
PubMed1994

Preloading with L-tyrosine increases the uptake of boronophenylalanine in mouse melanoma cells.

To improve the effectiveness of boron neutron capture therapy, the possibility of stimulating boron uptake was investigated in an experimental model. B16F1 mouse melanoma cells were exposed to boronophenylalanine (BPA). The intracellular boron concentration followed Michaelis-Menten kinetics in the early incubation phase. In the late phase, cellular boron concentration was linearly related to the BPA concentration in the culture medium. Incubation with L-tyrosine before exposure to BPA (preloading) increased the intracellular boron concentration by a factor of three. It is concluded that in B16F1 cells BPA is transported by L and presumably ASC (alanine, serine, and cysteine) transport systems, and that boron uptake can be effectively stimulated by L-tyrosine preloading.

Animals↗
PubMed1993

Boron neutron capture therapy of intracerebral melanoma using boronophenylalanine as a capture agent.

A rat brain tumor model has been developed utilizing nude rats and the human melanoma cell line MRA 27. For pharmacokinetic and tissue distribution studies, 2 10(5) MRA 27 cells were implanted intracerebrally (i.c.), and 30 days later, 120 mg of 10B-enriched L-boronophenylalanine were injected i.p. into nude rats. 10B concentrations in the tumor, blood, and normal brain were 23.7, 9.4, and 8.4 micrograms/g, respectively, 6 h following administration. For therapy experiments, tumor bearing rats were irradiated at the Brookhaven Medical Research Reactor 30 days following implantation. The median survival time was 44 days for untreated rats, 76 days for those receiving a physical dose of 2.7 Gy, and 93 days for those receiving 3.6 Gy. Animals receiving both 10B-L-boronophenylalanine and physical doses of 1.8, 2.7, or 3.6 Gy (total tumor physical doses of 5.0, 7.5, or 10.1 Gy) had median survival times of 170, 182, and 262 days, respectively. Forty % of rats that received the highest tumor dose (10.1 Gy) survived > 300 days. In a replicate experiment 21% of animals that had received L-boronophenylalanine and irradiation (total tumor physical dose of 10.1 Gy) were alive 220 days after therapy. In a parallel study, animals that were irradiated with gamma photons from a 137Cs source with 12 Gy or 2.0 Gy 9 delivered to the head had median survival times of 86 and 79 days, respectively, compared to 47 days for untreated animals. Our results indicate that boron neutron capture therapy is effective against i.c. melanoma in a rodent model and suggest that large animal studies are warranted to further assess its efficacy.

Animals↗
PubMed1996

Hydroxylforms of p-boronophenylalanine as potential boron carriers on boron neutron capture therapy for malignant brain tumors.

Hydroxylforms of boronophenylalanine (BPA) were synthesized by conjugation with a cascade of polyols to decrease the BPA uptake of normal parenchyma without affecting uptake into the tumor. We determined their tumor cell killing effect on boron neutron capture therapy (BNCT) against BPA using the human glioma cell line T98G. The thermal neutron doses yielding the D37 (dose used to inhibit 63% colony formation) values of dl-p-BPA(OH)n were 1.45 x 10(12)nvt (n = 1), 1.33 x 10(12)nvt (n = 2), 3.37 x 10(12)nvt (n = 4), and 1.72 x 10(12)nvt (n = 0). The relative tumor cell killing effect on BNCT of dl-p-BPA(OH)n against dl-p-BPA, which was defined as the ratio of D37-BPA to D37-BPA(OH)n, was 1.18 (n = 1) 1.29 (n = 2), and 0.51 (n = 4). The tumor:normal brain ratio of dl-p-BPA(OH)n in 9L rat brain tumor models was improved 1.2- (n = 1) and 1.4-fold (n = 2) against that of dl-p-BPA without a decrease of its uptake into the tumor. The water solubility of BPA(OH)n increased against BPA, and the toxicity represented as the IC50 value of dl-p-BPA(OH)2 was nearly one half that of dl-p-BPA, being established in our previous works. Hydroxylforms of BPA, especially dl-p-BPA(OH)2, might be more suitable boron carriers of BNCT to malignant brain tumors since the radiation injury to the normal parenchyma surrounding the tumor is reduced.

Animals↗
PubMed1996

Accumulation of boron in malignant and normal cells incubated in vitro with boronophenylalanine, mercaptoborane or boric acid.

The short (< 10 microns) ranges of alpha and 7Li particles produced during boron neutron capture therapy (BNCT) make the partitioning of the boronated drug within and without the cell of critical importance. The evaluation of the potential usefulness of a boron-containing substance for BNCT requires information about its intracellular accumulation. In the present report, an in vitro method is described for direct measurement of intracellular boron based on rapid centrifugation of cells through a layer of mineral oil and silicon oil to strip away extracellular growth medium. The intracellular concentrations of boronophenylalanine (BPA), mercaptoborane (BSH) and horic acid in malignant cells and in normal cells have been compared. The accumulation ratio is defined as the ratio of the intracellular to the extracellular boron concentration. Boric acid showed an accumulation ratio of 1 while the ratios for BSH and BPA were dependent on cell type and tended to be greater for BPA than for BSH in malignant but not in normal cells.

Animals↗
PubMed1997

Evaluation of fluorine-18-BPA-fructose for boron neutron capture treatment planning.

UNLABELLED: Boron neutron capture therapy (BNCT) using 4-[10B]boronophenylalanine-fructose (BPA-Fr) is in Phase II clinical trials to validate BNCT as a treatment for glioblastoma multiforme and melanoma. Successful BNCT depends on knowledge of the distribution of boron-containing agents in both tumor and normal tissue as currently determined by chemical confirmation of boron deposition in surgically removed malignant tissue before BNCT. METHODS: We used PET to noninvasively obtain in vivo information on the pharmacokinetics of the 18F-labeled analog of BPA-Fr in two patients with glioblastoma multiforme. Time-activity curves generated from the bolus injection of 18F-BPA-Fr were coinvolved to simulate a continuous infusion used for BNCT therapy. RESULTS: Distribution of 18F-BPA-Fr by PET was found to be consistent with tumor as identified by MR imaging. The 18F-BPA-Fr tumor-to-normal brain uptake ratio was 1.9 in Patient 1 and 3.1 in Patient 2 at 52 min after injection. The 18F-BPA-Fr uptake ratio in glioblastoma paralleled that of nonlabeled BPA-Fr seen in patients as previously determined by boron analysis of human glioblastoma tissue obtained from pre-BNCT surgical biopsy. CONCLUSION: Knowledge of the biodistribution of BPA-Fr enables pre-BNCT calculation of expected tissue dosimetry for a selected dose of BPA-Fr at a specific neutron exposure. Fluorine-18-BPA-Fr PET is capable of providing in vivo BPA-Fr biodistribution data that may prove valuable for patient selection and pre-BNCT treatment planning.

Boron Compounds↗
PubMed1998

Biodistribution of boronophenylalanine in patients with glioblastoma multiforme: boron concentration correlates with tumor cellularity.

Boron-10 (10B) concentrations were measured in 107 surgical samples from 15 patients with glioblastoma multiforme who were infused with 95 atom% 10B-enriched p-boronophenylalanine (BPA) intravenously for 2 h just prior to surgery at doses ranging from 98 to 290 mg BPA/kg body weight. The blood 10B concentration reached a maximum at the end of the infusion (ranging from 9.3 to 26.0 microg 10B/g) and was proportional to the amount of BPA infused. The boron concentrations in excised tumor samples ranged from 2.7 to 41.3 microg 10B/g over the range of administered BPA doses and varied considerably among multiple samples from individual patients and among patients at the same BPA dose. A morphometric index of the density of viable-appearing tumor cells in histological sections obtained from samples adjacent to, and macroscopically similar to, the tumor samples used for boron analysis correlated linearly with the boron concentrations. From that correlation it is estimated that 10B concentrations in glioblastoma tumor cells were over four times greater than concurrent blood 10B concentrations. Thus, in the dose range of 98 to 290 mg BPA/kg, the accumulation of boron in tumor cells is a linear function of BPA dose and the variations observed in boron concentrations of tumor specimens obtained surgically are largely due to differences in the proportion of nontumor tissue (i.e. necrotic tissue, normal brain) present in the samples submitted for boron analysis. The tumor:blood 10B concentration ratio derived from this analysis provides a rationale for estimating the fraction of the radiation dose to viable tumor cells resulting from the boron neutron capture reaction based on measured boron concentrations in the blood at the time of BNCT without the need for analysis of tumor samples from individual patients.

Boron↗
PubMed1998

Positron emission tomography-based boron neutron capture therapy using boronophenylalanine for high-grade gliomas: part I.

Determination of tumor boron-10 (10B) levels is required for accurate neutron dosimetry during boron neutron capture therapy. We assessed a new method for quantitative measurement of boronated drug uptake in high-grade gliomas. This method uses positron emission tomography (PET) with fluorine-18-labeled L-fluoroborono-phenylalanine (L-18F-10B-FBPA), which was synthesized as an analogue of L-boronophenylalanine. We studied the accumulation of L-18F-10B-FBPA by PET in patients with high-grade gliomas. Dynamic PET studies of brain tumors revealed that L-18F-10B-FBPA accumulated gradually after bolus injection, and the value of PET activity divided by the integrated plasma activity reached a constant level 42 min after injection, which was defined as the incorporation constant (Ic*). This constant reflected the appropriate L-18F-10B-FBPA accumulation in tumor tissue. Based on the Ic* constant, the methods for estimating tumor 10B concentration were devised. With this method, the estimated values of 10B concentration in gliomas were very close to the 10B levels in surgical specimens. This method was based solely on PET and can potentially provide data that would assist in the selection of patients for future treatment with boron neutron capture therapy after surgical resection of their brain tumors.

Boron↗