Antitumor properties of boron complexes with hydroxy biguanide and salicyl hydroxamic acid against Ehrlich ascites carcinoma

A new derivative of hydroxamic acid, hydroxy biguanido hydrochloride monohydrate and its boron derivative, dihydroxy-oxybiguanido boron (III) hydrochloride monohydrate were synthesized. Another boron compound, hydroxo-salicyl-hydroxamato boron (III) was synthesized from known salicyl hydroxamic acid. Antitumor properties of all the compounds evaluated against Ehrlich ascites carcinoma in mice show enhanced survival time when boron is incorporated in the compounds. Hematological parameters, alkaline phosphatase in serum of the treated animals show minimum toxic effects after boron is coupled with their respective hydroxamic acids.

Substituted carboranes and polyhedral hydroborate salts as anti-neoplastics

Substituted carboranes and polyhedral hydroborate salts were observed to be potent anti-neoplastic/cytotoxic agents inhibiting the growth of mouse and human leukemias, human uterine, colon adenocarcinoma, lung bronchogenic and gliomas. Amino-o-carborane-hydrochloride 7, one of the more potent compounds, preferentially inhibited Tmolt3 DNA synthesis. The target of the agent appears to be de novo purine synthesis with significant inhibition of the activities of both regulatory enzymes, PRPP-amido transferase and inosine monophosphate dehydrogenase as well as dihydrofolate reductase. The agent also inhibited nucleoside kinase activities leading to reductions in deoxyribonucleotide pools. The DNA molecule itself was not a target of the agent.

Evaluation of carborane-containing porphyrins as tumour targeting agents for boron neutron capture therapy

A number of carborane-containing porphyrins were administered to mice bearing subcutaneously transplanted mammary carcinomas. Administration was via serial intraperitoneal (i.p.) injections to assess their relative toxicities and tumour affinities. Three analogues of the natural porphyrin heme and four tetraphenylporphyrins (TPPs) were given at total doses of 78-245 micrograms g-1 body weight. The water-insoluble TPPs were less toxic to mice, and delivered greater amounts of boron to tumour than did the water-soluble TPPS and the heme analogues. One such compound, NiTCP-H, delivered more than 100 micrograms B g-1 to tumour tissue with a tumour:blood boron concentration ratio greater than 500:1 and a tumour: brain boron concentration ratio greater than 50:1, 4 days after the last of six i.p. injections given over 2 days. Another TPP analogue, NiTCP, delivered approximately 50 micrograms B g-1 to tumour with similar boron concentrations in normal tissues. Neither compound was toxic to mice at total doses of approximately 200 micrograms g-1 body weight. In contrast, the heme analogues were toxic and, with the exception of VCDP, delivered less boron to tumour than NiTCP and NiTCP-H. The two porphyrins with the greatest potential for application to boron neutron capture therapy (BNCT), NiTCP and NiTCP-H, yielded higher tumour:blood and tumour:brain boron concentration ratios in mice than could be achieved with p-boronophenylalanine (BPA) and sodium mercaptoundecahydrododecaborate (BSH), the compounds which are currently being used in clinical trials of BNCT in the treatment of glioblastoma. The boron delivered by each of the porphyrins tested remained in tumour tissue longer than did boron delivered by either BPA or BSH. The copper and nickel chelates of these porphyrins behave identically in vivo. The former offer the potential for imaging by 67Cu-mediated single photon emission computed tomography (SPECT) to aid BNCT treatment planning.

Specific inhibition of plasma kallikrein modulates chronic granulomatous intestinal and systemic inflammation in genetically susceptible rats

The kallikrein-kinin (K-K) (contact) system is activated during acute and chronic relapsing phases of enterocolitis induced in genetically susceptible Lewis rats by intramural injection of peptidoglycan-polysaccharide (PG-APS). Using the selective plasma kallikrein inhibitor P8720, we investigate whether activation of the K-K system plays a primary role in chronic granulomatous intestinal and systemic inflammation in this model. Group I (negative control) received human serum albumin intramurally. Group II (treatment) received PG-APS intramurally and P8720 orally. Group III (positive control) received PG-APS intramurally and albumin orally. P8720 attenuated the consumption of the contact proteins, high molecular weight kininogen (P<0.03), and factor XI (P<0.04) in group II vs. group III. P8720 decreased chronic intestinal inflammation measured by blinded gross (P<0.01) and histologic (P<0.0005) scores as well as systemic complications (arthritis, splenomegaly, hepatomegaly, leukocytosis, and acute-phase reaction) (P<0.01) in group II as compared with group III. We conclude that relapsing chronic enterocolitis and systemic complications are in part due to plasma K-K system activation, and that inhibition of this pathway is a potential therapeutic approach to human inflammatory bowel disease and associated extraintestinal manifestations.

General, reproductive, developmental, and endocrine toxicity of boronated compounds

Boric acid and inorganic borates are abundant in nature. They are widely used in industrial, agricultural, cosmetic, and numerous smaller applications. These compounds are toxic to all species tested at high doses, but they are not carcinogenic or mutagenic. The major toxicities are reproductive and developmental. Testicular effects occurred at approximately 26 mg boron equivalents/kg body weight (bw)/d (26 mg boron equivalent (BE)/kg bw/d). New data on endocrine toxicity includes altered follicle stimulating hormone and testosterone within 14 d of treatment. Because these hormonal changes may be secondary effects of testicular toxicity, borates are not suspect as endocrine disrupters. The most sensitive of all the endpoints are prenatal growth and morphologic development in the rat; these changes occurred at a dose of 12.9 mg BE/kg bw/d. The no observed adverse effect level for rat fetal development was 9.6 mg/kg BE. Considering the estimated human exposure levels and a safety factor of 30, humans are not at significant risk of reproductive failure due to borates from environmental sources. The margin of exposure is estimated at 72 for males and 129 for females. Thus, the likelihood of human toxicity caused by boric acid and inorganic borates from exposure during normal activities is remote.

Synthesis of carboranes containing an azulene framework and in vitro evaluation as boron carriers

3-(o-Carboranylhydroxymethyl)-7-isopropylazulene sodium carboxylate (1) and 3-(o-carboranylmethyl)-7-isopropylazulene sodium sulfonate (2) were synthesized from the palladium-catalyzed addition reaction of 1-carboranyltributylstannane (4) to azulene aldehydes (3 and 9). Although the water solubility of 1 was of the order of 10(-6) M, that of 2 was of the order of 10(-3) M and was enough for clinical use. The cytotoxicity of 1 (IC50) toward B-16 melanoma cells was of the order of 10(-5) M, whereas that of 2 was of the order of 10(-4) M. This value was close to that of BPA (approximately 9 x 10(-3) M) which is utilized for clinical use. The boron uptake by B-16 cells was 0.17 microgram of B/10(6) cells for 1 and 0.25 microgram of B/10(6) cells for 2. It is clear that compound 2 accumulates in B-16 melanoma cells with a significantly high level although it is highly water soluble and its cytotoxicity is significantly low.

A review: CNS effects and normal tissue tolerance in dogs

Large animal studies have been utilized to define tolerance of normal brain to irradiation and verify treatment planning programs with two recently installed epithermal neutron beams. The normal brain tolerance studies utilized two biological endpoints, magnetic resonance visible damage only and neurologic signs progressing to death. The studies focused on defining the proton RBE for the contaminant fast neutrons, and from nitrogen capture of thermal neutrons and boron capture reaction biologic effect. The proton RBE was approximately 3.0 to 6.7, depending on whether a dose reduction factor for the low gamma dose rate was employed. The microscopic distribution of the boron compounds, coupled with the extremely short length of the fission fragments from thermal neutron capture by 10B yields an observed biologic effect much less than would be expected from such high LET irradiation. This observed biologic effect, which is a product of the microdistribution of the boron atom and the relative biologic effect of the fission fragments has been termed compound factor. The compound factor was based on the calculated physical dose from the fission fragment in blood based on measured blood 10B concentration. The approximate compound factor for BSH was studied at the two institutions and it ranged from 0.27 to 0.55, depending on the site and the endpoint chosen. The mean compound factor for BPA was only studied at one site and was found to be 1.1 for both endpoints. The increase in the compound factor for BPA is in keeping with previous calculations based on the differences in compound distribution. Results of these studies has helped the initiation of phase I and phase II clinical trials at Brook haven National Laboratory and the planned European clinical trials at Petten, The Netherlands.

Enhanced survival of glioma bearing rats following boron neutron capture therapy with blood-brain barrier disruption and intracarotid injection of boronophenylalanine

Boronophenylalanine (BPA) has been used for boron neutron capture therapy (BNCT) of brain tumors in both experimental animals and humans. The purpose of the present study was to determine if the efficacy of BNCT could be enhanced by means of intracarotid (i.c.) injection of BPA with or without blood-brain barrier disruption (BBB-D) and neutron irradiation using a rat brain tumor model. For biodistribution studies, F98 glioma cells were implanted stereotactically into the brains of Fischer rats, and 12 days later BBB-D was carried out by i.c. infusion of 25% mannitol (1.373 mOsmol/ml), followed immediately by i.c. administration of 300, 500 or 800 mg of BPA/kg body weight (b.w.). At the 500 mg dose a fourfold increase in tumor boron concentration (94.5 micrograms/g) was seen at 2.5 hours after BBB-D. compared to 20.8 micrograms/g in i.v. injected animals. The best composite tumor to normal tissue ratios were observed at 2.5 hours after BBB-D, at which time the tumor: blood (T: Bl) ratio was 10.9, and the tumor: brain (T:Br) ratio was 7.5, compared to 3.2 and 5.0 respectively for i.v. injected rats. In contrast, animals that had received i.c. BPA without BBB-D had T : Bl and T:Br ratios of 8.5 and 5.9, respectively, and the tumor boron concentration was 42.7 micrograms/g. For therapy experiments, initiated 14 days after intracerebral implantation of F98 glioma cells, 500 mg/kg b.w. of BPA were administered i.v. or i.c. with or without BBB-D, and the animals were irradiated 2.5 hours later at the Brook-haven Medical Research Reactor with a collimated beam of thermal neutrons delivered to the head. The mean survival time for untreated control rats was 24 +/- 3 days, 30 +/- 2 days for irradiate controls, 37 +/- 3 days for those receiving i.v. BPA, 52 +/- 15 days for rats receiving i.c. BPA without BBB-D, and 95 +/- 95 days for BBB-D followed by i.c. BPA and BNCT. The latter group had a 246% increase in life span (ILS) compared to untreated controls and a 124% ILS compared to that of i.v. injected animals. These survival data are the best ever obtained with the F98 glioma model and suggest that i.c. administration of BPA with or without BBB-D may be useful as a means to increase the efficacy of BNCT.

Mitochondria are the functional intracellular target for a photosensitizing boronated porphyrin

A photosensitizing boron-containing porphyrin derivative denoted BOPP, which is selectively localised into mitochondria, has been tested on Namalwa cells, in each of two genetic configurations: rho+ cells containing normal mtDNA and mitochondrial respiratory functions, or rho0 cells lacking mtDNA and devoid of mitochondrial oxidative phosphorylation. After short-term cellular uptake for 18 h, BOPP (30 micrograms/ml) was not cytotoxic, but did show marked phototoxicity in Namalwa rho+ cells, concomitant with substantial reduction of mitochondrial respiratory activity. After long-term (3 days or more) exposure to BOPP without light, growth of Namalwa rho+ cells was inhibited at concentrations significantly above 30 micrograms/ml. At such concentrations BOPP was shown to have direct inhibitory effects on mitochondrial azide-sensitive respiration of p+ cells. By contrast, BOPP showed neither cytotoxic nor phototoxic effects in rho0 cells. These results indicate functional mitochondria to be a major cellular target in vivo after BOPP uptake and photoactivation.

Selective tumor kill of cerebral glioma by photodynamic therapy using a boronated porphyrin photosensitizer

The prognosis for patients with the high-grade cerebral glioma glioblastoma multiforme is poor. The median survival for primary tumors is < 12 months, with most recurring at the site of the original tumor, indicating that a more aggressive local therapy is required to eradicate the unresectable "nests" of tumor cells invading into adjacent brain. Two adjuvant therapies with the potential to destroy these cells are porphyrin-sensitized photodynamic therapy (PDT) and boron-sensitized boron neutron capture therapy (BNCT). The ability of a boronated porphyrin, 2,4-(alpha, beta-dihydroxyethyl) deuteroporphyrin IX tetrakiscarborane carboxylate ester (BOPP), to act as a photosensitizing agent was investigated in vitro with the C6 rat glioma cell line and in vivo with C6 cells grown as an intracerebral tumor after implantation into Wistar rats. These studies determined the doses of BOPP and light required to achieve maximal cell kill in vitro and selective tumor kill in vivo. The data show that BOPP is more dose effective in vivo by a factor of 10 than the current clinically used photosensitizer hematoporphyrin derivative and suggest that BOPP may have potential as a dual PDT/BNCT sensitizer.

A histopathological study of direct pulp capping with adhesive resins

This study evaluated the histological pulp responses of four different adhesive resin systems placed directly on exposed pulp tissue. Gap formation between the respective resin and cavity walls was observed and correlated to the pulpal response. Occlusal cavity preparations creating mechanical pulp exposures were prepared in molars of wistar rats. Preparations were filled using one of the following resin systems: 1) Superbond C&B system, 2) Clearfil Liner Bond system, 3) Tokuso Light Bond system, and 4) Scotchbond Multi-Purpose One All system. Although there were no significant differences in the pulpal responses after 3 days, significant differences were observed after 7 days. Results showed that the Superbond C&B system induced only a slight initial reaction, while secondary dentin was observed at the 30-day postoperative evaluation period. The Clearfil Liner Bond system showed a slight initial reaction to the materials, but exhibited slight pulpal necrosis and formation of secondary dentin at the 90-day evaluation period. The Tokuso Light Bond and One All systems showed severe pulpal reactions at all evaluation periods with no formation of secondary dentin. Microleakage formation correlated with the histopathological responses. Superbond C&B exhibited no microleakage, and only slight microleakage was observed when the Clearfil Bond system was used. The Tokuso and One All systems exhibited a wide area of microleakage. Further in vivo study evaluating the clinical use of adhesive resins for pulp capping is necessary to determine which resin systems may be used for direct pulp capping without incurring severe damage to pulpal tissue.

Evaluation of in vitro cytotoxicity of carboranyl amino acids, their chemical precursors and nido carboranyl amino acids for boron neutron capture therapy

The purpose of the present study was to define the in vitro cellular toxicity of three carborane-containing amino acids: p-(o-carboran-yl)-phenylalanine (CBPA), O-(o-carboran-1-ylmethyl)-tyrosine (CBT), and o-carboranylalanine (CBA), which are analogues of phenylalanine, tyrosine, and alanine respectively. In addition, two of their chemical precursors: CBACN (B10H11C2-CH2CHNH2CN) and CBTCN (B10H11C2-CH2OC6H4CH2CHNH2CN) and nido CBA were evaluated for their toxicity on human MRA 27 melanoma cells. Hydroxypropyl-beta-cyclodextrin (beta-CD) initially was used to solubilize all the compounds except nido CBA in the toxicity assays Cells were incubated with the test compounds at varying concentrations for 24 hrs, following which the proliferative activity of surviving cells was determined by pulsing with tritiated thymidine ([3H]-TdR) for an additional 18 hrs. CBT at a concentration of 280 micrograms/ml was non-toxic when solubilized with beta-CD. CBA at a concentration of 350 micrograms/ml was non-toxic when solubilized with beta-CD, but when solubilized with DMSO produced a 50% reduction in uptake of [3H]-TdR at a concentration of 75 micrograms/ml. CBPA, solubilized with beta-CD, was nontoxic at a concentration of 400 micrograms/ml, while CBTCN and CBACN at concentrations of 50 micrograms/ml and 40 micrograms/ml, respectively, were both toxic, even when solubilized with beta-CD. Nido CBA at a concentration of 400 micrograms/ml in medium was non-toxic. Although the toxicity of these boron compounds precludes their use as capture agents for Neutron Capture Therapy, they may have some potential for cytoreductive chemotherapy of cancer, and further evaluation may be warranted.

The cytotoxicity of 3'-aminocyanoborane-2', 3'-dideoxypyrimidines in murine and human tissue cultured cell lines

3'-Aminocyanoborane-2', 3'-dideoxythymidine (VIIa) and 3'-aminocyanoborane-2', 3'-dideoxyuridine (VIIIb) were successfully synthesized. The thymidine derivative (VIIIa) was shown to be a potent cytotoxic agent in murine and selected human suspended and solid tumor cell lines. Compound VIIIa inhibited L-1210 leukemia DNA and RNA synthesis with the protein synthesis requiring a higher concentration of drug for inhibition within 60 min. The purine pathway appeared to be the major target of Compound VIIIa with inhibition of IMP dehydrogenase and dihydrofolate reductase activities. The compound affected metabolic enzyme activities in the pyrimidine pathway as well as the nucleoside kinase activities. The DNA molecule did not appear to be target of the 3'-aminocyanoborane-2', 3'-dideoxythymidine (VIIIa), in that there was no change in ct-DNA viscosity, thermal denaturation or absorption of nucleosides of DNA nor was there any L-1210 DNA strand scission or inhibition of L-1210 DNA topoisomerase II activity when compound VIIIa was incubated at 100 microM.

Anti-inflammatory activity of amine-carboxyboranes in rodents

Amine-carboxyboranes are potent anti-inflammatory agents reducing induced edema and pleural effusion at 8 mg/Kg, i.p. They protect against LPS (Salmonella) induced septic shock from 2-8 mg/Kg/day and are effective in blocking pain mediated both locally and centrally. The mode of action of these agents is by blocking release of cytokines from macrophages, thus reducing lysosomal hydrolytic and proteolytic enzyme activities of affected cells. The agents also reduce prostaglandin and leukotriene synthesis by blocking the activities of regulatory enzymes of the respective pathways.

Oral toxicity of boric acid and other boron compounds to immature cat fleas (Siphonaptera: Pulicidae)

Oral toxicity was characterized in first-instar cat fleas, Ctenocephalides felis felis (Bouché), feeding on dried blood treated with boric acid. LC50 values ranged from 2.11% after 24 h to 0.21% after 7 d. In carpet tests with five different boron compounds and a number of different formulations, significant mortality for first instars was observed in all cases. In similar tests with prepupae and cocoons, there was no significant effect on mortality. The importance of these results is discussed in light of current application procedures for boron compounds, and suggestions are made for future research.

Synthesis and biological properties of 5-o-carboranyl-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil

A novel 5-o-carboranyl-containing nucleoside, 5-o-carboranyl-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil (6, CFAU), was synthesized as a potential intracellular neutron capture agent. This compound was prepared in five steps starting from 5-iodo-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil (1). The desired carboranyl derivative was obtained by addition of decaborane [as the bis(propionitrile) adduct] to the protected acetylenic nucleoside precursor followed by debenzoylation. The synthesis of CFAU was also performed by glycosylation of the suitably protected 5-o-carboranyluracil with the appropriate 2-fluoroarabinosyl derivative. This compound was evaluated for its cytotoxicity in human lymphocytes, monkey cells, and rat and human gliomas cells, as well as for antiviral activity against human immunodeficiency virus and herpes simplex virus type 1. Its biological activity was compared to 5-o-carboranyl-1-(2-deoxyribofuranosyl)uracil in these cell culture systems, human bone marrow cells, and mice. The results obtained to date suggest that CFAU has suitable characteristics as a sensitizer for boron neutron capture therapy.

Cytotoxicity of ribo-and arabinoside boron nucleosides in tissue culture cells

Ribose and arabinoside boron nucleoside derivatives were shown to be potent cytotoxic agents in murine and human suspended and solid tumor cell lines. The arabinoside derivative inhibited DNA and RNA synthesis with the protein synthesis requiring a higher concentration of drug for inhibition within 60 min. The purine pathway appeared to be the major target of the arabinoside 1 with inhibition of PRPP amido transferase and IMP dehydrogenase activities. Blockage of this pathway afforded reductions of deoxyadenosine and deoxyguanosine nucleotide pools. The DNA template did not appear to be target of the arabinoside 1, in that there was no change in DNA viscosity, thermal denaturation or absorption of nucleosides of DNA. However, compound 1 when incubated with L-1210 cells for 24 hr. showed a slight shift of the DNA in the gradient and moderate inhibition of ct-DNA topoisomerase II was demonstrated by 1 in vitro.

Synthesis, cytotoxicity, hypolipidemic and anti-inflammatory activities of amine-boranes and esters of boron analogues of choline and thiocholine

Boron analogues of carbamoylcholine and thiocholine and esters of these analogues were prepared. These compounds were fairly stable toward hydrolysis and demonstrated moderate anti-inflammatory and hypolipidemic activities in mice. The hypolipidemic activity of the compounds at a dose of 8 mg/kg/day was equivalent in reducing lipid levels in serum to those of clofibrate at 150 mg/kg/day and lovastatin at 8 mg/kg/day. The compounds demonstrated significant cytotoxic activity against the growth of murine and human tumor cells; all were active against the growth of human HeLa-S3 uterine suspended cells, and some were active against murine L1210 lymphoid leukemia, human Tmolt3 leukemia cells, colorectal adenocarcinoma, KB nasopharynx, osteosarcoma, and glioma. These studies demonstrated that antimetabolite analogues of acetylcholine exhibit the same types of pharmacological activity as other boron-substituted betaine and amino acids. Furthermore, a strong positive correlation exists between hypolipidemic activity and cytotoxicity for these new choline derivatives, as has previously been demonstrated for other boron-containing amino acids, amides, esters, and peptides.

Biodistribution and toxicity of 2,4-divinyl-nido-o-carboranyldeuteroporphyrin IX in mice

BALB/c mice with transplanted subcutaneous KHJJ mammary carcinomas were given 2,4-divinyl-nido-o-carboranyldeuteroporphyrin IX (VCDP), a prospective boron carrier for boron neutron-capture therapy, to determine the dose schedule that results in maximal boron uptake in tumor. A total dose of 270 +/- 10 micrograms/g body weight given in a 4-day multiple intraperitoneal injection schedule (3/day) resulted in 30-50 micrograms boron/g tumor. After such a dose, thrombocytopenia, granulocytosis and altered liver enzyme levels were measured in the blood. Blood boron clearance was followed for an 18 hr to 6 day post-injection period. Toxic effects of VCDP subsided within 4-6 days after the last injection. In view of the greater than 30 micrograms/g peak accumulation of boron in tumor from VCDP and the subsequent rapid reversal of VCDP toxicity, further studies of VCDP in small mammals relevant to its distribution, toxicity and potential clinical use for neutron-capture therapy of tumors appear warranted.

Acute toxicity of amine-boranes and related derivatives in mice

Three boron derivatives, i.e. trimethylamine-carbomethoxyborane, tetrakis-mu-(trimethylamine-boranecarboxylato)-bis(trimethylamine- carboxyborane)-dicopper(II), and N,N-dimethyl-n-octadecylamine borane were evaluated for acute toxicity in male mice, at 1, 2 or 5 x their therapeutic dose in rodents for pharmacological activity. Based on organ weights, clinical chemistry, hematopoietic parameters and tissue morphology, the trimethylamine-carbomethoxyborane was shown to be free of toxicity. The dicopper(II) complex and N,N-dimethyl-n-octadecylamine borane demonstrated slight toxicity with marginal disturbance in hepatic and kidney morphology. The dicopper(II) complex may cause marginal myocardial damage and the N,N-dimethyl-n-octadecylamine borane caused elevations in cholic acid. All three derivatives demonstrated reductions in hematocrit.

Acute and subacute toxicity of 10B-paraboronophenylalanine

The acute and subacute toxicities of 10B-paraboronophenylalanine (10B-BPA) were investigated in the rat, according to the Good Laboratory Practice Standard for safety studies on drugs in Japan. In the acute toxicity test of 10B-BPA, LD50 values of acidic 10B-BPA for intraperitoneal and subcutaneous injections were 640 mg/kg for male and 710 mg/kg for female rats, and more than 1,000 mg/kg for male and female rats, respectively. The LD50 values of neutral 10B-BPA for intraperitoneal and subcutaneous injections were more than 3,000 mg/kg for male and female rats. The difference in LD50 values between acidic and neutral 10B-BPA may be attributed to the acidity of material. From the subacute toxicity test, in which the rats were injected daily subcutaneously for 28 days, the following toxic effects of 10B-BPA were observed. Increase in ketone level in the urine was induced in all rats treated with 10B-BPA. High dose of 10B-BPA (1,500 mg/kg) induced increase in spleen weight and reticulocyte count, and decrease in hemoglobin count, thereby suggesting that 10B-BPA causes hemolysis. Increases in the leukocyte count and the ratio of neutrophils and lymphocytes were also observed in rats treated with a high dose of 10B-BPA. This may be attributed to local reactions at the injection site. There were no significant differences in the findings between control rats and rats treated with a low dose of 10B-BPA (300 mg/kg). Thus, low doses of neutral 10B-BPA may be available for use as a drug.

Neutron irradiation of human melanoma cells

The biological characteristics and in vitro radiosensitivity of melanoma cells to thermal neutrons were investigated as a guide to the effectiveness of boron neutron capture therapy. Plateau phase cultures of three human malignant melanoma-established cell lines were examined for cell density at confluence, doubling time, cell cycle parameters, chromosome constitution, and melanin content. Cell survival dose-response curves, for cells preincubated in the presence or absence of p-boronophenylalanine. HCl (10B1-BPA), were measured over the dose range 0.6-8.0 Gy (N + gamma). The neutron fluence rate was 2.6 x 10(9) n/cm2/s and the total dose rate 3.7 Gy/h (31% gamma). Considerable differences were observed in the morphology and cellular properties of the cell lines. Two cell lines (96E and 96L) were amelanotic, and one was melanotic (418). An enhanced killing for neutron irradiation was found only for the melanotic cells after 20 h preincubation with 10 micrograms/ml 10B1-BPA. In view of the doubling times of the cell lines of about 23 h (96E and 96L) or of 36 h (418), it seems likely that an increased boron uptake, and hence increased radiosensitivity, might result if the preincubation period with 10B1-BPA is extended to several hours longer than the respective cell cycle times.

Tetraphenylborate potentiates the respiratory inhibition by the dopaminergic neurotoxin MPP+ in both electron transport particles and intact mitochondria

The cytotoxicity of 1-methyl-4-phenylpyridinium (MPP+) is believed to arise as a consequence of its time- and energy-dependent accumulation inside mitochondria, followed by inhibition of electron transport at Complex I of the respiratory chain. Consistent with our proposal that the accumulation of MPP+ represents a passive Nernstian transport into mitochondria in response to the transmembrane electrochemical potential gradient, tetraphenylborate (TPB-) was found to accelerate the onset of the respiratory inhibition by MPP+ on intact mitochondria. Moreover, the ultimate level of inhibition reached was unexpectedly also increased. The latter is now explained by our finding that TPB- elicits a 12-fold enhancement of MPP+ inhibition of respiration in electron transport particles. It is suggested that TPB- facilitates access of MPP+ to its intramembrane site of inhibitory action in Complex I.

The influence of tetraphenylborates (hydrophobic anions) on yeast cell electro-rotation

The action of a series of tetraphenylborate ion (TPB) derivatives on yeast cells was studied by electro-rotation of the pre-treated cells. TPB derivatives in which all four phenyl groups were substituted with fluorine, chlorine or trifluoromethyl were much more toxic than the unsubstituted compound, the effect increasing dramatically with increasing size of substituents. These observations suggest that the toxicity of these hydrophobic ions is determined mainly by their size and possibly also by the chemical inductivity of their substituent groups. The order of the toxicities of these ions was in fair agreement with literature values for their translocation rates across artificial bilayers. Incubation times of 3 h were used as standard, longer incubations (up to 48 h) showed that the number of cells affected by low doses of TPB increased with the logarithm of time after the first hour of incubation. Although measurements of the percentage of cells showing co-field rotation showed that controls were not adversely affected by incubations as long as 9 h, rotation spectra showed that some cells suffer loss of internal conductivity during extended incubations. Decrease of the pH of the incubation medium, or inclusion of high concentrations of NaCl or KCl, potentiated the effects of these hydrophobic ions. The toxicity developed slowly, and the sensitivity of the assay was only very weakly dependent on the cell suspension density.

Toxicology and health impact of environmental exposure to boron. A review

The presence of high concentrations of boron in community water supplies has been reported as a localized problem in certain areas of United States, USSR and Italy. In this paper, current information on sources, occurrence, pollution potential and toxicity of environmental boron is reviewed. In animals, chronic low-level boron exposure has been shown to cause reduced growth, cutaneous disorders and suppression of male reproductive system function. The mechanisms underlying these effects and available data on dose-response relationships are discussed in connection with human health hazards possibly associated with continuous low-level absorption of boron compounds.

Toxic effects of a new boron containing heterocycle: 4,4,8,8-tetraethyl-3,3a,4,8-tetrahydro 3a,4a,4-diazabora-S-indacene

LD50 values in mice for 4,4,8,8-tetraethyl-3,3a,4,8-tetrahydro-3a,4a,4-diazabora-S-indacene (Myborin) were determined by the ip, po, and sc routes. The LD50 value for ip was 69.5 mg/kg found by the method of Litchfield and Wilcoxon, with upper and lower confidence limits of 77.8 and 62.1 mg/kg. Oral and sc LD50's were approximated after the method of Deichmann and LeBlanc and were found to be 180 mg/kg (po) and 420 mg/kg (sc). Each of these values has a confidence range of +/- 30%. Myborin induced convulsions, hyperreflexia, and death accompanied by tetany when given by either the ip or oral routes. Moreover, Myborin induced porphyria in animals surviving for 24 hr after these routes of administration and in virtually all animals dosed sc. Death by the sc route is probably a result of acute porphyria. Hepatomegaly and skin photosensitivity were demonstrated to be profound. Boron levels in the livers of mice were determined colorimetrically 24 hr after ip injections of Myborin and in untreated control mice. The quantity of boron found in the experimental group was 15.46 mug/g wet liver as compared to 8.11 mug/g wet liver for controls (P less than 0.01). The difference corresponds to 23% of the injected quantity of boron.