Plasma pharmacokinetics and tissue biodistribution of boron following administration of a boronated porphyrin in dogs

Evaluation of sodium borocaptate (BSH) and boronophenylalanine (BPA) as boron delivery agents for neutron capture therapy (NCT) of cancer: an update and a guide for the future clinical evaluation of new boron delivery agents for NCT

Boron neutron capture therapy (BNCT) is a cancer treatment modality based on the nuclear capture and fission reactions that occur when boron-10, a stable isotope, is irradiated with neutrons of the appropriate energy to produce boron-11 in an unstable form, which undergoes instantaneous nuclear fission to produce high-energy, tumoricidal alpha particles. The primary purpose of this review is to provide an update on the first drug used clinically, sodium borocaptate (BSH), by the Japanese neurosurgeon Hiroshi Hatanaka to treat patients with brain tumors and the second drug, boronophenylalanine (BPA), which first was used clinically by the Japanese dermatologist Yutaka Mishima to treat patients with cutaneous melanomas. Subsequently, BPA has become the primary drug used as a boron delivery agent to treat patients with several types of cancers, specifically brain tumors and recurrent tumors of the head and neck region. The focus of this review will be on the initial studies that were carried out to define the pharmacokinetics and pharmacodynamics of BSH and BPA and their biodistribution in tumor and normal tissues following administration to patients with high-grade gliomas and their subsequent clinical use to treat patients with high-grade gliomas. First, we will summarize the studies that were carried out in Japan with BSH and subsequently at our own institution, The Ohio State University, and those of several other groups. Second, we will describe studies carried out in Japan with BPA and then in the United States that have led to its use as the primary drug that is being used clinically for BNCT. Third, although there have been intense efforts to develop new and better boron delivery agents for BNCT, none of these have yet been evaluated clinically. The present report will provide a guide to the future clinical evaluation of new boron delivery agents prior to their clinical use for BNCT.

Nutrition, Physical Activity, and Dietary Supplementation to Prevent Bone Mineral Density Loss: A Food Pyramid

Bone is a nutritionally modulated tissue. Given this background, aim of this review is to evaluate the latest data regarding ideal dietary approach in order to reduce bone mineral density loss and to construct a food pyramid that allows osteopenia/osteoporosis patients to easily figure out what to eat. The pyramid shows that carbohydrates should be consumed every day (3 portions of whole grains), together with fruits and vegetables (5 portions; orange-colored fruits and vegetables and green leafy vegetables are to be preferred), light yogurt (125 mL), skim milk (200 mL,) extra virgin olive oil (almost 20 mg/day), and calcium water (almost 1 l/day); weekly portions should include fish (4 portions), white meat (3 portions), legumes (2 portions), eggs (2 portions), cheeses (2 portions), and red or processed meats (once/week). At the top of the pyramid, there are two pennants: one green means that osteopenia/osteoporosis subjects need some personalized supplementation (if daily requirements cannot be satisfied through diet, calcium, vitamin D, boron, omega 3, and isoflavones supplementation could be an effective strategy with a great benefit/cost ratio), and one red means that there are some foods that are banned (salt, sugar, inorganic phosphate additives). Finally, three to four times per week of 30-40 min of aerobic and resistance exercises must be performed.

Pivotal role of boron supplementation on bone health: A narrative review

BACKGROUND

Boron is a trace element that plays an important role in numerous biological functions, including calcium metabolism, growth and maintenance of bone tissue. However, there are still no precise indications regarding a possible role of boron supplementation, and its amount of supplementation, to maintain bone health. So the aim of this narrative review was to consider the state of the art on the effectiveness of boron supplementation (alone or with other micronutrients) on growth and maintenance of bone in humans through control of calcium, vitamin D and sex steroid hormone metabolism in order to suggest a daily dosage of boron supplementation.

MAIN FINDINGS

This review included 11 eligible studies: 7 regarding the supplementation with boron alone and 4 regarding supplementation with boron and other nutrients. Despite the number of studies considered being low, the number of subjects studied is high (594) and the results are interesting.

CONCLUSIONS

The studies considered in this narrative review have evaluated the positive effectiveness on bone, in humans, through control of calcium, vitamin D and sex steroid hormone metabolism, considering a dietary supplementation of 3 mg/day of boron (alone or with other nutrients); this supplementation is demonstrably useful to support bone health (in order to prevent and maintain adequate bone mineral density), also considering the daily dose of 3 mg is much lower than the Upper Level indicated by EFSA in the daily dose of 10 mg.

Carboranyl Analogues of Celecoxib with Potent Cytostatic Activity against Human Melanoma and Colon Cancer Cell Lines

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most common way of treating inflammatory disorders. Their widespread use helped reveal their other modes of action as pharmaceuticals, such as a profound effect on various cancers. Celecoxib has proven to be a very prominent member of this group with cytostatic activities. On the other hand, the highly dynamic field of drug design is constantly searching for new ways of modifying known structures to obtain more powerful and less harmful drugs. A very interesting development is the implementation of carboranes in pharmacologically active structures, mostly as phenyl mimetics. Herein we report the synthesis of three carborane-containing derivatives of the COX-2-selective NSAID celecoxib. The new compounds proved to have promising cytostatic potential against various melanoma and colorectal adenocarcinoma cell lines. Inhibited proliferation accompanied by caspase-independent apoptotic cell death was found to be the main cause of decreased cell viability upon treatment with the most efficient celecoxib analogue, 3 b (4-[5-(1,7-dicarba-closo-dodecaboranyl)-3-trifluoromethyl-1H-pyrazol-1-yl]-1-methylsulfonylbenzene).

The Physiological Role of Boron on Health

Boron is an essential mineral that plays an important role in several biological processes. Boron is required for growth of plants, animals, and humans. There are increasing evidences of this nutrient showing a variety of pleiotropic effects, ranging from anti-inflammatory and antioxidant effects to the modulation of different body systems. In the past few years, the trials showed disease-related polymorphisms of boron in different species, which has drawn attention of scientists to the significance of boron to health. Low boron profile has been related with poor immune function, increased risk of mortality, osteoporosis, and cognitive deterioration. High boron status revealed injury to cell and toxicity in different animals and humans. Some studies have shown some benefits of higher boron status, but findings have been generally mixed, which perhaps accentuates the fact that dietary intake will benefit only if supplemental amount is appropriate. The health benefits of boron are numerous in animals and humans; for instance, it affects the growth at safe intake. Central nervous system shows improvement and immune organs exhibit enhanced immunity with boron supplementation. Hepatic metabolism also shows positive changes in response to dietary boron intake. Furthermore, animals and human fed diets supplemented with boron reveal improved bone density and other benefits including embryonic development, wound healing, and cancer therapy. It has also been reported that boron affects the metabolism of several enzymes and minerals. In the background of these health benefits, low or high boron status is giving cause for concern. Additionally, researches are needed to further elucidate the mechanisms of boron effects, and determine the requirements in different species.

Convection enhanced delivery of carboranylporphyrins for neutron capture therapy of brain tumors

Boron neutron capture therapy (BNCT) is based on the nuclear capture and fission reactions that occur when non-radioactive 10B is irradiated with low energy thermal neutrons to produce α-particles (10B[n,α] Li). Carboranylporphyrins are a class of substituted porphyrins containing multiple carborane clusters. Three of these compounds, designated H2TBP, H2TCP, and H2DCP, have been evaluated in the present study. The goals were two-fold. First, to determine their biodistribution following intracerebral (i.c.) administration by short term (30 min) convection enhanced delivery (CED) or sustained delivery over 24 h by Alzet™ osmotic pumps to F98 glioma bearing rats. Second, to determine the efficacy of H2TCP and H2TBP as boron delivery agents for BNCT in F98 glioma bearing rats. Tumor boron concentrations immediately after i.c. pump delivery were high and they remained so at 24 h. The corresponding normal brain concentrations were low and the blood and liver concentrations were undetectable. Based on these data, therapy studies were initiated at the Massachusetts Institute of Technology (MIT) Research Reactor (MITR) with H2TCP and H2TBP 24 h after CED or pump delivery. Mean survival times (MST) ± standard deviations of animals that had received H2TCP or H2TBP, followed by BNCT, were of 35 ± 4 and 44 ± 10 days, compared to 23 ± 3 and 27 ± 3 days, respectively, for untreated and irradiated controls. However, since the tumor boron concentrations of the carboranylporphyrins were 3-5× higher than intravenous (i.v.) boronophenylalanine (BPA), we had expected that the MSTs would have been greater. Histopathologic examination of brains of BNCT treated rats revealed that there were large numbers of porphyrin-laden macrophages, as well as extracellular accumulations of porphyrins, indicating that the seemingly high tumor boron concentrations did not represent the true tumor cellular uptake. Nevertheless, our data are the first to show that carboranyl porphyrins can be used as delivery agents for BNCT of an experimental brain tumor. Based on these results, we now are in the process of synthesizing and evaluating carboranylporphyrins that could have enhanced cellular uptake and improved therapeutic efficacy.

Effects of Subacute Boric Acid Administration on Rat Kidney Tissue

BACKGROUND/AIMS

Boron is used in manufacturing processes and numerous consumer products. Clarification of boron toxicity is important because of industrial and consumer exposure to boron and boron-containing compounds. The aim of this study was to observe effects of subacute boric acid administration on rat kidney tissue.

MATERIALS AND METHODS

A total of 96 male albino Sprague-Dawley rats were used in this study. Seventy-two rats were selected for the experimental group and 24 rats constituted the control group. Experimental group rats were divided into three groups for exposure to three different doses of orally administered boric acid (100-275-400 mg/kg/day). Kidney tissues were removed at the 10th, 30th, and 45th day after sacrificing the rats. Kidney weights, kidney boron concentration and histopathological changes were determined.

RESULTS

In the experimental group, a significant accumulation of boron in kidney tissue was seen, but there was a significant drop in boron concentration on the 45th day compared with the 30th day. Histopathological degenerative changes were observed especially in the proximal tubule cells that were dose- and time-dependent.

CONCLUSION

Subacute boric acid exposure caused dose-dependent histopathological changes in kidney tissue.

Boronated protohaemins: synthesis and in vivo antitumour efficacy

The conjugates of porphyrin macrocycles with boron-containing polyhedra are under investigation as agents for binary treatment strategies of cancer. Aiming at the design of photoactive compounds with low-to-zero dark toxicity, we synthesized a series of carboranyl and monocarbon-carboranyl derivatives of protohaemin IX using the activation of porphyrin carboxylic groups with di-tert-butyl pyrocarbonate or pivaloyl chloride. The water-soluble 1,3,5,8-tetramethyl-2,4-divinyl-6(7)-[2'-(closo-monocarbon-carborane-1''-yl)methoxycarbonylethyl]-7(6)-(2'-carboxyethyl)porphyrin Fe(III) (compound 9) exerted no discernible cytotoxicity for cultured mammalian cells, nor did it cause general toxicity in rats. Importantly, 9 demonstrated dose-dependent activity as a phototoxin in photodynamic therapy of M-1 sarcoma-bearing rats. In animals injected with 20 mg kg(-1) of 9, the tumours shrank by day 3 after one single irradiation of the tumour with red laser light. Between 7 and 14 days post-irradiation, 88.9% of rats were tumour-free; no recurrence of the disease was detectable within at least 90 days. Protohaemin IX alone was without effect, indicating that boronation is important for the phototoxic activity of 9. This is the first study that presents the synthesis and preclinical in vivo efficacy of boronated derivatives of protohaemin as phototoxins. The applicability in photodynamic treatment broadens the therapeutic potential of boronated porphyrins beyond their conventional role as radiosensitizers in boron neutron capture therapy.

Synthesis and characterization of a carboranyl-tetrabenzoporphyrin

An expeditious synthetic route to a carboranyl-substituted tetrabenzoporphyrin is reported. The absorption and emission spectra of water-soluble tetrabenzoporphyrin 4 are distinct from those of a known carboranylporphyrin (5). Both tetrabenzoporphyrin 4 and porphyrin 5 were found to be non-toxic toward V79 hamster lung fibroblast cells at 300 microM, using an MTT assay. The X-ray structure of a Cu(II)-carboranyl-tetrabenzoporphyrin is presented and discussed.

Boron neutron capture therapy for undifferentiated thyroid carcinoma: preliminary results with the combined use of BPA and BOPP

We have shown the selective uptake of borophenylalanine (BPA) by undifferentiated human thyroid cancer (UTC) ARO cells both in vitro and in vivo. Moreover, a 50% histologic cure of mice bearing the tumor was observed when the complete boron neutron capture therapy was applied. More recently we have analyzed the biodistribution of BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha,beta-dihydroxyethyl)-deutero-porphyrin IX) and showed that when BOPP was injected 5 days before BPA, and the animals were sacrificed 60 min after the i.p. injection of BPA, a significant increase in boron uptake by the tumor was found (38-45 ppm with both compounds vs. 20 ppm with BPA alone). Five days post the i.p BOPP injection and 1h after BPA the ratios were: tumor/blood 3.75; tumor/distal skin 2. Other important ratios were tumor/thyroid 6.65 and tumor/lung 3.8. The present studies were performed in mice transplanted with ARO cells and injected with BOPP and BPA. Only in mice treated with the neutron beam and injected with the boronated compounds we observed a 100% control of tumor growth. Two groups of mice received different total absorbed doses: 3.00 and 6.01 Gy, but no further improvement in the outcome was found compared to the previous results using BPA alone (4.3 Gy).

Biodistribution of Boron Compounds in an Animal Model of Human Undifferentiated Thyroid Cancer for Boron Neutron Capture Therapy

Undifferentiated thyroid carcinoma (UTC) is a rapidly growing, highly invasive malignant tumor that currently lacks any effective treatment. Boron neutron capture therapy (BNCT) has been investigated recently for some types of tumors including glioblastoma multiforme and malignant melanoma. In previous studies we have shown the selective uptake of p-boronophenylalanine (BPA) by undifferentiated thyroid cancer cells in vitro and in vivo, as well as the histologic cure of 50% of the nude mice transplanted with human UTC cells when treated with BPA and an appropriate neutron beam. The present studies were performed to further optimize this treatment through the investigation of a boronated porphyrin, both alone and in combination with BPA. In vitro studies with cells in culture showed that BOPP (tetrakis-carborane carboxylate ester of 2,4-bis-(alpha,beta-dihydroxyethyl)-deutero-porphyrin IX) is localized intracellularly, with a highest concentration in the 11500g (mitochondrial-enriched pellet) fraction. When BOPP was administered alone to NIH nude mice transplanted with UTC human cells, no significant tumor uptake or selectivity in our in vivo model was observed. In contrast, when BOPP was injected 5-7 days before BPA and the animals were sacrificed 60 min after administration of BPA, a significant increase in boron uptake by the tumor was found (38-45 ppm with both compounds vs 20 ppm with BPA alone). On day 5 the tissue boron selectivity ratios were tumor/blood approximately 3.8 and tumor/distal skin approximately 1.8. Other important ratios were tumor/thyroid approximately 6.6 and tumor/lung approximately 2.9. These results open the possibility of improving the efficacy of BNCT for the treatment of this so far "orphan" tumor.

Boron neutron capture therapy: cellular targeting of high linear energy transfer radiation

Boron neutron capture therapy (BNCT) is based on the preferential targeting of tumor cells with (10)B and subsequent activation with thermal neutrons to produce a highly localized radiation. In theory, it is possible to selectively irradiate a tumor and the associated infiltrating tumor cells with large single doses of high-LET radiation while sparing the adjacent normal tissues. The mixture of high- and low-LET dose components created in tissue during neutron irradiation complicates the radiobiology of BNCT. Much of the complexity has been unravelled through a combination of preclinical experimentation and clinical dose escalation experience. Over 350 patients have been treated in a number of different facilities worldwide. The accumulated clinical experience has demonstrated that BNCT can be delivered safely but is still defining the limits of normal brain tolerance. Several independent BNCT clinical protocols have demonstrated that BNCT can produce median survivals in patients with glioblastoma that appear to be equivalent to conventional photon therapy. This review describes the individual components and methodologies required for effect BNCT: the boron delivery agents; the analytical techniques; the neutron beams; the dosimetry and radiation biology measurements; and how these components have been integrated into a series of clinical studies. The single greatest weakness of BNCT at the present time is non-uniform delivery of boron into all tumor cells. Future improvements in BNCT effectiveness will come from improved boron delivery agents, improved boron administration protocols, or through combination of BNCT with other modalities.

Synthesis, dark toxicity and induction of in vitro DNA photodamage by a tetra(4-nido-carboranylphenyl)porphyrin

The total synthesis of tetra(4-carboranylphenyl)porphyrins 4 and 6 and their zinc(II) complexes 5 and 7 are described. These compounds were characterized by analytical and spectroscopic methods and, in the case of 5, by X-ray crystallography. The water-soluble nido-carboranylporphyrins 6 and 7 were found to have low dark toxicity towards V79 hamster lung fibroblast cells, using a clonogenic assay (50% colony survival, CS(50)>300 microM). Upon light activation nido-carboranylporphyrin 6 effectively induced DNA damage in vitro. Two different methods were used to assess the extent of DNA damage: the super-coiled to nicked DNA and the alkaline Comet assay using human leukemia K562 cells. Significant PDT-induced DNA damage was observed for porphyrin 6 using both assays, compared to light-only and porphyrin-only experiments. It is concluded that this type of nido-carboranylporphyrin is a promising sensitizer for both the boron neutron capture therapy and the photodynamic therapy of tumors.

Phase I and pharmacokinetic study of photodynamic therapy for high-grade gliomas using a novel boronated porphyrin

PURPOSE

To determine the recommended dose, toxicity profile, and pharmacokinetics of a novel boronated porphyrin (BOPP) for photodynamic therapy (PDT) of intracranial tumors.

PATIENTS AND METHODS

BOPP was administered alone in increasing doses (0.25, 0.5, 1.0, 2.0, 4.0, or 8.0 mg/kg) preoperatively in patients with intracranial tumors undergoing postresection PDT until dose-limiting toxicity (DLT) was observed.

RESULTS

Twenty-nine assessable patients with intracranial tumors received BOPP intravenously 24 hours before surgery. The recommended dose was 4 mg/kg. Dose escalation was limited by thrombocytopenia. The most common nonhematologic toxicity was skin photosensitivity. Pharmacokinetic parameters showed increased area under the plasma concentration-time curve and maximum concentration with increased dose. Tumor BOPP concentrations also increased with increased dose.

CONCLUSION

BOPP at a dose of 4 mg/kg was well tolerated. DLT was thrombocytopenia, and photosensitivity was the only other toxicity of note. The efficacy of PDT using BOPP requires further exploration.