Oncogenicity evaluations of chemopreventive soy components in p53((+/-)) (p53 knockout) mice

Effects of phytochemicals on ionization radiation-mediated carcinogenesis and cancer therapy

Ionizing radiation (IR)-induced cellular damage is implicated in carcinogenesis as well as therapy of cancer. Advances in radiation therapy have led to the decrease in dosage and localizing the effects to the tumor; however, the development of radioresistance in cancer cells and radiation toxicity to normal tissues are still the major concerns. The development of radioresistance involves several mechanisms, including the activation of mitogenic and survival signaling, induction of DNA repair, and changes in redox signaling and epigenetic regulation. The current strategy of combining radiation with standard cytotoxic chemotherapeutic agents can potentially lead to unwanted side effects due to both agents. Thus agents are needed that could improve the efficacy of radiation killing of cancer cells and prevent the damage to normal cells and tissues caused by the direct and bystander effects of radiation, without have its own systemic toxicity. Chemopreventive phytochemicals, usually non-toxic agents with both cancer preventive and therapeutic activities, could rightly fit in this approach. In this regard, naturally occurring compounds, including curcumin, parthenolide, genistein, gossypol, ellagic acid, withaferin, plumbagin and resveratrol, have shown considerable potential. These agents suppress the radiation-induced activation of receptor tyrosine kinases and nuclear factor-κB signaling, can modify cell survival and DNA repair efficacy, and may potentiate ceramide signaling. These radiosensitizing and counter radioresistance mechanisms of phytochemicals in cancer cells are also associated with changes in epigenetic gene regulation. Because radioresistance involves multiple mechanisms, more studies are needed to discover novel phytochemicals having multiple mechanisms of radiosensitization and to overcome radioresistance of cancer cells. Pre-clinical studies are needed to address the appropriate dosage, timing, and duration of the application of phytochemicals with radiation to justify clinical trials. Nonetheless, some phytochemicals in combination with IR may play a significant role in enhancing the therapeutic index of cancer treatment.

Suppression of the later stages of radiation-induced carcinogenesis by antioxidant dietary formulations

We have previously reported data from a long-term carcinogenesis study indicating that dietary antioxidant supplements can suppress radiation-induced malignant lymphoma and harderian gland tumors induced by space radiations (specifically, 1 GeV/n iron ions or protons) in CBA/J mice. Two different antioxidant dietary supplements were used in these studies: a supplement containing a mixture of antioxidant agents [l-selenomethionine (SeM), N-acetyl cysteine (NAC), ascorbic acid, co-enzyme Q10, α-lipoic acid and vitamin E succinate], termed the AOX supplement, and another supplement known as Bowman-Birk Inhibitor Concentrate (BBIC). In the present report, the results from the earlier analysis of the harderian gland data from the published long-term animal study have been combined with new data derived from the same long-term animal study. In the earlier analysis, harderian glands were removed from animals exhibiting abnormalities (e.g. visibly swollen areas) around the eyes at the time of euthanasia or death in the long-term animal study. Abnormalities around the eyes were usually due to the development of tumors in the harderian glands of these mice. The new data presented here focused on the histopathological results obtained from analyses of the harderian glands of mice that did not have visible abnormalities around the eyes at the time of necropsy in the long-term animal study. In this paper, the original published data and the new data have been combined to provide a more complete evaluation of the harderian glands from animals in the long-term carcinogenesis study, with all available harderian glands from the animals processed and prepared for histopathological evaluation. The results indicate that, although dietary antioxidant supplements suppressed harderian gland tumors in a statistically significant fashion when all glands were analyzed, the antioxidant diets were less effective at suppressing the incidence of all harderian gland tumors than they were at suppressing the incidence of large harderian gland tumors (>2 mm) observed at animal necropsy. These results suggest that the dietary antioxidant formulations had major suppressive effects in the later stages of radiation-induced carcinogenesis in vivo. It is hypothesized that the dietary antioxidant formulations prevented the early-stage neoplastic growths from progressing to fully developed, malignant tumors. In addition, the antioxidant dietary formulations were very effective at preventing the development of proton- or iron-ion-induced malignant tumors, because, in contrast to irradiated controls, no malignant tumors were observed in the irradiated animals maintained on either of the dietary antioxidant diets.

Murine oncogenicity and pharmacokinetics studies of 9-cis-UAB30, an RXR agonist, for breast cancer chemoprevention

The synthetic retinoic acid analog, 9-cis-UAB30 [(2E,4E,6Z,8E)-8-(3',4'-dihydro-1'(2'H)-naphthalen-1'-ylidene)-3,7-dimethyl-2,4,6-octatrienoic acid], is a specific ligand for the retinoid X receptor. Murine oncogenicity and pharmacokinetics studies were performed as part of the preclinical development of 9-cis-UAB30 for breast cancer chemoprevention. In the oncogenicity study, TSG-p53((+/-)) (p53 knockout) mice (25 per sex per group) received daily gavage exposure to 9-cis-UAB30 doses of 0 (control), 30, 100, or 300 mg/kg/d for 6 months. Positive controls received p-cresidine (400 mg/kg/d) for 6 months. 9-cis-UAB30 had no biologically significant effects on survival, body weight, body weight gain, clinical signs, hematology, or clinical chemistry but induced dose-related hepatomegaly in both sexes and decreased thymus weights in high-dose females. Gross and microscopic pathology provided no evidence of 9-cis-UAB30 toxicity or oncogenicity; by contrast, p-cresidine induced urinary bladder neoplasms in more than 60% of male and female mice. It was concluded that 9-cis-UAB30 is not oncogenic in p53((+/-)) mice. In the pharmacokinetics study, C57BL/6 mice received daily gavage exposure to 9-cis-UAB30 (100 or 300 mg/kg/d) for 1 or 7 days. Pharmacokinetic parameters were similar after 1 and 7 days of dosing. Dose-related peak plasma levels of 9-cis-UAB30 were seen between 0.25 and 3 hours; volume of distribution was comparable at both dose levels. Increases in area under the curve were less than proportional to dose and were associated with an increased rate of apparent clearance and decreased elimination half-life. These results suggest decreased absorption and/or possible induction of clearance mechanisms. Enzyme induction may underlie the hepatomegaly seen in mice treated with 9-cis-UAB30 for 6 months in the oncogenicity study.

Dietary supplements reduce the cataractogenic potential of proton and HZE-particle radiation in mice

Abstract The present study was undertaken to investigate the ability of dietary supplements to reduce the formation and severity of cataracts in mice irradiated with high-energy protons or iron ions, which are important components of the radiation encountered by astronauts during space travel. The mice were exposed to proton or iron-ion radiation and fed with a control diet or diets supplemented with the soybean-derived protease inhibitor, Bowman-Birk inhibitor (BBI), in the form of BBI Concentrate (BBIC) or an antioxidant formulation [containing l-selenomethionine (SeM), N-acetyl cysteine (NAC), ascorbic acid, co-enzyme Q10, alpha-lipoic acid and vitamin E succinate] both before and after the radiation exposure. At approximately 2 years after the radiation exposure, the animals were killed humanely and lenses were harvested and characterized using an established classification system that assigns discrete scores based on the severity of the lens opacifications. The results showed that exposure to 1 GeV/nucleon proton (3 Gy) or iron-ion (50 cGy) radiation significantly increased the cataract prevalence and severity in CBA/J mice to levels above the baseline levels of age-induced cataract formation in this mouse strain. Treatment with BBIC or the antioxidant formulation significantly reduced the prevalence and severity of the lens opacifications in the mice exposed to iron-ion radiation. Treatment with BBIC or the antioxidant formulation also decreased the severity of the lens opacifications in the mice exposed to proton radiation; however, the decrease did not reach statistical significance. These results indicate that BBIC and the antioxidant formulation evaluated in this study could be useful for protecting astronauts against space radiation-induced cataracts during or after long-term manned space missions.

Complementary roles in cancer prevention: protease inhibitor makes the cancer preventive peptide lunasin bioavailable

BACKGROUND

The lower incidence of breast cancer among Asian women compared with Western countries has been partly attributed to soy in the Asian diet, leading to efforts to identify the bioactive components that are responsible. Soy Bowman Birk Inhibitor Concentrate (BBIC) is a known cancer preventive agent now in human clinical trials.

METHODOLOGY/PRINCIPAL FINDINGS

The objectives of this work are to establish the presence and delineate the in vitro activity of lunasin and BBI found in BBIC, and study their bioavailability after oral administration to mice and rats. We report that lunasin and BBI are the two main bioactive ingredients of BBIC based on inhibition of foci formation, lunasin being more efficacious than BBI on an equimolar basis. BBI and soy Kunitz Trypsin Inhibitor protect lunasin from in vitro digestion with pancreatin. Oral administration of (3)H-labeled lunasin with lunasin-enriched soy results in 30% of the peptide reaching target tissues in an intact and bioactive form. In a xenograft model of nude mice transplanted with human breast cancer MDA-MB-231 cells, intraperitoneal injections of lunasin, at 20 mg/kg and 4 mg/kg body weight, decrease tumor incidence by 49% and 33%, respectively, compared with the vehicle-treated group. In contrast, injection with BBI at 20 mg/kg body weight shows no effect on tumor incidence. Tumor generation is significantly reduced with the two doses of lunasin, while BBI is ineffective. Lunasin inhibits cell proliferation and induces cell death in the breast tumor sections.

CONCLUSIONS/SIGNIFICANCE

We conclude that lunasin is actually the bioactive cancer preventive agent in BBIC, and BBI simply protects lunasin from digestion when soybean and other seed foods are eaten by humans.

Induction of apoptosis in the LNCaP human prostate carcinoma cell line and prostate adenocarcinomas of SV40T antigen transgenic rats by the Bowman-Birk inhibitor

The soybean-derived serine protease inhibitor, Bowman-Birk inhibitor (BBI), has been reported as a potent chemoprevention agent against several types of tumors. The present study was undertaken to evaluate the effects of BBI on androgen-sensitive/dependent prostate cancers using a human prostate cancer cell (LNCaP) and the transgenic rats developing adenocarcinoma of the prostate (TRAP) model. Treatment of LNCaP prostate cancer cells with 500 microg/mL BBI resulted in inhibition of viability measured on WST-1 assays, with induction of connexin 43 (Cx43) and cleaved caspase-3 protein expression. Feeding of 3% roughly prepared BBI (BBIC) to TRAP from the age 3 weeks to 13 weeks resulted in significant reduction of the relative epithelial areas within the acinus and multiplicity of the adenocarcinomas in the lateral prostate lobes. Cx43- and terminal deoxynucleotidyl transferase mediated dUTP-biotin end labeling of fragmented DNA (TUNEL)-positive apoptotic cancer cells were more frequently observed in the lateral prostates treated with BBIC than in the controls. These in vivo and in vitro results suggest that BBI possesses chemopreventive activity associated with induction of Cx43 expression and apoptosis.

Effects of dietary antioxidant supplementation on the development of malignant lymphoma and other neoplastic lesions in mice exposed to proton or iron-ion radiation

Malignancy is considered to be a particular risk associated with exposure to the types of ionizing radiation encountered during extended space flight. In the present study, two dietary preparations were evaluated for their ability to prevent carcinogenesis in CBA mice exposed to different forms of space radiation: protons and highly energetic heavy particles (HZE particles). One preparation contained a mixture of antioxidant agents. The other contained the soybean-derived Bowman-Birk protease inhibitor (BBI), used in the form of BBI Concentrate (BBIC). The major finding was that there was a reduced risk of developing malignant lymphoma in animals exposed to space radiation and maintained on diets containing the antioxidant formulation or BBIC compared to the irradiated animals maintained on the control diet. In addition, the two different dietary countermeasures also reduced the yields of a variety of different rare tumor types observed in the animals exposed to space radiation. These results suggest that dietary supplements could be useful in the prevention of malignancies and other neoplastic lesions developing from exposure to space radiation.

Oncogenicity evaluation of resveratrol in p53(+/-) (p53 knockout) mice

A six-month study was conducted in p53(+/-) mice to evaluate the possible oncogenicity of resveratrol (3,5,4'-trihydroxy-trans-stilbene), a cancer chemopreventive agent present in grapes and other foods. p53(+/-) mice (25/sex/group) received daily gavage exposure to vehicle only (negative control), resveratrol doses of 1000, 2000, or 4000 mg/kg/day, or p-cresidine (400 mg/kg/day; positive control). No mortality was seen in mice receiving the low dose of resveratrol. However, the mid and high doses induced mortality associated with impaction of the test article in the gastrointestinal tract. Resveratrol had no effect on body weight, food consumption, or clinical signs in surviving mice in any dose group, but induced dose-related increases in liver weight and serum cholesterol in both sexes. Mild anemia was seen in male mice at the high dose only; hematologic effects were not seen in females. Histopathology identified the kidney (hydronephrosis) and urinary bladder (epithelial hyperplasia) as target tissues for resveratrol toxicity. The incidences of both benign and malignant tumors in mice exposed to resveratrol were comparable to those in vehicle controls. By contrast, the positive control article, p-cresidine, induced urinary bladder cancer in both sexes. When administered to p53(+/-) mice at its maximum tolerated dose, resveratrol demonstrates no evidence of oncogenicity.