Bowman-Birk protease inhibitor activates DNA-dependent protein kinase and reduces formation of radiation-induced dicentric chromosomes

Proteases, protease inhibitors and radiation carcinogenesis

PURPOSE

The purpose of the studies described in this mini review article was to identify nontoxic compounds that could prevent or suppress the radiation induced malignant transformation of cells and be useful as human cancer preventive agents.

CONCLUSIONS

(1) Many different types of potential anticarcinogenic substances were evaluated initially for their abilities to prevent or suppress radiation induced malignant transformation in vitro, and certain anticarcinogenic protease inhibitors (APIs) were observed to be the most powerful anticarcinogenic agents at suppressing this surrogate endpoint biomarker of radiation carcinogenesis. (2) Within the category of APIs, those that inhibited the activity of chymotrypsin were effective at far lower molar concentrations than other APIs. The soybean-derived protease inhibitor known as the Bowman-Birk inhibitor (BBI) is a particularly powerful chymotrypsin inhibitor that is able to prevent radiation induced transformation in vitro (at concentrations down to nanomolar levels) as well as radiation induced carcinogenesis in vivo without toxicity. (3) There were many other unusual characteristics of APIs that led to the selection of one of these APIs, BBI, as the most appropriate compound for us to develop as a human cancer preventive agent. As one example, the APIs have an irreversible effect on carcinogenesis, while the effects are reversible for most anticarcinogenic agents when they are removed from carcinogenesis assay systems. (4) Numerous studies were performed in attempts to determine the potential mechanisms by which the APIs could prevent or suppress radiation induced carcinogenesis in in vitro and in vivo systems, and the results of these studies are described in this review article. The APIs and the proteases which interact with them appear to play important roles in radiation carcinogenesis. (5) Preparations for human trials using BBI began decades ago. The cost of preparing purified BBI was far too high to consider performing human trials with this agent, so BBI Concentrate (BBIC), a soybean extract enriched in BBI, was developed for the specific purpose of performing human trials with BBI. BBIC achieved Investigational New Drug (IND) Status with the Food and Drug Administration in April,1992, and human BBIC trials began at that time. (6) Several human trials were performed using BBIC and they indicated many potentially beneficial health effects produced by BBIC administration to people in various forms (e.g. tablets). 7) It is hypothesized that BBI takes the place of α-1-antichymotrypsin, an important regulatory compound in the human body, and helps to maintain homeostasis.

Chemical and biological basis for development of novel radioprotective drugs for cancer therapy

Ionizing radiation (IR) causes chemical changes in biological systems through direct interaction with the macromolecules or by causing radiolysis of water. This property of IR is harnessed in the clinic for radiotherapy in almost 50% of cancers patients. Despite the advent of stereotactic radiotherapy instruments and other advancements in shielding techniques, the inadvertent deposition of radiation dose in the surrounding normal tissue can cause late effects of radiation injury in normal tissues. Radioprotectors, which are chemical or biological agents, can reduce or mitigate these toxic side-effects of radiotherapy in cancer patients and also during radiation accidents. The desired characteristics of an ideal radioprotector include low chemical toxicity, high risk to benefit ratio and specific protection of normal cells against the harmful effects of radiation without compromising the cytotoxic effects of IR on cancer cells. Since reactive oxygen species (ROS) are the major contributors of IR mediated toxicity, plethora of studies have highlighted the potential role of antioxidants to protect against IR induced damage. However, owing to the lack of any clinically approved radioprotector against whole body radiation, researchers have shifted the focus toward finding alternate targets that could be exploited for the development of novel agents. The present review provides a comprehensive insight in to the different strategies, encompassing prime molecular targets, which have been employed to develop radiation protectors/countermeasures. It is anticipated that understanding such factors will lead to the development of novel strategies for increasing the outcome of radiotherapy by minimizing normal tissue toxicity.

Potential utility of peptides against damage induced by ionizing radiation

Radioprotection is the process whereby biological systems are aided against undesirable radiation hazards. Primitive radioprotectors suffered from either having crucial side effects or low efficacy in clinical applications. Therefore, the search for less toxic but more capable radioprotectants has continued for decades. Peptides have been investigated as radioprotectants in a variety of preclinical models both in vitro and in vivo. Peptides exert their influence through scavenging free radicals, modifying cell signaling and inhibiting cell apoptosis. Demonstrating potential in vivo properties, peptide radiation countermeasures might find enough credit for use in humans in the future. This article reviews the potential therapeutic value of currently known radioprotective peptides and attempts to provide a comprehensive source for further scientific research in this area.

Radioprotectors and mitigators of radiation-induced normal tissue injury

Radiation is used in the treatment of a broad range of malignancies. Exposure of normal tissue to radiation may result in both acute and chronic toxicities that can result in an inability to deliver the intended therapy, a range of symptoms, and a decrease in quality of life. Radioprotectors are compounds that are designed to reduce the damage in normal tissues caused by radiation. These compounds are often antioxidants and must be present before or at the time of radiation for effectiveness. Other agents, termed mitigators, may be used to minimize toxicity even after radiation has been delivered. Herein, we review agents in clinical use or in development as radioprotectors and mitigators of radiation-induced normal tissue injury. Few agents are approved for clinical use, but many new compounds show promising results in preclinical testing.

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.

Blocked autophagy sensitizes resistant carcinoma cells to radiation therapy

Autophagy or "self eating" is frequently activated in tumor cells treated with chemotherapy or irradiation. Whether autophagy represents a survival mechanism or rather contributes to cell death remains controversial. To address this issue, the role of autophagy in radiosensitive and radioresistant human cancer cell lines in response to gamma-irradiation was examined. We found irradiation-induced accumulation of autophagosomes accompanied by strong mRNA induction of the autophagy-related genes beclin 1, atg3, atg4b, atg4c, atg5, and atg12 in each cell line. Transduction of specific target-siRNAs led to down-regulation of these genes for up to 8 days as shown by reverse transcription-PCR and Western blot analysis. Blockade of each autophagy-related gene was associated with strongly diminished accumulation of autophagosomes after irradiation. As shown by clonogenic survival, the majority of inhibited autophagy-related genes, each alone or combined, resulted in sensitization of resistant carcinoma cells to radiation, whereas untreated resistant cells but not sensitive cells survived better when autophagy was inhibited. Similarly, radiosensitization or the opposite was observed in different sensitive carcinoma cells and upon inhibition of different autophagy genes. Mutant p53 had no effect on accumulation of autophagosomes but slightly increased clonogenic survival, as expected, because mutated p53 protects cells by conferring resistance to apoptosis. In our system, short-time inhibition of autophagy along with radiotherapy lead to enhanced cytotoxicity of radiotherapy in resistant cancer cells.

The radioprotector Bowman-Birk proteinase inhibitor stimulates DNA repair via epidermal growth factor receptor phosphorylation and nuclear transport

BACKGROUND AND PURPOSE

The purpose of the study was to elucidate the underlying molecular mechanism of the radioprotector, Bowman-Birk proteinase inhibitor (BBI), and its interaction with EGFR nuclear transport.

MATERIALS AND METHODS

Molecular effects of BBI at the level of EGFR responses were investigated in vitro with wt. TP53 bronchial carcinoma cell line A549 and the transformed fibroblast cell line HH4dd characterized by a mt. TP53. EGFR and associated protein expression were quantified by Western blotting and confocal microscopy in the cytoplasmic and nuclear cell fraction. Residual DNA double strand breaks were quantified by means of a gammaH(2)AX focus assay.

RESULTS

Both irradiation and BBI-treatment stimulated EGFR internalization into the cytoplasm. This process involved src kinase activation, EGFR phosphorylation at Y845, and caveolin 1 phosphorylation at Y14. EGFR internalization correlated with nuclear EGFR transport and was associated with phosphorylation of EGFR at T654. Nuclear EGFR was linked with DNA-PK complex formation and activation. Furthermore, nuclear EGFR was found in complex with TP53, phosphorylated at S15, and with MDC1, following irradiation and BBI treatment. It is noteworthy that MDC1 was strongly decreased in the nuclear EGFR complex in cells with mt. TP53 and failed to be increased by either BBI treatment or irradiation. Interestingly, in cells with mt. TP53 the BBI mediated stimulation of double strand break repair was hampered significantly.

CONCLUSION

These data indicate that BBI stimulates complex formation between EGFR, TP53 and MDC1 protein in wt. TP53 cells only. Since MDC1 is essential for recruitment of DNA repair foci, this observation may explain how BBI selectively stimulated repair of DNA double strand breaks in wt. TP53 cells.

The radioprotector O-phospho-tyrosine stimulates DNA-repair via epidermal growth factor receptor- and DNA-dependent kinase phosphorylation

BACKGROUND AND PURPOSE

Purpose of the study was to elucidate the underlying molecular mechanism of the radioprotector O-phospho-tyrosine (P-Tyr).

METHODS

Molecular effects of P-Tyr at the level of EGFR responses were investigated in vitro with bronchial carcinoma cell line A549. Nuclear EGFR transport and DNA-PK activation were quantified after Western blotting. Residual DNA-damages were quantified by help of gammaH(2)AX focus assay.

RESULTS

As determined by dose-response curves, treatment of cells with P-Tyr for 16h before irradiation results in radioprotection. Simultaneous treatment with EGFR blocking antibody Cetuximab abolished P-Tyr associated radioprotection. At the molecular level P-Tyr mediated a general phosphorylation of EGFR and a pronounced phosphorylation of nuclear EGFR at residue Thr No. 654, also observed after treatment with ionizing radiation. This phosphorylation was associated with nuclear EGFR accumulation. Moreover, P-Tyr-triggered EGFR nuclear accumulation was associated with phosphorylation of DNA-PK at Thr 2609. This activated form of DNA-PK was not DNA associated, but after radiation, DNA binding increased, particularly after P-Tyr pre-treatment. These molecular effects of P-Tyr resulted in a reduction of residual DNA-damage after irradiation.

CONCLUSIONS

Radioprotection by P-Tyr is mediated through its stimulation of nuclear EGFR transport and concurrent, but DNA-damage independent, activation of DNA-PK. Thus, subsequent irradiation results in increased binding of DNA-PK to DNA, improved DNA-repair and increased cell survival.

Chemoprevention of Rat Prostate Carcinogenesis by Soy Isoflavones and by Bowman-Birk Inhibitor

Epidemiology studies suggest that soy consumption confers protection against human prostate cancer. To identify the soy component(s) that may be responsible for this chemopreventive activity, studies were conducted to determine the influence of a soy isoflavone mixture (PTI G-2535; 45% genistein, 22% daidzein, 2% glycitein) and a soy-derived protease inhibitor (Bowman-Birk Inhibitor Concentrate; BBIC) on prostate carcinogenesis in rats. Prostate cancers were induced in male Wistar-Unilever rats by a sequential regimen of cyproterone acetate and testosterone propionate, followed by a single intravenous injection of N-methyl-N-nitrosourea (MNU) and chronic androgen stimulation. In separate studies, PTI G-2535 and BBIC were administered continuously at 0 (control), 200, or 2000 mg/kg diet, beginning 1 wk post-MNU. PTI G-2535 and BBIC both conferred modest, but statistically significant and dose-related protection against carcinogenesis in the dorsolateral+anterior prostate. These data demonstrate that both the isoflavone and protein (protease inhibitor) components of soy can inhibit prostate carcinogenesis in the rat. However, the modest individual activities of soy isoflavones and BBIC suggest that while both components may contribute to the chemopreventive activity of soy, combination administration (or exposure to whole soy) may be more effective in prostate cancer prevention than is administration of either component alone.

Inhibition of DNA repair as a mechanism of enhanced radioresponse of head and neck carcinoma cells by a selective cyclooxygenase-2 inhibitor, celecoxib

PURPOSE

Previously, we reported that inhibitors of cyclooxygenase-2 (COX-2) enzyme enhanced murine and human tumor cell response to radiation in vitro and in vivo. However, the molecular mechanisms mediating the effects of COX-2 inhibitors are not clear. The present study was designed to investigate the ability of celecoxib, a selective COX-2 inhibitor, to sensitize human head-and-neck cancer cell line, HN5, to radiation, and examine its effects on DNA repair, which may be a potential mechanism of radiosensitization.

METHODS AND MATERIALS

Cells were assessed for the effect of celecoxib (5-50 microM), by 3-[4,5-dimethylthiozol-2-yl]-2,5-diphenyltetrazolium bromide assay for growth inhibition and by clonogenic cell survival assay for the radiosensitizing effect. Kinase assay and Western analysis were conducted to assess the effect of celecoxib on DNA-dependent protein kinase catalytic subunit (PKcs) and Ku proteins. Electrophoretic mobility shift assays (EMSA) were performed to determine the DNA-binding activity of Ku/DNA-PKcs protein complex and nuclear factor kappa B (NFkappaB).

RESULTS

Celecoxib (10 and 50 microM, for 2 days) inhibited the HN5 cell growth and significantly enhanced the cell radiosensitivity in a dose-dependent manner. It also reduced the shoulder region on the radiation-survival curve, suggesting that inhibition of DNA repair processes may have occurred. Western blot analysis demonstrated that celecoxib downregulated the expression of Ku70 protein and inhibited the kinase activity of DNA-PKcs, which are involved in the double-stranded DNA-break repair machinery. By EMSA, it was further shown that celecoxib reduced DNA-binding activity of Ku/DNA-PKcs protein complex. In addition, celecoxib inhibited the constitutively active NFkappaB and the radiation-induced NFkappaB in HN5 cells, suggesting that NFkappaB may play a role in mediating the effects of celecoxib.

CONCLUSIONS

Celecoxib strongly enhanced the sensitivity of HN5 carcinoma cells to radiation, which, mechanistically, can be attributed to the inhibition of DNA repair processes in radiation-damaged cells.

Radiosensitization of Ras-mutated human tumor cells in vitro by the specific EGF receptor antagonist BIBX1382BS

BACKGROUND AND PURPOSE

To investigate the cellular and molecular consequences of antagonizing radiation-induced EGFR-activation in vitro.

PATIENTS AND METHODS

The effect of the EGFR tyrosine kinase inhibitor BIBX1382BS on radiation sensitivity was determined after single- and fractionated-dose irradiation in human cell lines of bronchial carcinoma (A549), breast adeno-carcinoma (MDA-MB-231), pharyngeal squamous-cell carcinoma (FaDu), squamous-cell carcinoma of cervix (HTB-35) as well as normal (HSF-7) and transformed (HH4-DED) human skin fibroblasts. Applying immuno-precipitation and western blotting pattern of radiation-dependent activation of different components of EGFR-signaling after pre-treatment with and without BIBX1382BS or other tyrosine kinase inhibitors was analyzed.

RESULTS

Autophosphorylation of EGFR which occurred 1-5 min after irradiation (IR, 2 Gy) or treatment with EGF (100 ng/ml) could be inhibited in all cells tested by pre-treatment with BIBX1382BS for 30 min. Combination of drug treatment with fractionated irradiation (4x2 Gy) led to a strong radiosensitizing effect in Ras-mutated A549 and MDA-MB-231 cells, but not in normal Ras presenting cell lines FaDu and HTB-35 or normal and transformed human skin fibroblasts. Both BIBX1382BS as well as the PI3 kinase inhibitor LY294002 led to a blockage (for A549 cells) or reduction (for FaDu cells) of radiation-induced P-AKT. In contrast to FaDu cells, treatment of A549 cells with LY294002 resulted in a significant decrease of post-irradiation survival of A549 cells. Furthermore, only in Ras-mutated cells, but not in normal Ras cells clonogenic survival and phosphorylation of AKT was sensitive to pre-treatment with TGF-alpha-neutralizing antibody indicating an important role of TGF-alpha in regulating radiation-induced EGFR signaling.

CONCLUSIONS

Enhancement of radiation sensitivity by the specific EGFR-tyrosine kinase inhibitor BIBX1382BS is not generally achieved in human tumor cells, but depends most likely on the Ras genotype of the cell lines tested.

An examination of radiation hormesis mechanisms using a multistage carcinogenesis model

A multistage cancer model that describes the putative rate-limiting steps in carcinogenesis is developed and used to investigate the potential impact on cumulative lung cancer incidence of the hormesis mechanisms suggested by Feinendegen and Pollycove. In the model, radiation and endogenous processes damage the DNA of target cells in the lung. Some fraction of the misrepaired or unrepaired DNA damage induces genomic instability and, ultimately, leads to the accumulation of malignant cells. The model explicitly accounts for cell birth and death processes, the clonal expansion of initiated cells, malignant conversion, and a lag period for tumor formation. Radioprotective mechanisms are incorporated into the model by postulating dose and dose-rate-dependent radical scavenging. The accuracy of DNA damage repair also depends on dose and dose rate. As currently formulated, the model is most applicable to low-linear-energy-transfer (LET) radiation delivered at low dose rates. Sensitivity studies are conducted to identify critical model inputs and to help define the shapes of the cumulative lung cancer incidence curves that may arise when dose and dose-rate-dependent cellular defense mechanisms are incorporated into a multistage cancer model. For lung cancer, both linear no-threshold (LNT-), and non-LNT-shaped responses can be obtained. If experiments demonstrate that the effects of DNA damage repair and radical scavenging are enhanced at least three-fold under low-dose conditions, our studies would support the existence of U-shaped responses. The overall fidelity of the DNA damage repair process may have a large impact on the cumulative incidence of lung cancer. The reported studies also highlight the need to know whether or not (or to what extent) multiply damaged DNA sites are formed by endogenous processes. Model inputs that give rise to U-shaped responses are consistent with an effective cumulative lung cancer incidence threshold that may be as high as 300 mGy (4 mGy per year for 75 years) for low-LET radiation.

Molecular targeting in radiotherapy of lung cancer

Molecular targeting is a promising option to increase the radiation response of tumours and to decrease normal tissue reactions, i.e. to achieve therapeutic gain. Molecular targeting substances in themselves are not curative while radiation is a highly efficient cytotoxic agent, with local recurrences often occurring from only few surviving clonogenic cells. High-dose radiotherapy therefore offers optimal conditions to evaluate the potential of specific biology-driven drugs for oncology. This review summarises the current status of preclinical and clinical research on combined radiation with examples of molecular targeting substances relevant for the treatment of NSCLC (EGFR, COX-2, VEGFR, KGF, TGF-beta, BBI).