Acriflavine enhances radiosensitivity of colon cancer cells through endoplasmic reticulum stress-mediated apoptosis

3D-printed implants loaded with acriflavine for glioblastoma treatment

Drug delivery routes play an essential role in determining the efficacy and safety of medications. This study focused on the development and optimization of 3D-printed reservoir type implants as a combinational therapy drug delivery system for Glioblastoma Multiforme (GBM) post-surgery, possessing also antibacterial properties. In this study, we used a multimodal agent, Acriflavine (ACF) as an alternative drug to treat GBM. To date, ACF is used only as an antiseptic agent, although it has been shown to possess strong anticancer activities. ACF and a low molecular weight PCL were loaded into 3D-printed reservoir-type implants for sustained drug delivery. The study demonstrated that ACF implants exhibited sustained drug release kinetics, with faster release during the initial 30 days, followed by a gradual decrease over 90 days. This controlled release profile enhances the effectiveness of ACF delivery to tumour targets while minimizing side effects associated with systemic administration. In vitro experiments confirmed the inhibitory activity of ACF against GBM cells compared to non-tumour cells. The study also highlighted the bacteriostatic effects of ACF, making the implants potentially useful for post-surgery infection management, particularly against S. aureus, a common bacterial infection associated with brain surgery. The long-term drug-release capabilities of the implants make them attractive candidates for both tumour inhibition and antibacterial treatment. The study suggests that the developed ACF delivery systems have the potential for future clinical studies. Their ability to provide increased drug efficacy without systemic toxicity makes them promising candidates for cancer therapy and post-surgery infection management.

Acriflavine-Functionalized Silica@Manganese Ferrite Nanostructures for Synergistic Radiation and Hypoxia Therapies

Mesoporous and nonmesoporous SiO2@MnFe2O4 nanostructures were loaded with the hypoxia-inducible factor-1 inhibitor acriflavine for combined radiation and hypoxia therapies. The X-ray irradiation of the drug-loaded nanostructures not only triggered the release of the acriflavine inside the cells but also initiated an energy transfer from the nanostructures to surface-adsorbed oxygen to generate singlet oxygen. While the drug-loaded mesoporous nanostructures showed an initial drug release before the irradiation, the drug was primarily released upon X-ray radiation in the case of the nonmesoporous nanostructures. However, the drug loading capacity was less efficient for the nonmesoporous nanostructures. Both drug-loaded nanostructures proved to be very efficient in irradiated MCF-7 multicellular tumor spheroids. The damage of these nanostructures toward the nontumorigenic MCF-10A multicellular spheroids was very limited because of the small number of nanostructures that entered the MCF-10A spheroids, while similar concentrations of acriflavine without nanostructures were toxic for the MCF-10A spheroids.

The Activation of the Tumor Suppressor Protein p53 by Acriflavine Leads to Mitochondrial Dysfunction and Improves the Radiosensitivity of Colon Cancer Cells

Colon cancer ranks third worldwide, and it has a growing incidence with urbanization and industrialization. Drug resistance in colon cancer is gradually affecting the treatment. This study focused on the mechanisms by which acriflavine (ACF) enhances the radiosensitivity of colon cancer cells. First, the expression and activation levels of tumor suppressor protein p53 were shown high in normal cells and tissues in its detection, which suggests that p53 is likely to be a key factor in colon cancer. Then, the expression of p53 ended up increasing in ACF group after SW620 cells were cultured with ACF. In addition, ACF group had some other changes. The expression of mitochondrial related antiapoptotic protein Bcl-2 increased, while the expression of proapoptotic protein Bax, Bad, cytopigment C, and apoptotic inducer AIF decreased. At the same time, the ability of apoptosis was enhanced, and the ability of proliferation and invasion was decreased. This suggests that ACF can promote p53 expression and affect mitochondrial function and the radiosensitivity of SW620. The luciferase reporting experiment showed that there was a binding site between ACF and p53. Besides, when IR treatment was applied to SW620 with high p53 expression, there was an increase in the expression of Bcl-2 in SW620 and decrease in Bax, Bad, and cytopigment C in AIF. Meanwhile, the cell apoptosis became stronger, and the proliferation and invasion became weaker. The experimental results were similar to those of SW620 cells cultured with ACF, suggesting that p53 is an intermediate factor in the regulation of SW620 by ACF. Finally, in this study, cells were cultured with ACF, and p53 was knocked down at the same time. The experimental results showed that after p53 was knocked down. ACF's ability to regulate SW620 is partially removed. This confirms the view that ACF regulates SW620 cells by regulating p53. In summary, this study found the mechanism by which ACF causes mitochondrial dysfunction and improves the radiosensitivity of colon cancer cells by activating the tumor suppressor protein p53, which may contribute to solving the drug resistance in colon cancer.

Downregulation of topoisomerase 1 and 2 with acriflavine sensitizes bladder cancer cells to cisplatin-based chemotherapy

BACKGROUND

Resistance to cisplatin is a major obstacle to effective treatment of bladder cancer (BC). The present study aimed to determine whether a combination of acriflavine (ACF) with cisplatin could potentiate the antitumor property of cisplatin against the BC cells. Furthermore, the molecular mechanism behind the anticancer action of ACF was considered.

METHODS AND RESULTS

Two human BC cells (5637 and EJ138) contain mutated form of p53 was culture in standard condition. Cotreatment protocol (simultaneous combination of IC₃₀ value of ACF + various dose of cisplatin for 72 h) and pretreatment protocol (pretreatment with IC₁₅ value of ACF for 24 h + various dose of cisplatin for 48 h) was used to determine the effect of ACF on the cells' sensitivity to main drug cisplatin. To assess the mechanism of action of ACF, real-time PCR was used to evaluate mRNA levels of hypoxia-inducible factor-1α (HIF-1α), Bax, Bcl-2, topoisomerase1 (TOP1) and topoisomerase 2 (TOP2A). Combination of ACF with cisplatin either as cotreatment or opretreatment protocol could significantly reduce the IC₅₀ values of cisplatin as compared to the IC₅₀ of cisplatin when use as a single drug. In addition, ACF could markedly decrease mRNA expression of TOP1 and TOP2A without changing the expression of HIF-1ɑ, Bax and Bcl-2.

CONCLUSIONS

Our findings indicate that combination of cisplatin with ACF was able to significantly enhance the sensitivity of BC cells to cisplatin. The antitumor activity of ACF is exerted through the downregulation of TOP1 and TOP2A genes expression. ACF may serve as an adjuvant to boost cisplatin-based chemotherapy.

Acriflavine targets oncogenic STAT5 signaling in myeloid leukemia cells

Acriflavine (ACF) is an antiseptic with anticancer properties, blocking the growth of solid and haematopoietic tumour cells. Moreover, this compound has been also shown to overcome the resistance of cancer cells to chemotherapeutic agents. ACF has been shown to target hypoxia‐inducible factors (HIFs) activity, which are key effectors of hypoxia‐mediated chemoresistance. In this study, we showed that ACF inhibits the growth and survival of chronic myeloid leukaemia (CML) and acute myeloid leukaemia (AML) cell lines in normoxic conditions. We further demonstrated that ACF down‐regulates STAT5 expression in CML and AML cells but activates STAT3 in CML cells in a HIF‐independent manner. In addition, we demonstrated that ACF suppresses the resistance of CML cells to tyrosine kinase inhibitors, such as imatinib. Our data suggest that the dual effect of ACF might be exploited to eradicate de novo or acquired resistance of myeloid leukaemia cells to chemotherapy.

Inhibition of colorectal cancer-associated fibroblasts by lipid nanocapsules loaded with acriflavine or paclitaxel

Crosstalk between cancer-associated fibroblasts (CAFs) and colorectal cancer cells promotes tumor growth and contributes to chemoresistance. In this study, we assessed the sensitivity of a primary CAF cell line, CT5.3hTERT, to standard-of-care and alternative cytotoxic treatments. Paclitaxel (PTX) and acriflavine (ACF) were identified as the most promising molecules to inhibit CAF development. To allow the translational use of both drugs, we developed lipid nanocapsule (LNC) formulations for PTX and ACF. Finally, we mixed CAFs and tumor cell lines in a cocultured spheroid, and the effect of both drugs was investigated by histological analyses. We demonstrated CAF inhibition by LNC-ACF and whole tumor inhibition by LNC-PTX. Altogether, we proposed a new strategy to reduce CAF populations in the colorectal microenvironment that should be tested in vivo.

Radiosensitizing Effect of Novel Phenylpyrimidine Derivatives on Human Lung Cancer Cells via Cell Cycle Perturbation

Radiotherapy is one of the most common treatments for cancer, but radioresistance and injury to normal tissue are considered major obstacles to successful radiotherapy. Thus, there is an urgent need to develop radiosensitizers to improve the therapeutic outcomes of radiotherapy in cancer patients. Our previous efforts to identify novel radiosensitizers, using high-throughput screening targeting p53 and Nrf2 revealed a promising N-phenylpyrimidin-2-amine (PPA) lead compound. In the present study, 17 derivatives of this lead compound were examined, and it was found that 4-(4-fluorophenyl)-N-(4-nitrophenyl)-6-phenylpyrimidin-2-amine (PPA5), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)-3-methoxy-N-methyl -benzamide (PPA13), 4-((4-(4-fluorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA14), 4-((4-(2-chlorophenyl)pyrimidin-2-yl)amino)benzenesulfonamide (PPA15), and 4-((4-(2-chlorophenyl)pyrimidin-2-yl)amino)-N-methylbenzamide (PPA17) inhibited cell viability by more than 50%, with a marked increase in the proportion of cells arrested at the G₂/M phase of cell cycle. Among these compounds, PPA15 markedly increased the sub-G₁ cell population and increased the levels of cyclin B1 and the phosphorylation levels of cyclin-dependent kinase (CDK) 1. Combined treatment with radiation and PPA14 or PPA15 significantly decreased clonogenic survival. An in vitro kinase assay revealed that PPA15 inhibited multiple CDKs involved in cell cycle regulation. Compared with drug or radiation treatment alone, combined treatment with PPA15 and radiation resulted in the suppression of A549 tumor growth in mice by 59.5% and 52.7%, respectively. Treatment with PPA15 alone directly inhibited tumor growth by 25.7%. These findings suggest that the novel pan CDK inhibitor, PPA15, may be a promising treatment to improve the effectiveness of radiotherapy for the treatment of cancer. SIGNIFICANCE STATEMENT: Several inhibitors of CDK have been successfully evaluated in combination with other chemotherapeutics in clinical trials, but negative side effects have partially restricted their clinical use. In this study, we identified a novel pan-CDK inhibitor to increase radiosensitivity, and we hope this work will encourage the development of promising small-molecule radiosensitizers.

Molecular imaging of small molecule drugs in animal tissues using laser desorption postionization mass spectrometry

Localization and quantification of the target drug in tissues is a key indicator of efficacy in drug discovery. In contrast to established methods that require matrices and complex sample pretreatment steps, matrix-free and low cost in situ analysis of small molecule drugs by mass spectrometry (MS) remains challenging. Here, we present a novel approach, laser desorption postionization (LDPI), which is coupled to a linear time-of-flight (TOF) MS and used to image the distribution of acriflavine (ACF) directly from a histological section of mouse kidney without any matrix or sample pretreatment. The identification of the mass peaks assigned to ACF was further confirmed by DESI-MS/MS. Moreover, the matrix effect from the tissue section was explored, showing minimal desorption and ionization suppression in the LDPI-MS process. LDPI-MS imaging (LDPI-MSI) was performed on 30 μm kidney sections from mice 15 min postdose that were dosed with 30 mg kg^-1 of ACF by monitoring the fragment ion at m/z 209. The LDPI-MS image revealed a global view of the distribution of ACF in the kidney compartments (pelvis, medulla, and cortex). Estimated concentrations of ACF residue in mouse kidney were obtained by LDPI-MSI and LC-MS/MS and a 12.1% difference in measured tissue concentration was found. These results suggest that the use of LDPI-MS in small molecule drug localization and quantification directly from biological tissue at the same time is favorable.

Acriflavine enhances the antitumor activity of the chemotherapeutic drug 5-fluorouracil in colorectal cancer cells

5-Fluorouracil (5-FU)-based chemotherapy improves the overall survival rates of patients with colorectal cancer (CRC). However, only a small proportion of patients respond to 5-FU when used as a single agent. The aim of the present study was to investigate whether the anticancer property of 5-FU is potentiated by combination treatment with acriflavine (ACF) in CRC cells. Additionally, the potential underlying molecular mechanisms of the cytotoxic effect of ACF were determined. The cytotoxic effects of ACF, 5-FU and irinotecan on different CRC cell lines with different p53 status were investigated using an MTT assay. SW480 cells that express a mutated form of p53 and two other CRC cell lines were used, HCT116 and LS174T, with wild-type p53. To determine the effect of ACF on the sensitivity of cells to 5-FU, cells were co-treated with the 30% maximal inhibitory concentration (IC30) of ACF and various concentrations of 5-FU, or pretreated with the IC30 of ACF and various concentrations of 5-FU. To assess the mechanism of action of ACF, cells were treated with IC30 values of the compound and then the reverse transcription-quantitative polymerase chain reaction was used to evaluate mRNA levels of hypoxia-inducible factor-1α (HIF-1α) and topoisomerase 2. Results indicate that pretreatment with ACF markedly sensitized CRC cells to the cytotoxic effects of 5-FU, whereas simultaneous treatment with ACF and 5-FU were not able to alter the resistance of CRC cells to 5-FU. In comparison with irinotecan, ACF was a more potent agent for enhancing the antitumor activity of 5-FU. ACF did not alter the mRNA levels of either HIF-1α or topoisomerase 2. The results of the present study reveal for the first time that pretreatment of CRC cells with ACF markedly increases the cytotoxic effects of 5-FU, regardless of the p53 status of cells.

Enhanced radiation effect on SMCC7721 cells through endoplasmic reticulum stress induced by C225-GNPs in vitro and in vivo

The high atomic number of gold nanoparticles (GNPs) enables them to offer potential as practical and efficient radiosensitizing agents for cancer radiotherapy applications. In the present study, it was demonstrated that GNPs can significantly modulate the irradiation response of hepatocellular carcinoma (HCC) cells in vitro and in vivo, of which the underlying mechanisms were investigated. Cetuximab (C225) is a targeting agent, which binds to the extracellular domain of epidermal growth factor receptor (EGFR). Hepatocyte-targeting, EGFR-specific C225 was synthesized onto GNP surfaces (C225-GNPs) to increase the GNP targeting specificity. C225-GNPs was synthesized successfully and characterized. The cytotoxicity was tested using a Cell Counting Kit-8 assay and 50% inhibition concentration of SMCC7721 cells was calculated. Cell uptake assay was detected using transmission electron microscopy. Radiosensitization was tested using a cell colony formation assay and cell cycle was detected using flow cytometry. The expression of a number of apoptotic proteins were tested by western blot analysis. Orthotropic SMCC7721 xenografts were used in order to verify its radiosensitizing effect. The results revealed that a higher number of C225-GNPs were effectively uptaken by SMCC7721 cells and markedly enhanced cancer cell death. The sensitization mechanism of C225-GNPs was associated with the apoptotic gene signalling process activated by endoplasmic reticulum stress and the unfolded protein response in cancer cells. In orthotopic SMCC7721 xenografts, the C225-GNPs significantly enhanced the radiation-induced suppression of tumour growth. The results of the present study provided evidence that C225-GNPs are potent radiosensitizers with radiotherapeutic value for HCC with the overexpression of EGFR.

Quercetin suppresses DNA double-strand break repair and enhances the radiosensitivity of human ovarian cancer cells via p53-dependent endoplasmic reticulum stress pathway

Quercetin is proven to have anticancer effects for many cancers. However, the role of tumor suppressor p53 on quercetin's radiosensitization and regulation of endoplasmic reticulum (ER) stress response in this process remains obscure. Here, quercetin exposure resulted in ER stress, prolonged DNA repair, and the expression of p53 protein; phosphorylation on serine 15 and 20 increased in combination with X-irradiation. Quercetin pretreatment could potentiate radiation-induced cell death. The combination of irradiation and quercetin treatment aggravated DNA damages and caused typical apoptotic cell death; as well the expression of Bax and p21 elevated and the expression of Bcl-2 decreased. Knocking down of p53 could reverse all the above effects under quercetin in combination with radiation. In addition, quercetin-induced radiosensitization was through stimulation of ATM phosphorylation. In human ovarian cancer xenograft model, combined treatment of quercetin and radiation significantly restrained the growth of tumors, accompanied with the activation of p53, CCAAT/enhancer-binding protein homologous protein, and γ-H2AX. Overall, these results indicated that quercetin acted as a promising radiosensitizer through p53-dependent ER stress signals.

Disruption of the monocarboxylate transporter-4-basigin interaction inhibits the hypoxic response, proliferation, and tumor progression

We have previously shown that glioblastoma stem cells (GSCs) are enriched in the hypoxic tumor microenvironment, and that monocarboxylate transporter-4 (MCT4) is critical for mediating GSC signaling in hypoxia. Basigin is involved in many physiological functions during early stages of development and in cancer and is required for functional plasma membrane expression of MCT4. We sought to determine if disruption of the MCT-Basigin interaction may be achieved with a small molecule. Using a cell-based drug-screening assay, we identified Acriflavine (ACF), a small molecule that inhibits the binding between Basigin and MCT4. Surface plasmon resonance and cellular thermal-shift-assays confirmed ACF binding to basigin in vitro and in live glioblastoma cells, respectively. ACF significantly inhibited growth and self-renewal potential of several glioblastoma neurosphere lines in vitro, and this activity was further augmented by hypoxia. Finally, treatment of mice bearing GSC-derived xenografts resulted in significant inhibition of tumor progression in early and late-stage disease. ACF treatment inhibited intratumoral expression of VEGF and tumor vascularization. Our work serves as a proof-of-concept as it shows, for the first time, that disruption of MCT binding to their chaperon, Basigin, may be an effective approach to target GSC and to inhibit angiogenesis and tumor progression.

Proflavin suppresses the growth of human osteosarcoma MG63 cells through apoptosis and autophagy

Proflavin is one of the novel acridine derivatives that possess various pharmacological effects. Although numerous studies have been performed to investigate proflavin, its effects have not been investigated on the human osteosarcoma MG63 cell line. The core aim of the present study was to test the effects of proflavin on the viability of MG63 cells and the induction of apoptosis and autophagy in MG63 cells. The induction of apoptosis was examined by measuring the changes in the expression of the B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein mRNA and proteins. Apoptotic cell death was identified by the proteolytic cleavage of poly (adenosine diphosphate-ribose) polymerase and caspase-3 and caspase-9. In addition, the autophagic effects of proflavin were examined by the quantitation of the mRNA expression of autophagy protein 5 and Beclin 1, in addition to the identification of the accumulation of microtubule-associated protein 1 light chain 3-II. The present results revealed that proflavin inhibited the proliferation of MG63 cells in a dose-dependent manner. Proflavin-induced cell death was attributed to apoptosis and autophagy. Overall, the present results indicated that the antiseptic agent proflavin exerts anticancer potential through the synergistic activity of apoptosis and autophagy.

A novel pyrido-thieno-pyrimidine derivative activates p53 through induction of phosphorylation and acetylation in colorectal cancer cells

The tumor suppressor p53 plays a key role in regulation of the cell cycle, apoptosis and senescence in response to various stresses. We screened a library of 7920 chemical compounds for the p53 activator and identified N-[2-(dimethylamino)ethyl]-2,3-dimethyl-4-oxo-4H-pyrido[1,2-a]thieno[2,3-d]pyrimidine-9-carboxamide (PTP), which significantly increased p53-mediated reporter activity in colorectal cancer cells. PTP was found to induce p53 protein and activated transcription of downstream genes, such as p21 and PUMA, in HCT116 cells, leading to growth delay, G1-phase cell cycle arrest, cell senescence and cell death. Proximity ligation assay revealed that PTP weakened the interaction between p53 and murine double minute 2 (MDM2) in situ, thereby inhibiting MDM2-mediated p53 degradation. Although DNA damage has been known to promote phosphorylation of p53 and MDM2, thereby preventing their interaction and stabilizing p53, PTP did not cause DNA damage or activate any DNA damage response signaling. Instead, phosphorylation of p53 was mediated by Erk1/2 MAP kinase. In addition, PTP induced acetylation of p53 at Lys382 in a p300-dependent manner, but sirtuin (SIRT)1 and histone deacetylase (HDAC)1, a well-known p53-regulating deacetylase, were not involved. In the present study, the novel anticancer agent PTP was shown to cause the accumulation of p53 by inducing multiple post-translational modifications, as well as cell cycle arrest, senescence and cell death.

Acriflavine suppresses the growth of human osteosarcoma cells through apoptosis and autophagy

The aim of this study was to investigate the effects of acriflavine on viability and induction of apoptosis and autophagy in human osteosarcoma cell lines MG63. Inhibition of cell proliferation by acriflavine was determined using MTT assay. Induction of apoptosis was examined by measuring the changes in expression of Bcl-2 and Bax in messenger RNA (mRNA) and protein levels. Identification of the proteolytic cleavage of poly (ADP)-ribose polymerase (PARP) and caspase-3 and caspase-9 was carried out to study apoptotic cell death. Autophagic effects were examined by quantitation of mRNA expression of autophagy protein 5 (Atg5) and Beclin1 and identifying accumulation of microtubule-associated protein 1 light chain 3 (LC3)-II. The results showed acriflavine inhibited cell proliferation of osteosarcoma cells in dose-dependent fashion. Acriflavine-induced cell death was attributed to both apoptosis and autophagy. Moreover, it was associated with changes in the levels of Bcl-2 and Bax in the osteosarcoma cells. The antiseptic agent, acriflavine, has anticancer potential through synergistic activity of apoptosis and autophagy.

Investigation on the inclusion and toxicity of acriflavine with cyclodextrins: a spectroscopic approach

Acriflavine hydrochloride (AFN) is a prospective drug worn in the eradication of HIV1 infection. The toxicity and adverse side effects renders the potent drug to limits its usage. However, to overcome the dilemma we have aimed to select carriers with great complexation efficiencies in different cyclodextrins (CDs) of varying cavity size. The interaction of AFN with α, β and γ-CDs were investigated using absorption and steady state as well as lifetime measurements. From the obtained data it was found that AFN fits in the cavity of α and β-CDs but unable to form inclusion complex with γ-CD. The effect of quencher molecules during the inclusion phenomena of AFN with CDs was explored via steady state measurements. The nature of binding forces responsible for the inclusion of AFN with CDs was discussed by using thermodynamic parameters. Using Benesi-Hildebrand equation the stoichiometry of AFN with CDs was predominantly found to be 1:1. To get deeper in situ, the in vitro toxicity of AFN and its complexation product were probed by Artemia salina sp. The toxicity of AFN was reduced when complexed with α and β-CDs.

Inhibition of hypoxia-inducible factors limits tumor progression in a mouse model of colorectal cancer

Hypoxia-inducible factors (HIFs) accumulate in both neoplastic and inflammatory cells within the tumor microenvironment and impact the progression of a variety of diseases, including colorectal cancer. Pharmacological HIF inhibition represents a novel therapeutic strategy for cancer treatment. We show here that acriflavine (ACF), a naturally occurring compound known to repress HIF transcriptional activity, halts the progression of an autochthonous model of established colitis-associated colon cancer (CAC) in immunocompetent mice. ACF treatment resulted in decreased tumor number, size and advancement (based on histopathological scoring) of CAC. Moreover, ACF treatment corresponded with decreased macrophage infiltration and vascularity in colorectal tumors. Importantly, ACF treatment inhibited the hypoxic induction of M-CSFR, as well as the expression of the angiogenic factor (vascular endothelial growth factor), a canonical HIF target, with little to no impact on the Nuclear factor-kappa B pathway in bone marrow-derived macrophages. These effects probably explain the observed in vivo phenotypes. Finally, an allograft tumor model further confirmed that ACF treatment inhibits tumor growth through HIF-dependent mechanisms. These results suggest pharmacological HIF inhibition in multiple cell types, including epithelial and innate immune cells, significantly limits tumor growth and progression.

Mechanisms of radiation toxicity in transformed and non-transformed cells

Radiation damage to biological systems is determined by the type of radiation, the total dosage of exposure, the dose rate, and the region of the body exposed. Three modes of cell death—necrosis, apoptosis, and autophagy—as well as accelerated senescence have been demonstrated to occur in vitro and in vivo in response to radiation in cancer cells as well as in normal cells. The basis for cellular selection for each mode depends on various factors including the specific cell type involved, the dose of radiation absorbed by the cell, and whether it is proliferating and/or transformed. Here we review the signaling mechanisms activated by radiation for the induction of toxicity in transformed and normal cells. Understanding the molecular mechanisms of radiation toxicity is critical for the development of radiation countermeasures as well as for the improvement of clinical radiation in cancer treatment.