Carbon Ion Beam Irradiation Research Articles

PU-H71, a novel Hsp90 inhibitor, as a potential cancer-specific sensitizer to carbon-ion beam therapy.

PU-H71, a heat shock protein 90 (Hsp90) inhibitor, has yielded therapeutic efficacy in many preclinical models and is currently in clinical trials. Carbon-ion radiotherapy (CIRT) has provided successful tumor control; however, there is still room for improvement, particularly in terms of tumor-specific radiosensitization. The Hsp90 inhibitor PU-H71 has been shown to sensitize tumor cells to X-ray radiation. A murine osteosarcoma cell line (LM8) and a normal human fibroblast cell line (AG01522) were treated with PU-H71 before X-ray, 14- or 50-keV/µm carbon-ion beam (C-ion) irradiation. Cell survival and protein expression were evaluated with colony formation and western blot, respectively. Treatment with PU-H71 alone was shown to be non-toxic to both cell lines; however, PU-H71 was shown to significantly sensitize LM8 cells to not only X-ray, but also to C-ion irradiation, while only a minimal sensitizing effect was observed in AG01522 cells. PU-H71 treatment was found to suppress the protein expression levels of Rad51 and Ku70, which are associated with the homologous recombination pathway and the non-homologous end-joining pathway of double-strand break repair. The findings reported here suggest that PU-H71 could be a promising radiosensitizer for CIRT.

Flower color mutants induced by carbon ion beam irradiation of geranium (Pelargonium × hortorum, Bailey)

In an attempt to elucidate the biological effects and underlying mutations involving flower color in ornamental plants following carbon ion beam radiation, shoots of geranium were exposed at dosages of 0, 10, 15, 30, and 40 Gy, and one flower color mutant was obtained. The morphological characteristics, physiological aspects, and DNA polymorphisms between wild-type and flower color mutants were analyzed. The colors of petal, peduncle, pistil, and stamen of the mutant displayed significant differences compared to those of the wild-type. Compared to the original plants, the total anthocyanin content in the petals of the mutant significantly decreased, resulting in a light pink petal phenotype. DNA polymorphisms detected by random amplified polymorphic DNA analysis showed that the ratio of different bands between the wild-type and mutant reached up to 13.2 %. The present study demonstrates that carbon ion beam irradiation is effective in inducing genomic variations, resulting in flower color geranium mutants within a relatively short period of time. Meanwhile, the developed flower-color mutants may be potentially used in future mutational research studies involving ornamental plants.

Mutagenic effects of carbon ion beam irradiations on dry Lotus japonicus seeds

Carbon ion beam irradiation is a powerful method for creating mutants and has been used in crop breeding more and more. To investigate the effects of carbon ion beams on Lotus japonicus, dry seeds were irradiated by 80MeV/u carbon ion beam at dosages of 0, 100, 200, 300, 400, 500 and 600Gy. The germination rate, survival rate and root length of M1 populations were explored and the dose of 400Gy was selected as the median lethal dose (LD50) for a large-scale mutant screening. Among 2472 M2 plants, 127 morphological mutants including leaf, stem, flower and fruit phenotypic variation were found, and the mutation frequency was approximately 5.14%. Inter simple sequence repeat (ISSR) assays were utilized to investigate the DNA polymorphism between seven mutants and eight plants without phenotypic variation from M2 populations. No remarkable differences were detected between these two groups, and the total polymorphic rate was 0.567%.

Scintillation imaging of air during proton and carbon-ion beam irradiations

We previously reported that the luminescence imaging of water during proton or carbon-ion irradiation is possible using a charge-coupled device (CCD) camera, and these luminescence images can be used for the range estimations for these therapies. In the images during these irradiations to water phantoms, we observed scintillation images in the air parts. We conducted analysis of these images during proton and carbon-ion irradiations to use them for beam width estimations. We set profiles on the air part of the luminescence images of water during 100.2MeV proton and 241.5MeV/n carbon-ion irradiations. We estimated the widths of the beams from the scintillation images and compared them with those by simulation results. We also estimated the intensity and light spectrum of the scintillation of air and compared with those of the luminescence of water. The estimated widths of the proton and carbon-ion beams from the scintillation images of air were almost the same as those measured with simulations. The intensities of the scintillation of air were 3% and 5% of those of the luminescence of water for the proton and carbon-ion beams, respectively. The light spectrum of the scintillation of air peaked around 350–450nm while those of luminescence of water showed wide distribution which peaked 450–550nm. We confirmed that scintillation imaging of air during proton and carbon-ion beam irradiations were possible. The scintillation imaging of air could be used for the width estimations of proton and carbon-ion beams.

Radiological properties of nanocomposite Fricke gel dosimeters for heavy ion beams.

The radiological properties of nanocomposite Fricke gel (NC-FG) dosimeters prepared with different concentrations of nano-clay, perchloric acid and ferrous ions in deaerated conditions were investigated under carbon and argon ion beam irradiation covering a linear-energy-transfer (LET) range of 10 to 3000 eV/nm. We found that NC-FG exhibits radiological properties distinct from those of conventional Fricke gel. The radiation sensitivity of NC-FG is independent of the LET and is nearly constant even at very high LET (3000 eV/nm) values in the Bragg peak region of the argon ion beam. In addition, whereas conventional Fricke gel dosimeters only operate under acidic conditions, NC-FG dosimeters function under both acidic and neutral conditions. The radiation sensitivity decreases with decreasing nano-clay concentration in NC-FG, which indicates that the nano-clay plays a vital role in the radiation-induced oxidation of Fe2+.

Application of a Yield Approach for the Prediction of Positron Emitter Distributions Produced During Therapeutic Carbon-Ion Beam Irradiation

Positron emission tomography (PET) is a clinically implemented method for in vivo verification of treatment delivery in ion-beam therapy. The dose distribution is the relevant measure but PET captures a ${\beta ^ + }$ -activity distribution, that is created as a side product during the irradiation. Therefore, a prediction of the activity distribution is required. We present a simulation code that makes use of measured yields of ${\beta ^ + }$ -emitters to perform this task. The yields are available in three reference materials. A conversion from X-ray gray values to a combination of these materials has been set up. The lateral properties of the ion beam are described by means of a formulation of Moliere’s scattering theory in thick targets. A model of the annihilation point density around an emitting nuclide has been implemented in the software to describe the movement of the positrons. Simulations of phantom experiments as well as of a real patient case were performed. The results are comparable or superior to the results obtained from an established condensed history Monte Carlo code. We conclude that measured yields can be used as raw data for the calculation of ion-beam-induced ${\beta ^ + }$ -activity distribution instead of nuclear cross sections.

Breeding pleuromutilin protoplasts strains by carbon ion beam irradiation

Breeding pleuromutilin protoplasts strains by carbon ion beam irradiation

A comprehensive analysis of radiosensitization targets; functional inhibition of DNA methyltransferase 3B radiosensitizes by disrupting DNA damage regulation.

A comprehensive genome-wide screen of radiosensitization targets in HeLa cells was performed using a shRNA-library/functional cluster analysis and DNMT3B was identified as a candidate target. DNMT3B RNAi increased the sensitivity of HeLa, A549 and HCT116 cells to both γ-irradiation and carbon-ion beam irradiation. DNMT3B RNAi reduced the activation of DNA damage responses induced by γ-irradiation, including HP1β-, γH2AX- and Rad51-foci formation. DNMT3B RNAi impaired damage-dependent H2AX accumulation and showed a reduced level of γH2AX induction after γ-irradiation. DNMT3B interacted with HP1β in non-irradiated conditions, whereas irradiation abrogated the DNMT3B/HP1β complex but induced interaction between DNMT3B and H2AX. Consistent with radiosensitization, TP63, BAX, PUMA and NOXA expression was induced after γ-irradiation in DNMT3B knockdown cells. Together with the observation that H2AX overexpression canceled radiosensitization by DNMT3B RNAi, these results suggest that DNMT3B RNAi induced radiosensitization through impairment of damage-dependent HP1β foci formation and efficient γH2AX-induction mechanisms including H2AX accumulation. Enhanced radiosensitivity by DNMT3B RNAi was also observed in a tumor xenograft model. Taken together, the current study implies that comprehensive screening accompanied by a cluster analysis enabled the identification of radiosensitization targets. Downregulation of DNMT3B, one of the targets identified using this method, radiosensitizes cancer cells by disturbing multiple DNA damage responses.

Irradiation Response of Adipose-derived Stem Cells under Three-dimensional Culture Condition

ObjectiveAdipose tissue distributes widely in human body. The irradiation response of the adipose cells in vivo remains to be investigated. In this study we investigated irradiation response of adipose-derived stem cells (ASCs) under three-dimensional culture condition. MethodsASCs were isolated and cultured in low attachment dishes to form three-dimensional (3D) spheres in vitro. The neuronal differentiation potential and stem-liked characteristics was monitored by using immunofluoresence staining and flow cytometry in monolayer and 3D culture. To investigate the irradiation sensitivity of 3D sphere culture, the fraction of colony survival and micronucleus were detected in monolayer and 3D culture. Soft agar assays were performed for measuring malignant transformation for the irradiated monolayer and 3D culture. ResultsThe 3D cultured ASCs had higher differentiation potential and an higher stem-like cell percentage. The 3D cultures were more radioresistant after either high linear energy transfer (LET) carbon ion beam or low LET X-ray irradiation compared with the monolayer cell. The ASCs' potential of cellular transformation was lower after irradiation by soft agar assay. ConclusionThese findings suggest that adipose tissue cell are relatively genomic stable and resistant to genotoxic stress.

Growth Arrest and Cancer Stem Cell Marker Expression Following High Dose X-ray or Carbon Ion Beam Irradiation

Growth Arrest and Cancer Stem Cell Marker Expression Following High Dose X-ray or Carbon Ion Beam Irradiation

Cladding-like waveguide structure in Nd:YAG crystal fabricated by multiple ion irradiation for enhanced waveguide lasing.

We report on a cladding-like waveguide structure in Nd:YAG crystal fabricated by the multiple carbon ion beam irradiation. After the designed multiple irradiation process, the cladding-like waveguide with triple refractive-index layers were constructed in the region near the surface of the crystal. With such a structure, the waveguiding core was compressed and refractive index profile was modified, resulting in a higher light intensity than that of the single ion-beam-irradiated monolayer waveguide. The waveguide lasing at wavelength of 1064 nm was achieved with enhanced performance in the cladding-like structures with both planar and ridge configurations by the optical pump at 810 nm.

Carbon ion beam combined with cisplatin effectively disrupts triple negative breast cancer stem-like cells in vitro.

AimsAlthough a relatively small proportion of all breast cancer (BC), triple negative (TN) BC is responsible for a relatively large proportion of BC deaths because of its worse clinical outcome. To investigate whether a carbon ion beam alone or in combination with cisplatin (CDDP) has a beneficial effect compared to X-rays, we target triple negative (TN) breast cancer stem-like cells (CSCs).MethodsHuman breast CSCs sorted from MDA-MB-231 and MDA-MB-453 cells were treated with a carbon ion beam or X-ray irradiation alone or in combination with CDDP, and then colony, spheroid and tumor formation assays, RT-PCR Array analysis, and immunofluorescence γH2AX foci assay were performed.ResultsThe colony, spheroid formation, and tumorigenicity assays confirmed that CD44+/CD24- and ESA+/CD24- cells have CSC properties in MDA-MB-231 and MDA-MB-453 cells, respectively. The proportion of CSCs was more enriched after CDDP combination with either X-ray or carbon ion beam, however carbon ion beam combined with CDDP significantly suppressed colony and spheroid formation and more significantly inhibited cell cycle progression (sub-G1 arrest) compared to X-ray combined with CDDP or carbon ion beam alone. RT-PCR Array analysis showed that carbon ion beam combined with CDDP significantly induced apoptosis-related Cytochrome c, almost completely eliminated expression of the CSC markers CD44 and ESA, and significantly inhibited angiogenesis, and metastasis-related HIF1α and CD26 compared to carbon ion beam alone, X-ray alone, or X-ray combined with CDDP. The immunofluorescence assay showed that not only the number but also the size of γH2AX foci in CSCs were larger 24 h after carbon ion beam combined with CDDP compared to those of X-ray alone and X-ray combined with CDDP.ConclusionsCarbon ion beam combined with CDDP has superior potential to kill TN breast CSCs with irreparable severe DNA damage and enhanced apoptosis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0429-7) contains supplementary material, which is available to authorized users.

Combination of carbon ion beam and gemcitabine causes irreparable DNA damage and death of radioresistant pancreatic cancer stem-like cells in vitro and in vivo.

We try to elucidate whether a carbon ion beam alone or in combination with gemcitabine has advantages over X-ray in targeting putative pancreatic cancer stem-like cells (CSCs) in vitro and in vivo. Colony, spheroid formation and tumorigenicity assays confirmed that CD44+/ESA+ cells sorted from PANC1 and PK45 cells have more CSC properties than CD44-/ESA- cells. The number of colonies and spheroids formed from CSCs after carbon ion beam irradiation was significantly reduced compared to after X-ray irradiation, and they were extremely highly suppressed when carbon ion beam combined with gemcitabine. The relative biological effectiveness (RBE) values for the carbon ion beam relative to X-ray at the D10 levels for CSCs were 2.23-2.66. Expressions of multiple cell death-related genes were remarkably highly induced, and large numbers of γH2AX foci in CSCs were formed after carbon ion beam combined with gemcitabine. The highly expressed CSC markers were significantly inhibited after 30 Gy of carbon ion beam and almost lost after 25 Gy carbon ion beam combined with 50 mg/kg gemcitabine. In conclusion, a carbon ion beam combined with gemcitabine has superior potential to kill pancreatic CSCs via irreparable clustered DSB compared to a carbon ion alone or X-rays combined with gemcitabine.

Carbon ion beam triggers both caspase-dependent and caspase-independent pathway of apoptosis in HeLa and status of PARP-1 controls intensity of apoptosis.

High linear energy transfer (LET) carbon ion beam (CIB) is becoming very promising tool for various cancer treatments and is more efficient than conventional low LET gamma or X-rays to kill malignant or radio-resistant cells, although detailed mechanism of cell death is still unknown. Poly (ADP-ribose) polymerase-1 (PARP-1) is a key player in DNA repair and its inhibitors are well-known as radio-sensitizer for low LET radiation. The objective of our study was to find mechanism(s) of induction of apoptosis by CIB and role of PARP-1 in CIB-induced apoptosis. We observed overall higher apoptosis in PARP-1 knocked down HeLa cells (HsiI) compared with negative control H-vector cells after irradiation with CIB (0-4Gy). CIB activated both intrinsic and extrinsic pathways of apoptosis via caspase-9 and caspase-8 activation respectively, followed by caspase-3 activation, apoptotic body, nucleosomal ladder formation and sub-G1 accumulation. Apoptosis inducing factor translocation into nucleus in H-vector but not in HsiI cells after CIB irradiation contributed caspase-independent apoptosis. Higher p53 expression was observed in HsiI cells compared with H-vector after exposure with CIB. Notably, we observed about 37% fall of mitochondrial membrane potential, activation of caspase-9 and caspase-3 and mild activation of caspase-8 without any detectable apoptotic body formation in un-irradiated HsiI cells. We conclude that reduction of PARP-1 expression activates apoptotic signals via intrinsic and extrinsic pathways in un-irradiated cells. CIB irradiation further intensified both intrinsic and extrinsic pathways of apoptosis synergistically along with up-regulation of p53 in HsiI cells resulting overall higher apoptosis in HsiI than H-vector.

Radiosensitizing effect of carboplatin and paclitaxel to carbon-ion beam irradiation in the non-small-cell lung cancer cell line H460.

The present study investigated the ability of carboplatin and paclitaxel to sensitize human non-small-cell lung cancer (NSCLC) cells to carbon-ion beam irradiation. NSCLC H460 cells treated with carboplatin or paclitaxel were irradiated with X-rays or carbon-ion beams, and radiosensitivity was evaluated by clonogenic survival assay. Cell proliferation was determined by counting the number of viable cells using Trypan blue. Apoptosis and senescence were evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining and senescence-associated β-galactosidase (SA-β-gal) staining, respectively. The expression of cleaved caspase-3, Bax, p53 and p21 was analyzed by western blotting. Clonogenic survival assays demonstrated a synergistic radiosensitizing effect of carboplatin and paclitaxel with carbon-ion beams; the sensitizer enhancement ratios (SERs) at the dose giving a 10% survival fraction (D10) were 1.21 and 1.22, respectively. Similarly, carboplatin and paclitaxel showed a radiosensitizing effect with X-rays; the SERs were 1.41 and 1.29, respectively. Cell proliferation assays validated the radiosensitizing effect of carboplatin and paclitaxel with both carbon-ion beam and X-ray irradiation. Carboplatin and paclitaxel treatment combined with carbon-ion beams increased TUNEL-positive cells and the expression of cleaved caspase-3 and Bax, indicating the enhancement of apoptosis. The combined treatment also increased SA-β-gal-positive cells and the expression of p53 and p21, indicating the enhancement of senescence. In summary, carboplatin and paclitaxel radiosensitized H460 cells to carbon-ion beam irradiation by enhancing irradiation-induced apoptosis and senescence.

Phenotypic variation of sweet sorghum after carbon ion beam irradiation

The survival rate, DNA mutation rate, phenotype variation, sequence analysis of Hd1 and Hd3a were investigated after the dry seeds of sweet sorghum were irradiated by carbon ions. The results indicate that there was a marked stimulatory effect under low doses in terms of survival rate. The carbon ion irradiation also induced phenotypic variation and the mutation frequency differed as the dose increased. The maximum DNA mutation rate was 18.95%, which occurred at 200 Gy, whereas the mutation rate decreased to 17.87% at 240 Gy. The sequence analysis indicated that there was no difference between KF and KC for the Hd1 gene, but 2bp insertions were clearly observed in KF compared to KC in the case of the Hd3a gene. In conclusion, there was a significant phenotypic variation after carbon ion beam irradiation in sweet sorghum.

The Effect of p53 Status of Tumor Cells on Radiosensitivity of Irradiated Tumors With Carbon-Ion Beams Compared With γ-Rays or Reactor Neutron Beams.

BackgroundThe aim of the study was to clarify the effect of p53 status of tumor cells on radiosensitivity of solid tumors following accelerated carbon-ion beam irradiation compared with γ-rays or reactor neutron beams, referring to the response of intratumor quiescent (Q) cells.MethodsHuman head and neck squamous cell carcinoma cells transfected with mutant TP53 (SAS/mp53) or with neo vector (SAS/neo) were injected subcutaneously into hind legs of nude mice. Tumor-bearing mice received 5-bromo-2’-deoxyuridine (BrdU) continuously to label all intratumor proliferating (P) cells. They received γ-rays or accelerated carbon-ion beams at a high or reduced dose-rate. Other tumor-bearing mice received reactor thermal or epithermal neutrons at a reduced dose-rate. Immediately or 9 hours after the high dose-rate irradiation (HDRI), or immediately after the reduced dose-rate irradiation (RDRI), the tumor cells were isolated and incubated with a cytokinesis blocker, and the micronucleus (MN) frequency in cells without BrdU labeling (Q cells) was determined using immunofluorescence staining for BrdU.ResultsThe difference in radiosensitivity between the total (P + Q) and Q cells after γ-ray irradiation was markedly reduced with reactor neutron beams or carbon-ion beams, especially with a higher linear energy transfer (LET) value. Following γ-ray irradiation, SAS/neo tumor cells, especially intratumor Q cells, showed a marked reduction in sensitivity due to the recovery from radiation-induced damage, compared with the total or Q cells within SAS/mp53 tumors that showed little repair capacity. In both total and Q cells within both SAS/neo and SAS/mp53 tumors, carbon-ion beam irradiation, especially with a higher LET, showed little recovery capacity through leaving an interval between HDRI and the assay or decreasing the dose-rate. The recovery from radiation-induced damage after γ-ray irradiation was a p53-dependent event, but little recovery was found after carbon-ion beam irradiation. With RDRI, the radiosensitivity to reactor thermal and epithermal neutron beams was slightly higher than that to carbon-ion beams.ConclusionFor tumor control, including intratumor Q-cell control, accelerated carbon-ion beams, especially with a higher LET, and reactor thermal and epithermal neutron beams were very useful for suppressing the recovery from radiation-induced damage irrespective of p53 status of tumor cells.

Carbon-ion beam irradiation kills X-ray-resistant p53-null cancer cells by inducing mitotic catastrophe.

Background and PurposeTo understand the mechanisms involved in the strong killing effect of carbon-ion beam irradiation on cancer cells with TP53 tumor suppressor gene deficiencies.Materials and MethodsDNA damage responses after carbon-ion beam or X-ray irradiation in isogenic HCT116 colorectal cancer cell lines with and without TP53 (p53+/+ and p53-/-, respectively) were analyzed as follows: cell survival by clonogenic assay, cell death modes by morphologic observation of DAPI-stained nuclei, DNA double-strand breaks (DSBs) by immunostaining of phosphorylated H2AX (γH2AX), and cell cycle by flow cytometry and immunostaining of Ser10-phosphorylated histone H3.ResultsThe p53-/- cells were more resistant than the p53+/+ cells to X-ray irradiation, while the sensitivities of the p53+/+ and p53-/- cells to carbon-ion beam irradiation were comparable. X-ray and carbon-ion beam irradiations predominantly induced apoptosis of the p53+/+ cells but not the p53-/- cells. In the p53-/- cells, carbon-ion beam irradiation, but not X-ray irradiation, markedly induced mitotic catastrophe that was associated with premature mitotic entry with harboring long-retained DSBs at 24 h post-irradiation.ConclusionsEfficient induction of mitotic catastrophe in apoptosis-resistant p53-deficient cells implies a strong cancer cell-killing effect of carbon-ion beam irradiation that is independent of the p53 status, suggesting its biological advantage over X-ray treatment.

Abstract 3870: Effects of carbon ion beam, alone or in combination with cisplatin, on triple-negative breast cancer stem-like cells

Abstract Aims To investigate whether a carbon ion beam alone or in combination with cisplatin has beneficial effects compared to X-ray by targeting putative triple negative (TN) breast cancer stem cells (CSCs). Materials and Methods Human breast CSCs sorted from MDA MB231 cells were treated with carbon ion or X-ray irradiation alone or in combination with cisplatin, and then colony, spheroid and tumor formation assays, RT-PCR Array analysis as well as immunofluorescence γH2AX foci assay were performed. Results The colony, spheroid formation as well as tumorigenicity assays confirmed that CD44+/CD24- and CD44+/ESA+ cells exactly have CSC properties compared to CD44-/CD24- and CD44-/ESA- cells. CSCs were more highly enriched after X-ray or cisplatin compared to carbon ion beam. Carbon ion beam combined with cisplatin significantly suppressed colony and spheroid formation compared to that of X-ray combined with cisplatin as well as carbon ion alone. RT-PCR Array analysis showed that expression of DNA repair, apoptosis and autophagy related genes were differently altered between carbon ion beam and X-ray irradiation alone or in combination with cisplatin, and carbon ion beam combined with cisplatin more highly induced apoptosis and autophagy compared to X-ray combined with cisplatin. Immunofluorescence assay showed that not only the number but also the size of γH2AX foci in CSCs were lager 24 h after carbon ion beam combined with cisplatin compared to that of X-ray combined with cisplatin as well as carbon ion alone. Conclusion Carbon ion beam combined with cisplatin has superior potential to kill TN breast CSCs with unrepairable severe DNA damage and enhanced apoptosis as well as autophagy. Citation Format: Sei Sai, Kumiko Karasawa, Guillaume Gueal Vares, Toshiyuki Shirai. Effects of carbon ion beam, alone or in combination with cisplatin, on triple-negative breast cancer stem-like cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3870. doi:10.1158/1538-7445.AM2014-3870

Changes of Cancer Stem Cell Markers in Human Ependymoblastoma Following Carbon Ion Beam Irradiation

MTT assay were used to investigate mitochondrial respiration, cell proliferation and radio-resistant cell morphology. Genes involved in mitochondrial respiration, apoptosis, cell division and signaling were quantitatively analyzed by qRT-PCR. Mitochondrial inhibitors were used to block mitochondrial respiration in cells. Results: The apoptosis in melanoma cells were 30% higher and normal melanocyte survival was preserved 80 % with 50cGy delivered at 2400 MU/min than 50cGy delivered at a dose rate of 400MU/min in vitro setting (p<0.005). qRT-PCR data confirmed significant upregulation of apoptosis genes (AIF, FAS, FASL, Casp 3, Casp8, Casp9, TP53) in cancer cells and DNA repair and cell proliferation genes (MSH2, CCND1,CCND2, MDM2, MDM4) in HEM, HEK and HEF. Cell counts showed 60% and 68% reduction at 7 days post-radiation for the aggressive metastatic cells (p<.0.001) and for sensitive cells, respectively. Colony assays demonstrated 30% more cell killing with 2400MU/min than 400 MU/min and preserved 75% normal primary cells. Dose rate 2400 MU/min caused higher mitochondrial respiration than 400 MU/min which was directly related to total dose of radiation delivered to cells. However, the respiratory chain genes (NDUFS2, UCRC, SDHC, ATPAF2) were down regulated, suggesting that the increased respiration activity after radiation was related to post-translational activation. Mitochondrial inhibition increased cell kill to 74% (p<0.005) with inhibitor O and to 83% with inhibitor R while HEM maintained 60% survival. Conclusions: 10 MV x-rays at high dose rate with low total dose (2400 MU/minj50cGy) significantly enhances radio-sensitivity of melanoma cells while reducing radio-toxicity on normal cells. Additionally, blocking mitochondrial respiration proportionately increases melanoma cell kill with this dose rate. Our model implicates potential novel radio therapeutic options and opens untested field of radiation therapy research. Author Disclosure: S. Sarojini: None. N. Milinovikj: None. A. Pecora: None. J. Barbiere: None. M. Tuna: None. S. Jeong: None. J. Jun: None. L. Catello: None. J. Jiang: None. A. Ndlovu: None. A. Ingenito: None. K.S. Suh: None.