Doses Of High Linear Energy Transfer Research Articles

Exploratory Investigation of Dose-Linear Energy Transfer (LET) Volume Histogram (DLVH) for Adverse Events Study in Intensity Modulated Proton Therapy (IMPT).

We proposed a novel tool-a dose linear energy transfer (LET)-volume histogram (DLVH)-and performed an exploratory study to investigate rectal bleeding in prostate cancer treated with intensity modulated proton therapy. The DLVH was constructed with dose and LET as 2 axes, and the normalized volume of the structure was contoured in the dose-LET plane as isovolume lines. We defined the DLVH index, DLv%(d,l) (ie, v% of the structure) to have a dose of ≥d Gy and an LET of ≥l keV/μm, similar to the dose-volume histogram index Dv%. Nine patients with prostate cancer with rectal bleeding (Common Terminology Criteria for Adverse Events grade ≥2) were included as the adverse event group, and 48 patients with no complications were considered the control group. A P value map was constructed by comparison of the DLVH indices of all patients between the 2 groups using the Mann-Whitney U test. Dose-LET volume constraints (DLVCs) were derived based on the P value map with a manual selection procedure facilitated by Spearman's correlation tests. The obtained DLVCs were further cross-validated using a multivariate support vector machine (SVM)-based normal tissue complication probability (NTCP) model with an independent testing data set composed of 8 adverse event and 13 control patients. We extracted 2 DLVC constraints. One DLVC was obtained, Vdose/LETboundary:2.5keVμmat 75 Gy to 3.2keVμmat8.65Gy <1.27% (DLVC1), revealing a high LET volume effect. The second DLVC, V(72.2Gy,0keVμm) < 2.23% (DVLC2), revealed a high dose volume effect. The SVM-based NTCP model with 2 DLVCs provided slightly superior performance than using dose only, with an area under the curve of 0.798 versus 0.779 for the testing data set. Our results demonstrated the importance of rectal "hot spots" in both high LET (DLVC1) and high dose (DLVC2) in inducing rectal bleeding. The SVM-based NTCP model confirmed the derived DLVCs as good predictors for rectal bleeding when intensity modulated proton therapy is used to treat prostate cancer.

11Boron Delivery Agents for Boron Proton-capture Enhanced Proton Therapy.

The aim of this review was to define appropriate 11B delivery agents for boron proton-capture enhanced proton therapy (BPCEPT) taking into account the accumulated knowledge on boron compounds used for boron neutron capture therapy (BNCT). BPCEPT is a promising treatment approach which uses a high linear energy transfer (LET) dose component in conjunction with conventional proton therapy to increase the relative biological effectiveness of highly-selective charged particle therapy. Boron proton fusion reactions occur with highest cross section at certain proton energy level and thus can be tailored to the target volume with careful treatment planning that defines the 675 MeV proton distribution with high accuracy. Appropriate 11B compounds are required in order to achieve relevant high LET dose contribution from the boron proton-capture reaction. Previous scientific results and experiences with BNCT provide background knowledge and information regarding the optimization of boronated compound development, their characterization, measurement and imaging. However, there are substantial differences between BNCT and BPCEPT, which in turn places special unique chemical, physical and biological demands on 11B-carrier compounds for BPCEPT. In this review, we evaluate well-known and recently developed boron compounds for BPCEPT.

NON-TARGETED EFFECTS LEAD TO A PARIDIGM SHIFT IN RISK ASSESSMENT FOR A MISSION TO THE EARTH'S MOON OR MARTIAN MOON PHOBOS.

Cancer risk is an important limitation for galactic cosmic ray (GCR) exposures, which consist of a wide-energy range of protons, heavy ions and secondary radiation produced in shielding and tissues. Many studies suggest non-targeted effects (NTEs) occur for low doses of high-linear energy transfer (LET) radiation, leading to deviation from the linear dose response model used in radiation protection. We investigate corrections to quality factors (QF) for NTEs, which are used in predictions of fatal cancer risks for exploration missions. Prediction of fatal cancer risks for missions to the Martian moon, Phobos of 500-d and the Earth's moon of 365-d for average solar minimum condition show increases of 2- to 4-fold higher in the NTE model compared with the conventional model. Limitations in estimating uncertainties in NTE model parameters due to sparse radiobiology data at low doses are discussed.

Abstract 4806: Strategies to overcome the heterogeneity of tumor cells in breast cancer therapy

Abstract Breast carcinogenesis is a multistage process that involves mutations and alterations attributed to exposure to exogenous environmental substances and endogenous agents as female hormones. To overcome the heterogeneity of tumor cells in breast cancer therapy several strategies must be considered from the bench to clinical settings. It is proposed four strategies: Analysis to determine 1) Apoptosis, 2) Epithelial-mesenchymal transition (EMT), 3) CD44/CD24 gene and protein expression in cells derived from mammospheres and 4) MicroRNAs as miR34a and others by the effects of chemotherapeutic drugs (as pamidronate (Pam), 5-Fluorouracil (5-FU) and antioxidants as Curcumin (Cur) (diferuloylmethane) derived from Curcuma longa. Pam, a bisphosphonate is used in the treatment of breast cancer. 5-FU is a chemotherapeutic agent for the treatment of a variety of solid cancers that arrest cell cycle and induce apoptosis in cancer cells. We evaluated genes and proteins targeted by these drugs and antioxidants in a triple positive cell line, as MCF7 and a negative, MDA-MB-231 for hormonal receptors, respectively and in an in vitro breast cancer model induced by radiation and estrogen that was developed with a normal immortalized breast epithelial cell line, MCF-10F exposed to low doses of high LET (linear energy transfer) alpha particles (150 keV/μm) of radiation, and cultured in presence of 17β-estradiol. We used: i) MCF-10F, ii) Alpha3, a malignant non-tumorigenic, iii) Alpha5, a tumorigenic one and iv) Tumor2 cell line derived from Alpha5 injected into the nude mice. Previous results showed increased cell proliferation, anchorage independency, invasive capabilities and tumor formation in nude mice, microsatellite instability and loss of heterozygosity in chromosomes 6, 8, 11 and 17 and mutations of c-Ha-ras and Rho-A in Alpha5 and Tumor2 compared to the control MCF-10F and their counterparts. Pam, 5-FU and Cur inhibited migration and invasion in both cell lines, and also decreased c-Ha-ras, Rho-A, p53, and Cav-1 gene expression by RT-qPCR. These compounds also induced 1) apoptotic effect on Bcl-xL and Bax gene and protein expression and by flow cytometry; 2) changes in EMT markers such as Snail, Slug, Axl, 3) CD44/CD24 alterations and 4) target MicroRNAs as miR34a on different process. It can be concluded that strategies to overcome the heterogeneity of tumor cells can be used to interfere with genes involved in critical steps in breast carcinogenesis. Grant: Tarapacá University, Arica, Chile (GMC). Short tittle: Strategies in breast cancer therapy Citation Format: Gloria M. Calaf, Marcela Gallardo, Debasish Roy, Richard Ponce-Cusi. Strategies to overcome the heterogeneity of tumor cells in breast cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4806. doi:10.1158/1538-7445.AM2017-4806

Curcumin inhibits invasive capabilities through epithelial mesenchymal transition in breast cancer cell lines.

Curcumin (diferuloyl methane) is an antioxidant that exerts antiproliferative and apoptotic effects and has anti-invasive and anti-metastatic properties. Evidence strongly implicates that epithelial-mesenchymal transition (EMT) is involved in malignant progression affecting genes such as Slug, AXL and Twist1. These genes are abnormally expressed in many tumors and favor metastasis. The purpose of this study was to determine the potential effect of curcumin on EMT, migration and invasion. Triple-positive and triple-negative breast cancer cell lines for estrogen receptor (ER), progesterone receptor (PgR) and HER/neu were used: i)MCF-10F, a normal immortalized breast epithelial cell line (negative), ii)Tumor2, a malignant and tumorigenic cell line (positive) derived from Alpha5 cell line injected into the immunologically depressed mice and transformed by 60/60cGy doses of high LET (linear energy transfer) αparticles (150keV/µm) of radiation and estrogen, and iii) a commercially available MDA-MB‑231 (negative). The effect of curcumin (30µM for 48h) was evaluated on expression of EMT-related genes by RT-qPCR. Results showed that curcumin decreased E-cadherin, N-cadherin, β-catenin, Slug, AXL, Twist1, Vimentin and Fibronectin protein expression, independently of the positivity of the markers in the cell lines. Curcumin also decreased migration and invasive capabilities in comparison to their own controls. It can be concluded that curcumin influenced biochemical changes associated with EMT-related genes that seems to promote such transition and are at the core of several signaling pathways that mediate the transition. Thus, it can be suggested that curcumin is able to prevent or delay cancer progression through the interruption of this process.

Curcumin and epithelial-mesenchymal transition in breast cancer cells transformed by low doses of radiation and estrogen.

Breast cancer is a major cause of global mortality in women. Curcumin exerts anti-proliferative, anti-migratory and apoptotic effects. The aim of this study was to evaluate gene expression involved in epithelial-mesenchymal transition (EMT). An invitro model was developed with the MCF-10F immortalized breast epithelial cell line exposed to low radiation doses of high LET (linear energy transfer) α-particles (150keV/µm) and cultured in the presence of 17β-estradiol (estrogen). The following cell lines were used: i) MCF-10F, normal; ii) Alpha5, pre-tumorigenic, and iii) Tumor2 derived from Alpha5 injected into the nude mice. Our previous results have shown that Alpha5 and Tumor2 increased cell proliferation, anchorage independency, invasive capabilities and tumor formation in nude mice in comparison to control. Results indicated that curcumin decreased expression of EMT-related genes in Tumor2 cell line when compared to its counterpart as E-cadherin, N-cadherin, ZEB2, Twist1, Slug, Axl, vimentin, STAT-3, fibronectin; and genes p53 and caveolin-1, as well as apoptotic genes caspase-3, caspase-8, and others such as cyclinD1 and NFκB. All these changes induced a decrease in migratory and invasive capabilities of such a cell line. Thus, it seems that curcumin may impinge upon apoptosis and metastatic properties of the malignant cells exerting antitumor activity in breast cancer cells transformed by low doses of α-particles and estrogen invitro.

Abstract LB-086: Genes targeted by drugs and curcumin in a breast carcinogenesis model

Abstract Breast carcinogenesis is a multistage process that involves mutations and cellular phenotypic alterations attributed to exposure to exogenous environmental substances as well as endogenous agents as female hormones. Pamidronate (Pam), one of the nitrogen-containing bisphosphonates, is used in the treatment of bone metastases of breast cancer. It has recently been reported that it is also related to cell proliferation and apoptosis. 5-Fluorouracil (5-FU) is a chemotherapeutic agent for the treatment of a variety of solid cancers that arrest cell cycle and induce apoptosis in cancer cells. Curcumin (Cur) is an antioxidant known as a dietary natural yellow pigment derived from the rhizome of the herb Curcuma longa. The aim of this study was to evaluate genes that could be targeted by these drugs and curcumin in a breast carcinogenesis in vitro model induced by radiation and estrogen. Such model was developed with a normal immortalized breast epithelial cell line, MCF-10F that was exposed to low doses of high LET (linear energy transfer) alpha particles (150 keV/μm) of radiation, and cultured in presence of 17β-estradiol. This model consisted of the following cell lines: i) MCF-10F, ii) Alpha3, a malignant non-tumorigenic, iii) Alpha5, a tumorigenic one and iv) Tumor2, derived from Alpha5 injected into the nude mice. Previous results showed that Alpha5 and Tumor2 increased cell proliferation, presented anchorage independency, invasive capabilities and tumor formation in nude mice, as well as microsatellite instability and loss of heterozygosity in chromosomes 6, 8, 11 and 17 and mutations of c-Ha-ras and Rho-A among others. Pam, 5-FU and Cur were analyzed with MCF-10F by MTT indicating that the mean LD50 was 10, 2 and 30 μM after 48 hrs, respectively. Such substances inhibited migration and invasion in both Alpha5 and Tumor2 cell lines compared to the control MCF-10F and their counterparts, and also decreased c-Ha-ras, Rho-A, p53, Serpin-1 and Cav-1 gene expression in Alpha5 and significantly in Tumor2 cell lines by RT-qPCR. A significant apoptotic activity was observed by flow cytometry in Alpha5 and Tumor2 cell lines in comparison to control MCF-10F and their counterparts. These compounds had a direct antitumor and apoptotic effect on Bcl-xL and Bax by down-regulation of a transcription factor as NFĸB gene expression in Alpha5 and Tumor2 cell lines. It can be concluded that c-Ha-ras, RhoA, p53, Serpin-1 and Cav-1 genes were targeted by drugs and curcumin in a model transformed by low doses of alpha particles and estrogen. Such genes are involved in critical steps in breast carcinogenesis. Supported by FONDECYT #1120006 (GMC) and Ministry of Education (MINEDUC), Universidad de Tarapacá, Arica, Chile Citation Format: Gloria M. Calaf, Debasish Roy, Richard Ponce-Cusi. Genes targeted by drugs and curcumin in a breast carcinogenesis model. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-086. doi:10.1158/1538-7445.AM2015-LB-086

Antitumor activity of pamidronate in breast cancer cells transformed by low doses of α-particles and estrogen in vitro.

Human breast cancer is a major cause of global morbidity and mortality in women and it is a process that involves numerous molecular and cellular alterations attributed to environmental substances and agents such as hormones. Bisphosphonates, such as pamidronate, are potent antiresorptive drugs used to the treatment of metabolic bone disease, exerting anti-proliferative, anti-migratory and apoptotic effects. The aim of this study was to evaluate gene and protein expression involved in these processes. An in vitro model was developed with the MCF-10F immortalized breast epithelial cell line exposed to low radiation doses of high LET (linear energy transfer) α-particles (150 keV/µm) and cultured in the presence of 17β-estradiol (estrogen). This model consisted of the following cell lines: i) MCF-10F, normal; ii) Alpha3, non-malignant; iii) Alpha5, pre-tumorigenic, and iv) Tumor2, derived from Alpha5 injected into the nude mice. Our previous results have shown that Alpha5 and Tumor2 increased cell proliferation, anchorage independency, invasive capabilities and tumor formation in nude mice in comparison to control. Expression of the gene (RT-qPCR) and protein (western blotting, flow cyto-metry) was measured. The results indicated that pamidronate decreased invasion, migration and Rho-A, c-Ha-ras, p53, Serpin-1, Caveolin-1, Bcl-xL and NFκB gene and protein expression. Thus, it seems that pamidronate may impinge upon cellular proliferation, invasion, metastasis and apoptosis and it may exert antitumor activity in breast cancer cells transformed by low doses of α-particles and estrogen in vitro.

Development of a method for high LET irradiation of liquid systems

A variety of processes, from material sterilization and cancer treatment to used nuclear fuel recycling, benefit from quantifying the sensitivity of the system to radiation. Determining the effects of alpha irradiation on a system may be of complementary interest to the effects of gamma irradiation, as alpha radiation has higher linear energy transfer (LET) and will likely result in different chemical damage effects. This becomes important in advanced nuclear fuel cycle processes where the radioactive materials to be handled in solutions contain significant amounts of alpha emitters. Here we describe a method for studying high LET radiation in a liquid system using a TRIGA® reactor and the 10B(n,α)7Li reaction. By fitting a model based on neutron diffusion and absorption to experimentally obtained Fricke dosimetry data, the high LET dose to a sample was predictable over the full range of reactor power available and varying 10B concentration. This method may be applied to study the effects of high LET radiation on any liquid system as long as a suitable molecule containing boron is used and appropriate neutron diffusion coefficients are known. A wide range of high LET dose rates from 1,000 kGy/h may be obtained with this method.

Age and Hormonal Status as Determinants of Cataractogenesis Induced by Ionizing Radiation. II. Sparsely Ionizing (Low-LET) Radiation

Age at the time of exposure to sparsely ionizing radiation has been established as a key determinant of radiation cataractogenesis. However, while some reports suggest that the lenses of the young are hypersensitive, data from older studies are often conflicting and somewhat difficult to interpret when the radioresponse of young lenses is compared to that of adult lenses. Moreover, the mechanism of the age-response function for radiation cataractogenesis has yet to be identified. Since steroid sex hormones, notably estradiol, appear to play a role in age-related cataractogenesis, we hypothesized that the age response for radiation cataractogenesis could be dictated by estradiol status. We recently showed that exposure to high-linear energy transfer (LET) radiation resulted in a reduced latent period for, and enhanced progression of cataracts in rats that were 1 year old at the time of exposure compared to those that were 56 days old. However, the enhanced sensitivity of older lenses compared to younger lenses was independent of estradiol status. In the current study, we found that for 1-year-old rats exposed to 10 Gy of low-LET (60)Co γ rays, the rate of increase in the development of posterior and anterior subcapsular cataracts was higher in older ovary-intact rats compared to young rats. However, cataracts were detected much earlier in ovary-intact 56-day-old rats compared to 1-year-old rats, regardless of their treatment groups (ovary-intact, ovariectomized, or ovariectomized and implanted with capsules containing estradiol). Thus, despite a consistent estradiol response (potentiating effect of estrogen) within a given age group, the differences between the radiation response of old and young lenses cannot be accounted for solely by estradiol status.

Effect of curcumin on irradiated and estrogen-transformed human breast cell lines

Curcumin (diferuloyl methane) is a well known antioxidant that exerts antiproliferative and apoptotic effects. Curcumin effect was evaluated in a breast cancer model that was developed using the immortalized breast epithelial cell line MCF-10F after exposure to low doses of high LET (linear energy transfer) α particles (150 keV/µm) of radiation, and subsequently cultured in the presence of 17β-estradiol (estrogen). This model consisted of human breast epithelial cells in different stages of transformation: i) MCF-10F; ii) Estrogen cell line; iii) a malignant Alpha3 cell line; iv) a malignant and tumorigenic, Alpha5 cell line; and v) a cell line derived from Alpha5 injected into the nude mice that gave rise to Tumor2 cell line. Curcumin decreased anchorage-independent growh in transformed breast cancer cell lines in comparison to their counterparts and increased the percentage of cells from G₀/G₁ with a concomitant increase in G₂/M phases, as well as a decrease in PCNA and Rho-A protein expression. Among the oncogenes, c-Ha-Ras and Ras homologous A (Rho-A) are important cell signaling factors for malignant transformation and to reach their active GTP bound state, Ras proteins must first release bound GDP mediated by a guanine nucleotide releasing factor (GRF). Then curcumin decrease RasGRF1 protein expression in malignant cell lines. Further, differential expression levels of cleaved (ADP) ribose polymerase 1 (PARP-1) and phosphorylated histone H2AX (γ-H2AX) were observed after curcumin treatment. It seems that PARP-1 similar to H2AX, confers cellular protection against radiation and estrogen-induced DNA damage mediated by curcumin. Therefore, targeting either PARP-1 or H2AX may provide an effective way of maximizing the therapeutic value of antioxidants for cancer prevention.

Protective role of curcumin in oxidative stress of breast cells

Curcumin (diferuloylmethane) is a well known antioxidant that exerts anti-proliferative and apoptotic effects. The effects of curcumin were evaluated in a breast cancer model that was developed with the immortalized breast epithelial cell line, MCF-10F after exposure to low doses of high LET (linear energy transfer) α particles (150keV/µm) of radiation, and subsequently cultured in the presence of 17β-estradiol (estrogen). This model consisted of human breast epithelial cells in different stages of transformation: i) a control cell line, MCF-10F, ii) an estrogen-treated cell line, named Estrogen, iii) a malignant cell line, named Alpha3 and iv) a malignant and tumorigenic, cell line named Alpha5. Curcumin decreased the formation of hydrogen peroxide in the control MCF-10F, Estrogen and Alpha5 cell lines in comparison to their counterparts. Curcumin had little effect on NFκB (50kDa) but decreased the protein expression in the Estrogen cell line in comparison to their counterparts. Curcumin enhanced manganese superoxide dismutase (MnSOD) protein expression in the MCF-10F and Alpha3 cell lines. Results indicated that catalase protein expression increased in curcumin treated-Alpha3 and Alpha5 cell lines. Curcumin slightly decreased lipid peroxidation in the MCF-10F cell lines, but significantly (P<0.05) decreased it in the Alpha5 cell line treated with curcumin in comparison to their counterparts as demonstrated by the 8-iso-prostaglandin F2α (8-iso-PGF2α) levels. It can be concluded that curcumin acted upon oxidative stress in human breast epithelial cells transformed by the effect of radiation in the presence of estrogen.

Age and Hormonal Status as Determinants of Cataractogenesis Induced by Ionizing Radiation. I. Densely Ionizing (High-LET) Radiation

Astronauts participating in extended lunar missions or the projected mission to Mars would likely be exposed to significant doses of high-linear energy transfer (LET) heavy energetic charged (HZE) particles. Exposure to even relatively low doses of such space radiation may result in a reduced latent period for and an increased incidence of lens opacification. However, the determinants of cataractogenesis induced by densely ionizing radiation have not been clearly elucidated. In the current study, we show that age at the time of exposure is a key determinant of cataractogenesis in rats whose eyes have been exposed to 2 Gy of (56)Fe ions. The rate of progression of cataractogenesis was significantly greater in the irradiated eyes of 1-year-old rats compared to young (56-day-old) rats. Furthermore, older ovariectomized rats that received exogenous estrogen treatment (17-β-estradiol) commencing 1 week prior to irradiation and continuing throughout the period of observation of up to approximately 600 days after irradiation showed an increased incidence of cataracts and faster progression of opacification compared to intact rats with endogenous estrogen or ovariectomized rats. The same potentiating effect (higher incidence, reduced latent period) was observed for irradiated eyes of young rats. Modulation of estrogen status in the 1-year-old animals (e.g., removal of estrogen by ovariectomy or continuous exposure to estrogen) did not increase the latent period or reduce the incidence to that of intact 56-day-old rats. Since the rapid onset and progression of cataracts in 1-year-old compared to 56-day-old rats was independent of estrogen status, we conclude that estrogen cannot account for the age-dependent differences in cataractogenesis induced by high-LET radiation.

Abstract 3454: Molecular markers for breast carcinogenesis models induced by environmental substances and estrogen

Abstract Breast cancer is the most common cancer in women throughout the world. Exogenous and endogenous agents such as environmental carcinogens and female hormones seem to be involved in the etiology of breast cancer. It is a multistage process involving a series of genetic alterations, identification of potential genes responsible for breast carcinogenesis is critical for timely diagnosis and prevention of breast cancer. To gain insights into the mechanisms for breast cancer initiation and development processes by exogenous environmental agents, we have developed many experimental breast cancer model systems: In vitro model with the immortalized human breast epithelial cell line, MCF-10F exposed to (I) low doses of high LET (linear energy transfer) alpha particles (150 keV/μm) (Carcinogenesis 21: 769, 2000) and b), (II) organophosphorous pesticides, either with Parathion (P) or Malathion (M) and (III) combination of either P or M in the presence of estrogen (E). Results showed that MCF-10F cells treated either with double dose of 60 cGy alpha particles in the presence of E or pesticides induced malignant transformation of MCF-10F. The malignant transformation was determined by multiple biological assays: increased cell proliferation, anchorage independency, invasive capabilities and tumor formation in nude mice, microsatellite instability and loss of heterozygosity in chromosomes 17, 11, 6, 8. Gene expression analysis using cancer pathway specific and affymetrix arrays detected alterations in the expression levels of p53, ErbB2, BRCA1, c-Ha-ras, Rho-A, PTEN, RB, c-Ha-ras, transforming protein Rho-A, F, GDP, TGF alpha, beta receptor, integrin B6, Notch3 and cathepsin. In addition to the in vitro human model, in vivo rat mammary gland model was also generated: (I) control (II) either P or M (III) E and (IV) P or M and E. Animals were treated for 5 days. These combined treatments induced significant progressive morphological and molecular changes. Alterations in the expression levels of RNA and protein were observed for c-fos, c-myc, mutant p53, ErbB2, BRCA1, c-Ha-ras, Rho-A, CYP1A1 gene and protein expression in the rat mammary gland after 240 days of treatment in comparison to control. Such stimulation led to mammary tumor formation. Collectively, our study shows the molecular signature of oncogenic deregulation in breast cancer progression induced by the combination of environmental substances and estrogen. Thus, aberrant expression of multiple genes involved in key signaling pathways renders these models as important tools for monitoring carcinogenic progression and chemo-intervention. Grant FONDECYT # 1080482 (GMC). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3454.

Cell Cycle Perturbations and Genotoxic Effects in Human Primary Fibroblasts Induced by Low-energy Protons and X/γ-rays

The effect of graded doses of high-linear energy transfer (LET) low-energy protons to induce cycle perturbations and genotoxic damage was investigated in normal human fibroblasts. Furthermore, such effects were compared with those produced by low-LET radiations. HFFF2, human primary fibroblasts were exposed to either protons (LET = 28.5 keV/microm) or X/gamma-rays, and endpoints related to cell cycle kinetics and DNA damage analysed. Following both type of irradiations, unsynchronized cells suffered an inhibition to entry into S-phase for doses of 1-4 Gy and remained arrested in the G(1)-phase for several days. The levels of induction of regulator proteins, such as TP53 and CDKN1A showed a clear LET-dependence. DSB induction and repair as measured by scoring for gamma-H2AX foci indicated that protons, with respect to X-rays, yielded a lower number of DSBs per Gy, which showed a slower kinetics of disappearance. Such result was in agreement with the extent of MN induction in binucleated cells after X-irradiation. No significant differences between the two types of radiations were observed with the clonogenic assay, resulting anyway the slope of gamma-ray curve higher than that the proton one. In conclusion, in normal human primary fibroblasts cell cycle arrest at the G(1)/S transition can be triggered shortly after irradiation and maintained for several hours post-irradiation of both protons and X-rays. DNA damage produced by protons appears less amenable to be repaired and could be transformed in cytogenetic damage in the form of MN.

Low and high LET dose components in carbon beam

Clinical application of light ion beams requires correct understanding of the complex processes of ion interaction with matter and the development of accurate transport methods. Knowledge of the fluence differential in energy of primary and secondary particles is important since it allows evaluation of different linear energy transfer (LET) dose components in the patient. The low LET and high LET particle distributions and the corresponding absorbed doses due to primary and secondary particles were evaluated for different depths in a water phantom using the Monte Carlo code SHIELD-HIT. SHIELD-HIT calculations are compared with the experimental LET distributions for a carbon beam of energy 278 MeV u(-1) from the HIMAC facility in Japan. The capability of the code for the evaluation of particle transport in thin layers of a few micrometres is demonstrated.

Role of Vitamin D receptor gene in radiation-induced neoplastic transformation of human breast epithelial cell

1α,25-(OH) 2-Vitamin D 3, the physiologically active metabolite of Vitamin D is known for its pro-differentiating and antiproliferative activity on various cancer cell lines. It exerts its growth-regulatory effects through binding to the Vitamin D recepter (VDR), a member of the steroid/thyroid/retinoic acid receptor family, which functions as a ligand-dependent transcription factor. There is accumulating evidence that Vitamin D may be an important determinant of both the occurrence and progression of breast cancer. Since radiation is an important etiological factor for breast cancer progression, it is important to study the role of VDR gene in radiation-induced breast carcinogenesis. This study is focused on a human breast tumor model developed by irradiating the spontaneously immortalized MCF-10F cell line with graded doses of high-linear energy transfer (LET) radiation followed by treatment with estrogen. Study of VDR gene by restriction digestion with ApaI, BsmI and TaqI detected no polymorphism but direct sequencing analyses identified few single-base mutations within intron 8 and exon 9 of the gene. Over-expression of the VDR gene was noticed in irradiated and tumorigenic cell lines compared with control. Likewise, immunohistochemical data indicated a significant increase in VDR intensity in irradiated and tumorigenic cell lines. Considering all these evidence, it is likely that VDR can be used as a prognostic marker of tumor progression in radiation- and estrogen-induced breast carcinogenesis.

Depth dose and off-axis characteristics of TLD in therapeutic pion beams

The thermoluminescent (TL) response of LiF (TLD-100, TLD-600, TLD-700) and Li2B4O7 (TLD-800) has been measured as a function of depth and off-axis position in a therapeutic negative-pion beam in order to evaluate their usefulness in pion radiotherapy. TLD-100, TLD-600, and TLD-800 have been shown to be of little use as in vivo dosemeters because the neutron kerma relative to that in tissue changes grossly with depth. The neutron source comes primarily from pion absorption in the lead-alloy collimator. The 200 degrees C TLD-700 response agrees well with the depth dose spectra, except for small changes due to the varying linear energy transfer (LET) distributions. This variation can be partially accounted for by incorporating the known LET response of LiF. The 260 degrees C peak of TLD-700 has been found to be approximately four times more sensitive than the 200 degrees C peak to high LET dose. Using a simple model of the LET responses, the measured 200 degrees C and 260 degrees C peaks predict total dose within +or-4% and high LET dose within +or-50%, therefore indicating TLD-700 to be a good in vivo dosemeter for total dose but only an indicator of high LET dose.