Tumor Radiation Sensitivity Research Articles

Evaluating the Radiation Sensitivity Index and 12-chemokine gene expression signature for clinical use in a CLIA laboratory.

The radiation sensitivity index (RSI) and 12-chemokine gene expression signature (12CK GES) are two gene expression signatures (GES) that were previously developed to predict tumor radiation sensitivity or identify the presence of tertiary lymphoid structures in tumors, respectively. To advance the use of these GES into clinical trial evaluation, their assays must be assessed within the context of the Clinical Laboratory Improvement Amendments (CLIA) process. Using HG-U133Plus 2.0 arrays, we first established CLIA laboratory proficiency. Then the accuracy (limit of detection and macrodissection impact), precision (variability by time and operator), sample type (surgery vs. biopsy), and concordance with reference laboratory were evaluated. RSI and 12CK GES were reproducible (RSI: 0.01 mean difference, 12CK GES 0.17 mean difference) and precise with respect to time and operator. Taken together, the reproducibility analysis of the scores indicated a median RSI difference of 0.06 (6.47% of range) across samples and a median 12CK GES difference of 0.92 (12.29% of range). Experiments indicated that the lower limit of input RNA is 5 ng. Reproducibility with a second CLIA laboratory demonstrated reliability with the median RSI score difference of 0.065 (6% of full range) and 12CK GES difference of 0.93 (12 % of observed range). Overall, under CLIA, RSI and 12CK GES were demonstrated by the Moffitt Cancer Center Advanced Diagnostic Laboratory to be reproducible GES for clinical usage.

Abstract A011: Enhanced Radiosensitivity of Pancreatic Cancer Achieved through Inhibition of Cyclin-Dependent Kinase 1

Abstract Introduction: One of the major challenges in treating Pancreatic Ductal Adenocarcinoma (PDAC) is overcoming radioresistance. This study investigates the targeting of Cyclin-dependent kinase-1 (CDK1) through both genetic and pharmaceutical inhibition as a strategy to increase the radiosensitivity of PDAC cells. Methods: We conducted mass spectrometry and phosphoproteomics analyses to compare engineered radiation-resistant PDAC cell lines (MIA PaCa-2 and PANC-1) with their parental controls. Additionally, we examined the TCGA PDAC database to correlate clinical outcomes, such as overall survival (OS), with CDK1 mRNA expression levels in PDAC patients. Furthermore, we developed a microRNA-based TET-on inducible shRNA to specifically inhibit CDK1 expression in PDAC cell lines. In an orthotopic PDAC model, we evaluated the radiation sensitivity of PDAC tumors with or without doxycycline treatment. We also employed a selective CDK1 inhibitor, RO-3306, to target CDK1 activation, followed by in vitro experiments using immunoblotting, immunocytochemistry, and clonogenic assays. Results: Our phosphoproteomics analysis revealed a significant increase in phospho-CDK1 (Tyr15) levels in the radiation-resistant cell lines. High CDK1 expression was associated with poorer OS in PDAC patients. Additionally, we observed heightened CDK1 phosphorylation at the threonine tyrosine 14 (Tyr14) residue following radiation exposure. Through our in vivo and in vitro experiments, we demonstrated that CDK1 inhibition, in conjunction with radiation therapy, delayed tumor growth and enhanced radiosensitivity in PDAC cells. Treatment with RO-3306 caused a substantial shift of cells into the G2/M phase and disrupted DNA repair post-radiation exposure, further enhancing radiosensitivity. Conclusion: Our findings underscore the critical role of CDK1 in PDAC radioresistance. Targeting CDK1 in combination with radiotherapy shows promise for future exploration as a potential treatment strategy in PDAC. Citation Format: Stetson Van Matre, Saaimatul Huq, Lokesh Akana, Oscar Zuniga, Henrique Rodrigues, Adam Wolfe. Enhanced Radiosensitivity of Pancreatic Cancer Achieved through Inhibition of Cyclin-Dependent Kinase 1 [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr A011.

Enhanced radiosensitivity of pancreatic cancer achieved through inhibition of Cyclin-dependent kinase 1

Background and purposeOvercoming radioresistance is a critical challenge in pancreatic ductal adenocarcinoma (PDAC). Our study investigates the targeting of Cyclin-dependent kinase-1 (CDK1) through genetic and pharmaceutical inhibition to radiosensitize PDAC cells. Materials and MethodsMass spectrometry and phosphoproteomics were used to analyze engineered radiation-resistant PDAC cell lines (MIA PaCa-2 and PANC-1) compared to parental controls. The TCGA PDAC database was queried for clinical outcomes and patients were dichotomized based on the median CDK1 mRNA expression. We generated a microRNA-based TET-on inducible shRNA to inhibit CDK1 expression in two PDAC cell lines. We used an orthotopic model of PDAC to test the radiation sensitivity of PDAC tumors with or without doxycycline treatment. We targeted CDK1 activation with a selective CDK1 inhibitor, RO-3306, followed by in vitro experiments employing immunoblotting, immunocytochemistry, and clonogenic assays. ResultsPhosphoproteomics analysis revealed that phospho-CDK1 (Tyr15) was significantly elevated in the resistant clones. We found that high CDK1 expression was associated with worse OS in PDAC patients. Radiation exposure increased CDK1 phosphorylation. In MIA PaCa-2 and PANC-1 cells, CDK1 inhibition synergized with radiation therapy to delay tumor growth in vivo. CDK1 inhibition via. RO-3306 resulted in a significant shift of cells into the G2/M phase and disrupted DNA repair after radiation exposure. In vitro, pre-treatment with RO-3306 led to enhanced radiosensitivity of PDAC cells. ConclusionCDK1 plays a crucial role in PDAC radioresistance. Targeting CDK1 with radiotherapy holds promise for further investigation in PDAC treatment.

Differential regulation of radio-sensitivity/macrophage polarization in intestinal tissue and colorectal cancer for the optimized preoperative radiotherapy

Surgery is the preferred treatment for colorectal cancer, and the preoperative radiotherapy (pre-RT) improves surgical success and postoperative quality of life for patients. However, the therapeutic effect of pre-RT is limited by radiation resistance of tumor and radiation susceptibility of intestine, probably resulting in poor tumor suppression and postoperative anastomotic injury. Herein, we select carboxymethyl chitosan (CMCS) to complex with cerium oxide (CeO2) and calcium ion (Ca2+), obtaining CMCS/CeO2&Ca nano-enema for the optimized pre-RT of colorectal cancer. CMCS/CeO2 and CMCS/CeO2&Ca can mop up various kinds of reactive oxygen species (ROS) and decomposes H2O2 that largely exists in tumor tissue into OH and oxygen (some OH in acidic environment and main oxygen in neutral environment), enhancing free radical clearance in normal tissue and radiation sensitivity of tumor. Meanwhile, RT-induced M1 macrophage in intestinal tissue and the proportion of M2 macrophages in X-rays-treated tumor could be reduced, owing to CMCS/CeO2&Ca-induced change of ROS level. Moreover, CMCS/CeO2&Ca could also promote the proliferation of stem cells in intestine. Therefore, CMCS/CeO2&Ca improves the radio-immunotherapy outcome of colorectal cancer and reduces RT-induced intestinal inflammation/fibrosis, providing an optimal scheme and an effective enema for pre-RT for colorectal cancer.

Ras-Targeting Stabilized Peptide Increases Radiation Sensitivity of Cancer Cells.

Radiation therapy is one of the most common treatments for cancer. However, enhancing tumors' radiation sensitivity and overcoming tolerance remain a challenge. Previous studies have shown that the Ras signaling pathway directly influences tumor radiation sensitivity. Herein, we designed a series of Ras-targeting stabilized peptides, with satisfactory binding affinity (KD = 0.13 μM with HRas) and good cellular uptake. Peptide H5 inhibited downstream phosphorylation of ERK and increased radio-sensitivity in HeLa cells, resulting in significantly reduced clonogenic survival. The stabilized peptides, designed with an N-terminal nucleation strategy, acted as potential radio-sensitizers and broadened the applications of this kind of molecule. This is the first report of using stabilized peptides as radio-sensitizers, broadening the applications of this kind of molecule.

Evaluation of Radiation Sensitivity Differences in Mouse Liver Tumor Organoids Using CRISPR/Cas9-Mediated Gene Mutation.

To assess the radiosensitivity of liver tumors harboring different genetic mutations, mouse liver tumors were generated in vivo through the hydrodynamic injection of clustered regularly interspaced short palindromic repeat/caspase 9 (CRISPR/Cas9) constructs encoding single-guide RNAs (sgRNAs) targeting Tp53, Pten, Nf1, Nf2, Tsc2, Cdkn2a, or Rb1. The plasmid vectors were delivered to the liver of adult C57BL/6 mice via hydrodynamic tail vein injection. The vectors were injected into 10 mice in each group. Organoids were generated from mouse liver tumors. The radiation response of the organoids was assessed using an ATP cell viability assay. The mean survival period of mice injected with vectors targeting Nf2 (4.8 months) was lower than that of other mice. Hematoxylin and eosin staining, immunohistochemical (IHC) staining, and target sequencing analyses revealed that mouse liver tumors harbored the expected mutations. Tumor organoids were established from mouse liver tumors. Histological evaluation revealed marked morphological similarities between the mouse liver tumors and the generated tumor organoids. Moreover, IHC staining indicated that the parental tumor protein expression pattern was maintained in the organoids. The results of the ATP cell viability assay revealed that the tumor organoids with mutated Nf2 were more resistant to high-dose radiation than those with other gene mutations. This study developed a radiation response assessment system for mouse tumors with mutant target genes using CRISPR/Cas9 and organoids. The Tp53 and Pten double mutation in combination with the Nf2 mutation increased the radiation resistance of tumors. The system used in this study can aid in elucidating the mechanism underlying differential intrinsic radiation sensitivity of individual tumors.

Abstract 5979: Evaluating therapeutic strategies against lung cancer using multispectral optoacoustic tomography

Abstract Tumor hypoxia is an important feature of the microenvironment in various types of tumors. The leaky and compressed vessels in the tumor lead to impaired blood flow and oxygen delivery and cause hypoxia. Significant tumor hypoxia exists in non-small cell lung cancer (NSCLC) and is closely associated with radiation-resistant and poor survival. Recently, we have identified a new class of antitumor drugs, cyclopamine tartrate (CycT) and heme-sequestering peptide 2 (HeSP2). They are heme-targeting agents that effectively inhibit NSCLC oxidative metabolism, oxygen consumption, and ATP generation, which lead to the suppression of tumor progression. By using multispectral optoacoustic tomography (MSOT), an advanced noninvasive imaging modality that monitors the changes in blood oxygen saturation and vascular function in real-time, we observed the effect of heme-targeting agents in normalizing tumor vasculature and alleviating tumor hypoxia. To investigate the impact of heme-targeting agent on mediating the lung cancer radiotherapy response, we characterized the vasculature and antigenic profile of NSCLC growth during the treatment of CycT in combination with radiotherapy by performing MSOT, together with other imaging approaches including bioluminescence imaging (BLI) and immunohistochemistry (IHC). We demonstrated that the heme-targeting agents increased tumor radiation sensitivity by regulating tumor vasculature and oxygenation. Our novel combination therapy can be a powerful strategy in improving the treatment of lung cancer and potentially other radiation-resistant cancers. Citation Format: Tianyuan Wang, Hashini Wanniarachchi, Lorena Arango, Li Zhang, Li Liu. Evaluating therapeutic strategies against lung cancer using multispectral optoacoustic tomography [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5979.

Suppression of local IFN-I by commensal microbiota-derived butyrate impairs antitumor effects of ionizing radiation

Abstract The antitumor effects of ionizing radiation (IR) are mediated in part through activation of innate and adaptive immunity. Here, we report that gut microbiota influences tumor control following IR. Vancomycin decreased the abundance of butyrate-producing gut bacteria, accompanied with reduction of butyric acid in circulation and tumor tissues, and enhanced antitumor responses to IR. Oral administration of Lachnospiraceae, a family of vancomycin-sensitive bacteria, associated with increased systemic and intratumoral butyric acid levels and impaired the efficacy of IR in germ-free (GF) mice. Local butyrate inhibited STING-activated type I IFN expression in dendritic cells (DCs) through blockade of TBK 1 and IRF3 phosphorylation, which abrogated IR-induced tumor-specific cytotoxic T cell immune responses without directly protecting tumor cells from radiation. Our findings demonstrate that the selective targeting of butyrate-producing microbiota may provide a novel therapeutic option to enhance tumor radiation sensitivity. This work was supported by a grant from the Ludwig Foundation to R.R. Weichselbaum, and National Institutes of Health/National Cancer Institute Provocative Questions grants R21 CA227528 and R21 CA231273-01 (R.R. Weichselbaum).

Biomimetic multifunctional nanozymes enhanced radiosensitization for breast cancer via an X-ray triggered cascade reaction.

Radiotherapy has been widely applied for breast cancer treatment in the clinic, while improving the radiation sensitivity of tumors and protecting normal tissues from radiation damage has drawn considerable attention. In this study, we reported a biomimetic multifunctional nanozyme (BSA@CeO/Fe2+), which can be used as a radiosensitizer for breast cancer treatment. It was demonstrated that BSA@CeO/Fe2+ presented a pH dependent multiple enzyme like activity that enhances the hydroxyl radical level by cascade catalytic reactions in a tumor microenvironment to obtain a desirable tumor-suppression rate (83.07%). Moreover, BSA@CeO/Fe2+ was also proved to reduce reactive oxygen species levels in normal cells. Additionally, BSA@CeO/Fe2+ nanozymes showed no obvious toxicity by routine blood examination and blood biochemistry assays. Therefore, this work provided a promising strategy for nanocatalytic tumor therapy by rationally designing biomimetic nanozymes with multienzymatic activities for achieving high radiotherapy efficacy and excellent biosafety simultaneously.

Treatment strategies for pathological fractures of the spine

Pathological fractures and instabilities of the spine are most often caused by primary tumors that hematogenously metastasize into the spine. In this context breast, prostate, kidney cell and bronchial carcinomas are the most relevant causative diseases. Furthermore, multiple myeloma is another frequent entity. Primary tumors of the spine are correspondingly rare and only make up asmall proportion of all malignant processes in the spine. The main symptom of pain is prognostically unfavorable in this context and is often associated with progressive instability or pathological fractures. To objectify the treatment approach the neurological status, an oncological assessment, the biomechanical stability and (systemic) general condition (NOMS criteria) of the patient have to be considered. Another major factor is the radiation sensitivity of the tumor. The spinal instability neoplastic (SIN) score is recommended to assess stability. Regardless of whether conservative or surgical treatment is carried out, interdisciplinary cooperation between the specialist departments must be guaranteed in order to achieve adequate treatment for the patient. If acurative approach is followed an individualized and interdisciplinary surgical strategy must be performed to achieve an R0 resection, usually as aspondylectomy. In the case of palliative treatment, the goal of surgical treatment must be pain reduction, stability and avoidance or restoration of neurological deficits. This requires stabilization in a percutaneous or open technique, possibly in combination with decompression and local tumor debulking.

Measurement of dose enhancement factor for Xoft Axxent electronic brachytherapy device using nanoparticle-embedded alginate film and radiochromic film.

Inw nanoparticles-aided radiotherapy, the radiation sensitivity of tumor is increased with the infusion of nanoparticles in tumor. This therapeutic modality is capable of delivering enhanced dose to tumor, without exceeding the normal tissue tolerance dose. Further, the quantification of the enhanced dose using suitable dosimeter is important. The present study is aimed at measuring the dose enhancement factors (DEFs) using the combination of nanoparticles-embedded alginate (Alg) film and unlaminated Gafchromic EBT3 film. Gold nanoparticles (AuNPs)- and silver nanoparticles (AgNPs)-embedded Alg polymer films were synthesized and characterized using standard techniques. Further, a customized version of the Gafchromic EBT3 film, i.e., unlaminated EBT3 film, was specially fabricated. The DEFs were measured using Xoft Axxent electronic brachytherapy device. The surface plasmon resonance (SPR) and particle size of AuNPs were found to be 550 and 15 ± 2 nm, respectively. In the case of AgNPs, the SPR and particle size were recorded as 400 and 13 ± 2 nm, respectively. The DEFs measured, using unlaminated EBT3 film, for Xoft Axxent electronic brachytherapy using AuNPs and AgNPs were 1.35 ± 0.02 and 1.20 ± 0.01, respectively. The increase in dose enhancement during nanoparticles-aided electronic brachytherapy can be attributed to dominance of photoelectric effect, due to the presence of low-energy X-rays. The investigation indicates that the Xoft Axxent electronic brachytherapy device is suitable for nanoparticles-aided brachytherapy.

Suppression of local type I interferon by gut microbiota-derived butyrate impairs antitumor effects of ionizing radiation.

The antitumor effects of ionizing radiation (IR) are mediated in part through activation of innate and adaptive immunity. Here we report that gut microbiota influences tumor control following IR. Vancomycin decreased the abundance of butyrate-producing gut bacteria and enhanced antitumor responses to IR. Oral administration of Lachnospiraceae, a family of vancomycin-sensitive bacteria, was associated with increased systemic and intratumoral butyric acid levels and impaired the efficacy of IR in germ-free (GF) mice. Local butyrate inhibited STING-activated type I IFN expression in dendritic cells (DCs) through blockade of TBK1 and IRF3 phosphorylation, which abrogated IR-induced tumor-specific cytotoxic T cell immune responses without directly protecting tumor cells from radiation. Our findings demonstrate that the selective targeting of butyrate-producing microbiota may provide a novel therapeutic option to enhance tumor radiation sensitivity.

Hyaluronic Acid Binding to TLR4 Promotes Proliferation and Blocks Apoptosis in Colon Cancer.

Hyaluronic acid (HA), a constituent of the extracellular matrix, promotes colorectal cancer growth. CD44 is a relevant HA receptor in this context. However, HA is also a ligand for TLR4, a receptor of significance in colorectal cancer. In this study, we examine the relative contribution of HA interactions with CD44 and TLR4 in colon tumorigenesis. Colorectal cancer models included ApcMin/+ mice, azoxymethane/dextran sodium sulfate (AOM-DSS), and CT26 tumor isografts. We used knockout mice and CT26 colorectal cancer cells with CRISPR knockdown of CD44 and TLR4. HA activity was modulated by PEP1 (a 12-mer peptide that blocks HA from binding its receptors), hyaluronidase (which promotes HA degradation), or 4-MU (HA synthesis inhibitor). Blockade of HA binding via PEP1 decreased growth in all colorectal cancer models and in cell culture. The effects were significant in WT and with CD44 deletion, but not with TLR4 deletion. In the AOM-DSS model, mice deficient in CD44 or TLR4 had fewer tumors. CD44- and TLR4-deficient CT26 isografts grew more slowly, exhibiting decreased tumor cell proliferation and increased apoptosis. In vitro, endogenous HA blocked LPS binding to TLR4 suggesting that HA is a relevant TLR4 ligand in colon cancer. Finally, PEP1 enhanced tumor radiation sensitivity in the isograft model. Together, these results indicate that HA binding to TLR4, as well as CD44, plays a key role in colon tumorigenesis. These findings also raise the possibility that an agent that blocks HA binding, such as PEP1, may be useful as an adjuvant therapy in colon cancer.

LncRNA ANRIL target miR-195 experimental study of radiation sensitivity of HCT116 cells and nude mouse transplant tumors

Objective To investigate the effect and mechanism of LncRNA ANRIL on the radiosensitivity of HCT116 cells line and nude mouse transplant tumors. Methods The expression of LncRNA ANRIL in colorectal cancer cells was detected by qPCR. The negative control siRNA, ANRIL siRNA, miR-NC mimic, miR-195 mimic, miR-NC inhibitor and miR-195 inhibitor were transfected into HCT116 cells, and marked as negative control group, silencing ANRIL group, overexpressing miR-NC group, overexpressing miR-195 group, inhibiting miR-NC group and inhibiting miR-195 group, and the HCT116 cells without any treatment were marked as the blank control group. The clone formation assay was used to detect radiosensitivity of colorectal cancer cells, flow cytometry was used to detect apoptosis. The web site, StarBase, was used to predict the downstream miRNAs of ANRIL and dual luciferase reporter gene assay was used to further verify. Subcutaneous tumor transplantation assay was used to detect the effect of ANRIL on the growth of colorectal cancer cells after irradiation. Results After irradiation with 2, 4, 6 and 8 Gy, the cell survival fraction of silencing ANRIL group was significantly decreased when compared with that of negative control group (P<0.05), and the radiosensitivity ratio was 1.52. The apoptosis rate of the silencing ANRIL+ 4 Gy group was significantly higher than that of the negative control+ 4 Gy group ((27.86±2.78)% vs. (12.06±1.46)%, P<0.05). The results of the experiment on nude mouse transplant tumors showed that the tumor volume in the negative control group was lower than that of the silent ANRIL group on days 13, 16, 19, 22 and 25 ((234±66) mm3, (273±63) mm3, (296±72) mm3, (321±85) mm3 and (403±94) mm3vs. (357±79) mm3, (485±124) mm3, (617±143) mm3, (764±174) mm3 and (985±221) mm3P<0.05). MiR-195 is a target gene of ANRIL, and inhibition of miR-195 can reverse the inhibitory effect of silencing ANRIL on radiosensitivity, apoptosis and xenografts of HCT116 cells. Conclusions LncRNA ANRIL regulates the radiosensitivity of colorectal cancer cells by miR-195, which may provide a new sensitizing target for clinical colorectal cancer radiotherapy. Key words: ANRIL gene; miR-195 gene; HCT116 cell line; Nude mouse transplant tumors; Radiosensitivity

Oral administration of 3,3′-diselenodipropionic acid prevents thoracic radiation induced pneumonitis in mice by suppressing NF-kB/IL-17/G-CSF/neutrophil axis

The incidence of symptomatic radiation induced lung pneumonitis (RILP), a major dose limiting side effect of thoracic radiotherapy, is in the range of 15-40%. Therapeutic options for the prevention and treatment of RILP are limited. Hence there is a need for developing novel radioprotectors to prevent RILP which can be patient compliant. This study sought to evaluate the efficacy of oral 3,3′-diselenodipropionic acid (DSePA), a novel selenocystine derivative to prevent RILP. C3H/HeJ (pneumonitis responding) mice received a single dose of 18 Gy, whole thorax irradiation and a subset were treated with DSePA orally (2.5 mg/kg), three times per week beginning 2 h post irradiation and continued till 6 months. DSePA delayed onset of grade ≥ 2 RILP by 45 days compared to radiation control (~105 versus ~60 days). It also reversed the severity of pneumonitis in 3/10 radiation treated mice leading to significant improvement in asymptomatic survival compared to radiation control (~180 versus ~102 days). DSePA significantly (p < 0.05) reduced the radiation-mediated infiltration of polymorphonuclear neutrophils (PMN) and elevation in levels of cytokines such as IL1-β, ICAM-1, E-selectin, IL-17 and TGF-β in the bronchoalveolar lavage fluid. Moreover DSePA lowered PMN-induced oxidants, maintained glutathione peroxidase activity and suppressed NF-kB/IL-17/G-CSF/neutrophil axis in the lung of irradiated mice. Additionally, this compound did not protect A549 (lung cancer) derived xenograft tumor from radiation exposure in SCID mice. DSePA offers protection to normal lung against RILP without affecting radiation sensitivity of tumors. It has the potential to be developed as an oral agent for preventing RILP.

Modeling the effect of intratumoral heterogeneity of radiosensitivity on tumor response over the course of fractionated radiation therapy

BackgroundStandard radiobiology theory of radiation response assumes a uniform innate radiosensitivity of tumors. However, experimental data show that there is significant intratumoral heterogeneity of radiosensitivity. Therefore, a model with heterogeneity was developed and tested using existing experimental data to show the potential effects from the presence of an intratumoral distribution of radiosensitivity on radiation therapy response over a protracted radiation therapy treatment course.MethodsThe standard radiation response curve was modified to account for a distribution of radiosensitivity, and for variations in the repopulation rates of the tumor cell subpopulations. Experimental data from the literature were incorporated to determine the boundaries of the model. The proposed model was then used to show the changes in radiosensitivity of the tumor during treatment, and the effects of fraction size, α/β ratio and variation of the repopulation rates of tumor cells.ResultsIn the presence of an intratumoral distribution of radiosensitivity, there is rapid selection of radiation-resistant cells over a course of fractionated radiation therapy. Standard treatment fractionation regimes result in the near-complete replacement of the initial population of sensitive cells with a population of more resistant cells. Further, as treatment progresses, the tumor becomes more resistant to further radiation treatment, making each fractional dose less efficacious. A wider initial distribution induces increased radiation resistance. Hypofractionation is more efficient in a heterogeneous tumor, with increased cell kill for biologically equivalent doses, while inducing less resistance. The model also shows that a higher growth rate in resistant cells can account for the accelerated repopulation that is seen during the clinical treatment of patients.ConclusionsModeling of tumor cell survival with radiosensitivity heterogeneity alters the predicted tumor response, and explains the induction of radiation resistance by radiation treatment, the development of accelerated repopulation, and the potential beneficial effects of hypofractionation. Tumor response to treatment may be better predicted by assaying for the distribution of radiosensitivity, or the extreme of the radiosensitivity, rather than measuring the initial, general radiation sensitivity of the untreated tumor.

Abstract 4165: Novel genetic rat models to identify factors that modulate cardiac and tumor radiation sensitivity

Abstract Purpose/Objectives: Over 50% of breast cancer patients receive radiation therapy, but radiation doses can be limited by normal tissue toxicity. Radiation therapy can improve breast cancer-specific survival, but cardiac morbidity can be increased in patients with left-sided tumors. We used rat genetic models to identify targets to improve the therapeutic ratio of radiation. We assessed the radiation responsiveness of mammary tumors and the heart in genetically similar consomic rats conducive to genetic mapping. Materials/Methods: Female SS rats and SS.BN3 consomic rats, which are genetically identical to SS rats except that chromosome 3 is inherited from the BN strain, have previously been shown to exhibit different vascular dynamics and breast tumor growth. Human MDA-MD-231 cells or syngeneic mammary tumor cells developed from DMBA-induced mammary tumors were implanted orthotopically into immunodeficient or immunocompetent SS and SS.BN3 rats, respectively, and tumors were treated locally with mock or 5x4 Gy. To examine cardiac toxicity, adult female SS and SS.BN3 rats received image-guided localized whole-heart radiation to a dose of 24 Gy or 9 Gy x 5 (AP and 2 lateral fields, weighted 1:1:1). Echocardiograms with strain analysis were performed at baseline, 3 months and 5 months. The Student's t-test was used to compare values. Results: The BN strain-derived genetic variant(s) on rat chromosome 3 is important for tumor radiation sensitivity. Tumors in SS.BN3 rats were significantly more radiosensitive than tumors in the parental SS strain. A supra-additive effect was seen with both tumor cell lines, with recurrence-free survival of 30% vs. 67% at 137 days in SS vs SS.BN3 rats (p=0.02) in xenografts, and recurrence-free survival of 9% vs. 100% at 141 days in SS vs. SS.BN3 rats (p&amp;lt;0.0001) in syngeneic tumors. The SS female rats that received 24 Gy exhibited enhanced cardiac toxicity compared to SS.BN3 rats, with larger pericardial effusions in SS vs SS.BN3 rats (p&amp;lt;0.05), significantly elevated end diastolic volume (EDV) and end systolic volume (ESV) at 5 months (EDV: 0.62 vs. 0.49 mL, p&amp;lt;0.01; ESV: 0.12 vs. 0.03 mL, p&amp;lt;0.01), and increased cardiac mortality (5/11 SS vs. 0/7 SS.BN3 rats). Fractionated heart radiation yielded similar results. Taken together, the SS.BN3 tumors are more sensitive to radiation, while the hearts of SS.BN3 rats are protected against radiation toxicity, when compared to the SS strain. Conclusions: These results demonstrate that genetic variants on rat chromosome 3 alter the sensitivity to radiation therapy, enhancing tumor responses to radiation and protecting the heart, thus improving the therapeutic ratio. Gene expression analysis and genetic mapping will be performed to identify the causative target(s). This project has the potential to enhance the effectiveness and toxicity profile of radiation therapy in breast cancer. Citation Format: Rachel A. Schlaak, Anne Frei, Aronne M. Schottstaedt, Brian L. Fish, Leanne Harmann, Tracy Gasperetti, Michael J. Flister, Meetha Medhora, Jennifer L. Strande, Carmen R. Bergom. Novel genetic rat models to identify factors that modulate cardiac and tumor radiation sensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4165.

Highlights on molecular targets for radiosensitization of breast cancer cells: Current research status and prospects.

In the past, searching for effective radiotherapy sensitization molecular targets and improving the radiation sensitivity of malignant tumors was the hot topic for the oncologists, but with little achievements. We will summarize the research results about breast cancer irradiation sensitization molecular targets over the past two decades; we mainly focus on the following aspects: DNA damage repair and radiation sensitization, cell cycle regulation and radiation sensitization, cell autophagy regulation and radiation sensitization, and radiation sensitivity prediction and breast cancer radiotherapy scheme making. And based on this summary, we will put forward some of our viewpoints.

Abstract P2-11-18: The use of consomic animal models to identify genetic factors that modulate radiation-induced cardiac toxicity

Abstract Purpose/Objectives: Radiation therapy is used by more than 50% of breast cancer patients, but radiation doses can be limited by normal tissue side effects. For example, breast cancer radiation therapy can improve breast cancer-specific survival, but increase cardiac deaths in those with left-sided cancers. Identifying genetic factors that can enhance tumor radiation sensitivity while decreasing normal tissue toxicities has the potential to improve the therapeutic ratio of radiation therapy – leading to more cures and less long-term toxicities. The use of animal models with differing genetic backgrounds to assess radiation toxicity, followed by genetic mapping of radiosensitivity phenotypes, has the potential to identify new targets that can predict cardiac toxicity from radiation therapy. This project examines how genetic host factors alter normal tissue toxicity risks from breast cancer radiation. Materials/Methods: Inbred female SS rats and SS.BN3 consomic rats, that are genetically identical to SS rats except that chromosome 3 is inherited from the BN strain, have previously been shown to exhibit different vascular dynamics and breast tumor growth. For this study, adult female SS and SS.BN3 rats received image-guided whole heart radiation to a dose of 21 Gy (3 fields, AP and 2 laterals). Cardiac troponin was serially measured at 2, 6, and 12 weeks, and echocardiograms with strain analysis were performed at baseline and 3 months. The Student's t-test was used to compare values. Results: The SS female rats exhibited enhanced cardiac toxicity compared to SS.BN3 rats, with cardiac troponin levels elevated at 12 weeks (0.32 ng/ml vs.0.08 ng/ml for SS vs. SS.BN3, p=0.01), and moderate to severe pericardial effusions seen in 6 of 9 SS rats vs. 2 of 7 SS.BN3 rats. At 3 months post-radiation, echocardiograms revealed increased left ventricular posterior wall thickness at end diastole (LVPWd) in SS vs. SS.BN3 rats (0.25 vs. 0.20 cm, p=0.002) and increased left ventricular mass (LVM) in SS vs. SS.BN3 rats (1.54 vs. 1.28 g, p&amp;lt;0.001). Taken together, the SS female rats are more sensitive to cardiac irradiation than SS.BN3. Conclusions: These results demonstrate that genetic variant on rat chromosome 3 alter the radiosensitivity to single fraction cardiac radiation therapy. Gene expression analysis and genetic mapping will be performed to identify the causative target(s). These models will also be expanded to test whether similar results are seen with fractionated cardiac radiation therapy. This project has the potential to enhance the effectiveness and toxicity profile of radiation therapy in breast cancer. Citation Format: Bergom C, Schlaak R, Frei A, Fish BL, Harmann L, Gasperetti T, Schottstaedt AM, Flister MJ, Medhora M, Strande JL. The use of consomic animal models to identify genetic factors that modulate radiation-induced cardiac toxicity [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-11-18.

Expression of histone deacetylase 1 gene in human lung cancer cell line A549 and the effect on the radiation sensitivity of nude mouse transplantation tumor

Objective To investigate the expression of histone deacetylase 1 (HDAC1) gene in human lung cancer cell line A549 and the effect on the radiation sensitivity of nude mouse transplantation tumor. Methods HDAC1 small interfering RNA (siRNA) and recombinant expression vector pcDNA3.1-HDAC1 were transfected with A549 lung cancer cells, respectively. Stable transfected cell lines were screened by G418 selection. reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blotting were used to detect the expression levels of HDAC1 mRNA and HDAC1 protein in the cell; cell proliferation was measured by cell counting kit-8 (CCK-8). Clone formation experiment was used to observe the effect of up-regulation and down-regulation of HDAC1 expression on the radiation sensitivity of A549 cells, cell apoptosis was detected by transferase-mediated dUTP nick-end labelling (TUNEL) method. Nude mice experiment of transplantable tumor was applied for in vivo detection of the influence of up-regulated and down-regulation of HDAC1 expression combined with X-ray irradiation in the inhibition of lung cancer growth. Results The expression of HDAC1 gene and protein were significantly lower to 1.86±0.09 and 2.41±0.10 (P=0.015, 0.006) in HDAC1 cell line A549, and the HDAC1 up-regulation group were significantly higher to 3.65±0.14 and 5.41±0.12 (P=0.012, 0.008); The radiation sensitivity of lung cancer A549 cells was increased in the down-regulation group of HDAC1 (P=0.025), and the radiation sensitivity of lung cancer A549 cells was decreased (P=0.009)in the HDAC1 up-regulation group. Down-regulation of HDAC1 inhibited the proliferation of A549 lung cancer, increased the rate of apoptosis to (42.17±3.19)% (P=0.008), proliferation of A549 cells was significantly enhanced in HDAC1 up-regulated group, associated with reduced percentage of apoptotic cells (9.11±1.46)% (P=0.006); Average volume in the nude mice of HDAC1 down-regulated group (547.37±89.68) mm3 were significantly smaller than the control group (1 238.44±212.36) mm3 (P=0.008); furthermore, mean volume of tumor was greater in the HDAC1 up-regulated group than in the control group (1 681.27±195.37) mm3 (P=0.006). After 20 Gy γ irradiation, the average volume of HDAC1 down-regulated group were significantly decreased (214.15±54.26) mm3 (P=0.011). Compared with that before irradiation, the average volume of the tumor in the nude mice was not significantly changed after irradiation (P=0.264). Conclusion Down-regulated expression of HDAC1 can inhibit the growth of human lung cancer A549 cells in nude mice, enhance the radiation sensitivity of tumor cells, whereas up-regulated expression of HDAC1 can produce tumor radiation resistance. Key words: Lung cancer; A549 cell; Histone deacetylase 1; Transplantable tumor; Nude mice