- Email: [email protected]
Enhancing the Relative Biological Effectiveness of Proton Therapy Using EGFR-Targeted Gold Nanorods
S236
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): Patient-centric education in radiation oncology reviews the therapeutic ratio of risks and benefits. Part of this discussion covers the risk of mortality caused by radiation, and the measures that are taken to prevent this outcome. We analyzed 16 years of radiation oncology mortality to investigate trends in patient outcomes and to determine patient factors associated with mortality to identify potential opportunities for quality improvement. Materials/Methods: After IRB approval, we retrospectively collected morbidity and mortality (M&M) data from all consecutively treated patients in our department from January 2000 to January 2016. Collected patient characteristics included: age, sex, date of event, disease site and subsite, tumor histology, TMN stage, and anatomic stage/prognostic group. Treatment details collected included: intent of therapy (curative or palliative radiotherapy [RT]), timing of RT (neoadjuvant/adjuvant), RT modality (3D or IMRT), use, and timing of systemic therapy and surgery, prescribed and completed radiation dose and use of brachytherapy (BT). M&M, preventable/possibly preventable outcome, and outcome related to RT were determined only from departmentally required M&M reporting to the institutional Clinical Quality Improvement & Patient Safety office using a hospital-wide standardized reporting form. Statistical analyses were conducted using multivariate regression and t-test. Results: Over 16 years, 14,189 patients were treated with RT (887 patients/year average). There were 78 reported patient deaths (0.55%) with 63 patients dying on treatment. The range of annual mortality was 2-12 patients (median 4). T-test analysis of independent variable revealed that of patients who died, sex (P Z 0.005), stage IV disease (P Z 0.001), RT given with curative intent (P Z 0.0001), use of concurrent systemic therapy (P Z 0.0029), mean dose (Gy) (P Z 0.001), and completion of RT (P 0.0001) were all strongly predictive of mortality. However, on multivariate analysis the factor most strongly correlated with increased mortality was age (P Z 0.00066). Furthermore, RT was the leading cause of death in patients who died of a preventable cause (P Z 0.00181). Conclusion: Our study is the first in the literature to investigate mortality while on radiation treatment and investigate preventable causes. Our data shows a low overall rate of mortality during RT. Patients who die while receiving RT are more likely be older and have advanced disease and are being treated aggressively with systemic therapy and with curative intent. Age was the strongest predictor of mortality and preventable deaths were strongly correlated with RT, suggesting that RT may have caused harm. These findings reinforce the need for patient acuity of care stratification metrics to better identify and support those patients most likely to suffer from potentially preventable RT-induced morbidity or mortality. Author Disclosure: B.A. Dyer: None. X. Zhao: None. D. Hoffman: None. L. Kahn: None. M. Hodges: None. J.T. Hayes: None. A.L. Michaud: None. C.B. Hess: None. C. Kumaran Nair: None. R.C. Fragoso: None. R.K. Valicenti: Oversight of all departmental decisions; University of California Davis. J.S. Mayadev: None.
compounds. Cell lines tested included MCF7 (breast cancer), PC3 (prostate cancer), HL60 (leukemia) and SKMEL5 (melanoma). Every treatment against a small molecule was defined relative to a control consisting of cells grown in the same plate and tested with vehicle alone. Genome-wise mRNA expression data were collected by means of Affymetrix GeneChip microarrays. The previously tested RSI 10 gene assay was calculated before and after exposure to each small molecule using the previously published algorithm. RSI is modeled after the surviving fraction of cells at 2 Gy (SF2) (range Z 0-1) with a lower RSI indicating greater radiosensitivity. A change in the RSI value of 0.15 in either direction was used as a cut-point of clinical applicability. Results: We identified 20 small molecules meeting criteria as potential clinically applicable radiosensitizers and one potential radioprotective small molecule. The potential radiosensitizers included: camptothecin, cephaeline, emetine, alsterpaullone, cicloheximide, anisomycin, cantharidin, tyrphostin, terfenadine, daunorubicin, and doxorubicin among others. Several of these small molecules including camptothecin derivatives irinotecan and topotecan as well as doxorubicin have been previously identified in the literature as radiosensitizers. Furthermore, the identified radiosensitizing small molecules target DNA repair, cell cycle inhibition, apoptosis and tyrosine kinase signaling, all methods proven to be involved in modulating RT response. In contrast, sulindac sulfide, a non-steroidal anti-inflammatory drug (NSAID), was the sole compound identified as a potential radioprotector. Conclusion: In this robust analysis, we present a novel RSI based approach to screen small molecules to combine with RTas radiosensitizers. Initial validation confirms several of the identified molecules to be known radiosensitizers and mechanisms identified are involved in radiosensitization. This method may provide a systematic approach to screen small molecules as radiosensitizers. Author Disclosure: K.A. Ahmed: None. T. Strom: None. J.G. Scott: None. E.A. Welsh: None. H.L. McLeod: None. L.B. Harrison: None. S.A. Eschrich: Stock; CvergenX. Patent/License Fees/Copyright; RSI. J.F. Torres-Roca: Stock; CvergenX. Patent/License Fees/Copyright; RSI.
1171 The Radiosensitivity Index (RSI) and the Connectivity Map: A Genomically Guided Approach for the Identification of Novel Radiosensitizers K.A. Ahmed, T. Strom, J.G. Scott, E.A. Welsh, H.L. McLeod, L.B. Harrison, S.A. Eschrich, and J.F. Torres-Roca; Lee Moffitt Cancer Center and Research Institute, Tampa, FL Purpose/Objective(s): The development of genomically guided approaches to identify small molecule candidates to combine with radiation therapy (RT) as radiosensitizers is central to the advancement of combined modality therapy. We hypothesize the radiosensitivity index (RSI), a previously developed and extensively validated molecular signature of radiation sensitivity could be combined with data from the Connectivity Map to provide a systematic screening method for the identification of novel radiosensitizers. Materials/Methods: Gene expression profiling before and after exposure to 1309 distinct small molecules was downloaded from the Connectivity Map. Small molecules represented a broad range of activity including U.S. Food and Drug Administration (FDA) approved drugs as well nondrug bioactive tool
1172 Enhancing the Relative Biological Effectiveness of Proton Therapy Using EGFR-Targeted Gold Nanorods A. Khoo,1 N. Sahoo,2,3 S. Krishnan,3,4 and P. Diagaradjane1,3; 1 Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Department of Radiation Physics, UT MD Anderson Cancer Center, Houston, TX, 3Center for Radiation Oncology Research, The University of Texas MD Anderson Cancer Center, Houston, TX, 4Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX Purpose/Objective(s): In recent years, proton beam radiation therapy (PBRT) has gained attention as a treatment for tumors of anatomically complex organs. However, the therapeutic benefit of PBRT is limited by a relative biological effectiveness (RBE) of just 1.1. This limitation can be overcome by artificially enhancing the RBE. While the interaction of photon beams with gold nanoparticles (GNPs) is known to enhance therapeutic efficacy, little is known about the potential of GNPs to enhance the therapeutic efficacy of PBRT. This study evaluates the radiosensitization potential of gold nanorods (GNRs) using proton beams and characterizes RBE with respect to the standard clinical 6 MV photons. To enhance intracellular delivery, these GNRs are conjugated to Cetuximab e an antibody to epidermal growth factor receptor (EGFR) that is overexpressed in most tumors. Materials/Methods: GNRs were synthesized by the seed-mediated surfactant-assisted approach and characterized by transmission electron microscopy (TEM) for uniformity of size and shape, zeta potential for positive surface charge, and absorbance spectrophotometry for characteristic plasmon resonance peaks. Cetuximab-GNR (cGNR) conjugates were made using thiol-maleimide chemistry and characterized by absorbance and zeta potential. Binding affinity of cGNRs to head and neck cancer cells (HN5) was evaluated using dark field microscopy and TEM to optimize the incubation time for subsequent clonogenic assays. The radiosensitization potential of cGNRs when irradiated with 6 MV photon and proton beams (100 and 160 MeV) at central and distal locations along the spread-out Bragg peak (SOBP) was determined using clonogenic assays. The dose enhancement
Volume 96 Number 2S Supplement 2016 factor at 10% surviving fraction (DEF10) for GNRs + radiation was calculated with respect to radiation alone. The RBE at 10% surviving fraction (RBE10) for proton therapies was calculated with respect to 6 MV photons. IgG-conjugated GNRs (iGNRs) were used as controls in all experiments. Results: cGNRs demonstrated significant radiosensitization when compared to iGNRs for 6MV photons (DEF10 Z 1.14 vs 1.04, P < 0.05), 100 MeV protons (DEF10 Z 1.19 vs 1.04, P < 0.05), and 160 MeV protons (DEF10 Z 1.17 vs 1.04, P < 0.05). Calculation of cGNR RBE10 for proton beams at the center of SOBP revealed similar effects for both 100 and 160 MeV (1.39 vs 1.38; P > 0.05). However, a greater cGNR enhancement was observed at the distal SOBP with 100 MeV beams vs 160 MeV beams (RBE10 Z 1.79 vs 1.6; P < 0.05). Conclusion: EGFR-targeting GNRs significantly enhance the RBE of protons well above the accepted 1.1 value. The enhanced RBE observed for lower energy protons (100 MeV) and at the distal SOBP suggests that low energy components may play a role in the observed radiosensitization effect. This strategy holds promise for clinical translation and could evolve as a paradigm-changing approach in the field of radiation oncology. Author Disclosure: A. Khoo: None. N. Sahoo: None. S. Krishnan: None. P. Diagaradjane: None.
1173 Inhibiting Isocitrate Dehydrogenase 1-Mediated Reductive Biosynthesis to Augment Glioblastoma Therapy D.R. Wahl,1 J. Dresser,1 M.A. Davis,1 S.G. Zhao,1 M.A. Morgan,1 C. Lyssiotis,1 F.Y. Feng,1 and T.S. Lawrence2; 1University of Michigan, Ann Arbor, MI, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI Purpose/Objective(s): Glioblastoma (GBM) is nearly uniformly fatal with recurrences typically occurring within the high dose radiation field. Therefore, strategies to increase the sensitivity of GBM to radiation are urgently needed. NADPH is the main carrier of cellular reducing potential and its increased production is an emerging hallmark of cancer metabolism, where it drives the production of numerous metabolites related to the radiation response including deoxynucleotides and antioxidants. We therefore sought to determine the most upregulated NADPH-producing enzyme in GBM and hypothesized that its inhibition would selectively augment radiation therapy for this deadly disease. Materials/Methods: Transcript levels of all NADPH-producing genes in normal brain and GBM were analyzed in four independent clinical datasets using Oncomine. To assess radiation effects, cells were irradiated and plated at clonal density 3-4 days after knockdown using transfection of siRNA or doxycycline-induced expression of shRNA and colonies were counted 10-14 days later. Senescence was quantified using senescence-associated bGalactosidase staining. Metabolite analysis was performed using a UPLCQTOF mass spectrometry platform. Rescue experiments were performed by incubating cells with pooled nucleosides or N-acetyl cysteine. Results: Our investigation of multiple clinical datasets indicates that isocitrate dehydrogenase 1 (IDH1) is the most upregulated NADPH-producing enzyme in GBM with transcript levels up to 5-fold higher than normal brain. Both siRNA and shRNA-mediated knockdown of IDH1 sensitized multiple GBM cell lines to radiation with enhancement ratios of up to 1.6. Importantly, knockdown of IDH1 did not affect normal astrocytes, which is consistent with recent reports that IDH1 knockout mice are entirely healthy. The combination of IDH1 knockdown and radiation increased cellular senescence by 50-80%, suggesting that increased senescence is responsible for IDH1-mediated radiosensitization. IDH1 knockdown reduced NADPH-dependent metabolites related to the radiation response including glutathione and numerous deoxynucleotides by up to 60%. Supplementation with deoxynucleotide or antioxidant precursors entirely reversed IDH1-mediated radiosensitization, confirming an NADPHdependent mechanism. Tumor xenograft studies examining the efficacy of combining IDH1 inhibition and radiation in vivo are ongoing. Conclusion: IDH1 is the most upregulated producer of reducing potential in GBM and its inhibition radiosensitizes GBM but not normal astrocytes through a novel NADPH-dependent mechanism involving depletion of
ePoster Sessions S237 deoxynucleotides and antioxidants. Exploiting tumor-specific metabolic pathways is a promising strategy to selectively improve radiation therapy for GBM. Author Disclosure: D.R. Wahl: Stock; Lycera. J. Dresser: None. M.A. Davis: None. S.G. Zhao: None. M.A. Morgan: None. C. Lyssiotis: None. F.Y. Feng: Research Grant; Varian. President and Founder; PFS Genomics. Advisory Board Member; Astellas/Medivation, GenomeDx, Celgene. T. Lawrence: None.
1174 Bcl-XL as a Radiosensitizer in the Treatment of Group C Medulloblastoma K.D. Kelley, C. Powell, S. Chakraborty, A.C. Wright, S.B. Al Dimassi, M. Symons, and R. Ruggieri; Northwell Health, Manhasset, NY Purpose/Objective(s): Medulloblastoma is the most common malignant pediatric brain tumor. Although significant progress has been made in the treatment of medulloblastoma patients over the past several decades, the fiveyear disease-free survival for high-risk patients, characterized by metastatic dissemination at presentation or significant post-operative residual tumor, remains relatively poor (25-40%). Group C medulloblastoma has by far the worst prognosis with a 5-year survival probability of approximately 30% regardless of stage. Current therapeutic modalities, in particular ionizing radiation (IR), have significant long-term side-effects within the pediatric population. Enhancement of current therapies through targeted radiosensitization may allow for IR dose reduction and lead to decreased late radiation-induced sequelae. Materials/Methods: A bioinformatics approach was employed to select a number of candidate radioresistance genes that are preferentially expressed in group C medulloblastoma tumors. Candidate genes were screened using focused RNA interference to assay for sensitization to ionizing radiation using primary cell cultures derived from group C tumors. We have identified and validated the antiapoptotic gene Bcl-XL as an effective target for the radiosensitization of medulloblastoma group C tumors through this approach. Results: Radiosensitization of both sonic hedgehog (SHH) and group C cell lines was achieved in vitro with increasing doses of the Bcl-2 family small molecule inhibitor, ABT-263 (MW Z 974 Da). After a 24 hour drug pretreatment followed by irradiation (up to 9 Gy), a dose enhancement factor (DEF) after 40% cell death of 1.7 for UW228 (SHH) and 2.2 for D425MED (group C) cell lines was obtained. Group C cells were significantly more sensitive to treatment with 50 fold less drug required (10mM ABT-263 for the SSH subgroup vs. 200nM ABT-263 for group C). Similarly, siRNA targeting Bcl-XL was able to achieve a DEF of 1.9 in UW228 cells. A murine model utilizing a paramagnetic gadolinium-based nanoparticle delivery system to bypass the BBB is currently being developed to test ABT-263 in vivo as an effective radiosensitizer of human group C medulloblastoma tumors. Conclusion: In summary, radiosensitization of group C tumors is expected to be useful in improving local control and survival outcomes in patients with more aggressive subtypes of medulloblastoma. In the future, preclinical data generated from this approach will provide a rationale for the design of an early-phase clinical trial in order to test the safety and efficacy of pharmacological Bcl-family inhibition with concurrent radiation in the treatment of patients with group C medulloblastoma. Author Disclosure: K.D. Kelley: None. C. Powell: None. S. Chakraborty: None. A.C. Wright: None. S.B. Al Dimassi: None. M. Symons: None. R. Ruggieri: None.
1175 PARP1 Inhibition Radiosensitizes A Subset Of Genotype-Defined Bladder Cancers Through Modulation Of Reactive Oxygen Species H. Willers,1 Q. Liu,1 J.A. Efstathiou,1 L. Gheorghiu,1 M.R. Drumm,2 R.H. Clayman,2 A. Eidelman,2 M.F. Wszolek,3 A.S. Feldman,3 M. Wang,1 L. Marcar,1 D.E. Citrin,4 C.L. Wu,5 and C. Benes6; 1Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, 2 Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 3Department of Urology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 4 Radiation Oncology Branch, NCI, Bethesda, MD, 5Department of
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): Patient-centric education in radiation oncology reviews the therapeutic ratio of risks and benefits. Part of this discussion covers the risk of mortality caused by radiation, and the measures that are taken to prevent this outcome. We analyzed 16 years of radiation oncology mortality to investigate trends in patient outcomes and to determine patient factors associated with mortality to identify potential opportunities for quality improvement. Materials/Methods: After IRB approval, we retrospectively collected morbidity and mortality (M&M) data from all consecutively treated patients in our department from January 2000 to January 2016. Collected patient characteristics included: age, sex, date of event, disease site and subsite, tumor histology, TMN stage, and anatomic stage/prognostic group. Treatment details collected included: intent of therapy (curative or palliative radiotherapy [RT]), timing of RT (neoadjuvant/adjuvant), RT modality (3D or IMRT), use, and timing of systemic therapy and surgery, prescribed and completed radiation dose and use of brachytherapy (BT). M&M, preventable/possibly preventable outcome, and outcome related to RT were determined only from departmentally required M&M reporting to the institutional Clinical Quality Improvement & Patient Safety office using a hospital-wide standardized reporting form. Statistical analyses were conducted using multivariate regression and t-test. Results: Over 16 years, 14,189 patients were treated with RT (887 patients/year average). There were 78 reported patient deaths (0.55%) with 63 patients dying on treatment. The range of annual mortality was 2-12 patients (median 4). T-test analysis of independent variable revealed that of patients who died, sex (P Z 0.005), stage IV disease (P Z 0.001), RT given with curative intent (P Z 0.0001), use of concurrent systemic therapy (P Z 0.0029), mean dose (Gy) (P Z 0.001), and completion of RT (P 0.0001) were all strongly predictive of mortality. However, on multivariate analysis the factor most strongly correlated with increased mortality was age (P Z 0.00066). Furthermore, RT was the leading cause of death in patients who died of a preventable cause (P Z 0.00181). Conclusion: Our study is the first in the literature to investigate mortality while on radiation treatment and investigate preventable causes. Our data shows a low overall rate of mortality during RT. Patients who die while receiving RT are more likely be older and have advanced disease and are being treated aggressively with systemic therapy and with curative intent. Age was the strongest predictor of mortality and preventable deaths were strongly correlated with RT, suggesting that RT may have caused harm. These findings reinforce the need for patient acuity of care stratification metrics to better identify and support those patients most likely to suffer from potentially preventable RT-induced morbidity or mortality. Author Disclosure: B.A. Dyer: None. X. Zhao: None. D. Hoffman: None. L. Kahn: None. M. Hodges: None. J.T. Hayes: None. A.L. Michaud: None. C.B. Hess: None. C. Kumaran Nair: None. R.C. Fragoso: None. R.K. Valicenti: Oversight of all departmental decisions; University of California Davis. J.S. Mayadev: None.
compounds. Cell lines tested included MCF7 (breast cancer), PC3 (prostate cancer), HL60 (leukemia) and SKMEL5 (melanoma). Every treatment against a small molecule was defined relative to a control consisting of cells grown in the same plate and tested with vehicle alone. Genome-wise mRNA expression data were collected by means of Affymetrix GeneChip microarrays. The previously tested RSI 10 gene assay was calculated before and after exposure to each small molecule using the previously published algorithm. RSI is modeled after the surviving fraction of cells at 2 Gy (SF2) (range Z 0-1) with a lower RSI indicating greater radiosensitivity. A change in the RSI value of 0.15 in either direction was used as a cut-point of clinical applicability. Results: We identified 20 small molecules meeting criteria as potential clinically applicable radiosensitizers and one potential radioprotective small molecule. The potential radiosensitizers included: camptothecin, cephaeline, emetine, alsterpaullone, cicloheximide, anisomycin, cantharidin, tyrphostin, terfenadine, daunorubicin, and doxorubicin among others. Several of these small molecules including camptothecin derivatives irinotecan and topotecan as well as doxorubicin have been previously identified in the literature as radiosensitizers. Furthermore, the identified radiosensitizing small molecules target DNA repair, cell cycle inhibition, apoptosis and tyrosine kinase signaling, all methods proven to be involved in modulating RT response. In contrast, sulindac sulfide, a non-steroidal anti-inflammatory drug (NSAID), was the sole compound identified as a potential radioprotector. Conclusion: In this robust analysis, we present a novel RSI based approach to screen small molecules to combine with RTas radiosensitizers. Initial validation confirms several of the identified molecules to be known radiosensitizers and mechanisms identified are involved in radiosensitization. This method may provide a systematic approach to screen small molecules as radiosensitizers. Author Disclosure: K.A. Ahmed: None. T. Strom: None. J.G. Scott: None. E.A. Welsh: None. H.L. McLeod: None. L.B. Harrison: None. S.A. Eschrich: Stock; CvergenX. Patent/License Fees/Copyright; RSI. J.F. Torres-Roca: Stock; CvergenX. Patent/License Fees/Copyright; RSI.
1171 The Radiosensitivity Index (RSI) and the Connectivity Map: A Genomically Guided Approach for the Identification of Novel Radiosensitizers K.A. Ahmed, T. Strom, J.G. Scott, E.A. Welsh, H.L. McLeod, L.B. Harrison, S.A. Eschrich, and J.F. Torres-Roca; Lee Moffitt Cancer Center and Research Institute, Tampa, FL Purpose/Objective(s): The development of genomically guided approaches to identify small molecule candidates to combine with radiation therapy (RT) as radiosensitizers is central to the advancement of combined modality therapy. We hypothesize the radiosensitivity index (RSI), a previously developed and extensively validated molecular signature of radiation sensitivity could be combined with data from the Connectivity Map to provide a systematic screening method for the identification of novel radiosensitizers. Materials/Methods: Gene expression profiling before and after exposure to 1309 distinct small molecules was downloaded from the Connectivity Map. Small molecules represented a broad range of activity including U.S. Food and Drug Administration (FDA) approved drugs as well nondrug bioactive tool
1172 Enhancing the Relative Biological Effectiveness of Proton Therapy Using EGFR-Targeted Gold Nanorods A. Khoo,1 N. Sahoo,2,3 S. Krishnan,3,4 and P. Diagaradjane1,3; 1 Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX, 2Department of Radiation Physics, UT MD Anderson Cancer Center, Houston, TX, 3Center for Radiation Oncology Research, The University of Texas MD Anderson Cancer Center, Houston, TX, 4Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX Purpose/Objective(s): In recent years, proton beam radiation therapy (PBRT) has gained attention as a treatment for tumors of anatomically complex organs. However, the therapeutic benefit of PBRT is limited by a relative biological effectiveness (RBE) of just 1.1. This limitation can be overcome by artificially enhancing the RBE. While the interaction of photon beams with gold nanoparticles (GNPs) is known to enhance therapeutic efficacy, little is known about the potential of GNPs to enhance the therapeutic efficacy of PBRT. This study evaluates the radiosensitization potential of gold nanorods (GNRs) using proton beams and characterizes RBE with respect to the standard clinical 6 MV photons. To enhance intracellular delivery, these GNRs are conjugated to Cetuximab e an antibody to epidermal growth factor receptor (EGFR) that is overexpressed in most tumors. Materials/Methods: GNRs were synthesized by the seed-mediated surfactant-assisted approach and characterized by transmission electron microscopy (TEM) for uniformity of size and shape, zeta potential for positive surface charge, and absorbance spectrophotometry for characteristic plasmon resonance peaks. Cetuximab-GNR (cGNR) conjugates were made using thiol-maleimide chemistry and characterized by absorbance and zeta potential. Binding affinity of cGNRs to head and neck cancer cells (HN5) was evaluated using dark field microscopy and TEM to optimize the incubation time for subsequent clonogenic assays. The radiosensitization potential of cGNRs when irradiated with 6 MV photon and proton beams (100 and 160 MeV) at central and distal locations along the spread-out Bragg peak (SOBP) was determined using clonogenic assays. The dose enhancement
Volume 96 Number 2S Supplement 2016 factor at 10% surviving fraction (DEF10) for GNRs + radiation was calculated with respect to radiation alone. The RBE at 10% surviving fraction (RBE10) for proton therapies was calculated with respect to 6 MV photons. IgG-conjugated GNRs (iGNRs) were used as controls in all experiments. Results: cGNRs demonstrated significant radiosensitization when compared to iGNRs for 6MV photons (DEF10 Z 1.14 vs 1.04, P < 0.05), 100 MeV protons (DEF10 Z 1.19 vs 1.04, P < 0.05), and 160 MeV protons (DEF10 Z 1.17 vs 1.04, P < 0.05). Calculation of cGNR RBE10 for proton beams at the center of SOBP revealed similar effects for both 100 and 160 MeV (1.39 vs 1.38; P > 0.05). However, a greater cGNR enhancement was observed at the distal SOBP with 100 MeV beams vs 160 MeV beams (RBE10 Z 1.79 vs 1.6; P < 0.05). Conclusion: EGFR-targeting GNRs significantly enhance the RBE of protons well above the accepted 1.1 value. The enhanced RBE observed for lower energy protons (100 MeV) and at the distal SOBP suggests that low energy components may play a role in the observed radiosensitization effect. This strategy holds promise for clinical translation and could evolve as a paradigm-changing approach in the field of radiation oncology. Author Disclosure: A. Khoo: None. N. Sahoo: None. S. Krishnan: None. P. Diagaradjane: None.
1173 Inhibiting Isocitrate Dehydrogenase 1-Mediated Reductive Biosynthesis to Augment Glioblastoma Therapy D.R. Wahl,1 J. Dresser,1 M.A. Davis,1 S.G. Zhao,1 M.A. Morgan,1 C. Lyssiotis,1 F.Y. Feng,1 and T.S. Lawrence2; 1University of Michigan, Ann Arbor, MI, 2Department of Radiation Oncology, University of Michigan, Ann Arbor, MI Purpose/Objective(s): Glioblastoma (GBM) is nearly uniformly fatal with recurrences typically occurring within the high dose radiation field. Therefore, strategies to increase the sensitivity of GBM to radiation are urgently needed. NADPH is the main carrier of cellular reducing potential and its increased production is an emerging hallmark of cancer metabolism, where it drives the production of numerous metabolites related to the radiation response including deoxynucleotides and antioxidants. We therefore sought to determine the most upregulated NADPH-producing enzyme in GBM and hypothesized that its inhibition would selectively augment radiation therapy for this deadly disease. Materials/Methods: Transcript levels of all NADPH-producing genes in normal brain and GBM were analyzed in four independent clinical datasets using Oncomine. To assess radiation effects, cells were irradiated and plated at clonal density 3-4 days after knockdown using transfection of siRNA or doxycycline-induced expression of shRNA and colonies were counted 10-14 days later. Senescence was quantified using senescence-associated bGalactosidase staining. Metabolite analysis was performed using a UPLCQTOF mass spectrometry platform. Rescue experiments were performed by incubating cells with pooled nucleosides or N-acetyl cysteine. Results: Our investigation of multiple clinical datasets indicates that isocitrate dehydrogenase 1 (IDH1) is the most upregulated NADPH-producing enzyme in GBM with transcript levels up to 5-fold higher than normal brain. Both siRNA and shRNA-mediated knockdown of IDH1 sensitized multiple GBM cell lines to radiation with enhancement ratios of up to 1.6. Importantly, knockdown of IDH1 did not affect normal astrocytes, which is consistent with recent reports that IDH1 knockout mice are entirely healthy. The combination of IDH1 knockdown and radiation increased cellular senescence by 50-80%, suggesting that increased senescence is responsible for IDH1-mediated radiosensitization. IDH1 knockdown reduced NADPH-dependent metabolites related to the radiation response including glutathione and numerous deoxynucleotides by up to 60%. Supplementation with deoxynucleotide or antioxidant precursors entirely reversed IDH1-mediated radiosensitization, confirming an NADPHdependent mechanism. Tumor xenograft studies examining the efficacy of combining IDH1 inhibition and radiation in vivo are ongoing. Conclusion: IDH1 is the most upregulated producer of reducing potential in GBM and its inhibition radiosensitizes GBM but not normal astrocytes through a novel NADPH-dependent mechanism involving depletion of
ePoster Sessions S237 deoxynucleotides and antioxidants. Exploiting tumor-specific metabolic pathways is a promising strategy to selectively improve radiation therapy for GBM. Author Disclosure: D.R. Wahl: Stock; Lycera. J. Dresser: None. M.A. Davis: None. S.G. Zhao: None. M.A. Morgan: None. C. Lyssiotis: None. F.Y. Feng: Research Grant; Varian. President and Founder; PFS Genomics. Advisory Board Member; Astellas/Medivation, GenomeDx, Celgene. T. Lawrence: None.
1174 Bcl-XL as a Radiosensitizer in the Treatment of Group C Medulloblastoma K.D. Kelley, C. Powell, S. Chakraborty, A.C. Wright, S.B. Al Dimassi, M. Symons, and R. Ruggieri; Northwell Health, Manhasset, NY Purpose/Objective(s): Medulloblastoma is the most common malignant pediatric brain tumor. Although significant progress has been made in the treatment of medulloblastoma patients over the past several decades, the fiveyear disease-free survival for high-risk patients, characterized by metastatic dissemination at presentation or significant post-operative residual tumor, remains relatively poor (25-40%). Group C medulloblastoma has by far the worst prognosis with a 5-year survival probability of approximately 30% regardless of stage. Current therapeutic modalities, in particular ionizing radiation (IR), have significant long-term side-effects within the pediatric population. Enhancement of current therapies through targeted radiosensitization may allow for IR dose reduction and lead to decreased late radiation-induced sequelae. Materials/Methods: A bioinformatics approach was employed to select a number of candidate radioresistance genes that are preferentially expressed in group C medulloblastoma tumors. Candidate genes were screened using focused RNA interference to assay for sensitization to ionizing radiation using primary cell cultures derived from group C tumors. We have identified and validated the antiapoptotic gene Bcl-XL as an effective target for the radiosensitization of medulloblastoma group C tumors through this approach. Results: Radiosensitization of both sonic hedgehog (SHH) and group C cell lines was achieved in vitro with increasing doses of the Bcl-2 family small molecule inhibitor, ABT-263 (MW Z 974 Da). After a 24 hour drug pretreatment followed by irradiation (up to 9 Gy), a dose enhancement factor (DEF) after 40% cell death of 1.7 for UW228 (SHH) and 2.2 for D425MED (group C) cell lines was obtained. Group C cells were significantly more sensitive to treatment with 50 fold less drug required (10mM ABT-263 for the SSH subgroup vs. 200nM ABT-263 for group C). Similarly, siRNA targeting Bcl-XL was able to achieve a DEF of 1.9 in UW228 cells. A murine model utilizing a paramagnetic gadolinium-based nanoparticle delivery system to bypass the BBB is currently being developed to test ABT-263 in vivo as an effective radiosensitizer of human group C medulloblastoma tumors. Conclusion: In summary, radiosensitization of group C tumors is expected to be useful in improving local control and survival outcomes in patients with more aggressive subtypes of medulloblastoma. In the future, preclinical data generated from this approach will provide a rationale for the design of an early-phase clinical trial in order to test the safety and efficacy of pharmacological Bcl-family inhibition with concurrent radiation in the treatment of patients with group C medulloblastoma. Author Disclosure: K.D. Kelley: None. C. Powell: None. S. Chakraborty: None. A.C. Wright: None. S.B. Al Dimassi: None. M. Symons: None. R. Ruggieri: None.
1175 PARP1 Inhibition Radiosensitizes A Subset Of Genotype-Defined Bladder Cancers Through Modulation Of Reactive Oxygen Species H. Willers,1 Q. Liu,1 J.A. Efstathiou,1 L. Gheorghiu,1 M.R. Drumm,2 R.H. Clayman,2 A. Eidelman,2 M.F. Wszolek,3 A.S. Feldman,3 M. Wang,1 L. Marcar,1 D.E. Citrin,4 C.L. Wu,5 and C. Benes6; 1Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, 2 Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 3Department of Urology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 4 Radiation Oncology Branch, NCI, Bethesda, MD, 5Department of