ESTRO 36 Abstract Book

S200 ESTRO 36 2017 _______________________________________________________________________________________________

Conclusion We reveal a critical pathway linking ATM and SPOP in regulation of prostate cancer initiation and therapeutic responses to radiation. This also provides the first evidence for a pathophysiological relevant mutation linked to ATM phosphorylation in the DDR.

glutamine metabolism can be used to predict clinical outcome of prostate cancer patients. Conclusion Our studies suggest that radioresistant properties of prostate cancer cells are dynamic in nature and that combination of irradiation with therapeutic agents which prevent tumor cell reprogramming and metabolic switch may restore the cytotoxic effects of irradiation in radioresistant CSC populations. References: Cojoc M et al. Cancer Res. 2015; 75(7):1482-94; Peitzsch C et al. Cancer Res. 2016; 76(9):2637-51; Kurth I et al. Oncotarget 2015; 6(33):34494-509; Krause M et al. Advanced Drug Delivery Reviews, 2016, pii: S0169-409X(16)30052-7. PV-0374 Molecular insights into a disease-relevant DNA damage response pathway B. Xu 1 1 Southern Research Institute, Molecular Radiation Biology Laboratory, Birmingham, USA Purpose or Objective The optimal DNA damage response (DDR) is critical to prevent genetic instability. The DDR is also critical to promote cellular survival in response to DNA damage as targeting optimal DDR pathways leads to sensitization to radiotherapy. The Speckle type Poz Protein (SPOP), an E3 ubiquitin ligase adaptor, has recently been identified as the gene that has the most common somatic point mutations in prostate cancer. SPOP mutations are associated with genomic alterations, indicating a role for SPOP in the maintenance of genome stability. We, and others, have recently demonstrated a critical role of SPOP in the DDR, suggesting SPOP mutants may represent a subgroup of patients that have hyper sensitivity to DNA damaging therapies. However, how SPOP mutations might impact its function and their roles in the progress of prostate tumorigenesis remain to be extensively studied. The objective of this research is to elucidate the functional significnance of SPOP in the DNA damage response pathways and to identify a subgroup of prostate cancer patients that have distinctive radiotherapeutic responses. Material and Methods Using computational modeling, we assessed the importance of the Serine 119 residue in the SBC-MATH domain. We characterized prostate cancer cells expressing the S119N dominant negative mutation using Western blot analysis, immunofluorescence microscopy, flow cytometry, and radiosensitivity by colony formation analysis. We also used in situ proximity ligation assay to demonstrate the interaction of SPOP with ATM. By mass spectrometry we identified a list of proteins that displayed alterations in association with SPOP in response to DNA damage. Results We found that Serine 119 resideing in the SBC-MATH binding interface is in close contact with non-polar residue of the SPOP-binding consensus motif. We found that prostate cancer cells expressing mutation of S119 displayed impaired DNA damage responses. Using i n situ proximity ligation assay, we demonstrate that Serine 119 is essential for SPOP interaction with ATM. We show that ATM phosphorylates SPOP on Serine 119 in response to DNA damage. Characterization of the functional significance of ATM-mediated SPOP phosphorylation indicates a wide range of downstream targets regulating cell cycle progression and DNA repair. By mass spectrometry we have identified a list of proteins that displayed alterations in association with SPOP in response to DNA damage. We found that alterations of SPOP interaction with these proteins are required for activation of the pathways involved in cell cycle checkpoints and Non-Homologous End Joining (NHEJ).

Award Lecture: Jack Fowler University of Wisconsin Award

OC-0375 Dosimetric quantification of the „true“ ano- inguinal lymphatic drainage of anal cancer patients H. Dapper 1 , G. Habl 1 , M. Mayinger 1 , M. Oechsner 1 , S.E. Combs 1 , D. Habermehl 1 1 Klinikum rechts der Isar der Technischen Universität München, Department of Radiation Oncology, München, Germany Purpose or Objective The ano-inguinal lymphatic drainage (AILD) to the inguinal lymph nodes is located in the subcutaneous adipose tissue on the medial thigh. Even though those node-vessels are very thin and hardly to detect with lymphangiography, this fact is described and shown in standard anatomy atlases. New fluorescence-imaging methods like the indocyanine- green-method corroborate this fact. Anal cancer (AC) patients undergo a combined chemoradiation (CRT) protocol and the clinical target volume (CTV) encompasses the inguinal lymphdrainage because of its affection in about 30% of all patients. Current contouring atlases suggest delineation of the primary tumor region, the mesorectum, inguinal and iliacal lymph nodes but do not advise the inclusion of the true AILD. Aim of this work was the retrospective analysis of the incidental dose to the AILD in an anal cancer patient cohort who underwent definitive CRT with VMAT-IMRT and using structure sets according to current guidelines. Material and Methods VMAT-IMRT plans of 10 anal cancer patients who had been treated with CRT during 2014 and 2016 were analyzed. On these plans we created a new volume, the expected ano- inguinal lymph drain (AILD). Based on anatomic descriptions, we connected the soft tissue between the anus and the inguinal vessels with the following demarcations: The caudal demarcation was defined 2 cm below the tuberculum minus. The cranial end of AILD was at the level of the symphysis (anal) or where no more soft tissue connection between anus and inguinal could be identified (inguinal). Ventral demarcation was the femoral skin, dorsal was the transition of the gluteal muscles to the subcutaneous adipose tissue. The lateral demarcation was the adductor muscles (anal) and the medial femur bone or at least 0.5 cm around femoral vessels (inguinal). We examined dose parameters (minimum, maximum, median, V10, V20, V30, V40, V45, V50) that were delivered to the AILD target volume and the AILD outside of the previous PTV (AILD-PTV) as represented in the dose- volume histogram. Results All of the 10 patients received at least 39.6 Gy to the inguinal lymph nodes, 45 Gy to the iliacal lymph nodes and 50.4 Gy to the primary tumor side. The median volume of AILD and AILD-PTV was 1066 cm3 and 689 cm3, respectively. Mean Dmin, Dmax and Dmean were 5.5 Gy, 58.1 Gy and 38.4 Gy for AILD and 5.5 Gy, 55.2 Gy and 31.1 Gy for AILD-PTV, respectively. Mean V30, V40, V45, V50 for AILD was 71%, 55%, 45% and 31%, respectively. For AILD-PTV it was 57%, 29%, 18% and 5%, respectively. Conclusion At least 71% of the volume of the expected AILD received at least an expected required treatment dose of 30 Gy incidentally. Especially the caudal parts of the created volumes, with a clear distance to the previous PTVs,