Abstract Book

S304

ESTRO 37

OC-0581 SNPs at rs7459185 and rs11466353 of the TGFβ1 Gene are associated with esophagitis in lung cancer B.D. Delgado-León 1 , M.V. Enguix 1 , J. Cacicedo 2 , J.M. Nieto-Guerrero 1 , D. Herrero 3 , J.M. Praena 4 , P. Cabrera 1 , M.J. Ortiz Gordillo 1 , J.L. López Guerra 1 1 Hospital Universitario Virgen del Rocio, Radiation Oncology, Sevilla, Spain 2 HOSPITAL CRUCES, Radiation Oncology, Bilbao, Spain 3 Hospital Universitario Virgen del Rocio, Clinical Oncology, Sevilla, Spain 4 Hospital Universitario Virgen del Rocio, Methodologic Unit, Sevilla, Spain Purpose or Objective To investigate the association between single nucleotide polymorphisms (SNPs) in the transforming growth factor b1 (TGFb1) gene and the risk of radiation-induced esophageal toxicity (RE) in patients with lung cancer (LC). We present the preliminary results of a prospective multicentric study. Material and Methods From 2013 to 2017, 322 LC patients with available genomic DNA samples were treated at two hospitals. All patients were treated with radio(chemo)therapy. We studied both acute and late RE. We defined late toxicity when events occurred 3 months after the start of radiation therapy. We genotyped 14 SNPs of the TGFb1 gene (rs11466338; rs11466343; rs11466344; rs11466353; rs1800468; rs1800469; rs1800470; rs4803455; rs8110090; rs8179181; rs2868370; rs2868371; rs7459185; rs228590) by the polymerase chain reaction restriction fragment length polymorphism method. RE was scored prospectively and graded according to the National Cancer Institute’s Common Terminology Criteria for Adverse Events version 4.0. To assess the risk of RE we used Kaplan-Meier cumulative probability and Cox proportional hazards analyses to evaluate the effect of TGF-1 genotypes on such risk. Results There were 377 (86.5%) male and 74 women in the study, with median age of 65 years (range 35 to 88). Univariate analysis for the risk of acute grade ≥ 3 RE showed a statistically significantly effect of concomitant chemotherapy (hazard ratio [HR]= 6.881; 95% CI, 1.183 to 2.853; P= 0.02), dosimetric variables such as the gross and clinical tumour volumes, mean dose of esophagus and V40 to V70 of esophagus with a p<.005. CC/GG genotypes of TGF-1 rs7459185 SNP were associated with a statistically significantly higher risk of this endpoint (HR= 4.493; 95% CI, 1.449 to 13.934; P= 0.009). Specifically, 16 events of acute severe RE occurred, 44% in the wild type genotype (GG, n=186) and 31% (n=100) in G/C patients. Univariate analysis for the risk of late grade 2 RE showed a statistically significantly association with the radiation dose >60 Gy (HR= 2.579; 95% CI, 1.187 to 5.601; P= 0.017), small-cell histology (HR= 15.57; 95% CI, 3.381 to 71.704; P <0.001) and esophagus volume (HR= 1.004; 95% CI, 1 to 1.008; P= 0.037). Additionally, the SNP rs11466353 also associated with this enpoint (HR= 0.341; 95% CI, 0.124 to 0.939; P= 0.037). 21 events of late moderate RE occurred, 76.2% in wild type genotype (CC, n=295) and 19% in C/A patients (n=27). Conclusion We found that, among others, the TGFβ1 rs7459185 and rs11466353 SNPs are associated with acute and late RE, respectively. This response markers may be usefull biomarkers for guiding therapy intensity in an individualized therapy. OC-0582 Role of GDNF in the modulation of SGSCs radiation response; regeneration or senescence? X. Peng 1 , K. Varendi 2 , M. Maimets 3 , J.O. Andressoo 2 , R.P. Coppes 1 1 UMCG-University Medical Center Groningen, Cell

Biology, Groningen, The Netherlands 2 University of Helsinki, Institute of Biotechnology, Helsinki, Finland 3 BRIC, Biotech Research and Innovation Centre, Copenhagen, Denmark Purpose or Objective Secretory function restoration is a challenge for regenerative therapy of radiation-damaged salivary glands. Recently, stem cell therapy has been proposed to allow such a functional regeneration. It has been suggested that glial-cell-derived neurotrophic factor (GDNF) promotes survival of mice salivary gland stem cells (mSGSCs). GDNF-treatment in combination with stem cell based regenerative therapy could represent a promising treatment for radiation-induced hyposalivation and consequential xerostomia. However, the role of GDNF on SGSC survival and proliferation after therapeutic irradiation is still an enigma. The purpose of this study was to investigate the role of GDNF in the modulation of SGSC response to irradiation. Material and Methods Salivary gland organoid derived cells of Gdnf hypermorphic (Gdnf wt/hyper ) and wild-type mice (Gdnf wt/wt ) were irradiated (IR) with γ-rays at 0, 1, 2, 4 and 8Gy. mSGSC survival and stemness were assessed by calculating stem cell surviving fraction measured as post- IR organoid forming potential and population doublings. Flow cytometry was used to determine the CD24 hi /CD29 hi stem cell (SC) population. qPCR and immunofluorescence were used to detect GDNF expression. Six-day-old salivary gland organoids were irradiated with 7 Gy of y- rays, IR induced organoids senescence were confirmed by SA-ß-Gal and P16 staining. Results Exogenously added GDNF or increase expression of GDNF in hypermorphic mice SGSC induced an increase in secondary organoids formation efficiency when compared to wild-type mice/untreated SG (p<0.05). However, neither endogenous nor exogenous GDNF increased the CD24 hi CD29 hi stem cell-like population. Organoids IR surviving fraction (OSF) of mSGSCs were similar albeit resulted in larger spheres and an increased cell number in the Gdnf wt/hyper compared to Gdnf wt/wt group. Indeed, mSGSC of Gdnf wt/hyper mice showed high sphere forming efficiency upon replating. Cell cycle distribution of SGSC after irradiation had no difference with or without GDNF. Interestingly, GDNF expression was highly upregulated after irradiation both in vitro (p=0.008) and in vivo (p<0.05) but normalized in vivo after mSGSC transplantation-related regeneration. Receptor tyrosine kinase (RET) expression was strongly related to OSF (r=0.842, p=0.002) and co-localized with GDNF in salivary gland striated ducts. More than 90% IR induced senescence located in striated ducts where GDNF colocalized with senescence marker p16 and SA-ß-Gal. Interestingly, senescence cells were detected in organoids after IR. Conclusion GDNF does not protect mSGSCs against irradiation but seems to promote mSGSCs proliferation through the GDNF-RET signaling pathway. Post-transplantation stimulation of GDNF/RET pathway may enhance the regenerative potential of mSGSCs. IR induced upregulation of GDNF may be involved in IR induced senescence. OC-0583 Intestinal Stem Cells: Modeling of Reserve Stem Cell Population and Volume Effect E. Bahn 1 , M. Van Heerden 2 , J. Gueulette 3 , K. Slabbert 4 , W. Shaw 2 , J. Debus 1 , M. Alber 1 1 Heidelberg University Hospital, Department of Radiation Oncology, 69120 Heidelberg, Germany 2 University of the Free State, Department of Medical Physics, 9300 Bloemfontein, South Africa