ESTRO 2020 Abstract Book

S102

ESTRO 2020

Results Control untreated tumours had a mean (+ 1 S.E.) TGT5 of 6.6 days (+ 0.2). No significant change was found following treatment with anti-CTLA-4, the TGT5 being 7 days (+0.6). A significant increase was obtained with heating or OXi4503, the respective TGT5 values being 11.5 days (+ 0.6) and 18.6 days (+ 1). When heat or OXi4503 were combined with anti-CTLA4 an even greater effect was observed. With heating the TGT5 values was 18.0 days (+ 3.5). When combined with OXi4503 it was only 19.0 days (+ 1.3), but this did not include the measurements in 3 tumour which were completely controlled. Quantification of CD4 and CD8 expression showed a significant drop of 40- 60 % one day after injecting OXi4503 and around a 70 % drop 3 days after heating. However, these values had returned to pre-treatment levels by 3 to 4 and 7 to 10 days, respectively. HSP70 expression 4 hours after heating was not significantly different from control values, but at 24 hours there was a significant elevation (P=0.004). Conclusion Our C3H mammary carcinoma model did not respond to treatment with anti-CTLA-4, consistent with it being non- immunogenic. However, when treated with agents that induce significant cell kill both directly and indirectly via the induction of vascular damage, the tumour became sensitive to anti-CTLA-4 treatment. Surprisingly, rather than seeing an increase in CD4 or CD8 expression there was a transient decrease with both heating and OXi4503, returning to pre-treatment levels by the end of the anti- CTLA-4 treatment period. HSP70 did increase after applying heat. Thus, we do have possibilities to improve the anti-tumor effect of CIs, but the mechanism remains unclear. Supported by grants from the Danish Cancer Society and the Danish Council for Independent Research: Medical Sciences OC-0203 Eliminating tumour hypoxia to improve the impact of immunotherapy D. Marcus 1 , A. Van der Wiel 1 , R. Biemans 1 , N. Lieuwes 1 , A. Heyerick 2 , J. Smaill 3 , A. Patterson 3 , J. Theys 1 , A. Yaromina 1 , P. Lambin 1 , L. Dubois 1 1 GROW - School for Oncology and Developmental Biology- Maastricht Comprehensive Cancer Center- Maastricht University Medical Center- Maastricht- The Netherlands, Department of Precision Medicine- M-Lab, Maastricht, The Netherlands ; 2 Convert, Pharmaceuticals, Liege, Belgium ; 3 University of Auckland, Auckland Cancer Society Research Centre- School of Medical Science, Auckland, New Zealand Purpose or Objective Immunotherapy (IO) has become an important therapy for cancer. The immunocytokine L19-IL2 successfully attracts and activates immune cells at the tumour site by binding to the tumour vasculature and providing an IL2 stimuli. However, immunotherapies such as L19-IL2 are often not reaching its full potential due to an immune suppressive tumour microenvironment (TME). A key factor accountable for treatment resistance and immunosuppression is hypoxia. Specifically targeting hypoxia could hence improve the infiltration and function of immune cells. CP- 506 is a drug activated in hypoxic tumour regions where it has the ability of cell kill due to the induction of DNA damage. In addition, immune checkpoint inhibitor antibody anti-PD-L1 (aPD-L1) will be used due to the current standard of care status for a variety of cancers and the ability to overcome immune exhaustion. We hypothesise that targeting tumour hypoxia using CP-506 combined with immunotherapy increases therapeutic outcome. Material and Methods Balb/c mice were injected unilaterally with CT26 or C51 colon carcinoma cells and randomized at an average tumour volume of 200 mm 3 . Treatment groups (n=6 to 8)

consist of a control group, single agents, CP-506 + L19-IL2 or aPD-L1 and CP-506 + L19-IL2 + aPD-L1. L19-IL2 (1 µg/g, i.v.) was administered on day 1,3 and 5, aPD-L1 (10 µg/g, ip) at day 1,3,5,8 and 10 and CP-506 (600 mg/kg, i.p.) was administered for five consecutive days starting at day 1. Outcome was determined by growth delay of tumours followed-up until 4 times start volume was reached. In an additional experiment, tumours were taken out at day 4 and 6 of treatment for immunohistochemistry staining and flow cytometry analysis. Results Growth delay was significantly enhanced by CP-506 in combination with L19-IL2 compared to treatment with single agents (p< 0.05). Immunohistochemistry staining indicated an increased necrotic fraction in the combination group. Triple combination (CP-506 + L19-IL2 + aPD-L1) further prolonged survival. Flow cytometry analysis demonstrated increased intratumoural immune infiltration in the combination groups containing L19-IL2 with in the initial treatment response an increase in dendritic cells and a gradual increase in CD8 cytotoxic T cells in ratio to CD4 T regulatory cells. Conclusion Our study indicates that the use of the hypoxia-activated prodrug CP-506 enhances efficacy of L19-IL2 and L19-IL2 + aPD-L1. Triple combination therapy was most beneficial. Not only was tumour growth delayed, tumours were also more necrotic due to the synergy between CP-506 and L19- IL2. Intratumoural and systemically, innate and adaptive immune systems were upregulated upon treatment with L19-IL2 in double and triple combination treatment. Taken together, based on these results CP-506 appears to be an effective combination strategy with IO. OC-0204 Molecular imaging of the endogenous hypoxia related marker CA IX with 111In-labeled VHH B9 S. Van Lith 1 , F. Huizing 2 , B. Hoeben 2 , S. Doulkeridou 3 , M. Gotthardt 1 , P. Van Bergen en Henegouwen 3 , S. Heskamp 1 , J. Bussink 2 1 Radboud University Medical Center, Radiology and Nuclear Medicine, Nijmegen, The Netherlands ; 2 Radboud University Medical Center, Radation Oncology, Nijmegen, The Netherlands ; 3 Utrecht University, Cell Biology- Department of Biology- Science FacultyUtrecht, Utrecht, The Netherlands Purpose or Objective Hypoxia is present in the majority of solid tumors and is associated with poor outcome and radioresistance. Carbonic anhydrase IX (CAIX) is a transmembrane enzyme that is upregulated by cells under hypoxic conditions. Therefore, non-invasive imaging of CAIX could be of prognostic value and it may allow radiotherapy planning and treatment effect monitoring. The aim of this study was to validate and optimize SPECT imaging of CAIX expression in a head-and-neck squamous cell carcinoma model using an anti-CAIX variable domain of heavy chain antibody (VHH, nanobody). Material and Methods VHH B9 was conjugated site-specifically with maleimide- DTPA and labeled with 111 In. The binding affinity and internalization of [ 111 In]In-DTPA-B9 was analyzed using SKRC-52 cells, which ubiquitously express CAIX. Subsequently, a dose-escalation study was performed in athymic nude mice with subcutaneous SCCNij153 head- and-neck cancer xenografts. Targeting specificity was determined by blocking specific uptake with unlabeled VHH B9, and by analyzing tumor uptake of an 111 In-labeled irrelevant VHH R2. A subgroup of mice was co-injected with plasma expander gelofusin, to reduce renal retention of [ 111 In]In-DTPA-B9. Tracer uptake at 4 hours after injection was determined by ex vivo radioactivity counting and SPECT/CT scans. Furthermore, spatial correlation between tracer uptake on autoradiography images and