ESTRO 2022 - Abstract Book

S436

Abstract book

ESTRO 2022

1 N.N. Petrov NMRC of oncology, Radiotherapy, St Petersburg, Russian Federation; 2 N.N. Petrov NMRC of oncology, immunology, St Petersburg, Russian Federation; 3 N.N. Petrov NMRC of oncology, Immunology, St Petersburg, Russian Federation Purpose or Objective Systemic (abscopal) effects of stereotactic ablative radiation therapy (SABR) are associated with activation of immunologic response triggered by irradiation. Clinical manifestation of this phenomenon is rare and need further evaluation. In this study we determine dynamic of immune status before and at different time points after SABR. Materials and Methods In 38 patients with oligometastatic lesions in the lungs and/or liver SABR was performed as 4 fractions of 10-13.5Gy or 3 fractions of 15Gy-20Gy. A quantitative assessment and analysis of blood immunological parameters was conducted before SABR (point A), 3-4 weeks (point B) and 6-8 weeks (point C) after the end of SABR. Peripheral blood samples were analyzed by flow cytometry on a FACS Canto ™ II cytometer. We used Friedman test for multiple ( χ 2) and Nemenyi test for group comparisons. Depending on the radiation dose, we divided patients for two groups: total focal dose (TFD) ≤ 45 Gy (16 patients) and TFD> 45 Gy (22 patients). Also, we analyzed indicators of the immune status in groups with irradiation of one metastatic focus (25 patients) and group with irradiation of ≥ 2 metastatic foci (13 patients) Results We detected statistically significant increase of T-lymphocytes (CD3+CD19-), χ 2 = 13,9, p = 0,001, pairwise p(A, B) = 0,001; T-helpers (CD3+CD4+), χ 2 = 8,6, p = 0,01, pairwise p(A, B) = 0,01; activated T-helpers (CD3+CD4+HLA-DR+), χ 2 = 38,6; p = 0,001; pairwise p(A, B) = 0,001, p(A, C) = 0,001; and activated cytotoxic T lymphocytes (CD3+ С D8+HLA-DR+), χ 2 = 14,4; p = 0,001; pairwise p(A, B) = 0,002, p(A, C) = 0,01 and decrease of B-lymphocytes (CD3-CD19+), χ 2 = 35,4; p < 0,001, pairwise p(A, B) = 0,001, p(A, C) = 0,002. Interesting. that we noted decline of T-regulatory lymphocytes that associated with immunosuppressive mechanisms (CD4+CD25brightCD127low) in point B compared with the values obtained before radiotherapy χ 2 = 7,1; p = 0,03 pairwise p (A, B) = 0,03]. Also 6-8 weeks after SABR, in comparison with values obtained 3-4 weeks after SABR, we detected statistically significant decrease of T-lymphocytes (pairwise p (B, C) = 0.03) Conclusion Immunologic effects of SABR characterized by activation of the T- effectors and T-helpers with moderate but significant decline in T-regularity cells. In dynamic, this changes expressed by a greater extent 3-4 weeks after SABR. 1 Institute for Cancer Research, The Norwegian Radium Hospital, Radiation Biology, Oslo, Norway; 2 Institute for Cancer Research, The Norwegian Radium Hospital, Core Facilities, Oslo, Norway Purpose or Objective Radiotherapy works by causing lethal DNA damage to cancer cells. However, in response to the DNA damage, cancer cells can activate DNA repair mechanisms, which may limit treatment efficacy. One promising strategy is thus to combine radiotherapy with inhibitors of DNA damage repair. Interestingly, recent studies suggest that inhibition of DNA repair can also affect anti-tumor immunity. Here, we have developed a large-scale flow cytometry screening method to identify compounds that inhibit DNA damage repair after radiation. Our aim is to explore how these DNA repair inhibitors affect tumor radiosensitivity and anti-tumor immune effects. Materials and Methods Cancer cells were harvested at 30 minutes and six hours after treatment with radiation and compound libraries, and DNA repair was assessed by levels of the DNA damage marker γ H2AX. Barcoding with pacific blue staining was included to achieve highly accurate measurements of γ H2AX levels. A pipetting robot and a flow cytometer equipped with a plate loader were used for screen automation. In follow-up studies of candidate hits, cell death was monitored by clonogenic survival, and DNA repair and immune signaling were investigated by immunoblotting and flow cytometry. Results The screen was performed with more than 1900 compounds, from the Biomol kinase inhibitor, Enzo target and pathway, Cancer Selleck and Prestwick compound libraries, in A549 lung cancer and/or Reh leukemia cells. To verify the feasibility of our screening method for DNA repair, two repetitive screens were conducted in both cell lines with 357 of the compounds. The results were highly reproducible, and among the candidate hits were known regulators of DNA repair such as multiple HDAC inhibitors (e.g. SAHA). In addition, several previously unknown regulators of DNA repair were identified. Notably, largely similar results were obtained for the two cell lines. Results of screens performed in a single cell line will thus likely be widely applicable. A549 cells were further screened with the Cancer Selleck library, and Reh cells with the Prestwick library. Several screen results were validated by acquiring compounds from an independent source and testing the screen endpoints in independent experiments. Preliminary results suggest that some of the DNA repair inhibitors also promote anti-tumor immune effects after irradiation. Conclusion Altogether, our screens have identified more than 70 candidate hits. After further preclinical and clinical testing, the identified compounds may potentially be useful in combination with radiotherapy in future treatment approaches. PD-0486 A flow cytometry-based screen to identify compounds that inhibit DNA repair after radiation G.E. Rødland 1 , C. Naucke 1 , S. Hauge 1 , T. Stokke 2,1 , R. G. Syljuåsen 1