(P 288) IDENTIFICATION OF A DNA REPAIR INHIBITOR FOR THE COMBINATION WITH LURBINECTEDIN AND RADIOTHERAPY IN SARCOMA CELL LINES

Objective: Improved multimodal treatment could optimize therapeutic outcomes for sarcoma patients. We performed radiochemotherapy (RCT) by combining the chemotherapeutic agent lurbinectedin (LU) with radiotherapy (RT) in sarcoma cell lines. Moreover, our goal was to identify an inhibitor of the DNA damage response in order to improve the efficacy of RCT.

Methods: We treated four sarcoma cell lines, namely SW-684 (fibrosarcoma), SW-872 (liposarcoma), SW-982 (biphasic synovial sarcoma), and TE-671 (rhabdomyosarcoma) with 0.5 nM LU chemotherapy (CT) and a single dose of 2 Gy or 3 Gy or fractionated regimen with 2x 3 Gy or 3x 2 Gy ionizing radiation (IR). Furthermore, we combined RT and RCT with two ATM inhibitors (ATMi) (M4076, AZD1390) and two ATR inhibitors (ATRi) (BAY-1895344, VE-822). We determined cell death (Annexin V/7AAD) and cell cycle distribution (Hoechst) with flow cytometry and clonogenicity by the colony formation assay to find a useful triple combination.

Results: Initially, we examined the effect of the combined treatment of LU and IR. LU increased cell death (p=0.029) in three of four cell lines and intensified G2/M arrest (p=0.029) in all cell lines compared to control, but the combined treatment with IR had no further radiosensitizing effect. In contrast, clonogenicity was significantly reduced in the fractionated RCT compared to CT alone (TE-671, 3x 2 Gy, p=0.028; SW-982, 2x 3 Gy, p=0.007).
Secondly, we investigated the impact of different ATMi and ATRi in combination with a single dose of 2 Gy IR on cell death and cell cycle distribution. 5 µM M4076, 0.7 µM AZD1390, 50 nM BAY-1895344, and 1.5 µM VE-822 significantly (p=0.029) increased cell death compared to IR alone in at least two of four cell lines.
Finally, we combined the ATMi and ATRi with 0.5 nM LU and 2 Gy IR to identify the most suitable inhibitor for a triple therapy.1.5 µM VE-822 increased the amount of dead cells at least by 7 % in SW-872 and up to 27 % in TE-671.

Conclusion: Our preclinical data suggest that the combination of LU with RT has no sensitizing effect compared to LU treatment alone in sarcoma cell lines. However, combining LU and IR with DNA repair inhibitors such as the ATRi VE-822 is a promising way to improve sarcoma treatment.