ATR inhibition augments the efficacy of lurbinectedin in small-cell lung cancer

Small-cell lung cancer (SCLC) is the most lethal type of lung cancer. Specifically, MYC-driven non-neuroendocrine SCLC is particularly resistant to standard therapies. Lurbinectedin was recently approved for the treatment of relapsed SCLC, but combinatorial approaches are needed to increase the depth and duration of responses to lurbinectedin. Using high-throughput screens, we found inhibitors of ataxia telangiectasia mutated and rad3 related (ATR) as the most effective agents for augmenting lurbinectedin efficacy. First-in-class ATR inhibitor berzosertib synergized with lurbinectedin in multiple SCLC cell lines, organoid, and in vivo models. Mechanistically, ATR inhibition abrogated S-phase arrest induced by lurbinectedin and forced cell cycle progression causing mitotic catastrophe and cell death. High CDKN1A/p21 expression was associated with decreased synergy due to G1 arrest, while increased levels of ERCC5/XPG were predictive of increased combination efficacy. Importantly, MYC-driven non-neuroendocrine tumors which are resistant to first-line therapies show reduced CDKN1A/p21 expression and increased ERCC5/XPG indicating they are primed for response to lurbinectedin-berzosertib combination. The combination is being assessed in a clinical trial NCT04802174.

Abstract 2153: ATR inhibition augments the efficacy of the lurbinectedin in small cell lung cancer

Small cell lung cancer (SCLC) is a recalcitrant disease with only a 9% five-year survival rate. SCLCs display intertumoral heterogeneity; high neuroendocrine (NE) tumors evolve with treatment and time in a largely MYC driven manner to a chemotherapy resistant non-NE state. Lurbinectedin, an RNA Pol-II inhibitor which causes DNA damage through binding ERCC5 was approved as second line therapy in 2020, with an overall response rate of 35% in patients with relapsed SCLC. However, these responses are short-lived and the majority of patient still succumb to their disease. A trial testing the combination of lurbinectedin and doxorubicin failed to improve survival compared with standard-of-care. We assessed lurbinectedin in combination with 43 other agents in SCLC cells. The top synergistic hit was the clinically relevant ATR inhibitor berzosertib which was 4-fold more synergistic than doxorubicin. Compared with lurbinectedin alone, the combination with berzosertib caused a 3.5-fold increase in DNA damage while significantly reducing the ability of cells to sense this damage by inhibiting γH2AX induction. This led to continued DNA replication even in the presence of lurbinectedin induced DNA damage, causing mitotic catastrophe and cell death. The combination was highly synergistic in 6 of 9 SCLC cell lines tested. Synergy was inversely correlated with p21 RNA and protein expression. The canonical role of p21 is to inhibit G1/S transition, and we found that thymidine induced G1 arrest inhibited synergy, while p21 knock-down increased the synergy. Interestingly, we observed synergy was inversely correlated with NE differentiation. In a high NE high p21 mouse model of SCLC, lurbinectedin alone was highly effective, with the combination showing little improvement. Conversely in a non-NE low p21 mouse model, lurbinectedin treatment alone was less effective, however the addition of berzosertib was synergistic and significantly improved efficacy. Overall, this work demonstrated berzosertib augments lurbinectedin efficacy in the recalcitrant non-NE SCLC subsets, and supported the development of a clinical trial testing lurbinectedin and berzosertib in SCLC patients NCT04802174.

Citation Format: Christopher William Schultz, Yang Zhang, Haiqing Fu, Yasuhisa Murai, Darawalee Wangsa, Devon Atkinson, Liton Saha, Brian Elenbaas, Chien-Fei Lee, Astrid Zimmerman, Thomas Ried, Frank Zenke, Zoe Weaver, Rajaa Elmeskini, Yves Pommier, Anish Thomas. ATR inhibition augments the efficacy of the lurbinectedin in small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2153.