Abstract 2630: Preclinical identification of Venetoclax combination strategies with Idasanutlin, CUDC-907, Prexasertib or Talazoparib for neuroblastoma treatment
Authors: Dolman M. Emmy M. , Bate-Eya Laurel T. , Vernooij Lindy , Koopmans Bianca , Alles Lindy K. , Essing Anke H. , Lelieveld Daphne , Egan David A. , Kerstjens Mark , Stam Ronald W. , Caron Huib N. , Molenaar Jan J. 
Published: August 2018

Abstract
BACKGROUND: The anti-apoptotic protein B cell lymphoma/leukaemia 2 (BCL-2) is highly expressed in the majority of all neuroblastomas. In previous preclinical studies, we have shown that treatment of BCL-2-dependent neuroblastoma with BCL-2 inhibitors leads to programmed cell death. These results have contributed to the initiation of a phase I trial to study the safety and pharmacokinetics of Venetoclax in children with relapsed or refractory neuroblastoma.
AIM: The current study aims to identify and validate targeted combination strategies to prevent or overcome neuroblastoma resistance to Venetoclax.
METHODS: Targeted drug candidates for combination treatment with Venetoclax were identified by high-throughput drug screening of non-resistant and Venetoclax-resistant BCL-2-dependent neuroblastoma cell lines. Top hits were subsequently tested more extensively in vitro and in vivo to validate the screening results.
RESULTS: High-throughput drug screens identified the MDM2 inhibitor Idasanutlin as one of the strongest re-sensitizers for Venetoclax in Venetoclax-resistant BCL-2-dependent neuroblastoma cells with wild-type p53. Subsequent in vitro validation showed that Idasanutlin induced cyclin dependent kinase inhibitor 1 (p21)-mediated growth arrest in non-resistant neuroblastoma cells, but induced a BCL-2-associated X protein (BAX)-mediated apoptotic response in Venetoclax-resistant neuroblastoma cells in the presence of Venetoclax. In vivo combination of Venetoclax with Idasanultin resulted in a remarkably improved anticancer effect compared to single agent therapy, with very good partial and complete responses in BCL-2-dependent neuroblastoma xenografts. Combination screens additionally revealed that the clinically studied targeted inhibitors CUDC-907 (PI3K/HDAC), Prexasertib (CHK1) and Talazoparib (PARP1/2) improved the efficacy of Venetoclax more potently than ALK inhibitors in BCL-2-dependent neuroblastoma cells harboring ALK mutations.
CONCLUSION: Our findings suggest that the clinical use of Venetoclax for the treatment of children with BCL-2-dependent neuroblastoma tumors can be improved by combination therapy with targeted inhibitors. The presence of additional neuroblastoma driving genomic events is not always predictive of the optimal combination strategy for BCL-2-dependent neuroblastoma subgroups. These findings should guide the design of combination Phase 2 trials of Venetoclax with other targeted compounds such as Idasanutlin, CUDC-907, Prexasertib and Talazoparib.
Citation Format: M. Emmy M. Dolman, Laurel T. Bate-Eya, Lindy Vernooij, Bianca Koopmans, Lindy K. Alles, Anke H. Essing, Daphne Lelieveld, David A. Egan, Mark Kerstjens, Ronald W. Stam, Huib N. Caron, Jan J. Molenaar. Preclinical identification of Venetoclax combination strategies with Idasanutlin, CUDC-907, Prexasertib or Talazoparib for neuroblastoma treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2630.