Abstract 2606: ZN-c3, a potent and selective Wee-1 inhibitor demonstrates anti-tumor activities in combination with other targeted therapies and overcomes PARP inhibitor resistance
Authors: Li Jiali , Ma Jianhui , de Jong Petrus R. , Izadi Hooman , Hoang Tiffany , Ibrahim Noah , Boren Brant , Hegde Sayee Hegde , Doñate Fernando , Samatar Ahmed A. 
Published: June 2022

Abstract
Inhibition of the DNA damage response (DDR) pathway is an attractive approach to target cancers cells. Unlike normal cells which relay on two cell cycle checkpoints to repair DNA damage, most tumor cells only depend on the G2 checkpoint because their G1 checkpoint is defective. Wee1 regulates the G2/M checkpoint and abrogating the G2 checkpoint by inhibiting Wee-1 in cancer cells with DNA damage can preferentially sensitize cancer cells to undergo mitotic catastrophe. We have developed and characterized ZN-c3, a potent and selective Wee-1 inhibitor with a differentiated kinase selectivity and pharmacokinetics profile.
ZN-c3 was evaluated in ER-positive, triple negative, triple negative PARP inhibitor resistant, and Her-2 positive trastuzumab resistant breast cancers. In the ER-positive MCF-7 efficacy model, ZN-c3 demonstrated anti-tumor activity as a single agent as well as in combinations with a CDK4/6 inhibitor (Palbociclib) or ZN-c5, a selective estrogen receptor degrader (SERD). In the MDA-MB-436, a triple negative breast cancer tumor xenograft
model, ZN-c3 demonstrated efficacy as a single agent and in combination with the PARP inhibitors Olaparib or Niraparib. We extended these combination studies by evaluating the efficacy of Niraparib in combination with ZN-c3 in patient-derived xenograft (PDX) triple negative breast tumors. ZN-c3 was efficacious as a single agent and the efficacy was enhanced in the combination with Niraparib.
PARP inhibitors are effective and have been approved for treatment of some cancer types. However, most patients develop resistance to these agents. We sought to investigate whether ZN-c3 can overcome the acquired resistance to PARP inhibitors (Olaparib and Niraparib). We generated PARP inhibitor resistant breast tumor xenograft models. A significant tumor growth inhibition was observed in these resistant tumor xenograft models when treated with ZN-c3. These data suggest that ZN-c3 as a single agent can overcome the acquired PARP inhibitor resistance. Finally, we also evaluated ZN-c3 activity in a HER-2 positive trastuzumab resistant breast tumor xenograft model (JIMT-1) and ZN-c3 showed anti-tumor activity alone and in combination with trastuzumab. In summary, these results demonstrate that ZN-c3 is effective as a single agent and in combination with other targeted therapies in breast cancer models. Moreover, ZN-c3 can overcome the acquired resistance to PARP inhibitors and trastuzumab. ZN-c3 is currently in clinical trials for several indications and has demonstrated promising clinical activity and good tolerability.
Citation Format: Jiali Li, Jianhui Ma, Petrus R. de Jong, Hooman Izadi, Tiffany Hoang, Noah Ibrahim, Brant Boren, Sayee Hegde Hegde, Fernando Doñate, Ahmed A. Samatar. ZN-c3, a potent and selective Wee-1 inhibitor demonstrates anti-tumor activities in combination with other targeted therapies and overcomes PARP inhibitor resistance [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 2606.