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We recently described the identification of a new class of small molecule activators of the mitochondrial protease ClpP. These compounds synthesized by Madera Therapeutics showed increased potency of cancer growth inhibition over the related compound ONC201. In this study, we describe chemical optimization and characterization of the next generation of highly potent and selective small molecule ClpP activators (TR compounds) and demonstrate their efficacy against breast cancer models in vitro and in vivo. One of these compounds (TR-107) was selected for further studies because of excellent potency, specificity and drug-like properties. Examination of TR-107 effects in Triple Negative Breast Cancer (TNBC) cell models showed growth inhibition in the low nanomolar range, equipotent to paclitaxel, in a ClpP-dependent manner. TR-107 reduced specific mitochondrial proteins including OXPHOS and TCA cycle components, in a time, dose and ClpP-dependent manner. Seahorse XF Analysis and glucose deprivation experiments confirmed inactivation of OXPHOS and demonstrated an increased dependence on glycolysis following TR-107 exposure. The pharmacokinetic properties of TR-107 were compared to other known ClpP activators including ONC201 and ONC212. TR-107 displayed excellent exposure and serum t1/2 after oral administration. Using an orthotopic xenograft murine model of MDA-MB-231 cells, the anti-tumor response to TR-107 was investigated. Oral administration of TR-107 resulted in reduction in tumor volume and extension of survival in the treated vs. vehicle control groups. In summary, these studies describe the identification of highly potent new ClpP agonists with improved efficacy against TNBC, through targeted inactivation of OXPHOS and disruption of mitochondrial metabolism.
ONC201 is a novel anticancer compound currently in over 20 clinical trials for multiple different cancers, including triple negative breast cancer (TNBC). We recently demonstrated that ONC201 and the more potent TR compounds selectively activate the mitochondrial protease ClpP. While previous studies demonstrated substantial effects on mitochondrial metabolism, the consequences of ClpP activation on cancer cell metabolism are yet to be defined. To investigate this, we performed an unbiased metabolomics and proteomics analysis comparing the effects of ONC201 and TR-57 on the TNBC metabolome and proteome. Consistent with these compounds targeting the mitochondria, our studies identified multiple mitochondrial metabolites and enzymes that were impacted by ClpP activation, such as TCA cycle intermediates and enzymes, heat shock proteins and mitochondrial ribosomal proteins. In addition to previously reported elements of the integrated stress response (ATF4, CHOP), we identified several proteins that were upregulated as part of the mitochondrial-nuclear signaling process. qRT-PCR was used to determine the impact of ONC201 or TR-57 treatment on transcript levels of proteomic hits. Importantly, the effects of ONC201 and the TR compounds on these proteins and cell growth were abolished in ClpP null cells. In summary, our studies further demonstrate that loss of metabolic function in mitochondria contributes to the anticancer activity of these ClpP activator compounds. Citation Format: Emily M. Fennell, Lucas J. Aponte-Collazo, Blake R. Rushing, Yuan-Yuan Li, Wimal Pathmasiri, Joshua D. Wynn, Paul R. Graves, Ekhson L. Holmuhamedov, Laura E. Herring, Edwin J. Iwanowicz, Lee M. Graves. Disruption of mitochondrial metabolism by ClpP activation in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2398.
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