Abstract 293: Second-generation tricyclic pyrimido-pyrrolo-oxazine mTOR inhibitors suitable for the treatment of CNS disorders

Mechanistic target of rapamycin (mTOR) is activated downstream of phosphoinositide 3-kinase (PI3K), and is dysregulated in cancer and neurological disorders.[1,2] Tuberous Sclerosis Complex (TSC) is a genetic disease caused by TSC gene inactivation, where TSC loss of function leads to the hyperactivation of mTOR signaling. TSC is characterized by hyperplastic lesions in multiple organs, and in ~90% of patients it affects the brain causing epilepsy. Rapalogs have recently been explored to alleviate epileptic seizures in TSC[3], however a limited clinical success has been reported. Crossing the blood-brain barrier (BBB) opens up a new challenge in the development of highly selective mTOR inhibitors (TORKi) that could be applied in the treatment of CNS disorders.[4-7] Very recently, we have disclosed a conformational restriction strategy to explore a novel chemical space for TORKi. A first-generation highly selective tricyclic compounds had been developed, but they displayed a limited brain penetration.[8] Herein, we discovered the first pyrimido-pyrrolo-oxazine derivative with predicted BBB permeability using an CRISPR-Cas9 engineered MDCK in vitro assay containing only the human homolog of the P-gp protein[9]. An extensive exploration of the heteroaromatic ring engaging the binding affinity region in mTOR kinase was performed, and chemical moieties, including 3-CF3-substituted pyridine, thiazole and 1,3,4-thiadiazole, have been identified as building blocks providing exquisite mTOR selectivity. Computational modelling studies revealed that the 3-trifluoromethyl group is well accommodated in mTOR, while it induces a steric clash with Lys802 and Asp933 in PI3Kα, highlighting the possibility to further exploit this heteroaromatic ring in the development of highly selective mTOR inhibitors. In MDCK assays, compound 11 showed an excellent passive permeability and was not a human P-gp substrate. Our results pave the way for the application of second-generation tricyclic derivatives in the treatment of neurological disorders and epilepsy. [1] Rageot D. et al. J Med Chem. 2018, 61 (22), 10084-10105 [2] Tarantelli C. et al. Cancers (Basel) 2019, 11 (6), 775. [3] Krueger DA. et al. Neurology 2016, 87, 2408-2415. [4] Singer E. et al. Neuropharmacology 2020, 162, 107812. [5] Brandt C. et al. Neuropharmacology 2018, 140, 107-120. [6] Theilmann W. et al. Neuropharmacology 2020, 180, 108297 [7] Borsari C. et al. J Med Chem. 2020 [ahead of print] doi: 10.1021/acs.jmedchem.0c00620. [8] Borsari C. et al. J Med Chem. 2019, 62 (18), 8609-8630. [9] Karlgren M et al. Drug Metab Dispos. 2018, 46 (11), 1776-1786. Citation Format: Chiara Borsari, Erhan Keles, Andrea Treyer, Martina De Pascale, Paul Hebeisen, Matthias Hamburger, Matthias P. Wymann. Second-generation tricyclic pyrimido-pyrrolo-oxazine mTOR inhibitors suitable for the treatment of CNS disorders [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 293.