Abstract A140: Identification of substituted isoindolinones as potent inhibitors of the MDM2-p53 protein-protein interaction

The p53 tumor suppressor plays a pivotal role in the cell by reacting to stress, which may be caused by hypoxia, DNA damage, or oncogenic signalling. Activation of p53 protein results in the transcription of a number of genes that govern progression through the cell cycle, the initiation of DNA repair, and apoptosis. The activity of p53 is tightly regulated by the MDM2 protein, which is transcribed in response to p53 activation. MDM2 binds to and inactivates p53 and also ubiquitylates the MDM2-p53 complex to target it for proteosomal degradation. In normal cells the balance between active p53 and inactive MDM2-bound p53 is maintained in a negative feedback loop. Inhibition of the MDM2-p53 protein-protein complex by small molecule inhibitors is expected to reactivate normal p53 pathways in cells overexpressing MDM2, consequently exerting an anti-cancer effect. Potent small molecule inhibitors of the MDM2-p53 interaction have been identified e.g. the Nutlins [Science 2004, 303, 844], the benzodiazepinediones and indolinones [J. Med. Chem. 2006, 49, 3759–3762]. The antitumor activities of these compounds in cellular and in vivo models are promising. We have reported previously inhibitors of the MDM2-p53 interaction, based on an isoindolinone scaffold [J. Med. Chem. 2006, 49, 6209–6221], and SAR studies leading to compounds with improved potency e.g. NU8345A; IC50 = 171 ± 15 nM. NMR structural studies suggested that substitution of the isoindolinone A-ring may provide additional favourable interactions with the protein. A small series of examples was prepared, and 4-substitution with small hydrophobic groups was found to improve potency e.g. rac-4-methyl-3-(4-chlorophenyl)-3-((1-(hydroxymethyl) cyclopropyl)methoxy)-2-(4-nitrobenzyl)isoindolin-1-one (NU8405; IC50 = 274 ± 35 nM) and rac-4-chloro-3-(4-chlorophenyl)-3-((1-(hydroxymethyl)cyclopropyl)methoxy)-2-(4-nitrobenzyl)isoindolin-1-one (NU8406; IC50 = 143 ± 26 nM). Introduction of a 6-tert-butyl group was also found to be favourable i.e. rac-6-tert-butyl-3-(4-chlorophenyl)-3-((1-(hydroxymethyl)cyclopropyl)methoxy)-2-(4-nitrobenzyl)isoindolin-1-one (NU8399; IC50 = 152 ± 27 nM). Resolution of the enantiomers of NU8406, using chiral HPLC, gave NU8406A and NU8406B (IC50s of 43.8 ± 6.2 nM and 1.27 ± 0.08 M, respectively). The cellular activities of key compounds have been determined and show dose dependent induction of p53 regulated genes by Western blotting. NU8406 shows selective cytotoxicity in p53wt HCT116 cells compared with the HCT116−/− line (GI50s = 9.8 ± 1.1 and 21.3 ± 3.1 M, respectively) which is comparable to Nutlin-3 (ELISA IC50 = 66.2 ± 5.7 nM; GI50s = 8.9 ± 0.5 and 38.8 ± 3.4 M, respectively). Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A140.