Abstract

The transcription factor p53 acts as a molecular signaling node that determines a cell’s fate in response to stress, including DNA damage. MDM2 regulates p53 by binding its the transactivation domain resulting in its degradation, and in around 7% of tumours MDM2 overexpression inactivates p53, resulting in oncogenic transformation. Inhibition of the MDM2-p53 protein-protein interaction with peptides and small-molecules has been shown to reactivate p53, and a number of small-molecule MDM2-p53 inhibitors have entered clinical trials. Previously, we have identified isoindolinones with MDM2-p53 inhibitory activity. Introduction of the E69K70A (17-109) surface mutation into MDM2 enabled the first isoindolinone X-ray co-crystal structure to be solved, with 1 as the ligand (Figure 1). Similarly, the X-ray structure of 6-t-butyl isoindolinone (IC50 ≤ 40 nM) showed the 6-t-butyl group extending into the Phe binding pocket, accommodated by the movement of sidechain of MDM2 Tyr67 and with one CH3 in proximity to the backbone carbonyl of Gln72. As predicted, a 6-carbinol substituent (2, IC50 ≤ 11 nM) showed improved potency and drug-like properties. Extensive structure-guided and metabolism directed SAR studies identified isoindolinone 3 (IC50 ≤ 4.4 nM) as a lead compound that showed excellent potency. Deuteration of the C3-side-chain was demonstrated to improve metabolic stability. Compound 3 demonstrated in vivo antitumour activity in a SJSA-1 xenograft model with 50 mg/kg dosing. In conclusion, a combination of structure-guided and metabolism-directed optimisation of the isoindolinone MDM2-p53 inhibitors has yielded a robust lead compound 3 for further optimisation.