Anticancer potential of spirocompounds in medicinal chemistry: A pentennial expedition

A successful structure-based design of a class of non-peptide small-molecule MDM2 inhibitors targeting the p53-MDM2 protein-protein interaction is reported. The most potent compound 1d binds to MDM2 protein with a Ki value of 86 nM and is 18 times more potent than a natural p53 peptide (residues 16-27). Compound 1d is potent in inhibition of cell growth in LNCaP prostate cancer cells with wild-type p53 and shows only a weak activity in PC-3 prostate cancer cells with a deleted p53. Importantly, 1d has a minimal toxicity to normal prostate epithelial cells. Our studies provide a convincing example that structure-based strategy can be employed to design highly potent, non-peptide, cell-permeable, small-molecule inhibitors to target protein-protein interaction, which remains a very challenging area in chemical biology and drug design.

The search for novel anticancer agents with more selectivity and lower toxicity continues to be an area of intensive investigation. The unique structural features of spirooxindoles together with diverse biological activities have made them privileged structures in new drug discovery. Among them, spiro-pyrrolidinyl oxindoles have been extensively studied as potent inhibitors of p53-MDM2 interaction, finally leading to the identification of MI-888, which could achieve rapid, complete and durable tumor regression in xenograft models of human cancer with oral administration and is in advanced preclinical research for cancer therapy. This review highlights recent progress of biologically active spirooxindoles for their anticancer potentials, mainly focusing on the discussions of SARs and modes of action. This article also aims to discuss potential further directions on the development of more potent analogues for cancer therapy.

We previously reported the discovery of a class of spirooxindoles as potent and selective small-molecule inhibitors of the MDM2-p53 interaction (MDM2 inhibitors). We report herein our efforts to improve their pharmacokinetic properties and in vivo antitumor activity. Our efforts led to the identification of 9 (MI-888) as a potent MDM2 inhibitor (Ki = 0.44 nM) with a superior pharmacokinetic profile and enhanced in vivo efficacy. Compound 9 is capable of achieving rapid, complete, and durable tumor regression in two types of xenograft models of human cancer with oral administration and represents the most potent and efficacious MDM2 inhibitor reported to date.