Design and synthesis of anti-tumour agents targeting Sulf2 and MDMX:p53

Abstract

Replacement of standard chemotherapy with targeted therapy for the cure of cancer would be a desirable way to improve treatment, especially for those tumors with low survival rates, giving patients longer life expectancy and better quality of life with a reduction of the severity of side effects. Progress in the fields of genomics and proteomics and increased understanding of the mechanisms leading to cancer have allowed many potential biological targets to be identified for therapeutic intervention. The projects described herein aim to identify small molecules that interact with proteins that are relevant in pathways related to either uncontrolled proliferation or evasion of apoptosis in tumor cells. Endosulfatases Sulfl and Sulf2 are located in the extracellular matrix and the cell surface. They modify the sulfation state of heparan sulfate proteoglycans, which affect a number of cellular signaling events, ultimately resulting in proliferation and cell growth . Although there is evidence of the involvement of Sulfl and Sulf2 in cancer processes, their action is not clearly understood. Therefore, the development of potent (low micromolar range) inhibitors of these endosulfatases is desirable for target validation and hit discovery purposes. Published experimental evidence suggests that sulfatases have some degree of arylsulfatase activity and that sulfamates are often efficacious for the inhibition of this enzyme class. Therefore, a range of aromatic-based tertiary (35 and 37) and primary (38) sulfamates were synthesized and tested in a biochemical assay against Sulf2 and counter-screened against ARSA and ARSB. The tumor suppressor p53 is a transcription factor activating a number of genes responsible for cell growth arrest, senescence and apoptosis. Tumor cells evade apoptosis and proliferate by subverting the p53 pathway, either by mutation of the TPS3 gene, resulting in the expression of inactive p53 (50% of cancers), or through amplification or overexpression of proteins responsible for p53 regulation, most notably MDM2 and MDMX. As such, modulators of the interaction of MDM2 and MDMX with p53 are of potential interest as antitumor agents and are being actively pursued by many research groups. More recently, evidence that MDMX provides a mechanism of resistance when

inhibiting the MDM2:p53 interaction has focused efforts towards dual MDM2/MDMX:p53 inhibitors. Surprisingly, even though MDM2 and MDMX have a high sequence homology within the p53 binding domain (>53%), most of the small molecules designed to bind MDM2 show much lower binding affinity towards MDMX. Arising from a project aimed at developing inhibitors of the MDM2:p53 interaction, a small panel of isoindolinones showed low micromolar activity when counterscreened against MDMX. One of these compounds, 153, containing two stereogenic centres, was utilized as the starting point for further structure-activity relationships, SAR, investigation to identify either dual inhibitors of the MDM2/MDMX :p53 or selective MDMX:p53 antagonists.