Inhibitors of the Oncogenic PA2G4-MYCN Protein-Protein Interface

SIMPLE SUMMARY: Neuroblastoma is the commonest solid tumour of early childhood. Most children presenting with advanced disease have a poor survival rate, despite intensive chemotherapy treatment. One third of advanced NB tumours have MYCN oncogene amplification and overexpression, which predicts poor patient prognosis. However, the development of inhibitors directly targeting MYCN family proteins has proven challenging due to the absence of MYCN structural information. We have identified a protein called PA2G4, which is a cofactor for MYCN in promoting cancer cell growth. We have developed a compound WS6 and its analogous, which inhibits PA2G4 and MYCN protein levels and reduces tumour cell growth. The purpose of this study is to characterise and evaluate our novel WS6 analogous as inhibitors of MYCN and PA2G4 oncogenic functions in neuroblastoma. ABSTRACT: MYCN is a major oncogenic driver for neuroblastoma tumorigenesis, yet there are no direct MYCN inhibitors. We have previously identified PA2G4 as a direct protein-binding partner of MYCN and drive neuroblastoma tumorigenesis. A small molecule known to bind PA2G4, WS6, significantly decreased tumorigenicity in TH-MYCN neuroblastoma mice, along with the inhibition of PA2G4 and MYCN interactions. Here, we identified a number of novel WS6 analogues, with 80% structural similarity, and used surface plasmon resonance assays to determine their binding affinity. Analogues #5333 and #5338 showed direct binding towards human recombinant PA2G4. Importantly, #5333 and #5338 demonstrated a 70-fold lower toxicity for normal human myofibroblasts compared to WS6. Structure-activity relationship analysis showed that a 2,3 dimethylphenol was the most suitable substituent at the R(1) position. Replacing the trifluoromethyl group on the phenyl ring at the R(2) position, with a bromine or hydrogen atom, increased the difference between efficacy against neuroblastoma cells and normal myofibroblast toxicity. The WS6 analogues inhibited neuroblastoma cell phenotype in vitro, in part through effects on apoptosis, while their anti-cancer effects required both PA2G4 and MYCN expression. Collectively, chemical inhibition of PA2G4-MYCN binding by WS6 analogues represents a first-in-class drug discovery which may have implications for other MYCN-driven cancers.