By deciphering the mechanism of action of QN-302, we show that binding of QN-302 to the G4-positive P2 promoter region inhibits MDM2 transcription, leading to a pronounced increase in p53 protein levels and the consequent inhibition of cell growth and induction of apoptosis in vitro and tumour volume (TV) reduction in vivo. This evidence concerns the gene TP53 and neoplasm.