TP53 and neoplasm: To investigate the role of cysteine residues in mutant p53 reactivation by APR-246/MQ in tumor cells, we transiently transfected p53 null H1299 cells with vectors encoding R175H, R175H–C124A, R175H–C277A or R175H–C124A–C277A p53 mutant proteins, or with control vector (pCMV).