The tumour suppressor gene TP53 is the most frequently mutated gene in cancer. Wild-type p53 can suppress tumour development by multiple pathways. However, mutation of TP53 and the resultant inactivation of p53 allow evasion of tumour cell death and rapid tumour progression. The high frequency of TP53 mutation in tumours has prompted efforts to restore normal function of mutant p53 and thereby trigger tumour cell death and tumour elimination. Small molecules that can reactivate missense-mutant p53 protein have been identified by different strategies, and two compounds are being tested in clinical trials. Novel approaches for targeting TP53 nonsense mutations are also underway. This Review discusses recent progress in pharmacological reactivation of mutant p53 and highlights problems and promises with these strategies.

SummaryDNA damage can stall the DNA replication machinery, leading to genomic instability. Thus, numerous mechanisms exist to complete genome duplication in the absence of a pristine DNA template, but identification of the enzymes involved remains incomplete. Here, we establish that Primase-Polymerase (PrimPol; CCDC111), an archaeal-eukaryotic primase (AEP) in eukaryotic cells, is involved in chromosomal DNA replication. PrimPol is required for replication fork progression on ultraviolet (UV) light-damaged DNA templates, possibly mediated by its ability to catalyze translesion synthesis (TLS) of these lesions. This PrimPol UV lesion bypass pathway is not epistatic with the Pol η-dependent pathway and, as a consequence, protects xeroderma pigmentosum variant (XP-V) patient cells from UV-induced cytotoxicity. In addition, we establish that PrimPol is also required for efficient replication fork progression during an unperturbed S phase. These and other findings indicate that PrimPol is an important player in replication fork progression in eukaryotic cells.

Deregulation of the ubiquitin/proteasome system has been implicated in the pathogenesis of many human diseases, including cancer. Ubiquitin-specific proteases (USP) are cysteine proteases involved in the deubiquitination of protein substrates. Functional connections between USP7 and essential viral proteins and oncogenic pathways, such as the p53/Mdm2 and phosphatidylinositol 3-kinase/protein kinase B networks, strongly suggest that the targeting of USP7 with small-molecule inhibitors may be useful for the treatment of cancers and viral diseases. Using high-throughput screening, we have discovered HBX 41,108, a small-molecule compound that inhibits USP7 deubiquitinating activity with an IC 50 in the submicromolar range. Kinetics data indicate an uncompetitive reversible inhibition mechanism. HBX 41,108 was shown to affect USP7-mediated p53 deubiquitination in vitro and in cells. As RNA interference-mediated USP7 silencing in cancer cells, HBX 41,108 treatment stabilized p53, activated the transcription of a p53 target gene without inducing genotoxic stress, and inhibited cancer cell growth. Finally, HBX 41,108 induced p53-dependent apoptosis as shown in p53 wild-type and null isogenic cancer cell lines. We thus report the identification of the first lead-like inhibitor against USP7, providing a structural basis for the development of new anticancer drugs.