David Lane - Overview

The elucidation of the p53 and Rb pathways, which are aberrant in most cancers, has provided many new targets for drug development. In many tumours the wild type p53 gene remains intact but its function is compromised by loss of upstream signalling pathways or downstream effectors. Studying how the p53 response is activated in normal cells has suggested numerous routes to overcoming the loss of upstream signalling. The key regulator is Mdm2, an E3 ubiquitin ligase, that binds and ubiquitinates p53 and directs its degradation via the proteosome.We have established in vitro and in vivo assays for the ubiquitination of p53 and Mdm2. We have recently discovered that both proteins are also modified by the ubiquitin like protein SUMO.

Drugs that can block the p53 Mdm2 interaction are the subjects of intense effort and small potent peptides that can activate the p53 response have been described by our team. Recently the p14 ARF tumour suppressor protein has been shown to act as an inhibitor of Mdm2 and we have localised this activity to the N terminus of the molecule. Growing selections of lead small molecules that mimic the action of these peptides have also been recently discovered using cell based screens. In the case of HPV16/18 transformed cells, p53 is inactivated by the HPV16/18 E6 protein directing the E3 ubiquitin ligase activity of the E6AP protein to p53. We have overcome this response by selective inhibition of E6 mRNA levels using a combination of Actinomycin D and Leptomycin B. In combination these two drugs can reactivate the p53 response in HPV 16/18 expressing tumour cells.

In tumours that lack p53 and Rb the E2F1 pathway can induce apoptosis. Blocking cyclin A/cdk2 function can activate this. We have discovered promising lead small molecule inhibitors of both CDK catalytic activity and Cyclin docking activity. The compounds selectively induce apoptosis in tumour cells and temporary stasis in normal cells. They show clear anti-tumour activity in pre-clinical models and the first Cdk inhibitors are now in clinical trial with Cyclacel Ltd and the CRC Drug development team.