A67: Olaparib toxicity observed using a new and improved p21 reporter mouse

Tanya Frangova1,Colin Henderson1,Roland Wolf1,Michael McMahon1

1University of Dundee, Dundee, UK

Presenting date: Monday 2 November
Presenting time: 12.20-13.10

Background

Genomic instability is one of the most pervasive liabilities of tumour cells. To exploit this liability in the clinic many drugs that target the DNA damage response have been developed and are in clinical trial. The first successful such drug, the PARP inhibitor olaparib, has recently been licensed for use. However, our understanding of the DNA damage response (DDR) is founded largely on in vitro studies and the phenomenon is underexplored in vivo. It is essential that we reduce this knowledge gap if we are to optimally use drugs targeting the DDR.

Method

To enable DNA damage measurement in vivo, we have created a new and improved DDR reporter mouse line based on the DDR-responsive p21 gene. Using viral 2A technology we have expressed two separate reporter molecules, luciferase and LacZ, from a single endogenous p21 locus.

Results

Both luciferase and LacZ reporters rise-and-fall concomitantly with p21 protein levels. This enabled us to not only to follow DNA damage non-invasively in live mice (luciferase) but also to map DNA damage at single-cell resolution (LacZ ). Constitutive p21 expression was observed in a number of tissues in particularly in the bronchiolar epithelium, the gastro-intestinal tract, myocardiocytes and certain subpopulations of neurons. Exposure of the mice to ionising radiation induced the p21 reporter in essentially all tissues . Moreover, olaparib pretreatment markedly increased ionising radiation (IR)-induced DNA damage signalling in the kidney and gastro-intestinal tract.

Conclusion

The combination of olaparib with IR is currently being trialled in cancer patients in the hope that the former sensitises tumours to the DNA damaging effects of the latter. Our data suggest that this ambition might not be realised in practice due to increased, dose-limiting toxicity to normal tissues.