Abstract SY23-03: Exploiting oncogene-induced replicative stress for the targeting of cancer cells

Abstract

Abstract One of the most discussed recent models for cancer development is based on the finding of an activated DNA damage response in early stages of cancer development. We now know that this DNA damage occurs due to replication stress (RS) induced by oncogenes. In mammalian cells, RS is chiefly limited by the action of ATR and Chk1 kinases. In what regards to cancer, several Chk1 inhibitors have been (and are being) tested in clinical trials, so far with modest results. However, we believe that whereas Chk1 (or ATR) inhibitors might fail as generic anti-cancer therapies, they might be much more efficient for the treatment of tumours with high levels of oncogene-induced RS. To address this hypothesis, we have (1) provided genetic proof-of-principle to show that limited ATR levels are indeed particularly toxic for tumours with high levels of RS (Murga et al Nat Struct Mol Biol, 2011), and (2) generated ATR inhibitors which show synthetic lethal interactions with cancer-associated mutations (Toledo et al Nat Struct Mol Biol, 2011). In what regards to the genetics, and with the use of an ATR hypomorphic mouse strain previously developed in our lab (Murga et al Nat Genet, 2009), we now know that limited ATR levels fully prevent the development of Myc-induced lymphomas or pancreatic tumours. Moreover, we also showed that Chk1 inhibitors are very effective for the treatment of Myc-induced lymphomas. In contrast, these inhibitors were largely ineffective in the treatment of Ras-induced pancreatic tumours, which had no detectable evidences of RS. Hence, these data strongly suggest that the use of Chk1 (or ATR) inhibitors would be particularly beneficial for the treatment of tumours harbouring high levels of RS. Importantly, the levels of RS in tumours can be analyzed in tumour biopsies. Hence, we have provided a rationale that could be readily used in the clinic for a more efficient use of ATR and Chk1 inhibitors in cancer chemotherapy. Until recently, no potent inhibitors of ATR existed. One of the limitations for the discovery of ATR inhibitors is that the activity of the kinase is restricted to replicating cells. This hindered cell-based screenings due to the large number of false positives that would derive from an indirect effect of the tested compound on the cell cycle. Overcoming this limitation, we previously developed a cellular system in which ATR activity can be unleashed at will, throughout the cell cycle and in the absence of any actual DNA damage (Toledo et al Genes & Dev 2008). After adapting this system for a High-Throughput Imaging pipeline, and with the help of the Experimental Therapeutics Programme of the CNIO, we have now identified several compounds that can inhibit ATR in the nanomolar range (Toledo et al Nat Struct Mol Biol, 2011). We are now at the early stages of characterizing these inhibitors and their potential uses, and have shared these reagents with many investigators around the world. Besides the published ones, we have now also identified some compounds with good pharmacological properties in vivo, so that we are now ready to test the effect of ATR inhibitors in mouse preclinical models of cancer.