Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - TRANSREAD (Restoration of tumor suppressor function by induction of translational read-through of premature termination codons - a strategy for improved cancer therapy)

Teaser

Cancer is a major public health problem around the world. According to statistics from the World Health Organization (WHO), there were 18.1 million new cases of cancer and 9.6 million cancer deaths in 2018. Thus, improved cancer therapy is urgently needed. Novel anti-cancer...

Summary

Cancer is a major public health problem around the world. According to statistics from the World Health Organization (WHO), there were 18.1 million new cases of cancer and 9.6 million cancer deaths in 2018. Thus, improved cancer therapy is urgently needed. Novel anti-cancer drugs have been developed that can inhibit certain activated kinases in tumor cells, and so called immunocheckpoint inhibitors can unleash the immune response against tumors. Yet despite significant progress in diagnosis and therapy, efficient treatment is still lacking for many cancer patients. The TP53 tumor suppressor gene is inactivated by mutation in around 50% of all tumors. We and others have explored the possibility of restoring normal function to mutant p53 protein and thereby trigger tumor cell death and eliminate the tumor. This type of strategy could potentially be applied to a large number of cancer patients worldwide. We have identified the small molecules APR-246 that can reactivate missense mutant p53 and trigger tumor cell death by apoptosis. APR-246 is now being tested in several clinical trials. However, around 10% of TP53 mutations are nonsense mutations in which a premature stop codon in inserted in the coding sequence, leading to expression of a trucnated inactive p53 protein. Can expression of full length p53 be restored by pharmacological induction of translational readthrough across a premature termination codon? Can this strategy also be applied to nonsense mutations in other tumor suppressor genes, e.g. RB1, PTEN and APC?

Our overall objective with this project is to develop novel cancer therapy by pharmacological induction of readthrough of nonsense mutant TP53, RB1, PTEN and APC. We have screened chemical libraries to identify novel non-toxic molecules that induce efficient translational readthrough of R213X nonsense mutant TP53. We have identified several promising molecules and shall characterize these further with the aim of identifying one or several compounds for studies in mice to demonstrate anti-tumor effect in vivo. Compounds will also be tested for effect on nonsense mutant RB1, PTEN and APC. Our ultimate aim is to take promising hit molecules through preclinical development to clinical trials in cancer patients.

Work performed

We have first studied aminoglycosides antibiotics (G418, Gentamicin) that are known to induce readthrough of some nonsense mutant genes, including TP53. We have confirmed results from others showing that they can induce full length active p53 protein, leading to upregulation of p53 target genes and induction of tumor cell death. Moreoever, we have demonstrated that the Mdm2 inhibitor Nutlin3a synergizes with G418 in inducing tumor cell death. However, aminoglycosides have severe side effects that make them less suitable for clinical use as anti-cancer agents. Our focus is therefore the identification and characterization of novel molecules with higher potency and lower toxicity.

We have screened chemical libraries and analyzed available database information for compounds with potential readthrough activity. This has allowed us to identify a small set of promising compounds. These compounds are currently being examined in detail using various assays for p53 activity and tumor cell death. We will also try to clarify the molecular mechanism by which the identified compounds induce readthrough, and test the compounds for their ability to induce readthrough of nonsense mutant RB1, PTEN and APC and other tumor suppressor genes carrying nonsense mutations.

Final results

We already have several promising compounds with readthrough activity according to our preliminary data. This is new knowledge with potential significance for cancer therapy. We expect to have a more complete characterization of these compounds in terms of translational readthrough of nonsense mutant TP53, RB1, PTEN and APC, induction of tumor cell death, and anti-tumor efficacy in vivo during the continuation of the project. We also expect to achieve an understanding of their molecular mechanism of action, which may facilitate the design of compounds with even higher readthrough activity. We also hope to be able to initiate preclinical development later during the project, with the long-term aim of clinical trials in relevant tumor indications.