Targeting lung tumors expressing mutant p53 with oncolytic viruses and suicide genes

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Mutations of the p53 gene are found in the majority of lung cancers and most of these mutations are single amino acid changes instilling gain-of-function (GOF) oncogenic phenotypes, making the GOF p53 oncoprotein an excellent cancer therapeutic target. We propose a radically different approach to current GOF p53 targeting therapeutic concepts in which instead of inhibiting the protein, we weaponize GOF p53 in promoting lung cancer cell death, either by suicide, viral lysis, or both, while leaving normal cells unscathed. This innovative strategy is possible based on our discovery of a unique transactivation mechanism for GOF p53, and from that, our creation of a GOF p53 inducible promoter. Our GOF p53 inducible promoter directs expression of any gene cloned downstream only if the cell has a GOF p53 mutation, with wild-type (WT) p53 having no effect on the promoter and cells with WT p53 or p53 null mutations showing no expression. For our first major goal, we propose using an exciting new oncolytic virus that only replicates, propagates, and kills cancer cells with GOF p53 while having no effect on normal cells. We have placed two adenoviral early genes, E1A and E1B, the genes needed for adenoviral replication, under the control of the GOF p53 inducible promoter within an adenoviral vector. Initial studies show that this virus has remarkable oncolytic ability and specificity for lung cancer cells with GOF p53, with no effect or viral growth whatsoever in cells with WT p53. The killing effects in xenograft tumors with GOF p53 appear as though there is sustained accelerated tumor killing after a short delay of when the virus is injected. We propose to enhance the oncolytic virus by adding additional lysis abilities and by combining the suicide strategy with the oncolytic strategy. Preliminary results look very promising for this combination. For our second goal, we propose devising a means of specifically killing lung cancer cells with GOF p53 mutations by cloning a suicide gene downstream of our GOF p53 inducible promoter. This construct will be introduced into an adenoviral vector so that when the virus infects cells, only cells with a GOF p53 mutation (cancer cells) will die from prodrug treatment. We have created such a virus using the Herpes Thymidine Kinase suicide gene and show striking killing effects and specificity for lung cancer cells with GOF p53 both in culture and in xenograft tumors. We aim to further discover how this strategy works and ways to improve it. We propose the use of the bacterial Cytosine Deaminase suicide gene (bCD) to enhance the bystander effect of our GOF p53 specific suicide virus. In addition, we propose to improve the inducibility of our GOF p53 inducible promoter to further enhance the suicide and oncolytic viruses. The potential impact of this work is far-reaching since these strategies should be applicable for any cancer with GOF p53 mutations, which constitutes over half of all cancers.