Abstract B40: X-MANTM isogenic disease models: Precision tools for synthetic lethality screening
Authors: Francis Jo , Hunt Jessica , Grimshaw Kyla , Chicas Agustin , Yu Lihua , Zhu Ping , Warmuth Markus , Torrance Chris 
Published: August 2014

Cancer is a genetic disease, and as such, genetic variation is almost exclusively responsible for onset and progression, and critically is also a key component in an individual's response to therapeutics. Understanding the complex of genetics of cancer and identifying the key mutations driving phenotype requires patient-relevant disease models. Horizon Discovery's expertise in translational genomics has led to the development of GENESIS™ a proprietary genome-editing platform based on the unique ability of rAAV to stimulate homologous recombination. By exploiting a cell's natural means of repairing its own DNA in an error-free manner, rAAV GENESIS™ enables the precise insertion, deletion or substitution of a desired DNA sequence into any endogenous gene loci in mammalian cells.

Horizon has generated over 500 X-MAN™ (gene-X mutant and normal) isogenic cell lines, the world's first source of genetically-defined and patient-relevant human cellular models. We are currently using multiple panels of these disease models in combination with high-throughput RNAi screens to create a large scale synthetic lethality target identification platform. Our platform consists of lines that are identical except for the targeted modification, enabling us to identify gene target hits that have tumor selective properties. Here we have selected isogenically matched HCT116 parental, p53 null (-/-) and p53 mutant (R248W/+) lines; by use of reverse transfection methodologies we achieved &gt;80% knockdown efficiency for a library of over 2,200 druggable targets. This approach yielded targets that selectively induce lethality in the presence of a p53 mutation for both the null (-/-) and mutant lines (R248W/+), interestingly two of the top hits inducing synthetic lethality in the p53 null lines are p21 and the p21 binding partner CDKN1A.

The full power of these experiments comes from comparisons of the isogenically matched lines. Our results demonstrate that the p53 null lines (-/-) have a marked resistance to siRNA mediated synthetic lethality when compared to the mutant (R248W/+) lines, hit rates being 0.6% and 13% respectively. The number of p53 R248W/+ mutant hits are also of great interest. It is well reported that p53 transgenic mice rapidly succumb to certain types of cancers not commonly observed in p53 null mice (Song et. al. Nat Cell Biol. 2007). It is thought this mutation promotes tumorigenesis by a novel mechanism involving active disruption of critical DNA damage-response pathways. This mechanism of action clearly renders these cells more susceptible to therapeutic intervention.

Overall these results highlight the challenge of identifying therapeutics that are able to target p53 null tumors. The mutant (R248W/+) hits, however may offer a therapeutic opportunity, especially when considering that mutations at this locus are the most commonly occurring p53 mutations reported in human tumors.

Citation Format: Jo Francis, Jessica Hunt, Kyla Grimshaw, Agustin Chicas, Lihua Yu, Ping Zhu, Markus Warmuth, Chris Torrance. X-MANTM isogenic disease models: Precision tools for synthetic lethality screening. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr B40.