Genome-Wide Screening in Haploid Stem Cells Reveals Synthetic Lethality Targeting MLH1 and TP53 Deficient Tumours

Synthetic lethality is defined as a type of genetic interaction where the combination of two genetic events results in cell death, whereas each of them separately does not. Synthetic lethality can be a useful tool in personalised oncology. MLH1 is a cancer-related gene that has a central role in DNA mismatch-repair and TP53 is the most frequently mutated gene in cancer. To identify genetic events that can lead to tumour death once either MLH1 or TP53 is mutated, a genome-wide genetic screening was performed. Thus, mutations in all protein-coding genes were introduced into haploid human embryonic stem cells (hESCs) with and without loss-of-function mutations in the MLH1 or TP53 genes. These experiments uncovered a list of putative hits with EXO1, NR5A2, and PLK2 genes for MLH1, and MYH10 gene for TP53 emerging as the most promising candidates. Synthetic lethal interactions of these genes were validated genetically or chemically using small molecules that inhibit these genes. The specific effects of SR1848, which inhibits NR5A2, ON1231320 or BI2536, which inhibits PLK2, and blebbistatin, which inhibits MYH10, were further validated in cancer cell lines. Finally, animal studies with CCL xenografts showed the selective effect of the small molecule BI2536 on MLH1-null tumours and of blebbistatin on TP53-mutated tumours. Thus, demonstrating their potential for personalised medicine, and the robustness of genetic screening in haploid hESCs in the context of cancer therapeutics.