Une nouvelle approche thérapeutique pour le Carcinome Hépatocellulaire : cibler la réponse au stress de réplication

Hepatocellular carcinoma (HCC) is a major health problem, causing over 700,000 deaths worldwide every year. To date, no effective therapy is available. It remains essential to elucidate the mechanisms leading to the progression of HCC, in order to improve diagnosis and treatment. In recent years, components of the DNA damage response have become key therapeutic targets for the treatment of various cancers. During my PhD, I sought to define whether targeting the DNA damage response, and more specifically the ATR kinase, could offer therapeutic opportunities for HCC with a high Replication Stress (RS) genomic signature. For this study, we accessed cohorts of HCC patients from the TCGA (N=307) and LICA-FR (N=222) databases. These cohorts were categorized into two groups based on genomic signatures of "Replication Stress": high RS and low RS. Preclinical mouse models of HCC (non-germline mosaic GEMMs) were also established. Specific deletion of the ATR gene in hepatocytes (ATR'hep or ROSA26'hep (control)) was performed using the AAV8-CRISPR/Cas9 method. Our results demonstrate that HCC patients with a high RS signature (High-RS HCC) had poorer overall survival and disease-specific survival than HCC patients with a low RS signature (Low-RS HCC). By subtyping HCC mutations, we demonstrate that p53-mutated HCCs had a higher RS signature than CTNNB1-mutated HCCs or HCCs with other types of mutations. To mimic human High-RS HCC, we have developed a preclinical model of murine HCC overexpressing MYC and mutated for p53. In this model, we demonstrate that reducing ATR kinase expression in hepatocytes leads to a reduction in: (1) tumor incidence; (2) tumor size and number. We also demonstrate a better median survival of mice with decreased ATR expression (55 days for ATR'hep versus 43 days for ROSA26'hep). We also showed that hepatocyte proliferation was reduced in the paraneoplastic tissues of ATR'hep livers compared with ROSA26'hep. Bulk RNA-seq analyses of ATR'hep/ROSA26'hep tumors demonstrate that ATR inhibition leads to overexpression of specific antitumor immune response pathways: "IFN-' production", "up-regulation of cell activation", "IFN-' response", "T cell activation". These data were validated by flow cytometry. ATR'hep tumors show an enrichment of CD4+ iNKT cells, IFN-'+ iNKT cells and a decrease in Treg cells compared with ROSA26'hep tumors. In conclusion, inhibition of ATR in a mouse model of high-RS HCC may delay tumor development by, among other things, modifying the antitumor immune response. Further work will determine whether targeting ATR could be a potentially effective strategy for the treatment of high-RS HCC in humans.