RAF1 as therapeutic target in Non-Small Cell Lung Cancer

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Bioquímica. Fecha de lectura: 10-07-2020 ; Esta tesis tiene embargado el acceso al texto completo hasta el 10-01-2022 ; In genetically engineered mouse models of KrasG12V-driven lung adenocarcinoma, genetic elimination of RAF1 has been demonstrated to prevent tumor development. However, this therapeutic benefit needed to be validated in completely formed tumors. In this thesis, we have reported that ablation of RAF1 in advanced KrasG12V/Trp53KO lung adenocarcinomas leads to significant tumor regression. In addition, protein expression levels in these tumors revealed that systemic abrogation of RAF1 expression does not inhibit canonical MAPK signaling, hence, resulting in limited toxicities. Furthermore, the therapeutic effect observed upon RAF1 elimination in those tumors that regressed seems to be associated with high levels of apoptosis and activation of the ROKα pathway. Nonetheless, few tumors still progress, though slower, upon RAF1 ablation, evidencing that combination treatments should be designed as possible future therapeutic strategies. As most of the RAF inhibitors target the kinase domain of the protein, we further interrogated whether this effect relies or not on the catalytic activity of RAF1. For that purpose, we have generated a new conditional RAF1 kinase dead mouse model (Raf1LmLK375M). Interestingly, germline expression of this mutant protein causes embryonic lethality due to fetal liver apoptosis, recapitulating the data from the Raf1 knock-out mouse model. Moreover, expression of the RAF1K375M isoform in full-blown tumors slows their growth but does not cause significant regressions. This effect was confirmed to be due to RAF1K375M protein instability, as demonstrated by the low levels of protein detected by Western Blot. These data together with previous evidences from our group, suggest that inhibition of RAF1 kinase activity is dispensable for KrasG12V-driven lung adenocarcinoma ...