Analysis of KRAS phosphorylation and KRAS effector domain as targets for cancer therapy

Abstract

[eng] Analysis of KRAS phosphorylation and KRAS effector domain as targets for cancer therapy Oncogenic mutations of KRAS are found in the most aggressive human tumors, including colorectal cancer (CRC). It has been suggested that oncogenic KRAS phosphorylation at Ser181 modulates its activity and favors cell transformation. Using non-phosphorylatable (S181A), phosphomimetic (S181D) and phospho/dephosphorylatable (S181) oncogenic KRAS mutants, we analyzed the role of this phosphorylation to the maintenance of tumorigenic properties of CRC cells. Surprisingly, oncogenic KRAS phosphomutants did not show great differences in cell growth and signaling activation between them in 2D cell cultures. However, the presence of phospho/dephosphorylatable oncogenic KRAS is required for α-E-catenin expression and for preserving the epithelial organization of CRC cells, and for supporting subcutaneous tumor growth in mice. Interestingly, the expression of other genes differed according to the phosphorylation status of KRAS. Lack of oncogenic KRAS phosphorylation leaded to changes in expression of SERPINE1, PRSS1,2,3 and NEO1 and to a decreased cell invasion capacity, while expression of phosphomimetic oncogenic KRAS resulted in a diminished expression of genes involved in enterocyte differentiation, such as HNF4G. Interestingly, activating or inhibiting PKC in cells expressing the phosphorylatable mutant reproduced the expression of SERPINE1, PRSS1,2,3 and HNF4G observed in the phosphomutant expressing cells. Finally, the analysis, in a public data set of human CRCs, of the gene expression signatures associated with phosphomimetic and non-phosphorylatable oncogenic KRAS suggests that this post-translational modification regulates tumor progression in patients. In conclusion, CRC cells depend on KRAS phosphorylation at Ser181 to maintain their tumorigenic properties. Therefore, specific interference with this modification may have therapeutic benefits. On the other hand, one of the strategies that is widely being followed to inhibit RAS is to search for drugs able to disrupt RAS interactions with other proteins, among them its effectors. For that reason, peptidomimetics have emerged as a promising tool to modulate the biological activity of protein-protein interactions. Accordingly, we studied whether different peptidomimetics against the effector domain of RAS, designed by the Iproteos technology to inhibit RAS, were able to interfere with oncogenic KRAS activity. The cancer model selected for this research was the pancreatic ductal adenocarcinoma, which is a highly metastatic disease with a high mortality rate. Our data have demonstrated that the compound P1.3 negatively affected downstream KRAS signaling in non-transformed cells. Moreover, it efficiently inhibited the interaction of oncogenic KRAS with its effectors. Finally, the compound P1.3 showed high selectivity killing pancreatic cancer cells expressing oncogenic KRAS versus normal cells. Therefore, from the therapeutic point of view, the compound P1.3 has been a promising lead compound. Nevertheless, the impact of this project will be determined once the bioavailability of P1.3 has been assessed along with its pharmacokinetic properties. Consequently, more experiments will be conducted in the near future in order to reach the preclinical phase.