Abstract A169: The role of the RAS-PI3K interaction in tumor maintenance and metastasis.
Authors: Murillo Miguel M. , Tilley Frances , Lassailly Francois , Downward Julian 
Published: June 2012

RAS is the most frequently activated dominant oncogene in human cancer. The importance of the RAS-PI3K connection in physiological and pathological situations has been demonstrated by different findings: RAS directly binds to and modulates PI3K activity through a RAS Binding Domain (RBD) in the p110-α subunit of PI3K; mice harbouring a mutation in the RBD of p110-α are resistant to RAS-induced lung-tumor formation; MEFs derived from these mice show defective signaling from some Receptor Tyrosine Kinases, like the EGFR, to PI3K. However, little is known about its role in host-tumor relationship, tumor maintenance and metastasis processes. We have created a conditional mouse model where one wild type, floxed allele of the p110-α gene can be conditionally knocked out upon tamoxifen activation of a CRE-ER recombinase. These mice have been crossed with mice harbouring a RBD-WT or RBD-Mutant p110-α allele, obtaining a mouse model with either a wild type or a mutant p110-α allele and one floxed allele. The ubiquitously expressed CRE-ER allows us to tightly manipulate the timing of p110-α knocking out.

Here we provide evidence that disruption of the RAS-PI3K interaction is important for tumor maintenance. B16F10 (B-RAF mutant) and LLC1 (N-RAS mutant) tumor cells were injected subcutaneously in RBD-WT and RBD-Mutant mice and tumor growth was monitored by caliper measurement. Tumors in the RBD-Mutant group showed a reduced tumor growth compared to RBD-WT mice, and overall survival was increased in the RBD-Mutant group. Further analysis of the tumors suggested that neoangiogenesis was somehow affected in tumors growing in RBD-Mutant mice. We then analyzed the capability of these mice to produce new blood vessels upon stimulation with different cytokines. We performed a matrigel plug assay where matrigel-diluted cytokines where injected subcutaneously in both RBD-WT and RBD-Mutant mice to promote an angiogenic response. Vessel growth inside the matrigel plugs was analyzed, showing that RBD-Mutant mice were not able to induce neoangiogenesis to the same extent as the RBD-WT mice. These results suggest that the RAS-PI3K interaction in the host tissue plays an important role in neoangiogenesis induced by tumoral cells.

In order to analyze the importance of the RAS-PI3K interaction in metastasis processes, experimental metastasis experiments were performed. B16F10 cells expressing a luciferase gene were injected intravenously through the tail vein. Cell growth in the lungs was monitored by bioluminescence. Results show that cells injected in RBD-WT mice are capable to engraft and grow in the lungs while cells injected in the RBD-Mutant mice show a lower degree of both engraftment and growth.

Altogether, these results show that the RAS-PI3K interaction is important for tumor maintenance and metastasis, providing an interesting molecular target for future pharmacological and clinical research. Further work is needed to fully unveil the molecular mechanisms specifically modulated by the RAS-PI3K interaction and its importance within the host tissue-tumor molecular relationship.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A169.