It is well established that PTEN, a phosphatidylinositol (PtdIns) phosphatase, is a tumor suppressor while PIK3CA, a PtdIns kinase, is an oncogene. However, there are many more enzymes in PtdIns metabolism, opening up the possibility for a broader role of PtdIns metabolism in cancer. This is especially significant as the pathway is comprised of druggable enzymes, thus a comprehensive understanding of how PtdIns metabolism modulates cancer pathways could lead to new therapeutic agents to treat cancer. We recently discovered that the PtdIns kinase PIP5K1A binds to the oncoprotein KRAS, one of the most commonly mutated genes in human cancers, to drive transformation. Admittedly this is but a single example of targeting PtdIns metabolism to block oncogenic KRAS signaling, and the analysis was performed with cultured cells. Thus, to identify the role of PtdIns metabolism in KRAS-driven tumorigenesis, I created and validated a loss-of-function sgRNA library to knock out each component of PtdIns metabolism by CRISPR/Cas9 technology. With this library now in hand, I propose in AIM 1 to introduce this library into a panel of KRAS-mutant pancreatic ductal adenocarcinoma cancer (PDAC) cell lines, which are uniformly KRAS mutant, to screen for components of PtdIns metabolism that promote the orthotopic growth of these cell lines. Completion of this aim will therefore identify PtdIns metabolism components that drive KRAS-mediated tumorigenesis in PDAC, laying the groundwork for future mechanistic studies and informing therapeutic development. As noted above, PIP5K1A bound to and promoted oncogenic KRAS function. However, we also discovered that PIP5K1A did not bind to and promote transformation of other highly related RAS oncoproteins, suggesting that PtdIns metabolism modulates different oncogenic signaling in an individualized fashion. As such, it is unlikely that any one component will have a uniform effect on cancer, and instead are more likely to affect specific pathways. Given this, I propose in AIM 2 to comprehensively interrogate PtdIns metabolism in the major cancer pathways. To this end, I propose to introduce the PtdIns metabolism sgRNA library in a panel of 84 cell lines each engineered to express a specific mutant protein representing all the major cancer pathways, and screen for sgRNAs enriched in each. Completion of this aim will provide a comprehensive understanding of which PtdIns metabolism components are required for or synergize with which major cancer pathways. In turn, this will provide the basis for identifying how mechanistically these vulnerabilities affect oncogenesis, ultimately leading to the goal of new therapeutics. In sum, completion of this proposal will identify how PtdIns metabolism modulates RAS and other cancer pathways, laying the foundation to develop new therapeutic strategies that have the potential to treat many different cancers.
The project is relevant to the NCI?s mission to improve the health of cancer patients because there is a critical need to identify and target addressable nodes of cancer pathways. Phosphatidylinositol metabolism stands out as a possible target as many of the genes involved encode druggable enzymes and have been shown to play a major role in oncogenesis. I propose a systematic approach to screen for oncogenic vulnerabilities in phosphatidylinositol metabolism to identify new therapeutic targets.
