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Towards understanding non-canonical phosphatidylinositol kinases in the maintenance of prostate metabolism.

Periodic Reporting for period 1 - PCAPIP (Towards understanding non-canonical phosphatidylinositol kinases in the maintenance of prostate metabolism.)

Reporting period: 2018-06-01 to 2020-05-31

A strong body of evidence suggests that a large network of signaling enzymes, called lipid kinases, can add phosphate tags onto components of cellular membranes and are essential hubs for regulating cell metabolism. The most established is PI3K that can be specifically inhibited with drugs that are being tested in combination with AR treatments for PCa. Preclinical studies have revealed a direct connection between AR and PI3K signaling; however, clinical trials targeting both pathways have lacked efficacy, leading scientists to predict there are other related enzymes functioning to influence critical tumor survival programs. Herein, I propose exploring PI5P4K lipid kinases in PCa. This family of enzymes is closely related to PI3K and early work has implicated them as druggable cornerstones of tumorigenesis in other cancer types. This is the first project to examine PI5P4K function in the biology of the prostate. Preliminary data shows that PI5P4K protein is present in PCa tissue and cell models generated from patient tumors. Digging deeper, I have found a potentially important inverse relationship between PI5P4K expression and levels of AR pathway activity using genetic manipulation of PI5P4K levels in prostate cells. Perhaps most promising, I discovered that inhibiting PI5P4K in AR dependent PCa results in the exit of cell replication programs that tumors use to grow in size. I believe PI5P4K lipid kinases are unexplored cornerstones of cell metabolism and aim to be the first to establish their role in prostate biology.

My hypothesis is that PI5P4K is a critical regulator of AR signaling that supports PCa cell survival by influencing metabolic stress cooping mechanisms. To test this I have the following objectives: (1) Establish the biological phenotype associated with PI5P4K expression in prostate cells, (2) Examine how targeting PI5P4K influences the molecular and tumorigenic characteristics of PCa, and (3) Uncover how PI5P4K supports changes to androgen dependence through control of prostate cell metabolism. In attempt to answer these questions I generated the first prostate-specific knock-out mouse model PI5P4K in both normal prostate and in combination with an established model of aggressive cancer. As well, advanced metabolomics technology was used to measure how PI5P4K influences metabolic networks that drive the survival of cancer cells. This first-in-class study aims to establish the role of a novel pathway that could be a key control in the progression to untreatable PCa.
The work performed involved model development, metabolic assessment, and in vitro validation of observations of PI5P4K in prostate tissue and cancer models. I was successful in generating and characterizing multiple new mouse models during PCAPIP. Specifically, the first prostate-specific knock out of Pip4k2a in prostate luminal cells. Based on the novel observation that PI5P4K was highly expressed in the basal cell layer of the prostate, I also generated the first basal cell-specific knock out mouse for inducibility targeting Pip4k2a. I also generated mice with gene combinations that will lead to prostate tumor development, specifically through deletions of the cancer gene Pten.
A major objective of PCAPIP was to uncover what metabolism processes are influenced by PI5P4K in normal cells and prostate cancer. I used experimental approaches to characterize multiple metabolic pathways when PI5P4K is depleted in PCa cell models. I used a large-scale metabolomics approach that detected relative levels of 153 metabolites from 37 pathways. I also ran a state-of-the-art lipidomic analysis that characterized 282 lipid species in samples with and without PI5P4K depletion. These experiments were paired with RNA sequencing analysis, which enabled the identification of changes to metabolic signaling pathways.
Finally, I performed validation experiments using in vitro models to confirm metabolic phenotypes from PI5P4K depletion. This involved previously characterized human prostate cancer cell lines and newly generated mouse organoid cells. I verified that the mouse models were effective at genetically eliminating Pip4k2a expression in animals in the cells of interest (luminal and basal). This confirms the molecular changes are indeed being activated in the in vivo setting. I also found that normal mouse luminal prostate cells have much lower relative expression of PI5P4K compared to tissue from Pten mutant tumors. Using human prostate cancer cells, I validated the inverse expression changes of AR transcript signature genes with depletion of PI5P4K. As well, I found that depletion of PI5P4K in various stress conditions could induce lipid droplet accumulation and increases in the level of reactive oxygen species. I discovered that genetically altered LNCaP cells that lack PI5P4K are significantly more vulnerable to stress conditions such as drug treatments (enzalutamide) and lipid overdose compared to controls.
These results are being composed into a high-impact publication from our group at the University of Bern. As well, were incorporated into a co-authored article submitted to the journal Cell Metabolism with collaborators. PCAPIP results were additionally disseminated in local seminars across Switzerland and at international conferences in France, USA, and Canada in the format of talks and posters.
This study advances the basic understanding of how the prostate functions and what unique characteristics promote the high frequency of PCa incidence. Canonical type I signaling of the PI3K pathway has highlighted the biological importance of phosphoinositide (PI) regulation. Here, I have added knowledge beyond the current state of the art to expand the plausibility of targeting the getter network of PI kinases. PCAPIP is the first project to characterize the PI5P4K in the prostate and generate tissue-specific tools to launch further studies.
I expect to find that depletion of PI5P4K impacts the ability of PCa to coup with metabolic stress. This will be apparent in changes to cellular metabolite abundance, cell cycle, cancer survival, and reactive oxygen species. By developing novel mouse models, I will characterize PI5P4K expression patterns in normal and cancer tissue to provide insights into tissue-specific phenotypes of type II PI kinases. Most importantly, I aim to characterize an inverse relationship of PI5P4K and the AR pathway. I expect to find that PI5P4K is upregulated in AR-indifferent cancer models that require additional metabolic stress pathways to survive the stress of cancer progression.
The results of PCAPIP have potential impacts on the field of medical biology and pharmaceutical development. By uncovering non-canonical pathways that may have interplay with AR and PI3K signaling, drug development for PI5P4K may prove to be attractive in a clinical setting. This extends beyond cancer biology, but also to other diseases such as diabetes or rare metabolic disorders. Through this understanding, we hope to determine better how to improve the efficacy of AR targeted drugs and establish a new treatment option that has previously been unexplored.
Schematic of phosphatidylinositol-5-phosphate 4-kinases (PI5P4Ks) localization.