Project 1 - Targeting PIKfyve-driven lipid homeostasis as a metabolic vulnerability in neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is an aggressive form of advanced prostate cancer (PCa) with few treatment options other than systemic chemotherapies, for which patients invariably develop resistance. Targeted therapies are, thus, urgently needed for this lethal disease. Although NEPC can arise de novo, most cases result from an adenocarcinoma to neuroendocrine transdifferentiation process that occurs in tumors of castration-resistant PCa (CRPC) patients receiving standard of care therapies targeting the androgen receptor (AR). The tumor microenvironment of NEPC is often hypoxic and nutrient-depleted, leading to enhanced dependence on autophagy and lysosome-dependent nutrient survival pathways within cancer cells. Blocking autophagy with genetic methods suppresses tumor growth and increases survival in preclinical models. Here, we have identified the lipid kinase PIKfyve as a key player mediating autophagy and lysosomal adaptation processes in NEPC. Interestingly, although AR-positive CRPC is sensitive to PIKfyve inhibitors in vitro, PIKfyve inhibitor treatment results in cytotoxicity in NEPC cells and enhanced tumor growth inhibition and regression. Our preliminary data also suggest that PIKfyve inhibition results in increased de novo lipid synthesis and that combined targeting of the MAPK pathway and PIKfyve may be a synthetic lethal strategy for NEPC. Here, we will develop potent, selective PIKfyve degraders and employ them to validate PIKfyve as a viable therapeutic target for NEPC. Pathways leading to enhanced activity of PIKfyve inhibition (e.g., MEK inhibition) in NEPC will also be delineated. The following Specific Aims are proposed: Aim 1: Employ novel proteolysis-targeting chimera (PROTAC) degraders to define the mechanism by which PIKfyve loss preferentially impacts NEPC. PIKfyve inhibitors (apilimod, ESK981) and PROTAC degraders will be used in this aim to confirm the molecular mechanisms through which PIKfyve mediates preferential effects in NEPC, focusing on key nutrient survival pathways, endoplasmic reticulum stress/unfolded protein response, and lipid homeostasis. Aim 2: Define synthetic lethality relationships with PIKfyve antagonism in NEPC. Our preliminary data suggests that MAPK pathway inhibition antagonizes de novo lipid synthesis. Here, we will determine whether MEK inhibitors sensitize NEPC cells to PIKfyve degraders in vitro and in vivo. Aim 3: Determine whether PIKfyve degradation combined with standard of care therapies for NEPC enhances outcomes in preclinical models. Cell line and patient-derived organoid and xenograft models will be used to test the efficacy and safety of PIKfyve degraders alone and in combination with cisplatin for NEPC. Aim 4: Establish an investigator- initiated phase II trial evaluating a clinical PIKfyve inhibitor (ESK981) in NEPC. Biomarkers of response will be identified through correlative studies. This project will define PIKfyve as a new therapeutic target for NEPC, thereby adding to the limited treatment options for these patients. As an alternate strategy, orally bioavailable PIKfyve degraders will be transitioned into the clinic.