Dissecting and Targeting MAPK - PPARG Crosstalk in Bladder Cancer - Bladder cancer (BC) accounts for 80,000 new cancer diagnoses and 20,000 deaths annually in the US. Recent large-scale studies have comprehensively mapped the genetic landscape of BC, yet the median survival for patients with metastatic BC is only 14 months. Therefore, there is an urgent need for mechanistic studies informed by new genomic data to define the role of specific alterations in BC biology and guide novel therapeutic strategies. Aberrant activation of the mitogen-activated protein kinase (MAPK) pathway is a common feature of cancer, and ~20% of bladder tumors harbor MAPK activation driven by RAF1 (CRAF) amplification or an activating HRAS mutation. Peroxisome proliferator activating receptor gamma (PPARG) is a nuclear receptor and transcription factor that regulates lipid and glucose homeostasis. PPARG also has an important role in urothelial cell differentiation and a subset of BCs have genomic PPARG alterations leading to increased PPARG signaling and an immune-excluded, luminal-like phenotype driven at least in part by changes in NFkB-mediated gene expression. We recently found that MAPK and PPARG pathway alterations co-occur in a subset of BCs and the central hypothesis of this proposal is that aberrant MAPK and PPARG signaling cooperate to drive the unique phenotype of these MAPK/PPARG-altered tumors. Furthermore, we hypothesize that targeting MAPK signaling with novel MAPK-directed agents such as RAF dimerization inhibitors will provide dual therapeutic benefit by directly inhibiting oncogenic MAPK signaling as well as by restraining PPARG signaling, thereby promoting immune infiltration and increased sensitivity to immune checkpoint inhibition. In Aim 1, we will dissect the signaling interplay between MAPK and PPARG by measuring the effects of MAPK pathway modulation on PPARG phosphorylation and activation state as well as on PPARG and luminal gene expression programs in MAPK/PPARG altered and non-altered BC cell line and patient-derived models. We will also define the transcriptional networks that orchestrate MAPK-PPARG signaling in BC cells. In Aim 2, we will investigate the impact of MAPK pathway activity on NFkB-mediated cytokine signaling and macrophage properties in BC models. We will test whether MAPK signaling in BC cells drives macrophage polarization via direct or paracrine mechanisms and we will define the impact of MAPK pathway perturbations on BC cytokine gene transcription. In Aim 3, we will investigate the combined activity of MAPK inhibition and immune checkpoint inhibition (ICI) in multiple MAPK/PPARG-altered immunocompetent BC models. We will measure treatment effect on tumor growth and survival and will define the impact of MAPK pathway inhibition on immune contexture. Finally, we will investigate the association among PPARG signaling, MAPK signaling, and treatment outcomes in ICI-treated and untreated clinical BC cohorts. Together, these integrated studies will define the mechanism(s) through which MAPK pathway activity regulates the unique tumor cell intrinsic and immune microenvironmental features of MAPK/PPARG-altered BC, potentially informing novel therapeutic approaches for this subset of BCs.
