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.