PROJECT SUMMARY
The treatment of pancreatic ductal adenocarcinoma (PDAC) remains a major hurdle with 5-year survival of
12%. PDAC resistance to chemotherapy and immunotherapy is thought to arise from the immunosuppressive
tumor microenvironment (TME), characterized by a fibrotic stroma and high infiltrates of immunosuppressive
cells, including tumor associated macrophages (TAMs). TAMs block anti-tumor effector T cell function and
trigger exhaustion. It has been postulated that reprogramming TAMs to an immunostimulatory phenotype
could improve therapy response. Recent studies suggest that metabolites originating from the gut microbiome
influence phenotype of immune cells, including TAMs. However, little is understood about such metabolites,
including their identity, the signaling pathways by which they alter TAM phenotype, and whether these
metabolites influence cancer development. We are identifying microbial metabolites that modulate TAMs in
the PDAC TME. Using unbiased, global, LC-MS/MS metabolomic screens, we found a gut microbe-derived
metabolite, trimethylamine N-oxide (TMAO) that induced significant anti-tumor effects in the PDAC TME.
Specifically, delivery of TMAO intraperitoneally, or by supplementing diet with the TMAO precursor choline,
to PDAC-bearing mice reduced tumor growth and was associated with an immunostimulatory TAM phenotype
and activated effector T cell response in the TME. The immunostimulatory macrophage phenotype was due
to a direct effect of TMAO and the TMAO-conditioned macrophages could activate CD8+ T cells. Combining
TMAO with immune checkpoint blockade reduced tumor burden and improved anti-tumor immune responses.
These data support our hypothesis that the diet and microbiome-derived metabolites shape anti-tumor
immunity and treatment response in PDAC. Aim 1 will characterize dietary and microbial sources of TMAO
for anti-tumor responses in PDAC. We will characterize the (i) dietary (l-carnitine or betaine), and (ii) the
microbiome (e.g., Enterococcus asini, engineered E. coliCutC/D) sources of TMAO for their anti-tumor effects.
Aim 2 will test the hypothesis that TMAO induces its anti-tumor effects by potentiating the type I IFN and/or
STING signaling in TAMs. We will determine (i) the requirement of type-I IFN and/or STING specifically in
macrophages for the anti-tumor effects, and (ii) the impact of TMAO on the transcriptional activity of type-I
IFN responsive STAT1 and/or STAT3. Aim 3 will test the efficacy of TMAO to improve treatment response in
pre-clinical models of PDAC. We will evaluate the translational relevance of TMAO using (i) a genetically
engineered mouse model of PDAC and patient derived PDAC organoid cultures, and (ii) a treatment strategy
combining TMAO with STING agonists. Our studies will characterize the sources, mechanism of action, and
translational relevance of a novel, minimally understood, high impact microbial metabolite, TMAO, in boosting
anti-tumor immune responses in the PDAC TME and rendering PDAC responsive to chemo-immunotherapy.
In the longer term, this work may lay the groundwork for new diet/microbiome-based treatments for PDAC.
