PROJECT SUMMARY
Pancreatic ductal adenocarcinoma (PDAC) is characterized by resistance to current therapies, a high degree of
desmoplasia, and an immunosuppressive tumor microenvironment (TME). This scientific proposal focuses on
cyclic AMP Response Element Binding protein 1 (CREB) as a transcriptional factor downstream of KRAS that
promotes disease aggressiveness and poor survival. Genetic loss or pharmacological inhibition of CREB leads
to significant attenuation of PDAC tumor burden and improved survival in multiple murine PDAC models. Utilizing
high throughput sequencing approaches, we have identified tumor cell-derived leukemia inhibitory factor (LIF)
as a key CREB-regulated immunomodulatory cytokine, serving as a possible paracrine mediator of tumor-
macrophage crosstalk in the TME. We hypothesize that targeting the CREB-LIF signaling axis can remodel the
immunosuppressive TME by significantly impacting tumor-associated macrophages (TAM)s and reinvigorating
the T cell-based adaptive anti-tumor immune response to improve the efficacy of checkpoint immunotherapy.
Based on our preliminary data, the critical role of the CREB regulated LIF signaling will be investigated through
three specific aims. 1) Elucidate the molecular mechanism and impact of CREB regulated LIF in PDAC
oncogenesis. Here, we will assess the CREB-mediated regulation and functional roles of tumor cell-derived LIF
by exploring the nucleo-cytoplasmic localization, interaction with transcriptional complexes, and gene regulatory
networks. We identify the CREB-LIF axis requirement in the tumor cell growth using CRISPR/Cas9 genome
editing with CREB on or off in vivo pancreas tissues and evaluate the expression of LIF relative to CREB in
patient PDAC tissues, patient-derived xenografts, and primary tumor derivative organoids. 2) Determine how
CREB-dependent LIFR signaling in macrophages impacts the tumor immune landscape. We hypothesize that
the CREB modulates LIF release and promotes TAM infiltration/polarization towards a tumor-promoting M2-like
phenotype via activating STAT3 in macrophages. We will determine the effect of CREB-regulated LIF release
on TAM activity using CREB on or off with LIF knockout tumor cells and assess the impact of CREB-regulated
LIF signaling on the adaptive immune response and TME during PDAC progression in myeloid-specific knockout
models of Lifr and Stat3, and 3) Determine if CREB inhibition and conventional immunotherapeutic approaches
reduce tumor growth and improve overall survival. We hypothesize that the tumor cell-intrinsic CREB-LIF
activation is a pivotal switch that drives immune suppression in the pancreatic TME, which can synergize with
immune checkpoint inhibition. We will use CREB inhibitor with checkpoint inhibitor to establish the safety of the
therapies and study tumor growth and overall survival in genetic mouse models, patient-derived xenografts, and
organoids to further complement these preclinical studies. Together, these results will provide new therapeutic
strategies to reduce mortality from this disease. Furthermore, these studies can be broadly applicable to the
myriad of other malignancies where CREB-LIF signaling is altered.