Project Abstract
The main objectives of this proposal are to elucidate the mechanisms of YAP1-mediated metastatic niche and
immunosuppression in gastric adenocarcinoma (GAC) with peritoneal carcinomatosis (PC) for novel therapeutic
discoveries. GAC is a major health burden in the US and worldwide. PC is common affecting ~45% of GAC
patients. GAC patients with PC have short survival and treatments are ineffective. Molecular understanding for
PC is limited. To address this unmet clinical challenge, we have established PC banking infrastructure aiming to
utilize these patient-derived specimens to discover and validate our novel targets. Our preliminary RNAseq
profiling of PC specimens revealed an enrichment of unique immune suppressive molecules, including TIM3 and
it’s ligand Galectin-9 (Gal-9), TGF-ß and VISTA, but less expression of PD-1/PDL-1 and CTLA-4. YAP1 has
been implicated in human development, lineage plasticity, and upregulated in many tumor types. However, its
role in mediating PC metastases and immune suppression in tumor microenvironment (TME) remain unclear.
Our preliminary data suggest that YAP1 is highly expressed in primary and metastatic tumor cells of GAC
patients and is significantly associated with poor survival. Genetic knockout (KO) YAP1 significantly decreased
cancer stemness traits, tumor formation and PC in mice. Further, depletion of YAP1 in tumor cells consistently
increased CD3 and CD8 T cell responses from GAC. Through a single cell RNAseq (scRNAseq) of PC samples
and validation using immunofluorescent staining, we noticed that YAP1, TIM3 ligand Gal-9 and DKK1 are highly
expressed in tumor cells of PC; while TIM3 is enriched in immune cells. RNAseq from YAP1high and YAP1 KO
patient-derived tumor cells revealed that Gal-9 and DKK1 were significantly decreased upon depletion of YAP1
and these factors are associated with poor survival of patients. We hypothesize that YAP1high PC cells are
metastasis-initiating cells that orchestrate a niche by conferring cancer stemness attributes to the tumor cells
and promote tumor immunosuppression through activating TIM3/Gal-9 axis and increasing paracrine of DKK1
in PC TME. Therefore, simultaneously targeting Hippo/YAP1 and immune checkpoint (TIM3/Gal-9) could be an
enhanced strategy. To test our hypothesis, we propose three Specific Aims: Aim 1. Determine the functional
relevance of YAP1 in PC stemness and metastases in tumor cells using novel stem cell cloning technology and
PDX/PDO models in vivo. Aim 2. To investigate the mechanisms whereby YAP1 mediates immunosuppression
in TME of PC. Aim 3. Elucidating efficacy of inhibition of YAP1 alone or in combination with TIM3 inhibition using
the PDO models, KP-Luc2 syngeneic mouse model, GEMM, and ongoing YAP1 clinical trial. By utilizing patient-
derived PC cells, we will uncover functional importance of YAP1-mediated PC and elucidate the mechanisms by
which YAP1 mediated immunosuppression for novel therapeutic strategies. Upon completion of this study, we
will have a strong rationale for a novel combination that could overcome the shortcomings we experience in the
clinics today.
