IDDF2023-ABS-0090 Squalene epoxidase promotes pancreatic ductal adenocarcinoma tumorigenesis and drives gemcitabine resistance by activating the PI3K-Akt pathway

Background

Squalene epoxidase (SQLE), originally identified as a rate-limiting enzyme for cholesterol biosynthesis, is associated with multiple malignancies. We aim to investigate the regulatory role, molecular mechanisms and clinical implications of SQLE in pancreatic ductal adenocarcinoma (PDAC).

Methods

SQLE expression was analyzed using tissue microarray, proteomic mass-spectrometry and RNA-seq of PDAC patients from our cohort and TCGA datasets. The biological functions of SQLE were determined by cell viability, migration, invasion and metastasis assays in vitro and in vivo. Xenograft tumors with SQLE overexpression were administrated with SQLE inhibitor terbinafine or in combination with gemcitabine in mouse models. The downstream pathways regulated by SQLE were identified by RNA-seq and western blot. The clinical implication of SQLE was assessed in 181 primary PDAC cases.

Results

SQLE was upregulated in PDAC tumors compared to adjacent normal tissues (P<0.001) and was overexpressed in 5/7 PDAC cell lines. Ectopic expression of SQLE in PDAC cells BxPC-3 and MIA PaCa-2 promoted cell proliferation, migration and invasion abilities, accordingly depletion of SQLE in PANC-1 exhibited the opposite effects. Stable overexpression of SQLE facilitated subcutaneous tumor growth and lung metastasis (P<0.05) in mice, indicating SQLE functions as an oncogenic factor in PDAC. Survival analysis demonstrated that elevated SQLE was associated with poor overall survival and high recurrence risk in PDAC patients treated with gemcitabine. Accordingly, we found that higher SQLE expression enhanced gemcitabine resistance in PDAC cells. Mechanistically, SQLE promoted gemcitabine resistance through the upregulation of RRM1 and downregulation of ENT1, the key factors modulating gemcitabine efficacy in PDAC, simultaneously activating the PI3K-Akt signaling. In keeping with this, targeting the PI3K-Akt pathway with PI3K inhibitor LY294002 sensitized PDAC cells to gemcitabine. Finally, we showed that combined gemcitabine with SQLE inhibitor terbinafine exerted synergistic effects in PDAC with high SQLE expression, leading to tumor regression in xenograft models (P<0.01).

Conclusions

Our work suggests the oncogenic function of SQLE in PDAC that enhances RRM1 and reduces ENT1 and activates the PI3K-Akt signaling, which contributes to gemcitabine resistance. Targeting SQLE by pharmacological blockade combined with gemcitabine could be a promising therapy for PDAC patients.