H. Hariri1, K. Xu1, S.H. Patel1, S.A. Ahmad1, E. Gulbins1, G.C. Wilson1 1University Of Cincinnati, College Of Medicine, Division Of Surgical Oncology, Cincinnati, OH, USA
Introduction: Despite decades of advancement in pancreatic adenocarcinoma (PDAC), the outlook remains grim with five-year overall survival only recently rising above 10%. We have previously shown variable expression and prognostic implications of acid sphingomyelinase (ASM) in PDAC. ASM is a lysosomal hydrolase that catalyzes the degradation of sphingomyelin to phosphorylcholine and ceramide. ASM, ceramide, and its derivatives have been implicated in the pathogenesis and treatment of tumors with chemotherapy and irradiation. The level of ASM expression within the cancer cell may determine response to specific chemotherapy regimens.
Methods: Orthotopic PDAC model was used for in-vivo experiments with established cell lines injected orthotopically into the pancreas of wildtype, ASM knock-out, and ASM transgenic mice. In-vitro studies were performed with established murine and human PDAC cell lines. Knock-down of ASM was performed by shRNA lentiviral transfection. Cell migration was determined by scratch wound assay with gap closure quantified with ImageJ analysis. Treatment effect was determined by proliferation assay.
Results: To further evaluate the effects of ASM expression in PDAC, a murine orthotopic model was established in wildtype mice, acid sphingomyelinase-deficient mice, and wt mice treated with an ASM inhibitor. The results show that PDAC grows much faster in mice lacking ASM compared to wildtype mice (fig1a). Additionally, wildtype mice treated with an inhibitor of ASM at therapeutic doses resulted in increased tumor growth. In vitro studies in both human and murine pancreatic cancer cell lines demonstrated the effects of ASM expression on the cancer cell itself. Pharmacologic inhibition of ASM and genetic knock-down of ASM expression resulted in a more aggressive cancer cell phenotype (figs 1b, c). In-vitro treatment of PDAC cells with gemcitabine was further enhanced with sphingomyelinase supplementation (fig. 1d). In the orthotopic model, tumor response to gemcitabine treatment was markedly improved in ASM overexpressing mice (fig. 1e).
Conclusion: ASM activity in PDAC not only is prognostic but also contributes to tumor phenotype and response to gemcitabine chemotherapy. Future studies should focus on the potential clinical implications of ASM activity in PDAC.