Inhibition of phospholipase D1 reduces pancreatic carcinogenesis in mice partly through a FAK-dependent mechanism

Phospholipase D (PLD) plays a critical role in cancer progression. However, its role in pancreatic cancer remains unclear. Thus, we evaluated the role of PLD1, one of two classical isoforms of PLD, in pancreatic carcinogenesis in vivo. The role of PLD1 in tumor growth was evaluated by subcutaneously transplanting human MIA PaCa-2 cells expressing endogenous PLD1 levels (Ctr KD cells) or cells in which PLD1 was knocked down (Pld1 KD cells) into immunodeficient mice. Twenty days post-implantation, tumors that arose from Pld1-KD cells were significantly smaller, compared to controls (Ctr KD). Then, we assessed the role of PLD1 in the tumor microenvironment, by subcutaneously implanting mouse LSL-Kras^G12D/+;Trp53^R172H/+;Pdx-1-Cre (KPC) cells into wild-type or PLD1 knockout (Pld1^−/−) mice. Compared to wild type, tumor growth was attenuated in Pld1^−/− mice by 39%, whereas treatment of Pld1^−/− mice with gemcitabine reduced tumor growth by 79%. When PLD1 was ablated in LSL-Kras^G12D;Ptf1^Cre/+ (KC) mice, no reduction in acinar cell loss was observed, compared to KC mice. Finally, treatment of KC mice with a small molecule inhibitor of PLD1 and PLD2 (FIPI) significantly reduced acinar cell loss and cell proliferation, compared to vehicle-treated mice. Mechanistically, the effect of PLD on tumor growth is mediated, partly, by the focal adhesion kinase pathway. In conclusion, while PLD1 is a critical regulator of pancreatic xenograft and allograft growth, playing an important role at the tumor and at the microenvironment levels, the inhibition of PLD1 and PLD2 is necessary to reduce pancreatic carcinogenesis in KC mice and might represent a novel therapeutic target.