Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer mortality, with new treatment options urgently needed. Neuropilins-1/-2 (NRP1, NRP2) are receptors for semaphorins and angiogenic growth factors, while the GAIP interacting protein C-terminus 1 (GIPC1, aka Synectin) interacts with the neuropilins. They are overexpressed in PDAC and associated with poor survival as well as tumor-promoting activities. Thus, neuropilin and/or GIPC1 silencing may inhibit PDAC growth. In this study, we directly compare the various tumor-inhibitory effects of transient RNAi-mediated depletion of NRP1, NRP2 and GIPC1, alone or in combination, in a set of cell lines with different expression levels. Inhibition of anchorage-dependent and -independent proliferation, colony formation and cell migration, alterations of 3D-spheroid size and shape as well as retardation of cell cycle and induction of apoptosis have been analyzed and found to vary between cell lines. The observed effects are independent of initial expression levels. Knocking down NRP1, NRP2, and GIPC1 alone demonstrates significant effects. Only small additive effects upon combined knockdown and no counter-upregulation of the respective other genes could be detected. Making the study more translational, we show that systemic treatment of PDAC xenograft-bearing mice with polymeric nanoparticles for delivery of specific siRNAs results in tumor inhibition, reduces proliferation, and induces apoptosis. In conclusion, NRP and GIPC1 inhibition emerges as a promising avenue in PDAC treatment due to pleiotropic tumor-inhibitory effects.