Background: Nanoliposomal irinotecan (nal-IRI, MM-398) recently gained approval in combination with 5-fluorouracil/leucovorin (5-FU/LV) in post-gemcitabine metastatic pancreatic ductal adenocarcinoma (PDAC) based on the extended survival and manageable safety profile observed in the Phase 3 NAPOLI-1 trial. Preclinically, we have previously demonstrated the anti-tumor activity of nal-IRI with 5-FU and oxaliplatin, standard of care agents in first-line PDAC, and are currently investigating this combination in patients with previously untreated metastatic PDAC in a Phase 2 clinical trial (NCT02551991). Herein, we further evaluate nal-IRI as a potential backbone of first-line metastatic PDAC by assessing the preclinical anti-tumor activity of nal-IRI relative to, and in combination with, gemcitabine and nanoparticle albumin-bound-paclitaxel (nab-P). Methods: Nal-IRI tumor metabolite (CPT-11 and SN-38) levels were measured in mice treated with nal-IRI in combination with gemcitabine or nab-P. Anti-tumor activity and tolerability of nal-IRI, 5-FU, gemcitabine and nab-P monotherapies and combinations were evaluated using pancreatic cancer cell line (ASPC-1 and CFPAC-1)-derived xenograft models, as well as a panel of five patient-derived xenograft models. Results: Administration of gemcitabine or nab-P prior to or simultaneously with nal-IRI resulted in unchanged or increased nal-IRI deposition, as measured by tumor CPT-11 and SN-38 levels at 24 hours post-injection. Moreover, in both cell line-derived and patient-derived xenograft models of PDAC, nal-IRI monotherapy demonstrated comparable or improved anti-tumor activity relative to gemcitabine or nab-P monotherapies. Further, nal-IRI consistently improved tumor growth inhibition and survival when used in combination with either 5-FU, gemcitabine and/or nab-P, relative to the combination of gemcitabine plus nab-P. All treatments were well-tolerated in these preclinical models. Conclusions: These findings illustrate the compatibility and therapeutic potential of nal-IRI as a foundation of first-line PDAC combination regimens, and warrant clinical evaluation.