Combining a gemcitabine-derived prodrug, GEM-C18, with nanoparticles to counteract acidic ph-dependent chemoresistance of pancreatic adenocarcinoma

Gemcitabine (GEM) is still the standard chemotherapeutic drug for advanced pancreatic cancer (PDAC) but with dismal results as most patients develop chemoresistance and metastasis. Chemoresistance is also supported by the particular PDAC tumor microenvironment (TME), in which the parenchymal tumor cells and the cancer stem cells (CSCs) grow in an extracellular matrix (ECM) with areas of low extracellular pH (pHe 6.6-6.8), which are now considered a new hallmark of cancer, being a driver of invasion and a niche for the CSCs. Therefore, reproducing the tumor ECM composition and acidic pHe could improve our understanding of PDAC malignant progression and chemoresistance. In PDAC organotypic cultures mimicking the stromal TME, we have already determined the effect of different ECM compositions on the growth of tumor parenchymal cells and CSCs, their invasion, vasculogenic abilities and their chemiosensitivity to both GEM and to a GEM prodrug, GEM-C18, which is more cytotoxic to CSCs than GEM. Here we have characterized the role of acidic pHe on PDAC malignancy, its transcriptomic landscape and its chemosensitivity to GEM- and GEM-C18. While cell exposition to acidic pHe increases PDAC cell growth, invadopodia-mediated ECM digestion, vasculogenic mimicry (VM) and chemoresistance to both drugs, GEM-C18 is more effective than GEM in increasing cell death and inhibiting ECM digestion at both physiological and acidic pHe. Further, to increase the efficacy of GEM-C18, we have now assembled this prodrug in two different liposomal formulations, DPPC and DSPC. We found that while an early treatment with free GEM-C18 doesn’t have any cytotoxic effect either in Panc1 or in CSCs, GEM-C18 incorporated into the liposomes increased cytotoxicity with a greater effect of the DSPC for both the Panc1 and the CSCs. Importantly, DSPC-containing GEM-C18 also showed an improved anti-invadopodia activity compared to free GEM-C18. Our data highlights the importance of the TME in the development of new therapeutic strategies and suggest that the incorporation of GEM-C18 in DSPC liposomes could be a strategic approach to enhance GEM-C18 cytotoxicity and its anti-invasive activity.