In vitro studies on CSC-targeted therapy in pancreatic adenocarcinoma with nanoparticle formulations

Pancreatic ductal adenocarcinoma (PDAC) is a lethal disease and one of the major causes of death among cancer patients. Diagnosis of PDAC during the early stages of cancer is difficult because no effective screening for detection of early stage tumors is yet available. PDAC is sustained by a distinct subset of quiescent cells, called cancer stem cells (CSCs) that are responsible for resistance to standard therapy, metastatic potential and disease relapse following treatments. The current therapy for PDAC preferentially targets the more differentiated cancer cell population, leaving CSCs as a source that supports the tumour, causing recurrence. For this reason, targeting pancreatic CSCs could contribute to the clinical development of more efficacious drugs treatment, aimed to permanently remove the tumor and prevent recurrence. In this study, we investigated two therapeutic approaches for the treatment of PDAC. First of all, we studied a pro-drug approach using gemcitabine conjugated with fatty acid chains, C12 GEM and C18 GEM, by testing their cytotoxic activity on Panc1 cell line and the derived CSCs. Both cell lines were more sensitive to the treatment with the lipophilic pro-drugs than GEM, but only Panc1 CSCs showed a high sensitivity to C18 GEM treatment. Furthermore, the two cell lines exhibited different intracellular uptake mechanisms of the drugs that involved mainly membrane nucleoside transporters in Panc1 parental cells or fatty acid translocase CD36 for C18 GEM uptake in both cell lines. Furthermore, we have highlighted a peculiar feature of CSCs regarding the apoptotic response to treatment. In Panc1 parental cells, the treatments induced a PARP-dependent apoptosis, while in Panc1 CSCs they involved a mechanism of caspase-independent apoptosis mediated by AIF. The second therapeutic approach concerned a targeted drug delivery system using PEGylated liposomes containing disulfiram (DSF) or diethyldithiocarbamate-copper (Cu(DDC)2) and liposomes selective for pancreatic CSCs expressing CD44 coated with HA. We evaluated the effect on cell proliferation of the various DSF formulations using pancreatic CSCs derived from cell lines or patients. The encapsulation of Cu(DDC)2 complex in liposomes increased its anti-proliferative activity on our cell models. This method represents a good strategy to make the Cu(DDC)2 complexes suitable for PDAC patients. In this study, we propose two valid and alternative therapeutic approaches with a promising potential to achieve efficient and encouraging results in PDAC treatment.