Translational research in pancreatic ductal adenocarcinoma: current evidence and future concepts

Pancreatic ductal adenocarcinoma(PDA) is one of the major causes for cancer death worldwide. Treatment of metastatic disease remains challenging as only certain patients benefit from advances made with the intensified chemotherapy regimen folinic acid, irinotecan and oxaliplatin, the epidermal growth factor receptor inhibitor erlotinib or the recently FDA-approved nab-paclitaxel. Up to date, no established approach for prediction of treatment response or specific treatment allocation exists. Translational research was able to identify a number of potential biomarkers that might help to improve the dismal prognosis of PDA by facilitating upfront treatment allocation. This topic highlight is focused on current evidence on potential biomarkers for tumor biology, prognosis and prediction of treatment efficacy.

Addressing chemoresistance with a lipid gemcitabine nanotherapeutic strategy for effective treatment of pancreatic cancer

Resistance to gemcitabine in pancreatic cancer poses a significant clinical challenge.Further investigation is warranted to assess whether nano-formulation strategy can be employed to enhance the sensitivity of resistant strains to gemcitabine therapy.In this study,using gemcitabine-resistant pancreatic cancer cell lines,we examined the therapeutic potential of a gemcitabine nanodelivery platform and assessed the ability to overcome drug resistance against resistant strains.Silencing of human equilibrative nucleoside transporter 1(hENT1)led to reduced cellular uptake of gemcitabine,resulting in chemoresistance in pancreatic cancer.Gemcitabine nanoparticles circumvented the entry blockade caused by hENT1 silencing through endocytosis.Nanoparticle entry via clathrin-mediated endocytosis increased intracellular gemcitabine accumulation in gemcitabine-resistant pancreatic cancer cells.Moreover,gemcitabine nanoparticles are preferential in vivo delivery to tumor tissues,likely due to the enhanced permeability and retention effect.In comparison to free gemcitabine,gemcitabine nanoparticles demonstrate a more pronounced cytotoxic effect on gemcitabine-resistant pancreatic cancer cells,with favorable biosafety.This study improved the efficacy of gemcitabine through nanotechnology,providing a novel strategy to address gemcitabine-resistant pancreatic cancer.

Development of gemcitabine-resistant patient-derived xenograft models of pancreatic ductal adenocarcinoma

Aim:Gemcitabine is a frontline agent for locally-advanced and metastatic pancreatic ductal adenocarcinoma(PDAC),but neither gemcitabine alone nor in combination produces durable remissions of this tumor type.We developed three PDAC patient-derived xenograft(PDX)models with gemcitabine resistance(gemR)acquired in vivo,with which to identify mechanisms of resistance relevant to drug exposure in vivo and to evaluate novel therapies.Methods:Mice bearing independently-derived PDXs received 100 mg/kg gemcitabine once or twice weekly.Tumors initially responded,but regrew on treatment and were designated gemR.We used immunohistochemistry to compare expression of proteins previously associated with gemcitabine resistance[ribonucleotide reductase subunit M1(RRM1),RRM2,human concentrative nucleoside transporter 1(hCNT1),human equilibrative nucleoside transporter 1(hENT1),cytidine deaminase(CDA),and deoxycytidine kinase(dCK)]in gemR and respective gemcitabine-naïve parental tumors.Results:Parental and gemR tumors did not differ in tumor cell morphology,amount of tumor-associated stroma,or expression of stem cell markers.No consistent pattern of expression of the six gemR marker proteins was observed among the models.Increases in RRM1 and CDA were consistent with in vitro-derived gemR models.However,rather than the expected decreases of hCNT1,hENT1,and dCK,gemR tumors expressed no change in or higher levels of these gemR marker proteins than parental tumors.Conclusion:These models are the first PDAC PDX models with gemcitabine resistance acquired in vivo.The data indicate that mechanisms identified in models with resistance acquired in vitro are unlikely to be the predominant mechanisms when resistance is acquired in vivo.Ongoing work focuses on characterizing unidentified mechanisms of gemR and on identifying agents with anti-tumor efficacy in these gemR models。

Attempts to remodel the pathways of gemcitabine metabolism: Recent approaches to overcoming tumours with acquired chemoresistance

Gemcitabine is a cytidine analogue frequently used in the treatment of various cancers.However,the development of chemoresistance limits its effectiveness.Gemcitabine resistance is regulated by various factors,including aberrant genetic and epigenetic controls,metabolism of gemcitabine,the microenvironment,epithelial-to-mesenchymal transition,and acquisition of cancer stem cell properties.In many situations,results using cell lines offer valuable lessons leading to the first steps of important findings.In this review,we mainly discuss the factors involved in gemcitabine metabolism in association with chemoresistance,including nucleoside transporters,deoxycytidine kinase,cytidine deaminase,and ATP-binding cassette transporters,and outline new perspectives for enhancing the efficacy of gemcitabine to overcome acquired chemoresistance.