Unraveling the complexity of autophagy: Potential therapeutic applications in Pancreatic Ductal Adenocarcinoma.

Autophagy is a highly dynamic, evolutionary conserved cellular homeostatic process that occurs at baseline levels in most cells. It exerts predominantly cytoprotective effects by removing damaged organelles and protein aggregates. In cancer, however, autophagy acts as both a tumor suppressor by preventing ROS-induced tumorigenesis and as a tumor inducer by providing nutrients to tumor cells under hypoxic, low-energy conditions and protecting them against therapeutically induced stress. Pancreatic Ductal Adenocarcinoma is an extremely lethal and aggressive neoplasm with a 5 year-survival rate between 1% and 5%. One of the most important factors affecting its poor prognosis is its high resistance to most of the existing chemotherapeutic regimens. The role of autophagy in PDAC has been investigated by different research groups and the results are quite divergent; some research lines point at autophagy as a tumor promoting mechanism, whereas other studies assign oncosuppressive functions to it. Nevertheless, several distinct preclinical studies and clinical trials have evaluated the efficacy of both autophagy inducers and autophagy inhibitors as therapeutic compounds against PDAC, many of them providing promising results. Although a better understanding of the complexity of autophagy is needed, the modulation of this process opens new opportunities for prognostic and therapeutic purposes.

Development of bioluminescent chick chorioallantoic membrane (CAM) models for primary pancreatic cancer cells: a platform for drug testing.

The aim of the present study was to develop chick-embryo chorioallantoic membrane (CAM) bioluminescent tumor models employing low passage cell cultures obtained from primary pancreatic ductal adenocarcinoma (PDAC) cells. Primary PDAC cells transduced with lentivirus expressing Firefly-luciferase (Fluc) were established and inoculated onto the CAM membrane, with >80% engraftment. Fluc signal reliably correlated with tumor growth. Tumor features were evaluated by immunohistochemistry and genetic analyses, including analysis of mutations and mRNA expression of PDAC pivotal genes, as well as microRNA (miRNA) profiling. These studies showed that CAM tumors had histopathological and genetic characteristic comparable to the original tumors. We subsequently tested the modulation of key miRNAs and the activity of gemcitabine and crizotinib on CAM tumors, showing that combination treatment resulted in 63% inhibition of tumor growth as compared to control (p < 0.01). These results were associated with reduced expression of miR-21 and increased expression of miR-155. Our study provides the first evidence that transduced primary PDAC cells can form tumors on the CAM, retaining several histopathological and (epi)genetic characteristics of original tumors. Moreover, our results support the use of these models for drug testing, providing insights on molecular mechanisms underlying antitumor activity of new drugs/combinations.

A specific inhibitor of lactate dehydrogenase overcame the resistance toward gemcitabine in hypoxic mesothelioma cells, and modulated the expression of the human equilibrative transporter-1.

Malignant pleural mesothelioma (MPM) is a very hypoxic malignancy, and hypoxia has been associated with resistance towards gemcitabine. The muscle-isoform of lactate dehydrogenase (LDH-A) constitutes a major checkpoint for the switch to anaerobic glycolysis. Therefore we investigated the combination of a new LDH-A inhibitor (NHI-1) with gemcitabine in MPM cell lines. Under hypoxia (O2 tension of 1%) the cell growth inhibitory effects of gemcitabine, were reduced, as demonstrated by a 5- to 10-fold increase in IC50s. However, the simultaneous addition of NHI-1 was synergistic (combination index < 1). Flow cytometry demonstrated that hypoxia caused a G1 arrest, whereas the combination of NHI-1 significantly increased gemcitabine-induced cell death. Finally, the mRNA expression levels of the human equilibrative transporter-1 (hENT1) were significantly down-regulated under hypoxia, but treatment with NHI-1 was associated with a recovery of hENT1 expression. In conclusion, our data show that hypoxia increased MPM resistance to gemcitabine. However, cell death induction and modulation of the key transporter in gemcitabine uptake may contribute to the synergistic interaction of gemcitabine with the LDH-A inhibitor NHI-1 and support further studies for the rational development of this combination.

Using RNA-sequencing to Detect Novel Splice Variants Related to Drug Resistance in In Vitro Cancer Models.

Drug resistance remains a major problem in the treatment of cancer for both hematological malignancies and solid tumors. Intrinsic or acquired resistance can be caused by a range of mechanisms, including increased drug elimination, decreased drug uptake, drug inactivation and alterations of drug targets. Recent data showed that other than by well-known genetic (mutation, amplification) and epigenetic (DNA hypermethylation, histone post-translational modification) modifications, drug resistance mechanisms might also be regulated by splicing aberrations. This is a rapidly growing field of investigation that deserves future attention in order to plan more effective therapeutic approaches. The protocol described in this paper is aimed at investigating the impact of aberrant splicing on drug resistance in solid tumors and hematological malignancies. To this goal, we analyzed the transcriptomic profiles of several in vitro models through RNA-seq and established a qRT-PCR based method to validate candidate genes. In particular, we evaluated the differential splicing of DDX5 and PKM transcripts. The aberrant splicing detected by the computational tool MATS was validated in leukemic cells, showing that different DDX5 splice variants are expressed in the parental vs. resistant cells. In these cells, we also observed a higher PKM2/PKM1 ratio, which was not detected in the Panc-1 gemcitabine-resistant counterpart compared to parental Panc-1 cells, suggesting a different mechanism of drug-resistance induced by gemcitabine exposure.