nu-7026 and Pancreatic-Neoplasms

Gemcitabine sensitization is important for the treatment of pancreatic cancer. We have previously shown that DNA-dependent protein kinase catalytic subunit (DNA-PKcs) over-expression causes Akt activation and gemcitabine resistance in pancreatic cancer cells. Here, we aim to downregulate DNA-PKcs via introduction of micorRNA-101 ("miR-101"). We showed that forced-expression of miR-101 downregulated DNA-PKcs and potentiated gemcitabine-induced PANC-1 pancreatic cancer cell death and apoptosis. Contrarily, miR-101 depletion through expressing antagomiR-101 in PANC-1 cells resulted in DNA-PKcs upregulation and gemcitabine resistance. DNA-PKcs downregulation is the primary reason of gemcitabine-sensitization by miR-101. DNA-PKcs inhibition (by NU7026) or silence (by targeted siRNAs) disabled miR-101-mediaetd gemcitabine sensitization. Significantly, Akt Ser-473 phosphorylation in PANC-1 cells was also inhibited by miR-101, but was augmented with antagomiR-101 expression. Importantly, we showed that miR-101 level was downregulated in gemcitabine-resistant human pancreatic cancer tissues, which was correlated with DNA-PKcs upregulation. Together, these results suggest that miR-101 sensitizes PANC-1 cells to gemcitabine possibly via downregulating DNA-PKcs.

Topics: Antagomirs; Antimetabolites, Antineoplastic; Apoptosis; Cell Line, Tumor; Chromones; Deoxycytidine; DNA-Activated Protein Kinase; Down-Regulation; Drug Resistance, Neoplasm; Gemcitabine; Gene Silencing; Humans; MicroRNAs; Morpholines; Nuclear Proteins; Pancreatic Neoplasms; Phosphorylation

Pancreatic ductal adenocarcinoma (PDAC) is amongst the deadliest of human cancers, due to its late diagnosis as well as its intense resistance to currently available therapeutics. To identify mechanisms as to why PDAC are refractory to DNA damaging cytoxic chemotherapy and radiation, we performed a global interrogation of the DNA damage response of PDAC. We find that PDAC cells generally harbor high levels of spontaneous DNA damage. Inhibition of Non-Homologous End Joining (NHEJ) repair either pharmacologically or by RNAi resulted in a further accumulation of DNA damage, inhibition of growth, and ultimately apoptosis even in the absence of exogenous DNA damaging agents. In response to radiation, PDAC cells rely on the NHEJ pathway to rapidly repair DNA double strand breaks. Mechanistically, when NHEJ is inhibited there is a compensatory increase in Homologous Recombination (HR). Despite this upregulation of HR, DNA damage persists and cells are significantly more sensitive to radiation. Together, these findings support the incorporation of NHEJ inhibition into PDAC therapeutic approaches, either alone, or in combination with DNA damaging therapies such as radiation.

Topics: Carcinoma, Pancreatic Ductal; Cell Line, Tumor; Cell Proliferation; Chromones; DNA Breaks, Double-Stranded; DNA Damage; DNA End-Joining Repair; DNA-Activated Protein Kinase; Humans; Morpholines; Pancreatic Neoplasms; Radiation Tolerance; Radiation-Sensitizing Agents; Recombination, Genetic