Regulation of pancreatic cancer growth by superoxide

Abstract

K-ras mutations have been identified in up to 95% of pancreatic cancers, implying their critical role in the molecular pathogenesis. Expression of K-ras oncogene in an immortalized human pancreatic ductal epithelial cell line, originally derived from normal pancreas (H6c7), induced the formation of carcinoma in mice. We hypothesized that K-ras oncogene correlates with increased non-mitochondrial-generated superoxide (O2·−), which could be involved in regulating cell growth contributing to tumor progression. In the H6c7 cell line and its derivatives, H6c7er-Kras+ (H6c7 cells expressing K-ras oncogene), and H6c7eR-KrasT (tumorigenic H6c7 cells expressing K-ras oncogene), there was an increase in hydroethidine fluorescence in cell lines that express K-ras. Western blots and activity assays for the antioxidant enzymes that detoxify O2·− were similar in these cell lines suggesting that the increase in hydroethidine fluorescence was not due to decreased antioxidant capacity. To determine a possible non-mitochondrial source of the increased levels of O2·−, Western analysis demonstrated the absence of NADPH oxidase-2 (NOX2) in H6c7 cells but present in the H6c7 cell lines expressing K-ras and other pancreatic cancer cell lines. Inhibition of NOX2 decreased hydroethidine fluorescence and clonogenic survival. Furthermore, in the cell lines with the K-ras oncogene, overexpression of superoxide dismutases, that detoxify non-mitochondrial sources of O2·−, and treatment with the small molecule O2·− scavenger Tempol, also decreased hydroethidine fluorescence, inhibited clonogenic survival and inhibited growth of tumor xenografts. Thus, O2·− produced by NOX2 in pancreatic cancer cells with K-ras, may regulate pancreatic cancer cell growth.

Pharmacological Ascorbate Radiosensitizes Pancreatic Cancer

“…Consistent with this study, our current study demonstrates that H6c7 cells are also resistant to the combination treatment of IR and ascorbate. The selective ascorbate-induced cytotoxicity may be due to the combination of low levels of antioxidant enzymes and high endogenous levels of ROS in cancer cells ( 43, 44, 45 ). Moreover, tumor cells are often defective in DNA repair, whereas normal cells are proficient ( 46 ).…”

Metformin decreases growth of pancreatic cancer cells by decreasing reactive oxygen species: Role of NOX4

“…Protein expression of NOX2 and NOX4 are increased in pancreatic cancer compared to normal tissue (17). There is evidence that metformin reduces intracellular ROS in endothelial and smooth muscle cells (18 -20).…”

Genetics and biology of pancreatic ductal adenocarcinoma

“…It is well documented that oncogenic RAS plays a major role in ROS generation, with several studies establishing that ROS is critical for oncogenic KRAS-mediated transformation and growth of PDAC cells (Irani et al 1997;Mitsushita et al 2004;Vaquero et al 2004;Weinberg et al 2010;Hu et al 2012;Du et al 2013). However, while most cancer cells exhibit elevated ROS levels, excessively high ROS levels are detrimental, thus requiring potent oxidative defense mechanisms in order to maintain redox balance for viability (Gorrini et al 2013;Schieber and Chandel 2014).…”