Acidic priming enhances metastatic potential of prostate cancer cells in vivo and in vitro
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1
Martin-Luther-Universität Halle-Wittenberg, Julius-Bernstein-Institut für Physiologie, Germany
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2
Westfälische Wilhelms-Universität Münster, Institut für Physiologie II, Germany
Background and aim. Far-distance tumor metastasis involves several steps such as tumor cell detachment and migration, local invasion by degradation of extracellular matrix, intravasation and circulation in the bloodstream followed by extravasation and growth at a distant site. Since the metabolic microenvironment has an impact on the proliferative behavior and malignant progression of tumors, the question arises whether the metastatic potential of tumor cells is affected by pathophysiological parameters. Therefore, we studied the role of an acidic pH on cell motility, invasiveness and metastasis formation in vivo and in vitro as well as the underlying molecular mechanisms.
Methods. Rat prostate carcinoma cells (AT-1) and cells derived from normal tissue (NRKE, NRKF) were serum-starved for 24 h and subsequently incubated for 3 h or 6 h in Ringer solutions adjusted to either pH 7.4 or pH 6.6, respectively. Metastatic ability of fluorescent labeled AT-1 cells in vivo was analyzed after intravenous injection of pre-incubated cells into the tail vein of male Copenhagen rats (2x106 cells/animal). After 4 days the lungs were isolated and lung metastases were quantified by fluorescence imaging. Migratory speed of AT-1 cells in vitro was determined by single cell microscopy and the invasive capability was defined by the ability to disrupt an intact epithelial layer (transepithelial electrical resistance) as well as to invade the basement membrane (invasion chamber). Production of ROS was monitored using ROS detecting fluorescent dyes and phosphorylation of ERK1/2 and p38 was determined with phospho-specific antibodies.
Results. Pre-incubation of AT-1 cells at low pH enhanced the formation of lung metastases by 156±55%. In vitro, AT-1 cells were able to disrupt a tight epithelium and to invade basement membranes. However, this capability was independent of previous priming of the cells in an acidic environment. Extracellular acidosis raised migratory speed of AT-1 cells by 32±4%, but not of NRKE or NRKF non-tumor cells. The acidosis-induced increase in motility remained for at least 3 h after the cells were retransferred back to normal pH, but was lost after longer periods (24 h). Therefore, this behavior represents a “short-term memory effect”. The basal migratory speed (at pH 7.4) depended on the MAP kinases ERK1/2 and p38. Even though acidic pH activated both MAPK (ERK1/2 232±22%; p38 561±142%), the acidosis-induced augmentation of motility was not be prevented by MAPK inhibition. However, when reactive oxygen species (which were markedly increased at pH 6.6) were scavenged the migratory speed was significantly reduced.
Conclusions. An acidic tumor pH can accelerate tumor cell motility, even if the cells leave their acidic milieu (e.g., by entering the blood stream with its normal pH). The results indicate that increased ROS formation plays a causative role for the pH-dependent motility. The increased migratory behavior may contribute to the augmented metastases formation of acidosis-primed tumor cells.
Acknowledgements
Supported by the Deutsche Krebshilfe (grants 106774/106906) and the BMBF ProNet-T3 (Ta-04).
Keywords:
Acidosis,
metastasis,
Migration,
MAP Kinase Signaling System,
reactive oxygen species (ROS)
Conference:
4th Annual Meeting of the International Society of Proton Dynamics in Cancer, Garching, Germany, 10 Oct - 12 Oct, 2013.
Presentation Type:
Abstract
Topic:
7. pH and stroma-tumor interactions, metastasis
Citation:
Riemann
A,
Schneider
B,
Gündel
D,
Stock
C,
Thews
O and
Gekle
M
(2014). Acidic priming enhances metastatic potential of prostate cancer cells in vivo and in vitro.
Front. Pharmacol.
Conference Abstract:
4th Annual Meeting of the International Society of Proton Dynamics in Cancer.
doi: 10.3389/conf.fphar.2014.61.00042
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Received:
17 Dec 2013;
Published Online:
07 Feb 2014.
*
Correspondence:
Dr. Anne Riemann, Martin-Luther-Universität Halle-Wittenberg, Julius-Bernstein-Institut für Physiologie, Halle/Saale, Germany, anne.riemann@medizin.uni-halle.de