Furthermore, this miRNA was also found to be involved in multi drug resistance [44]. There are a few limitations of the current study that have to be considered for proper interpretation of our results. Firstly, the current study represents an in-vitro study with only one esophageal adenocarcinoma and one squamous cell carcinoma cell line. This means that our data cannot be immediately transferred into clinical settings,

as results might be limited to the selected cell lines and reproducibility might be limited. However, this is the first study that investigates CDK inhibitor the effect of PPI treatment on esophageal cancer, and we selected well known and commonly used esophageal cancer cell lines. Therefore, in our opinion this data provides a valid basis for further investigations in additional in-vitro or in-vivo experiments. Secondly, we used esomeprazole doses of up to 250 μM in our experiments. In this context, maximal tissue concentrations after esomeprazole administration in humans have to be considered in order to achieve clinically relevant data on the effect of esomeprazole on tumour characteristics. Based on product information from Astra Zeneca, 40 mg i.v. esomeprazole (which is the standard dose of esomprazole per day in the therapy of peptic RGFP966 cell line ulcer and gastritis) would achieve a steady state tissue concentration

of 6 μM for an 80 kg human. However, in specific situations such as hypersecretory conditions, recommended adult oral starting dose of esopmeprazole is 60 mg once daily with subsequent adjustment of individual doses, and doses up to 120 mg three times daily have been administered. Dapagliflozin The doses used in our experiments are higher than the currently clinically used doses. However, PPIs are considered to be generally safe in application. Despite some reported adverse side effects such as osteoporosis and bone fracture, PLX-4720 mouse hypomagnesaemia, the development of gastric polyps, enteric infections, interstitial nephritis and pneumonia, and the absolute risk of complications attributed to PPIs is low [45]. Moreover,

the doses used in our experiments are similar to those of other research groups [14]. Thirdly, we did not include an analysis of the expression pattern of proton pumps in the cell membrane or in membranes of intracellular vesicles, or of the exact percentage and strength of inhibition of the proton pumps via esomeprazole. We only analysed the intra- and extracellular pH and concluded from these data that both cell lines were still able to excrete protons into the extracellular space. However, as several other authors observed that PPI treatment lead to intracellular acidification, in our opinion the absence of this accumulation of protons in the intracellular space in our experiments justifies the conclusion that this is not the main effect of action of esomeprazole in esophageal cancer cell lines.