Blocking angiotensin II type1 receptor triggers cell cycle arrest and apoptotic cell death in human pancreatic cancer cells

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Aims: Pancreatic ductal adenocarcinoma (PDA), one of the most lethal malignancies, is virtually therapy-resistant. We have recently shown that blocking angiotensin II (AngII) by an AngII type 1 receptor (AT1R) blocker, losartan, reduces PDA angiogenesis and viability. Here, we investigated the effects of blocking AT1R on PDA cell cycle and apoptosis and explored the molecular mechanisms involved.
 
 Methods: Panc10.01 PDA cell cycle was analyzed using flow cytometric analysis of DNA content by PI staining; apoptosis by annexin V-FITC and TUNEL staining; p53, p21^WAF1, Bax and bcl-2 mRNA and protein by real time PCR and Western blotting; caspase-3 activity by colorimetric assay.
 
 Results: Blocking AT1R by losartan inhibited PDA cell growth and induced G₀-G₁ phase cell cycle arrest with upregulation of p21^WAF1. Losartan also triggered dose-dependent apoptosis, an effect that was associated with Bax and p53 upregulation, bcl-2 reduction, and activation of caspase-3. Blocking p53 by an inhibitor, pifithrin-α, or siRNA completely restored the transcription of bcl-2 and suppressed the losartan-induced apoptosis but had no effect on p21^WAF1 transcription or cell cycle.
 
 Conclusions: Our data describe a previously unknown involvement of AT1R in PDA cell cycle and apoptosis, and provide the first mechanistic evidence that losartan might mediate its antineoplastic effects through restoration of p53 proapoptotic activities in p53 mutant cells. As loss of p53 function is frequently observed in PDA patients, our data suggest that AT1R could represent a novel molecular target to control tumor growth and angiogenesis, prevent metastasis, and prolong survival in patients with primary or metastatic PDA.