Abstract 3557: Pterostilbene, a natural polyphenol with anticancer activity, induces tumor cell death through autophagy activation

Abstract

Abstract Polyphenols (PFs) conform a large class of plants/fruits-derived molecules with potential benefits for human health. Resveratrol (Resv) (3,4′,5-trihydroxy-trans-stilbene), has been extensively studied for its anti-diabetic, neuroprotective, anti-adipogenic, cardioprotective and anti-tumoral properties. However its low bioavailability (half-life in blood was 10.2 minutes after i.v. adm. of 20 mg/kg to mice) strongly limits Resv potential in vivo. Thus, compounds that may mimic Resv effects, but showing more bioavailability, may improve health benefits and should be investigated. Pterostilbene (Pter) (3,5-dimethoxy-4′-hydroxystilbene, another natural phytoalexin), has shown similar or even more potent antitumor activities than Resv. However, Pter's half-life in mouse blood (77.9 min) is approx. 7.5 times higher. Pter causes cancer cell death in vitro at bioavailable concentrations, and decreases tumor growth in mice. The aim of our present study was a) to determine whether Pter causes cytotoxicity in human tumors at concentrations that are reliable under in vivo conditions; and b) identify which death-related molecular mechanisms are activated by Pter. For these purposes we used a panel of different human tumors: melanoma, breast cancer, lung cancer, and colon cancer. Resv and Pter were assayed in a μM range, between 10 μM (below the IC50 for all cell lines) and 200 μM (an unachievable in vivo concentration). Cell cycle and death induction were determined by flow cytometry. The effects observed in the presence of Resv or Pter, under in vitro conditions, were concentration and exposure time dependent. In fact, an increase in PF concentration switched the type tumor cell death. Resv or Pter induced inhibition of tumor cell division and autophagy activation, although no caspase 3 activation was detected within a 24 h-period in the presence of either PF. On the other hand by further increasing Resv or Pter concentration, apoptosis and necrosis were progressively activated as shown by flow cytometry, caspase 3 activity and lactate dehydrogenase activity released to the culture medium. The main difference between Resv and Pter is the effective concentration, much lower for Pter and thus close to bioavailable levels. Whereas bioavailable levels of Resv do not cause tumor cell death. Different molecular events associated Pter with autophagy activation: a) an increase of LC3-II form, indicating the processing of LC3 protein to its lipidated form; b) an increase in P62 bands and GFP-LC3 punctation were observed thus indicating P62 accumulation and translocation of LC3 to autophagic membranes, respectively. Besides low levels of Pter, in addition of activating autophagy, also cause a rapid loss of tubulin organization as detected by immunochemistry. Therefore our results demonstrate that Pter induces tumor cell cycle arrest and autophagy activation at bioavailable concentrations. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3557.