Abstract 4219: Lysosomal membrane permeabilization, a novel anticancer mechanism induced by pterostilbene

Abstract

Abstract Pterostilbene (Pter) (3,5-dimethoxy-4′-hydroxystilbene), a natural dimethylated analog of resveratrol, is a phytoalexin abundant in plants and fruits with a number of potential benefits for human health. Darakchasava, an Indian herbal preparation of Vitis Vinifera, contains Pter and is prescribed as a cardiotonic in ayurvedic and traditional medicine. Furthermore, some observations indicate that Pter can be beneficial in the prevention and treatment of different diseases such as diabetes, dyslipidemia, or cancer. Pter shows higher bioavailability than resveratrol. The substitution of two OH groups (positions 3 and 5) by methyl groups increases the stabilityof the molecule and its resistance to hepatic glucuronidation and sulfonation. Nevertheless, despite these pharmacokinetic advantages, the anticancer potential of Pter is still undefined. Lysosomal membrane permeabilization (LMP) has been postulated as a mechanism leading to cell death. In an initial step LMP causes cytosol acidification and release of cathepsins and other hydrolases from the lysosomal lumen. Ectopic presence of proteases causes the hydrolysis of vital proteins and the activation of other cell death-related proteases such as caspases. Thus linking LMP and cell death type I. In addition, LMP may also induce caspase-independent cell death mechanisms. In fact morphology of cells affected by LMP may be confused with a subapoptotic or necrotis appearance. The aim of our present study was to investigate the mechanisms of cell death activated by Pter in different tumor cells. For this purpose we used a range of Pter concentration between 10uM (below the IC50) and 100uM (an unachievable in vivo concentration). Acridin orange staining was determined by flow cytometry and fluorescence microscopy. Total and cytosolic cathepsin extractions were performed with different digitonin concentration and activity was measured by spectrofluorimetry. Cytosolic pH was evaluated by staining cultured cells with the fluorochrome SNARF. Apoptosis induction was checked through caspase 3 and 7 measurements. The effects observed in the presence of Pter, under in vitro conditions, were concentration and time dependent. An increase in LMP induced an acidification of cytosolic pH, an increase in cathepsin activity and, only at long time exposure, apoptosis stimulation. Our results demonstrate that tumor cell death induction elicited by Pter is preferentially mediated through LMP. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4219. doi:10.1158/1538-7445.AM2011-4219