The plant alkaloid voacamine induces apoptosis-independent autophagic cell death on both sensitive and multidrug resistant human osteosarcoma cells

Abstract

In our previous studies, the bisindolic alkaloid voacamine (VOA), isolated from the plant Peschiera fuchsiaefolia, proved to exert a chemosensitizing effect on cultured multidrug resistant (MDR) osteosarcoma cells exposed to doxorubicin (DOX). In particular, VOA was capable of inhibiting P-glycoprotein action in a competitive way, thus explaining the enhancement of the cytotoxic effect induced by DOX on MDR cells. Afterwards, preliminary observations suggested that such an enhancement did not involve the apoptotic process but was due instead to the induction of autophagic cell death. The results of the present investigation demonstrate that the plant alkaloid VOA is an autophagy inducer able to exert apoptosis-independent cytotoxic effect on both wild-type and MDR tumor cells. In fact, under treatment condition causing about 50 percent of cell death, no evidence of apoptosis could be revealed by microscopical observations, Annexin V-FITC labeling and analysis of PARP cleavage, whereas the same cells underwent apoptosis when treated with apoptosis inducers, such as doxorubicin and staurosporine. Conversely, VOA-induced autophagy was clearly evidentiated by electron microscopy observations, monodansylcadaverine staining, LC3 expression, and conversion. These results were confirmed by the analysis of the modulating effects of the pretreatment with autophagy inhibitors prior to VOA administration. In addition, transfection of osteosarcoma cells with siRNA against ATG genes reduced VOA cytotoxicity. In conclusion, considering the very debated dual role of autophagy in cancer cells (protective or lethal, pro-or anti-apoptotic) our findings seem to demonstrate, at least in vitro, that a natural product able to induce autophagy can be effective against drug resistant tumors, either used alone or in association with conventional chemotherapeutics.

Voacamine Modulates the Sensitivity to Doxorubicin of Resistant Osteosarcoma and Melanoma Cells and Does Not Induce Toxicity in Normal Fibroblasts

“…Also, voacamine ( 1 ) administered at higher concentrations (>3.0 μg/mL) has been demonstrated to be an autophagy inducer able to exert apoptosis-independent cytotoxic effects on both wild-type and MDR tumor cells. 15 …”

Guidelines for the use and interpretation of assays for monitoring autophagy

“…Several studies have been performed using this technique on yeast, 53 as well as on mammalian cells or tissue, first on mouse exocrine pancreas, 54 then on mouse and rat liver, 55,56 mouse seminal vesicle epithelium 24,51 or cancer cell lines (e.g., breast cancer MDA-MB-231) 57 to investigate the various phases of autophagosome maturation, and to reveal useful details about the origin and evolution of their limiting membranes. 2,8,[58][59][60] The phagophore and the limiting membranes of autophagosomes contain few, or no detectable, IMPs ( Fig. 3A and B), when compared with other cellular membranes and to the membranes of lysosomes.…”

The autophagic paradox in cancer therapy

“…Autophagy is induced by different forms of cancer therapy, including conventional chemotherapeutic drugs, novel targeted cancer therapeutics and ionizing radiation, in various types of solid and hematological malignancies (Table 2) (Han et al, 2007(Han et al, , 2008Kim et al, 2007Kim et al, , 2008bKim et al, , 2009aMaiuri et al, 2007b;Kamitsuji et al, 2008;Meschini et al, 2008;Qadir et al, 2008;Turcotte et al, 2008;Fu et al, 2009;Lorin et al, 2009;Tormo et al, 2009;Fan et al, 2010;Gupta et al, 2010;Huang and Sinicrope, 2010;Li and Fan, 2010;Voss et al, 2010;Yacoub et al, 2010;Wu et al, 2010c;Lian et al, 2011;O'Donovan et al, 2011). In some circumstances, autophagy mediates the cytotoxic or cytostatic effect of anticancer agents, in which blockade of autophagy abolishes the therapeutic actions.…”