Altered membrane rigidity via enhanced endogenous cholesterol synthesis drives cancer cell resistance to destruxins

// Daniela Heilos 1, 2 , Clemens Rohrl 3 , Christine Pirker 1 , Bernhard Englinger 1 , Dina Baier 1, 4 , Thomas Mohr 1 , Michaela Schwaiger 5 , Shahid Muhammad Iqbal 2 , Sushilla van Schoonhoven 1 , Kristaps Klavins 6 , Tanja Eberhart 3 , Ursula Windberger 4 , Judith Taibon 7 , Sonja Sturm 7 , Hermann Stuppner 7 , Gunda Koellensperger 5, 8 , Rita Dornetshuber-Fleiss 1, 2 , Walter Jager 9 , Rosa Lemmens-Gruber 2 and Walter Berger 1 1 Institute of Cancer Research, Department of Internal Medicine I, Medical University of Vienna, Comprehensive Cancer Center of the Medical University of Vienna, Vienna, Austria 2 Department of Pharmacology and Toxicology, University of Vienna, Vienna, Austria 3 Center for Pathobiochemistry and Genetics, Medical University of Vienna, Vienna, Austria 4 Decentralized Biomedical Facilities of the Medical University of Vienna, Vienna, Austria 5 Department of Analytical Chemistry, Faculty of Chemistry, University of Vienna, Vienna, Austria 6 BIOCRATES Life Sciences AG, Innsbruck, Austria 7 Institute of Pharmacy, Pharmacognosy and Center for Molecular Biosciences Innsbruck, University of Innsbruck, Innsbruck, Austria 8 Vienna Metabolomics Center, University of Vienna, Vienna, Austria 9 Department of Pharmaceutical Chemistry, Division of Clinical Pharmacy and Diagnostics, University of Vienna, Vienna, Austria Correspondence to: Walter Berger, email: walter.berger@meduniwien.ac.at Keywords: cholesterol synthesis pathway; cancer cell resistance; destruxins; mycotoxins; cell membrane alterations Received: January 15, 2018     Accepted: April 25, 2018     Published: May 22, 2018 ABSTRACT Destruxins, secondary metabolites of entomopathogenic fungi, exert a wide variety of interesting characteristics ranging from antiviral to anticancer effects. Although their mode of action was evaluated previously, the molecular mechanisms of resistance development are unknown. Hence, we have established destruxin-resistant sublines of HCT116 colon carcinoma cells by selection with the most prevalent derivatives, destruxin (dtx)A, dtxB and dtxE. Various cell biological and molecular techniques were applied to elucidate the regulatory mechanisms underlying these acquired and highly stable destruxin resistance phenotypes. Interestingly, well-known chemoresistance-mediating ABC efflux transporters were not the major players. Instead, in dtxA- and dtxB-resistant cells a hyper-activated mevalonate pathway was uncovered resulting in increased de-novo cholesterol synthesis rates and elevated levels of lanosterol, cholesterol as well as several oxysterol metabolites. Accordingly, inhibition of the mevalonate pathway at two different steps, using either statins or zoledronic acid, significantly reduced acquired but also intrinsic destruxin resistance. Vice versa, cholesterol supplementation protected destruxin-sensitive cells against their cytotoxic activity. Additionally, an increased cell membrane adhesiveness of dtxA-resistant as compared to parental cells was detected by atomic force microscopy. This was paralleled by a dramatically reduced ionophoric capacity of dtxA in resistant cells when cultured in absence but not in presence of statins. Summarizing, our results suggest a reduced ionophoric activity of destruxins due to cholesterol-mediated plasma membrane re-organization as molecular mechanism underlying acquired destruxin resistance in human colon cancer cells. Whether this mechanism might be valid also in other cell types and organisms exposed to destruxins e.g. as bio-insecticides needs to be evaluated.