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

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.

Reprogramming of fatty acid metabolism in cancer

“…This is particularly relevant for the development of multi-drug-resistant tumours, which typically contain lower levels of endogenously synthesised cholesterol and are consequently less permeable to anticancer agents. 145 Epidemiological studies have highlighted controversial roles for aberrant cholesterol metabolism in cancer, thus raising important considerations for how tumours actually utilise cholesterol, and how it may be therapeutically exploited. 146 For instance, elevated serum cholesterol levels are associated with increased incidence and recurrence of prostate cancer, whilst inhibition of its biosynthesis by using statins reduces colorectal, breast and endometrial cancer mortality.…”

Cholesterol Metabolic Reprogramming in Cancer and Its Pharmacological Modulation as Therapeutic Strategy

“…Indeed, ABCA1 deregulation leads to cholesterol accumulation in the mitochondrial compartment, which in turn supports the malignant transformation ( 32 , 155 ). Moreover, higher levels of intracellular cholesterol directly affect the lipid composition of plasma membranes, as well as their physical properties: cholesterol enrichment increases the phospholipids’ degree of order in the bilayer while reducing its permeability, thereby promoting tumor resistance to membrane-active anticancer drugs ( 226 ). Peroxisome proliferator-activated receptors (PPAR) α and γ play a pivotal role in modulating both intracellular and extracellular cholesterol fluctuations ( 227 , 228 ).…”

“…The variation in cholesterol content, in fact, affects membrane fluidity, permeability and rigidity, thus impacting several processes, such as invasion, migration or tumor development, growth and metastasis ( 233 ). In particular, different studies reported that increased cholesterol percentage deriving from higher de novo biosynthesis leads to enhanced rigidity and decreased fluidity, thus contributing to decreased cell mobility ( 234 ), or to altered membrane permeability, which is involved in altered cancer cell response to drug treatments ( 226 ). In line with this, variations in intracellular cholesterol levels mediated by ABCA1 overexpression drive the onset of EMT and the promotion of tumor invasiveness, whilst human solid tumors at advanced stages are characterized by high levels of ABCA1 expression ( 235 ).…”

Entomopathogenic fungi: unconventional applications

“…Dtxs inhibit the action of V-ATPase proton pumps, which allows them to be used in cancer therapies or osteoporosis treatment (Liu and Tzeng 2012). However, sublines of HCT116 colon carcinoma cells are resistant to dtxs A, B, and E because of changes in membrane properties and reduction in ionophoric activity during increased activation of cholesterol synthesis (Heilos et al 2018). Dtxs are also helpful in the treatment of Alzheimer's disease as they can inhibit and prevent the generation of b-amyloid (Ab) ).…”