Direct Observation of Sophorolipid Micelle Docking in Model Membranes and Cells by Single Particle Studies Reveals Optimal Fusion Conditions.

Pradeep Kumar Singh,Pradeep Kumar Singh,Nikos S Hatzakis,Nikos S Hatzakis,Søren S-R Bohr,Søren S-R Bohr

doi:10.3390/biom10091291

Pradeep Kumar Singh, Pradeep Kumar Singh + Show 4 more

Open Access

https://doi.org/10.3390/biom10091291

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Abstract

Sophorolipids (SLs) are naturally produced glycolipids that acts as drug delivery for a spectrum of biomedical applications, including as an antibacterial antifungal and anticancer agent, where they induce apoptosis selectively in cancerous cells. Despite their utility, the mechanisms underlying their membrane interactions, and consequently cell entry, remains unknown. Here, we combined a single liposome assay to observe directly and quantify the kinetics of interaction of SL micelles with model membrane systems, and single particle studies on live cells to record their interaction with cell membranes and their cytotoxicity. Our single particle readouts revealed several repetitive docking events on individual liposomes and quantified how pH and membrane charges, which are known to vary in cancer cells, affect the docking of SL micelles on model membranes. Docking of sophorolipids micelles was found to be optimal at pH 6.5 and for membranes with −5% negatively charge lipids. Single particle studies on mammalian cells reveled a two-fold increased interaction on Hela cells as compared to HEK-293 cells. This is in line with our cell viability readouts recording an approximate two-fold increased cytotoxicity by SLs interactions for Hela cells as compared to HEK-293 cells. The combined in vitro and cell assays thus support the increased cytotoxicity of SLs on cancer cells to originate from optimal charge and pH interactions between membranes and SL assemblies. We anticipate studies combining quantitative single particle studies on model membranes and live cell may reveal hitherto unknown molecular insights on the interactions of sophorolipid and additional nanocarriers mechanism.

Highlights

Sophorolipids (SLs) are glycolipids naturally produced by Candida bombicola [1]
Cytotoxic effects of SLs produced by Wickerhamiella domercqiae show excellent results against esophageal cancer KYSE109, liver cancer H7402, and human lung cancer A549 [18]
Imaging was performed by Total Internal Reflection Fluorescence microscopy (TIRFm), which allowed us to monitor in parallel 200–300 liposomes of different diameters per frame [26,31]

Summary

Introduction

Sophorolipids (SLs) are glycolipids naturally produced by Candida bombicola [1] They are amphiphiles composed of a sophorose disaccharide coupled to long fatty acid and they exist in equilibrium between an acidic and lactonic form [2]. Apoptosis-inducing activities of SLs against liver cancer H7402 marked by morphological changes, i.e., membrane blebbing, cell shrinkage, and chromosomes condensation [19] It shows promising cytotoxic behavior against lung adenocarcinoma A549 and hepatocellular carcinoma HepG2 by inhibition of histone deacetylase and urokinase activities, respectively [21]. The chemoenzymatic alteration of SLs has been applied to achieve greater biological applications [25] Despite their emerging medicinal and industrial applications and cytotoxicity towards cancer cells [12], the mechanism underlying interactions with the cellular membrane and subsequent entry are not fully understood

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