Markus Fischer: performed the experiments, analyzed the data

Markus Fischer: performed the experiments, analyzed the data. of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3.3. Influence of ruxolitinib on membrane structure/integrity Furthermore it was investigated whether the membrane incorporation AZD6244 (Selumetinib) of ruxolitinib as shown by the NMR measurements has an influence on membranes. For this purpose we employed different assays which characterize the membrane integrity. The experiments were performed on large unilamellar vesicles (LUVs) of POPC or POPC/cholesterol using a lipid to drug ratio up to 2 : 1. First, the influence on the membrane permeation of dithionite was measured by following the reduction-kinetics of the fluorescent lipid 1-palmitoyl-2-(12-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]dodecanoyl]- em sn /em -glycero-3-phosphocholine (NBD-PC) upon addition of the drug (see Supplementary Material). For POPC LUVs, we found a small but significant increase ( em t /em -Test, P??0.05) of the transmembrane permeation of dithionite in the presence of ruxolitinib (Fig. 3A). In contrast, no significant effect of the drug on dithionite permeation was observed for POPC/cholesterol LUVs. Second, measuring the leakage of AZD6244 (Selumetinib) the water-soluble fluorophore 6-carboxyfluorescein (CF) from LUVs showed that after addition of ruxolitinib the release kinetics of CF was similar to that of control vesicles, i.e. in the absence of the drug (Fig. 3B). Third, the fluorescence lifetime of NBD-PC in LUVs was determined. We observed no differences of the average lifetime in AZD6244 (Selumetinib) the absence and the presence of ruxolitinib (Fig. 3C). Open in a separate window Fig. 3 Influence of ruxolitinib on membrane structure The experiments were done with POPC and POPC/cholesterol (molar ratio 4:1) LUVs. (A) The rate constants (kP) for dithionite permeation across vesicles each containing 0.5?mol% NBD-PC were determined in the presence of ruxolitinib and normalized to those measured in the absence of the drug (control) measured at 37?C. The data represent the mean??SE of at least 6 (POPC) and 11 (POPC/cholesterol) independent samples. (B) The CF leakage from LUVs in the absence and in the presence of ruxolitinib measured at 37?C and the calculation of leakage degree CCNE1 (percentage of fluorescence) was performed as described in the Supplementary Material. The values represent the mean??SD ( 3 samples). (C) NBD fluorescence lifetimes of LUVs containing 0.5?mol% NBD-PC were measured AZD6244 (Selumetinib) (ex?=?467?nm, em?=?540?nm) without or with ruxolitinib at room temperature. The average fluorescence lifetime (av) was calculated as described in the Supplementary Material. The values represent the mean??SD of 2 independent samples each measured seven times. The molar lipid/drug ratio was 2:1 for all measurements. 4.?Discussion The JAK kinase inhibitor ruxolitinib is a small-molecule protein kinase inhibitor FDA approved for the treatment of several diseases (see Introduction). Due to its anti-inflammatory impact, it has been proposed for the treatment of Covid-19-associated cytokine-induced inflammatory processes recently. For understanding the molecular mechanism(s) of the efficacy of ruxolitinib, its specific influence on the respective proteins/enzymes is of great importance. However, the investigation of the drug’s interaction with membranes is also of high relevance in order to characterize (i) the general impact of the drug on plasma membranes, (ii) its cellular uptake mechanism, and (iii) the cause of side effects. This aspect of cellular effects has not been studied for ruxolitinib so far. Therefore, we investigated its interaction with lipid membranes. The analysis of the MAS NMR NOESY spectra revealed that ruxolitinib molecules incorporate into the lipid bilayer of vesicles in the upper chain/glycerol region. The broad distribution function of ruxolitinib reflects a high mobility within the membrane with regard to molecular rotation and movement along the membrane normal. This dynamic behavior might indicate the drug’s disposition for a passive cellular uptake mechanism. Accordingly, the drug may permeate across plasma membranes by passive diffusion followed by release.