Quinacrine reactivity with prion proteins and prion-derived peptides

Abstract

Quinacrine is a drug that is known to heal neuronal cell culture infected with prions, which are the causative agents of neurodegenerative diseases called transmissible spongiform encephalopathies. However, the drug fails when it is applied in vivo. In this work, we analyzed the reason for this failure. The drug was suggested to "covalently" modify the prion protein via an acridinyl exchange reaction. To investigate this hypothesis more closely, the acridine moiety of quinacrine was covalently attached to the thiol groups of cysteines belonging to prion-derived peptides and to the full-length prion protein. The labeled compounds were conveniently monitored by fluorescence and absorption spectroscopy in the ultraviolet and visible spectral regions. The acridine moiety demonstrated characteristic UV-vis spectrum, depending on the substituent at the C-9 position of the acridine ring. These results confirm that quinacrine almost exclusively reacts with the thiol groups present in proteins and peptides. The chemical reaction alters the prion properties and increases the concentration of the acridine moiety in the prion protein.

Reactivity of 9‐aminoacridine drug quinacrine with glutathione limits its antiprion activity

“…1 H NMR: 8.67 (d, 1H, J 8,7 = 9.3, H‐8), 8.41 (d, 1H, J NH,α = 8.3, Cys‐NH), 8.37 (t, 1H, J NH,α = 5.9, Gly‐NH), 8.23 (bs, 3H, NH 3 + ), 8.23 (d, 1H, J 5,7 = 2.2, H‐5), 8.12 (d, 1H, J 4,3 = 9.4, H‐4), 7.90 (d, 1H, J 1,3 = 2.8, H‐1), 7.69 (dd, 1H, J 7,8 = 9.3, J 7,5 = 2.2, H‐7), 7.61 (dd, 1H, J 3,4 = 9.4, J 3,1 = 2.8, H‐3), 4.41 (ddd, 1H, J α,NH = 8.3, J α,β = 9.4 and 4.6, Cys‐α), 4.02 (s, 3H, OCH 3 ), 3.90 (m, 1H, Glu‐α), 3.59 (d, 2H, J α,NH = 5.9, Gly‐α), 3.34 (dd, 1H, J gem = 13.4, J β,α = 4.8, Cys‐β), 3.19 (dd, 1H, J gem = 13.4, J β,α = 9.4, Cys‐β), 2.18–2.25 (m, 2H, Glu‐γ), 1.91–2.00 (m, 2H, Glu‐β). 1 H‐NMR and 13 C‐NMR agreed with previously published one . For copies of spectra, see Supplementary Information (Figures S3 and S4 for NMR, and Figures S6 and S7 for HRMS spectra).…”

“…The recombinant full‐length mouse prion protein with N ‐terminal His tag (His‐mPrP23‐231) was prepared and purified as described previously . The assay based on quenching of prion protein intrinsic fluorescence was adapted according to previous work .…”

“…Prior to distribution experiment, 5 ml of each of saturated phases was intensively mixed with 16 μmol acridine compound overnight at 6°C. The low temperature was used to prevent hydrolysis of acridines to corresponding acridones . The phases were separated by centrifugation and examined by UV–Vis spectroscopy at 18°C.…”

“…As we have previously shown, quinacrine reacts with thiol‐containing peptides including glutathione (GSH) with which it forms S ‐acridinylated product—GlutQui (Figure ). We hypothesize that this could be another factor responsible for quinacrine failure in clinical trials.…”

Quinacrine promotes replication and conformational mutation of chronic wasting disease prions

“…First, the effects of "antiprion" compounds are clearly species/strain-dependent, in that drugs found to restrain prions in one situation may improve replicative ability in another. Based on initial reports of quinacrine's effects on mouse prion propagation in cell culture, a plethora of studies were designed to discern the mechanism of its presumed antiprion effects (19,20,(29)(30)(31)(38)(39)(40)(41)(42)(43)(44)(45), to assess its pharmacokinetics (21,36,42,46) and to derive similar compounds with improved antiprion efficacy (18,20,(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59). These studies continue to this day, despite multiple failed clinical studies in patients with human prion diseases (10)(11)(12)(13)(14)(15).…”