Therapeutic effect of curcumin derivative GT863 on prion-infected mice

Abstract

In prion diseases, the cellular prion protein (PrP^C) forms an abnormal, infectious, and disease-causing form known as PrP^Sc. Inhibition of prion propagation is a key approach for the treatment of these diseases. We report on a curcumin-based compound, GT863 (formerly known as PE859) that displays therapeutic efficacy when administered orally. GT863 inhibited abnormal prion protein formation in prion-infected neuroblastoma cells in a prion strain dependent manner: effectively for RML prion and marginally for 22 L prion. Treatment with ad libitum GT863-containing feed prolonged the incubation period of intracerebrally RML prion infected Tga20 mice by 217% increase in mean. Although the 263 K prion-infected Tg7 mice were less sensitive to GT863 than RML prion infected Tga20, treatment with ad libitum GT863-containing feed prolonged the incubation period by 39% increase in mean. The mechanism of the anti-prion effectiveness in vivo needs to be elucidated and managed. Nevertheless, GT863 could inspire the development of oral chemotherapy for prion diseases.

Fig. 1

Chemical structure of GT863.

Fig. 2

GT863 effects on PrP^res formation in prion-infected cells. (a) Immunoblots of PrP^res in ScN2a and N167 cell lines treated with GT863. Cells were treated for 3 days with the indicated dose. β-actin signals are controls for sample integrity. The left end of each blot represents the vehicle control. Molecular markers on the left denote sizes in kilodaltons. The full immunoblotting data are shown in Fig. S1. The non-cropped image of the blot in Fig. S1 for obtaining blot data is shown in Fig. S11. Arrows indicate the signal disappearance due to cytotoxicity. (b) Graphical representations of PrP^res monomer levels in ScN2a (solid line) and N167 (dashed line) relative to those of the vehicle control. (c) Cytotoxic assay for GT863 in N2a cells.

Fig. 3

Effects of GT863 in prion-infected mice. Kaplan–Meier graphs for intracerebrally RML prion-infected Tga20 (a) and 263 K prion-infected Tg7 (b). Mice treated by ad libitum feeding of a GT863-containing diet are indicated in dark orange and vehicle control in gray. The proportional hazard assumption was evaluated as shown in Fig. S2.

Fig. 4

Immunoblot and histological analyses of GT863-treated mouse brains. (a) Representative immunoblots of PrP^total and PrP^res in the brains of prion-infected mice treated with GT863 or untreated. Each lane represents an aliquot corresponding to 0.16 mg and 0.64 mg of terminally ill brain tissue for PrP^total and PrP^res, respectively. Molecular markers on the left denote sizes in kilodaltons. PrP^total contains PrP^C and PrP^Sc. Fig. S4 shows data for all mice in Fig. 3; Table 1. (b) Representative histological analysis of brain sections from terminally ill prion-infected mice treated with GT863 or untreated. Nc neocortex, Hp hippocampus, Th thalamus. Figures S4 and S5 show the data for all available mice.

Fig. 5

GT863 effects at various timing of ad libitum feeding of a GT863-containing diet. RML prion-infected Tga20 mice were treated with an ad libitum feeding GT863-containing diet beginning 35 or 49 days after prion inoculation. Open bars indicate feeding duration without GT863. Shaded bars indicate the duration of the GT863 treatment. The results of the statistical analysis are summarized in Table 2. The Kaplan–Meier plot in Fig. S6 shows the progress of each individual mouse.

Fig. 6

Changes in PrP glycosylation in ScN2a cells by GT863. (a) A representative immunoblot for PrP^total. (b) Densitometry plot of the mean intensity of six pairs of immunoblot profiles (Fig. S7). Densities were obtained using ImageJ software, and data were analyzed using Python and R.