Inhibition of protease-resistant prion protein formation by porphyrins and phthalocyanines

Abstract

A central aspect of pathogenesis in the transmissible spongiform encephalopathies or prion diseases is the conversion of normal protease-sensitive prion protein (PrPsen) to the abnormal protease-resistant form, PrP-res. Here we identify porphyrins and phthalocyanines as inhibitors of PrP-res accumulation. The most potent of these tetrapyrroles had IC 50 values of 0.5-1 M in scrapie-infected mouse neuroblastoma (ScNB) cell cultures. Inhibition was observed without effects on protein biosynthesis in general or PrP-sen biosynthesis in particular. Tetrapyrroles also inhibited PrPres formation in a cell-free reaction composed predominantly of hamster PrP-res and PrP-sen. Inhibitors were found among phthalocyanines, deuteroporphyrins IX, and meso-substituted porphines; examples included compounds containing anionic, neutral protic, and cationic peripheral substituents and various metals. We conclude that certain tetrapyrroles specifically inhibit the conversion of PrP-sen to PrP-res without apparent cytotoxic effects. The inhibition observed in the cell-free conversion reaction suggests that the mechanism involved direct interactions of the tetrapyrrole with PrP-res and͞or PrP-sen. These findings introduce a new class of inhibitors of PrP-res formation that represents a potential source of therapeutic agents for transmissible spongiform encephalopathies.

Hot spots in prion protein for pathogenic conversion

“…Over the past 10 years there have been various efforts to find out small compounds to reduce PrP Sc population. These include porphyrins (26,27), Congo red and its derivatives (28)(29)(30), acridine and phenothiazine derivatives (17,31,32), heparan sulfate (33), aminoglycan, and polyamines (34,35). Simultaneously, various technological developments have been reported including structure-based drug design (36) followed by the structure-activity relationship study (37), small interfering RNA (38), library screening (18), high-throughput screening (39), chimeric ligand approach (40), and so on.…”

Pharmacological chaperone for the structured domain of human prion protein

“…Indeed, the ability of anionic tetrapyrroles to stack in solution correlated well with their antiprion activity (31). In contrast, the cationic porphyrin Fe(III)-TMPyP [Fe(III) meso-tetra (N-methyl-4-pyridyl) porphine] has good antiprion activity in cell culture (32) and animal models (33) in spite of its preference for the monomeric state (34) and its positive charge, suggesting this porphyrin may have a different mode of action.…”

Hemin Interactions and Alterations of the Subcellular Localization of Prion Protein

“…PrP Sc is generated post-translationally from the normal cellular prion protein (PrP C ) (12,13). Some inhibitory cTPs have been shown to bind to PrP C (10,14,15) and may thereby inhibit PrP Sc formation. These findings suggest that PrP C may also bind to physiological cTPs, such as hemin.…”

“…1), have potent activity against transmissible spongiform encephalopathies or prion diseases (8 -11). The anti-transmissible spongiform encephalopathy mechanism of action of cTPs appears to be inhibition of the formation of abnormal prion protein (PrP Sc ) (10), which is the primary component of the infectious agent of these diseases. PrP Sc is generated post-translationally from the normal cellular prion protein (PrP C ) (12,13).…”