Ralf Klingenstein

Tricyclic antidepressants, quinacrine and a novel, synthetic chimera thereof clear prions by destabilizing detergent-resistant membrane compartments

Prion diseases are invariably fatal, neurodegenerative diseases transmitted by an infectious agent, PrPSc, a pathogenic, conformational isoform of the normal prion protein (PrPC). Heterocyclic compounds such as acridine derivatives like quinacrine abolish prion infectivity in a cell culture model of prion disease. Here, we report that these compounds execute their antiprion activity by redistributing cholesterol from the plasma membrane to intracellular compartments, thereby destabilizing membrane domains. Our findings are supported by the fact that structurally unrelated compounds with known cholesterol‐redistributing effects – U18666A, amiodarone, and progesterone – also possessed high antiprion potency. We show that tricyclic antidepressants (e.g. desipramine), another class of heterocyclic compounds, displayed structure‐dependent antiprion effects and enhanced the antiprion effects of quinacrine, allowing lower doses of both drugs to be used in combination. Treatment of ScN2a cells with quinacrine or desipramine induced different ultrastructural and morphological changes in endosomal compartments. We synthesized a novel drug from quinacrine and desipramine, termed quinpramine, that led to a fivefold increase in antiprion activity compared to quinacrine with an EC50 of 85 nm. Furthermore, simvastatin, an inhibitor of cholesterol biosynthesis, acted synergistically with both heterocyclic compounds to clear PrPSc. Our data suggest that a cocktail of drugs targeting the lipid metabolism that controls PrP conversion may be the most efficient in treating Creutzfeldt‐Jakob disease.

Quinpramine is a novel compound effective in ameliorating brain autoimmune disease

Acridine-iminodibenzyl chimeric compounds were previously introduced as a class of cholesterol-redistributing substances with antiprion effects. Here, we show that administration of the lead compound quinpramine to mice with experimental autoimmune encephalitis, an animal model of multiple sclerosis (MS), significantly ameliorates disease in preventive and therapeutic paradigms. Quinpramine treatment decreased the number of inflammatory CNS lesions, antigen-specific T-cell proliferation, and pro-inflammatory cytokines IFNgamma and IL-17. Quinpramine is thus an immunoregulatory drug that is a candidate pharmaceutical for MS.

Structure-activity relationship of tocopherol derivatives suggesting a novel non-antioxidant mechanism in antiprion potency.

Beneficial effects of tocopherols, or vitamin E, on degenerative brain conditions have been attributed mainly to their antioxidant effects. Non-antioxidant effects of the tocopherols have been shown to be mediated by inhibition of protein kinase C (PKC) signaling. Prion disease is a paradigmatic protein conformational disease characterized by the induced conversion of a normal host protein PrP(C) to adopt a pathogenic conformation PrP(Sc). The molecular regulation of prion replication is poorly understood. Here, we show that tocopherols inhibit prion replication by a structure-activity relationship for antiprion activity independent of antioxidant activity with tocopherol succinate (TS) posessing highest EC(50) at 7 microM. Only TS but not an equally antiprion active PKC inhibitor could be partially antagonized by substochiometric 1 nM rapamycin suggesting that there are pathways via mammalian target of rapamycin (mTOR) that interfere with tocopherols biological effects. Interaction with the mTOR pathway is a yet undescribed characteristic of tocopherol derivatives, potentially significant for pathophysiological processes other than prion propagation.

Hybrid Molecules Synergistically Acting Against Protein Aggregation Diseases

An emerging common feature of the age-associated neurodegenerative disorders like Alzheimers disease (AD) and Creutzfeldt-Jakob disease (CJD) is the ability of many disease-associated protein aggregates to induce conversion of a normal counterpart conformer leading to an acceleration of disease progression. Curative pharmacotherapy has not been achieved so far despite successes in elucidating pathomechanisms. Here, we review the pharmaceutical strategy of generating hybrid compounds, i.e. compounds consisting of several independently acting moieties with synergistic effects, on key molecular players in AD and CJD. For prion diseases, we review hybrid compounds consisting of two different heterocyclic compounds, their synergistic effects on prion replication in a cell culture model and their ability to prolong survival of experimentally prion-infected mice in vivo. While a combination therapy of several antiprion compounds including quinacrine, clomipramine, simvastatin and tocopherol prolonged survival time to 10-25%, administration of hybrid compound quinpramine alone, a chimera of acridine and iminodibenzyl scaffolds, led to 10% survival time extension. For AD, we review a hybrid compound consisting of an Aβ recognizing D-peptide fused to a small molecule β-sheet breaker, an aminopyrazole. This molecule was able to diminish Aβ oligomers in cell culture and significantly decrease synaptotoxicity as measured by miniature excitatory postsynaptic responses in vitro. Hybrid compounds can dramatically increase potency of their single moieties and lead to novel functions when they act in a simultaneous or sequential manner thereby revealing synergistic properties. Their systematic generation combining different classes of compounds from peptides to small molecules has the potential to significantly accelerate drug discovery.