Identification of a Cardiac Glycoside Exhibiting Favorable Brain Bioavailability and Potency for Reducing Levels of the Cellular Prion Protein

Abstract

Several strands of investigation have established that a reduction in the levels of the cellular prion protein (PrPC) is a promising avenue for the treatment of prion diseases. We recently described an indirect approach for reducing PrPC levels that targets Na,K-ATPases (NKAs) with cardiac glycosides (CGs), causing cells to respond with the degradation of these pumps and nearby molecules, including PrPC. Because the therapeutic window of widely used CGs is narrow and their brain bioavailability is low, we set out to identify a CG with improved pharmacological properties for this indication. Starting with the CG known as oleandrin, we combined in silico modeling of CG binding poses within human NKA folds, CG structure-activity relationship (SAR) data, and predicted blood–brain barrier (BBB) penetrance scores to identify CG derivatives with improved characteristics. Focusing on C4′-dehydro-oleandrin as a chemically accessible shortlisted CG derivative, we show that it reaches four times higher levels in the brain than in the heart one day after subcutaneous administration, exhibits promising pharmacological properties, and suppresses steady-state PrPC levels by 84% in immortalized human cells that have been differentiated to acquire neural or astrocytic characteristics. Finally, we validate that the mechanism of action of this approach for reducing cell surface PrPC levels requires C4′-dehydro-oleandrin to engage with its cognate binding pocket within the NKA α subunit. The improved brain bioavailability of C4′-dehydro-oleandrin, combined with its relatively low toxicity, make this compound an attractive lead for brain CG indications and recommends its further exploration for the treatment of prion diseases.

Plant glycosyltransferases for expanding bioactive glycoside diversity

“…66 This class of compounds inhibits the Na + /K + -ATPase pumps, resulting in the improvement of cardiac contraction force, increasing left ventricular systolic function. 67 Due to the prevalence of their molecular target in various tissues, cardiotonic steroids have also been proposed as a possible treatment for cancer, 68 reducing cellular prion protein, 69 and intraocular pressure; 70 however, they also exhibit many potential systemic off-target effects. Thus, cardiotonic steroids' applications in therapeutics is challenging and limited to a small therapeutic window.…”

Selective (α)-l-Rhamnosylation and Neuroprotective Activity Exploration of Cardiotonic Steroids

“…Due to this effect, cardiotonic steroids digoxin and digitoxin have been essential therapeutics for the treatment of heart failure and arrhythmia. ,− However, the biological activity of cardenolides extends well beyond their cardiotonic activity. Among numerous other applications, cardiotonic steroids have been explored as potential therapeutic agents for the treatment of cancer, − viral infections, , neurodegenerative diseases, , and stroke − and as anti-inflammatory ,, and senolytic agents. Particularly interesting are the recent reports indicating that cardiotonic steroids, such as ouabain and digoxin, may influence the peripheral and central nervous systems.…”

Development of α-Selective Glycosylation with l-Oleandral and Its Application to the Total Synthesis of Oleandrin

“…The hot (Anvirzel) or cold (PBI-05204) extracts of Nerium oleander containing oleandrin have been recently explored in phase I and II clinical trials for the treatment of cancer and antiviral diseases including SARS-CoV-2 . In addition, oleandrin holds potential for the treatment of neurodegenerative diseases due to its unique ability to pass the blood–brain barrier and reduce the amount of cellular prion protein (PrP C ) in the brain . This improved brain bioavailability was attributed to the presence of the C16-acetate and α- l -oleandrose at the C3 position of oleandrin.…”