Selectivity of cation transport across lipid membranes by the antibiotic salinomycin

Area of Science:

• Biochemistry
• Membrane Biophysics
• Pharmacology

Background:

• Salinomycin is an ionophoric antibiotic undergoing preclinical evaluation for various cancers, including breast cancer.
• Its therapeutic efficacy is linked to ion selectivity, but data remain limited.
• Understanding ion transport mechanisms is vital for its application in cancer therapy.

Purpose of the Study:

• To investigate the cation selectivity of salinomycin.
• To elucidate the mechanism of salinomycin's ion transport across lipid bilayers.
• To correlate ion selectivity with potential anti-cancer activity.

Main Methods:

• Utilized artificial bilayer lipid membranes (BLM) to measure electrical potential changes.
• Employed a protonophore and a pH-sensitive dye (pyranine) in liposomes for fluorescence measurements.
• Assessed cation binding using thallium ion fluorescence quenching in methanol.
• Measured Ca2+ transport in liposomes and mitochondria using the Fluo-5N dye.

Main Results:

• Established the ion selectivity order: K+ > Na+ > Rb+ > Cs+ > Li+ using BLM and liposome assays.
• Demonstrated effective binding of salinomycin to potassium (K+) and calcium (Ca2+) ions.
• Showed poor binding to sodium (Na+) and lithium (Li+) ions.
• Confirmed salinomycin's ability to transport Ca2+ across liposome and mitochondrial membranes at high concentrations.

Conclusions:

• Salinomycin exhibits distinct cation selectivity, with a preference for K+ and Ca2+.
• These ion transport properties are fundamental to its anti-cancer mechanisms.
• The findings support further research into salinomycin's selective cytotoxicity against cancer stem cells.