New method for recognition of sterol signalling molecules: Methinium salts as receptors for sulphated steroids

• Polymethinium receptors for sulphated steroids: opening new way of their detection.
• Dual mode of recognition: combination of electrostatic and hydrophobic interactions.
• A high selectivity and affinity for sulphated steroids against nonsulphated ones.
• A strong spectral response in the presence of sulphated steroids.

In this work, we studied indolium and benzothiazolium pentamethine salts 1–3 as novel type of receptors for the recognition of sulphated signalling molecules (sulphated steroids: oestrone, pregnenolone and cholesterol sulphate). A recognition study was performed in an aqueous medium (1 mM phosphate buffer (H2O:MeOH; 99:1 (v/v))) at pH 7.34. The tested salts displayed a high affinity for these sulphated analytes, mainly for cholesterol sulphate. However, no interaction between the salts and control, non-sulphated sterol analytes (cholesterol and bile acid) was observed. The highest affinity for the sulphated steroids was observed for benzothiazole salt 1. This salt also displayed different spectral behaviour from that observed for carbocyanine salts 2 and 3. In this presence of cholesterol sulphate, benzothiazole salt 1 displayed significant spectral changes depending on the medium used: a blue shift in the aqueous medium and a red shift in the methanolic one (H2O:MeOH; 2:1 (v/v)). Subsequently preliminary in vivo study showed that, salt 1 significantly inhibits a growth of breast carcinoma on Nu/nu mice model.

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