Selective binding of naphthoquinone derivatives to serum albumin proteins and their effects on cytotoxicity

•Selective binding of BSA or HSA with carboxylic acid tethered naphthoquinones are shown.•Pyridine tethered naphthoquinones selectively bind to BSA but do not bind to HSA.•BSA and HSA also show specificity in recognition of isomers of hydroxy and mercaptobenzoic acids.•The cytotoxicity of naphthoquinone derivatives improves on increase concentration of BSA in media.

Naphthoquinone derivatives such as lapachol, plumbagin, dichloroallyl lawsone show anticancer activity and generally cytotoxicity measurements are carried out in presence of bovine serum albumin; so understanding on the ability of serum albumin binding with such derivatives are essential. We have investigated cytotoxicity and serum albumin binding of a series of structurally related naphthoquinone derivatives. Substrate dependency and high selectivity in binding of naphthoquinone tethered carboxylic acids or pyridines with bovine serum albumin (BSA) and human serum albumin (HSA) are observed. For example, the binding constant of BSA with 3-(1,4-dihydro-2-methyl-1,4-dioxonaphthalen-3yl-thio)propanoic acid is ∼594 times higher than 3-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid; whereas 4-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid shows ∼367 times higher binding constant than the latter compound. The BSA weakly bind to pyridine tethered naphthoquinones, whereas HSA does not binds with them. The binding constant of HSA with 2-(1,4-dihydro-2-methyl-1,4-dioxonaphthalene-3-ylthio)benzoic acid is 134 times higher than the HSA binding constant with 2,2′-(1,4-dihydro-1,4-dioxo-naphthalen-2,3-diylthio)dipropanoic acid. Among the naphthoquinone carboxylic acids, the 3-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid binds selectively to BSA, but it does not bind to HSA. The 2-hydroxybenzoic acid or 4-mercaptobenzoic acid strongly binds to BSA. The binding of BSA with 4-hydroxybenzoic acid or 2-mercaptobenzoic acid are insignificant. We have not observed clear relationships of structure of naphthoquinone derivatives versus serum albumin binding, but could identify the compound having the best IC50 values of cytotoxicity among the twelve naphthoquinone compounds. The compound 3-(1,2-dihydro-1,2-dioxonaphthalen-4-yl-thio)propanoic acid in four cancer cell lines has IC50 values in the range 2.7–7.6 μM. This compound also has optimum binding constant with BSA (35.042 × 103 L mol−1) or HSA (21.427 × 103 L mol−1). The cytotoxicity values of the compounds were influenced by concentration of BSA.

Graphical abstractThe binding of serum albumin proteins to a series of pyridine or carboxylic acid tethered naphthoquinone derivatives as well as their cytotoxicity were studied. Substrate selectivity to protein binding was observed. The cytotoxicity of these compounds depends on BSA concentration. 3-(1,2-dihydro-1,2-dioxonaphthalen-4-yl-thio)propanoic acid shows IC50 values in four cancer cell lines in the range 2.7–7.6 μM. This compound also has optimum binding constant with BSA (35.042 × 103 L mol−1) or with HSA (21.427 × 103 L mol−1).Figure optionsDownload full-size imageDownload as PowerPoint slide