Thermodynamics of doxorubicin - bile salt association: An investigation based on isothermal titration calorimetry

Association of doxorubicin (DOX), a positively charged anthracycline, with bile salts (sodium cholate, NaC; sodium deoxycholate, NaDC, and sodium taurodeoxy cholate, NaTDC) has been studied by isothermal titration calorimetry (ITC). These bile salts form micelles in physiological conditions, and subsequent micellization parameters vary in accordance to their hydrophobicity. In this study, we show that thermodynamics of micellization of bile salts can be modulated via incorporation of DOX and changes in solution temperature. DOX incorporation was accompanied with reduction in critical micelle concentration (CMC) of bile salts. This was mediated through expulsion of structured water from the hydrophobic part of bile salt, and it was verifiable from the appearance of additional thermodynamic events in demicellization process. Interestingly, free energy of bile salts increased upon adding DOX which is suggestive of loss in the spontaneity of their micellization following this association. We assert that micelle formation in case of bile salt – DOX complex may not have occurred instantly. Instead, it was preceded by a bile salt - DOX equilibrium as a result of changes in the interfacial characteristics of bile salts in question. [Display omitted] •Thermodynamics of micellization of bile salts in association with doxorubicin has been studied.•Characterizations have been performed using isothermal titration calorimetry.•Aggregation behavior of specific DOX-bile salt complex appeared to be driven by the steric factors.•DOX-bile salt aggregates of a defined morphology can be used as anticancer therapeutics.