Lipossomas contendo ácido ursólico: desenvolvimento, caracterização química e físico-química e avaliação da citotoxicidade

Abstract

Ursolic acid (UA) is a triterpene that has been shown significant antitumor activity. However, UA presents a low solubility in aqueous medium, which presents a barrier to its biological applications due to pharmacokinetic limitations related to the administration and bioavailability. The use of liposomes presents a promising strategy to overcome this inconvenience.Thereby, the aims of this work were the development, physicochemical characterization and evaluation of the stability of long-circulating and pH-sensitive liposomes containing ursolic acid (SpHL-UA), as well as the investigation of their cytotoxicity. The results of this study showed that the SpHL-UA presented adequate properties including a mean diameter of 191.1 ± 6.4 nm, a zeta potential of 1.2 ± 1.4 mV, and an amount of UA entrapped equal to 0.77 ± 0.01 mg/mL. The images of SpHL-UA obtained by TEM showed vesicles of varying diameters, but with a predominance of vesicle sizes of less than 100 nm. Moreover, this formulation showed a good stability after storage at 4 C for 1 year. Studies of Differential Scanning Calorimetry (DSC) and Small Angle X-ray Scattering (SAXS), under low hydration conditions, revealed interactions between UA and the lipid bilayer without compromising the phase transitions of the structural lipid of SpHL-UA, dioleoylphosphatidylethanolamine (DOPE). SAXS studies, under higher hydration conditions, revealed that the UA interaction with the lipid membrane of the liposomes resulted in an increased stability at the lamellar phase, thus hindering the occurrence of the lamellar to hexagonal phase transition under conditions of low pH. It was also observed that UA promoted greater stabilization of the lipid bilayer toward interactions with components of the biological medium which may represent an advantage, since the formulation would suffer minor changes in the bloodstream. The viability studies on breast (MDA-MB-231) and prostate (LNCaP) cancer cell lines demonstrated that, after 48h, SpHL-UA treatment significantly inhibited cancer cell proliferation. These results suggest that SpHL-UA may represent a promising alternative to intravenous administration of UA in cancer treatment.