Tuning structure and morphology of lipidic cubosomes by encapsulation of novel porphyrin-derivatives

Cubosomes are non-lamellar lipid nanoparticles that have drawn a significant attention in the field of nanomedicine due to their tunable properties. However, the formation of vesicles during the preparation of cubosomes, and the presence of mixed bicontinuous cubic phases, may lead to artifacts and lack of correlation between the physico-chemical and biological characterization. In this work, we have formulated cubosomes composed by monoolein as building block and triblock copolymer Pluronic® F108 as a stabilizer, encapsulating three porphyrin derivatives: two attached to bile acid moieties and one to a tetrapeptide to be used for potential theranostic applications. First, the effect of the cargo concentration (0.25, 0.50 and 1.00 mg/mL, for all three molecules) was evaluated on the structure, showing that the bile acid derivatives did not affect the self-assembly of the lipid providing only Pn3m phases; however, a mixed phase Pn3m + Im3m and a subsequent loss in crystallinity were induced by increasing concentrations of the tetrapeptide derivative. Overall, the encapsulation of the three molecules at 25 and 37 ^∘C did not affect neither the hydrodynamic size nor the polydispersity of the cubosomes, influencing mainly the ζ-potential - positive in the case of the tetrapeptide and negative for the bile acid derivatives. The samples formulated with 0.50 mg/mL exhibited higher colloidal stability over time, with no significant changes in size or ζ-potential for over a month. Interestingly, the formulations containing the bile acid derivatives displayed the typical morphology of cubosomes in solution and a reduced number of vesicles (ca. 60:40 as cubosomes-to-vesicles ratio), whereas the sample containing the porphyrin attached to the tetrapeptide led to a ratio of cubosomes-to-vesicles estimated as 26:74, similar to the results of the empty formulation. The experiments at body temperature highlighted that the structure of the different formulations was not affected in a significant manner with retention of the phases observed at room temperature. The promising physico-chemical properties, especially at body temperature, could make these samples suitable as nanoplatforms for drug delivery applications.