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 nano- medicine due to their tunable properties. However, the formation of vesicles during the preparation of cubo- somes, 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 crys- tallinity 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.