A Novel Pseudo-Protein-Based Biodegradable Nanomicellar Platform for the Delivery of Anticancer Drugs

Amino acid-based poly(ester amide)s are a new family of biodegradable polymers that exhibit “pseudo-protein” characteristics and the structural varieties of poly(ester amide)s make them hold great potential in multiple biomedical applications. In this study, a lysine-phenylalanine-based pseudo-protein is developed as the self-assembled nanomicellar carrier for efficient delivery of doxorubicin. The lysine moieties from the pseudo-protein provide available sites for further functionalization, and methylcoumarin is introduced for easy and photocontrollable crosslinking, to effectively improve the micellar stability in serum containing environment and against dilution. However, photocrosslinks do not bring in any barrier for the intracellular release of doxoubicin. Doxorubicin release is significantly accelerated by proteolytic enzyme, due to the biodegradability of pseudo-protein micelles. In addition, pseudo-protein delivery system exhibits unique interactions with HCT116 human colon cancer cells. Doxorubicin loaded in pseudo-protein micelles colocalizes with mitochondria and endolysosomes, while free doxorubicin is distributed only in the nuclei. Doxorubicin-loaded pseudo-protein micelles stimulate increased level of intracellular reactive oxygen species and mitochondrial damage. Free doxorubicin induces conditional apoptosis in HCT116 cells between 0.5× 10⁻⁶ and 2 × 10⁻⁶ m, while DOX loaded in pseudo-protein micelles induces apoptosis over a higher/broader concentration range (2 × 10⁻⁶–10 × 10⁻⁶ m).