Protein Nanoparticles Encapsulating Doxorubicin as a pH-Dependent Drug Delivery System

Our research has focused on engineering a 25 nm dodecahedron protein scaffold from the E2 subunit of pyruvate dehydrogenase (PDH) multienzyme complex of B. stearothermophilus as a drug delivery system. To encapsulate drug molecules into the hollow cavity of the protein scaffold, we genetically introduced 60 cysteines to the internal surface of E2 scaffold (D381C). Green fluorescent dye Alexa Fluor^® 532 (AF532) and the antitumor drug doxorubicin (DOX) were successfully encapsulated into the cavity of D381C through maleimide groups. The pH dependent hydrolysis of hydrazone linkage allowed 90% doxorubicin release from D381C within 72 hrs at pH 5.0.  Cellular response to this drug carrier was investigated and results showed significant cellular uptake and therapeutic efficacy.  We confirmed the cellular uptake of AF532 coupled and DOX-coupled D381C by fluorescent imaging and observed significant therapeutic efficacy for DOX-coupled D381C.