An Albumin-Holliday Junction Biomolecular Modular Design for Programmable Multifunctionality and Prolonged Circulation.

Combinatorial properties such as long-circulation and site- and cell-specific engagement need to be built into the design of advanced drug delivery systems to maximize drug payload efficacy. This work introduces a four-stranded oligonucleotide Holliday Junction (HJ) motif bearing functional moieties covalently conjugated to recombinant human albumin (rHA) to give a "plug-and-play" rHA-HJ multifunctional biomolecular assembly with extended circulation. Electrophoretic gel-shift assays show successful functionalization and purity of the individual high-performance liquid chromatography-purified modules as well as efficient assembly of the rHA-HJ construct. Inclusion of an epidermal growth factor receptor (EGFR)-targeting nanobody module facilitates specific binding to EGFR-expressing cells resulting in approximately 150-fold increased fluorescence intensity determined by flow cytometric analysis compared to assemblies absent of nanobody inclusion. A cellular recycling assay demonstrated retained albumin-neonatal Fc receptor (FcRn) binding affinity and accompanying FcRn-driven cellular recycling. This translated to a 4-fold circulatory half-life extension (2.2 and 0.55 h, for the rHA-HJ and HJ, respectively) in a double transgenic humanized FcRn/albumin mouse. This work introduces a novel biomolecular albumin-nucleic acid construct with extended circulatory half-life and programmable multifunctionality due to its modular design.