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.

Albumin-based drug designs for pharmacokinetic modulation.

INTRODUCTION: A poor pharmacokinetic profile due to inadequate distribution and rapid renal clearance limits site-specific target engagement and drug efficacy. The inherent properties of human serum albumin for broad tissue distribution, prolonged circulation, and ligand transport have been engineered into albumin-based drug designs to modulate the pharmacokinetics to increase efficacy and reduce the frequency of dose. AREAS COVERED: This review highlights albumin structural features, ligand binding, and molecular interactions key to albumin-drug designs and an overview of the repertoire of albumin-drugs and approaches, with focus on pharmacokinetics of marketed products and clinical trials. EXPERT OPINION: Comparison, and advantages as well as disadvantages of the endogenous albumin-binding versus recombinant albumin construct approach, and half-life extension and intracellular drug delivery applications. The section addresses current challenges and solutions to the different drug designs, and considerations needed to progress the field such as conjugation chemistries, drug loading, and animal models. The section highlights the need for a paradigm shift in the field from 'utilizing' to 'controlling' albumin transport with recombinant human albumin variants engineered for tuned affinity to albumin cellular receptors.