An Albumin-Oligonucleotide Assembly for Potential Combinatorial Drug Delivery and Half-Life Extension Applications

Lipidated DNA Nanostructures Target and Rupture Bacterial Membranes

Chemistry has the power to endow supramolecular nanostructures with new biomedically relevant functions. Here it is reported that DNA nanostructures modified with cholesterol tags disrupt bacterial membranes to cause microbial cell death. The lipidated DNA nanostructures bind more readily to cholesterol-free bacterial membranes than to cholesterol-rich, eukaryotic membranes. These highly negatively charged, lipidated DNA nanostructures cause bacterial cell death by rupturing membranes. Strikingly, killing is mediated by clusters of barrel-shaped nanostructures that adhere to the membrane without the involvement of expected bilayer-puncturing barrels. These DNA nanomaterials may inspire the development of polymeric or small-molecule antibacterial agents that mimic the principles of selective binding and rupturing to help combat antimicrobial resistance.

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.

A Modular Albumin-Oligonucleotide Biomolecular Assembly for Delivery of Antisense Therapeutics

Antisense nucleic acid drugs are susceptible to nuclease degradation, rapid renal clearance, and short circulatory half-life. In this work, we introduce a modular-based recombinant human albumin-oligonucleotide (rHA-cODN) biomolecular assembly that allows incorporation of a chemically stabilized therapeutic gapmer antisense oligonucleotide (ASO) and FcRn-driven endothelial cellular recycling. A phosphodiester ODN linker (cODN) was conjugated to recombinant human albumin (rHA) using maleimide chemistry, after which a complementary gapmer ASO, targeting ADAMTS5 involved in osteoarthritis pathogenesis, was annealed. The rHA-cODN/ASO biomolecular assembly production, fluorescence labeling, and purity were confirmed using polyacrylamide gel electrophoresis. ASO release was triggered by DNase-mediated degradation of the linker strand, reaching 40% in serum after 72 h, with complete release observed following 30 min of incubation with DNase. Cellular internalization and trafficking of the biomolecular assembly using confocal microscopy in C28/I2 cells showed higher uptake and endosomal localization by increasing incubation time from 4 to 24 h. FcRn-mediated cellular recycling of the assembly was demonstrated in FcRn-expressing human microvascular endothelial cells. ADAMTS5 in vitro silencing efficiency reached 40%, which was comparable to free gapmer after 72 h incubation with human osteoarthritis patients' chondrocytes. This work introduces a versatile biomolecular modular-based "Plug-and-Play" platform potentially applicable for albumin-mediated half-life extension for a range of different types of ODN therapeutics.

Comparative studies of structure and dynamics of caprine, leporine, ovine, and equine serum albumins

Serum albumin (SA) is the most prevalent protein found in blood. Human albumin was used as an albumin substitute in hypoalbuminemia pets due to high sequence similarity. SAs from furry animals were also reported to be the major indoor allergens. Sensitizing to one of SAs coupled with high sequence identity can lead to cross-reactive antibodies in allergic individuals. Thus, understanding the structural and dynamic characters of SAs is crucial for not only albumin substitution but also allergen therapy. Herein, Molecular dynamics (MD) simulations were performed to elucidate the structural and dynamic dissimilarity and similarity of economic animals [equine (ESA), caprine (CASA), ovine (OSA), and leporine (LSA)] to albumins from human (HSA), bovine (BSA), porcine (PSA), and pets [cat (FSA) and dog (CSA)]. The aim is to explore the feasibility of HSA substitution and understand how albumins cause the cross-reactivity. Generally, all albumins studied here show the scissoring motion like other mammalian albumins. The uniqueness of each albumin is defined by different sequence identity of domain I. Also, the drug binding affinity of studied albumins differs from HSA, CSA, FSA, BSA, and PSA. Especially, LSA displays the most deviated behavior from the group. So, such albumin may not be suitable for albumin therapy for pets and humans. CASA, OSA, and ESA share similar characteristics, therefore it is possible to use them to monitor the osmotic pressure among their species, but the allergenic response must be seriously considered. An insight obtained here can be useful to develop albumin therapy and understand clinical allergy.Communicated by Ramaswamy H. Sarma.

Conformational variation of site specific glycated albumin: A Molecular dynamics approach

Human serum albumin (HSA) is a major cargo protein, which undergoes glycation in hyperglycaemic conditions and results in impaired function. In physiological conditions, HSA plays a crucial role in pharmacological activities such as drug transport or delivery through its binding capacity and also by its enzymatic activity, which enables the translation of pro-drugs into active drugs. In this study, the impact of the methylglyoxal-mediated glycation on dynamic behaviour of inter-domain motion, Cys34 reactivity, binding site residual interaction and secondary structure transition were investigated through molecular dynamics simulation. The alteration in inter-domain motion reflects the effect of glycation-mediated changes on the structural conformation of albumin. The binding site residue interactions and volume analysis revealed the impact of glycation on the geometry of the binding site. We also found the correlation of Cys34 reactivity with increase of turns in the region between Ia-h4 and Ia-h5. The rise in turn formation in that region keeps Tyr84 farther away from Cys34 which could lead to higher Cys34 reactivity. In parallel, significant alterations in alpha helical content of helices in the binding sites were observed. These structural and conformational changes in glycated albumin could be the causative agents for functional impairment which leads to diabetic complications.

Recent progress of aptamer‒drug conjugates in cancer therapy

Aptamers are single-stranded DNA or RNA sequences that can specifically bind with the target protein or molecule via specific secondary structures. Compared to antibody-drug conjugates (ADC), aptamer‒drug conjugate (ApDC) is also an efficient, targeted drug for cancer therapy with a smaller size, higher chemical stability, lower immunogenicity, faster tissue penetration, and facile engineering. Despite all these advantages, several key factors have delayed the clinical translation of ApDC, such as in vivo off-target effects and potential safety issues. In this review, we highlight the most recent progress in the development of ApDC and discuss solutions to the problems noted above.

Strategies for developing long-lasting therapeutic nucleic acid aptamer targeting circulating protein: The present and the future

Aptamers are short, single-stranded DNA or RNA oligonucleotide sequences that can bind specific targets. The molecular weight of aptamers (<20 kDa) is lower than the renal filtration threshold (30∼50 kDa), resulting in very short half-lives in vivo, which limit their druggability. The development of long-lasting modification approaches for aptamers can help address the druggability bottleneck of aptamers. This review summarized two distinct kinds of long-lasting modification approaches for aptamers, including macromolecular modification and low-molecular-weight modification. Though it is a current approach to extend the half-life of aptamers, the macromolecular modification approach could limit the space for the dosage increases, thus causing potential compliance concerns due to large molecular weight. As for the other modification approach, the low-molecular-weight modification approach, which uses low molecular weight coupling agents (LMWCAs) to modify aptamers, could greatly increase the proportion of aptamer moiety. However, some LMWCAs could bind to other proteins, causing a decrease in the drug amounts in blood circulation. Given these issues, the outlook for the next generation of long-lasting modification approaches was proposed at the end, including improving the administration method to increase dosage for aptamer drugs modified by macromolecule and developing Artificial intelligence (AI)-based strategies for optimization of LMWCAs.

Albumin Biomolecular Drug Designs Stabilized through Improved Thiol Conjugation and a Modular Locked Nucleic Acid Functionalized Assembly

Albumin-nucleic acid biomolecular drug designs offer modular multifunctionalization and extended circulatory half-life. However, stability issues associated with conventional DNA nucleotides and maleimide bioconjugation chemistries limit the clinical potential. This work aims to improve the stability of this thiol conjugation and nucleic acid assembly by employing a fast-hydrolyzing monobromomaleimide (MBM) linker and nuclease-resistant nucleotide analogues, respectively. The biomolecular constructs were formed by site-selective conjugation of a 12-mer oligonucleotide to cysteine 34 (Cys34) of recombinant human albumin (rHA), followed by annealing of functionalized complementary strands bearing either a fluorophore or the cytotoxic drug monomethyl auristatin E (MMAE). Formation of conjugates and assemblies was confirmed by gel shift analysis and mass spectrometry, followed by investigation of serum stability, neonatal Fc receptor (FcRn)-mediated cellular recycling, and cancer cell killing. The MBM linker afforded rapid conjugation to rHA and remained stable during hydrolysis. The albumin-nucleic acid biomolecular assembly composed of stabilized oligonucleotides exhibited high serum stability and retained FcRn engagement mediating FcRn-mediated cellular recycling. The MMAE-containing assembly exhibited cytotoxicity in the human MIA PaCa-2 pancreatic cancer cell line with an IC50 of 342 nM, triggered by drug release from breakdown of an acid-labile linker. In summary, this work presents rHA-nucleic acid module-based assemblies with improved stability and retained module functionality that further promotes the drug delivery potential of this biomolecular platform.

Efficient synthesis of 2'-O-methoxyethyl oligonucleotide - cationic peptide conjugates

Single-stranded phosphorothioate (PS) oligonucleotide drugs have shown potential for the treatment of several rare diseases. However, a barrier to their widespread use is that they exhibit activity in only a narrow range of tissues. One way to circumvent this constraint is to conjugate them to cationic cell-penetrating peptides (CPPs). Although there are several examples of morpholino and peptide nucleic acids conjugated with CPPs, there are noticeably few examples of PS oligonucleotide-CPP conjugates. This is surprising given that PS oligonucleotides presently represent the largest class of approved RNA-based drugs, including Nusinersen, that bears the 2'- O -methoxyethyl (MOE) chemistry. In this work, we report a method for in-solution conjugation of cationic, hydrophobic peptides or human serum albumin to a 22-nucleotide MOE-PS oligonucleotide. Conjugates were obtained in high yields and purities. Our findings pave the way for their large-scale synthesis and testing in vivo .

Roadmap on nanomedicine

Since the launch of the Alliance for Nanotechnology in Cancer by the National Cancer Institute in late 2004, several similar initiatives have been promoted all over the globe with the intention of advancing the diagnosis, treatment and prevention of cancer in the wake of nanoscience and nanotechnology. All this has encouraged scientists with diverse backgrounds to team up with one another, learn from each other, and generate new knowledge at the interface between engineering, physics, chemistry and biomedical sciences. Importantly, this new knowledge has been wisely channeled towards the development of novel diagnostic, imaging and therapeutic nanosystems, many of which are currently at different stages of clinical development. This roadmap collects eight brief articles elaborating on the interaction of nanomedicines with human biology; the biomedical and clinical applications of nanomedicines; and the importance of patient stratification in the development of future nanomedicines. The first article reports on the role of geometry and mechanical properties in nanomedicine rational design; the second articulates on the interaction of nanomedicines with cells of the immune system; and the third deals with exploiting endogenous molecules, such as albumin, to carry therapeutic agents. The second group of articles highlights the successful application of nanomedicines in the treatment of cancer with the optimal delivery of nucleic acids, diabetes with the sustained and controlled release of insulin, stroke by using thrombolytic particles, and atherosclerosis with the development of targeted nanoparticles. Finally, the last contribution comments on how nanomedicine and theranostics could play a pivotal role in the development of personalized medicines. As this roadmap cannot cover the massive extent of development of nanomedicine over the past 15 years, only a few major achievements are highlighted as the field progressively matures from the initial hype to the consolidation phase.

Aptamers: A Review of Their Chemical Properties and Modifications for Therapeutic Application

Aptamers are short, single-stranded oligonucleotides that bind to specific target molecules. The shape-forming feature of single-stranded oligonucleotides provides high affinity and excellent specificity toward targets. Hence, aptamers can be used as analogs of antibodies. In December 2004, the US Food and Drug Administration approved the first aptamer-based therapeutic, pegaptanib (Macugen), targeting vascular endothelial growth factor, for the treatment of age-related macular degeneration. Since then, however, no aptamer medication for public health has appeared. During these relatively silent years, many trials and improvements of aptamer therapeutics have been performed, opening multiple novel directions for the therapeutic application of aptamers. This review summarizes the basic characteristics of aptamers and the chemical modifications available for aptamer therapeutics.

Emerging applications of aptamers for anticoagulation and hemostasis

PURPOSE OF REVIEW

Since the selection of the first thrombin-binding aptamer in 1992, the use of nucleic acid aptamers to target specific coagulation factors has emerged as a valuable approach for generating novel anticoagulant and procoagulant therapeutics. Herein, we highlight the most recent discoveries involving application of aptamers for those purposes.

RECENT FINDINGS

Learning from the successes and pitfalls of the FIXa-targeting aptamer pegnivacogin in preclinical and clinical studies, the latest efforts to develop antidote-controllable anticoagulation strategies for cardiopulmonary bypass that avoid unfractionated heparin involve potentiation of the exosite-binding factor X (FX)a aptamer 11F7t by combination with either a small molecule FXa catalytic site inhibitor or a thrombin aptamer. Recent work has also focused on identifying aptamer inhibitors of contact pathway factors such as FXIa and kallikrein, which may prove to be well tolerated and effective antithrombotic agents in certain clinical settings. Finally, new approaches to develop procoagulant aptamers to control bleeding associated with hemophilia and other coagulopathies involve targeting activated protein C and tissue plasminogen activator.

SUMMARY

Overall, these recent findings exemplify the versatility of aptamers to modulate a variety of procoagulant and anticoagulant factors, along with their capacity to be used complementarily with other aptamers or drugs for wide-ranging applications.

Structural and Functional Stability of DNA Nanopores in Biological Media

DNA nanopores offer a unique nano-scale foothold at the membrane interface that can help advance the life sciences as biophysical research tools or gate-keepers for drug delivery. Biological applications require sufficient physiological stability and membrane activity for viable biological action. In this report, we determine essential parameters for efficient nanopore folding and membrane binding in biocompatible cell media. The parameters are identified for an archetypal DNA nanopore composed of six interwoven strands carrying cholesterol lipid anchors. Using gel electrophoresis and fluorescence spectroscopy, the nanostructures are found to assemble efficiently in cell media, such as LB and DMEM, and remain structurally stable at physiological temperatures. Furthermore, the pores’ oligomerization state is monitored using fluorescence spectroscopy and confocal microscopy. The pores remain predominately water-soluble over 24 h in all buffer systems, and were able to bind to lipid vesicles after 24 h to confirm membrane activity. However, the addition of fetal bovine serum to DMEM causes a significant reduction in nanopore activity. Serum proteins complex rapidly to the pore, most likely via ionic interactions, to reduce the effective nanopore concentration in solution. Our findings outline crucial conditions for maintaining lipidated DNA nanodevices, structurally and functionally intact in cell media, and pave the way for biological studies in the future.

A new class of recombinant human albumin with multiple surface thiols exhibits stable conjugation and enhanced FcRn binding and blood circulation

Human serum albumin is an endogenous ligand transport protein whose long circulatory half-life is facilitated by engagement with the human cellular recycling neonatal Fc receptor (hFcRn). The single free thiol located at Cys-34 in domain I of albumin has been exploited for monoconjugation of drugs. In this work, we increased the drug-to-albumin ratio potential by engineering recombinant human albumin (rHSA) variants with varying hFcRn affinity to contain three free, conjugation-competent cysteines. Structural analysis was used to identify positions for cysteine introduction to maximize rHSA stability and formation of the conjugated product without affecting hFcRn binding. The thiol rHSA variants exhibited up to 95% monomeric stability over 24 months and retained hFcRn engagement compared with a WT unconjugated control demonstrated by Biolayer Interferometry. The additional cysteines were further introduced into a panel of rHSA variants engineered with different affinities for hFcRn. After conjugation with three Alexa Fluor 680 (AF680) fluorophores, hFcRn binding was similar to that of the original triple-thiol nonconjugated rHSA variants (0.88 and 0.25 μm for WT albumin with or without 3xAF680 respectively, and 0.04 and 0.02 μm for a high hFcRn-binding variant with or without 3xAF680, respectively). We also observed a 1.3-fold increase in the blood circulatory half-life of a high hFcRn-binding triple-thiol variant conjugated with AF680 (t _½ = 22.4 h) compared with its WT counterpart (t _½ = 17.3 h) in mice. Potential high drug-to-albumin ratios combined with high hFcRn engagement are attractive features of this new class of albumins that offer a paradigm shift for albumin-based drug delivery.

Aptamer chemistry

Aptamers are single-stranded DNA or RNA molecules capable of tightly binding to specific targets. These functional nucleic acids are obtained by an in vitro Darwinian evolution method coined SELEX (Systematic Evolution of Ligands by EXponential enrichment). Compared to their proteinaceous counterparts, aptamers offer a number of advantages including a low immunogenicity, a relative ease of large-scale synthesis at affordable costs with little or no batch-to-batch variation, physical stability, and facile chemical modification. These alluring properties have propelled aptamers into the forefront of numerous practical applications such as the development of therapeutic and diagnostic agents as well as the construction of biosensing platforms. However, commercial success of aptamers still proceeds at a weak pace. The main factors responsible for this delay are the susceptibility of aptamers to degradation by nucleases, their rapid renal filtration, suboptimal thermal stability, and the lack of functional group diversity. Here, we describe the different chemical methods available to mitigate these shortcomings. Particularly, we describe the chemical post-SELEX processing of aptamers to include functional groups as well as the inclusion of modified nucleoside triphosphates into the SELEX protocol. These methods will be illustrated with successful examples of chemically modified aptamers used as drug delivery systems, in therapeutic applications, and as biosensing devices.

Harnessing albumin as a carrier for cancer therapies

Serum albumin, a natural ligand carrier that is highly concentrated and long-circulating in the blood, has shown remarkable promise as a carrier for anti-cancer agents. Albumin is able to prolong the circulation half-life of otherwise rapidly cleared drugs and, importantly, promote their accumulation within tumors. The applications for using albumin as a cancer drug carrier are broad and include both traditional cancer chemotherapeutics and new classes of biologics. Strategies for leveraging albumin for drug delivery can be classified broadly into exogenous and in situ binding formulations that utilize covalent attachment, non-covalent association, or encapsulation in albumin-based nanoparticles. These methods have shown remarkable preclinical and clinical successes that are examined in this review.