Cholesterol Anchors Enable Efficient Binding and Intracellular Uptake of DNA Nanostructures

Geometrically constrained cytoskeletal reorganisation modulates DNA nanostructures uptake

DNA nanostructures (DNs) have gained popularity in various biomedical applications due to their unique properties, including structural programmability, ease of synthesis and functionalization, and low cytotoxicity. Effective utilization of DNs in biomedical applications requires a fundamental understanding of their interactions with living cells and the mechanics of cellular uptake. Current knowledge primarily focuses on how the physicochemical properties of DNs, such as mass, shape, size, and surface functionalization, affect uptake efficacy. However, the role of cellular mechanics and morphology in DN uptake remains largely unexplored. In this work, we show that cells subjected to geometric constraints remodel their actin cytoskeleton, resulting in differential mechanical force generation that facilitates DN uptake. The length, number, and orientation of F-actin fibers are influenced by these constraints, leading to distinct mechanophenotypes. Overall, DN uptake is governed by F-actin forces arising from filament reorganisation under geometric constraints. These results underscore the importance of actin dynamics in the cellular uptake of DNs and suggest that leveraging geometric constraints to induce specific cell morphology adaptations could enhance the uptake of therapeutically designed DNs.

Folding and Functionalizing DNA Origami: A Versatile Approach Using a Reactive Polyamine

DNA nanotechnology is a powerful synthetic approach to crafting diverse nanostructures through self-assembly. Chemical decoration of such nanostructures is often required to tailor their properties for specific applications. In this Letter, we introduce a pioneering method to direct the assembly and enable the functionalization of DNA nanostructures using an azide-bearing functional polyamine. We first demonstrate the successful polyamine-assisted folding of a scaffolded DNA origami nanostructure equipped with reactive azide groups. Leveraging this reactivity, we next showcase the decoration of the DNA origami via strain-promoted azide-alkyne cycloaddition with dibenzocyclooctyne-containing functional molecules. Specifically, we incorporate a fluorophore (Cy5), polyethylene glycol (PEG), and a hydrophobic phosphatidylethanolamine (PE) tag to tailor the properties of our DNA origami nanostructures. Our approach is expected to streamline and reduce the cost of chemical customization of intricate DNA nanostructures, paving the way for enhanced versatility and applicability.

Cholesterol-Modified DNA Nanostructures Serve as Effective Non-Viral Carriers for Delivering siRNA to the Kidneys to Prevent Acute Kidney Injury

With the emergence of gene therapy utilizing viral vectors, the potential risks associated with these vectors have prompted increased attention toward non-viral alternatives. DNA nanotechnology enables the assembly of specific oligonucleotide chains into nanostructures possessing defined spatial configurations. Due to their inherent characteristics, DNA nanostructures possess natural advantages as carriers for regulating gene expression in a non-viral manner. Cholesterol modification can convert DNA nanostructures from hydrophilic materials to amphiphilic materials, thereby extending their systemic circulation time. In this study, the high-dimensional design and cholesterol modification are shown to prolong the systemic circulation half-life of DNA nanostructures in mice. Specifically, the tetrahedron structure modified with three cholesterol molecules (TDN-3Chol) exhibit excellent circulation time and demonstrate a preference for renal uptake. The unique characteristics of TDN-3Chol can effectively deliver p53 siRNA to the mouse renal tubular tissue, resulting in successful knockdown of p53 and demonstrating its potential for preventing acute kidney injury. Furthermore, TDN-3Chol is not exhibited significant toxicity in mice, highlighting its promising role as a non-viral vector for targeted gene expression regulation in the kidneys. The designed non-viral vector as a prophylactic medication shows potential in addressing the current clinical challenges associated with nephrotoxic drugs.

Cell-Surface Binding of DNA Nanostructures for Enhanced Intracellular and Intranuclear Delivery

DNA nanostructures (DNs) have found increasing use in biosensing, drug delivery, and therapeutics because of their customizable assembly, size and shape control, and facile functionalization. However, their limited cellular uptake and nuclear delivery have hindered their effectiveness in these applications. Here, we demonstrate the potential of applying cell-surface binding as a general strategy to enable rapid enhancement of intracellular and intranuclear delivery of DNs. By targeting the plasma membrane via cholesterol anchors or the cell-surface glycocalyx using click chemistry, we observe a significant 2 to 8-fold increase in the cellular uptake of three distinct types of DNs that include nanospheres, nanorods, and nanotiles, within a short time frame of half an hour. Several factors are found to play a critical role in modulating the uptake of DNs, including their geometries, the valency, positioning and spacing of binding moieties. Briefly, nanospheres are universally preferable for cell surface attachment and internalization. However, edge-decorated nanotiles compensate for their geometry deficiency and outperform nanospheres in both categories. In addition, we confirm the short-term structural stability of DNs by incubating them with cell medium and cell lysate. Further, we investigate the endocytic pathway of cell-surface bound DNs and reveal that it is an interdependent process involving multiple pathways, similar to those of unmodified DNs. Finally, we demonstrate that cell-surface attached DNs exhibit a substantial enhancement in the intranuclear delivery. Our findings present an application that leverages cell-surface binding to potentially overcome the limitations of low cellular uptake, which may strengthen and expand the toolbox for effective cellular and nuclear delivery of DNA nanostructure systems.

Assessing the influence of small structural modifications in simple DNA-based nanostructures on their role as drug nanocarriers

DNA nanotechnology leverages Watson-Crick-Franklin base-pairing interactions to build complex DNA-based nanostructures (DNS). Due to DNA specific self-assembly properties, DNS can be designed with a total control of their architecture, which has been demonstrated to have an impact on the overall DNS features. Indeed, structural properties such as the shape, size and flexibility of DNS can influence their biostability as well as their ability to internalise into cells. We present here two series of simple DNS with small and precise variations related to their length or flexibility and study the influence that these structural changes have on their overall properties as drug nanocarriers. Results indicate that shorter and more flexible DNS present higher stability towards nuclease degradation. These structural changes also have a certain effect on their cell internalisation ability and drug release rate. Consequently, drug-loaded DNS cytotoxicity varies according to the design, with lower cell viability values obtained in the DNS exhibiting faster drug release and larger cell interaction rates. In summary, small changes in the structure of simple DNS can have an influence on their overall capabilities as drug nanocarriers. The effects reported here could guide the design of simple DNS for future therapeutic uses.

Heterochiral modifications enhance robustness and function of DNA in living human cells

Oligonucleotide therapeutics are becoming increasingly important as more are approved by the FDA, both for treatment and vaccination. Similarly, dynamic DNA nanotechnology is a promising technique that can be used to sense exogenous input molecules or endogenous biomarkers and integrate the results of multiple sensing reactions in situ via a programmed cascade of reactions. The combination of these two technologies could be highly impactful in biomedicine by enabling smart oligonucleotide therapeutics that can autonomously sense and respond to a disease state. A particular challenge, however, is the limited lifetime of standard nucleic acid components in living cells and organisms due to degradation by endogenous nucleases. In this work, we address this challenge by incorporating mirror-image, ʟ-DNA nucleotides to produce heterochiral "gapmers". We use dynamic DNA nanotechnology to show that these modifications keep the oligonucleotide intact in living human cells for longer than an unmodified strand. To this end, we used a sequential transfection protocol for delivering multiple nucleic acids into living human cells while providing enhanced confidence that subsequent interactions are actually occurring within the cells. Taken together, this work advances the state of the art of ʟ-nucleic acid protection of oligonucleotides and DNA circuitry for applications in vivo.

Nucleic acid amphiphiles: Synthesis, properties, and applications

Nucleic acid amphiphiles, referring to nucleic acids modified with large hydrophobic groups, have been widely used in programmable bioengineering. Since nucleic acids are intrinsically hydrophilic, the hydrophobic groups endow nucleic acid amphiphiles with unique properties, such as self-assembling, interactions with artificial or biological membranes, and transmembrane transport. Importantly, the hybridization or target binding capability of oligonucleotide itself supplies nucleic acid amphiphiles with excellent programmability. As a result, this type of molecule has attracted considerable attention in academic studies and has enormous potential for further applications. For a comprehensive understanding of nucleic acid amphiphiles, we review the reported research on nucleic acid amphiphiles from their molecular design to final applications, in which we summarize the synthetic strategies for nucleic acid amphiphiles and draw much attention to their unique properties in different contexts. Finally, a summary of the applications of nucleic acid amphiphiles in drug development, bioengineering, and bioanalysis are critically discussed.

Programming Aggregate States of DNA Nanorods with Sub-10 nm Hydrophobic Patterns for Tunable Cell Entry

The intracellular application of DNA nanodevices is challenged by their inadequate cellular entry efficiency, which may be addressed by the development of amphiphilic DNA nanostructures. However, the impact of the spatial distribution of hydrophobicity in cell entry has not been fully explored. Here, we program a spectrum of amphiphilic DNA nanostructures displaying diverse sub-10 nm patterns of cholesterol, which result in distinct aggregate states in the aqueous solution and thus varied cell entry efficiencies. We find that the hydrophobic patterns can lead to discrete aggregate states, from monomers to low-number oligomers (n = 1-6). We demonstrate that the monomers or oligomers with moderate hydrophobic density are preferred for cell entry, with up to ∼174-fold improvement relative to unmodified ones. Our study provides a new clue for the rational design of amphiphilic DNA nanostructures for intracellular applications.

Nucleic acid nanostructures for in vivo applications: The influence of morphology on biological fate

The development of programmable biomaterials for use in nanofabrication represents a major advance for the future of biomedicine and diagnostics. Recent advances in structural nanotechnology using nucleic acids have resulted in dramatic progress in our understanding of nucleic acid-based nanostructures (NANs) for use in biological applications. As the NANs become more architecturally and functionally diverse to accommodate introduction into living systems, there is a need to understand how critical design features can be controlled to impart desired performance in vivo. In this review, we survey the range of nucleic acid materials utilized as structural building blocks (DNA, RNA, and xenonucleic acids), the diversity of geometries for nanofabrication, and the strategies to functionalize these complexes. We include an assessment of the available and emerging characterization tools used to evaluate the physical, mechanical, physiochemical, and biological properties of NANs in vitro. Finally, the current understanding of the obstacles encountered along the in vivo journey is contextualized to demonstrate how morphological features of NANs influence their biological fates. We envision that this summary will aid researchers in the designing novel NAN morphologies, guide characterization efforts, and design of experiments and spark interdisciplinary collaborations to fuel advancements in programmable platforms for biological applications.

Ethane groups modified DNA nanopores to prolong the dwell time on live cell membranes for transmembrane transport

Transmembrane transport, mostly relying on biological channels, is crucial for the metabolic processes of live cells including sensing, signaling, cellular communicating and molecular transport. Artificial biomimetic channels offer excellent opportunities for studying the mechanisms of the metabolic processes of live cells and promote the applications of gene transfection, drug delivery, and regulations of cellular communications. DNA nanopores can be designed flexibly and operated easily while maintaining good biocompatibility, offering a good candidate for applications in basic research. However, because of the small size and good biocompatibility of DNA nanopores, it is still difficult to form stable channels on the plasma membrane of live cells by DNA nanopores. As a result, it significantly limits the applications of DNA nanopores in vivo. Thus, in this work, we have constructed ethane-phosphorothioate (PPT) groups modified DNA nanopores (E-DNA nanopores) to simulate biological channels for the transmembrane transport of small molecules. The E-DNA nanopores were found to be more hydrophobic and stable to anchor at the plasma membrane of live cells for a longer time window for subsequent transmembrane transport after the modification of ethane-PPT groups. The membrane-spanning E-DNA nanopores with a longer dwell time window could inspire the design of new DNA nanostructures and expand their biological applications including biosensing and sequencing, construction of artificial cells and regulation of transmembrane transport.

Recent Advances in DNA-Based Cell Surface Engineering for Biological Applications

Due to its excellent programmability and biocompatibility, DNA molecule has unique advantages in cell surface engineering. Recent progresses provide a reliable and feasible way to engineer cell surfaces with diverse DNA molecules and DNA nanostructures. The abundant form of DNA nanostructures has greatly expanded the toolbox of DNA-based cell surface engineering and gave rise to a variety of novel and fascinating applications. In this review, we summarize recent advances in DNA-based cell surface engineering and its biological applications. We first introduce some widely used methods of immobilizing DNA molecules on cell surfaces and their application features. Then we discuss the approaches of employing DNA nanostructures and dynamic DNA nanotechnology as elements for creating functional cell surfaces. Finally, we review the extensive biological applications of DNA-based cell surface engineering and discuss the challenges and prospects of DNA-based cell surface engineering.

DNA-assisted selective electrofusion (DASE) of Escherichia coli and giant lipid vesicles

Synthetic biology and cellular engineering require chemical and physical alterations, which are typically achieved by fusing target cells with each other or with payload-carrying vectors. On one hand, electrofusion can efficiently induce the merging of biological cells and/or synthetic analogues via the application of intense DC pulses, but it lacks selectivity and often leads to uncontrolled fusion. On the other hand, synthetic DNA-based constructs, inspired by natural fusogenic proteins, have been shown to induce a selective fusion between membranes, albeit with low efficiency. Here we introduce DNA-assisted selective electrofusion (DASE) which relies on membrane-anchored DNA constructs to bring together the objects one seeks to merge, and applying an electric impulse to trigger their fusion. The DASE process combines the efficiency of standard electrofusion and the selectivity of fusogenic nanostructures, as we demonstrate by inducing and characterizing the fusion of spheroplasts derived from Escherichia coli bacteria with cargo-carrying giant lipid vesicles.

The interactions between DNA nanostructures and cells: A critical overview from a cell biology perspective

DNA nanotechnology has yielded remarkable advances in  composite materials with diverse applications in biomedicine. The specificity and predictability of building 3D structures at the nanometer scale make DNA nanotechnology a promising tool for uses in biosensing, drug delivery, cell modulation, and bioimaging. However, for successful translation of DNA nanostructures to real-world applications, it is crucial to understand how they interact with living cells, and the consequences of such interactions. In this review, we summarize the current state of knowledge on the interactions of DNA nanostructures with cells. We identify key challenges, from a cell biology perspective, that influence progress towards the clinical translation of DNA nanostructures. We close by providing an outlook on what questions must be addressed to accelerate the clinical translation of DNA nanostructures. STATEMENT OF SIGNIFICANCE: Self-assembled DNA nanostructures (DNs) offers unique opportunities to overcome persistent challenges in the nanobiotechnology field. However, the interactions between engineered DNs and living cells are still not well defined. Critical systematization of current cellular models and biological responses triggered by DNs is a crucial foundation for the successful clinical translation of DNA nanostructures. Moreover, such an analysis will identify the pitfalls and challenges that are present in the field, and provide a basis for overcoming those challenges.

Minimizing Cholesterol-Induced Aggregation of Membrane-Interacting DNA Origami Nanostructures

DNA nanotechnology provides methods for building custom membrane-interacting nanostructures with diverse functions, such as shaping membranes, tethering defined numbers of membrane proteins, and transmembrane nanopores. The modification of DNA nanostructures with hydrophobic groups, such as cholesterol, is required to facilitate membrane interactions. However, cholesterol-induced aggregation of DNA origami nanostructures remains a challenge. Aggregation can result in reduced assembly yield, defective structures, and the inhibition of membrane interaction. Here, we quantify the assembly yield of two cholesterol-modified DNA origami nanostructures: a 2D DNA origami tile (DOT) and a 3D DNA origami barrel (DOB), by gel electrophoresis. We found that the DOT assembly yield (relative to the no cholesterol control) could be maximised by reducing the number of cholesterols from 6 to 1 (2 ± 0.2% to 100 ± 2%), optimising the separation between adjacent cholesterols (64 ± 26% to 78 ± 30%), decreasing spacer length (38 ± 20% to 95 ± 5%), and using protective ssDNA 10T overhangs (38 ± 20% to 87 ± 6%). Two-step folding protocols for the DOB, where cholesterol strands are added in a second step, did not improve the yield. Detergent improved the yield of distal cholesterol configurations (26 ± 22% to 92 ± 12%), but samples re-aggregated after detergent removal (74 ± 3%). Finally, we confirmed functional membrane binding of the cholesterol-modified nanostructures. These findings provide fundamental guidelines to reducing the cholesterol-induced aggregation of membrane-interacting 2D and 3D DNA origami nanostructures, improving the yield of well-formed structures to facilitate future applications in nanomedicine and biophysics.

Functionalizing DNA nanostructures for therapeutic applications

Recent advances in nanotechnology have enabled rapid progress in many areas of biomedical research, including drug delivery, targeted therapies, imaging, and sensing. The emerging field of DNA nanotechnology, in which oligonucleotides are designed to self-assemble into programmable 2D and 3D nanostructures, offers great promise for further advancements in biomedicine. DNA nanostructures present highly addressable and functionally diverse platforms for biological applications due to their ease of construction, controllable architecture and size/shape, and multiple avenues for chemical modification. Both supramolecular and covalent modification with small molecules and polymers have been shown to expand or enhance the functions of DNA nanostructures in biological contexts. These alterations include the addition of small molecule, protein, or nucleic acid moieties that enable structural stability under physiological conditions, more efficient cellular uptake and targeting, delivery of various molecular cargos, stimulus-responsive behaviors, or modulation of a host immune response. Herein, various types of DNA nanostructure modifications and their functional consequences are examined, followed by a brief discussion of the future opportunities for functionalized DNA nanostructures as well as the barriers that must be overcome before their translational use. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures.

Protein Corona Inhibits Endosomal Escape of Functionalized DNA Nanostructures in Living Cells

DNA nanostructures (DNs) can be designed in a controlled and programmable manner, and these structures are increasingly used in a variety of biomedical applications, such as the delivery of therapeutic agents. When exposed to biological liquids, most nanomaterials become covered by a protein corona, which in turn modulates their cellular uptake and the biological response they elicit. However, the interplay between living cells and designed DNs are still not well established. Namely, there are very limited studies that assess protein corona impact on DN biological activity. Here, we analyzed the uptake of functionalized DNs in three distinct hepatic cell lines. Our analysis indicates that cellular uptake is linearly dependent on the cell size. Further, we show that the protein corona determines the endolysosomal vesicle escape efficiency of DNs coated with an endosome escape peptide. Our study offers an important basis for future optimization of DNs as delivery systems for various biomedical applications.

Membrane-Interacting DNA Nanotubes Induce Cancer Cell Death

DNA nanotechnology offers to build nanoscale structures with defined chemistries to precisely position biomolecules or drugs for selective cell targeting and drug delivery. Owing to the negatively charged nature of DNA, for delivery purposes, DNA is frequently conjugated with hydrophobic moieties, positively charged polymers/peptides and cell surface receptor-recognizing molecules or antibodies. Here, we designed and assembled cholesterol-modified DNA nanotubes to interact with cancer cells and conjugated them with cytochrome c to induce cancer cell apoptosis. By flow cytometry and confocal microscopy, we observed that DNA nanotubes efficiently bound to the plasma membrane as a function of the number of conjugated cholesterol moieties. The complex was taken up by the cells and localized to the endosomal compartment. Cholesterol-modified DNA nanotubes, but not unmodified ones, increased membrane permeability, caspase activation and cell death. Irreversible inhibition of caspase activity with a caspase inhibitor, however, only partially prevented cell death. Cytochrome c-conjugated DNA nanotubes were also efficiently taken up but did not increase the rate of cell death. These results demonstrate that cholesterol-modified DNA nanotubes induce cancer cell death associated with increased cell membrane permeability and are only partially dependent on caspase activity, consistent with a combined form of apoptotic and necrotic cell death. DNA nanotubes may be further developed as primary cytotoxic agents, or drug delivery vehicles, through cholesterol-mediated cellular membrane interactions and uptake.

Accessing and Assessing the Cell-Surface Glycocalyx Using DNA Origami

The cell-surface glycocalyx serves as a physiological barrier regulating cellular accessibility to macromolecules and other cells. Conventional glycocalyx characterization has largely been morphological rather than functional. Here, we demonstrated direct glycocalyx anchoring of DNA origami nanotiles and performed a comprehensive comparison with traditional origami targeting to the phospholipid bilayer (PLB) using cholesterol. While DNA nanotiles effectively accessed single-stranded DNA initiators anchored on the glycocalyx, their accessibility to the underlying PLB was only permitted by extended nanotile-to-initiator spacing or by enzymatic glycocalyx degradation using trypsin or pathogenic neuraminidase. Thus, the DNA nanotiles, being expelled by the physiologic glycocalyx, provide an effective functional measure of the glycocalyx barrier integrity and faithfully predict cell-to-cell accessibility during DNA-guided multicellular assembly. Lastly, the glycocalyx-anchoring mechanism enabled enhanced cell-surface stability and cellular uptake of nanotiles compared to PLB anchoring. This research lays the foundation for future development of DNA nanodevices to access the cell surface.

Hydrophobic Interactions between DNA Duplexes and Synthetic and Biological Membranes

Equipping DNA with hydrophobic anchors enables targeted interaction with lipid bilayers for applications in biophysics, cell biology, and synthetic biology. Understanding DNA-membrane interactions is crucial for rationally designing functional DNA. Here we study the interactions of hydrophobically tagged DNA with synthetic and cell membranes using a combination of experiments and atomistic molecular dynamics (MD) simulations. The DNA duplexes are rendered hydrophobic by conjugation to a terminal cholesterol anchor or by chemical synthesis of a charge-neutralized alkyl-phosphorothioate (PPT) belt. Cholesterol-DNA tethers to lipid vesicles of different lipid compositions and charges, while PPT DNA binding strongly depends on alkyl length, belt position, and headgroup charge. Divalent cations in the buffer can also influence binding. Our MD simulations directly reveal the complex structure and energetics of PPT DNA within a lipid membrane, demonstrating that longer alkyl-PPT chains provide the most stable membrane anchoring but may disrupt DNA base paring in solution. When tested on cells, cholesterol-DNA is homogeneously distributed on the cell surface, while alkyl-PPT DNA accumulates in clustered structures on the plasma membrane. DNA tethered to the outside of the cell membrane is distinguished from DNA spanning the membrane by nuclease and sphingomyelinase digestion assays. The gained fundamental insight on DNA-bilayer interactions will guide the rational design of membrane-targeting nanostructures.

Tumor-Targeting Cholesterol-Decorated DNA Nanoflowers for Intracellular Ratiometric Aptasensing

Probing endogenous molecular profiles is of fundamental importance to understand cellular function and processes. Despite the promise of programmable nucleic-acid-based aptasensors across the breadth of biomolecular detection, target-responsive aptasensors enabling intracellular detection are as of yet infrequently realized. Several challenges remain, including the difficulties in quantification/normalization of quencher-based intensiometric signals, stability issues of the probe architecture, and complex sensor operations often necessitating extensive structural modeling. Here, the biomimetic crystallization-empowered self-assembly of a tumor-targetable DNA-inorganic hybrid nanocomposite aptasensor is presented, which enables Förster resonance energy transfer (FRET)-based quantitative interpretation of changes in the cellular target abundance. Leveraging the design programmability and high-throughput fabrication of rolling circle amplification-driven DNA nanoarchitecture, this designer platform offers a method to self-assemble a robust nanosensor from a multifunctionality-encoded template that includes a cell-targeting aptamer, a ratiometric aptasensor, and a cholesterol-decorating element. Taking prostate cancer cells and intracellular adenosine triphosphate molecules as a model system, a synergistic effect in the targeted delivery by cholesterol and aptamers, and the feasibility of quantitative intracellular aptasensing are demonstrated. It is envisioned that this approach provides a highly generalizable strategy across wide-ranging target systems toward a biologically deliverable nanosensor that enables quantitative monitoring of the abundance of endogenous biomolecules.

Synthetic DNA for Cell-Surface Engineering

The cell membrane is not only a physical barrier, but also a functional organelle that regulates the communication between a cell and its environment. The ability to functionalize the cell membrane with synthetic molecules or nanostructures would advance cellular functions beyond what evolution has provided. The aim of this Minireview is to introduce recent progress in using synthetic DNA and DNA-based nanostructures for cell-surface engineering. We first introduce chemical conjugation and physical binding methods for monovalent and polyvalent surface engineering. We then introduce the application of these methods for either the promotion or inhibition of cell-environment communication in numerous applications, including the promotion of cell-cell recognition, regulation of intracellular pathways, protection of therapeutic cells, and sensing of the intracellular and extracellular microenvironments. Lastly, we summarize current challenges existing in this area and potential solutions to solve these challenges.

Strategies to target bioactive molecules to subcellular compartments. Focus on natural compounds

Many potential pharmacological targets are present in multiple subcellular compartments and have different pathophysiological roles depending on location. In these cases, selective targeting of a drug to the relevant subcellular domain(s) may help to sharpen its impact by providing topological specificity, thus limiting side effects, and to concentrate the compound where needed, thus increasing its effectiveness. We review here the state of the art in precision subcellular delivery. The major approaches confer "homing" properties to the active principle via permanent or reversible (in pro-drug fashion) modifications, or through the use of special-design nanoparticles or liposomes to ferry a drug(s) cargo to its desired destination. An assortment of peptides, substituents with delocalized positive charges, custom-blended lipid mixtures, pH- or enzyme-sensitive groups provide the main tools of the trade. Mitochondria, lysosomes and the cell membrane may be mentioned as the fronts on which the most significant advances have been made. Most of the examples presented here have to do with targeting natural compounds - in particular polyphenols, known as pleiotropic agents - to one or the other subcellular compartment.