A less stringent definition would include any materials with at least one dimension in the range 1–100 nm, thus including nanowires and nanotubes.In this introduction, I considered nanocarriers with at least one dimension smaller than 1000 nm and their use for the targeted delivery of active ingredients to achieve greater efficacy. I will focus on the translation of nanocarriers from the bench to the market in the medical, veterinary, and agricultural industries in order to describe the current landscape and potential future directions for active ingredient delivery systems. Specifically, I discuss research articles , patents , clinical trials , and commercially available nanocarrier formulations approved by: the US Food and Drug Administration and/or European Medicines Agency for medical use; the American Veterinary Medical Association for use in animals, i.e. products listed in the Approved Animal Drug Products and/or AVMA Animal Health Studies database; and the US Environmental Protection Agency , i.e. products listed in the National Pesticide Information Center database. Nanoparticles have also been used for diagnosis, drug discovery, gene delivery, immunotherapy, photothermal/photodynamic therapy, and biosensor applications, which are reviewed elsewhere.The term “nanotechnology” was coined in 1974 by the Japanese scientist Norio Taniguchi,nursery grow bag but the worldwide proliferation of nanotechnology started in the 1990s and has thus far led to the publication of more than 60,000 research articles in the pharmaceutical and environmental sciences.
More than 93% of these articles relate to medical research, whereas nanoparticles in agriculture and veterinary research emerged later in the 2010s and represent only ~4% and ~3% of the publications, respectively . Even so, the growing political and consumer interest in global food security and environmental protection is likely to drive additional research in the use of nanocarriers in agriculture and veterinary research in the future. Nanoparticle-based innovations also account for more than 150,000 patents . Since the Bayh-Dole Act was ratified in the United States, allowing small businesses, non-profit institutions, and universities to own inventions created via research funded by the federal government, the majority of these patents have been filed by universities. The University of California is the largest patent holder in this field, with more than 1200. Interestingly, 16% of all nanotechnology patents are held by the pharmaceutical sector, highlighting the growing interest in nanoparticles for drug delivery, diagnosis, and imaging. Nanocarriers for medical and veterinary applications are regulated by the FDA in the United States and the EMA in Europe. Since 1990, the FDA and EMA have approved 19 nanocarriers , and more candidates are undergoing pre-clinical and clinical testing . Most of these nanocarriers are administered orally or intravenously, and some transdermally. The materials used in these formulations include polymers, micelles, liposomes, proteins and viruses. Most clinical trials involve micellar formulations, whereas viruses account for only 1% . In contrast, most approved nanocarriers are based on liposomes , followed by viral , micellar , polymeric , and proteinaceous formulations . Most of these nanocarriers have demonstrated lower toxicity rather than improved efficacy compared to the active ingredient alone.Accordingly, novel nanocarriers may not survive clinical trials because they do not achieve greater efficacy and because the reduction in toxicity might be achieved using an already-approved nanocarrier formulation.
The regulation of nanocarriers for agricultural applications is not yet harmonized because a clear definition of agricultural nanocarriers has not yet been agreed, which makes it difficult to determine how many products are already commercialized. Such products are overseen by the EPA in the United States and the European Commission in Europe. In 2011, the EPA became the first regulatory agency to approve a nanopesticide, but this nanosilver-based product was approved as an antimicrobial agent for use in clothing, not for agricultural applications. The first true agricultural product was a nanoparticle formulation based on Tobacco mild green mosaic virus , which was approved by the EPA as a herbicide in the state of Florida for the treatment of tropical soda apple, an invasive weed.No commercialized agricultural nanoformulations for pesticide or fertilizer delivery are yet branded as nanocarriers. This is most likely a marketing strategy to deal with the unclear regulation of agricultural nanocarriers while ensuring public acceptance. However, 42 microencapsulated products have been approved by the EPA . Although most of these formulations are used as herbicides or insecticides, a growing body of literature has demonstrated the usefulness of nanocarriers based on clay, chitosan, silica, or zeolites for the delivery of fertilizers, as discussed elsewhere.The cargos delivered by nanocarriers include small molecules, peptides and proteins, nucleic acids, or combinations of the above. Small molecules are low-molecular-weight organic compounds with beneficial biological activities, such as cancer drugs, antibiotics, fertilizers and pesticides. Relevant examples in clinical and veterinary medicine include the antimetabolites paclitaxel and vincristine, the DNA intercalator doxorubicin, and the antibiotic amphotericin B. When delivered systemically, hydrophobic small molecules are rapidly metabolized and eliminated, narrowing their therapeutic window.
Large doses are therefore required for therapeutic efficacy, which in the case of cancer drugs can lead to off-target effects such as cardiotoxicity and nephrotoxicity.Similarly, only a small fraction of pesticides and fertilizers applied to fields ever reach their target, due to leaching, evaporation, photolysis, chemical hydrolysis, and bio-degradation. To feed the growing world population, today’s yields must increase by 60–100%, and this must be achieved in part by more effective treatment methods to eliminate pests and by increasing the efficiency of fertilizers.Peptide and protein pharmaceuticals may act as receptor agonists, essentially fulfilling the functions of endogenous molecules, whereas others act as antagonists. Neuroprotective proteins such as nerve growth factor and brain-derived neurotrophic factor are examples of agonists. They may help to combat Alzheimer’s disease and Parkinson’s disease, although they remain at the preclinical development stage.The blood brain barrier remains a major hurdle to deliver these proteins to the central nervous system, and nanocarriers have been engineered to deliver protein aceous active ingredients across the BBB.Small peptides and proteins are often unstable in vivo due to the presence of proteases, and may also be removed by renal filtration, reducing their bioavailability. Nanocarriers can also overcome this challenge. For example, the antimicrobial peptide HPA3PHis was delivered using aptamer-targeted gold nanoparticles, which led to the complete inhibition of Vibrio vulnificus colonization in infected mice.As well as stabilizing peptide and protein drugs with nanocarriers, multivalent display can be used as a strategy to enhance therapeutic efficacy,plastic growing bag as demonstrated by the delivery of TNF-related apoptosisinducing ligand using liposomal and plant viral nanoparticle formulations.For example, Herceptin is a mAb approved by the FDA for the treatment of HER2+ breast, gastric, and esophageal cancers by blocking HER2 receptor signaling.Herceptin is one of 59 therapeutic mAbs that have been approved since 1992, when the first mAb formulation was launched.Four antibody–drug conjugates have also been approved, with another 22 currently undergoing clinical trials.Antibody–nanoparticle conjugates can be targeted to specific cells using the properties of nanocarrier, the antibody, or both. Similarly, the target specificity of the antibody can be combined with the cargo-loading capacity of nanoparticles, which has proven effective in many research studies but has yet to be deployed successfully in the clinic.Nanoparticle-mediated antibody delivery is particularly useful when the target is intracellular.For example, a liposomal nanocarrier was designed to display CD44-specific antibodies on the surface in order to target CD44+ cells but to carry a second IL6R-specific antibody as a cargo, which was taken up by the target cells to inhibit the intracellular IL6R-Stat3 signaling pathway in mice with triple-negative breast cancer. The treated mice showed a significant reduction in metastatic events.Like antibodies, peptides and proteins can also be used as targeting ligands to direct nanoparticles to disease sites. Such ligands displayed on nanoparticles promote cell binding, internalization and endosomal escape, allowing the nanoparticles to accumulate and release their active ingredient within target cells while sparing healthy tissue from damage.However, actively targeted nanocarriers developed for the treatment of cancer have yet to progress beyond clinical trials.
Targeted nanoparticles are more complex than their passive counterparts, which makes them more difficult to produce according to good manufacturing practice and significantly increases the cost of therapy. Furthermore, it is unclear whether active targeting improves therapeutic efficacy. A meta-analysis of the literature over the past 10 years has shown that, onaverage, 0.9% of each dose of active nanocarriers reaches its target, compared to 0.6% for the passive nanocarriers.Finally, nucleic acids can be used as active agents in medical, veterinary and agricultural applications, particularly DNA, microRNA and short interfering RNA .30 Gene therapy in humans and domestic animals involves the delivery of DNA to the nucleus in order to augment or repair malfunctioning genes, whereas gene transfer to crops can introduce new functionalities, such as resistance to pests and diseases, or pesticide tolerance.MicroRNA is non-coding RNA ~20 nucleotides in length that regulates endogenous genes, and the delivery of miRNA to the cytoplasm of target cells can be used to suppress the expression of disease-causing genes.The delivery of non-coding double-stranded dsRNA or siRNA derived from it promotes the assembly of a protein complex that binds complementary mRNA, leading to its cleavage and the targeted suppression of gene expression. The systemic delivery of miRNA and siRNA is generally ineffective because such molecules are rapidly degraded and cleared, and often trigger an innate immune response, the exact nature of which is sequence dependent. Furthermore, miRNA and siRNA are hydrophilic and cannot penetrate the hydrophobic cell membrane to reach the cytoplasm. In the cytoplasm, they are rapidly degraded by nucleases and multiple doses are therefore needed to suppress gene expression enough for a therapeutic effect. The drawbacks of conventional nucleic acid therapies can be addressed by encapsulating them in nanocarriers and five such carriers have already reached the market . Genetic engineering has facilitated significant advances in human and veterinary medicine, and has also helped to improve the yield of crops by enhancing pest and disease resistance and abiotic stress tolerance.Most genetically engineered plants are produced by transformation using the soil bacterium Agrobacterium tumefaciens, which introduces DNA via a type IV secretion system, or by biolistic delivery systems, which introduce DNA by physically penetrating the cell wall using high-velocity metal particles. Nanocarrier-based delivery systems would need to find an alternative strategy to pass through the cell wall, and current research is focusing on the size, charge and surface properties of metallic, liposomal, silicon-based, and polymeric nanocarriers to enable cell wall penetration.The limitations of small molecules, peptides, proteins, and nucleic acids can be overcome by using nanocarriers to achieve three key goals: enhance the aqueous solubility and therefore bio-availability of active ingredients; increase the stability of active ingredients by inhibiting their degradation in vivo or in the environment, effectively increasing their half-life; and promote the accumulation of the active ingredient at the target site. If all three goals are achieved, the dose of active ingredient required for efficacy is greatly reduced, thus limiting overall costs and avoiding off-target effects. These goals can be achieved using nanocarriers made from a wide range of materials , which are discussed in more detail below.Liposomes are spherical vesicles comprising one or more concentric lipid bilayers with an aqueous core.These amphiphilic structures are uniquely suited to entrap both lipophilic and hydrophilic compounds, making them attractive nanocarriers for a diverse range of active ingredients. Hydrophobic ingredients can be inserted into the lipid bilayer or sequestered in the core, whereas hydrophilic ingredients can be encapsulated in the core. The lipid bilayer is usually composed of phospholipids and sterols such as cholesterol, the latter controlling membrane permeability and fluidity. In the medical and veterinary fields, conventional liposomal nanocarriers can reduce the off-target effects of active ingredients by modifying their pharmacokinetic properties and bio-distribution, promoting their accumulation at the target site and avoiding non-target tissues.Most liposomal nanocarriers deliver their cargo by fusing with the plasma membrane of the target cell, causing the active ingredient to be deposited in the cytoplasm. For example, Myocet is a conventional liposomal carrier approved by the EMA for the delivery of doxorubicin to metastatic breast cancer cells.Commercially available liposomal nanocarriers range from 30 to 1000 nm in diameter, which makes them the largest nanocarriers used in the clinic . The physicochemical properties of liposomes are determined by the lipid composition, sterol concentration, surface charge, and nanoparticle size.