Nanocarriers for antibiotics: a promising solution to treat intracellular bacterial infections

Invasin-functionalized liposome nanocarriers improve the intracellular delivery of anti-infective drugs

Liposomes containing gentamicin and surface-functionalized with InvA497 showed a reduced infection load of both cytosolic and vacuolar intracellular bacteria.

Glyconanomaterials for Combating Bacterial Infections

Bacterial infections constitute an increasing problem to human health in response to build-up of resistance to present antibiotics and sluggish development of new pharmaceuticals. However, a means to address this problem is to pinpoint the drug delivery to-and into-the bacteria. This results in a high local concentration of the drug, circumventing the increasingly high doses otherwise necessary. Combined with other effectors, such as covalent attachment to carriers, rendering the drugs less degradable, and the combination with efflux inhibitors, old drugs can be revived. In this context, glyconanomaterials offer exceptional potential, since these materials can be tailored to accommodate different effectors. In this Concept article, we describe the different advantages of glyconanomaterials, and point to their potential in antibiotic "revitalization".

Poly(Propylene Imine) Dendrimers and Amoxicillin as Dual-Action Antibacterial Agents

Besides acting as antimicrobial compounds, dendrimers can be considered as agents that improve the therapeutic effectiveness of existing antibiotics. In this work we present a new approach to using amoxicillin (AMX) against reference strains of common Gram-negative pathogens, alone and in combination with poly(propylene imine) (PPI) dendrimers, or derivatives thereof, in which 100% of the available hydrogen atoms are substituted with maltose (PPI 100%malG3). The concentrations of dendrimers used remained in the range non-toxic to eukaryotic cells. The results indicate that PPI dendrimers significantly enhance the antibacterial effect of amoxicillin alone, allowing antibiotic doses to be reduced. It is important to reduce doses of amoxicillin because its widespread use in medicine could lead to the development of bacterial resistance and environmental pollution. This is the first report on the combined antibacterial activity of PPI surface-modified maltose dendrimers and amoxicillin.

Not just for tumor targeting: unmet medical needs and opportunities for nanomedicine

During the last 3 decades, nanomedicines have provided novel opportunities to improve the delivery of chemotherapeutics in cancer therapy effectively. However, many principles learnt from there have the potential to be transferred to other diseases. This perspective article, on the one hand, critically reflects the limitations of nanomedicines in tumor therapy and, on the other hand, provides alternative examples of nanomedicinal applications in immunotherapy, noninvasive drug deliveries across epithelial barriers and strategies to combat intra- and extra-cellular bacterial infections. Looking ahead, access to highly complex nanoparticular delivery vehicles given nowadays may allow further improved therapeutic concepts against several diseases in the future too.

Toward an optimized treatment of intracellular bacterial infections: input of nanoparticulate drug delivery systems

Intracellular pathogenic bacteria can lead to some of the most life-threatening infections. By evolving a number of ingenious mechanisms, these bacteria have the ability to invade, colonize and survive in the host cells in active or latent forms over prolonged period of time. A variety of nanoparticulate systems have been developed to optimize the delivery of antibiotics. Main advantages of nanoparticulate systems as compared with free drugs are an efficient drug encapsulation, protection from inactivation, targeting infection sites and the possibility to deliver drugs by overcoming cellular barriers. Nevertheless, despite the great progresses in treating intracellular infections using nanoparticulate carriers, some challenges still remain, such as targeting cellular subcompartments with bacteria and delivering synergistic drug combinations. Engineered nanoparticles should allow controlling drug release both inside cells and within the extracellular space before reaching the target cells.

An efficient system for intracellular delivery of beta-lactam antibiotics to overcome bacterial resistance

The "Golden era" of antibiotics is definitely an old story and this is especially true for intracellular bacterial infections. The poor intracellular bioavailability of antibiotics reduces the efficency of many treatments and thereby promotes resistances. Therefore, the development of nanodevices coupled with antibiotics that are capable of targeting and releasing the drug into the infected-cells appears to be a promising solution to circumvent these complications. Here, we took advantage of two natural terpenes (farnesyl and geranyl) to design nanodevices for an efficient intracellular delivery of penicillin G. The covalent linkage between the terpene moieties and the antibiotic leads to formation of prodrugs that self-assemble to form nanoparticles with a high drug payload between 55-63%. Futhermore, the addition of an environmentally-sensitive bond between the antibiotic and the terpene led to an efficient antibacterial activity against the intracellular pathogen Staphylococcus aureus with reduced intracellular replication of about 99.9% compared to untreated infected cells. Using HPLC analysis, we demonstrated and quantified the intracellular release of PenG when this sensitive-bond (SB) was present on the prodrug, showing the success of this technology to deliver antibiotics directly into cells.

Solvent selection causes remarkable shifts of the "Ouzo region" for poly(lactide-co-glycolide) nanoparticles prepared by nanoprecipitation

Polymer nanoparticles (NPs) offer versatile novel biological features of interest for drug delivery applications. "Ouzo diagrams" allowed for a systematic manufacture of specified colloidal formulations by the widely used nanoprecipitation process. Surprisingly, despite the well-documented relevance of the applied organic solvent for nanoprecipitation, its effect on the actual status of the "Ouzo region" was so far not studied. Herein, investigations were undertaken to account for the potential impact of the solvent type on the "Ouzo diagrams" for poly(lactide-co-glycolide) (PLGA) and tetrahydrofuran (THF), 1,4-dioxane, acetone and dimethyl sulfoxide (DMSO). The "Ouzo region" shifted considerably to higher polymer fractions upon solvent change (rank order: THF < 1,4-dioxane < acetone < DMSO). Assuming a one-to-one transformation of detached PLGA-bearing solvent droplets (droplet diameter for THF: ∼800 nm, 1,4-dioxane: ∼700 nm, acetone: ∼500 nm and DMSO: ∼300 nm) into non-divisible polymer aggregates upon solvent displacement, facilitated to predict the size of NPs found within the "Ouzo region" (size range: 40-200 nm). In conclusion, application of "Ouzo diagrams" is a valuable tool for drug delivery research and will most-likely replace the "trial-and-error"-approach to identify the operating window for the production of stable colloidal formulations by the nanoprecipitation technique.