Eliška Rydvalová

The increasing prevalence of multidrug-resistant bacteria necessitates innovative antibiotic strategies beyond the discovery of new active compounds. Here, we report N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer–ciprofloxacin conjugates combining controlled drug release with siderophore-mediated targeting via a deferoxamine–Fe³⁺ (DFX–Fe) complex. The conjugates differed in linker type (non-cleavable amide vs. reductively cleavable disulfide) and in the presence of the DFX–Fe targeting unit. Non-cleavable conjugates showed strongly reduced antibacterial activity, whereas disulfide-linked systems enabled the release of chemically intact and biologically active ciprofloxacin under reducing conditions. DFX–Fe targeting significantly enhanced the efficacy of non-cleavable conjugates, while modulating drug release kinetics in cleavable systems due to the redox activity of Fe³⁺. Antibacterial activity against Escherichia coli and Staphylococcus aureus strongly depended on the conjugate structure and bacterial species. Importantly, in a macrophage intracellular infection model, stimuli-responsive conjugates exhibited high bactericidal activity, reducing intracellular bacteria to below 1% at a 2× MIC concentration. This observation indicates the great potential of these nanotherapeutics in the treatment of challenging bacterial infections. All systems showed good biocompatibility toward human fibroblasts. Overall, this study highlights the critical roles of linker cleavability and siderophore-mediated targeting in the design of polymeric antibiotics for intracellular bacterial infections.

In this report, we synthesized hexagonal NaYF₄:Yb,Er upconverting nanoparticles (UCNPs) of 171 nm in size with a narrow particle size distribution. To address their colloidal stabi-lity in aqueous media and to incorporate a photosensitizer that can produce reactive singlet oxygen (¹O₂) to kill tumor cells, UCNPs were conjugated with 6-bromohexanoic acid-functionalized Rose Bengal (RB) and coated with PEG-alendronate (PEG-Ale). The particles were thoroughly characterized by transmission electron microscopy, dynamic light scattering, ATR FTIR, X-ray photoelectron spectroscopy, thermogravimetric analysis, and spectrofluorometry, and ¹O₂ formation was detected using a 9,10-diphenylanthracene spectrophotometric probe. Cytotoxicity determination on rat mesenchymal stem cells by using the MTT assay showed that neutralization of the large positive surface charge of neat UCNPs with PEG-Ale and the bound RB sensitizer significantly reduced the concentration-dependent cytotoxicity. The presented strategy shows great potential for the use of these particles as a novel agent for the photodynamic therapy of tumors.

Giant unilamellar polymer vesicles (GUPVs) capable of selectively delivering protected payloads into intracellular environments and releasing them in stimuli-triggered, precise spatially and temporally controlled manners are attractive bioactive cargo delivery tools. Herein, we present highly size-defined and monodisperse (42.1 ± 1.2, 60.5 ± 1.0, 80.4 ± 1.4 and 97.9 ± 1.2 μm in diameter, respectively) pH-responsive giant GUPVs prepared via microfluidic droplet generation using a flow-focusing poly(dimethylsiloxane) (PDMS)-based microfluidic device. Poly(ethylene oxide)-block-poly[2-(diisopropylamino)ethyl methacrylate] (PEO-b-PDPA) is a pH-responsive polymer that was synthesized via reversible addition–fragmentation chain-transfer (RAFT) polymerization and used in combination with poly(ethylene oxide)-block-poly(1,2-butadiene) (PEO-b-PBD) to produce homogeneous pH-responsive giant GUPVs. To demonstrate the spatiotemporal control provided by this approach, we studied in detail the pH-responsiveness of GUPVs according to the disruption and release of dye cargo under distinct acidic conditions using fluorescence confocal microscopy. This approach can be utilized to fabricate pH-responsive delivery systems for various active compounds, microreactors, and artificial organelles, thereby paving the way towards cell mimicry.

High-quality upconverting NaYF₄:Yb³⁺,Er³⁺ nanoparticles (UCNPs; 26 nm in diameter) based on lanthanides were synthesized by a high-temperature coprecipitation method. The particles were modified by bisphosphonate-terminated poly(ethylene glycol) (PEG) and Rose Bengal (RB) photosensitizer. The particles were thoroughly characterized using transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, FTIR, and X-ray photoelectron and upconversion luminescence spectroscopy in terms of morphology, hydrodynamic size, composition, and energy transfer to the photosensitizer. Moreover, the singlet oxygen generation from RB-containing UCNPs was investigated using 9,10-diphenylanthracene probe under 980 nm excitation. The cytotoxicity of UCNPs before and after conjugation with RB was evaluated on highly sensitive rat mesenchymal stem cells (rMSCs) and significant differences were found. Correspondingly, consi-derable variations in viability were revealed between the irradiated and non-irradiated rat glioma cell line (C6) exposed to RB-conjugated UCNPs. While the viability of rMSCs was not affected by the presence of UCNPs themselves, the cancer C6 cells were killed after the irradiation at 980 nm due to the reactive oxygen species (ROS) production, thus suggesting the potential of RB-conjugated PEG-modified UCNPs for applications in photodynamic therapy of cancer.

Multimodal gadolinium fluoride nanoparticles belong to potential contrast agents useful for bimodal optical fluorescence and magnetic resonance imaging. However, the metallic nature of the nanoparticles, similarly to some paramagnetic iron oxides, might induce allergic and anaphylactic reactions in patients after administration. A reduction of these adverse side effects is a priority for the safe application of the nanoparticles. Herein, we prepared paramagnetic poly(4-styrenesulfonic acid-co-maleic acid) (PSSMA)-stabilized GdF₃ nanoparticles with surface modified by Atto 488-labeled poly(styrene-grad-2-dimethylaminoethyl acrylate)-block-poly(2-dimethylaminoethyl acrylate) (PSDA-A488) with reactive amino groups for introduction of an additional imaging (luminescence) modality and possible targeting of anticancer drugs. The saturation magnetization of GdF₃@PSSMA particles according to SQUID magnetometry reached 157 Am² kg⁻¹ at 2 K and magnetic field of 7 T. GdF₃@PSSMA-PSDA-A488 nanoparticles were well tolerated by human cervical adenocarcinoma (HeLa), mouse bone marrow-derived mast cells (BMMC), and rat basophilic mast cells (RBL-2H3); the particles also affected cell morphology and protein tyrosine phosphorylation in mast cells. Moreover, the nanoparticles interfered with the activation of mast cells by multivalent antigens and inhibited calcium mobilization and cell degranulation. These findings show that the new multimodal GdF₃-based nanoparticles possess properties useful for various imaging methods and might minimize mast cell degranulation incurred after future nanoparticle diagnostic administration.