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26 February 2025 Inhalation plexes with a narrow size distribution, as visualized by transmission electron microscopy (TEM). Another advantageous aspect of a polymer-based NA carrier system is the possibility of active target- ing for precise uptake into individual cell types. For example, targeting lung epithelial cells with polysper- mine-based nanocarriers, which are modified with ACE2-antibodies or similar targeting strategies, can facilitate uptake into ACE2-expressing cells. By fol- lowing this approach, siRNA doses could be decreased, leading to a favorable profit-damage-profile of the drug. After successful uptake, siRNA must finally be released into the cytosol via endosomal escape mech- anisms to prevent degradation and ensure RNA can exert its biological effect [26]. is is the rationale behind the addition of lipophilic moieties like acyl- amines or oleylamines, which were shown to facil- itate endosomal escape through the transformation of a lamellar phase to a fusogenic hexagonal phase [23, 27]. Balancing RNA binding strength with the carrier system is further crucial for successful delivery and release, which is also supported by the addition of lipophilic moieties, as internal data are suggesting. Route and mode of administration: Pulmonary delivery via vibrating mesh nebulizers Pulmonary drug delivery offers several advantages over systemic administration, including a reduced first-pass effect, localized treatment with decreased systemic side effects and a non-invasive method of application. e lungs, with an extensive surface area of approximately 100 m 2 , present an optimal envi- rent work [6, 16]. Our main goal is prospectively to broaden its application. Initially, we will use com- puter-based genome analysis of commonly studied coronaviruses to identify sequences with the most significant effects on various CoV species. Addition- ally, we will focus on improving the delivery system by transitioning to more tolerable carrier systems, as discussed in the next section. The drug delivery system: Polymer-based nanoparticles Given we selected siRNA as our API in the previous section of this article, the subsequent focus must be directed towards optimizing its delivery. RNA mol- ecules are negatively charged due to their phosphate backbone, making cell membrane penetration nearly impossible for free siRNA. Delivery systems for RNA therapeutics are divided into viral and non-viral vec- tors. Although viral vectors like adeno-associated virus vectors have a high transfection efficiency and potency [17], their safety concerns include immu- nogenicity and insertional mutagenesis [18]. ere- fore, positively charged NA carrier systems, divided into lipid- and polymer-based materials, were devel- oped. In recent years, lipid-based gene delivery sys- tems, so-called lipid nanoparticles (LNPs), have gained great interest. Main components of LNPs are PEG-lipids, ionizable lipids, phospholipids and cho- lesterol. In particular, the ionizable lipids as a further development of permanently charged cationic lipids have significantly improved gene delivery efficiency of LNPs and are therefore the pivotal component [19]. However, recent literature shows that aerosolization of LNPs results in a change of physicochemical prop- erties due to their fragile nature [20, 21], which will also be discussed in the next section. Polymer-based vectors represent the second group of non-viral RNA delivery vectors. ey can be easily modified and con- sequently their properties can be adjusted as needed. In contrast to viral NA vectors, polymer-based vec- tors are suitable for large-scale production, more sta- ble during storage and cost-effective. Commonly used in polymeric siRNA delivery, PEI is known for in vitro gene delivery with high transfec- tion efficiencies and good buffering capacities but due to its high amine-density, often causes high toxicity [22]. erefore, other polymers with better toxicity profiles are being investigated. Biodegradable poly- mers, like poly(β-amino) esters (PBAEs), offer these benefits [23-25]. Recently developed PBAEs from our group, composed of lipophilic moieties and sper- mines, efficiently encapsulate RNA to protect it from degradation by serum nucleases. Spermine moieties form polyplexes with siRNA through their positively charged amino groups, which enhance encapsulation efficiency. Additionally, their natural occurrence, therefore biodegradability, reduces toxicity. As can be seen in Figure 2, these PBAE form well-defined poly- Figure 2 Transmission electron microscopy (TEM) images of PBAE polyplexes, which were reproduced from reference 25, licensed under a Creative Commons Attribution- NonCommercial 3.0 Unported Licence.