LAUSR

The vast majority of pharmaceuticals penetrate into tissues and cells regardless of their actual requirements for treatment. This leads to side effects, which restrict the use of drugs and require decrease of the treatment doses. In addition, many of potential pharmaceuticals cannot be used due to poor cell permeation, because their charge or large size limit their penetration through biological membranes. For these reasons, subcellular drug delivery became a rapidly growing area of research in the medical and pharmaceutical field. Many biologically active agents can be transported into a specific cell compartment in order to exert their activity or to achieve higher activity. There are drugs, like photosensitizers (Rosenkranz et al., 2000), radionuclides emitting short-range particles (Sobolev, 2018; Rosenkranz et al., 2020), anticancer, antimicrobial, and antiviral drugs (Torchilin, 2014), that can exert their maximum effect within a certain compartment. In spite of considerable progress in development of subcellular delivery approaches, many types of biologically active molecules, potentially exploitable in clinical settings, are on the waiting list. Special interest is attracted by approaches to make macromolecules, like antibodies (Slastnikova et al., 2018), aptamers (Marshall and Wagstaff) or natural regulatory proteins, e.g., transcription factors (Ulasov et al., 2018) cell-penetrable and capable to specifically interact with subcellular target molecules of choice within the target cells. All the above agents could be named as locally-acting ones, because their actions or interactions are limited to specific subcellular compartments; they also might need special delivering vehicles and can be employed for cell-specific impact. The main goal of this Research Topic is to highlight the current state of delivery vehicles for locally-acting drugs into target compartments of particular cells. Some previous achievements in this field were discussed in the Research Topic “Targeted Subcellular Delivery of Anti-Cancer Agents” published in “Frontiers in Pharmacology” (2018-2019). The most recent findings and reviews of new ideas to show the way forward in developing strategies to efficiently deliver drugs to specific subcellular sites of target cells are presented in this Research Topic. Intracellular membrane trafficking pathways, which promote the transport of the active molecule into the subcellular locations, have a fundamental importance for design of subcellular targeting. This issue is discussed in detail in the review article by Kumar and colleagues (Kumar et al.). Another task of intracellular targeted delivery for treatment of a number of diseases, particularly cancer, is design of highly specific molecular targeting. DNA aptamer molecules are a rapidly growing tool in this field that can be applied for specific cell surface targeting, subsequent internalization and interaction with intracellular target molecules (Marshall and Wagstaff). Currently, aptamers have a few limitations to overcome before they can be broadly