Figure 7.

Targeted delivery of cargo. The scheme illustrates some examples of the reported methods for the targeted cargo delivery and release inside the cell. (A) The expression of CP subunits containing the inserted SpyTag allows for the decoration of the P22 VLP WB particles with large molecules, such as affibodies for EGFR (EGFRaf) and HER2 (HER2af) modified with the SpyCatcher sequence. These modifications allow for the targeted delivery of Aldoxorubicin (AlDox), which can be bound to the WB particle interior/exterior surface through thiol-maleimide coupling with inserted cysteine residues (S133C or K118C, respectively). The ligands will interact with the particle’s specific receptor, promoting the particle’s endocytosis, and once inside the cell, the acidic pH will promote the cleaving of AlDox’s hydrazine crosslink between Dox and its maleimide moiety, resulting in the drug’s release [12]. (B) Another pH-dependent release strategy involves the use of a catechol-mal ligand to incorporate BTZ into P22 WB particles and release the dipeptide when submitted to low-pH conditions. After BTZ internalization, the loaded P22 WB particles were chemically modified with the peptide SP94 to HCCs, as the ligand binds to surface receptors of the tumoral cells. After internalization, the acid–diol complex that formed between BTZ’s boronic acid and catechol-mal’s maleimide moieties is undone, resulting in the release of the drug inside the cell [9]. (C) Other methods for the environmentally triggered release of cargo can exploit enzymes to propitiate drug exit, one example using the lysosomal cysteine CTB to promote the release of peptide cargo from within the P22 VLP after endocytosis. The NuBCP-9 and the KLAK therapeutic peptides were encapsulated in vivo into the P22 VLP by being inserted into the N-terminus of CP subunits and coexpressed with SP-EGFP fusion. The peptides were incorporated in an intermittent way with CP, and both therapeutic peptides were intercalated with linker sequences that can be cleaved by CTB. The loaded P22 VLP was chemically modified with cyclic RGD peptide, conferring specificity to αVβ3 and αVβ5 integrins. Once inside the cell, CTB cleaved the linker sequences and released the peptides into the cell [85].