Table 4.
Strategies implemented into MSNs for achieving enzyme-responsive drug delivery.
| Enzyme | Description | Reference |
|---|---|---|
| Peptides as Gatekeepers | ||
| CatB | Large peptidic sequences that close the mesopores and allow drug release upon enzymatic degradation | [341,345] |
| MMP-2 | [346,347] | |
| Peptide as Linkers | ||
| CatB | Short peptidic sequences employed to graft different types of bulky gatekeepers (small nanoparticles, proteins, nanovalves) to the surface of MSNs | [342,343,344] |
| MMP-2 | [348] | |
| MMP-9 | [349] | |
| MMP-13 | [351] | |
| Other Enzyme-Degradable Gatekeepers | ||
| MMP-9 | MSNs covered with a gelatin that degrade in the presence of MMP-9 | [350] |
| Hyaluronidase | MSNs functionalized with large carbohydrates (hyaluronic acid, chondroitin sulfate) that act simultaneously targeting agents and gatekeepers | [156,158,160,162,352] |
| Trypsin | MSNs gated with BSA, which can be degraded by overexpressed trypsin in liver cancer | [353] |
| Alkaline phosphatase | ATP-capped mesoporous silica-based materials that allow drug release upon enzymatic degradation of ATP | [354] |
| Esterases | MSNs functionalized with ester-containing gatekeepers that are degraded in the presence of such enzymes | [355,356,357] |