Strategies in the design of endosomolytic agents for facilitating endosomal escape in nanoparticles

Nanoparticles (NPs) are one of the leading and promising technologies for gene and drug delivery. However, despite continuous advancements in the delivery of NPs, endosomal escape remains a major issue and a matter of grave concern for developing an efficient and targeted delivery system for therapeutic applications. Most of NPs generally follow endocytic pathway for internalization into the cells. Following the internalization process, NPs must escape into the cell cytoplasm for evading degradation by hydrolytic enzymes present in the lysosomes. Various types of lipids have been used in the past viz. fusogenic lipid dioleoylphosphatidylethanolamine (DOPE), pH-sensitive lipids, cationic lipid and multiple charges containing lipid to escape from endosomes. Recently, several novel polymers, pH-sensitive peptides, proteins and many others endosomolytic agents have been identified and developed for incorporating into gene and drug delivery system to facilitate endosomal escape. In this review, endosomal escape mechanisms of different types of NPs have been discussed in detail and compared with endosomal escape mechanisms of viruses and other synthetic gene delivery systems to escape from endosomes. Also, the designing of endosomolytic agents to facilitate endosomal escape based on different approaches and strategies is explored. Moreover, this review article highlights the recent advancements in the development of NPs equipped with endosomolytic agents including its future directions and applications in the field of nanomedicine.