Prospects and challenges in intracellular delivery of therapeutic proteins.

Small-molecule drugs have gained significant interest in therapeutic development. However, their therapeutic efficacy is often limited by poor target specificity, low bioavailability, and increased toxicity at higher doses. In recent years, biomolecule-based therapeutics such as proteins and peptides have emerged as promising alternatives due to their high specificity, solubility, and low toxicity. Despite these advantages, the intracellular delivery of these molecules remains challenging due to their poor stability, short half-life, and endo-lysosomal entrapment. Several delivery strategies have been developed to overcome these limitations, such as chemical modifications, structural modifications like poly(ethylene glycol) conjugation (PEGylation), and advanced carrier systems such as cell-penetrating peptides (CPPs), nanoparticles (NPs), functional polymers, and antibody-based delivery systems. Non-viral delivery systems have gained considerable attention due to their biocompatibility, low toxicity, and relatively high efficiency. This review provides a comprehensive overview of the various intracellular delivery strategies of therapeutic proteins, highlighting their mechanisms of cellular uptake, advantages, limitations, and future perspectives in biomedical applications.