Hydrazone linker

The hydrazone linker is a pH-sensitive chemical bond used to conjugate the chemotherapeutic agent doxorubicin to a delivery vehicle, such as a dendronized gold nanoparticle. It is not a biological target (e.g., a receptor or enzyme) but rather a structural component of a nanomedicine formulation designed for triggered drug release (Journal of Controlled Release, 2017). The linker is engineered to remain stable at the physiological pH of 7.4, ensuring that the doxorubicin remains attached to the nanoparticle while circulating in the blood, which helps minimize systemic toxicity and cardiotoxicity (Nanoscale Research Letters, 2018). Upon internalization into cancer cells via endocytosis, the construct enters the acidic environment of endosomes and lysosomes (pH 5.0–6.0), where the hydrazone bond undergoes rapid hydrolysis (ACS Applied Materials & Interfaces, 2014). This cleavage releases the active doxorubicin, allowing it to reach its actual biological targets, such as Topoisomerase II and DNA, to exert its cytotoxic effects (National Cancer Institute). This strategy utilizes the inherent acidity of the tumor microenvironment to achieve site-specific drug activation and improve the therapeutic index of the treatment (Biomaterials, 2016).

Other names

pH-sensitive hydrazone bondAcid-labile hydrazone linkerDoxorubicin-dendron-AuNP linkerpH-responsive covalent linker

The hydrazone linker undergoes acid-catalyzed hydrolysis in acidic environments (pH 5.0–6.0), such as the tumor microenvironment or endo-lysosomal compartments, to release the conjugated doxorubicin payload (Bioconjugate Chem., 2015).