Bioorthogonal chemistry conjugates: ADCs and beyond.

Bioorthogonal click chemistry has played a transformative role in developing advanced hybrid conjugates. These molecular constructs are formed by chemically linking a targeting component to a functional moiety through a suitable linker. Therapeutic conjugates are designed to deliver a biologically active agent to a specific target to treat, prevent, or modify a disease process. By directing the payload to a defined site of action, these conjugates can improve efficacy while reducing off-target effects and systemic toxicity. Among these, antibody-drug conjugates stand out as the most clinically successful compounds. Where various chemical strategies, such as thiol-maleimide additions and site-selective glycan engineering, are employed to attach toxic payloads to antibodies with high precision and reduced sample heterogeneity. Beyond delivery of potent therapeutic payloads, click chemistry approaches have expanded into radioimmunoconjugates for diagnostics, oligonucleotide conjugates for gene silencing, and the creation of bispecific antibodies that can target multiple disease pathways simultaneously. These modular approaches often utilize combinations of ligation and chemical conjugation to preserve the structural integrity and immune functions of the original proteins. These techniques are now being applied to modulate living systems, including cell surface engineering, where metabolic machinery is exploited to install chemical handles on living cells for therapeutic tracking and "click-to-release" drug activation in vivo. Ultimately, current and emerging molecular "click" technologies emphasize a shift toward homogeneous, site-specific methods that expand the functionality and improve the stability, efficacy, and clinical potential of diverse bioconjugates to enhance the precision of modern medicine.