This Review aims
to highlight key aspects of tetrapyrrole-based
antibody–drug conjugates (ADCs) and significant developments
in the field since 2010. Many new conjugation methods have been developed
and employed in the past decade, and associated with this, there has
been a rising interest in theranostic conjugates. We have investigated
the physicochemical properties that tetrapyrroles need to possess
in order to be viable photosensitizers for conjugation to antibodies.
Differences in conjugation strategies are discussed, and structure–activity
relationships of tetrapyrrole–antibody conjugates are reported,
where available. As the elegance of bioconjugation techniques has
increased, it has paved the way for exceptionally phototoxic, yet
highly selective, tetrapyrrole–antibody conjugates, with photocytotoxicities
in the nanomolar range, to be synthesized and biologically evaluated.