Current strategies for the discovery and bioconjugation of smaller, targetable drug conjugates tailored for solid tumour therapy.

Introduction: Antibody-Drug Conjugates (ADCs) have undergone a recent resurgence with 5 product approvals over the last 2 years but for those close to the field, it's been repeated cycles of setbacks and new innovations. A new wave of innovation is in the type of format used to deliver the cytotoxic payloads, with smaller bio-molecules being designed to have more optimal penetration and elimination properties tailored for solid tumours. Areas Covered: In this review, the authors cover many of the recently described smaller-format drug conjugates (including formats such as diabodies, Fabs, scFvs, domain antibodies) with an emphasis on the types of conjugation technologies used to attach the chemical linker-payload. Expert opinion: Smaller formats are highly influenced by the structure of the linker-payload, arguably more-so than larger ADCs, so careful consideration is needed where solublising and pharmacokinetic modulation is required. High-quality conjugates are being developed with in vivo tumour efficacy and tolerability properties competitive with ADCs and with a few formats already in clinical development, we expect the pipeline to expand and to reach the market.