A Link Means a Lot: Disulfide Tethering in Structure-Based Drug Design

Tethering is a disulfide-based drug-discovery technology that grew out of the era when combinatorial chemistry was a burgeoning new development. What separates Tethering from other combinatorial approaches is its site-directed nature. The disulfide link that is formed allows a wide variety of advantages and analysis not available with other drug methods, thus in Tethering a link means a lot. Site-directedness makes it ideal for interrogating traditionally difficult drug targets, such as protein–protein interaction surfaces, and new binding sites. It has also led to candidates for linking in a combinatorial manner, new fragments for addition to existing scaffolds, and entirely new classes of pharmacophores for several different protein targets. At the very essence of tethering is the concept that structural information can and should inform drug design and discovery. Tethering was conceptualized and developed by a team assembled and directed by James Wells at Sunesis Pharmaceuticals and first publicly reported by Erlanson and coworkers in 2000. The progress of Tethering and its many applications has been extensively reviewed, thus overlap in content between this chapter and those reviews are bound to exist. Nevertheless, this review focuses on the practical considerations during Tethering and on the strong role that structural information plays during Tethering interrogation. The inaugural report of Tethering focused on the cysteine-containing active site of thymidylate synthase (TS), a protein that is essential to synthesis of deoxythymidine monophosphate (dTMP) from deoxyuridine monophosphate