Indoleamine 2,3-dioxygenase 1 (IDO1) is considered as a promising target for the treatment of several diseases, including neurological disorders and cancer. We report here the crystal structures of two IDO1/IDO1 inhibitor complexes, one of which shows that Amg-1 is directly bound to the heme iron of IDO1 with a clear induced fit. We also describe the identification and preliminary optimization of imidazothiazole derivatives as novel IDO1 inhibitors. Using our crystal structure information and structure−activity relationships (SAR) at the pocket-B of IDO1, we found a series of urea derivatives as potent IDO1 inhibitors and revealed that generation of an induced fit and the resulting interaction with Phe226 and Arg231 are essential for potent IDO1 inhibitory activity. The results of this study are very valuable for understanding the mechanism of IDO1 activation, which is very important for structure-based drug design (SBDD) to discover potent IDO1 inhibitors.

Cysteine-maleimide chemistry is widely used for peptide and protein modification. However, the formed succinimide linkage is readily hydrolyzed and is susceptible to an exchange reaction in vivo. We demonstrate that methylsulfonyl phenyloxadiazole compounds react specifically with cysteine under various buffer conditions and found that the resulting protein conjugates had superior stability to cysteine-maleimide conjugates in human plasma. This Thiol-Click chemistry promises a new approach to stable protein conjugates and pegylated proteins.

Current routes for synthesizing antibody–drug conjugates commonly rely on maleimide linkers to react with cysteine thiols. However, thioether exchange with metabolites and serum proteins can compromise conjugate stability and diminish in vivo efficacy. We report the application of a phenyloxadiazole sulfone linker for the preparation of trastuzumab conjugates. This sulfone linker site-specifically labeled engineered cysteine residues in THIOMABs and improved antibody conjugate stability in human plasma at sites previously shown to be labile for maleimide conjugates. Similarly, sulfone conjugation with selenocysteine in an anti-ROR1 scFv-Fc improved human plasma stability relative to maleimide conjugation. Kinetically controlled labeling of a THIOMAB containing two cysteine substitutions was also achieved, offering a strategy for producing antibody conjugates with expanded valency.

Eine hervorragende Chemoselektivität für Cystein zeichnet Methylsulfonylphenyloxadiazol‐Verbindungen in verschiedenen Puffern aus. Die resultierenden Proteinkonjugate sind in Humanplasma beständiger als Cystein‐Maleimid‐Konjugate (HSA=Human‐Serumalbumin, MBP‐C‐HA=Maltose bindendes Protein). Diese neue Thiol‐Klickreaktion sollte einen Weg für die Bildung stabiler Proteinkonjugate und PEGylierter Proteine eröffnen.

Conjugation to human serum albumin (HSA) has emerged as a powerful approach for extending the in vivo half-life of many small molecule and peptide/protein drugs. Current HSA conjugation strategies, however, can often yield heterogeneous mixtures with inadequate pharmacokinetics, low efficacies, and variable safety profiles. Here, we designed and synthesized analogues of TAK-242, a small molecule inhibitor of Toll-like receptor 4, that primarily reacted with a single lysine residue of HSA. These TAK-242-based cyclohexene compounds demonstrated robust reactivity, and Lys64 was identified as the primary conjugation site. A bivalent HSA conjugate was also prepared in a site-specific manner. Additionally, HSA-cyclohexene conjugates maintained higher levels of stability both in human plasma and in mice than the corresponding maleimide conjugates. This new conjugation strategy promises to broadly enhance the performance of HSA conjugates for numerous applications.