Identification of a Monovalent Pseudo-Natural Product Degrader Class Supercharging Degradation of IDO1 by its native E3 KLHDC3

Targeted protein degradation (TPD) modulates protein function beyond inhibition of enzyme activity or protein-protein interactions. Most degrader drugs function by directly mediating proximity between a neosubstrate and hijacked E3 ligase. Here, we identified pseudo-natural products derived from (-)-myrtanol, termed iDegs that inhibit and induce degradation of the immunomodulatory enzyme indoleamine-2,3-dioxygenase 1 (IDO1) by a distinct mechanism. iDegs boost IDO1 ubiquitination and degradation by the cullin-RING E3 ligase CRL2KLHDC3, which we identified to natively mediate ubiquitin-mediated degradation of IDO1. Therefore, iDegs increase IDO1 turnover using the native proteolytic pathway. In contrast to clinically explored IDO1 inhibitors, iDegs reduce formation of kynurenine by both inhibition and induced degradation of the enzyme and, thus, would also modulate non-enzymatic functions of IDO1. This unique mechanism of action may open up new therapeutic opportunities for the treatment of cancer beyond classical inhibition of IDO1.

Regiodivergent synthesis of sulfone-tethered lactam-lactones bearing four contiguous stereocenters

Sulfone-tethered lactones/amides/amines display a diverse spectrum of biological activities, including anti-psychotic and anti-hypertensive. Sulfones are also widely present in functional materials and fragrances. We therefore reasoned that a regiodivergent and stereocontrolled strategy that merges the sulfone, lactone, and lactam motifs would likely lead to the discovery of new pharmacophores and functional materials. Here, we report mild conditions for the sulfonyllactonization of γ-lactam-tethered 5-aryl-4(E)-pentenoic acids. The annulation is highly modular, chemoselective, and diastereoselective. With respect to regioselectivity, trisubstituted alkenoic acids display a preference for 5-exo-trig cyclization whereas disubstituted alkenoic acids undergo exclusive 6-endo-trig cyclization. The lactam-fused sulfonyllactones bear angular quaternary as well as four contiguous stereocenters. The products are post-modifiable, especially through a newly developed Co-catalyzed reductive cross-coupling protocol.

Structural Basis of Selective Human Indoleamine-2,3-dioxygenase 1 (hIDO1) Inhibition

hIDO1 is a heme-dioxygenase overexpressed in the tumor microenvironment and is implicated in the survival of cancer cells. Metabolism of tryptophan to N-formyl-kynurenine by hIDO1 leads to immune suppression to result in cancer cell immune escape. In this article, we discuss the discovery of selective hIDO1 inhibitors for therapeutic intervention that have been promoted to clinical trials and for which crystallographic structural information is available for the respective inhibitor-enzyme complex. The structural insights are based on the complex crystal structures and the relative biological data profiles. The structural basis of selective hIDO1 inhibition, as discussed herein, opens new avenues to the discovery of novel inhibitors with improved activity profiles, selectivity, and distinct structure frameworks.