Fifteen Years since the Development of KRN7000 – Structure-Activity Relationship Studies on Novel Glycosphingolipids Which Stimulate Natural Killer T Cells

Abstract

Invariant natural killer (NK) T cells bridge innate and acquired immunity and play an important role in both protective and regulatory responses. NKT cell responses are induced by recognition of a complex of glycolipid antigens with CD1d, an antigen presenting protein of the immune system, with its invariant T cell receptors. KRN7000, an α-galactosyl ceramide developed by KIRIN Brewery Co. in 1995, stimulates NKT cells strongly to induce the production of a large amount of cytokines, and is used as a standard reagent for a positive control of NKT cell studies. At the beginning, KRN7000 was developed as an anticancer drug candidate. However, it induces both helper T (Th)1-type cytokines, which induce immunostimulatory activity, and Th2-type ones, which induce immunosuppressive activities, in large quantities at the same time. Its therapeutical use, therefore, is limited. Fifteen years has passed since the discovery of KRN7000, and a number of analogues of KRN7000 have been developed worldwide to solve the above problem. Many researchers are also trying to understand how NKT cells recognize the structure of glycolipids and induce cytokines. In this minireview, we discuss the structure-activity relationship studies on novel glycolipids which stimulate NKT cells efficiently.

Structure Elucidation of Calyxoside B, a Bipolar Sphingolipid from a Marine Sponge Cladocroce sp. through the Use of Beckmann Rearrangement

“…It is interesting to note that the aglycone showed the most potent activity and conversion of the ketone in the aglycone to an amide resulted in diminished activity. Calyxosides are distantly related to agelasphins—sponge-derived sphingolipids—by possessing 1-glycosylated sphingolipid partial structures [ 12 ]. Agelasphins and their synthetic analogue KRN7000 are presented by MHC class I-like antigens presenting molecule CD1d and exhibit antitumor activity through enhanced production of cytokines by direct stimulation of invariant natural killer T cells (iNKT cells) [ 12 ].…”

“…Calyxosides are distantly related to agelasphins—sponge-derived sphingolipids—by possessing 1-glycosylated sphingolipid partial structures [ 12 ]. Agelasphins and their synthetic analogue KRN7000 are presented by MHC class I-like antigens presenting molecule CD1d and exhibit antitumor activity through enhanced production of cytokines by direct stimulation of invariant natural killer T cells (iNKT cells) [ 12 ]. Therefore, we wondered whether a mixture of 1 and 2 exhibits similar activities.…”

“…Therefore, the activity of the mixture of 1 and 2 was 1/50,000 of that of KRN7000. This result suggests that either calyxosides have very weak activity in enhancing the production of cytokines, or our preparation of calyxosides contains a very small amount of α-glycosides that are known to exhibit potent activity [ 12 ]. Further research is required to clarify the biological activity of calyxosides toward iNKT cells.…”

A practical and scalable synthesis of KRN7000 using glycosyl iodide as the glycosyl donor

“…Introduction KRN7000, also referred to as α-galactosyl ceramide (α-GalCer), is an analogue of natural α-GalGSLs isolated from the marine sponge Agelasmauritianus, 1 and is the most extensively studied ligand for invariant natural killer T (iNKT) cells, 2,3 demonstrating immune stimulatory activity and antitumor properties. 4,5 KRN7000 binds to the protein CD1d, contributes to the glycolipid-protein complex and is recognized by T cell receptors (TCRs) positioned on the exterior of iNKT cells resulting in activation of the immune response by releasing both Th1 (IFN-γ) and Th2 (IL-4) cytokines.…”

C-galactosylceramide: Synthesis and immunology

“…The analogs can be categorized by (i) fatty amide chain variation, (ii) phytosphingosine chain and functionality variation, (iii) substituent variation at the carbohydrate 2,3,4 and 6 positions, (iv) replacement of the anomeric O linker by other atoms, (v) replacement of the ring O by C. These studies have been thoroughly and very recently reviewed. [5]…”