Synthesis and Biological Activities of 5-Thio-α-GalCers

Abstract

NKT cells, a unique subset of T cells that recognizes glycolipid antigens presented by CD1d molecules, are believed to produce key cytokines of both Th1 and Th2 T cells and are thus involved in the control of several types of immune response. As an active glycolipid antigen having α-galactosyl ceramide core structure, KRN7000 showed promising immunostimulation activity and was selected as an anticancer drug candidate for further clinical application. In this report, three new KRN7000 structural analogues were designed and synthesized, in which the ring oxygen of the galactopyranose residue is replaced by a sulfur atom along with the variation on the lipid chain. Their abilities for stimulating mouse NKT cells to produce IFN-γ and IL-4 were evaluated both in vivo and in vitro. KEYWORDS: KRN7000, 5-thio-α-GalCer, iNKT cells, antitumor activity I nvariant natural killer T (iNKT) cells are a specialized subset of T cells that play an important role in tumor immunity and preventing autoimmunity.1−4 The anti-infective activity of iNKT cells can be triggered by various viruses, bacteria, and parasites. 5,6 When stimulated by glycolipid antigens such as marine natural product agelasphin-9b, 7 the iNKT cells could rapidly release T helper 1 (Th1) cytokines (e.g., IFN-γ, TNF-α, IF-2) and Th2 cytokines (e.g., IL-4, IL-10).8,9 Th1-biased cytokines are believed to be concerned with the antitumor, antibacterial, and antiviral activities, whereas the release of Th2-biased cytokines may relieve some autoimmune diseases.10−12 KRN7000 (1), 13 a synthetic α-GalCer (1, Figure 1) derived from the structural modification on the ceramide part of agelasphin-9b, presented convincing effects on the treatment of liver tumors, 14,15 metastatic cancers, 16,17 parasitic infections, 11,18 and autoimmune diseases. 19,20 The action mechanism of KRN7000 has been suggested in approximately three sequential steps. First, KRN7000 is combined with the CD1d protein to form a glycolipid−protein complex. Second, the KRN7000/CD1d complex is recognized by the T cell receptor (TCR) on the surface of NKT cells to form a three-molecule complex. Lastly, it stimulates NKT cells to release Th1 and Th2 cytokines rapidly. 21 Because of the mutual repulsion of Th1 and Th2 cytokines, the simultaneous high level production of both cytokines weaken the therapeutic effectiveness of KRN7000. 22Therefore, some KRN7000 derivatives modifying on either sugar or ceramide moieties were synthesized and expected to selectively control the release of Th1 and Th2 cytokines. 23−27For example, KRN7000 analogue with a longer acyl tail (2, Figure 1) exhibited a greater ability for activation of B cells and induced IL-2 from mouse NKT cells, and IL-4 and IFN-γ from human Vα24i NKT cells in vitro, 28,29 while the analogue with a relative shorter chain (3, Figure 1) influenced cytokine release toward Th2 bias with an immunomodulatory response. 30 In consideration of the intrinsic instability of O-glycosides in vivo, both C-bridged glycoside (α-C-GalCer) 31−33 and S-bridged ...

Synthesis of 5-Thio-α-GalCer Analogues with Fluorinated Acyl Chain on Lipid Residue and Their Biological Evaluation

“…We have successfully prepared three 5-thio-galactopyranosyl substituted KRN7000 analogues, 24 namely, 5-thio-KRN7000, 5-thio-α-GalCer 566, and 5-thio-PBS-25. Compared to the original KRN7000, 5-thio-KRN7000 showed a similar ability and tendency in inducing IFN-γ and IL-4 both in vitro and in vivo.…”

Optical Control of Cytokine Production Using Photoswitchable Galactosylceramides

“…A modular synthesis strategy based on previous work by Tsuji, Wong, and co‐workers was developed, which allowed the late‐stage introduction of the FAAzo side‐chains and thereby for the rapid synthesis of multiple derivatives (Figure ) . Ceramide building block 2 was obtained from commercially available phytosphingosine ( 1 ) through standard protection and deprotection chemistry . For the galactose building block 5 , β‐ d ‐galactose pentaacetate ( 3 ) was thiolated at the anomeric center and fully deprotected under Zemplén conditions .…”

“…[10] Ceramide buildingb lock 2 was obtained from commercially available phytosphingosine (1)t hrough standard protection and deprotection chemistry. [11] For the galactose building block 5, b-d-galactose pentaacetate( 3)w as thiolated at the anomeric center and fully deprotected under ZemplØnc onditions. [12] Selective reprotection of the hydroxyl groups at C4 and C6 as a benzylidene acetal then afforded galactose acetal 4.…”

Designing sugar mimetics: non-natural pyranosides as innovative chemical tools

“…Substitution of the glycosidic oxygen atom with sulfur [35–37] or carbon [38,39] is a now common method to enhance stability of glycosides. Substitution of the pyranose oxygen, such as in 5- S glycosides, can possibly minimize structural changes [40] and such sugar mimics have shown increased cytotoxic activity towards cancer cell lines compared to their O counterpart [41]. Similarly, substitution of the ring oxygen with carbon shows increased stability and lower clearance in vivo [42].…”