Title:

Sulfavants, new generation of molecular vaccine adjuvants inspired by marine sulfoglycolipids 

Emiliano Manzo1, Laura Fioretto1, Dario Pagano1, Genoveffa Nuzzo1, Carmela Gallo1, Giusi Barra2, Marina Della Greca3, Raffaele De Palma2 and Angelo Fontana1

1Bio-Organic Chemistry Unit, CNR-Institute of Biomolecular Chemistry, Via Campi Flegrei 34, IT-80078 Pozzuoli, 80078 (Napoli, Italy).

2Department of Internal and Experimental Clinic, Clinical Immunology and Allergology, University of Campania, c/o II Policlinico (Bd. 3), Via S.Pansini 5, 80131 Napoli, Italy.

3Department of Chemical Sciences, University of Naples, Federico II, Complesso Universitario di Monte Sant’Angelo, via Cintia 4 80126 Napoli, Italy.

 

Abstract

b-6’-sulfoquinovosyldiacylglycerols (b-SQDGs) show uncommon immonomodulatory activities and represent a promising new class of vaccine adjuvants. Sulfavant A, chemically b-6’-sulfoquinovosyl-1,2-O-distearoylglycerol, is the prototype of this class of molecules exhibiting the ability to activate antigen-presenting cells (APCs), such as dendritic cells (DCs), and trigger immune response both in vitro and in vivo. As the lipid part plays a fundamental role in the activation of DCs, the chemical preparation of a series of b-SQDGs analogs, differing in the acyl portions, was the necessary requisite for the investigation and development of these products as molecular adjuvant of vaccines. To achieve this task, the design of a versatile, simple and efficient strategy for the synthesis of analogs of Sulfavant A is mandatory.

 

Supplement:

Vaccination consists of the stimulation of immune response by vaccines. Long-term protection requires the persistence of specific antibodies above protective thresholds and/or the maintenance of immune memory cells capable of rapid and effective reactivation with subsequent exposure to the antigens.1 The induction of these mechanisms requires activation by specific antigen-presenting cells (APCs), essentially dendritic cells (DCs) that must be recruited into the reaction.2 When exposed to antigens (e.g. inactivated pathogens or synthetic molecules), immature DCs undergo rapid maturation, modulate specific surface receptors, and migrate toward secondary lymph nodes, where the induction of T- and B-cell responses occurs. In order to increase the potency of this response, modern vaccines contain adjuvants, chemical constituents that essentially enhance vaccine response and shape adaptive immunity by modulating innate immunity.

In our ongoing research on immunomodulatory substances, we have focused our study on the immunological properties of natural a-6’-sulfoquinovosyldiacylglycerols (a-SQDGs),3 plant glycoglycerolipids that have wide distribution in terrestrial and marine photosynthetic organisms. This class of molecules is localized in the inner membranes of chloroplast but their function is still unclear. From a chemical point of view, their structure is featured by a sulfur atom directly linked to the carbon 6’ of a single unit of monosaccharide referred to as sulfoquinovose (figure 1). Differently from immunogenic bacterial glycolipids that usually have β configuration of the anomeric carbon, natural SQDGs have α-configuration of the sugar unit and the lipid composition included saturated and/or monounsaturated fatty acids. Starting from the immunostimulatory activity of this class of glycolipids able to elicit maturation and IL-12 production of DCs and in order to enhance the immunogenic activity, we designed and prepared non-natural b-SQDGs,3 synthetic analogs of a-SQDGs, that combine the presence of the sulfonic residue of α-SQDG with the β-configuration of the glycosidic bond common in immunogenic bacterial lipopolysaccharides.4

 

 

Figure 1

 

In this frame, Sulfavant A,3 b-6’-sulfoquinovosyl-1,2-O-distearoylglycerol, is the prototype of this class of synthetic derivatives inspired by natural a-SQDGs and able to prime human DCs by a TLR2/TLR4-independent mechanism.3c Sulfavant A induced maturation of DC with expression of high levels of MHC II molecules and upregulation of costimulatory proteins (CD83, CD86) and proinflammatory cytokines (IL-12 and INF-γ).3c On the other hand mice immunized with the antigen ovalbumin (OVA) associated to Sulfavant A as adjuvant produced a concentration of anti-OVA immunoglobulin equivalent to traditional adjuvants.3c In an experimental model of melanoma, vaccination of C57BL/6 mice by Sulfavant A-adjuvanted hgp10 peptide elicited a protective response with reduction of tumour growth and increase of survival.3c

Synthesis of Sulfavant A is achieved by a versatile chemical procedure based on a trichloroacetimidate methodology and peracetate sugar precursor (figure 2), involving stereoselective glycosylation of trichloroacetimidate-glucose acetate  donor with 1,2-O-isopropylidene glycerol acceptor and following conventional reactions aimed to introduce sulfonic function on carbon 6’ of the sugar.3 The choice of acetate as protecting group for the hydroxyl functions of the sugar moiety allowed us to get an excellent stereoselectivity in the formation of the β glycosidic bond by anchimeric assistance of carbon 2’ acetoxy to anomeric carbon. Furthermore the methodology was particularly suitable for the preparation of Sulfavant A analogs with mixed composition both with saturated and unsaturated acyl chains at carbon 1 and 2 of the glycerol part; this was also possible thanks to an appropriate choice of different experimental conditions, depending on the presence or not of double bonds, in the final step of oxidation to sulphonic function, thus expanding the class of molecules to be developed as adjuvants.3,5 Furthermore the acetate group promoted clean and efficient synthetic steps, along with simple and easy workup, which makes the synthetic procedure suitable for scaling-up3 and use of b-SQDGs in the formulation of vaccine for in vivo tests and future pharmacological development.

 

Figure 2. Synthetic strategy for the preparation of Sulfavant A analogs with mixed composition of saturated and unsaturated acyls.

 

 

References

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