The major results and achievements of the project are the following:
- Design, synthesis, immunological evaluation, and conformational analysis of saponin variants derived from the QS-21 natural product, leading to improved saponin adjuvants and key structure-activity relationships.
In a first study, we introduced modifications at the triterpene and central linkage regions of the saponin scaffold providing lead synthetic saponins that elicited comparable antibody responses to QS-21 with lower toxicity. Moreover, we studied their three-dimensional structure using a combination of NMR and molecular dynamics simulations, yielding molecular level insights into saponin conformation that correlated with their in vivo adjuvant activity [Chemical Communications 2020, 56, 719].
In a second work, we developed a divergent, streamlined strategy for the expedient and versatile synthesis of oligosaccharide saponin variants and explored the importance of the terminal disaccharide moiety on adjuvant activity in in vivo immunological studies. The attenuated antibody responses showed by these analogues indicated the negative impact of such carbohydrate modifications on adjuvant activity, which could be associated with increased saponin conformational flexibility as assessed by molecular dynamics simulations [Chemistry 2021, 27, 4731].
In the most recent study, we have improved upon our previous lead compounds with the synthesis of novel saponin variants functionalized at key triterpene functionalities via oxime linkages. These new molecules induced significantly enhanced antibody responses compared to our most potent saponin candidates, emerging as the most promising synthetic adjuvants for further development [Frontiers Immunology 2022, in press].
- Development of saponin-antigen conjugates as potential self-adjuvanting vaccine constructs.
We have exploited our privileged saponin scaffold for conjugation of a variety of synthetic carbohydrate-based antigens to provide a novel glycoconjugate platform for the development of self-adjuvanting cancer vaccines.
In our first design incorporating the Tn antigen on the acyl chain domain of the saponins, the synthetic conjugates induced moderate antibody responses with no toxicity in mice, highlighting opportunities for further improvement of this chemical platform by additional structural and/or formulation optimization [Chemical Communications 2021, 57, 11382]. Furthermore, within this project we have performed detailed immunological studies of related QS-21-adjuvanted synthetic constructs bearing T cell epitopes and multiple Tn antigen copies their structure [Chemical Science 2020, 11, 4488].
Building upon these results, we have developed novel saponin conjugates incorporating a more advanced Tn-MUC1 glycopeptide antigen as well as additional immunogenic epitopes on the saponin scaffold for improved immunogenicity. The in vivo immunological evaluation indicated the positive impact of including a helper T cell peptide fragment to the dicomponent saponin-MUC1 construct, eliciting increased antigen-specific antibody responses in mice. Moreover, NMR experiments showed concentration-dependent aggregation of the saponin–antigen molecules with potential micelle formation, especially for the tricomponent conjugates, which could be connected to their higher immunogenicity. The corresponding manuscript is already prepared and ready for imminent submission to a top multidisciplinary journal.
- Design, synthesis, and immunological evaluation of saponin photoaffinity probes for ongoing studies investigating the cellular and molecular mechanisms of saponin immunopotentiation.
Thus, these results have been communicated in several important research journals as well as various scientific conferences. In addition, we have filed three patent applications and have established R&D contracts with a biopharmaceutical company interested in the development of our adjuvant assets.
