Program 1. Synthesis of chemical probes to investigate enzymes involved in trehalose utilization.
Trehalose is a disaccharide and an essential metabolite found in Mtb. Several enzymes involved in the utilization of trehalose have been found to be essential to the organism’s survival. We are developing probe molecules which can be used to understand the detailed molecular interactions that occur between the enzymes involved in trehalose utilization and their substrates. For example, we are using carbohydrates as components of substrate analogues and transition state analogues of Mtb Antigen 85s (Ag85s). Ag85s are mycolyl transferases responsible for the synthesis of the virulence factor trehalose dimycolate (TDM). Ag85s are also involved in mycolation of carbohydrates on the cell wall. Collectively, this process can be thought of as mycolyl membrane maintenance. Since Ag85s act on ß-D-arabinofuranoside- and trehalose-based cell wall structures these carbohydrates are prominent in our inhibitor designs, see Figure 1 for example. The compounds resulting from these investigations are believed to be useful for understanding key steps in the bacterial cell wall synthesis of Mtb. Since the bacterial cell wall is a well-established target for a number of anti-bacterial therapies these studies may potentially lead to an improved understanding of cell wall synthesis targets or to new antibiotics useful for treating the growing threat of multi-drug resistant Mtb. In addition to Ag85s, we are exploring essential enzymes such as GlgE, a maltosyl transferase. GlgE is one enzyme responsible for α-glucan synthesis. It has been reported that absence of GlgE leads to self-poisoning by the accumulation of phosphosugar maltose-1-phosphate (M1P), directed by a self-amplifying feedback response leading to cell death. GlgE is essential for survival of the pathogen, and the absence of a human homologue substantiates GlgE as a new drug target.
Figure 1. A thiophene-arbinoside bound to Ag85C
Program 2. Targeting APCs to generate improved immunotherapeutics.
Carbohydrates found as naturally occurring glycoconjugates frequently serve as important markers for cancer and are potential targets for active immune therapy. One example is the human epithelial type 1 mucin (MUC1), a large polymorphic transmembrane mucin, expressed on normal glandular epithelia. In cancer cells the MUC1 glycoform distribution changes to reduced glycosylation with many of the glycan chains truncated relative to normal cells exposing hidden glycan epitopes on the molecule. Together these aberrant structures are referred to as tumor-associated antigens (TAAs). Individuals with early breast cancer who possess natural anti-MUC1 antibodies have been shown to have a reduced likelihood of distant metastases and better disease-specific survival. We are interested in synthesizing homogenous MUC1 glycopeptides which contain TAA epitopes. We are also exploring the use endogenous anti-L-rhamnose antibodies found in humans to augment immunogenicity of cancer vaccines by an antibody dependent mechanism mediated by Fc receptors on antigen presenting cells, see Figure 2 for an illustration of the concept.
Figure 2. A liposomal immunotherapeutic which uses L-rhamnose moieties to enhance activity. (L-rhamnose groups in red)