Synthesis and Evaluation of Novel TLR2 Agonists as Potential Adjuvants for Cancer Vaccines.

Cancer immunotherapy has gained increasing attention due to its potential specificity and lack of adverse side effects when compared to more traditional modes of treatment. Toll-like receptor 2 (TLR2) agonists are lipopeptides possessing the -[2,3-bis(palmitoyloxy)propyl]-l-cysteine (PamCys) motif and exhibit potent immunostimulatory effects. These agonists offer a means of providing "danger signals" in order to activate the immune system toward tumor antigens. Thus, the development of TLR2 agonists is attractive in the search of potential immunostimulants for cancer. Existing SAR studies of PamCys with TLR2 indicate that the structural requirements for activity are, for the most part, very intolerable. We have investigated the importance of stereochemistry, the effect of -terminal acylation, and homologation between the two ester functionalities in PamCys-conjugated lipopeptides on TLR2 activity. The diastereomer is significantly more potent than the diastereomer and -terminal modification generally lowers TLR2 activity. Most notably, homologation gives rise to analogues which are comparatively active to the native PamCys containing constructs.