Hyaluronic Acid Conjugates of TLR7/8 Agonists for Targeted Delivery to Secondary Lymphoid Tissue.

Immunogens carried in lymphatic fluid drain via afferent vessels into regional lymph nodes and facilitate the efficient induction of appropriate immune responses. The lymphatic system possesses receptors recognizing hyaluronic acid (HA). Covalent conjugates of small-molecule TLR7/8 agonists with HA are entirely devoid of immunostimulatory activity in vitro. In murine models of immunization, however, such conjugates traffic to lymph nodes, where they are "unmasked", releasing the small molecule TLR7/8 agonist from the carrier polysaccharide. The resulting focal immunostimulation is manifested in potent adjuvantic effects with negligible systemic exposure. The efficient delivery of immunogens has been a major challenge in the development of subunit vaccines, and enhancing targeted delivery of immunogens to secondary lymphoid organs might be a promising approach for improving vaccine efficacy, as well as safety.

Identification of Human Toll-like Receptor 2-Agonistic Activity in Dihydropyridine-Quinolone Carboxamides.

Using a multiplexed, reporter gene-based, high-throughput screen, we identified 9-fluoro-7-hydroxy-3-methyl-5-oxo-N-(pyridin-3-ylmethyl)-2,3-dihydro-1H,5H-pyrido[3,2,1-ij]quinoline-6-carboxamide as a TLR2 agonist. Preliminary structure-activity relationship studies on the carboxamide moiety led to the identification of analogues that induce chemokines and cytokines in a TLR2-dependent manner. These results represent new leads for the development of vaccine adjuvants.

Identification of High-Potency Human TLR8 and Dual TLR7/TLR8 Agonists in Pyrimidine-2,4-diamines.

The induction of toll-like receptor 7 (TLR7)-dependent type I interferons (IFN-α/ß) from plasmacytoid dendritic cells as well as the production of TLR8-dependent type II interferon (IFN-γ), TNF-α, and IL-12 in myeloid dendritic cells are of importance in generating T helper-1 biased adaptive immune responses. In an effort to identify novel dual TLR7/TLR8-active compounds, we undertook structure-activity relationship studies in pyrimidine 2,4-diamines, focusing on substituents at C5. Several analogues substituted with aminopropyl appendages at C5 displayed dominant TLR8-agonistic activity. N4-Butyl-6-methyl-5-(3-morpholinopropyl)pyrimidine-2,4-diamine was found to be a very potent dual TLR7/TLR8 agonist. Employing novel cytokine reporter cell assays, we verified that potency at TLR7 correlates with IFN-α/ß production in human blood, whereas IFN-γ and TNF-α induction is largely TLR8-dependent. Dual TLR7/TLR8 agonists markedly upregulate CD80 expression in multiple dendritic cell subsets, providing insight into the immunological basis for the superior adjuvantic properties of such innate immune stimuli.

Human Toll-like Receptor (TLR) 8-Specific Agonistic Activity in Substituted Pyrimidine-2,4-diamines.

Activation of human toll-like receptor-8 (TLR8) evokes a distinct cytokine profile favoring the generation of Type 1 helper T cells. A multiplexed high-throughput screen had led to the identification of N(4)-butyl-5-iodo-6-methylpyrimidine-2,4-diamine as a pure TLR8 agonist, and a detailed structure-activity relationship study of this chemotype was undertaken. A butyl substituent at N(4) was optimal, and replacement of the 5-iodo group with chloro, bromo, or fluoro groups led to losses in potency, as did the introduction of aromatic bulk. Drawing from our previous structure-based design, several 5-alkylamino derivatives were evaluated. Significant enhancement of potency was achieved in 5-(4-aminobutyl)-N(4)-butyl-6-methylpyrimidine-2,4-diamine. This compound potently induced Th1-biasing IFN-γ and IL-12 in human blood, but lower levels of the proinflammatory cytokines IL-1ß, IL-6, and IL-8. These results suggest that the inflammatory and reactogenic propensities of this compound could be considerably more favorable than other TLR8 agonists under evaluation.