Identification of Biologically Active Pyrimido[5,4-<i>b</i>]indoles That Prolong NF-κB Activation without Intrinsic Activity
作者:Michael Chan、Alast Ahmadi、Shiyin Yao、Fumi Sato-Kaneko、Karen Messer、Minya Pu、Brandon Nguyen、Tomoko Hayashi、Maripat Corr、Dennis A. Carson、Howard B. Cottam、Nikunj M. Shukla
DOI:10.1021/acscombsci.7b00080
日期:2017.8.14
Most vaccine adjuvants directly stimulate and activate antigen presenting cells but do not sustain immunostimulation of these cells. A high throughput screening (HTS) strategy was designed to identify compounds that would sustain NF-kappa B activation by a stimulus from the Toll-like receptor (TLR)4 ligand, lipopolysaccharide (LPS). Several pilot studies optimized the parameters and conditions for a cell based NF-kappa B reporter assay in human monocytic THP-1 cells. The final assay evaluated prolongation of LPS induced NF-kappa B activation at 12 h. The dynamic range of the assay was confirmed in a pilot screen of 14 631 compounds and subsequently in a main extensive screen with 166 304 compounds. Hit compounds were identified using an enrichment strategy based on unsupervised chemoinformatic clustering, and also by a naive "Top X" approach. A total of 2011 compounds were then rescreened for levels of coactivation with LPS at 5 h and 12 h, which provided kinetic profiles. Of the 407 confirmed hits, compounds that showed correlation of the kinetic profiles with the structural similarities led to identification of four chemotypes: pyrimido[5,4-b]indoles, 4H-chromene-3-carbonitriles, benzo[d][1,3]dioxol-2-ylureas, and tetrahydrothieno[2,3-c]pyridines, which were segregated by 5 h and 12 h kinetic characteristics. Unlike the TLR4 agonistic pyrimidoindoles identified in previous studies, the revealed pyrimidoindoles in the present work did not intrinsically stimulate TLR4 nor induce NF-kappa B but rather prolonged NF-kappa B signaling induced by LPS. A 42-member combinatorial library was synthesized which led to identification of potent N3-alkyl substituted pyrimidoindoles that were not only active in vitro but also enhanced antibody responses in vivo when used as a coadjuvant. The novel HTS strategy led to identification of compounds that are intrinsically quiescent but functionally prolong stimulation by a TLR4 ligand and thereby potentiate vaccine efficacy.