Youngjoo Kwon

Bacterial-Derived Uracil as a Modulator of Mucosal Immunity and Gut-Microbe Homeostasis in Drosophila

All metazoan guts are subjected to immunologically unique conditions in which an efficient antimicrobial system operates to eliminate pathogens while tolerating symbiotic commensal microbiota. However, the molecular mechanisms controlling this process are only partially understood. Here, we show that bacterial-derived uracil acts as a ligand for dual oxidase (DUOX)-dependent reactive oxygen species generation in Drosophila gut and that the uracil production in bacteria causes inflammation in the gut. The acute and controlled uracil-induced immune response is required for efficient elimination of bacteria, intestinal cell repair, and host survival during infection of nonresident species. Among resident gut microbiota, uracil production is absent in symbionts, allowing harmonious colonization without DUOX activation, whereas uracil release from opportunistic pathobionts provokes chronic inflammation. These results reveal that bacteria with distinct abilities to activate uracil-induced gut inflammation, in terms of intensity and duration, act as critical factors that determine homeostasis or pathogenesis in gut-microbe interactions.

A Small Molecule That Blocks Fat Synthesis By Inhibiting the Activation of SREBP

Sterol regulatory element binding proteins (SREBPs) are transcription factors that activate transcription of the genes involved in cholesterol and fatty acid biosynthesis. In the present study, we show that a small synthetic molecule we previously discovered to block adipogenesis is an inhibitor of the SREBP activation. The diarylthiazole derivative, now called fatostatin, impairs the activation process of SREBPs, thereby decreasing the transcription of lipogenic genes in cells. Our analysis suggests that fatostatin inhibits the ER-Golgi translocation of SREBPs through binding to their escort protein, the SREBP cleavage-activating protein (SCAP), at a distinct site from the sterol-binding domain. Fatostatin blocked increases in body weight, blood glucose, and hepatic fat accumulation in obese ob/ob mice, even under uncontrolled food intake. Fatostatin may serve as a tool for gaining further insights into the regulation of SREBP.

Synthesis, topoisomerase I and II inhibitory activity, cytotoxicity, and structure―activity relationship study of hydroxylated 2,4-diphenyl-6-aryl pyridines

A new series of 2,4-diphenyl-6-aryl pyridines containing hydroxyl group(s) at the ortho, meta, or para position of the phenyl ring were synthesized, and evaluated for topoisomerase I and II inhibitory activity and cytotoxicity against several human cancer cell lines for the development of novel anticancer agents. Structure-activity relationship study revealed that the substitution of hydroxyl group(s) increased topoisomerase I and II inhibitory activity in the order of meta > para > ortho position. Substitution of hydroxyl group on the para position showed better cytotoxicity.

2-Thienyl-4-furyl-6-aryl pyridine derivatives: Synthesis, topoisomerase I and II inhibitory activity, cytotoxicity, and structure-activity relationship study

Designed and synthesized 60 2-thienyl-4-furyl-6-aryl pyridine derivatives were evaluated for their topoisomerase I and II inhibitory activities at 20 microM and 100 microM and cytotoxicity against several human cancer cell lines. Compounds 8, 9, 11-29 showed significant topoisomerase II inhibitory activity and compounds 10 and 11 showed significant topoisomerase I inhibitory activity. Most of the compounds (7-21) possessing 2-(5-chlorothiophen-2-yl)-4-(furan-3-yl) moiety showed higher or similar cytotoxicity against HCT15 cell line as compared to standards. Most of the selected compounds displayed moderate cytotoxicity against MCF-7, HeLa, DU145, and K562 cell lines. Structure-activity relationship study revealed that 2-(5-chlorothiophen-2-yl)-4-(furan-3-yl) moiety has an important role in displaying biological activities.

Dihydroxylated 2,4,6-triphenyl pyridines: Synthesis, topoisomerase I and II inhibitory activity, cytotoxicity, and structure—activity relationship study

Twelve dihydroxylated 2,4,6-triphenyl pyridines were designed and synthesized which contain hydroxyl groups at ortho, meta or para position of 2- and 6-phenyl, or 2- and 4-phenyl rings attached to the central pyridine. They were evaluated for topoisomerase I and II inhibitory activity, and cytotoxicity against several human cancer cell lines for the development of novel anticancer agents. Generally, dihydroxylated 2,4,6-triphenyl pyridines exhibited stronger topoisomerase II inhibitory activity, and cytotoxicity compared to those of monohydroxylated 2,4,6-triphenyl pyridines. The concrete structure-activity relationship was observed that dihydroxylated 2,4,6-triphenyl pyridines with hydroxyl group at meta or para position of 2-phenyl ring displayed significant topoisomerase II inhibitory activity as well as cytotoxicity. Positive correlation between topoisomerase II inhibitory activity and cytotoxicity was observed for compounds 10, 12, 13, 17-20 and 22.

New insight for fluoroquinophenoxazine derivatives as possibly new potent topoisomerase I inhibitor.

Fluoroquinolones, represented by ciproxacin and norfloxacin, are well-known clinical antimicrobial agents, and their phenyl ring expanded quinophenoxazines are reported as possible antitumor active compounds. These quinophenoxazines are known to inhibit DNA topoisomerase II essential for cell replication cycle. But there were no reports for topoisomerase I inhibition study for these compounds. In this report, we have prepared a few quinophenoxazine analogues and tested their topoisomerases I and II inhibitory activities and cytotoxicity. From the result, we found that quinophenoxazine analogues possessed strong topoisomerase I inhibitory capacity as well as topoisomerase II inhibition. Among the compounds prepared, A-62176 analogues showed strong topoisomerases I and II inhibitory activities. Interestingly, compound 8 missing the 3-aminopyrrolidine moiety at C2 position has similar potent inhibitory capacity against topoisomerases I and II at higher concentrations (20 and 10 microM, respectively). But compound 8 inhibited topoisomerase I function more selectively at lower concentration, 2 microM. Our observation might strongly implicate that fluoroquinophenoxazines can be developed as efficient topoisomerase I inhibitor with the elaborate modification.

Molecular design, synthesis and docking study of benz[b]oxepines and 12-oxobenzo[c]phenanthridinones as topoisomerase 1 inhibitors.

Benz[b]oxepines 4a-g and 12-oxobenzo[c]phenanthridines 5a-d were designed and synthesized as constrained forms of 3-arylisoquinolines through an intramolecular radical cyclization reaction. Radical cyclization of O-vinyl compounds preferentially led to the 7-endo-trig cyclization pathway to the benz[b]oxepines and 12-oxobenzo[c]phenanthridines through 6-exo-trig path as minor products. Among the synthesized compounds, benz[b]oxepine derivative 4e exhibited potent in vitro cytotoxicity against three different tumor cell lines, as well as topoisomerase 1 inhibitory activity. A Surflex-Dock docking study was performed to clarify the topoisomerase 1 activity of 4e.

Novel N-4-piperazinyl-ciprofloxacin-chalcone hybrids: Synthesis, physicochemical properties, anticancer and topoisomerase I and II inhibitory activity

A group of novel N-4-piperazinyl-ciprofloxacin-chalcone hybrids was prepared. One-dose anticancer test results indicated that compounds 3a and 3g exhibited the highest ability to inhibit the proliferation of different cancer cell lines. Compound 3a exhibited a broad-spectrum of anti-tumor activity without pronounced selectivity while compound 3g revealed high selectivity toward the leukemia subpanel with selectivity ratio of 6.71 at GI₅₀ level. Moreover, compounds 3e and 3j have shown remarkable topo II inhibitory activity compared to etoposide at 100 μM and 20 μM concentrations. Compounds 3e and 3j exhibited comparably potent topo I inhibitory activity at 20 μM concentration compared to camptothecin. Compounds 3e and 3j exhibited strong topo II inhibitory activities compared to topo I at 20 μM concentration. Studying of the solubility and partition coefficient revealed higher lipophilicity of the hybrids 3a-j compared to the parent ciprofloxacin.

Synthesis, biological evaluation, and molecular docking study of 3-(3′-heteroatom substituted-2′-hydroxy-1′-propyloxy) xanthone analogues as novel topoisomerase IIα catalytic inhibitor

Epoxide ring-opened xanthone derivatives were synthesized and tested for their topoisomerase inhibitory activity and cytotoxicity. Most of the compounds showed topo IIα specific inhibitory activity. To clarify the mechanism of action of these compounds, the most potent compound (compound 14) of the synthesized analogues was further studied by testing its ATPase inhibitory activity and through molecular docking experiments. The results showed that the topo IIα inhibitory activity of compound 14 was inversely proportional to ATP concentration. In the ATPase inhibitory test, ATP hydrolysis was reduced less efficiently by compound 14 (28.5±4.6%) than novobiocin (60.4±8.1%). Molecular docking study revealed compound 14 to have a stable binding pattern to the ATP-binding domain of human topo II.

2,6-Dithienyl-4-furyl pyridines: Synthesis, topoisomerase I and II inhibition, cytotoxicity, structure–activity relationship, and docking study

For the development of novel antitumor agents, 2,6-dithienyl-4-furyl pyridine derivatives were prepared and evaluated for their topoisomerase I and II inhibitory activity as well as cytotoxicity against several human cancer cell lines. Among the 21 prepared compounds, compound 24 exhibited strong topoisomerase I inhibitory activity. In addition, a docking study with topoisomerase I and compound 24 was performed.