Structure-activity relationships (SAR) of some tetracyclic heterocycles related to the immunosuppressive agent Brequinar Sodium

Development of thyroglobulin antibodies after GVAX immunotherapy is associated with prolonged survival

Cancer immunotherapy induces a variety of autoinflammatory responses, including those against the thyroid gland, which can be exploited to predict clinical outcomes. Considering the paucity of information about thyroid autoimmunity in patients receiving cancer vaccines, we designed our study to assess the development of thyroglobulin antibodies (TgAbs) in patients treated with GVAX (vaccine made of a tumor cell type transfected with GM-CSF) and/or ipilimumab and correlated seroconversion with survival. Using both in house and commercial ELISA assays, we measured TgAbs in patients with pancreatic (No. = 53), prostate (No. = 35) or colon (No. = 8) cancer, before and after treatment with GVAX only (No. = 34), GVAX plus ipilimumab (No. = 42) or ipilimumab (No. = 20), and correlated their levels with patient's survival, disease status and T-cell surface markers. Antibodies to thyroperoxidase, myeloperoxidase, proteinase 3, insulin and actin were also measured. TgAbs specifically developed after GVAX, independent of the underlying cancer (81% in prostate, 75% colon cancer and 76% pancreatic cancer) and co-administration of ipilimumab (75% in GVAX only and 78% in GVAX plus ipilimumab). This TgAbs seroconversion could be detected mainly by the in house assay, suggesting that the thyroglobulin epitopes recognized by the antibodies induced by GVAX are different from the epitopes seen in the classic form of Hashimoto thyroiditis. Notably, TgAbs seroconversion was associated with significantly prolonged survival (p = 0.01 for pancreas and p = 0.005 for prostate cancer). In conclusion, GVAX immunotherapy induces the appearance of TgAbs that recognize a unique antigenic repertoire and associate with prolonged survival.

SAR Based Optimization of a 4-Quinoline Carboxylic Acid Analog with Potent Anti-Viral Activity

It is established that drugs targeting viral proteins are at risk of generating resistant strains. However, drugs targeting host factors can potentially avoid this problem. Herein we report structure-activity relationship studies leading to the discovery of a very potent lead compound 6-fluoro-2-(5-isopropyl-2-methyl-4-phenoxyphenyl)quinoline-4-carboxylic acid (C44) that inhibits human dihydroorotate dehydrogenase (DHODH) with an IC₅₀ of 1 nM, and viral replication of VSV and WSN-Influenza with an EC₅₀ of 2 nM and 41 nM. We also solved the X-ray structure of human DHODH bound to C44, providing structural insight into the potent inhibition of biaryl ether analogs of brequinar.

On dihydroorotate dehydrogenases and their inhibitors and uses

Proper nucleosides availability is crucial for the proliferation of living entities (eukaryotic cells, parasites, bacteria, and virus). Accordingly, the uses of inhibitors of the de novo nucleosides biosynthetic pathways have been investigated in the past. In the following we have focused on dihydroorotate dehydrogenase (DHODH), the fourth enzyme in the de novo pyrimidine nucleosides biosynthetic pathway. We first described the different types of enzyme in terms of sequence, structure, and biochemistry, including the reported bioassays. In a second part, the series of inhibitors of this enzyme along with a description of their potential or actual uses were reviewed. These inhibitors are indeed used in medicine to treat autoimmune diseases such as rheumatoid arthritis or multiple sclerosis (leflunomide and teriflunomide) and have been investigated in treatments of cancer, virus, and parasite infections (i.e., malaria) as well as in crop science.

Inhibition of pyrimidine synthesis reverses viral virulence factor-mediated block of mRNA nuclear export

The NS1 protein of influenza virus is a major virulence factor essential for virus replication, as it redirects the host cell to promote viral protein expression. NS1 inhibits cellular messenger ribonucleic acid (mRNA) processing and export, down-regulating host gene expression and enhancing viral gene expression. We report in this paper the identification of a nontoxic quinoline carboxylic acid that reverts the inhibition of mRNA nuclear export by NS1, in the absence or presence of the virus. This quinoline carboxylic acid directly inhibited dihydroorotate dehydrogenase (DHODH), a host enzyme required for de novo pyrimidine biosynthesis, and partially reduced pyrimidine levels. This effect induced NXF1 expression, which promoted mRNA nuclear export in the presence of NS1. The release of NS1-mediated mRNA export block by DHODH inhibition also occurred in the presence of vesicular stomatitis virus M (matrix) protein, another viral inhibitor of mRNA export. This reversal of mRNA export block allowed expression of antiviral factors. Thus, pyrimidines play a necessary role in the inhibition of mRNA nuclear export by virulence factors.

Brequinar derivatives and species-specific drug design for dihydroorotate dehydrogenase

Therapeutic agents brequinar sodium and leflunomide (Arava) work by binding in a hydrophobic tunnel formed by a highly variable N-terminus of family 2 dihydroorotate dehydrogenase (DHODH). The X-ray crystallographic structure of an analog of brequinar bound to human DHODH was determined. In silico screening of a library of compounds suggested another subset of brequinar analogs that do not inhibit human DHODH as potentially effective inhibitors of Plasmodium falciparum DHODH.

Malarial dihydroorotate dehydrogenase. Substrate and inhibitor specificity

The malarial parasite relies on de novo pyrimidine biosynthesis to maintain its pyrimidine pools, and unlike the human host cell it is unable to scavenge preformed pyrimidines. Dihydroorotate dehydrogenase (DHODH) catalyzes the oxidation of dihydroorotate (DHO) to produce orotate, a key step in pyrimidine biosynthesis. The enzyme is located in the outer membrane of the mitochondria of the malarial parasite. To characterize the biochemical properties of the malarial enzyme, an N-terminally truncated version of P. falciparum DHODH has been expressed as a soluble, active enzyme in E. coli. The recombinant enzyme binds 0.9 molar equivalents of the cofactor FMN and it has a pH maximum of 8.0 (k(cat) 8 s(-1), K(m)(app) DHO (40-80 microm)). The substrate specificity of the ubiquinone cofactor (CoQ(n)) that is required for the oxidation of FMN in the second step of the reaction was also determined. The isoprenoid (n) length of CoQ(n) was a determinant of reaction efficiency; CoQ(4), CoQ(6) and decylubiquinone (CoQ(D)) were efficiently utilized in the reaction, however cofactors lacking an isoprenoid tail (CoQ(0) and vitamin K(3)) showed decreased catalytic efficiency resulting from a 4 to 7-fold increase in K(m)(app). Five potent inhibitors of mammalian DHODH, Redoxal, dichloroallyl lawsone (DCL), and three analogs of A77 1726 were tested as inhibitors of the malarial enzyme. All five compounds were poor inhibitors of the malarial enzyme, with IC(50)'s ranging from 0.1-1.0 mm. The IC(50) values for inhibition of the malarial enzyme are 10(2)-10(4)-fold higher than the values reported for the mammalian enzyme, demonstrating that inhibitor binding to DHODH is species specific. These studies provide direct evidence that the malarial DHODH active site is different from the host enzyme, and that it is an attractive target for the development of new anti-malarial agents.

Synthetic study on novel immunosuppressant KF20444

The two new synthetic routes to 6,7-dihydro-10-fluoro-3-(2-fluorophenyl)-5H- benzo[6,7]cyclohepta[1,2-b]-quinoline-8-carboxylic acid (1), a novel immunosuppressant KF20444, are described. The seven-membered ring construction from 2-[4-(2-fluorophenyl)phenyl]-3-(2-carboxyethyl)-4-chloromethyl-6-fluoroquinoline (17c) was achieved by intramolecular Friedel-Crafts reaction under acidic conditions as the key step. Subsequently, the oxidation of 4-chloromethyl group followed by reduction of carbonyl group on the seven-membered ring afforded 1. This route provides a new method for the synthesis of 1.

Heteroatom- and carbon-linked biphenyl analogs of Brequinar as immunosuppressive agents

Structure-activity relationships were explored for some analogs of Brequinar having a linking atom between the 2-biphenyl substituent and the quinoline ring. Activities as inhibitors of dihydroorotate dehydrogenase and the mixed lymphocyte reaction were related to the overall shape and lipophilicity of the 2-substituent.