2,4-Diamino-5-methyl-6-substituted arylthio-furo[2,3-d]pyrimidines as novel classical and nonclassical antifolates as potential dual thymidylate synthase and dihydrofolate reductase inhibitors

A novel classical antifolate N-{4-[(2,4-diamino-5-methyl-furo[2,3-d]pyrimidin-6-yl)thio]-benzoyl}-l-glutamic acid 5 and 11 nonclassical antifolates 6–16 were designed, synthesized, and evaluated as inhibitors of dihydrofolate reductase (DHFR) and thymidylate synthase (TS). The nonclassical compounds 6–16 were synthesized from 20 via oxidative addition of substituted thiophenols using iodine. Peptide coupling of the intermediate acid 21 followed by saponification gave the classical analog 5. Compound 5 is the first example, to our knowledge, of a 2,4-diamino furo[2,3-d]pyrimidine classical antifolate that has inhibitory activity against both human DHFR and human TS. The classical analog 5 was a nanomolar inhibitor and remarkably selective inhibitor of Pneumocystis carinii DHFR and Mycobacterium avium DHFR at 263-fold and 2107-fold, respectively, compared to mammalian DHFR. The nonclassical analogs 6–16 were moderately potent against pathogen DHFR or TS. This study shows that the furo[2,3-d]pyrimidine scaffold is conducive to dual human DHFR-TS inhibitory activity and to high potency and selectivity for pathogen DHFR.     

The sphingosine kinase 1 inhibitor 2-(p-hydroxyanilino)-4-(p-chlorophenyl)thiazole induces proteasomal degradation of sphingosine kinase 1 in mammalian cells

Sphingosine kinase 1 (SK1) is an enzyme that catalyzes the phosphorylation of sphingosine to produce the bioactive lipid sphingosine 1-phosphate (S1P). We demonstrate here that the SK1 inhibitor, SKi (2-(p-hydroxyanilino)-4-(p-chlorophenyl)thiazole) induces the proteasomal degradation of SK1 in human pulmonary artery smooth muscle cells, androgen-sensitive LNCaP prostate cancer cells, MCF-7 and MCF-7 HER2 breast cancer cells and that this is likely mediated by ceramide as a consequence of catalytic inhibition of SK1 by SKi. Moreover, SK1 is polyubiquitinated under basal conditions, and SKi appears to increase the degradation of SK1 by activating the proteasome. In addition, the proteasomal degradation of SK1a and SK1b in androgen-sensitive LNCaP cells is associated with the induction of apoptosis. However, SK1b in LNCaP-AI cells (androgen-independent) is less sensitive to SKi-induced proteasomal degradation and these cells are resistant to SKi-induced apoptosis, thereby implicating the ubiquitin-proteasomal degradation of SK1 as an important mechanism controlling cell survival.     

Antiangiogenic activity of 2-deoxy-D-glucose

Background

During tumor angiogenesis, endothelial cells (ECs) are engaged in a number of energy consuming biological processes, such as proliferation, migration, and capillary formation. Since glucose uptake and metabolism are increased to meet this energy need, the effects of the glycolytic inhibitor 2-deoxy-D-glucose (2-DG) on in vitro and in vivo angiogenesis were investigated.

Methodology/Principal Findings

In cell culture, 2-DG inhibited EC growth, induced cytotoxicity, blocked migration, and inhibited actively forming but not established endothelial capillaries. Surprisingly, 2-DG was a better inhibitor of these EC properties than two more efficacious glycolytic inhibitors, 2-fluorodeoxy-D-glucose and oxamate. As an alternative to a glycolytic inhibitory mechanism, we considered 2-DG''s ability to interfere with endothelial N-linked glycosylation. 2-DG''s effects were reversed by mannose, an N-linked glycosylation precursor, and at relevant concentrations 2-DG also inhibited synthesis of the lipid linked oligosaccharide (LLO) N-glycosylation donor in a mannose-reversible manner. Inhibition of LLO synthesis activated the unfolded protein response (UPR), which resulted in induction of GADD153/CHOP and EC apoptosis (TUNEL assay). Thus, 2-DG''s effects on ECs appeared primarily due to inhibition of LLOs synthesis, not glycolysis. 2-DG was then evaluated in two mouse models, inhibiting angiogenesis in both the matrigel plug assay and the LH_BETAT_AG transgenic retinoblastoma model.

Conclusions/Significance

In conclusion, 2-DG inhibits endothelial cell angiogenesis in vitro and in vivo, at concentrations below those affecting tumor cells directly, most likely by interfering with N-linked glycosylation rather than glycolysis. Our data underscore the importance of glucose metabolism on neovascularization, and demonstrate a novel approach for anti-angiogenic strategies.     

Comparison of dengue virus type 2-specific small RNAs from RNA interference-competent and -incompetent mosquito cells

The exogenous RNA interference (RNAi) pathway is an important antiviral defense against arboviruses in mosquitoes, and virus-specific small interfering (si)RNAs are key components of this pathway. Understanding the biogenesis of siRNAs in mosquitoes could have important ramifications in using RNAi to control arbovirus transmission. Using deep sequencing technology, we characterized dengue virus type 2 (DENV2)-specific small RNAs produced during infection of Aedes aegypti mosquitoes and A. aegypti Aag2 cell cultures and compared them to those produced in the C6/36 Aedes albopictus cell line. We show that the size and mixed polarity of virus-specific small RNAs from DENV-infected A. aegypti cells indicate that they are products of Dicer-2 (Dcr2) cleavage of long dsRNA, whereas C6/36 cells generate DENV2-specific small RNAs that are longer and predominantly positive polarity, suggesting that they originate from a different small RNA pathway. Examination of virus-specific small RNAs after infection of the two mosquito cell lines with the insect-only flavivirus cell fusing agent virus (CFAV) corroborated these findings. An in vitro assay also showed that Aag2 A. aegypti cells are capable of siRNA production, while C6/36 A. albopictus cells exhibit inefficient Dcr2 cleavage of long dsRNA. Defective expression or function of Dcr2, the key initiator of the RNAi pathway, might explain the comparatively robust growth of arthropod-borne viruses in the C6/36 cell line, which has been used frequently as a surrogate for studying molecular interactions between arboviruses and cells of their mosquito hosts.     

Effective inhibition of K(b)- and D(b)-restricted antigen presentation in primary macrophages by murine cytomegalovirus

Macrophages play an important role in murine cytomegalovirus (MCMV) infection in vivo, both in disseminating infection and in harboring latent virus. MCMV encodes three immune evasion genes (m4, m6, and m152) that interfere with the ability of cytotoxic T cells (CTL) to detect virus-infected fibroblasts, but the efficacy of immune evasion in macrophages has been controversial. Here we show that MCMV immune evasion genes function in H-2(b) primary bone marrow macrophages (BMMphi) in the same way that they do in fibroblasts. Metabolic labeling experiments showed that class I is retained in the endoplasmic reticulum by MCMV infection and associates with m4/gp34 to a similar extent in fibroblasts and BMMphi. We tested a series of K(b)- and D(b)-restricted CTL clones specific for MCMV early genes against a panel of MCMV wild-type virus and mutants lacking m152, m4, or m6. MCMV immune evasion genes effectively inhibited antigen presentation. m152 appeared sufficient to abolish D(b)-restricted presentation in infected macrophages, as has been previously observed in infected fibroblasts. However, for inhibition of recognition of infected macrophages by K(b)-restricted CTL, m4, m6, and m152 were all required. The contribution of m4 to inhibition of recognition appeared much more important in macrophages than in fibroblasts. Thus, MCMV immune evasion genes function effectively in primary macrophages to prevent CTL recognition of early antigens and show the same pattern of major histocompatibility complex class I allele discrimination as is seen in fibroblasts. Furthermore, for inhibition of K(b)-restricted presentation, a strong synergistic effect was noted among m152, m4, and m6.     

Analyzing antibody specificity with whole proteome microarrays

Although approximately 10,000 antibodies are available from commercial sources, antibody reagents are still unavailable for most proteins. Furthermore, new applications such as antibody arrays and monoclonal antibody therapeutics have increased the demand for more specific antibodies to reduce cross-reactivity and side effects. An array containing every protein for the relevant organism represents the ideal format for an assay to test antibody specificity, because it allows the simultaneous screening of thousands of proteins for possible cross-reactivity. As an initial test of this approach, we screened 11 polyclonal and monoclonal antibodies to approximately 5,000 different yeast proteins deposited on a glass slide and found that, in addition to recognizing their cognate proteins, the antibodies cross-reacted with other yeast proteins to varying degrees. Some of the interactions of the antibodies with noncognate proteins could be deduced by alignment of the primary amino acid sequences of the antigens and cross-reactive proteins; however, these interactions could not be predicted a priori. Our findings show that proteome array technology has potential to improve antibody design and selection for applications in both medicine and research.     

HLA-B27 misfolding in transgenic rats is associated with activation of the unfolded protein response

The mechanism by which the MHC class I allele, HLA-B27, contributes to spondyloarthritis pathogenesis is unknown. In contrast to other alleles that have been examined, HLA-B27 has a tendency to form high m.w. disulfide-linked H chain complexes in the endoplasmic reticulum (ER), bind the ER chaperone BiP/Grp78, and undergo ER-associated degradation. These aberrant characteristics have provided biochemical evidence that HLA-B27 is prone to misfold. Recently, similar biochemical characteristics of HLA-B27 were reported in cells from HLA-B27/human beta2-microglobulin transgenic (HLA-B27 transgenic) rats, an animal model of spondyloarthritis, and correlated with disease susceptibility. In this study, we demonstrate that the unfolded protein response (UPR) is activated in macrophages derived from the bone marrow of HLA-B27 transgenic rats with inflammatory disease. Microarray analysis of these cells also reveals an IFN response signature. In contrast, macrophages derived from premorbid rats do not exhibit a strong UPR or evidence of IFN exposure. Activation of macrophages from premorbid HLA-B27 transgenic rats with IFN-gamma increases HLA-B27 expression and leads to UPR induction, while no UPR is seen in cells from nondisease-prone HLA-B7 transgenic or wild-type (nontransgenic) animals. This is the first demonstration, to our knowledge, that HLA-B27 misfolding is associated with ER stress that results in activation of the UPR. These observations link HLA-B27 expression with biological effects that are independent of immunological recognition, but nevertheless may play an important role in the pathogenesis of inflammatory diseases associated with this MHC class I allele.     

Plant catechols prevent lipid peroxidation in human plasma and erythrocytes

The antioxidant activity of several plant catechol derivatives was tested in buffer, plasma, and human erythrocytes. In buffer, chlorogenic acid (CGA), caffeic acid (CA), and dihydrocaffeic acid (DCA) reduced ferric iron equally well in the ferric reducing antioxidant power (FRAP) assay. Low concentrations of the polyphenols enhanced the ability of plasma to reduce ferric iron by about 10%. In plasma, lipid hydroperoxide and F₂-isoprostane formation induced by a water-soluble free radical initiator were reduced by CGA at concentrations as low as 20 M. During incubation at 37°C, human erythrocytes took up DCA, but not CGA, and intracellular DCA enhanced the ability of erythrocytes to reduce extracellular ferricyanide. When intact erythrocytes were exposed to oxidant stress generated by liposomes containing small amounts of lipid hydroperoxides, extracellular CGA at a concentration of 5 M decreased both lipid peroxidation in the liposomes, and spared -tocopherol in erythrocyte membranes. These results suggest that the catechol structure of these compounds convey the antioxidant effect in plasma and in erythrocytes.