Synthesis and in vitro cytotoxicity evaluation of β-carboline-combretastatin carboxamides as apoptosis inducing agents: DNA intercalation and topoisomerase-II inhibition

To explore a new set of cytotoxic agents, β-carboline-combretastatin carboxamide conjugates were designed, synthesized and evaluated for their in vitro cytotoxicity potential, DNA binding affinity and Topoisomerase-II (topo-II) inhibition activity. Among the designed hybrids, 10v and 10af have shown significant cytotoxic effect against A549 (lung cancer) cell line having IC₅₀ value 1.01 µM and 1.17 µM respectively. Further, it was speculated that treatment with compound 10v may induce apoptosis among A549 cells, which was supported by Hoechst staining, DCFDA, Annexin V-FITC and morphological assays. Flow cytometric analysis revealed that the hybrid 10v arrests A549 cells in G2/M phase of cell cycle in a dose dependent manner. Amongst the active hybrids, most potent hybrid 10v was tested for DNA topo-II inhibition activity. Moreover, to further support the biological activity and to infer the mode of interaction between ligands and DNA, spectroscopy and molecular docking studies were carried out. The docking and spectroscopy results showed that the ligands exhibited an intercalative mode of binding with DNA and could efficiently bind to DNA and form topo-II ternary complex. Based on these experiments, the hybrids 10v and 10af were identified as proficient new scaffolds which need to be developed as hit molecules for therapeutic interest.     

Impaired methylation as a novel mechanism for proteasome suppression in liver cells

The proteasome is a multi-catalytic protein degradation enzyme that is regulated by ethanol-induced oxidative stress; such suppression is attributed to CYP2E1-generated metabolites. However, under certain conditions, it appears that in addition to oxidative stress, other mechanisms are also involved in proteasome regulation. This study investigated whether impaired protein methylation that occurs during exposure of liver cells to ethanol, may contribute to suppression of proteasome activity. We measured the chymotrypsin-like proteasome activity in Huh7CYP cells, hepatocytes, liver cytosols and nuclear extracts or purified 20S proteasome under conditions that maintain or prevent protein methylation. Reduction of proteasome activity of hepatoma cell and hepatocytes by ethanol or tubercidin was prevented by simultaneous treatment with S-adenosylmethionine (SAM). Moreover, the tubercidin-induced decline in proteasome activity occurred in both nuclear and cytosolic fractions. In vitro exposure of cell cytosolic fractions or highly purified 20S proteasome to low SAM:S-adenosylhomocysteine (SAH) ratios in the buffer also suppressed proteasome function, indicating that one or more methyltransferase(s) may be associated with proteasomal subunits. Immunoblotting a purified 20S rabbit red cell proteasome preparation using methyl lysine-specific antibodies revealed a 25 kDa proteasome subunit that showed positive reactivity with anti-methyl lysine. This reactivity was modified when 20S proteasome was exposed to differential SAM:SAH ratios. We conclude that impaired methylation of proteasome subunits suppressed proteasome activity in liver cells indicating an additional, yet novel mechanism of proteasome activity regulation by ethanol.     

Islet cell antigens and autoantigen(s): Monoclonal antibodies and further characterization

A novel series of murine monoclonal antibodies to islet cells (1–45, 1–51, 1–52 and 1–39) have been generated using human insulinoma homogenate as the immunogen in order to characterize pathogenetically relevant islet cell autoantigen(s). Differentiation antigens recognized by these islet cell monoclonal antibodies displayed varied cytological distribution (pan-islet or peripheral mantle only). Monoclonal antibody 1–45 reacted with all endocrine subsets of the pancreatic islet, similar to the reactivity of islet cell autoantibody positive sera from type I diabetes subjects. Preexposure to pH2 abolished the immunoreactivity of the autoantigen; 1–45 antigen was also sensitive to low pH. Preexposure to 100° C for 1 h did not significantly alter the immunoreactivity of islet antigens recognized by ICAb positive patient sera and monoclonal antibody 1–39, thus demonstrating the extraordinary heat stability of the corresponding epitopes; those recognized by 1–45 were less heat stable. Islet cells were found to share 1–45 differentiation antigen(s)/epitope(s) with other neuroendocrine cells,viz. amerior pituitary, adrenal medulla and gut endocrine cells.     

Clonal dominance patterns of CD8 T cells in relation to disease progression in HIV-infected children

CD8 T cells are important mediators of cellular immune responses as evidenced by clonal expansions in the CD8 TCR V beta repertoire during primary HIV infection in adults. This study investigated the CD8 TCR V beta repertoire by complementarity-determining region 3 length analysis using multiplex PCR in purified peripheral blood CD8 T cells of 22 HIV-infected children (age range was 0.75-15 yr, mean was 8.2 +/- 4.1 yr). Evidence of clonal dominance in one or more V beta families was obtained in 15 of 22 children. The patterns of clonal dominance were designated as major, minor, single, and none to indicate the involvement of three or more, two, one, or no V beta families, respectively. A pattern of major or minor clonal dominance was observed in 12 children (group 1), whereas 10 children had single or no clonal dominance (group 2). In comparison with group 2, the children in group 1 had a higher percentage of CD4 cells (28.3 +/- 11.6 vs 8.6 +/- 4.8, p < 0.001); a higher stimulation index in lymphoproliferative responses to Candida (92.0 +/- 59.5 vs 12.3 +/- 14.4, p = 0.002), tetanus (76.3 +/- 51.2 vs 11.2 +/- 12.7, p = 0.002), and alloantigens (178.3 +/- 298.9 vs 32.9 +/- 35.2, p < 0.001); and a lower percentage of CD8+HLA-DR+CD38+ cells (37.4 +/- 13.1 vs 54.6 +/- 14.2, p < 0.01). The number of dominant CD8 T cell clones was significantly correlated with the percentage of CD4 T cells (r = 0.669, p < 0.001) but not with plasma HIV RNA. Compared with group 1, patients in group 2 had a 4.8 times greater probability of having < 15% CD4 cells. These findings indicate that CD8 clonal dominance in HIV-infected children reflects robustness of immune responses, regardless of time since infection and virus load.     

Mitochondrial targeting of JNK/SAPK in the phorbol ester response of myeloid leukemia cells

Treatment of human U-937 myeloid leukemia cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) is associated with activation of the stress-activated protein kinase (SAPK) and induction of terminal monocytic differentiation. The present studies demonstrate that TPA targets SAPK to mitochondria by a mechanism dependent on activation of protein kinase C (PKC) beta. Translocation of SAPK to mitochondria in response to TPA is associated with release of cytochrome c, caspase-3 activation and induction of apoptosis. The results show that TPA induces the association of SAPK with the mitochondrial anti-apoptotic Bcl-x(L) protein. Overexpression of Bcl-x(L) attenuated the apoptotic response to TPA treatment. Moreover, expression of Bcl-x(L) mutated at sites of SAPK phosphorylation (Thr-47, -115) was more effective than wild-type Bcl-x(L) in abrogating TPA-induced cytochrome c release and apoptosis. By contrast, expression of Bcl-x(L) had little effect on induction of the monocytic phenotype. These findings indicate that myeloid leukemia cells respond to TPA with targeting of SAPK to mitochondria and that this response contributes to terminal differentiation through the release of cytochrome c and induction of apoptosis.