P53 status influences regulation of HSPs and ribosomal proteins by PDTC and radiation

Novel hydrazide-hydrazone and amide substituted coumarin derivatives: Synthesis, cytotoxicity screening, microarray, radiolabeling and in vivo pharmacokinetic studies

The current work presents the synthesis and biological evaluation of new series of coumarin hydrazide-hydrazone derivatives that showed in vitro broad spectrum antitumor activities against resistant pancreatic carcinoma (Panc-1), hepatocellular carcinoma (HepG2) and leukemia (CCRF) cell lines using doxorubicin as reference standard. Bromocoumarin hydrazide-hydrazone derivative (BCHHD) 11b showed excellent anticancer activity against all tested cancer cell lines. Enzyme assays showed that BCHHD 11b induced apoptosis due to activation of caspases 3/7. Moreover, 11b inhibited GST and CYP3A4 in a dose dependent manner and the induced cell death could be attributed to metabolic inhibition. Moreover, 11b microarray analysis showed significant up- and down-regulation of many genes in the treated cells related to apoptosis, cell cycle, tumor growth and suppressor genes. All of the above presents BCHHD 11b as a potent anticancer agent able to overcome drug resistance. In addition, compound 11b was able to serve as a chemical carrier for ^99mTc and the in vivo biodistribution study of ^99mTc-11b complex revealed a remarkable targeting ability of ^99mTc into solid tumor showing that ^99mTc-11b might be used as a promising radiopharmaceutical imaging agent for cancer.

The Role of Sulfhydryl Reactivity of Small Molecules for the Activation of the KEAP1/NRF2 Pathway and the Heat Shock Response

The KEAP1/NRF2 pathway and the heat shock response are two essential cytoprotective mechanisms that allow adaptation and survival under conditions of oxidative, electrophilic, and thermal stress by regulating the expression of elaborate networks of genes with versatile protective functions. The two pathways are independently regulated by the transcription factor nuclear factor-erythroid 2 p45-related factor 2 (NRF2) and heat shock factor 1 (HSF1), respectively. The activity of these transcriptional master regulators increases during conditions of stress and also upon encounter of small molecules (inducers), both naturally occurring as well as synthetically produced. Inducers have a common chemical property: the ability to react with sulfhydryl groups. The protein targets of such sulfhydryl-reactive compounds are equipped with highly reactive cysteine residues, which serve as sensors for inducers. The initial cysteine-sensed signal is further relayed to affect the expression of large networks of genes, which in turn can ultimately influence complex cell fate decisions such as life and death. The paper summarizes the multiple lines of experimental evidence demonstrating that the reactivity with sulfhydryl groups is a major determinant of the mechanism of action of small molecule dual activators of the KEAP1/NRF2 pathway and the heat shock response.

Pyrrolidine dithiocarbamate (PDTC) blocks apoptosis and promotes ionizing radiation-induced necrosis of freshly-isolated normal mouse spleen cells

Ionizing radiation (IR) is a pro-oxidant that kills cells by both apoptotic and necrotic mechanisms. Pyrrolidine dithiocarbamate (PDTC) is a thiol-containing compound that may act either as a pro- or anti-oxidant depending on the experimental conditions. This study was designed to determine whether PDTC would reduce or enhance IR-induced cell death of freshly-isolated normal mouse B6/129 spleen cells (NMSC). We determined the effect of increasing doses of IR, PDTC alone and PDTC followed by IR on the viability of NMSC. Annexin V and propidium iodide (Annexin V/PI) staining demonstrated a dose and time-dependent relationship in which PDTC enhanced the percentage of IR-induced apoptotic/necrotic NMSC. Trypan blue dye inclusion confirmed that a loss of membrane integrity was occurring 1 h after incubation with PDTC plus IR. Reduction in the glutathione (GSH)/glutathione disulfide (GSSG) ratio and GSH demonstrated that both IR (8.5 Gy) and PDTC acted as pro-oxidants, but their mechanisms of action differed: In contrast to IR, which promoted p53 activation and caspase 3/7-mediated apoptosis, PDTC inhibited IR-induced p53 and caspase 3/7 activity. However, PDTC increased H(2)O(2) formation and necrosis, resulting in an overall increase in IR-induced cell death. Catalase prevented the PDTC-induced increase in IR cytotoxicity implicating the generation of H(2)O(2) as a major factor in this mechanism. These results demonstrate that in NMSC PDTC acts as pro-oxidant and enhances IR-induced cell cytotoxicity by increasing H(2)O(2)formation and thiol oxidation. As such, they strongly suggest that the use of PDTC as an adjunct to reduce radiation toxicity should be avoided.

S-glutathionylation impairs signal transducer and activator of transcription 3 activation and signaling

S-glutathionylation is a physiological, reversible protein modification of cysteine residues with glutathione in response to mild oxidative stress. Because the key cell growth regulator signal transducer and activator of transcription (STAT) 3 is particularly susceptible to redox regulation, we hypothesized that oxidative modification of cysteine residues of STAT3 by S-glutathionylation may occur. Herein, we show that the cysteine residues of STAT3 are modified by a thiol-alkylating agent and are the targets of S-glutathionylation. STAT3 protein thiol reactivity was reversibly attenuated with concomitant increase in the S-glutathionylation of STAT3 upon treatment of human HepG2 hepatoma cells with pyrrolidine dithiocarbamate, glutathione disulfide, or diamide. Under these conditions there was a marked reduction in IL-6-dependent STAT3 signaling, including decreased STAT3 tyrosine phosphorylation, loss in nuclear accumulation of STAT3, and impaired expression of target genes, such as fibrinogen-gamma. In a cell-free system, diamide induced glutathionylation of STAT3, which was decreased upon addition of glutaredoxin (GRX)-1, a deglutathionylation enzyme, or the reducing agent, dithiothreitol. Glutathionylated STAT3 was a poor Janus protein tyrosine kinase 2 substrate in vitro, and it exhibited low DNA-binding activity. Cellular GRX-1 activity was inhibited by diamide and pyrrolidine dithiocarbamate treatment; however, ectopic expression of GRX-1 was accompanied by a modest increase in phosphorylation, nuclear translocation, and DNA-binding ability of STAT3 in response to IL-6. These results are the first to show S-glutathionylation of STAT3, a modification that may exert regulatory function in STAT3 signaling.

Augmentation of innate immunity by low-dose irradiation

The effect of low-dose irradiation on the immune system was investigated in mice. When a 0.2 Gy dose of X-ray irradiation was administered every other day for a total of four times, the number of lymphocytes yielded by the liver, spleen and thymus decreased at the initial stage (around day 10). At this stage, NK cells, extrathymic T cells and NKT cells were found to be radioresistant. In other words, conventional lymphocytes were radiosensitive, even in the case of low-dose irradiation. However, the number of lymphocytes in all tested immune organs increased beyond the control level at the recovery stage (around day 28). Enumeration of the absolute number of lymphocyte subsets showed that the most prominently expanding populations were NK cells, extrathymic T cells and NKT cells, especially in the liver where primordial lymphocytes are primarily present. Functional and phenotypic activation of these populations also occurred at the recovery stage. It raised a possibility that an initial activation of macrophages by low-dose irradiation then mediated the present phenomenon. These results suggest that low-dose irradiation eventually has the potential to induce a hormesis effect on the immune system.