Role of poly(ADP-ribose) polymerase activity in imatinib mesylate-induced cell death

Imatinib modulates pro-inflammatory microenvironment with angiostatic effects in experimental lung carcinogenesis

Lung cancer has second highest rate of incidence and mortality around the world. Smoking cigarettes is the main stream cause of lung carcinogenesis along with other factors such as spontaneous mutations, inactivation of tumor suppressor genes. The present study was aimed to identify the mechanistic role of Imatinib in the chemoprevention of experimental lung carcinogenesis in rat model. Gross morphological observations for tumor formation, histological examinations, RT-PCR, Western blotting, fluorescence spectroscopy and molecular docking studies were performed to elucidate the chemopreventive effects of Imatinib and support our hypothesis by various experiments. It is evident that immuno-compromised microenvironment inside solid tumors is responsible for tumor progression and drug resistance. Therefore, it is inevitable to modulate the pro-inflammatory signaling inside solid tumors to restrict neoangiogenesis. In the present study, we observed that Imatinib could downregulate the inflammatory signaling and also attributed angiostatic effects. Moreover, Imatinib also altered the biophysical properties of BAL cells such as plasma membrane potential, fluidity and microviscosity to restrict their infiltration and thereby accumulation to mount immuno-compromised environment inside the solid tumors during angiogenesis. Our molecular docking studies suggest that immunomodulatory and angiostatic properties of Imatinib could be either independent of each other or just a case of synergistic pleiotropy. Imatinib was observed to activate the intrinsic or mitochondrial pathway of apoptosis to achieve desired effects in cancer cell killings. Interestingly, binding of Imatinib inside the catalytic domain of PARP-1 also suggests that it has caspase-independent properties in promoting cancer cell deaths.

Poly ADP-ribose polymerase inhibition suppresses cisplatin toxicity in chronic myeloid leukemia cells

Cancer cells may acquire drug resistance by activating DNA repair signaling. Poly ADP-ribose polymerase (PARP) plays an important role in DNA repair and it is overexpressed in many cancers including chronic myeloid leukemia (CML). PARP inhibitors have been used either alone or with other drugs to augment cancer cell death. However, whether PARP inhibitors may also augment cell death induced by chemotherapeutic agents in CML cells has not been studied. K562 cells with or without PARP-1 knockdown were treated with cisplatin alone or together with olaparib. The cell death was investigated by propidium iodide staining and apoptosis-related proteins were detected by western blotting. Olaparib suppressed cisplatin-induced cell death in K562 and MEG01 cells. Moreover, PARP-1 knockdown also attenuated cisplatin toxicity in CML cells. Inhibition of PARP decreased cisplatin toxicity by attenuating caspase-3 and caspase-9 activity. These results indicated that the toxicity of cisplatin in CML cells requires PARP activity. Therefore, PARP inhibitors may not be useful with DNA-damaging agents such as cisplatin in CML treatment.

MTLD, a Database of Multiple Target Ligands, the Updated Version

Polypharmacology plays an important role in drug discovery and polypharmacology drug strategies provide a novel path in drug design. However, to develop a polypharmacology drug with the desired profile remains a challenge. Previously, we developed a free web-accessible database called Multiple Target Ligand Database (MTLD, www.mtdcadd.com). Herein, the MTLD database has been updated, containing 2444 Multiple Target Ligands (MTLs) that bind with 21,424 binding sites from 18,231 crystal structures. Of the MTLs, 304 entries are approved drugs, and 1911 entries are drug-like compounds. Also, we added new functions such as multiple conditional search and linkage visualization. Through querying the updated database, extremely useful information for the development of polypharmacology drugs may be provided.

Anti-fibrotic activity and enhanced interleukin-6 production by hepatic stellate cells in response to imatinib mesylate

OBJECTIVE

To examine imatinib mesylate's effects on stellate cell responses in vivo and in vitro. The hepatic stellate cell (HSC) is a key target of anti-fibrotic therapies. Imatinib mesylate is a small molecule receptor tyrosine kinase inhibitor indicated for treatment of chronic myelogenous leukaemia and GI stromal tumours.

DESIGN

Because imatinib inhibits β-PDGFR signalling, which stimulates HSC proliferation, we assessed its activity in culture and in vivo, and examined downstream targets in a human stellate cell line (LX-2) using cDNA microarray.

METHODS AND RESULTS

Imatinib inhibited proliferation of LX-2 cells (0.5-10 mM) but not primary human stellate cells, with no effect on viability, associated with attenuated β-PDGFR phosphorylation. Mitochondrial activity and superoxide anion production were decreased in response to imatinib. cDNA microarray uncovered up-regulation of 29 genes in response to imatinib, including interleukin-6 (IL-6) mRNA, which was correlated with progressive IL-6 secretion. Imatinib also decreased gene expression of collagen α(1) (I), alpha smooth muscle actin, β-PDGFR, transforming growth factor β receptor type 1, matrix metalloproteinase 2 and tissue inhibitor of metalloproteinase 2. In vivo, imatinib administered to rats beginning 4 weeks after starting thioacetamide (TAA) led to reduced collagen content, with significant reductions in portal pressure and down-regulation of fibrogenic genes in whole liver. Importantly, hepatic IL-6 mRNA levels were significantly increased in TAA-treated animals receiving imatinib.

CONCLUSIONS

These findings reinforce the anti-fibrotic activity of imatinib and uncover an unexpected link between inhibition of HSC activation by imatinib and enhanced secretion of IL-6, a regenerative cytokine.

BGP-15, a PARP-inhibitor, prevents imatinib-induced cardiotoxicity by activating Akt and suppressing JNK and p38 MAP kinases

In this study, we investigate the cardiotoxic effects of the well-known cytostatic agent imatinib mesylate (Gleevec), and presented evidence for the cardioprotective effect of BGP-15 which is a novel insulin sensitizer. The cardiotoxic effect of imatinib mesylate was assessed in Langendorff rat heart perfusion system. The cardiac high-energy phosphate levels (creatine phosphate (PCr) and ATP) were monitored in situ by (31)P NMR spectroscopy. The protein oxidation, lipid peroxidation, and the activation of signaling pathways were determined from the freeze-clamped hearts. Prolonged treatment of the heart with imatinib mesylate (20 mg/kg) resulted in cardiotoxicity, which were characterized by the depletion of high-energy phosphates (PCr and ATP), and significantly increased protein oxidation and lipid peroxidation. Imatinib mesylate treatment-induced activation of MAP kinases (including ERK1/2, p38, and JNK) and the phosphorylation of Akt and GSK-3beta. BGP-15 (200 μM) prevented the imatinib mesylate-induced oxidative damages, attenuated the depletion of high-energy phosphates, altered the signaling effect of imatinib mesylate by preventing p38 MAP kinase and JNK activation, and induced the phosphorylation of Akt and GSK-3beta. The suppressive effect of BGP-15 on p38 and JNK activation could be significant because these kinases contribute to the cell death and inflammation in the isolated perfused heart.

Global proteome quantification for discovering imatinib-induced perturbation of multiple biological pathways in K562 human chronic myeloid leukemia cells

Imatinib mesylate, currently marketed by Novartis as Gleevec in the U.S., has emerged as the leading compound to treat the chronic phase of chronic myeloid leukemia (CML), through its inhibition of Bcr-Abl tyrosine kinases, and other cancers. However, resistance to imatinib develops frequently, particularly in late-stage disease. To identify new cellular pathways affected by imatinib treatment, we applied mass spectrometry together with stable isotope labeling by amino acids in cell culture (SILAC) for the comparative study of protein expression in K562 cells that were untreated or treated with a clinically relevant concentration of imatinib. Our results revealed that, among the 1344 quantified proteins, 73 had significantly altered levels of expression induced by imatinib and could be quantified in both forward and reverse SILAC labeling experiments. These included the down-regulation of thymidylate synthase, S-adenosylmethionine synthetase, and glycerol-3-phosphate dehydrogenase as well as the up-regulation of poly(ADP-ribose) polymerase 1, hemoglobins, and enzymes involved in heme biosynthesis. We also found, by assessing alteration in the acetylation level in histone H4 upon imatinib treatment, that the imatinib-induced hemoglobinization and erythroid differentiation in K562 cells are associated with global histone H4 hyperacetylation. Overall, these results provided potential biomarkers for monitoring the therapeutic intervention of CML using imatinib and offered important new knowledge for gaining insight into the molecular mechanisms of action of imatinib.

Short term culture of breast cancer tissues to study the activity of the anticancer drug taxol in an intact tumor environment

BACKGROUND

Sensitivity of breast tumors to anticancer drugs depends upon dynamic interactions between epithelial tumor cells and their microenvironment including stromal cells and extracellular matrix. To study drug-sensitivity within different compartments of an individual tumor ex vivo, culture models directly established from fresh tumor tissues are absolutely essential.

METHODS

We prepared 0.2 mm thick tissue slices from freshly excised tumor samples and cultivated them individually in the presence or absence of taxol for 4 days. To visualize viability, cell death, and expression of surface molecules in different compartments of non-fixed primary breast cancer tissues we established a method based on confocal imaging using mitochondria- and DNA-selective dyes and fluorescent-conjugated antibodies. Proliferation and apoptosis was assessed by immunohistochemistry in sections from paraffin-embedded slices. Overall viability was also analyzed in homogenized tissue slices by a combined ATP/DNA quantification assay.

RESULTS

We obtained a mean of 49 tissue slices from 22 breast cancer specimens allowing a wide range of experiments in each individual tumor. In our culture system, cells remained viable and proliferated for at least 4 days within their tissue environment. Viability of tissue slices decreased significantly in the presence of taxol in a dose-dependent manner. A three-color fluorescence viability assay enabled a rapid and authentic estimation of cell viability in the different tumor compartments within non-fixed tissue slices.

CONCLUSION

We describe a tissue culture method combined with a novel read out system for both tissue cultivation and rapid assessment of drug efficacy together with the simultaneous identification of different cell types within non-fixed breast cancer tissues. This method has potential significance for studying tumor responses to anticancer drugs in the complex environment of a primary cancer tissue.