Characterization and drug sensitivity of four newly established colon adenocarcinoma cell lines to antifolate inhibitors of thymidylate synthase

Antigen presentation capability and AP-1 activation accompany methotrexate-induced colon cancer cell senescence in the context of aberrant β-catenin signaling

Reversible cellular senescence was demonstrated previously to constitute colon cancer cell response to methotrexate. The current study presents a comparison of two senescent states of colon cancer cells, arrested and reversing, resulting from respectively, 120 h exposure to the drug, and 48 h exposure followed by 96 h regrowth in drug-free media. The upregulation of immunoproteasome subunit-coding genes and the increase in human leukocyte antigen HLA-A/B/C membrane level indicated MHC-I-restricted antigen presentation as common to both senescent states. Nuclear factor NF-κB p65 level decreased and activating protein AP-1: c-Jun, Fra2 and JunB nuclear levels increased in both senescent cell populations. Notably, the increase in AP-1- dependent transcription occurred after 48 h exposure to methotrexate. β-catenin nuclear level increased after 48 h exposure to the drug and remained as such only in senescence-arrested cells. β-catenin level was found uncoupled from the protein phosphorylation status indicating the deregulation of β-catenin signaling in colon cancer cells employed in the study. These findings carry implications for both, a general mechanism of senescence establishment and putative advantages for colon cancer treatment.

Suppression of Cytosolic NADPH Pool by Thionicotinamide Increases Oxidative Stress and Synergizes with Chemotherapy

NAD(+) kinase (NADK) is the only known cytosolic enzyme that converts NAD(+) to NADP(+), which is subsequently reduced to NADPH. The demand for NADPH in cancer cells is elevated as reducing equivalents are required for the high levels of nucleotide, protein, and fatty acid synthesis found in proliferating cells as well as for neutralizing high levels of reactive oxygen species (ROS). We determined whether inhibition of NADK activity is a valid anticancer strategy alone and in combination with chemotherapeutic drugs known to induce ROS. In vitro and in vivo inhibition of NADK with either small-hairpin RNA or thionicotinamide inhibited proliferation. Thionicotinamide enhanced the ROS produced by several chemotherapeutic drugs and produced synergistic cell kill. NADK inhibitors alone or in combination with drugs that increase ROS-mediated stress may represent an efficacious antitumor combination and should be explored further.

Novel targets in drug design: enzymes in the protein ubiquitylation pathway

Protein ubiquitylation is a pathway by which many proteins are selectively degraded. Its role has been shown in processes such as cell division and differentiation, oncogenesis, apoptosis, DNA repair, membrane transport and the removal of abnormal proteins. The ubiquitylation pathway enzymes are an insufficiently researched area for drug development. A genetic method has been developed (supported by computational biology) to identify potentially useful small molecules that will have a positive impact on our battle against cancer and other diseases. In silico screening is used for initial selection of drug-like compounds. This method is based on docking three-dimensional chemical libraries onto the target enzyme's functional site for initial screens using a computational scheme, followed by genetic and in vivo methods for hit optimisation. Focus has been on using the ubiquitin conjugation pathway as target for therapeutic intervention against cancer and potent inhibitors of ubiquitylation subpathways have been obtained (including those that are vital for the survival of aggressive cancer cells/tumours). Leads from the development of in vitro inhibitors provided a direction for the development of in vivo inhibitors as investigational tools, and as promising therapeutic agents.

Functional gene expression profile underlying methotrexate-induced senescence in human colon cancer cells

Cellular functions accompanying establishment of premature senescence in methotrexate-treated human colon cancer C85 cells are deciphered in the present study from validated competitive expression microarray data, analyzed with the use of Ingenuity Pathways Analysis (IPA) software. The nitrosative/oxidative stress, inferred from upregulated expression of inducible nitric oxide synthase (iNOS) and mitochondrial dysfunction-associated genes, including monoamine oxidases MAOA and MAOB, β-amyloid precursor protein (APP) and presenilin 1 (PSEN1), is identified as the main determinant of signaling pathways operating during senescence establishment. Activation of p53-signaling pathway is found associated with both apoptotic and autophagic components contributing to this process. Activation of nuclear factor κB (NF-κB), resulting from interferon γ (IFNγ), integrin, interleukin 1β (IL-1β), IL-4, IL-13, IL-22, Toll-like receptors (TLRs) 1, 2 and 3, growth factors and tumor necrosis factor (TNF) superfamily members signaling, is found to underpin inflammatory properties of senescent C85 cells. Upregulation of p21-activated kinases (PAK2 and PAK6), several Rho molecules and myosin regulatory light chains MYL12A and MYL12B, indicates acquisition of motility by those cells. Mitogen-activated protein kinase p38 MAPK β, extracellular signal-regulated kinases ERK2 and ERK5, protein kinase B AKT1, as well as calcium, are identified as factors coordinating signaling pathways in senescent C85 cells.

Methotrexate-induced senescence in human adenocarcinoma cells is accompanied by induction of p21(waf1/cip1) expression and lack of polyploidy

Human colorectal adenocarcinoma C85 cells, treated with high dose methotrexate (1 microM; IC(50)=51 nM), undergo accelerated senescence, as the cells (i) are growth arrested at the G(1) and S phases of the cell cycle, (ii) are SA-beta-galactosidase-positive, (iii) show induced expression of p21(waf1/cip1) and decreased expression of p16(INK4a), and (iv) show DNA synthesis continued at the reduced level. The fraction of C85 cells with DNA content higher than 4N is maintained at the same level (14%) in cells untreated, as well as regrown after the treatment. Multinucleation is found as the main karyotypic abnormality.

EGFP fluorescence as an indicator of cancer cells response to methotrexate

Methotrexate action in viable cells was monitored by registering changes in EGFP (Enhanced Green Fluorescent Protein) fluorescence intensity. Treatment with 1 microM methotrexate for 48 h of human colorectal adenocarcinoma C85 cells, stably transfected to express EGFP, caused 5-fold increase in EGFP fluorescence assayed by flow cytometry with no distinct increase in EGFP protein level. This was correlated with morphological changes, including an increase of cell granularity and cell shape flattening, as well as cell cycle G1 phase arrest revealed by DNA content analysis. Methotrexate removal allowed the morphology of the cells in culture to revert in 10 days to normal. The cells that survived methotrexate exposure were propagated as C85r cell subline and displayed kinetics of methotrexate sensitivity parallel to that of the parental C85 line. As the increase in EGFP fluorescence could also be visualized by fluorescence microscopy, this reporter system may be employed to image methotrexate action in cancer cells in living models.

Differential gene expression associated with migration of mesenchymal stem cells to conditioned medium from tumor cells or bone marrow cells

Distinct signals that guide migration of mesenchymal stem cells (MSCs) to specific in vivo targets remain unknown. We have used rat MSCs to investigate the molecular mechanisms involved in such migration. Rat MSCs were shown to migrate to tumor microenvironment in vivo, and an in vitro migration assay was used under defined conditions to permit further mechanistic investigations. We hypothesized that distinct molecular signals are involved in the homing of MSCs to tumor sites and bone marrow. To test this hypothesis, gene expression profiles of MSCs exposed in vitro to conditioned medium (CM) from either tumor cells or bone marrow were compared. Analysis of the microarray gene expression data revealed that 104 transcripts were upregulated in rat MSCs exposed to CM from C85 human colorectal cancer cells for 24 hours versus control medium. A subset of 12 transcripts were found to be upregulated in rat MSCs that were exposed to tumor cell CM but downregulated when MSCs were exposed to bone marrow CM and included CXCL-12 (stromal cell-derived factor-1 [SDF-1]), CXCL-2, CINC-2, endothelial cell specific molecule-1, fibroblast growth factor-7, nuclear factor-kappaB p105, and thrombomodulin. Exposure to tumor cell CM enhanced migration of MSCs and correlated with increased SDF-1 protein production. Moreover, knockdown of SDF-1 expression in MSCs inhibited migration of these cells to CM from tumor cells, but not bone marrow cells, confirming the importance of SDF-1 expression by MSCs in this differential migration. These results suggest that increased SDF-1 production by MSCs acts in an autocrine manner and is required for migratory responses to tumor cells.