A second target of benzamide riboside Roussel, Breton; Johnson-Farley, Nadine; Kerrigan, John E. ...
Cancer biology & therapy,
11/2012, Letnik:
13, Številka:
13
Journal Article
Recenzirano
Odprti dostop
Dihydrofolate reductase (DHFR) is an essential enzyme involved in de novo purine and thymidine biosynthesis. For several decades, selective inhibition of DHFR has proven to be a potent therapeutic ...approach in the treatment of various cancers including acute lymphoblastic leukemia, non-Hodgkin's lymphoma, osteogenic sarcoma, carcinoma of the breast, and head and neck cancer. Therapeutic success with DHFR inhibitor methotrexate (MTX) has been compromised in the clinic, which limits the success of MTX treatment by both acquired and intrinsic resistance mechanisms. We report that benzamide riboside (BR), via anabolism to benzamide adenine dinucleotide (BAD) known to potently inhibit inosine monophosphate dehydrogenase (IMPDH), also inhibits cell growth through a mechanism involving downregulation of DHFR protein. Evidence to support this second site of action of BR includes the finding that CCRF-CEM/R human T-cell lymphoblasic leukemia cells, resistant to MTX as a consequence of gene amplification and overexpression of DHFR, are more resistant to BR than are parental cells. Studies of the mechanism by which BR lowers DHFR showed that BR, through its metabolite BAD, reduced NADP and NADPH cellular levels by inhibiting nicotinamide adenine dinucleotide kinase (NADK). As consequence of the lack of NADPH, DHFR was shown to be destabilized. We suggest that, inhibition of NADK is a new approach to downregulate DHFR and to inhibit cell growth.
Mesenchymal stem cells (MSCs) are multipotent cells that exhibit two main characteristics which define stem cells: self-renewal and differentiation. MSCs can migrate to sites of injury, inflammation, ...and tumor. Moreover, MSCs undergo myofibroblast-like differentiation, including increased production of α-SMA in response to transforming growth factor-β (TGF-β), a growth factor commonly secreted by tumor cells to evade immune surveillance. Based on our previous findings, hMSCs become activated and resemble carcinoma-associated myofibroblasts upon prolonged exposure to a conditioned medium from MDAMB231 human breast cancer cells. In this section, we show using immunofluorescence that keratinocyte-conditioned medium (KCM) induces differentiation of MSCs to resemble dermal myofibroblast-like cells with punctate vinculin staining and F-actin filaments.
Methotrexate (MTX) uptake is mediated by the reduced folate carrier (RFC). Defective drug uptake in association with decreased RFC expression is a common mechanism of MTX resistance in many tumor ...types. Heavy promoter methylation was previously identified as a basis for the complete silencing of RFC in MDA-MB-231 breast cancer cells, its role and prevalence in RFC transcription regulation are, however, not widely studied.
In the current study, RFC promoter methylation was assessed using methylation specific PCR in a panel of malignant cell lines (n = 8), including MDA-MB-231, and M805, a MTX resistant cell line directly established from the specimen of a patient with malignant fibrohistocytoma, whom received multiple doses of MTX. A quantitative approach of real-time PCR for measuring the extent of RFC promoter methylation was developed, and was validated by direct bisulfite genomic sequencing. RFC mRNA levels were determined by quantitative real-time RT-PCR and were related to the extent of promoter methylation in these cell lines.
A partial promoter methylation and RFC mRNA down-regulation were observed in M805. Using the quantitative approach, a reverse correlation (correlation coefficient = -0.59, p < 0.05) was identified between the promoter methylation and RFC mRNA levels in this a panel of malignant cell lines.
This study further suggests that promoter methylation is a potential basis for MTX resistance. The quantitative correlation identified in this study implies that promoter methylation is possibly a mechanism involved in the fine regulation of RFC transcription.
Thermal stability of the ESR signals from barites in chimneys deposited from hydrothermal vents is investigated using isothermal and isochronal annealing experiments. A combination of first and ...second order kinetics is required to explain the results. The Arrhenius plots of the decay rate constants give the activation energies of 1.0–1.3
eV. From the estimated decay rate constants at the sea bottom (3
°C), the decay rate of the signal was calculated to be less than 2% for the period of 20
ka, suggesting the applicability of the ESR method for dating barites up to about twenty thousand years.
To investigate the role of thymidylate synthase (TS),p53, and epidermal growth factor receptor (EGF-R) expressions in hepatic tumors in predicting overall survival (OS), progression-free survival ...(PFS), and hepatic progression-free survival (HPFS) in patients with resectable metastatic colorectal cancer who were randomly assigned to receive either systemic chemotherapy (SYS) alone or systemic and hepatic arterial infusion (HAI+SYS) chemotherapy following liver surgery.
Tissues from metastatic tumors were collected during liver resection from 156 patients, and marker expressions were determined using immunohistochemistry on frozen samples. Univariate associations between marker expressions and baseline variables with OS, PFS, and HPFS were examined. Independent predictors of outcome were determined using a multivariate Cox model.
In multivariate analyses, TS overexpression was found to be an independent factor of poor prognosis in OS (P <.01), PFS (P =.06), and HPFS (P <.01). In addition, resection margin was a significant independent factor for all three outcomes. Patients who received HAI+SYS experienced delayed progression in general, and in the liver, specifically. Increased levels of serum alkaline phosphatase correlated with hepatic progression. We also found a significant TS-treatment interaction for OS (P =.01) in multivariate analysis. In particular, TS+ patients receiving HAI+SYS had significantly higher survival than those receiving SYS (64 month sv 21 months; P =.01).
TS levels in hepatic tumors and resection margin are independent predictors of survival and progression in patients with metastatic colorectal cancer, whereas p53 and EGFR are not independent predictors. Treatment with HAI + SYS significantly improved the survival profile of TS+ patients.
Ecteinascidin 743 (ET-743) is a potent antitumor agent from the Caribbean tunicate Ecteinascidin turbinata and is presently in clinical trials for human cancers. To better understand how ET-743 might ...be used clinically, the present study used SRB assays to examine the cytotoxicity resulting from combining ET-743 with three other antineoplastic agents: doxorubicin (DXR), trimetrexate, and paclitaxel in different administration schedules in two soft tissue sarcoma cell lines, HT-1080 and HS-18, in vitro. Concurrent exposure of ET-743 with DXR resulted in synergistic interactions in both cell lines. Addition of ET-743 for 24 h before DXR was the most effective cytotoxic regimen against both cell lines. Morphological study by fluorescence microscopy revealed that combination treatment of both cells with ET-743 and DXR induced apoptosis. Exposure to paclitaxel before ET-743 was also an effective regimen. These results encourage studies of the combination of ET-743 and DXR in the treatment of soft tissue sarcoma, because each of these agents have activity in this disease.
A comparison between analytic theory and numerical simulations of axisymmetric modes in magnetically confined, cylindrical plasma with non-circular cross-section bounded by a conducting wall is ...presented. If the wall is close to the plasma, modes are oscillatory, with frequency scaling with the Alfvén frequency. The two frequencies differ when the plasma cross-section is elongated, but they become equal in the circular limit. The mechanism for oscillatory behavior is a consequence of the currents induced on the perfectly conducting wall when the plasma is displaced from its equilibrium positions. The induced currents exert a restoring force on the plasma, and the oscillation frequency is a combination of the strength of this force and the plasma mass density. An additional parameter, depending on the distance between the wall and the plasma boundary, also affects the oscillation frequency so that the frequency becomes large when the wall-plasma boundary distance approaches zero.
•Comparison between analytic theory and numerical simulations of axisymmetric modes in plasma bounded by a conducting wall.•Derivation of an analytic dispersion relation for n=0 oscillatory modes.•Possible explanation of n=0 modes observed in recent JET experiments.•Comparison between analytic theory and numerical simulation is highly satisfactory.•Valuable insight for the analytic and numerical study of axisymmetric modes in magnetically confined plasma.
We have observed that rodent cell lines (mouse, hamster) contain approximately 10 times the levels of dihydrofolate reductase as human cell lines, yet the sensitivity to methotrexate (ED(50)), the ...folate antagonist that targets this enzyme, is similar. Our previous studies showed that dihydrofolate reductase protein levels increased after methotrexate exposure, and we proposed that this increase was due to the relief of feedback inhibition of translation as a consequence of methotrexate binding to dihydrofolate reductase. In the current report, we show that unlike what was observed in human cells, dihydrofolate reductase (DHFR) levels do not increase in hamster cells after methotrexate exposure. We provide evidence to show that although there are differences in the putative mRNA structure between hamster and human mRNA in the dihydrofolate reductase binding region previously identified, "hamsterization" of this region in human dihydrofolate reductase mRNA did not change the level of the enzyme or its induction by methotrexate. Further experiments showed that human dihydrofolate reductase is a promiscuous enzyme and that it is the difference between the hamster and human dihydrofolate reductase protein, rather than the DHFR mRNA, that determines the response to methotrexate exposure. We also present evidence to suggest that the translational up-regulation of dihydrofolate reductase by methotrexate in tumor cells is an adaptive mechanism that decreases sensitivity to this drug.
PDF
