Long-term cultivation of colorectal carcinoma cells with anti-cancer drugs induces drug resistance and telomere elongation: an in vitro study

Background

The role of telomerase activation in the expression and/or maintenance of drug resistance is not clearly understood. Therefore, we investigated the relationships, among the telomerase activity, telomere length and the expression of multidrug resistance genes in colorectal cancer cell lines cultivated with anti-cancer drugs.

Methods

LoVo and DLD-1 cells were continuously grown in the presence of both CDDP and 5-FU for up to 100 days. Cell proliferation, telomerase activity, telomere length and the expression of multidrug resistance genes were serially monitored as the PDL increased.

Results

The expression of multidrug resistance genes tended to increase as the PDL increased. However, an abnormal aneuploid clone was not detected as far as the cells were monitored by a DNA histogram analysis. Tumor cells showing resistance to anti-cancer drugs revealed a higher cell proliferation rate. The telomere length gradually increased with a progressive PDL. The telomerase activity reached a maximum level at 15 PDL in LoVo cells and at 27 PDL in DLD-1 cells. An increase in the mRNA expression of the telomerase components, especially in hTERT and in hTR, was observed at the same PDLs.

Conclusions

These results suggest that a high telomerase activity and an elongation of telomeres both appear to help maintain and/or increase drug resistance in colorectal cancer cells. Cancer cells with long telomeres and a high proliferative activity may thus be able to better survive exposure to anti-cancer drugs. This is presumably due to an increased chromosome stability and a strong expression of both mdr-1 and MRP genes.     

Different mechanisms between premitotic apoptosis and postmitotic apoptosis in X-irradiated U937 cells

PURPOSE: Apoptosis is currently being evaluated for its importance as a pathway of radiation-induced cell death. However, the difference in the mechanisms between premitotic and postmitotic apoptosis following X-irradiation remains not well understood. We show here that the human monoblastoid cell line U937 can be induced to undergo these two different types of apoptosis. METHODS AND MATERIALS: U937 cells were irradiated at a dose of 5 or 20 Gy, and the DNA fragmentation rate was measured by both flow cytometric analysis and gel electrophoresis. Activation of caspase-3 was detected by Western blot analysis and fluorogenic assay using acetyl-Asp-Glu-Val-Asp-7-amino-4-methyl-coumarin (Ac-DEVD-AMC). Detection of mitochondrial transmembrane potential (DeltaPsi) was performed by using Rho123. Chasing of S-phase fraction following X-irradiation was performed after labeling with 5-bromo-2'-deoxyuridine (BrdU). Thymidine was used for synchronization of the cells. Inhibition of caspase-3 activity was achieved by Acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO). RESULTS: Time courses of the apoptotic rates, caspase activation, and DeltaPsi indicated that two different types of cell death were induced by the different X-ray doses. High-dose X-ray (20 Gy) induced a rapid and strong apoptosis, whereas low-dose X-ray (5 Gy) induced a slow and mild apoptosis. Cell-cycle analyses revealed that there was cell death before cell division in the former apoptosis but the cells must be dying after cell division in the latter apoptosis. By means of cell-cycle synchronization, the S-phase cells proved to be the most sensitive fraction to premitotic apoptosis, but an obvious difference in the susceptibility to cell death among the cell-cycle phases was not observed in postmitotic apoptosis. Ac-DEVD-CHO treatment effectively blocked caspase activity and premitotic apoptosis, but it failed to block postmitotic apoptosis. CONCLUSIONS: Irradiation of U937 cells at different X-ray doses induced two different types of apoptotic cell death, premitotic apoptosis and postmitotic apoptosis, which are characterized by the time course and cell-cycle specificity. Decision concerning these two types of apoptotic cell death may be made by the difference in the magnitude of cell damage following X-irradiation.     

Urokinase type plasminogen activator and its receptor regulate the invasive potential of gastric cancer cell lines

To assess the role of urokinase-type plasminogen activator (uPA) and uPA receptor (uPAR) on the invasive potential of cancer cells, in vitro experiments were performed using two human gastric cancer cell lines, NUGC-3 and MKN-28. NUGC-3 cells secreted a higher level of uPA than MKN-28 cells, while the uPAR expression of NUGC-3 cells was lower than that of MKN-28 cells. Both cancer cell lines expressed Met protein and did not express hepatocyte growth factor (HGF). In Matrigel invasion assay, MKN-28 cells demonstrated significantly lower invasion index than NUGC-3 cells. The addition of exogenous uPA significantly increased the invasive activity of MKN-28 cells. The uPA expression in NUGC-3 cells was enhanced by adding conditioned media of fibroblast cells or HGF. These results suggest that uPA promotes the invasive capacity of the uPAR-positive cancer cells, and that stromal cells may play an important role in cancer cell invasion by supplying uPA and/or promoting uPA production.     

Methylenetetrahydrofolate reductase polymorphism and risk of colorectal adenomas

A homozygous mutation at bp 677 in the gene for the methylenetetrahydrofolate reductase (MTHFR) was previously shown to be associated with a decreased risk of colorectal cancer. We examined the relation between the MTHFR genetic polymorphism and risk of colorectal adenoma in Japanese men using 205 cases of colorectal adenomas and 220 controls of normal total colonoscopy. The homozygous mutation was not measurably associated with colorectal adenomas. The findings corroborate the lack of an association between the MTHFR genotype and colorectal adenomas, but do not deny the possibility that the genotype may be involved in the late stage of colorectal carcinogenesis.     

Role of Th2 responses in the development of allergen-induced airway remodelling in a murine model of allergic asthma

(1) To clarify the involvement of Th2 responses in the development of allergen-induced airway remodelling, we investigated the effect of anti-CD4 monoclonal antibody (mAb) and anti-CD8 mAb, and the responses of IL-4 gene-knockout (KO) mice in a murine model of allergic asthma. (2) Mice were immunized twice by intraperitoneal injections of ovalbumin (OA), and exposed to aeroallergen (OA, 1% w v(-1)) for 3 weeks. Twenty-four hours after the final challenge, airway responsiveness to acetylcholine was measured, and bronchoalveolar lavage (BAL) and histological examinations were carried out. (3) Anti-CD4 mAb (1 mg kg(-1)) clearly inhibited allergen-induced increases in airway responsiveness to acetylcholine, the number of eosinophils in BAL fluid, serum OA-specific IgE levels, IL-13 and transforming growth factor-beta1 levels in BAL fluid, and amount of hydroxyproline in the lung by 100, 99, 100, 100, 84, and 60%, respectively. Furthermore, the antibody (1 mg kg(-1)) also attenuated allergen-induced goblet cell hyperplasia in the epithelium and subepithelial fibrosis by 72 and 83%, respectively. In contrast, anti-CD8 mAb (1 mg kg(-1)) showed no effect on each parameter. Furthermore, all these parameters were attenuated in IL-4KO mice by 57, 93, 100, 45, 84 and 60%, and also 72 and 83%, respectively. (4) These findings suggest that Th2 responses play a critical role for the development of allergen-induced airway remodelling, and that the inhibition of Th2 responses, e.g. using anti-CD4 mAb, is a therapeutic approach for the treatment of airway remodelling in asthma.     

Effects of [Arg8]-vasopressin on regional cerebral blood flow in spontaneously hypertensive rats

The effects of [Arg(8)]-vasopressin (AVP) and related compounds on regional cerebral blood flow (rCBF) in the hippocampus were studied using conscious spontaneously hypertensive rats (SHR). rCBF in the hippocampus decreased gradually with age in proportion to an increase in mean blood pressure. Subcutaneous injection of AVP caused a dose-dependent increase in rCBF in the hippocampus. The effects of the metabolic fragments AVP4-9 and AVP4-8 on rCBF were relatively weak. OPC-31260, a vasopressin V(2) antagonist, antagonized the AVP-induced increase in rCBF in the hippocampus. Furthermore, subcutaneous injection of DDAVP, a V(2) agonist, increased rCBF in the hippocampus. On the other hand, the AVP-induced increase in rCBF in the hippocampus was not antagonized by OPC-21268, a vasopressin V(1) antagonist. Intracerebroventricular injection of AVP caused no significant changes in rCBF in the hippocampus, even at a dose of 10 ng/site.     

Effects of RS-601, a novel leukotriene D(4)/thromboxane A(2) dual receptor antagonist,on asthmatic responses in guinea pigs

The effects of 4-[4-[5,5,6,6,6-pentafluoro-1-(4-fluorobenzene-sulfonamido)hexyl]phenyl]butyric acid (RS-601), a novel leukotriene D(4) (LTD(4))/thromboxane A(2) (TxA(2)) dual receptor antagonist, on bronchial asthmatic responses in guinea pigs were examined. The effects were compared with those of pranlukast (LTD(4) receptor antagonist) and S-1452 (TxA(2) receptor antagonist). RS-601 inhibited the increase in airway resistance caused by LTD(4) and TxA(2) mimetic compound, U-46619, but not by histamine. RS-601 and pranlukast but not S-1452 inhibited an antigen-induced late asthmatic response. In addition, RS-601 inhibited an antigen-induced airway hyperresponsiveness (AHR), whereas pranlukast and S-1452 had no effect on the AHR. The antigen-induced increase in inflammatory cells in airway was not affected by all examined agents. Furthermore, bacterial lipopolysaccharide-induced AHR in guinea pigs was clearly suppressed by RS-601 but not by pranlukast and S-1452. The increase in airway inflammatory cells caused by lipopolysaccharide was not affected by all three drugs. These findings indicate that RS-601 has a potent antiasthmatic efficacy, especially on AHR, but does not affect accumulation of eosinophils in the airways.