Effects of tyrosine kinase inhibitor, erbstatin, on cell growth and growth-factor/receptor gene expression in human gastric carcinoma cells

Monitoring the cytoskeletal EGF response in live gastric carcinoma cells

Altered cell motility is considered to be a key factor in determining tumor invasion and metastasis. Epidermal growth factor (EGF) signaling has been implicated in this process by affecting cytoskeletal organization and dynamics in multiple ways. To sort the temporal and spatial regulation of EGF-dependent cytoskeletal re-organization in relation to a cell's motile behavior time-lapse microscopy was performed on EGF-responsive gastric carcinoma-derived MKN1 cells co-expressing different fluorescently labeled cytoskeletal filaments and focal adhesion components in various combinations. The experiments showed that EGF almost instantaneously induces a considerable increase in membrane ruffling and lamellipodial activity that can be inhibited by Cetuximab EGF receptor antibodies and is not elicited in non-responsive gastric carcinoma Hs746T cells. The transient cell extensions are rich in actin but lack microtubules and keratin intermediate filaments. We show that this EGF-induced increase in membrane motility can be measured by a simple image processing routine. Microtubule plus-ends subsequently invade growing cell extensions, which start to accumulate focal complexes at the lamellipodium-lamellum junction. Such paxillin-positive complexes mature into focal adhesions by tyrosine phosphorylation and recruitment of zyxin. These adhesions then serve as nucleation sites for keratin filaments which are used to enlarge the neighboring peripheral keratin network. Focal adhesions are either disassembled or give rise to stable zyxin-rich fibrillar adhesions which disassemble in the presence of EGF to support formation of new focal adhesion sites in the cell periphery. Taken together the results serve as a basis for modeling the early cytoskeletal EGF response as a tightly coordinated and step-wise process which is relevant for the prediction of the effectiveness of anti-EGF receptor-based tumor therapy.

Alkyl isothiocyanates suppress epidermal growth factor receptor kinase activity but augment tyrosine kinase activity

AIM

We have reported the in vitro and in vivo anticancer activities of 6-(methylsulfinyl)hexyl isothiocyanate (6-MITC) derived from a Japanese spice, wasabi. In order to obtain some clues about the mechanism of the anticancer activity, we have studied the effect of alkyl isothiocyanates (MITCs) on protein kinase activities.

METHODS

The anti-autophosphorylation activity of MITCs with respect to the epidermal growth factor (EGF)-stimulated receptor kinase of A431 epidermoid carcinoma cells was examined by incorporation of radioactive ATP into an acid-insoluble fraction. Their anti-phosphorylation activity with respect to the non-receptor protein kinase was analyzed by a standard SDS-PAGE method.

RESULTS

All the tested MITCs interfered with the EGF-stimulated receptor kinase activity in a dose-dependent manner, although their effects were less than 1/10 of that of erbstatin in microg/ml. On the other hand, the MITCs did not interfere with non-receptor kinases (kinase A, kinase C, tyrosine kinase and calmodulin dependent kinase III), but enhanced non-receptor tyrosine kinase.

DISCUSSION

A possible anticancer mechanism of MITCs may involve the suppression of EGF receptor kinase activity and augmentation of non-receptor PTK.

Reg IV enhances peritoneal metastasis in gastric carcinomas

OBJECTIVES

The role of Regenerating (Reg) IV on peritoneal metastasis was examined in gastric cancer using.

MATERIAL AND METHODS

Reg IV-transfected human gastric cancer cells (MKN28-R1, MKN28-R2, TMK1-R1), control transfectants (MKN28-R0, TMK1-R0), and REG4-knocked down MKN45 cells were examined in in vitro and in nude mice peritoneal metastasis models.

RESULTS AND DISCUSSION

Increase of expression and secretion of Reg IV, and levels of BCL-2, BCL-XL,survivin, phosphorylated AKT, and phosphorylated EGFR, and decrease of nitric oxide-induced apoptosis were found in Reg IV-transfectants, whereas those were abrogated in the knockdown cells. In mice models, increased number and size of peritoneal tumors and decreased apoptosis were found in Reg IV-transfectants, whereas those were abrogated by the knockdown cells. Mice survivals were worsened in Reg IV-transfectants-inoculated mice, but were improved in Reg IV-knockdown cell-inoculated mice. Levels of Reg IV protein in peritoneal lavage fluids increased in Reg IV-transfectants inoculated mice, but decreased in Reg IV-knockdown cell inoculated mice. In metastasized human gastric cancers, Reg IV positivity in peritoneum-metastasis cases was higher than those in negative cases. Reg IV was detected in peritoneal lavage fluids from human gastric cancer patients, in whose lavages keratin mRNA was detected by reverse transcriptase-polymerase chain reaction. Collectively, Reg IV might accelerate peritoneal metastasis in gastric cancer. Reg IV in lavage fluids might be a good marker for peritoneal metastasis.

EGFR tyrosine kinase inhibitor "gefitinib (Iressa)" for cancer therapy

Many malignant tumors including non-small cell lung cancer (NSCLC) express or over-express EGFR that have shown correlations with rapid growth, metastases, resistance to conventional chemotherapy or radiotherapy, and poor prognosis. Gefitinib is a potent and selective inhibitor of EGFR tyrosine kinase (EGFRTK). Gefitinib specifically inhibited EGF-stimulated cell proliferation in vitro and it also exhibited a broad anti-tumor spectrum against NSCLC, prostate, colorectal, and ovarian cancers in vivo. Gefitinib showed dose-dependent and reversible reduction of c-fos mRNA level and decreased Ki67 significantly in tumors in vivo. In in vitro studies, gefitinib arrested the cell cycle at G1 phase by inducing intrinsic cyclin-dependent kinase (cdk) inhibitors and following inhibition of cdk2. Apoptosis was also seen in gefitinib-treated tumor cells and skin biopsy samples from clinical study. Gefitinib inhibited VEGF production in tumor cells through inhibition of EGFR signaling, leading to suppression of angiogenesis. In clinical studies, gefitinib demonstrated therapeutic benefit in patients who failed conventional chemotherapy. No correlation has been established between the anti-tumor activity of gefitinib and EGFR expression level, whilst sensitivity factors to gefitinib are yet to be elucidated. Identification of sensitivity factors will be a key for effective use of EGFRTK inhibitors including gefitinib for cancer treatment.

Blockade of growth factor receptors in ductal carcinoma in situ inhibits epithelial proliferation

BACKGROUND

Ductal carcinoma in situ (DCIS) expresses c-erbB-2 receptor and epidermal growth factor receptor (EGFR). The aim of this study was to determine whether blocking of c-erbB-2 receptor with a humanized monoclonal antibody, 4D5 (HerceptinTM), or of EGFR with an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI), ZD1839 (IressaTM), would decrease epithelial proliferation in DCIS.

METHODS

DCIS tissue from 18 women undergoing surgery was implanted into 16 to 20 athymic nude mice per experiment (eight xenografts per mouse). Treatment commenced 2 weeks after implantation and consisted either of twice-weekly intraperitoneal injections of 4D5 10 mg/kg or of daily gavage with ZD1839 at 100-200 mg/kg for 14 days; appropriate controls were included. Xenografts were removed on days 14, 21 and 28. Proliferation was assessed by counting 1000 epithelial cells after Ki67 immuno- staining.

RESULTS

ZD1839 inhibited proliferation compared with that in controls after 14 days (P < 0.01), whereas 4D5 did not.

CONCLUSION

Proliferation in DCIS was decreased by EGFR tyrosine kinase inhibition but not by c-erbB-2 receptor blockade. ZD1839, an orally active and selective EGFR-TKI, has potential as adjuvant therapy in DCIS.

Characterization and application of a gastric surface mucous cell line GSM06 established from temperature-sensitive simian virus 40 large T-antigen transgenic mice

It has been indicated that transgenic mouse harboring a temperature-sensitive simian virus 40 large T-antigen gene is useful for establishing cell lines from tissues that have proved difficult to culture in vitro. The gastric surface mucous cell line GSM06 was established from a primary culture of gastric fundic mucosal cells of the transgenic mice. GSM06 cells showed temperature-sensitive growth in culture and expressed large T-antigen at a permissive temperature (33 degrees C) but not at a nonpermissive temperature (39 degrees C). At 39 degrees C, the cells produced periodic acid-Schiff positive glycoconjugates that formed a mucous sheet like the gastric surface mucosa in the stomach. Insulin markedly increased the production of glycoconjugates. In addition, proprotein-processing endoprotease furin suppression retarded cell growth, but accelerated cell differentiation. An air-liquid interface promoted the differentiation of GSM06 cells in a reconstruction culture with nitrocellulose membrane and collagen gel. The gastric surface mucous cell line GSM06 with unique characteristics, therefore, should be useful as an in vitro model of the gastric mucosa for physiological and pharmacological investigations. Moreover, experiments using immortalized cells established in vitro and having specific functions may offer an alternative to experiments using living animals and thereby offer a solution to this ethical issue.

Post-transcriptional control regulates transforming growth factor alpha in the human carcinoma KB cell line

Expression of epidermal growth factor receptor (EGF-R) antisense RNA results in a drastic reduction of EGF-R levels in the human carcinoma KB cell line and induces a reversion of their transformed phenotype (Moroni, M. C., Willingham, M. C., and Beguinot, L. (1992) J. Biol. Chem. 267, 2714-2722). We used parental and EGF-R antisense KB clones as a genetic system to study, in the same cell line, the role of transforming growth factor alpha (TGF-alpha) in the establishment and maintenance of the transformed phenotype. KB cells produce TGF-alpha mRNA, and their conditioned medium is able to sustain growth of antisense cells, mimicking the effect of exogenous EGF or TGF-alpha. In antisense cells there is a marked reduction of TGF-alpha mRNA steady-state levels. In addition, the decrease in TGF-alpha parallels the levels of residual EGF-R in the various antisense clones, indicating a direct correlation between receptors and growth factor levels. The addition of exogenous TGF-alpha (10 ng/ml) to antisense clones induces TGF-alpha levels. The half-life of TGF-alpha mRNA is 40-60 min in antisense cells and more than 8 h in parental KB cells, as determined by actinomycin D decay curves. This result indicates a predominant regulation of TGF-alpha mRNA at the post-transcriptional level. Nuclear run-on experiments show that there is only a marginal effect at the transcriptional level. We conclude that the autocrine loop responsible for the transformed phenotype of the human carcinoma KB cell line is dependent on both elevated levels of EGF-R and the presence of TGF-alpha. In addition, TGF-alpha is able to induce its own mRNA via a signal due to activation of the EGF-R acting predominantly at the post-transcriptional level.

c-erbB-2 anti-sense phosphorothioate oligodeoxynucleotides inhibit growth and serum-induced cell spreading of P185c-erbB-2-overexpressing ovarian carcinoma cells

Overexpression of the c-erbB-2 proto-oncogene product (p185c-erbB-2) occurs frequently in different types of human cancer and is correlated with a significantly decreased survival in ovarian cancer patients. The effect of c-erbB-2 anti-sense phosphorothioate oligodeoxynucleotides (S-ODNs) was examined on the ovarian cancer cell line SK-OV-3. p185c-erbB-2 levels were specifically reduced by a single-dose application of 5 microM c-erbB-2 anti-sense S-ODNs. This was accompanied by a 60% inhibition of anchorage-dependent cell growth. More strikingly, c-erbB-2 anti-sense S-ODNs almost completely abrogated serum-induced cell spreading. A control of complementary sense oligodeoxynucleotides did not show significant inhibitory effects on cell growth or on cell spreading. The inhibition of cell spreading was imitated by a monoclonal antibody (9G6) targeting the extracellular domain of p185c-erbB-2 and by the tyrosine kinase inhibitor erbstatin. The inhibitory activity of these 2 compounds was lost after a few hours, while the inhibition of serum-induced cell spreading by anti-sense S-ODNs was still present after 24 hr. Our results show that c-erbB-2 anti-sense S-ODNs effectively inhibit the mitogenic and spreading activity of p185c-erbB-2 in ovarian cancer cells. Thus, anti-sense strategies have the potential of providing new strategies for the therapy of ovarian cancer.

Effect of tyrosine kinase inhibition on basal and epidermal growth factor-stimulated human Caco-2 enterocyte sheet migration and proliferation

Mucosal healing requires enterocyte migration (restitution) supplemented by proliferation. Proliferation and migration may be studied independently by thymidine uptake and proliferation-blocked cell migration using human Caco-2 enterocyte monolayers in culture. Since epidermal growth factor (EGF) promotes mucosal healing and the EGF receptor is a tyrosine kinase, we hypothesized that tyrosine kinases might therefore modulate enterocyte migration and proliferation. The tyrosine kinase inhibitors genistein and 2,5-dihydroxymethylcinnamate, which block kinase ATP-binding and substrate-binding sites, respectively, were studied alone and with EGF. Proliferation was blocked with mitomycin. Although each inhibitor decreased basal and EGF-stimulated monolayer expansion when cell proliferation occurred, neither genistein nor 2,5-dihydroxymethylcinnamate decreased migration when proliferation was blocked. However, each inhibitor prevented EGF stimulation of proliferation-blocked migration and thymidine uptake. More substantial inhibition of basal proliferation by genistein correlated with increased protein-linked DNA breaks, which may reflect nonspecific inhibition of DNA topoisomerase activity by genistein. The more specific 2,5-dihydroxymethylcinnamate blocked changes in the alpha 2 integrin subunit organization which may modulate EGF-stimulated migration. Antiproliferative effects of tyrosine kinase inhibitors decrease basal monolayer expansion but true basal enterocyte migration appears independent of tyrosine kinase regulation. However, a specific tyrosine kinase-dependent modulation of cell-matrix interaction inhibits EGF-stimulated migration.