Growth suppression of a tumorigenic rat liver cell line by the anticancer agent, ET-18-O-CH(3), is mediated by inhibition of cytokinesis.
OBJECTIVE
This study was undertaken to elucidate the potential mechanism of the antitumor activity of ET-18-O-CH(3), a synthetic analogue of lysophosphatidyl choline, and a known antitumor agent and specific inhibitor of phosphoinositide phospholipase C (PI-PLC).


METHODS
A normal rat liver epithelial "oval" cell line (WB-F344) was neoplastically transformed by the H-ras oncogene (WB-ras2) and treated with a series of ET-18-O-CH(3) concentrates for a number of days. Cell growth, morphological "differentiation", cell cycle regulation, karyotypic changes, growth in soft agar (anchorage-independent growth) and the expression of cdk2, cdc2 and ERK genes were studied to determine the effect of ET-18-O-CH(3) on these neoplastic cells.


RESULTS
ET-18-O-CH(3) at 5 and 10 microg/ml was found to cause an increase in cell size, suppress cell growth, reduce the colony-forming efficiency and inhibit the anchorage-independent growth of the WB-ras2 cells. Significantly, flow-cytometric analysis revealed that while control cells and cells treated with concentrations of ET-18-O-CH(3) below 5 microg/ml were diploid, cell populations treated with 5 and 10 microg/ml ET-18-O-CH(3) comprised 33-37% diploid cells and over 60% tetraploid cells (4n-8n cycle cells). ET-18-O-CH(3) was found to induce aberrant cytokinesis as evidenced by the presence of a high frequency of enlarged cells, which were binucleated or multinucleated and mitotic cells with 4n and 8n numbers of chromosomes. ET-18-O-CH(3) was also capable of inhibiting both the expression of cdk2 and cdc2 and the activation of ERK1/2, while no effect was found on the expression of p21 ras.


CONCLUSIONS
The effect of ET-18-O-CH(3) on neoplastically transformed H-ras rat liver cells has been interpreted as the result of an altered phenotype characterized by an enlarged and flattened cell morphology with ploidy changes caused by inhibition of cytokinesis.
Na
Hye-Kyung
HK
Department of Pediatrics and Human Development, National Food Safety Toxicology Center, Michigan State University, East Lansing, Michigan 48824, USA.
Chang
Chia-Cheng
CC
Trosko
James E
JE
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D005786:Gene Expression Regulation; D008113:Liver Neoplasms / Q000473:pathology*; D010742:Phospholipid Ethers / Q000494:pharmacology*; D051381:Rats; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D010742:Phospholipid Ethers; C026659:edelfosine