Influence of chelidonine, an inhibitor of tubulin polymerisation on tyrosine kinase activity in normal, transformed and malignant cell lines

Chelidonine, a tertiary hexahydro-benzophenanthridine alkaloid is an inhibitor of tubulin polymerisation and has been revealed to arrest cells in G2/M. Since enhanced tyrosine kinase (TK) activity is linked to the transition from normal to the immortal malignant phenotype, the effect of 10 mM chelidonine was evaluated on TK activity in normal, transformed and malignant cell lines after 2 hours of exposure. Chelidonine caused a stimulation of TK activity in two normal cell lines (human foreskin fibroblast (Hs27) and normal monkey kidney (NMK)). In contrast, an inhibition of TK activity was observed in transformed human embryonic kidney (Graham 293) and transformed African green monkey kidney (Vero), as well as in human cervical carcinoma (HeLa) and squamous oesophageal carcinoma (WHCO5) cells. Hs27 cells exposed to chelidonine, revealed an increase in TK activity of 1.27-fold (P < 0.05). NMK cells showed a 1.15-fold increase in TK activity. A decrease in TK activity was observed in Graham 293 (0.91-fold) and Vero (0.45-fold) (P < 0.005) cells. In both HeLa and WHCO5 cells, the TK activity was reduced to 0.68-fold (P < 0.05) and 0.56-fold (P < 0.005) respectively. These data, including results from our previous studies, suggest a potential cross talk between the SAPK/JNK and TK signal transduction pathways and a possible differential effect of chelidonine on the phosphorylation status of role players involved in determining the length of G2 arrest in normal versus transformed and malignant cells

C2- and C4-position 17β-estradiol metabolites and their relation to breast cancer

C2- and C4-position 17β-estradiol metabolites play an important role in breast carcinogenesis. 2-Hydroxyestradiol and 4-hydroxyestradiol are implicated in tumorigenesis via two pathways. These pathways entail increased cell proliferation and the formation of reactive oxygen species that trigger an increase in the likelihood of deoxyribonucleic acid mutations. 2-Methoxyestradiol, a 17β-estradiol metabolite, however, causes induction of apoptosis in transformed and tumor cells; thus exhibiting an antiproliferative effect on tumor growth. The 4-hydroxyestradiol:2- methoxyestradiol and 2-hydroxyestradiol:2-methoxyestradiol ratios therefore ought to be taken into account as possible indicators of carcinogenesis.This work was supported by grants from the Medical Research Council of South Africa (AG374, AK076), the Cancer Association of South Africa (AK246) and the Struwig-Germeshuysen Cancer Research trust of South Africa (AJ038, AN074)

In vitro effects of 2-methoxyestradiol on MCF-12A and MCF-7 cells

The influence of 2-methoxyestradiol (2ME) was investigated on cell growth, morphology and spindle formation in a tumorigenic (MCF-7) and non-tumorigenic (MCF-12A) epithelial breast cell line. Inhibition of cell growth was more pronounced in the MCF-7 cells compared to the MCF-12A cells following 2ME treatment. Dose-dependent studies (10-5 – 10-9 M) revealed that 10-6 M 2ME inhibited cell growth by 44% in MCF-12A cells and by 84% in MCF-7 cells (P-value < 0.05). 2ME-treated MCF-7 cells showed abnormal metaphase cells, membrane blebbing, apoptotic cells and disrupted spindle formation. These observations were either absent, or less prominent in MCF-12A cells. 2ME had no effect on the length of the cell cycle between S-phase and the time a mitotic peak was reached in either cell line but MCF-7 cells were blocked in mitosis with no statistically significant alterations in the phosphorylation status of Cdc25C. Nevertheless, Cdc2 activity was significantly increased in MCF-7 cells compared to MCF-12A cells (P-value < 0.05). The results indicate that 2ME disrupts mitotic spindle formation and enhances Cdc2 kinase activity, leading to persistence of the spindle checkpoint and thus prolonged metaphase arrest that may result in the induction of apoptosis. The tumorigenic MCF-7 cells were especially sensitive to 2ME treatment compared to the normal MCF-12A cells. Therefore, differential mechanism(s) of growth inhibition are evident between the normal and tumorigenic cells.This research was supported by grants from the Medical Research Council of South Africa (AG374, AK076), the Cancer Association of South Africa (AK246) and the Struwig-Germeshuysen Cancer Research trust of South Africa (AJ038