G0/G1 arrest and S phase inhibition of human cancer cell lines by inositol hexaphosphate (IP6).
BACKGROUND
Inositol hexaphosphate (InsP6 or IP6) has shown a striking anti-cancer activity in both in vivo and in vitro models. In an attempt to elucidate the mechanism(s) underlying the anti-neoplastic potential of IP6, we investigated its effect on cell cycle progression of MCF-7 estrogen receptor (ER)-positive and MDA-MB 231 ER-negative human breast cancer cell lines and HT-29 human colon cancer cells.


METHODS
The anti-proliferative effect of IP6 was evaluated using dual-parameter flow cytometric measurements of DNA content, versus the incorporation of 5-bromo-2-deoxyuridine (BrdU) to determine cells actively synthesizing DNA. Combined analysis of the expression of cell cycle-related proteins, proliferation marker Ki-67 and proliferating cell nuclear antigen (PCNA) versus DNA content were used to determine the amount of proliferating cells in each phase, engaged in cell cycle transit.


RESULTS
After 3 days of treatment with 5 mM IP6, S-phase, as estimated by BrdU uptake, was significantly decreased in all three cell lines (p = 0.002). MCF-7 and HT-29 cells accumulated in the G0/G1 range of DNA contents (p = 0.002 and p = 0.001, respectively). MDA MB-231 cells transiently accumulated in G0/G1 only after 2 days (p = 0.01). There was a significant decrease in the percentage of Ki-67 expression in IP6-treated cells, from 82.8+/-3.0% to 66.8+/-4.2% in MCF-7 (p = 0.007), from 93.4+/-4.6% to 71.7+/-3.3% in MDA-MB 231 (p = 0.004), and from 95.2+/-1.2% to 73.5+/-2.5% in HT-29 cells (p = 0.002) respectively. PCNA expression levels were also significantly decreased by IP6 in all three cell lines (MCF-7 p = 0.0007; MDA-MB 231 p = 0.0006; HT-29 p = 0.0001).


CONCLUSIONS
These results show that IP6 controls the progression of cells through the cycle by decreasing S- phase and arresting cells in the G0/G1-phase of the cell cycle. A significant decrease in the expression of proliferation markers indicated that IP6 disengaged cells from actively cycling. Further investigations of cell cycle regulators may lead us to a better understanding of the mechanism(s) of the anti-neoplastic action of IP6.
El-Sherbiny
Y M
YM
Department of Clinical Pathology University of Minia School of Medicine, Egypt.
Cox
M C
MC
Ismail
Z A
ZA
Shamsuddin
A M
AM
Vucenik
I
I
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects*; D018797:Cell Cycle Proteins / Q000096:biosynthesis; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects; D019073:HT29 Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D019394:Ki-67 Antigen / Q000096:biosynthesis; D010833:Phytic Acid / Q000494:pharmacology*; D018809:Proliferating Cell Nuclear Antigen / Q000096:biosynthesis; D016192:Resting Phase, Cell Cycle / Q000187:drug effects; D016196:S Phase / Q000187:drug effects; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D019394:Ki-67 Antigen; D018809:Proliferating Cell Nuclear Antigen; D010833:Phytic Acid