G0/G1 arrest and S phase inhibition of human cancer cell lines by inositol hexaphosphate (IP6)

Anticancer Res. Jul-Aug 2001;21(4A):2393-403.

Abstract

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).

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Cell Cycle / drug effects*
  • Cell Cycle Proteins / biosynthesis
  • Flow Cytometry
  • G1 Phase / drug effects
  • HT29 Cells / cytology
  • HT29 Cells / drug effects
  • HT29 Cells / metabolism
  • Humans
  • Ki-67 Antigen / biosynthesis
  • Phytic Acid / pharmacology*
  • Proliferating Cell Nuclear Antigen / biosynthesis
  • Resting Phase, Cell Cycle / drug effects
  • S Phase / drug effects
  • Tumor Cells, Cultured

Substances

  • Antineoplastic Agents
  • Cell Cycle Proteins
  • Ki-67 Antigen
  • Proliferating Cell Nuclear Antigen
  • Phytic Acid