Login to Access Video or Poster Abstract: MP73-13
Sources of Funding: none

Introduction

There are no curative agents for advanced renal cancer, and a novel treatment approach is urgently needed. Soy isoflavones are dietary nutrients that have been shown to inhibit cancer development and progression, and phenoxodiol is a novel isoflavone analog being tested in clinical trials. Because its efficacy in renal cancer is unknown, in the present study we investigated its antineoplastic activity and mechanism of action in renal cancer cells.

Methods

A panel of renal cancer cells (769-P, 786-O, Caki-2) was treated with phenoxodiol (5-20 µM). The cell viability and clonogenicity were assessed by MTS assay and colony formation assay. Cell cycle analysis was done using flow cytometry. Apoptosis and necrosis were detected by flow cytometry after staining the cells with annexin V and 7-amino-actinomycin D (7-AAD). The expression of cyclin D1, cyclin-dependent kinase (CDK) 4, cleaved poly(ADP-ribose) polymerase (PARP), FLICE inhibitory protein (FLIP), and Akt was evaluated by western blotting.

Results

MTS assay results showed that phenoxodiol decreased renal cancer viability in a time- and dose-dependent manner (IC50: 19.9-28.8 µM). It also inhibited colony formation significantly (p <0.05) and perturbed the cell cycle: 24-hour treatment with 20 µM phenoxodiol induced marked G1-S arrest but prolonged treatment (48-72 hours) increased the number of cells in the sub-G1 fraction, suggesting that phenoxodiol disrupted cell cycle checkpoints. These changes were associated with decreased expression of the cell-cycle regulators cyclin D1 and CDK4. Treatment with phenoxodiol increased the numbers of 7-AAD-positive cells as well as annexin-V positive cells and increased the expression of cleaved PARP, demonstrating that the phenoxodiol-induced apoptosis was late apoptosis. Phenoxodiol also inhibited the Akt pathway by causing dephosphorylation of Akt. This inhibition of the Akt pathway inhibited expression of the apoptosis inhibitor FLIP and thus led to renal cancer apoptosis.

Conclusions

Phenoxodiol induces apoptosis of renal cancer cells by inhibiting the Akt pathway.

Funding

none