Research article

Conjugated docosahexaenoic acid suppresses KPL-1 human breast cancer cell growth in vitro and in vivo: potential mechanisms of action

Miki Tsujita-Kyutoku^1,2, Takashi Yuri¹, Naoyuki Danbara¹, Hideto Senzaki¹, Yasuhiko Kiyozuka¹, Norihisa Uehara¹, Hideho Takada³, Takahiko Hada⁴, Teruo Miyazawa⁵, Yutaka Ogawa² and Airo Tsubura^1*

• * Corresponding author: Airo Tsubura tsubura@takii.kmu.ac.jp

Author Affiliations

¹ Department of Pathology II, Kansai Medical University, Moriguchi, Osaka, Japan

² Department of Plastic and Reconstructive Surgery, Kansai Medical University, Moriguchi, Osaka, Japan

³ Division of Surgery, Kansai Medical University Kori Hospital, Neyagawa, Osaka, Japan

⁴ R&D Division, Bizen Chemical Co., Ltd, Okayama, Japan

⁵ Laboratory of Biodynamic Chemistry, Tohoku University Graduate School of Life Science and Agriculture, Sendai, Japan

For all author emails, please log on.

Breast Cancer Res 2004, 6:R291-R299 doi:10.1186/bcr789

Published: 26 April 2004

Abstract

Introduction

The present study was conducted to examine the effect of conjugated docosahexaenoic acid (CDHA) on cell growth, cell cycle progression, mode of cell death, and expression of cell cycle regulatory and/or apoptosis-related proteins in KPL-1 human breast cancer cell line. This effect of CDHA was compared with that of docosahexaenoic acid (DHA).

Methods

KPL-1 cell growth was assessed by colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay; cell cycle progression and mode of cell death were examined by flow cytometry; and levels of expression of p53, p21^Cip1/Waf1, cyclin D₁, Bax, and Bcl-2 proteins were examined by Western blotting analysis. In vivo tumor growth was examined by injecting KPL-1 cells subcutaneously into the area of the right thoracic mammary fat pad of female athymic mice fed a CDHA diet.

Results

CDHA inhibited KPL-1 cells more effectively than did DHA (50% inhibitory concentration for 72 hours: 97 μmol/l and 270 μmol/l, respectively). With both CDHA and DHA growth inhibition was due to apoptosis, as indicated by the appearance of a sub-G₁ fraction. The apoptosis cascade involved downregulation of Bcl-2 protein; Bax expression was unchanged. Cell cycle progression was due to G₀/G₁ arrest, which involved increased expression of p53 and p21^Cip1/Waf1, and decreased expression of cyclin D₁. CDHA modulated cell cycle regulatory proteins and apoptosis-related proteins in a manner similar to that of parent DHA. In the athymic mouse system 1.0% dietary CDHA, but not 0.2%, significantly suppressed growth of KPL-1 tumor cells; CDHA tended to decrease regional lymph node metastasis in a dose dependent manner.

Conclusion

CDHA inhibited growth of KPL-1 human breast cancer cells in vitro more effectively than did DHA. The mechanisms of action involved modulation of apoptosis cascade and cell cycle progression. Dietary CDHA at 1.0% suppressed KPL-1 cell growth in the athymic mouse system.