Lipid-soluble polyphenols from sweet potato exert antitumor activity and enhance chemosensitivity in breast cancer

Abstract

Polyphenols are abundant in vegetables and fruit. They have been shown to have various antitumor, antioxidant, and anti-inflammatory effects. Here, we extracted the lipid-soluble fraction of polyphenols from fermented sweet potato (Ipomoea batatas). These lipid-soluble polyphenols mainly contained caffeic acid derivatives with strong antioxidant ability, which we hypothesized to affect diseases for which oxidative stress is a factor, such as cancer. We therefore investigated the antitumor and chemo-sensitizing effects of lipid-soluble polyphenols on E0771 murine breast cancer cells. The lipid-soluble polyphenols accumulated in the cells' cytoplasm due to its high lipophilicity, and reduced reactive oxygen species through its strong antioxidant activity. The lipid-soluble polyphenols also arrested the cell cycle at G₀/G₁ by suppressing Akt activity, and enhanced the cytotoxicity of anticancer agents. In this model, lipid-soluble polyphenols inhibited tumor growth and enhanced the efficacy of chemotherapy drugs. These results suggest the potential of lipid-soluble polyphenols as a functional food to support cancer therapy.

Keywords: antioxidant; breast cancer; chemotherapy; functional food; polyphenol.

Fig. 1

Cytotoxicity, cell localization and antioxidant activity of PPL in E0771 cells. (A) Colony formation assay of cells treated with PPL for 48 h at the indicated concentrations. (B) Confocal laser micrograph of PPL intracellular uptake in cells after PPL treatment (50 µM, 48 h). (C) Cellular ROS measurement after 24-h treatment with PPL or NAC at indicated concentrations, using DCFDA staining. (D) DPPH assay of PPL and NAC antioxidant activities, showing k_obs for PPL or NAC with DPPH in MeCN at 25°C. White bar: 10 µm. Error bars: SD, **p<0.01.

Fig. 2

PPL arrests cell cycle and suppresses Akt phosphorylation. (A) Cell-cycle histogram. (B) Cell populations at G₀/G₁-, S- and G₂/M-phases were analyzed by flow cytometry (propidium iodide staining). (C) Western blot shows Akt phosphorylation of E0771 cells and MDA-MD-231 cells after PPL treatment (20 µM). (C) Representative western blot images of pSer473-Akt, Akt and β-Actin in E0771 cells and MDA-MB-231 cells. (D) Quantitative analyses of pSer473-Akt and Akt in Western blots of E0771 cells and MDA-MB-231 cells. Error bars: SD, *p<0.05, **p<0.01.

Fig. 3

Colony formation assay shows PPL enhances cytotoxicity of anticancer agents. (A) Colony formation assay in cells simultaneously treated for 48 h with 20 µM PPL + CBDCA, or 5 mM NAC + CBDCA, at the indicated CBDCA concentrations. (B) CFA in cells simultaneously treated for 48 h with 20 µM PPL + VCR or 5 mM NAC + VCR at the indicated VCR concentrations. Error bars: SD, *p<0.05, **p<0.01.

Fig. 4

PPL suppresses transplanted E0771 tumors. Tumors were formed by injecting E0771 cells into mammary fat pads of C57BL/6N mice. (A) E0771 tumor-bearing mice were treated with PPL for 7 consecutive days, and their tumor volumes were measured. (B) Kaplan–Meier survival curves for E0771 tumor-bearing mice treated with PPL. Control group treated with methyl cellulose by oral administration. Survival end point was set when tumor volume = 1,500 mm³. Survival curves of individual groups were compared by log-rank tests. (C) Body weights for E0771 tumor-bearing mice treated with PPL. Error bars: SE, *p<0.05, **p<0.01.

Fig. 5

PPL enhances chemo-sensitization of E0771 tumors. The chemo-sensitizing effect of PPL was evaluated in tumors formed by E0771 cells inoculated into mammary fat pads of C57BL/6N mice. (A) Tumor volumes in E0771 tumor-bearing mice that were treated with PPL for 7 consecutive days, CBDCA once or both PPL and CBDCA. (B) Survival curves for E0771 tumor-bearing mice treated with PPL, CBDCA or both. (C) Immunohistochemical staining for cleaved caspase-3 in allograft E0771 tumors. (D) Cleaved caspase-3⁺ cells per mm² were quantified by counting in 10 random microscopic fields. Error bars: SE, *p<0.05, **p<0.01. Black bar: 100 µm. Control group treated with methyl cellulose by oral administration and saline by intraperitoneally administration.