α-linolenic acid and docosahexaenoic acid, alone and combined with trastuzumab, reduce HER2-overexpressing breast cancer cell growth but differentially regulate HER2 signaling pathways

Abstract

BackgroundDiets rich in the n-3 fatty acid alpha-linolenic acid (ALA) have been shown to reduce breast tumor growth, enhance the effectiveness of the HER2-targeted drug trastuzumab (TRAS) and reduce HER2 signaling in mouse models. It is unclear whether this is due to direct effects of ALA or due to its long-chain n-3 fatty acids metabolites including docosahexaenoic acid (DHA).MethodsThe ability of HER2-overexpressing BT-474 human breast cancer cells to convert ALA to long-chain n-3 fatty acids was determined by measurement of phospholipid fatty acids by gas chromatography following treatment with 100 μM ALA. The effects of 96 h treatment with ALA or DHA, at serum levels seen in mice (50–100 μM), alone and combined with TRAS (10 μg/ml), on BT-474 cell growth measured by trypan blue exclusion, apoptosis measured by flow cytometric analysis of Annexin-V/7-AAD stained cells (ALA and TRAS treatment only) and protein biomarkers HER2 signaling measured by western blot were determined.ResultsALA-treated BT-474 cells had higher phospholipid ALA but no increase in downstream n-3 metabolites including DHA. Both ALA and DHA reduced cell growth with and without TRAS. ALA had no effect on apoptosis. ALA and DHA showed opposite effects on Akt and MAPK phosphorylation; ALA increased and DHA decreased phosphorylation.ConclusionsTogether these data suggest that, while both ALA and its DHA metabolite can reduce HER2-overexpressing breast cancer growth with and without TRAS, they demonstrate for the first time that DHA is responsible for the effects of ALA-rich diets on HER2 signaling pathways.

Modulation of Ras/ERK and Phosphoinositide Signaling by Long-Chain n-3 PUFA in Breast Cancer and Their Potential Complementary Role in Combination with Targeted Drugs

“…Moreover, new therapies are also being experimented by combining different targeted inhibitors or combining targeted inhibitors with other existing non-targeted anticancer agents. In particular, recent studies have addressed the possibility of combining anticancer targeted therapies with natural agents, known for their broad antineoplastic activities, and relatively low toxicity, including LCn-3 PUFA fatty acids [25,26]. …”

“…In the case of the RAS/ERK pathway, these therapeutic agents mainly consist of inhibitors of the upstream GR Receptors (GFR, such as EGFR or HER/neu), RAF or MEK1/2 [44], and in the case of the phosphoinositide cascade, principally consist of inhibitors of GFR, as well as of PI3K. Recently, for their known antineoplastic properties and their ability to powerfully modulate both these signaling pathways in breast cancer, the potential of LCn-3 PUFA to function as adjuvants in combination with Trastuzumab has been investigated in in vitro and in preclinical models [26,45,46]. Trastuzumab is a specific inhibitor of the overexpressed receptor tyrosine kinase HER2/neu placed upstream of the activation of the Ras/ERK pathway [47].…”

“…In other studies, (Figure 4) [26,65,66,67,68] the anti-neoplastic effect of LCn-3 PUFA was investigated on the BT-474 and SK-BR-3 breast cancer cell lines, which are models of HER2/neu positive breast cancer (Figure 2). …”

“…Multiple antineoplastic effects induced by DHA (cell death and viability, apoptosis, cell migration and invasion) were investigated, and always strictly related to the inhibiting activity exerted by the fatty acid on the expression p-ERK and/or p-Akt. For example, Mason et al [26] found that BT-474 cell exposition to 50 and 100 µM DHA for four days markedly inhibited cell viability (by 30% and 70%, respectively). However, they did not investigate whether the effect of DHA was due to the inhibition of cell proliferation or induction of apoptosis.…”

Chemical Profile and Cytotoxic Activity of Leaf Extracts fromSennaspp. from Northeast of Brazil

“…However, these studies did not confirm whether the effects were caused by ALA or its metabolites. 34 No compound was correlated with the cytotoxicity of the samples in cluster B, which included two methanolic extracts, most likely because several of the polar compounds in these extracts did not elute in the chromatographic conditions used in this study.…”