Stearidonic acid-enriched flax oil reduces the growth of human breast cancer in vitro and in vivo

Abstract

The 20 and 22 carbon n-3 long-chain polyunsaturated fatty acids (LCPUFA) inhibit the growth of tumors in vitro and in animal models, but less is known about the 18 carbon n-3, stearidonic acid (SDA). This study aimed to establish and determine a mechanism for the anti-cancer activity of SDA-enriched oil (SO). SO (26 % of lipid) was produced by genetically engineering flax and used to treat human tumorigenic (MDA-MB-231, MCF-7) and non-tumorigenic (MCF-12A) breast cells. Nu/nu mice bearing MDA-MB-231 tumor were fed SO (SDA, 4 % of fat). Cell/tumor growth, phospholipid (PL) composition, apoptosis, CD95, and pro-apoptotic molecules were determined in SO-treated cells/tumors. Compared to a control lipid mixture, SO reduced (p < 0.05) the number of tumorigenic, but not MCF-12A cells, and resulted in higher concentration of most of the n-3 fatty acids in PL of all cells (p < 0.05). However, docosapentaenoic acid increased only in tumorigenic cells (p < 0.05). SO diet decreased tumor growth and resulted in more n-3 LCPUFA, including DPA and less arachidonic acid (AA) levels in major tumor PL (p < 0.05). Treatment of MDA-MB-231 cells/tumors with SO resulted in more apoptotic cells (in tumors) and in vivo and in vitro, more CD95+ positive cells and a higher expression of apoptotic molecules caspase-10, Bad, or Bid (p < 0.05). Supplementing SO alters total PL and PL classes by increasing membrane content of n-3 LCPUFA and lowering AA (in vivo), which is associated with increased CD95-mediated apoptosis, thereby suggesting a possible mechanism for reduce tumor survival.

Bypassing the Δ6‐desaturase enzyme and directly providing n‐3 and n‐6 PUFA pathway intermediates reduces the survival of two human breast cancer cell lines

“…The concentration of AA in breast tumors has been reported to be directly associated with tumorigenesis , suggesting a mechanism for effects on cell survival. However, we have previously demonstrated that treating MDA‐MB‐231 cells with a mixture of fatty acids containing SDA (26%) and DGLA (15%) reduced survival of MDA‐MB‐231 cells despite a 25% increased content of AA in cellular PL . Similar to our findings for both SDA and ETA, treatment with SDA has been reported to increase the content EPA and DPA in MDA‐MB‐231 cells .…”

“…Our study demonstrates that all of the n‐3 (SDA, ETA) and n‐6 (GLA and DGLA) fatty acid intermediates reduced the survival of tumorigenic but not non‐tumorigenic MCF‐12A cells. It has been found that treatment of MDA‐MB‐231 cells with SDA (50–200 μM) reduced cell survival more effectively than ALA and this was associated with a greater reduction in COX‐2 protein and mRNA levels , and we previously demonstrated that feeding a diet containing 0.8% w/w SDA reduced the growth of MDA‐MB‐231 tumors implanted in nu/nu mice . Similarly, feeding SDA (3% w/w) reduced mammary tumor growth in the APC (min/+) mouse .…”

“…There are a number of metabolic intermediates that are in low supply in the food supply: in the n‐3 PUFA pathway, they are stearidonic acid (SDA, C18:4n‐3) and eicosatetraenoic acid (ETA, C20:4n‐3); in the n‐6 pathway, they are γ‐linolenic acid (GLA, C18:3n‐6) and dihomo γ‐linolenic acid (DGLA, C20:3n‐6). There are some published data on SDA , GLA , and DGLA that support the suggestion that the mechanism for the activity is to provide the substrate to increase the supply of EPA, DHA, and AA to the tumor. The majority of these in vitro studies have focused on comparing the fatty acid treatment to cells incubated in the absence of exogenous fatty acids.…”

“…Cells were plated in triplicate in a 24‐well flat bottomed cell‐culture plate (Fisher Scientific, Edmonton, AB, Canada) at a density of 2.6 × 10 4 cells per well for MDA‐MB‐231 and MCF‐12A cells, and 5.2 × 10 4 cells per well for MCF‐7 cells, and allowed to adhere for 72 h. At about 50% confluence, cells were treated with different types of experimental n‐3 and n‐6 PUFA for 48 h. SDA, ETA, EPA, GLA, DGLA (Cedarlane, Burlington, ON, Canada), OA (oleic acid, C18:1n‐9), ALA, DHA, AA, and LA (MJS, Biolynx, Brockville, ON, Canada) were purchased and conjugated to bovine serum albumin (Fisher Scientific, Edmonton, AB, Canada), as described previously . Based on preliminary experiments, experimental fatty acids were added at a concentration of 150 µM to the cells on a background mixture of OA (40 µM) and LA (40 µM) to optimize cell growth as previously described .…”

Metformin Accumulation Correlates with Organic Cation Transporter 2 Protein Expression and Predicts Mammary Tumor Regression In Vivo

“…It is tempting to speculate that intracellular metformin acts on tumor fatty acid metabolism potentially to alleviate proliferative n-6 series ligands (AA or its derivatives), and enrich n-3 series ligands (LNA or its derivatives) that can oppose proliferation. Indeed, dietary n-3 supplementation increased mammary tumor phospholipids containing n-3 PUFA, concomitantly with decreased phospholipid AA, resulting in decreased tumor growth in vivo (49). At present, we do not understand if this observation is dependent on HFD consumption, or if metformin might generally affect the balance of n-6 and n-3 FA only in OCT2 positive mammary tumors.…”