Lipogenic phenotype (genetic program activation involved inde novo fatty acid –FA-synthesis and key metabolic regulators) is associated to oncogenic transformation and malignancy. We hypothesize that in HER2 overexpressing breast cancer cells, HER2 function is affected by cell membrane lipid profile, mainly lipid rafts, necessary to HER2 location and activation within the cell membrane. Therefore, metabolic lipid imbalance could be a potential factor and marker associated to HER2 expression. To evaluate if cell lipogenesis and membrane lipid composition are affected by HER2 overexpression, we used an oncogenic transformed cell line engineered to overexpress HER2 receptor (HB4aC5.2), but identical to their parental strain (HB4a) in all other aspects. Several lipid related molecules including synthesis-FASN, uptake-CD36, transport-FABP4 and FA storage-DGAT by RT-PCR; and lipogenic regulatory pathways (mTOR, DEPTOR, SREBP1 and PPARγ) were evaluated in both cells. Lipogenic contribution to lipid rafts formation was evaluated by gas chromatography and confocal microscopy. The influence of HER2 overexpression and lipogenic phenotype on proteins activated by HER2 (AKT, ERK1/2 and FASN) was analyzed by western blot. Next, HB4a and HB4aC5.2 cells were treated, alone or in combination with DHA (omega-3 polyunsaturated fatty acid), by Trastuzumab (anti-HER2), and GW9662 (anti-PPARγ) for 72h, and all above experiments were repeated. Cell death was analyzed by flow cytometry. In vitro results were confirmed in Primary tumor and adjacent tissue samples from a cohort of 182 European breast cancer patients through metabolomics analysis. Statistical analysis was performed by MetaboAnalyst software (p <0.05). In HB4aC5.2 cells, the HER2 overexpression was associated with a lipogenic phenotype, which increase in cholesterol and saturated FA synthesis for the lipid rafts formation, suggesting that large amounts of HER2 require cell membrane changes to favor rafts saturation and formation, when compared to HB4a. Lipid rafts were associated with survival and proliferation signals hiper activation (p<0.001). Cell lipogenesis was independent ofmTOR/SREBP/PPARγpathway and occur concomitantly to DEPTOR (mTOR inhibitor) increased expression. Moreover, GW9662 or Trastuzumab treatment did not influence lipogenesis in cell culture. In HB4aC5.2 cells, only DHA treatment decreased the lipogenic phenotype, DEPTOR expression, saturated FA synthesis, disrupted lipid raft, inhibited HER2 signaling, and induced apoptosis (p<0.001). In addition, when added to Trastuzumab DHA potentiated cell death. In tumor tissue samples an increased FA synthesis was observed, such as palmitic acid, sphingolipids and phosphatidylcholines saturated FA enriched, synthesis of cholesterol, suggesting an increase of lipid rafts when compared to normal breast adjacent tissue. Our results indicate that lipogenic phenotype is associated with HER2 superexpression in breast cancer cells, and it seems important to promote survival and proliferation, through lipid rafts increase. DHA modulation increased death in tumor cells, suggesting that cell membrane lipogenesis and lipid composition may represent a treatment target. Lipogenic phenotype confirmation in tumor tissue samples strengthens this hypothesis.
Citation Format: Ravacci GR, Santos JR, Brentani MM, Tortelli T, Dale I, Logullo AF, Waitzberg DL. HER2-associated lipogenic phenotype as a potential therapeutical target in breast cancer patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-21-29.