Obesity-associated Leptin Activation of Cancer Stem Cell Signaling in Triple Negative Breast Cancer

Nick Shriver

Introduction.  Triple Negative Breast Cancer (TNBC) accounts for 15-20% of all breast cancers and is negative for Estrogen, Progesterone and Human epidermal growth factor 2 (HER2) receptors1. The lack of these receptors makes it inherently more difficult to treat, resulting in a more aggressive disease with a worse prognosis2. Without targeted therapies, it is important to enhance efficacy of chemotherapy. One method is through attenuation of pathways that mediate cancer stem cells (CSC), which have been shown to stimulate chemotherapy resistance3. Epidemiological studies have shown higher incidence of TNBC in obese patients4. During obesity, mammary adipocytes undergo multiple changes, including the upregulation of leptin. Enhanced leptin receptor expression is seen in breast cancer cells compared to normal mammary tissue, with the highest levels found in cancer stem cells3, leading to a hypothesis that obesity-associated leptin may activate TNBC stem cell activity5,6. Methods.  Diet-induced-obesity (DIO) mouse model was utilized to measure serum leptin levels and investigate if DIO serum is correlated with altered in vitro TNBC CSC activity. If so, the study would investigate if a leptin-mediated pathway is involved. Mouse models were prepared with a diet of 60% of Kcal from fat vs 10% control. DIO mouse serum was co-cultured with E-WNT line of TNBC cells. CSC transcription factor activity was observed via PCR. If significant alteration in CSC gene activity was confirmed, leptin-mediated activity would be identified by PCR analysis of CSC transcription factors in Leptin Receptor knockdown E-WNT cells following co-culture with DIO mouse serum. Results.  Serum DIO mice showed Leptin of 31ng/mL vs 5.3ng/mL control. Co-culture of DIO mouse serum with E-WNT cells showed statistically significant upregulation of multiple CSC genes, including a 5-fold increase in Twist2. Leptin Receptor knockdown cells showed significant downregulated activity of CSC genes FOXc2 and Twist2 in comparison to control, with a near elimination of all Twist2 activity5, confirming the suspected link to a leptin pathway. Conclusions.  Studies have shown a direct link between leptin-associated obesity and the activation of TNBC CSC genes. Of note, the pro-metastatic CSC genes FOXc2 and Twist27 were upregulated, signifying that targeted disruption of the leptin pathway is a potential treatment approach in TNBC, and may be especially important for obese patients.

 

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