Mikaila Singleton

Introduction. Breast cancer is the number one non-cutaneous cancer among women in the United States.^1,2 Leptin is derived from adipocytes and acts as a hormone that can advance the progression of breast cancer.³  Previously it’s been demonstrated that leptin can act via the LKB1/AMPK pathway to stimulate aromatase expression, which is important for estrogen production, but the p53-HIF1αPKM2-aromatase axis has yet to be investigated.⁴ In previous studies, it has also been demonstrated that leptin receptor deficient obese mice in the presence of leptin do not develop mammary cancer.⁵  The p53-HIF1αPKM2-aromatase axis has been upregulated in Li-Fraumeni Syndrome, therefore the same variable were measured in response to leptin treatment.⁵ Methods Immortalized human mammary adipose stromal cells were treated with leptin then aromatase, PKC, MAPK, p53, Aha1, HSP90, HIF1α and PKM2 were measured with activity assays and western blots.⁴ Additionally, those components were measured in the presence of an inhibitor.⁴ Targeting the leptin receptor, the leptin peptide antagonist, LFD1, was created using solid phase methods.⁵ MCF-7 and SKBR3 cell lines were treated with leptin and increasing doses of LDF1.⁵ Cell growth was analyzed via MTT and soft agar anchorage-independent assay.⁵ Cell migration was assessed with wound closure assays.⁵ MCF-7 and TAM-R cells were cultured, treated with leptin, tamoxifen and ObRb- siRNA then proliferation was determined by EdU retention assays.⁶ Results. Leptin treatment caused and increased expression of aromatase, PKC, MAPK, Aha1, HSP90, HIF1α and PKM2.⁴ Aromatase expression increased in a dose dependent manner.⁴ Downstream components such as PKC, MAPK, Aha1, HSP90, HIF1α and PKM2 increased aromatase expression.⁴ When any components were inhibited, aromatase expression decreased.⁴ p53 normally binds to the aromatase promoter II to inhibit activity, but when ERK1/2 is active due to leptin binding, p53 is decreased therefore there is increased aromatase promoter activity.⁴ LFD1 limited cell migration and viability.⁵ Cell proliferation decreased in a dose dependent manner with LFD1.⁵ Tamoxifen resistant cells didn’t respond to tamoxifen alone yet when the leptin receptor is inhibited, there’s a decrease in cell proliferation and an increase in apoptosis in tamoxifen resistant cells in the presence of tamoxifen.⁶ Conclusions. Previous studies demonstrate leptins influence in mammary cancer, but do not show data for aromatase expression mediated by leptin. Circulating leptin increases aromatase expression by upregulating the p53-HIF1αPKM2-aromatase axis.⁴   Cell growth and viability are inhibited by LDF1.⁵ Discovering the novel axis and inhibiting the leptin receptor can be new targets for future breast cancer treatment.

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