Abstract P5-06-05: Palmitate induces a senescent-like phenotype in fibroblasts resulting in altered phenotypes in cells of the breast tumor microenvironment

Background: Obese breast cancer patients face a worse prognosis, including an increased risk of recurrence and mortality. While the causative mechanisms have yet to be fully uncovered, emerging evidence implicates palmitate, increased in the obese state, in development of cellular senescence, an inflammatory state associated with proliferation, metastasis, and tumor-associated neutrophil (TAN) polarization, among other measures of carcinogenesis. However, studies have yet to investigate the impact of palmitate on induction of senescence in breast fibroblasts, and no studies have assessed the effect of senescent fibroblasts on neutrophil polarization in the breast tumor microenvironment. This said, we hypothesize that palmitate alters breast cancer cell gene expression and neutrophil phenotype via induction of a senescent-like phenotype in fibroblasts. Methods: HCA2, IMR-90, and human mammary fibroblasts were exposed to palmitate or vehicle in media supplemented with 2% charcoal-stripped fetal bovine serum, after which the cells were measured through qPCR for expression of IL-1a, IL-6 and IL-8, some of the most prominent members of the senescence-associated secretory phenotype. Palmitate-exposed fibroblasts were also subjected to chromogenic staining for senescence-associated beta-galactosidase and immunoenzymatic BrdU analysis, two well-established measures of senescence. Next, in order to study the influence of these fibroblasts on other cells of the breast tumor microenvironment, we assessed their impact on polarization of DMSO-differentiated HL-60 neutrophils by using flow cytometry to measure neutrophil expression of CD54 and CD95, differentially expressed on N1 and N2 neutrophils. Finally, we employed PCR arrays to assess the impact of palmitate-exposed fibroblasts on the expression of 84 genes in MCF-7 and 231 breast cancer cells, measuring activation of pathways related to apoptosis, cell cycle, DNA damage, senescence, telomere maintenance, metabolism, angiogenesis, and the endothelial-to-mesenchymal transition. Results and Conclusions: Palmitate induced pro-inflammatory gene expression and SA-beta-gal activity and decreased BrdU incorporation in fibroblasts. Palmitate also exhibited non-cell-autonomous effects, as palmitate-exposed fibroblasts induced phenotypic changes in both neutrophils and breast cancer cells. These findings are among the first to implicate palmitate-induced fibroblast senescence in the stimulation of non-cell-autonomous changes in the breast tumor microenvironment and will ultimately inform our understanding of the mechanistic connection between the obesity-associated factor palmitate and breast tumorigenesis.

Citation Format: Brittany Susanne Harlow, Albert Davalos, Bryan McClellan, Andrew Brenner, Christopher Jolly, Stefano Tiziani, Steve Hursting, Linda deGraffenried. Palmitate induces a senescent-like phenotype in fibroblasts resulting in altered phenotypes in cells of the breast tumor microenvironment [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-06-05.

Abstract 2022: Palmitate promotes breast cancer progression in vitro through induction of a senescent-like phenotype in fibroblasts

Background: Obesity confers a worse breast cancer prognosis, including an increased risk of recurrence and mortality. While the causative mechanisms have yet to be fully uncovered, emerging evidence implicates palmitate, increased in the obese state, in development of cellular senescence, an inflammatory state associated with breast tumorigenesis in preclinical models. However, studies are warranted to corroborate the impact of palmitate on induction of a cohesive senescent-like phenotype as well as the extent to which palmitate-induced senescence impacts breast tumorigenesis either in vitro or in vivo. This said, we hypothesize that palmitate exposure induces a senescent-like phenotype in fibroblasts, contributing to measures of breast cancer progression.

Methods: HCA2, IMR-90, and human mammary fibroblasts were exposed to bovine serum albumin or palmitate in media supplemented with 2% charcoal-stripped fetal bovine serum, after which the cells were measured through qPCR for expression of IL-1a, IL-6 and IL-8, some of the most prominent members of the senescence-associated secretory phenotype. Palmitate-exposed fibroblasts were also stained for senescence-associated beta-galactosidase and BrdU incorporation, well-established senescence markers. Experiments were then repeated with administration of eicosapentaenoic and docosahaexanoic acids to evaluate the potential of omega-3 fatty acids to limit the effects of palmitate on fibroblast senescence. Finally, we assessed the tumor-promoting potential of these palmitate-exposed fibroblasts by culturing MCF-7 and T47D breast cancer cells in their conditioned media and assessing changes in carcinogenic measures.

Results and Conclusions: Palmitate induced pro-inflammatory gene expression and SA-beta-gal positivity and decreased proliferation in fibroblasts, while omega-3 fatty acid supplementation reversed these effects. These palmitate-exposed fibroblasts also appeared to be of pathological impact, as exposure to their CM increased proliferation in breast cancer cells. These findings are important in that they support emerging evidence implicating obesity-associated factors in the exacerbation of breast cancer progression as well as indicate the potential of omega-3 fatty acids to improve outcome.

Citation Format: Brittany Susanne Harlow, Albert R. Davalos, Andrew J. Brenner, Christopher Jolly, Stefano Tiziani, Stephen D. Hursting, Linda A. deGraffenried. Palmitate promotes breast cancer progression in vitro through induction of a senescent-like phenotype in fibroblasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2022.

Abstract PS19-13: Palmitate exacerbates breast tumorigenesis in vitro via induction of a senescent-like phenotype in fibroblasts

Background: Obesity is associated with a worse breast cancer prognosis, conferring an increased risk of recurrence and mortality. At the same time, recent evidence suggests that obesity is also correlated with development of cellular senescence, an inflammatory state associated with exacerbation of breast tumorigenesis in preclinical models. As obese individuals present greater levels of inflammation at baseline, research efforts are warranted to examine the means by which obesity promotes the development of a senescent phenotype, which may further exacerbate inflammation. Additionally, studies have yet to determine whether obesity-induced senescence modulates the tumorigenic process in the context of breast cancer specifically. Methods: To this end, we exposed fibroblasts to the obesity-associated circulating factor palmitate and used qPCR and western immunoblotting to assess the expression of genes and proteins involved in the senescent state, including interleukin (IL)-1a, IL-6, IL-8, senescence-associated beta-galactosidase (SA-beta-gal), and matrixmetalloproteinase (MMP)-9. As a mechanistic investigation, we next assessed the impact of palmitate on activation of NF-kB signaling using western immunoblotting, immunofluorescence, and NF-kB luciferase reporter assays. Finally, we utilized cell counting, MTT, wound healing, and colony formation assays to examine the impact of these palmitate-exposed fibroblasts on breast cancer cell proliferation, viability, motility, and survival, respectively. Results: We found that palmitate induced fibroblast gene expression of IL-1a, IL-6, and IL-8, major components of the senescent secretome, as well as expression of the senescent markers SA-beta-gal and MMP-9. The mechanism at least partially involved activation of NF-kB, responsible for production of about 75% of senescent secretome components. More importantly, these palmitate-exposed fibroblasts were of pathological impact, exacerbating in vitro measures of breast cancer cell aggressiveness. Conclusions: These findings contribute to our understanding of the impact of obesity-associated factors on breast tumorigenesis, demonstrating a mechanistic link between palmitate and the pro-tumorigenic effects of senescent cells. Our studies will ultimately aid in the identification of a therapeutic target that can be used to improve the comparably worse outcomes of the obese breast cancer patient.

Citation Format: Brittany Susanne Harlow, Albert Davalos, Andrew Brenner, Christopher Jolly, Stefano Tiziani, Steve Hursting, Linda deGraffenried. Palmitate exacerbates breast tumorigenesis in vitro via induction of a senescent-like phenotype in fibroblasts [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS19-13.