Screening of a kinase inhibitor library identified novel targetable kinase pathways in triple-negative breast cancer.

Triple-negative breast cancer (TNBC) is a highly invasive breast cancer subtype that is challenging to treat due to inherent heterogeneity and absence of estrogen, progesterone, and human epidermal growth factor 2 receptors. Kinase signaling networks drive cancer growth and development, and kinase inhibitors are promising anti-cancer strategies in diverse cancer subtypes. Kinase inhibitor screens are an efficient, valuable means of identifying compounds that suppress cancer cell growth in vitro, facilitating the identification of kinase vulnerabilities to target therapeutically. The Kinase Chemogenomic Set is a well-annotated library of 187 kinase inhibitor compounds that indexes 215 kinases of the 518 in the known human kinome representing various kinase networks and signaling pathways, several of which are understudied. Our screen revealed 14 kinase inhibitor compounds effectively inhibited TNBC cell growth and proliferation. Upon further testing, three compounds, THZ531, THZ1, and PFE-PKIS 29, had the most significant and consistent effects across a range of TNBC cell lines. These cyclin-dependent kinase (CDK)12/CDK13, CDK7, and phosphoinositide 3-kinase inhibitors, respectively, decreased metabolic activity in TNBC cell lines and promote a gene expression profile consistent with the reversal of the epithelial-to-mesenchymal transition, indicating these kinase networks potentially mediate metastatic behavior. These data identified novel kinase targets and kinase signaling pathways that drive metastasis in TNBC.

Bone Marrow-Derived Mononuclear Cells in the Treatment of Neurological Diseases: Knowns and Unknowns.

Bone marrow-derived mononuclear cells (BMMNCs) have been used for decades in preclinical and clinical studies to treat various neurological diseases. However, there is still a knowledge gap in the understanding of the underlying mechanisms of BMMNCs in the treatment of neurological diseases. In addition, prerequisite factors for the efficacy of BMMNC administration, such as the optimal route, dose, and number of administrations, remain unclear. In this review, we discuss known and unknown aspects of BMMNCs, including the cell harvesting, administration route and dose; mechanisms of action; and their applications in neurological diseases, including stroke, cerebral palsy, spinal cord injury, traumatic brain injury, amyotrophic lateral sclerosis, autism spectrum disorder, and epilepsy. Furthermore, recommendations on indications for BMMNC administration and the advantages and limitations of BMMNC applications for neurological diseases are discussed. BMMNCs in the treatment of neurological diseases. BMMNCs have been applied in several neurological diseases. Proposed mechanisms for the action of BMMNCs include homing, differentiation and paracrine effects (angiogenesis, neuroprotection, and anti-inflammation). Further studies should be performed to determine the optimal cell dose and administration route, the roles of BMMNC subtypes, and the indications for the use of BMMNCs in neurological conditions with and without genetic abnormalities.

The role of MEK1/2 and MEK5 in melatonin-mediated actions on osteoblastogenesis, osteoclastogenesis, bone microarchitecture, biomechanics, and bone formation.

Melatonin, the primary hormone involved in circadian entrainment, plays a significant role in bone physiology. This study aimed to assess the role of MEK1/2 and MEK5 in melatonin-mediated actions in mouse and human mesenchymal stem cells (MSCs) and on bone using small-molecule inhibitors and CRISPR/Cas9 knockout approaches. Consistent with in vitro studies performed in mMSCs and hMSCs, nightly (25 mg/kg, i.p., 45 days) injections with PD184352 (MEK1/2 inhibitor) or Bix02189 (MEK5 inhibitor) or SC-1-151 (MEK1/2/5 inhibitor) demonstrated that MEK1/2 and MEK5 were the primary drivers underlying melatonin's actions on bone density, microarchitecture (i.e., trabecular number, separation, and connectivity density), and bone mechanical properties (i.e., ultimate stress) through increases in osteogenic (RUNX2, BMP-2, FRA-1, OPG) expression and decreases in PPARγ. Furthermore, CRISPR/Cas9 knockout of MEK1 or MEK5 in mMSCs seeded on PLGA scaffolds and placed into critical-size calvarial defects in Balb(c) mice (male and female) revealed that treatment with melatonin (15 mg/L; p.o., nightly, 90 days) mediates sex-specific actions of MEK1 and MEK5 in new bone formation. This study is the first to demonstrate a role for MEK1/2 and MEK5 in modulating melatonin-mediated actions on bone formation in vivo and in a sex-specific manner.

Clinically relevant preservation conditions for mesenchymal stem/stromal cells derived from perinatal and adult tissue sources.

The interplay between mesenchymal stem/stromal cells (MSCs) and preservation conditions is critical to maintain the viability and functionality of these cells before administration. We observed that Ringer lactate (RL) maintained high viability of bone marrow-derived MSCs for up to 72 h at room temperature (18°C-22°C), whereas adipose-derived and umbilical cord-derived MSCs showed the highest viability for 72 h at a cold temperature (4°C-8°C). These cells maintained their adherence ability with an improved recovery rate and metabolic profiles (glycolysis and mitochondrial respiration) similar to those of freshly harvested cells. Growth factor and cytokine analyses revealed that the preserved cells released substantial amounts of leukaemia inhibitory factors (LIFs), hepatocyte growth factor (HGF) and vascular endothelial growth factor-A (VEGF-A), as well as multiple cytokines (eg IL-4, IL-6, IL-8, MPC-1 and TNF-α). Our data provide the simplest clinically relevant preservation conditions that maintain the viability, stemness and functionality of MSCs from perinatal and adult tissue sources.

The protein kinase MAP3K19 phosphorylates MAP2Ks and thereby activates ERK and JNK kinases and increases viability of KRAS-mutant lung cancer cells.

Identifying additional mitogen-activated protein kinase (MAPK) pathway regulators is invaluable in aiding our understanding of the complex signaling networks that regulate cellular processes, including cell proliferation and survival. Here, using in vitro kinase assays and by expressing WT or kinase-dead MAPK kinase kinase 19 (MAP3K19) in the HEK293T cell line and assessing activation of the extracellular signal-regulated kinase (ERK) and JUN N-terminal kinase (JNK) signaling pathways, we defined MAP3K19 as a novel regulator of MAPK signaling. We also observed that overexpression of WT MAP3K19 activates both the ERK and JNK pathways in a panel of cancer cell lines. Furthermore, MAP3K19 sustained ERK pathway activation in the presence of inhibitors targeting the RAF proto-oncogene Ser/Thr protein kinase (RAF) and MAPK/ERK kinase, indicating that MAP3K19 activates ERK via a RAF-independent mechanism. Findings from in vitro and in-cell kinase assays demonstrate that MAP3K19 is a kinase that directly phosphorylates both MAPK/ERK kinase (MEK) and MAPK kinase 7 (MKK7). Results from an short-hairpin RNA screen indicated that MAP3K19 is essential for maintaining survival in KRAS-mutant cancers; therefore, we depleted or inhibited MAP3K19 in KRAS-mutant cancer cell lines and observed that this reduces viability and decreases ERK and JNK pathway activation. In summary, our results reveal that MAP3K19 directly activates the ERK and JNK cascades and highlight a role for this kinase in maintaining survival of KRAS-mutant lung cancer cells.

Dual inhibition of MEK1/2 and MEK5 suppresses the EMT/migration axis in triple-negative breast cancer through FRA-1 regulation.

Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. Constitutive activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway has been linked to chemoresistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT) when cells adopt a motile and invasive phenotype through loss of epithelial markers (CDH1), and acquisition of mesenchymal markers (VIM, CDH2). Although MAPK/ERK1/2 kinase inhibitors (MEKi) are useful antitumor agents in a clinical setting, including the Food and Drug Administration (FDA)-approved MEK1,2 dual inhibitors cobimetinib and trametinib, there are limitations to their clinical utility, primarily adaptation of the BRAF pathway and ocular toxicities. The MEK5 (HGNC: MAP2K5) pathway has important roles in metastatic progression of various cancer types, including those of the prostate, colon, bone and breast, and elevated levels of ERK5 expression in breast carcinomas are linked to a worse prognoses in TNBC patients. The purpose of this study is to explore MEK5 regulation of the EMT axis and to evaluate a novel pan-MEK inhibitor on clinically aggressive TNBC cells. Our results show a distinction between the MEK1/2 and MEK5 cascades in maintenance of the mesenchymal phenotype, suggesting that the MEK5 pathway may be necessary and sufficient in EMT regulation while MEK1/2 signaling further sustains the mesenchymal state of TNBC cells. Furthermore, additive effects on MET induction are evident through the inhibition of both MEK1/2 and MEK5. Taken together, these data demonstrate the need for a better understanding of the individual roles of MEK1/2 and MEK5 signaling in breast cancer and provide a rationale for the combined targeting of these pathways to circumvent compensatory signaling and subsequent therapeutic resistance.

Standardized xeno- and serum-free culture platform enables large-scale expansion of high-quality mesenchymal stem/stromal cells from perinatal and adult tissue sources.

BACKGROUND AIMS: Mesenchymal stem/stromal cells (MSCs) are of interest for the treatment of graft-versus-host disease, autoimmune diseases, osteoarthritis and neurological and cardiovascular diseases. Increasing numbers of clinical trials emphasize the need for standardized manufacturing of these cells. However, many challenges related to diverse isolation and expansion protocols and differences in cell tissue sources exist. As a result, the cell products used in numerous trials vary greatly in characteristics and potency. METHODS: The authors have established a standardized culture platform using xeno- and serum-free commercial media for expansion of MSCs derived from umbilical cord (UC), bone marrow and adipose-derived (AD) and examined their functional characteristics. RESULTS: MSCs from the tested sources stably expanded in vitro and retained their biomarker expression and normal karyotype at early and later passages and after cryopreservation. MSCs were capable of colony formation and successfully differentiated into osteogenic, adipogenic and chondrogenic lineages. Pilot expansion of UC-MSCs and AD-MSCs to clinical scale revealed that the cells met the required quality standard for therapeutic applications. CONCLUSIONS: The authors' data suggest that xeno- and serum-free culture conditions are suitable for large-scale expansion and enable comparative study of MSCs of different origins. This is of importance for therapeutic purposes, especially because of the numerous variations in pre-clinical and clinical protocols for MSC-based products.

Allogeneic administration of human umbilical cord-derived mesenchymal stem/stromal cells for bronchopulmonary dysplasia: preliminary outcomes in four Vietnamese infants.

BACKGROUND: Bronchopulmonary dysplasia (BPD) is a severe condition in premature infants that compromises lung function and necessitates oxygen support. Despite major improvements in perinatal care minimizing the devastating effects, BPD remains the most frequent complication of extreme preterm birth. Our study reports the safety of the allogeneic administration of umbilical cord-derived mesenchymal stem/stromal cells (allo-UC-MSCs) and the progression of lung development in four infants with established BPD. METHODS: UC tissue was collected from a healthy donor, followed by propagation at the Stem Cell Core Facility at Vinmec Research Institute of Stem Cell and Gene Technology. UC-MSC culture was conducted under xeno- and serum-free conditions. Four patients with established BPD were enrolled in this study between May 25, 2018, and December 31, 2018. All four patients received two intravenous doses of allo-UC-MSCs (1 million cells/kg patient body weight (PBW) per dose) with an intervening interval of 7 days. Safety and patient conditions were evaluated during hospitalization and at 7 days and 1, 6 and 12 months postdischarge. RESULTS: No intervention-associated severe adverse events or prespecified adverse events were observed in the four patients throughout the study period. At the time of this report, all patients had recovered from BPD and were weaned off of oxygen support. Chest X-rays and CT scans confirmed the progressive reductions in fibrosis. CONCLUSIONS: Allo-UC-MSC administration is safe in preterm infants with established BPD. Trial registration This preliminary study was approved by the Vinmec International Hospital Ethics Board (approval number: 88/2019/QD-VMEC; retrospectively registered March 12, 2019).

A novel screening approach comparing kinase activity of small molecule inhibitors with similar molecular structures and distinct biologic effects in triple-negative breast cancer to identify targetable signaling pathways.

Breast cancer affects women globally; the majority of breast cancer-related mortalities are due to metastasis. Acquisition of a mesenchymal phenotype has been implicated in the progression of breast cancer cells to an invasive, metastatic state. Triple-negative breast cancer (TNBC) subtypes have high rates of metastases, recurrence, and have poorer prognoses compared to other breast cancer types, partially due to lack of commonly targeted receptors. Kinases have diverse and pivotal functions in metastasis in TNBC, and discovery of new kinase targets for TNBC is warranted. We previously used a screening approach to identify intermediate-synthesis nonpotent, nonselective small-molecule inhibitors from the Published Kinase Inhibitor Set that reversed the mesenchymal phenotype in TNBC cells. Two of these inhibitors (GSK346294A and GSK448459A) are structurally similar, but have unique kinase activity profiles and exhibited differential biologic effects on TNBC cells, specifically on epithelial-to-mesenchymal transition (EMT). Here, we further interrogate these effects and compare activity of these inhibitors on transwell migration, gene (qRT-PCR) and protein (western blot) expressions, and cancer stem cell-like behavior. We incorporated translational patient-derived xenograft models in these studies, and we focused on the lead inhibitor hit, GSK346294A, to demonstrate the utility of our comparative analysis as a screening modality to identify novel kinase targets and signaling pathways to pursue in TNBC. This study introduces a new method for discovering novel kinase targets that reverse the EMT phenotype; this screening approach can be applied to all cancer types and is not limited to breast cancer.

Drug resistance profiling of a new triple negative breast cancer patient-derived xenograft model.

BACKGROUND: Triple-negative breast cancer (TNBC) represents an aggressive subtype with limited therapeutic options. Experimental preclinical models that recapitulate their tumors of origin can accelerate target identification, thereby potentially improving therapeutic efficacy. Patient-derived xenografts (PDXs), due to their genomic and transcriptomic fidelity to the tumors from which they are derived, are poised to improve the preclinical testing of drug-target combinations in translational models. Despite the previous development of breast and TNBC PDX models, those derived from patients with demonstrated health-disparities are lacking. METHODS: We use an aggressive TNBC PDX model propagated in SCID/Beige mice that was established from an African-American woman, TU-BcX-2 K1, and assess its metastatic potential and drug sensitivities under distinct in vitro conditions. Cellular derivatives of the primary tumor or the PDX were grown in 2D culture conditions or grown in mammospheres 3D culture. Flow cytometry and fluorescence staining was used to quantify cancer stem cell-like populations. qRT-PCR was used to describe the mesenchymal gene signature of the tumor. The sensitivity of TU-BcX-2 K1-derived cells to anti-neoplastic oncology drugs was compared in adherent cells and mammospheres. Drug response was evaluated using a live/dead staining kit and crystal violet staining. RESULTS: TU-BcX-2 K1 has a low propensity for metastasis, reflects a mesenchymal state, and contains a large burden of cancer stem cells. We show that TU-BcX-2 K1 cells have differential responses to cytotoxic and targeted therapies in 2D compared to 3D culture conditions insofar as several drug classes conferred sensitivity in 2D but not in 3D culture, or cells grown as mammospheres. CONCLUSIONS: Here we introduce a new TNBC PDX model and demonstrate the differences in evaluating drug sensitivity in adherent cells compared to mammosphere, or suspension, culture.

A novel patient-derived xenograft model for claudin-low triple-negative breast cancer.

BACKGROUND: Triple-negative breast cancer (TNBC) subtypes are clinically aggressive and cannot be treated with targeted therapeutics commonly used in other breast cancer subtypes. The claudin-low (CL) molecular subtype of TNBC has high rates of metastases, chemoresistance and recurrence. There exists an urgent need to identify novel therapeutic targets in TNBC; however, existing models utilized in target discovery research are limited. Patient-derived xenograft (PDX) models have emerged as superior models for target discovery experiments because they recapitulate features of patient tumors that are limited by cell-line derived xenograft methods. METHODS: We utilize immunohistochemistry, qRT-PCR and Western Blot to visualize tumor architecture, cellular composition, genomic and protein expressions of a new CL-TNBC PDX model (TU-BcX-2O0). We utilize tissue decellularization techniques to examine extracellular matrix composition of TU-BcX-2O0. RESULTS: Our laboratory successfully established a TNBC PDX tumor, TU-BCX-2O0, which represents a CL-TNBC subtype and maintains this phenotype throughout subsequent passaging. We dissected TU-BCx-2O0 to examine aspects of this complex tumor that can be targeted by developing therapeutics, including the whole and intact breast tumor, specific cell populations within the tumor, and the extracellular matrix. CONCLUSIONS: Here, we characterize a claudin-low TNBC patient-derived xenograft model that can be utilized for therapeutic research studies.

Reduced hematopoietic stem cell frequency predicts outcome in acute myeloid leukemia.

In patients with acute myeloid leukemia and low percentages of aldehyde-dehydrogenase-positive cells, non-leukemic hematopoietic stem cells can be separated from leukemic cells. By relating hematopoietic stem cell frequencies to outcome we detected poor overall- and disease-free survival of patients with low hematopoietic stem cell frequencies. Serial analysis of matched diagnostic and follow-up samples further demonstrated that hematopoietic stem cells increased after chemotherapy in patients who achieved durable remissions. However, in patients who eventually relapsed, hematopoietic stem cell numbers decreased dramatically at the time of molecular relapse demonstrating that hematopoietic stem cell levels represent an indirect marker of minimal residual disease, which heralds leukemic relapse. Upon transplantation in immune-deficient mice cases with low percentages of hematopoietic stem cells of our cohort gave rise to leukemic or no engraftment, whereas cases with normal hematopoietic stem cell levels mostly resulted in multi-lineage engraftment. Based on our experimental data, we propose that leukemic stem cells have increased niche affinity in cases with low percentages of hematopoietic stem cells. To validate this hypothesis, we developed new mathematical models describing the dynamics of healthy and leukemic cells under different regulatory scenarios. These models suggest that the mechanism leading to decreases in hematopoietic stem cell frequencies before leukemic relapse must be based on expansion of leukemic stem cells with high niche affinity and the ability to dislodge hematopoietic stem cells. Thus, our data suggest that decreasing numbers of hematopoietic stem cells indicate leukemic stem cell persistence and the emergence of leukemic relapse.

The rarity of ALDH(+) cells is the key to separation of normal versus leukemia stem cells by ALDH activity in AML patients.

To understand the precise disease driving mechanisms in acute myeloid leukemia (AML), comparison of patient matched hematopoietic stem cells (HSC) and leukemia stem cells (LSC) is essential. In this analysis, we have examined the value of aldehyde dehydrogenase (ALDH) activity in combination with CD34 expression for the separation of HSC from LSC in 104 patients with de novo AML. The majority of AML patients (80 out of 104) had low percentages of cells with high ALDH activity (ALDH(+) cells; <1.9%; ALDH-rare AML), whereas 24 patients had relatively numerous ALDH(+) cells (≥1.9%; ALDH-numerous AML). In patients with ALDH-rare AML, normal HSC could be separated by their CD34(+) ALDH(+) phenotype, whereas LSC were exclusively detected among CD34(+) ALDH(-) cells. For patients with ALDH-numerous AML, the CD34(+) ALDH(+) subset consisted mainly of LSC and separation from HSC was not feasible. Functional analyses further showed that ALDH(+) cells from ALDH-numerous AML were quiescent, refractory to ARA-C treatment and capable of leukemic engraftment in a xenogenic mouse transplantation model. Clinically, resistance to chemotherapy and poor long-term outcome were also characteristic for patients with ALDH-numerous AML providing an additional risk-stratification tool. The difference in spectrum and relevance of ALDH activity in the putative LSC populations demonstrates, in addition to phenotypic and genetic, also functional heterogeneity of leukemic cells and suggests divergent roles for ALDH activity in normal HSC versus LSC. By acknowledging these differences our study provides a new and useful tool for prospective identification of AML cases in which separation of HSC from LSC is possible.

Current cell therapies for systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease in which multiple organs are damaged by the immune system. Although standard treatment options such as hydroxychloroquine (HCQ), glucocorticoids (GCs), and other immunosuppressive or immune-modulating agents can help to manage symptoms, they do not offer a cure. Hence, there is an urgent need for the development of novel drugs and therapies. In recent decades, cell therapies have been used for the treatment of SLE with encouraging results. Hematopoietic stem cell transplantation, mesenchymal stem cells, regulatory T (Treg) cell, natural killer cells, and chimeric antigen receptor T (CAR T) cells are advanced cell therapies which have been developed and evaluated in clinical trials in humans. In clinical application, each of these approaches has shown advantages and disadvantages. In addition, further studies are necessary to conclusively establish the safety and efficacy of these therapies. This review provides a summary of recent clinical trials investigating cell therapies for SLE treatment, along with a discussion on the potential of other cell-based therapies. The factors influencing the selection of common cell therapies for individual patients are also highlighted.

Perforated appendicitis due to fishbone.

Appendicitis is a common condition in daily clinical practice. Appendicitis due to foreign bodies is uncommon and may result from obstruction or perforation mechanism. We present a rare case of a 43-year-old male patient who was diagnosed with perforated appendicitis due to a fish bone by imaging studies and confirmed postoperatively. Confirming the fish bone causing the perforation on images is sometimes difficult, requiring the radiologist to actively search and determine the source. In addition to appendectomy, the surgeon also needs to pay attention to removing all foreign objects and treating perforations of surrounding organs.

Impact of tissue factor expression and administration routes on thrombosis development induced by mesenchymal stem/stromal cell infusions: re-evaluating the dogma.

BACKGROUND: Hyperactive coagulation might cause dangerous complications such as portal vein thrombosis and pulmonary embolism after mesenchymal stem/stromal cell (MSC) therapy. Tissue factor (TF), an initiator of the extrinsic coagulation pathway, has been suggested as a predictor of this process. METHODS: The expression of TF and other pro- and anticoagulant genes was analyzed in xeno- and serum-free manufactured MSCs. Furthermore, culture factors affecting its expression in MSCs were investigated. Finally, coagulation tests of fibrinogen, D-dimer, aPPTs, PTs, and TTs were measured in patient serum after umbilical cord (UC)-MSC infusions to challenge a potential connection between TF expression and MSC-induced coagulant activity.  RESULTS: Xeno- and serum-free cultured adipose tissue and UC-derived MSCs expressed the highest level of TF, followed by those from dental pulp, and the lowest expression was observed in MSCs of bone marrow origin. Environmental factors such as cell density, hypoxia, and inflammation impact TF expression, so in vitro analysis might fail to reflect their in vivo behaviors. MSCs also expressed heterogeneous levels of the coagulant factor COL1A1 and surface phosphatidylserine and anticoagulant factors TFPI and PTGIR. MSCs of diverse origins induced fibrin clots in healthy plasma that were partially suppressed by an anti-TF inhibitory monoclonal antibody. Furthermore, human umbilical vein endothelial cells exhibited coagulant activity in vitro despite their negative expression of TF and COL1A1. Patients receiving intravenous UC-MSC infusion exhibited a transient increase in D-dimer serum concentration, while this remained stable in the group with intrathecal infusion. There was no correlation between TF expression and D-dimer or other coagulation indicators. CONCLUSIONS: The study suggests that TF cannot be used as a solid biomarker to predict MSC-induced hypercoagulation. Local administration, prophylactic intervention with anticoagulation drugs, and monitoring of coagulation indicators are useful to prevent thrombogenic events in patients receiving MSCs. Trial registration NCT05292625. Registered March 23, 2022, retrospectively registered, https://www. CLINICALTRIALS: gov/ct2/show/NCT05292625?term=NCT05292625&draw=2&rank=1 . NCT04919135. Registered June 9, 2021, https://www. CLINICALTRIALS: gov/ct2/show/NCT04919135?term=NCT04919135&draw=2&rank=1 .

Obesity and leptin in breast cancer angiogenesis.

At the time of breast cancer diagnosis, most patients meet the diagnostic criteria to be classified as obese or overweight. This can significantly impact patient outcome: breast cancer patients with obesity (body mass index > 30) have a poorer prognosis compared to patients with a lean BMI. Obesity is associated with hyperleptinemia, and leptin is a well-established driver of metastasis in breast cancer. However, the effect of hyperleptinemia on angiogenesis in breast cancer is less well-known. Angiogenesis is an important process in breast cancer because it is essential for tumor growth beyond 1mm3 in size as well as cancer cell circulation and metastasis. This review investigates the role of leptin in regulating angiogenesis, specifically within the context of breast cancer and the associated tumor microenvironment in obese patients.

Obesity-associated epigenetic alterations and the obesity-breast cancer axis.

Both breast cancer and obesity can regulate epigenetic changes or be regulated by epigenetic changes. Due to the well-established link between obesity and an increased risk of developing breast cancer, understanding how obesity-mediated epigenetic changes affect breast cancer pathogenesis is critical. Researchers have described how obesity and breast cancer modulate the epigenome individually and synergistically. In this review, the epigenetic alterations that occur in obesity, including DNA methylation, histone, and chromatin modification, accelerated epigenetic age, carcinogenesis, metastasis, and tumor microenvironment modulation, are discussed. Delineating the relationship between obesity and epigenetic regulation is vital to furthering our understanding of breast cancer pathogenesis.