Quercetin attenuates metastatic ability of human metastatic ovarian cancer cells via modulating multiple signaling molecules involved in cell survival, proliferation, migration and adhesion

A Narrative Review of Quercetin's Role as a Bioactive Compound in Female Reproductive Disorders

Lifestyle, nutrition, and metabolic status are central to maintaining women's reproductive health. With the rising prevalence of infertility, the need for effective strategies to preserve and enhance women's reproductive well-being has become increasingly urgent. Quercetin, a plant-derived polyphenol, has attracted growing interest for its potential to support reproductive health, regulate the hormonal balance, and improve fertility. This narrative review examines Quercetin's role in women's reproductive health and delineates its possible mechanisms of action in female reproductive system disorders, including polycystic ovary syndrome, recurrent miscarriage, and cervical, ovarian, and endometrial cancer (EC). By highlighting the biological pathways through which quercetin may exert its effects, this article underscores the need for further research and clinical trials to validate its therapeutic potential and its applications as a bioactive compound in foods aimed at enhancing women's reproductive health.

Interleukin-6 Modulation in Ovarian Cancer Necessitates a Targeted Strategy: From the Approved to Emerging Therapies

Despite significant advances in treatments, ovarian cancer (OC) remains one of the most prevalent and lethal gynecological cancers in women. The frequent detection at the advanced stages has contributed to low survival rates, resistance to various treatments, and disease recurrence. Thus, a more effective approach is warranted to combat OC. The cytokine Interleukin-6 (IL6) has been implicated in various stages of OC development. High IL6 levels are also correlated with a lower survival rate in OC patients. In this current review, we summarized the pivotal roles of IL6 in OC, including the initiation, development, invasion, metastasis, and drug resistance mechanisms. This article systematically highlights how targeting IL6 improves OC outcomes by altering various cancer processes and reports the ongoing clinical trials that would further shape the IL6-based targeted therapies. This review also suggests how combining IL6-targeted therapies with other therapeutic strategies could further enhance their efficacy to combat OC.

Quercetin regulates pulmonary vascular remodeling in pulmonary hypertension by downregulating TGF-β1-Smad2/3 pathway

BACKGROUND

Pulmonary arterial hypertension (PAH) is a worldwide challenging disease characterized by progressive elevation of pulmonary artery pressure. The proliferation, migration and phenotypic transformation of pulmonary smooth muscle cells are the key steps of pulmonary vascular remodeling. Quercetin (3,3', 4', 5, 6-pentahydroxyflavone, Que) is a natural flavonol compound that has antioxidant, anti-inflammatory, anti-tumor and other biological activities. Studies have shown that Que has therapeutic effects on PAH. However, the effect of quercetin on pulmonary vascular remodeling in PAH and its mechanism remain unclear.

METHODS AND RESULTS

In vivo, PAH rats were constructed by intraperitoneal injection of monocrotaline (MCT) at 60 mg/kg. Human pulmonary artery smooth muscle cells (HPASMCs) were treated with platelet-derived growth factor BB (PDGF-BB) 20 ng/mL to construct PAH cell model in vitro. The results showed that in vivo studies, MCT could induce right ventricular wall hyperplasia, narrow the small and medium pulmonary artery cavity, up-regulate the expression of proliferating and migration-related proteins proliferating cell nuclear antigen (PCNA) and osteopontin (OPN), and down-regulate the expression of alpha-smooth muscle actin (α-SMA). Que reversed the MCT-induced results. This process works by down-regulating the transforming growth factor-β1 (TGF-β1)/ Smad2/3 signaling pathway. In vitro studies, Que had the same effect on PDGF-BB-induced proliferation and migration cell models.

CONCLUSIONS

Que inhibits the proliferation, migration and phenotypic transformation of HPASMCs by down-regulating TGF-β1/Smad2/Smad3 pathway, thereby reducing right ventricular hyperplasia (RVH) and pulmonary vascular remodeling, providing potential pharmacological and molecular explanations for the treatment of PAH.

Cancer Prevention and Treatment with Polyphenols: Type IV Collagenase-Mediated Mechanisms

Polyphenols are natural compounds found in many plants and their products. Their high structural diversity bestows upon them a range of anti-inflammatory, anti-oxidant, proapoptotic, anti-angiogenic, and anti-metastatic properties, and a growing body of research indicates that a polyphenol-rich diet can inhibit cancer development in humans. Polyphenolic compounds may modulate the expression, secretion, or activity of compounds that play a significant role in carcinogenesis, including type IV collagenases, such as matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9), by suppressing cellular signaling pathways such as nuclear factor-kappa B. These enzymes are responsible for the degradation of the extracellular matrix, thus promoting the progression of cancer. This review discusses the current state of knowledge concerning the anti-cancer activity of polyphenols, particularly curcumin, resveratrol, epigallocatechin-3-gallate, genistein, and quercetin, with a specific focus on their anti-invasive and anti-metastatic potential, based on the most recent in vitro and in vivo studies. It appears that polyphenols may be valuable options for the chemoprevention and treatment of cancer via the inhibition of MMP-2 and MMP-9 and the suppression of signaling pathways regulating their expression and activity.

Exploring the therapeutic potential of quercetin in cancer treatment: Targeting long non-coding RNAs

The escalating global incidence of cancer, which results in millions of fatalities annually, underscores the pressing need for effective pharmacological interventions across diverse cancer types. Long noncoding RNAs (lncRNAs), a class of RNA molecules that lack protein-coding capacity but profoundly impact gene expression regulation, have emerged as pivotal players in key cellular processes, including proliferation, apoptosis, metastasis, cellular metabolism, and drug resistance. Among natural compounds, quercetin, a phenolic compound abundantly present in fruits and vegetables has garnered attention due to its significant anticancer properties. Quercetin demonstrates the ability to inhibit cancer cell growth and induce apoptosis-a process often impaired in malignant cells. In this comprehensive review, we delve into the therapeutic potential of quercetin in cancer treatment, with a specific focus on its intricate interactions with lncRNAs. We explore how quercetin modulates lncRNA expression and function to exert its anticancer effects. Notably, quercetin suppresses oncogenic lncRNAs that drive cancer development and progression while enhancing tumor-suppressive lncRNAs that impede cancer growth and dissemination. Additionally, we discuss quercetin's role as a chemopreventive agent, which plays a crucial role in mitigating cancer risk. We address research challenges and future directions, emphasizing the necessity for in-depth mechanistic studies and strategies to enhance quercetin's bioavailability and target specificity. By synthesizing existing knowledge, this review underscores quercetin's promising potential as a novel therapeutic strategy in the ongoing battle against cancer, offering fresh insights and avenues for further investigation in this critical field.

Co-delivery of Paclitaxel/Atovaquone/Quercetin to regulate energy metabolism to reverse multidrug resistance in ovarian cancer by PLGA-PEG nanoparticles

Ovarian cancer is a malignant tumor that seriously endangers the lives of women, with chemotherapy being the primary clinical treatment. However, chemotherapy encounters the problem of generating multidrug resistance (MDR), mainly due to drug efflux induced by P-glycoprotein (P-gp), which decreases intracellular accumulation of chemotherapeutic drugs. The drugs efflux mediated by P-gp requires adenosine triphosphate (ATP) hydrolysis to provide energy. Therefore, modulating energy metabolism pathways and inhibiting ATP production may be a potential strategy to reverse MDR. Herein, we developed a PTX-ATO-QUE nanoparticle (PAQNPs) based on a PLGA-PEG nanoplatform capable of loading the mitochondrial oxidative phosphorylation (OXPHOS) inhibitor atovaquone (ATO), the glycolysis inhibitor quercetin (QUE), and the chemotherapeutic drug paclitaxel (PTX) to reverse MDR by inhibiting energy metabolism through multiple pathways. Mechanistically, PAQNPs could effectively inhibit the OXPHOS and glycolytic pathways of A2780/Taxol cells by suppressing the activities of mitochondrial complex III and hexokinase II (HK II), respectively, ultimately decreasing intracellular ATP levels in tumor cells. Energy depletion can effectively inhibit cell proliferation and reduce P-gp activity, increasing the chemotherapeutic drug PTX accumulation in the cells. Moreover, intracellular reactive oxygen species (ROS) is increased with PTX accumulation and leads to chemotherapy-resistant cell apoptosis. Furthermore, PAQNPs significantly inhibited tumor growth in the A2780/Taxol tumor-bearing NCG mice model. Immunohistochemical (IHC) analysis of tumor tissues revealed that P-gp expression was suppressed, demonstrating that PAQNPs are effective in reversing MDR in tumors by inducing energy depletion. In addition, the safety study results, including blood biochemical indices, major organ weights, and H&E staining images, showed that PAQNPs have a favorable in vivo safety profile. In summary, the results suggest that the combined inhibition of the two energy pathways, OXPHOS and glycolysis, can enhance chemotherapy efficacy and reverse MDR in ovarian cancer.

Therapeutic effects and molecular mechanisms of quercetin in gynecological disorders

Quercetin is a representative flavonoid that is widely present in fruits, herbs, and vegetables. It is also an important active core component in traditional Chinese medicines. As an important flavonoid, quercetin has various properties and exerts antioxidant, anti-inflammatory, and cardioprotective effects. The public interest in quercetin is increasing, and quercetin has been used to prevent or treat numerous of diseases, such as polycystic ovary syndrome (PCOS), cancer, autoimmune diseases and chronic cardiovascular diseases, in clinical experiments and animal studies due to its powerful antioxidant properties and minimal side effects. Quercetin exerts marked pharmacological effects on gynecological disorders; however, there have been no reviews about the potential health benefits of quercetin in the context of gynecological disorders, including PCOS, premature ovary failure (POF), endometriosis (EM), ovarian cancer (OC), cervical cancer (CC) and endometrial carcinoma (EC). Thus, this review aimed to summarize the biological effects of quercetin on gynecological disorders and its mechanisms.

Nanoformulations of quercetin for controlled delivery: a review of preclinical anticancer studies

One of the well-studied older molecules, quercetin, is found in large quantities in many fruits and vegetables. Natural anti-oxidant quercetin has demonstrated numerous pharmacological properties in preclinical and clinical research, including anti-inflammatory and anti-cancer effects. Due to its ability to control cell signaling pathways, including NF-κB, p53, activated protein-1 (AP-1), STAT3, and epidermal growth response-1 (Egr-1), which is essential in the initiation and proliferation of cancer, it has gained a lot of fame as an anticancer molecule. Recent research suggests that using nanoformulations can help quercetin to overcome its hydrophobicity while also enhancing its stability and cellular bioavailability both in vitro and in vivo. The main aim of this review is to focus on the comprehensive insights of several nanoformulations, including liposomes, nano gels, micelles, solid lipid nanoparticles (SLN), polymer nanoparticles, gold nanoparticles, and cyclodextrin complexes, to transport quercetin for application in cancer.

Quercetin suppresses retinoblastoma cell proliferation and invasion and facilitates oxidative stress-induced apoptosis through the miR-137/FNDC5 axis

Retinoblastoma (RB) constitutes a prevalent malignancy in clinic and usually occurs in children under the age of 5 years old. The increased frequency of malignant tumor metastases and the delayed diagnosis and treatment caused unsatisfactory therapeutic efficiency. Quercetin was formerly identified to impede tumor growth in certain malignancies. Our study attempted to investigate the effects and mechanisms of quercetin in Rb development, in order to provide an effective clinical therapeutic approach. Rb cell lines (WER1-RB1 and Y79) were incubated with different concentrations of quercetin, and then cell proliferation, invasion, apoptosis, and oxidative stress were determined. It was showed that quercetin restrained Rb cell proliferation and invasion, and induced cell apoptosis and oxidative stress in a dose dependent manner. Moreover, we found that quercetin incubation upregulated miR-137 expression in Rb cells. MiR-137 inhibition abrogated quercetin-mediated inhibition of Rb cell progression. Furthermore, dual-luciferase reporter gene assay validated that fibronectin type III domain-containing protein 5 (FNDC5) was a target for miR-137. MiR-137 overexpression restrained proliferation and invasion, and enhanced apoptosis and oxidative stress in Rb cells, whereas FNDC5 overexpression abrogated these effects. Additionally, nude mice were injected with WER1-RB1 cells to establish a xenograft tumor model, and then treated with 50 or 100 mg/kg quercetin. Quercetin treatment mitigated xenograft tumor growth in nude mice. In conclusion, quercetin restrained proliferation and invasion, and induced apoptosis and oxidative stress in Rb cells through regulating the miR-137/FNDC5 pathway. We expected that our study could provide an effective approach for Rb treatment. However, quercetin and miR-137 may have off-target effects in Rb cells, and our study still has certain limitations. Therefore, we will investigate the effects of quercetin on other signaling pathways in Rb cells and explore the application of combination therapy in follow-up experiments, in order to provide a rigorous research basis for the treatment of Rb with quercetin.

Quercetin action on health and female reproduction in mammals

This paper reviews the current information concerning availability, metabolism of quercetin, its effects on physiological processes and illnesses with focus on the effects, mechanisms of action and areas of possible application of quercetin in control of female reproductive processes, prevention and treatment of their disorders in mammals.The available information demonstrated the ability of quercetin and its analogues to inhibit proliferation and to promote apoptosis, to activate regenerative processes, to treat immune, inflammatory, cardiovascular, neurodegenerative, gastric and metabolic disorders and cancer, to suppress microorganisms, to protect bones and liver, to relieve pain, to improve physical and mental performance, and to prolong life span.The positive influences of quercetin on mammalian female reproductive processes are well documented. It can promote ovarian follicullo- and oogenesis, improve quality of oocytes and embryos, increase fecundity in various species. These effects can be mediated by changes in pituitary and ovarian hormones, growth factors and cytokines, in their receptors and post-receptory signaling pathways. Due to these effect, quercetin can be applicable as biostimulator of reproduction, for prevention, mitigation and treatment of several female reproductive disorders, as well as to increase resistance of female reproductive system to adverse effect of chemotherapy, temperature stress and environmental contaminants.

Selected Flavonols in Breast and Gynecological Cancer: A Systematic Review

The consumption of foods that are rich in phenolic compounds has chemopreventive effects on many cancers, including breast cancer, ovarian cancer, and endometrial cancer. A wide spectrum of their health-promoting properties such as antioxidant, anti-inflammatory, and anticancer activities, has been demonstrated. This paper analyzes the mechanisms of the anticancer action of selected common flavonols, including kemferol, myricetin, quercetin, fisetin, galangin, isorhamnetin, and morin, in preclinical studies, with particular emphasis on in vitro studies in gynecological cancers and breast cancer. In the future, these compounds may find applications in the prevention and treatment of gynecological cancers and breast cancer, but this requires further, more advanced research.

miR-152-3p facilitates cell adhesion and hepatic metastases in colorectal cancer via targeting AQP11

BACKGROUND

Tumor metastasis is a fundamental reason for the poor prognosis of colorectal cancer (CRC) patients. Publications suggested that upregulated Aquaporin-11 (AQP11) can improve CRC patients' prognoses, but few articles investigated the regulation of AQP11 in CRC cell adhesion and hepatic metastases. Therefore, this study will explore the regulatory mechanism of AQP11 regulating CRC cell adhesion and hepatic metastases at the molecular level.

METHODS

AQP11 and miR-152-3p expression were analyzed based on The Cancer Genome Atlas-Colon Adenocarcinoma/Rectum Adenocarcinoma (TCGA-COAD/READ) dataset and several other datasets. The upstream genes of AQP11 were predicted via StarBase and MicroRNA Data Integration Portal (mirDIP) databases. The signaling pathways in which the downregulated AQP11 enriched were analyzed via Gene Set Enrichment Analysis (GSEA). Cell proliferation, migration, invasion, and adhesion were respectively tested via western blot, Transwell, and cell adhesion assays. The expression of adhesion-related proteins was determined via enzyme-linked immunosorbent assay (ELISA). AQP11 protein level was examined via western blot, and AQP11 functions were validated via nude mice xenograft experiment.

RESULTS

AQP11 was downregulated in CRC, and the upregulated AQP11 remarkably repressed cell proliferation, migration, invasion, and adhesion. The silenced AQP11 notably facilitated the above cell functions in CRC. In addition, AQP11 was negatively regulated by miR-152-3p. In vitro cellular assays revealed that miR-152-3p, by targeting AQP11, facilitated CRC cell proliferation, migration, invasion, and adhesion. An in vivo assay suggested that AQP11 could notably repress CRC growth and metastasis.

CONCLUSION

The above results confirmed that miR-152-3p/AQP11 axis could regulate CRC hepatic metastases and would be a promising target in anti-cancer treatment.

The Role of Natural and Semi-Synthetic Compounds in Ovarian Cancer: Updates on Mechanisms of Action, Current Trends and Perspectives

Ovarian cancer represents a major health concern for the female population: there is no obvious cause, it is frequently misdiagnosed, and it is characterized by a poor prognosis. Additionally, patients are inclined to recurrences because of metastasis and poor treatment tolerance. Combining innovative therapeutic techniques with established approaches can aid in improving treatment outcomes. Because of their multi-target actions, long application history, and widespread availability, natural compounds have particular advantages in this connection. Thus, effective therapeutic alternatives with improved patient tolerance hopefully can be identified within the world of natural and nature-derived products. Moreover, natural compounds are generally perceived to have more limited adverse effects on healthy cells or tissues, suggesting their potential role as valid treatment alternatives. In general, the anticancer mechanisms of such molecules are connected to the reduction of cell proliferation and metastasis, autophagy stimulation and improved response to chemotherapeutics. This review aims at discussing the mechanistic insights and possible targets of natural compounds against ovarian cancer, from the perspective of medicinal chemists. In addition, an overview of the pharmacology of natural products studied to date for their potential application towards ovarian cancer models is presented. The chemical aspects as well as available bioactivity data are discussed and commented on, with particular attention to the underlying molecular mechanism(s).

Quercetin induces autophagy-associated death in HL-60 cells through CaMKKβ/AMPK/mTOR signal pathway

Acute myeloid leukemia (AML) is one of the most common malignancies of the hematopoietic progenitor cell in adults. Quercetin has gained recognition over the years because of its anti-cancer effect with minimal toxicity. Herein, we aim to investigate the anti-leukemia mechanism of quercetin and to decipher the signaling pathway of quercetin in HL-60 leukemic cells. We observed that quercetin induces apoptosis and autophagic cell death, in which both pathways play an important role in suppressing the viability of leukemia cells. Phosphorylated AMPK (p-AMPK) protein expressions are lower in primary AML cells, HL-60 cells, KG-1 and THP-1 cells than in peripheral blood monocular cells. After quercetin treatment, the expression of p-AMPK is increased while the expression of p-mTOR is decreased in a dose-dependent manner. Mechanistically, compound C, an AMPK phosphorylation inhibitor, upregulates the phosphorylation of mTOR and inhibits autophagy and apoptosis in quercetin-induced HL-60 cells, while silencing of CaMKKβ inhibits the quercetin-induced phosphorylation of AMPK, resulting in increased mTOR phosphorylation. Furthermore, silencing of CaMKKβ inhibits the autophagy in HL-60 cells. Taken together, our data delineate that quercetin plays its anti-leukemia role by inhibiting cell viability and inducing apoptosis and autophagy in leukemia cells. Quercetin inhibits the phosphorylation of mTOR by regulating the activity of AMPK, thus playing a role in the regulation of autophagy and apoptosis. CaMKKβ is a potential upstream molecule for AMPK/mTOR signaling pathway, through which quercetin induces autophagy in HL-60 cells.

Molecular and Cellular Mechanisms of Propolis and Its Polyphenolic Compounds against Cancer

In recent years, interest in natural products such as alternative sources of pharmaceuticals for numerous chronic diseases, including tumors, has been renewed. Propolis, a natural product collected by honeybees, and polyphenolic/flavonoid propolis-related components modulate all steps of the cancer progression process. Anticancer activity of propolis and its compounds relies on various mechanisms: cell-cycle arrest and attenuation of cancer cells proliferation, reduction in the number of cancer stem cells, induction of apoptosis, modulation of oncogene signaling pathways, inhibition of matrix metalloproteinases, prevention of metastasis, anti-angiogenesis, anti-inflammatory effects accompanied by the modulation of the tumor microenvironment (by modifying macrophage activation and polarization), epigenetic regulation, antiviral and bactericidal activities, modulation of gut microbiota, and attenuation of chemotherapy-induced deleterious side effects. Ingredients from propolis also "sensitize" cancer cells to chemotherapeutic agents, likely by blocking the activation of the transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). In this review, we summarize the current knowledge related to the the effects of flavonoids and other polyphenolic compounds from propolis on tumor growth and metastasizing ability, and discuss possible molecular and cellular mechanisms involved in the modulation of inflammatory pathways and cellular processes that affect survival, proliferation, invasion, angiogenesis, and metastasis of the tumor.

A Comparative Study of Quercetin-Loaded Nanocochleates and Liposomes: Formulation, Characterization, Assessment of Degradation and In Vitro Anticancer Potential

Quercetin, a flavonoid, has antioxidant and anti-inflammatory properties and the potential to inhibit the proliferation of cancer, but its therapeutic efficacy is lowered due to poor solubility and bioavailability. Quercetin-loaded nanocochleates (QN) were developed using a trapping method by the addition of calcium ions into preformed negatively charged liposomes (QL) prepared by a thin-film hydration method. Liposomes were optimized by varying the concentration of Dimyristoyl phosphatidyl glycerol and quercetin by applying D-optimal factorial design using Design-Expert^® software. Stable rods were observed using TEM with an average particle size, zeta potential and encapsulation efficiency of 502 nm, −18.52 mV and 88.62%, respectively, for QN which were developed from spherical QL showing 111.06 nm, −40.33 mV and 74.2%, respectively. In vitro release of quercetin from QN and QL was extended to 24 h. Poor bioavailability of quercetin is due to its degradation in the liver, so to mimic in vivo conditions, the degradation of quercetin released from QL and QN was studied in the presence of rat liver homogenate (S9G) and results revealed that QN, due to its unique structure, i.e., series of rolled up solid layers, shielded quercetin from the external environment and protected it. The safety and biocompatibility of QL and QN were provenby performing cytotoxicity studies on fibroblast L929 cell lines. QN showed superior anticancer activity compared to QL, as seen for human mouth cancerKB cell lines. Stability studies proved that nanocochleates were more stable than liposomal formulations. Thus, nanocochleates might serve as pharmaceutical nanocarriers for the improved efficacy of drugs with low aqueous solubility, poor bioavailability, poor targeting ability and stability.

Plants as a Source of Anticancer Agents: From Bench to Bedside

Cancer is the second leading cause of death after cardiovascular diseases. Conventional anticancer therapies are associated with lack of selectivity and serious side effects. Cancer hallmarks are biological capabilities acquired by cancer cells during neoplastic transformation. Targeting multiple cancer hallmarks is a promising strategy to treat cancer. The diversity in chemical structure and the relatively low toxicity make plant-derived natural products a promising source for the development of new and more effective anticancer therapies that have the capacity to target multiple hallmarks in cancer. In this review, we discussed the anticancer activities of ten natural products extracted from plants. The majority of these products inhibit cancer by targeting multiple cancer hallmarks, and many of these chemicals have reached clinical applications. Studies discussed in this review provide a solid ground for researchers and physicians to design more effective combination anticancer therapies using plant-derived natural products.

Molecular and cellular outcomes of quercetin actions on healthy and tumor osteoblasts

There is a global trend in the use of natural bioactive compounds to complement conventional therapies in bone diseases. In this work, we studied the effects of the phytoestrogen quercetin (QUE) in healthy and tumor osteoblasts. We found that QUE (1 μM, 48 h) significantly increased the cell number and the viability of healthy human osteoblasts (hFOB cells) determined by a trypan blue and a MTS assay, respectively, among other concentrations tested. In addition, wound healing and cellular adhesion assays also demonstrated that 1 μM of QUE significantly stimulated both parameters in osteoblasts. Moreover, osteoblast differentiation was also triggered by QUE in an osteogenic medium by measuring alkaline phosphatase activity, calcium deposition, and collagen levels. Herein, a concentration of 0.01 μM of QUE showed an increment in these differentiation markers and an activation of AKT/GSK3β/β-catenin pathway, determined by a Western blot analysis. In addition, immunocytochemistry and subcellular fraction studies indicated an increase of β-catenin localization in the plasma membrane after QUE treatment. Otherwise, QUE (20-100 μM) decreased the cell number and the viability in tumor osteoblasts (ROS 17/2.8 cells) after 48 h. Furthermore, QUE (100 μM) decreased AKT(Ser473) and the pro-apoptotic protein BAD(Ser136) phosphorylation. In addition, the ERK1/2 phosphorylation increased leading to osteosarcoma cell death since pre-treatment with the MEK inhibitor PD98059 had reverted QUE effect. Altogether, these results indicate that to stimulate the osteoblastogenesis low concentrations of QUE are required; however, these concentrations are not effective in inhibiting the growth of tumor osteoblasts, for which higher concentrations are required.

Quercetin nanoformulations: a promising strategy for tumor therapy

Phytochemicals as dietary constituents are being widely explored for the prevention and treatment of various diseases. Quercetin, a major constituent of various dietary products, has attracted extensive interest due to its anti-proliferative capability, reversal of multidrug resistance, autophagy promotion and tumor microenvironment modulation on different cancer types. Although quercetin has shown potent medical value, its application as an antitumor drug is limited. Problems like poor solubility, bioavailability and stability, short half-life and weak tumor-targeting biodistribution make quercetin an unreliable candidate for cancer therapy. Nanoparticle based platforms have shown a number of advantages in delivering a hydrophobic drug like quercetin to diseased tissues. Quercetin nanoparticles have demonstrated high encapsulation efficiency, stability, sustained release, prolonged circulation time, improved accumulation at tumor sites and therapeutic efficiency. Moreover, a combination of quercetin with other diagnostic or therapeutic agents in one nanocarrier has achieved enhancements in detecting or treating tumors. In this review, we have tried to summarize the pharmacological activities of quercetin with regard to tumor cells and microenvironments in vitro and in vivo. Furthermore, various nanoformulations have been highlighted for quercetin delivery for cancer treatment. These results suggest that quercetin nanoparticles may be a promising antitumor therapeutic agent.