Silibinin meglumine, a water-soluble form of milk thistle silymarin, is an orally active anti-cancer agent that impedes the epithelial-to-mesenchymal transition (EMT) in EGFR-mutant non-small-cell lung carcinoma cells

Silibinin is a suppressor of the metastasis-promoting transcription factor ID3

BACKGROUND

ID3 (inhibitor of DNA binding/differentiation-3) is a transcription factor that enables metastasis by promoting stem cell-like properties in endothelial and tumor cells. The milk thistle flavonolignan silibinin is a phytochemical with anti-metastatic potential through largely unknown mechanisms.

HYPOTHESIS/PURPOSE

We have mechanistically investigated the ability of silibinin to inhibit the aberrant activation of ID3 in brain endothelium and non-small cell lung cancer (NSCLC) models.

METHODS

Bioinformatic analyses were performed to investigate the co-expression correlation between ID3 and bone morphogenic protein (BMP) ligands/BMP receptors (BMPRs) genes in NSCLC patient datasets. ID3 expression was assessed by immunoblotting and qRT-PCR. Luciferase reporter assays were used to evaluate the gene sequences targeted by silibinin to regulate ID3 transcription. In silico computational modeling and LanthaScreen TR-FRET kinase assays were used to characterize and validate the BMPR inhibitory activity of silibinin. Tumor tissues from NSCLC xenograft models treated with oral silibinin were used to evaluate the in vivo anti-ID3 effects of silibinin.

RESULTS

Analysis of lung cancer patient datasets revealed a top-ranked positive association of ID3 with the BMP9 endothelial receptor ACVRL1/ALK1 and the BMP ligand BMP6. Silibinin treatment blocked the BMP9-induced activation of the ALK1-phospho-SMAD1/5-ID3 axis in brain endothelial cells. Constitutive, acquired, and adaptive expression of ID3 in NSCLC cells were all significantly downregulated in response to silibinin. Silibinin blocked ID3 transcription via BMP-responsive elements in ID3 gene enhancers. Silibinin inhibited the kinase activities of BMPRs in the micromolar range, with the lower IC50 values occurring against ACVRL1/ALK1 and BMPR2. In an in vivo NSCLC xenograft model, tumoral overexpression of ID3 was completely suppressed by systematically achievable oral doses of silibinin.

CONCLUSIONS

ID3 is a largely undruggable metastasis-promoting transcription factor. Silibinin is a novel suppressor of ID3 that may be explored as a novel therapeutic approach to interfere with the metastatic dissemination capacity of NSCLC.

The importance of integrated therapies on cancer: Silibinin, an old and new molecule

In the landscape of cancer treatments, the efficacy of coadjuvant molecules remains a focus of attention for clinical research with the aim of reducing toxicity and achieving better outcomes. Most of the pathogenetic processes causing tumour development, neoplastic progression, ageing, and increased toxicity involve inflammation. Inflammatory mechanisms can progress through a variety of molecular patterns. As is well known, the ageing process is determined by pathological pathways very similar and often parallel to those that cause cancer development. Among these complex mechanisms, inflammation is currently much studied and is often referred to in the geriatric field as 'inflammaging'. In this context, treatments active in the management of inflammatory mechanisms could play a role as adjuvants to standard therapies. Among these emerging molecules, Silibinin has demonstrated its anti-inflammatory properties in different neoplastic types, also in combination with chemotherapeutic agents. Moreover, this molecule could represent a breakthrough in the management of age-related processes. Thus, Silibinin could be a valuable adjuvant to reduce drug-related toxicity and increase therapeutic potential. For this reason, the main aim of this review is to collect and analyse data presented in the literature on the use of Silibinin, to better understand the mechanisms of the functioning of this molecule and its possible therapeutic role.

An Update on Potential Molecular Biomarkers of Dietary Phytochemicals Targeting Lung Cancer Interception and Prevention

Since ancient times, dietary phytochemicals are known for their medicinal properties. They are broadly classified into polyphenols, terpenoids, alkaloids, phytosterols, and organosulfur compounds. Currently, there is considerable interest in their potential health effects against various diseases, including lung cancer. Lung cancer is the leading cause of cancer deaths with an average of five-year survival rate of lung cancer patients limited to just 14%. Identifying potential early molecular biomarkers of pre-malignant lung cancer cells may provide a strong basis to develop early cancer detection and interception methods. In this review, we will discuss molecular changes, including genetic alterations, inflammation, signal transduction pathways, redox imbalance, epigenetic and proteomic signatures associated with initiation and progression of lung carcinoma. We will also highlight molecular targets of phytochemicals during lung cancer development. These targets mainly consist of cellular signaling pathways, epigenetic regulators and metabolic reprogramming. With growing interest in natural products research, translation of these compounds into new cancer prevention approaches to medical care will be urgently needed. In this context, we will also discuss the overall pharmacokinetic challenges of phytochemicals in translating to humans. Lastly, we will discuss clinical trials of phytochemicals in lung cancer patients.

Polyphenols as Potential Protectors against Radiation-Induced Adverse Effects in Patients with Thoracic Cancer

Radiotherapy is one of the standard treatment approaches used against thoracic cancers, occasionally combined with chemotherapy, immunotherapy and molecular targeted therapy. However, these cancers are often not highly sensitive to standard of care treatments, making the use of high dose radiotherapy necessary, which is linked with high rates of radiation-induced adverse effects in healthy tissues of the thorax. These tissues remain therefore dose-limiting factors in radiation oncology despite recent technological advances in treatment planning and delivery of irradiation. Polyphenols are metabolites found in plants that have been suggested to improve the therapeutic window by sensitizing the tumor to radiotherapy, while simultaneously protecting normal cells from therapy-induced damage by preventing DNA damage, as well as having anti-oxidant, anti-inflammatory or immunomodulatory properties. This review focuses on the radioprotective effect of polyphenols and the molecular mechanisms underlying these effects in the normal tissue, especially in the lung, heart and esophagus.

Silibinin Overcomes EMT-Driven Lung Cancer Resistance to New-Generation ALK Inhibitors

Epithelial-to-mesenchymal transition (EMT) may drive the escape of ALK-rearranged non-small-cell lung cancer (NSCLC) tumors from ALK-tyrosine kinase inhibitors (TKIs). We investigated whether first-generation ALK-TKI therapy-induced EMT promotes cross-resistance to new-generation ALK-TKIs and whether this could be circumvented by the flavonolignan silibinin, an EMT inhibitor. ALK-rearranged NSCLC cells acquiring a bona fide EMT phenotype upon chronic exposure to the first-generation ALK-TKI crizotinib exhibited increased resistance to second-generation brigatinib and were fully refractory to third-generation lorlatinib. Such cross-resistance to new-generation ALK-TKIs, which was partially recapitulated upon chronic TGFβ stimulation, was less pronounced in ALK-rearranged NSCLC cells solely acquiring a partial/hybrid E/M transition state. Silibinin overcame EMT-induced resistance to brigatinib and lorlatinib and restored their efficacy involving the transforming growth factor-beta (TGFβ)/SMAD signaling pathway. Silibinin deactivated TGFβ-regulated SMAD2/3 phosphorylation and suppressed the transcriptional activation of genes under the control of SMAD binding elements. Computational modeling studies and kinase binding assays predicted a targeted inhibitory binding of silibinin to the ATP-binding pocket of TGFβ type-1 receptor 1 (TGFBR1) and TGFBR2 but solely at the two-digit micromolar range. A secretome profiling confirmed the ability of silibinin to normalize the augmented release of TGFβ into the extracellular fluid of ALK-TKIs-resistant NSCLC cells and reduce constitutive and inducible SMAD2/3 phosphorylation occurring in the presence of ALK-TKIs. In summary, the ab initio plasticity along the EMT spectrum may explain the propensity of ALK-rearranged NSCLC cells to acquire resistance to new-generation ALK-TKIs, a phenomenon that could be abrogated by the silibinin-driven attenuation of the TGFβ/SMAD signaling axis in mesenchymal ALK-rearranged NSCLC cells.

Silibinin Schiff Base Derivatives Counteract CCl4-Induced Acute Liver Injury by Enhancing Anti-Inflammatory and Antiapoptotic Bioactivities

Background

Purpose

Patients and Methods

Results

Conclusion

Synthesis and antitumor activity of novel silibinin and 2,3-dehydrosilybin derivatives with carbamate groups

A novel series of silibinin and 2,3-dehydrosilybin derivatives bearing carbamate groups were designed, synthesized and their in vitro anticancer activities were screened against human cancer cell lines including MCF-7, NCI-H1299, HepG2 and HT29 by CCK-8 assay. The results showed that most of the compounds significantly suppressed the proliferation of tested cancer cells. Among them, compounds 2h, 3h and 3f demonstrated markedly higher antiproliferative activity on MCF-7 cells with IC₅₀ values of 2.08, 5.54 and 6.84 µM, respectively. Compounds 3e, 3g and 2g displayed better cytotoxic activity against NCI-H1299 cells with IC₅₀ values of 8.07, 8.45 and 9.09 µM, respectively. Compounds 3g, 3c and 3h exhibited a promising inhibitory effect against HepG2 cells with IC₅₀ values of 8.88, 9.47 and 9.99 µM, respectively. Compounds 3e, 2e and 3c revealed effective biological potency on HT29 cells with IC₅₀ values of 6.27, 9.13 and 9.32 µM, respectively. In addition, the outcomes of the docking studies between compounds 2f, 2h, 3e, 3g and Hsp90 receptor (PDB ID: 4AWO) suggest the possible mechanism of inhibition against MCF-7 cell lines.

Role of Silymarin in Cancer Treatment: Facts, Hypotheses, and Questions

The flavonoid silymarin extracted from the seeds of Sylibum marianum is a mixture of 6 flavolignan isomers. The 3 more important isomers are silybin (or silibinin), silydianin, and silychristin. Silybin is functionally the most active of these compounds. This group of flavonoids has been extensively studied and they have been used as hepato-protective substances for the mushroom Amanita phalloides intoxication and mainly chronic liver diseases such as alcoholic cirrhosis and nonalcoholic fatty liver. Hepatitis C progression is not, or slightly, modified by silymarin. Recently, it has also been proposed for SARS COVID-19 infection therapy. The biochemical and molecular mechanisms of action of these substances in cancer are subjects of ongoing research. Paradoxically, many of its identified actions such as antioxidant, promoter of ribosomal synthesis, and mitochondrial membrane stabilization, may seem protumoral at first sight, however, silymarin compounds have clear anticancer effects. Some of them are: decreasing migration through multiple targeting, decreasing hypoxia inducible factor-1α expression, inducing apoptosis in some malignant cells, and inhibiting promitotic signaling among others. Interestingly, the antitumoral activity of silymarin compounds is limited to malignant cells while the nonmalignant cells seem not to be affected. Furthermore, there is a long history of silymarin use in human diseases without toxicity after prolonged administration. The ample distribution and easy accessibility to milk thistle-the source of silymarin compounds, its over the counter availability, the fact that it is a weed, some controversial issues regarding bioavailability, and being a nutraceutical rather than a drug, has somehow led medical professionals to view its anticancer effects with skepticism. This is a fundamental reason why it never achieved bedside status in cancer treatment. However, in spite of all the antitumoral effects, silymarin actually has dual effects and in some cases such as pancreatic cancer it can promote stemness. This review deals with recent investigations to elucidate the molecular actions of this flavonoid in cancer, and to consider the possibility of repurposing it. Particular attention is dedicated to silymarin's dual role in cancer and to some controversies of its real effectiveness.

Lung Cancer Management with Silibinin: A Historical and Translational Perspective

The flavonolignan silibinin, the major bioactive component of the silymarin extract of Silybum marianum (milk thistle) seeds, is gaining traction as a novel anti-cancer therapeutic. Here, we review the historical developments that have laid the groundwork for the evaluation of silibinin as a chemopreventive and therapeutic agent in human lung cancer, including translational insights into its mechanism of action to control the aggressive behavior of lung carcinoma subtypes prone to metastasis. First, we summarize the evidence from chemically induced primary lung tumors supporting a role for silibinin in lung cancer prevention. Second, we reassess the preclinical and clinical evidence on the effectiveness of silibinin against drug resistance and brain metastasis traits of lung carcinomas. Third, we revisit the transcription factor STAT3 as a central tumor-cell intrinsic and microenvironmental target of silibinin in primary lung tumors and brain metastasis. Finally, by unraveling the selective vulnerability of silibinin-treated tumor cells to drugs using CRISPR-based chemosensitivity screenings (e.g., the hexosamine biosynthesis pathway inhibitor azaserine), we illustrate how the therapeutic use of silibinin against targetable weaknesses might be capitalized in specific lung cancer subtypes (e.g., KRAS/STK11 co-mutant tumors). Forthcoming studies should take up the challenge of developing silibinin and/or next-generation silibinin derivatives as novel lung cancer-preventive and therapeutic biomolecules.

Evaluation of Silibinin-Loaded Microbubbles Combined with Ultrasound in Ovarian Cancer Cells: Cytotoxicity and Mechanisms

BACKGROUND

The anticancer activity of silibinin (SB) has been demonstrated in various cancer cell types. However, its low solubility and poor bioavailability limit its clinical potential in biomedical applications. Microbubbles in combination with ultrasound are promising vehicles for local drug delivery.

OBJECTIVE

The present study determined the antitumour effects and molecular mechanism of silibinin-loaded microbubbles (SBMBs) in combination with ultrasound on ovarian cancer in vitro.

METHODS

SBMBs were prepared using mechanical vibration. The viability of A2780 cells was determined using the MTT assay. Flow cytometry was performed to detect cell apoptosis and the cell cycle. The expression of receptor tyrosine kinase (RTK)-associated downstream proteins was detected using multiplex assays and Western blots.

RESULTS

The present study designed and synthesized SBMBs. SBMBs in combination with ultrasound decreased A2780 cell viability in a dose- and time-dependent manner. The half maximal inhibitory concentration (IC50) showed that the cytotoxicity of the SBMBs was approximately 1.5 times greater than that of the SB in A2780 cells. SBMBs in combination with ultrasound resulted in significantly higher apoptosis efficiency compared to the SB group, and the SBMB population of cells was arrested in the G1/G0 phase. Further experiments demonstrated that SBMBs decreased the expression of signal transducer and activator of transcription 3 (STAT3), Ak strain transforming (AKT), and extracellular signal-regulated kinase (Erk) and had a greater effect than SB in A2780 cells. Inhibitors of AKT, Erk and STAT3 promoted the cytotoxicity of SBMBs.

CONCLUSION

SBMBs in combination with ultrasound may enhance the cytotoxicity efficiency of SB via the promotion of apoptosis and cell cycle arrest in ovarian cancer cells and the inactivation of the STAT3, AKT and Erk signalling pathways.

Effect of Pharmaceutical Excipients on Intestinal Absorption of Metformin via Organic Cation-Selective Transporters

Growing evidence has shown that some pharmaceutical excipients can act on drug transporters. The present study was aimed at investigating the effects of 13 commonly used excipients on the intestinal absorption of metformin (MTF) and the underlying mechanisms using Caco-2 cells and an ex vivo mouse non-everted gut sac model. First, the uptake of MTF in Caco-2 cells was markedly inhibited by nonionic excipients including Solutol HS 15, polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, and crospovidone. Second, transport profile studies showed that MTF was taken up via multiple cation-selective transporters, among which a novel pyrilamine-sensitive proton-coupled organic cation (H⁺/OC⁺) antiporter played a key role. Third, Solutol HS 15, polysorbate 40, and polysorbate 60 showed cis-inhibitory effects on the uptake of either pyrilamine (prototypical substrate of the pyrilamine-sensitive H⁺/OC⁺ antiporter) or 1-methyl-4-phenylpyridinium (substrate of traditional cation-selective transporters including OCTs, MATEs, PMAT, SERT, and THTR-2), indicating that their suppression on MTF uptake is due to the synergistic inhibition toward multiple influx transporters. Finally, the pH-dependent mouse intestinal absorption of MTF was significantly decreased by Solutol HS 15, polysorbate 20, polysorbate 40, polysorbate 60, polysorbate 80, and pyrilamine. In conclusion, this study revealed that a novel transport process mediated by the pyrilamine-sensitive H⁺/OC⁺ antiporter contributes to the intestinal absorption of MTF in conjunction with the traditional cation-selective transporters. Mechanistic understanding of the interaction of excipients with cation-selective transporters can improve the formulation design and clinical application of cationic drugs.

Natural Compounds as Therapeutic Agents: The Case of Human Topoisomerase IB

Natural products are widely used as source for drugs development. An interesting example is represented by natural drugs developed against human topoisomerase IB, a ubiquitous enzyme involved in many cellular processes where several topological problems occur due the formation of supercoiled DNA. Human topoisomerase IB, involved in the solution of such problems relaxing the DNA cleaving and religating a single DNA strand, represents an important target in anticancer therapy. Several natural compounds inhibiting or poisoning this enzyme are under investigation as possible new drugs. This review summarizes the natural products that target human topoisomerase IB that may be used as the lead compounds to develop new anticancer drugs. Moreover, the natural compounds and their derivatives that are in clinical trial are also commented on.

Perspectives and controversies regarding the use of natural products for the treatment of lung cancer

Lung cancer is the leading cause of cancer‐related mortality both in men and women and accounts for 18.4% of all cancer‐related deaths. Although advanced therapy methods have been developed, the prognosis of lung cancer patients remains extremely poor. Over the past few decades, clinicians and researchers have found that chemical compounds extracted from natural products may be useful for treating lung cancer. Drug formulations derived from natural compounds, such as paclitaxel, doxorubicin, and camptothecin, have been successfully used as chemotherapeutics for lung cancer. In recent years, hundreds of new natural compounds that can be used to treat lung cancer have been found through basic and sub‐clinical research. However, there has not been a corresponding increase in the number of drugs that have been used in a clinical setting. The probable reasons may include low solubility, limited absorption, unfavorable metabolism, and severe side effects. In this review, we present a summary of the natural compounds that have been proven to be effective for the treatment of lung cancer, as well as an understanding of the mechanisms underlying their pharmacological effects. We have also highlighted current controversies and have attempted to provide solutions for the clinical translation of these compounds.

Molecular mechanism and pharmacokinetics of flavonoids in the treatment of resistant EGF receptor-mutated non-small-cell lung cancer: A narrative review

Here, we review the molecular mechanism and pharmacokinetics of flavonoids in the treatment of resistant EGF receptor (EGFR)-mutated non-small-cell lung cancer (NSCLC) and particularly the possible mechanism(s) of delicaflavone, a biflavonoid extracted from Selaginella doederleinii Hieron. EGFR TK inhibitors (EGFR-TKI) are ubiquitously used in the treatment of NSCLC bearing EGFR mutations. However, patients treated with EGFR-TKI inevitably and continuously develop resistance. In laboratory studies, flavonoids, as potential adjuvants for cancer chemotherapy, exhibited anti-cancer properties such as inhibition of chemoresistance by interference with ABC transporters-induced drug efflux, curbing of c-MET amplification, or reversal of T790M mutation-mediated resistance. The current review aims at summarizing the association between the anti-cancer potentials of flavonoids and their possible regulatory roles in certain types of mutation that could trigger EGFR-TKI resistance in NSCLC. Potential practical applications of these phytochemicals, as well as the relevant pharmacokinetics, are also discussed.

Transcriptome profiling reveals Silibinin dose-dependent response network in non-small lung cancer cells

Silibinin (SIL), a natural flavonolignan from the milk thistle (Silybum marianum), is known to exhibit remarkable hepatoprotective, antineoplastic and EMT inhibiting effects in different cancer cells by targeting multiple molecular targets and pathways. However, the predominant majority of previous studies investigated effects of this phytocompound in a one particular cell line. Here, we carry out a systematic analysis of dose-dependent viability response to SIL in five non-small cell lung cancer (NSCLC) lines that gradually differ with respect to their intrinsic EMT stage. By correlating gene expression profiles of NSCLC cell lines with the pattern of their SIL IC50 response, a group of cell cycle, survival and stress responsive genes, including some prominent targets of STAT3 (BIRC5, FOXM1, BRCA1), was identified. The relevancy of these computationally selected genes to SIL viability response of NSCLC cells was confirmed by the transient knockdown test. In contrast to other EMT-inhibiting compounds, no correlation between the SIL IC50 and the intrinsic EMT stage of NSCLC cells was observed. Our experimental results show that SIL viability response of differently constituted NSCLC cells is linked to a subnetwork of tightly interconnected genes whose transcriptomic pattern can be used as a benchmark for assessment of individual SIL sensitivity instead of the conventional EMT signature. Insights gained in this study pave the way for optimization of customized adjuvant therapy of malignancies using Silibinin.

Health Benefits of Silybum marianum: Phytochemistry, Pharmacology, and Applications

Silybum marianum (SM), a well-known plant used as both a medicine and a food, has been widely used to treat various diseases, especially hepatic diseases. The seeds and fruits of SM contain a flavonolignan complex called silymarin, the active compounds of which include silybin, isosilybin, silychristin, dihydrosilybin, silydianin, and so on. In this review, we thoroughly summarize high-quality publications related to the pharmacological effects and underlying mechanisms of SM. SM has antimicrobial, anticancer, hepatoprotective, cardiovascular-protective, neuroprotective, skin-protective, antidiabetic, and other effects. Importantly, SM also counteracts the toxicities of antibiotics, metals, and pesticides. The diverse pharmacological activities of SM provide scientific evidence supporting its use in both humans and animals. Multiple signaling pathways associated with oxidative stress and inflammation are the common molecular targets of SM. Moreover, the flavonolignans of SM are potential agonists of PPARγ and ABCA1, PTP1B inhibitors, and metal chelators. At the end of the review, the potential and perspectives of SM are discussed, and these insights are expected to facilitate the application of SM and the discovery and development of new drugs. We conclude that SM is an interesting dietary medicine for health enhancement and drug discovery and warrants further investigation.

Silymarin-Loaded, Lactobionic Acid-Conjugated Porous PLGA Nanoparticles Induce Apoptosis in Liver Cancer Cells

HepG2 cells (HCC), characterized by epithelial-like morphology, high proliferation rates, and nontumorigenicity, require cost-effective and efficient treatment. Silymarin, a flavonoid extract of Silybum marianum, is effective in the treatment of HCC. Here, we have reported a comparative anticancer study of the well-characterized nanoformulations of lactobionic acid-adorned porous PLGA-encapsulated silymarin (LA-PLGA-Sil) with only porous PLGA-encapsulated silymarin (PLGA-Sil) against HepG2 cells. Treatment of HepG2 cells with LA-PLGA-Sil produced a significant deterioration in cell viability at an essentially low dose as compared with PLGA-Sil, due to the adorned lactobionic acid moiety, which results in better targeting. p53, a tumor suppressor gene, essentially initiates apoptosis in cells procuring wild-type p53 (p53 +/+). In our report, treatment of HepG2 cells (p53 +/+) with LA-PLGA-Sil activated p53, which in turn inhibited the proliferation of cells by instigating cell-cycle arrest and apoptosis in a concentration-dependent manner and simultaneously stabilized the nuclear translocation of NFκB-p65. To explore the effect of LA-PLGA-Sil on the expression of microRNA, we observed that LA-PLGA-Sil markedly upregulated the miR-29b in human HCC cells. Reactivation of the p53 gene by miR-29b targeted Bcl-2 and triggered the sequential activation of mediators such as proapoptotic Bax protein, release of cytochrome c, and the activation of caspase proteins (caspase-3 and caspase-9). Furthermore, the overexpression of NFκB-p65 in HepG2 cells reversed the repression, and this stabilization effect of LA-PLGA-Sil on the nuclear translocation of p65 led to the significant downregulation of miR-29b and successively decreased the p53 expression in LA-PLGA-Sil-treated cells, thereby providing a survival mechanism to HepG2. In entirety, our study demonstrated the extensive potential of LA-PLGA-Sil to instigate the cell death of HepG2 cells via apoptosis by targeting the miR-29b/p53 axis through the stabilization of NFκB. It also impaired the migratory activity of HepG2 cells and thereby furnished a comprehensive way to HCC therapeutic treatment.

Trehalose Conjugates of Silybin as Prodrugs for Targeting Toxic Aβ Aggregates

Alzheimer's disease (AD) is linked to the abnormal accumulation of amyloid β peptide (Aβ) aggregates in the brain. Silybin B, a natural compound extracted from milk thistle (Silybum marianum), has been shown to significantly inhibit Aβ aggregation in vitro and to exert neuroprotective properties in vivo. However, further explorations of silybin B's clinical potential are currently limited by three main factors: (a) poor solubility, (b) instability in blood serum, and (c) only partial knowledge of silybin's mechanism of action. Here, we address these three limitations. We demonstrate that conjugation of a trehalose moiety to silybin significantly increases both water solubility and stability in blood serum without significantly compromising its antiaggregation properties. Furthermore, using a combination of biophysical techniques with different spatial resolution, that is, TEM, ThT fluorescence, CD, and NMR spectroscopy, we profile the interactions of the trehalose conjugate with both Aβ monomers and oligomers and evidence that silybin may shield the "toxic" surfaces formed by the N-terminal and central hydrophobic regions of Aβ. Finally, comparative analysis with silybin A, a less active diastereoisomer of silybin B, revealed how even subtle differences in chemical structure may entail different effects on amyloid inhibition. The resulting insight on the mechanism of action of silybins as aggregation inhibitors is anticipated to facilitate the future investigation of silybin's therapeutic potential.

Natural tyrosine kinase inhibitors acting on the epidermal growth factor receptor: Their relevance for cancer therapy

Epidermal growth factor receptor (EGFR), also known as ErbB-1/HER-1, plays a key role in the regulation of the cell proliferation, migration, differentiation, and survival. Since the constitutive activation or overexpression of EGFR is nearly found in various cancers, the applications focused on EGFR are the most widely used in the clinical level, including the therapeutic drugs of targeting EGFR, monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs).Over the past decades, the compounds from natural sources have been a productive source of novel drugs, especially in both discovery and development of anti-tumor drugs by targeting the EGFR pathways as the TKIs. This work presents a review of the compounds from natural sources as potential EGFR-TKIs involved in the regulation of cancer. Moreover, high-throughput drug screening of EGFR-TKIs from the natural compounds has also been summarized.

Silibinin and SARS-CoV-2: Dual Targeting of Host Cytokine Storm and Virus Replication Machinery for Clinical Management of COVID-19 Patients

COVID-19, the illness caused by infection with the novel coronavirus SARS-CoV-2, is a rapidly spreading global pandemic in urgent need of effective treatments. Here we present a comprehensive examination of the host- and virus-targeted functions of the flavonolignan silibinin, a potential drug candidate against COVID-19/SARS-CoV-2. As a direct inhibitor of STAT3—a master checkpoint regulator of inflammatory cytokine signaling and immune response—silibinin might be expected to phenotypically integrate the mechanisms of action of IL-6-targeted monoclonal antibodies and pan-JAK1/2 inhibitors to limit the cytokine storm and T-cell lymphopenia in the clinical setting of severe COVID-19. As a computationally predicted, remdesivir-like inhibitor of RNA-dependent RNA polymerase (RdRp)—the central component of the replication/transcription machinery of SARS-CoV-2—silibinin is expected to reduce viral load and impede delayed interferon responses. The dual ability of silibinin to target both the host cytokine storm and the virus replication machinery provides a strong rationale for the clinical testing of silibinin against the COVID-19 global public health emergency. A randomized, open-label, phase II multicentric clinical trial (SIL-COVID19) will evaluate the therapeutic efficacy of silibinin in the prevention of acute respiratory distress syndrome in moderate-to-severe COVID-19-positive onco-hematological patients at the Catalan Institute of Oncology in Catalonia, Spain.

Silymarin suppresses HepG2 hepatocarcinoma cell progression through downregulation of Slit-2/Robo-1 pathway

BACKGROUND

14 million people are diagnosed with new cancer and approximately 8 million people die from cancer every year. Hepatocellular carcinoma is the most common type of liver cancer and covers almost 5-6% of cancer deaths worldwide. Silybum marianum, a plant that contains silymarin, has been used traditionally in the treatment of liver diseases for centuries. The antioxidant, anti-inflammatory and anti-fibrotic anti-cancer properties of silymarin have been demonstrated in several studies in vivo and in vitro. The Slit/Robo signaling pathway plays a role in many processes such as neurogenesis, angiogenesis, cell proliferation, cell movement, cancer progression, cell invasion, migration and metastasis. In this study, we aimed to investigate the effects of silymarin on HepG2 Hepatocellular carcinoma cells on Slit-2/Robo-1 signaling pathway and CXCR-4 which plays a role in the metastasis process.

METHODS

HepG2 Hepatocellular carcinoma cells were used in the study. Different doses of silymarin's effect on HepG2 cells were observed by hematoxylin and eosin staining. Immunoblotting techniques were used to test the expression of Slit-2/Robo-1 and CXCR4 protein level. Immunocytochemistry was used to visualize the localization of Slit-2/Robo-1 and CXCR4 protein within the cells.

RESULTS

Silymarin caused apoptosis in HepG2 cells, decreased the level of CXCR-4 protein dose-dependently, and decreased the Slit-2/Robo-1 protein level at low doses and increased it at high doses.

CONCLUSIONS

Silymarin doses showed anti-carcinogenic, anti-metastatic and apoptotic effects in a dose-dependent manner on HepG2 cells through the Slit-2/Robo-1 pathway.

Formulation Strategies for Enhancing the Bioavailability of Silymarin: The State of the Art

Silymarin, a mixture of flavonolignan and flavonoid polyphenolic compounds extractable from milk thistle (Silybum marianum) seeds, has anti-oxidant, anti-inflammatory, anti-cancer and anti-viral activities potentially useful in the treatment of several liver disorders, such as chronic liver diseases, cirrhosis and hepatocellular carcinoma. Equally promising are the effects of silymarin in protecting the brain from the inflammatory and oxidative stress effects by which metabolic syndrome contributes to neurodegenerative diseases. However, although clinical trials have proved that silymarin is safe at high doses (>1500 mg/day) in humans, it suffers limiting factors such as low solubility in water (<50 μg/mL), low bioavailability and poor intestinal absorption. To improve its bioavailability and provide a prolonged silymarin release at the site of absorption, the use of nanotechnological strategies appears to be a promising method to potentiate the therapeutic action and promote sustained release of the active herbal extract. The purpose of this study is to review the different nanostructured systems available in literature as delivery strategies to improve the absorption and bioavailability of silymarin.

Intestinal Permeability Study of Clinically Relevant Formulations of Silibinin in Caco-2 Cell Monolayers

An ever-growing number of preclinical studies have investigated the tumoricidal activity of the milk thistle flavonolignan silibinin. The clinical value of silibinin as a bona fide anti-cancer therapy, however, remains uncertain with respect to its bioavailability and blood⁻brain barrier (BBB) permeability. To shed some light on the absorption and bioavailability of silibinin, we utilized the Caco-2 cell monolayer model of human intestinal absorption to evaluate the permeation properties of three different formulations of silibinin: silibinin-meglumine, a water-soluble form of silibinin complexed with the amino-sugar meglumine; silibinin-phosphatidylcholine, the phytolipid delivery system Siliphos; and Eurosil85/Euromed, a milk thistle extract that is the active component of the nutraceutical Legasil with enhanced bioavailability. Our approach predicted differential mechanisms of transport and blood⁻brain barrier permeabilities between the silibinin formulations tested. Our assessment might provide valuable information about an idoneous silibinin formulation capable of reaching target cancer tissues and accounting for the observed clinical effects of silibinin, including a recently reported meaningful central nervous system activity against brain metastases.

Cabazitaxel and silibinin co-encapsulated cationic liposomes for CD44 targeted delivery: A new insight into nanomedicine based combinational chemotherapy for prostate cancer

Cancer stem cells (CSCs) are the promising targets for cancer chemotherapy that cannot be eliminated by conventional chemotherapy. In this study cationic liposomes of cabazitaxel (CBX) and silibinin (SIL) were prepared with an aim to kill cancer cells and CSCs for prostate cancer. CBX act as cancer cell inhibitor and SIL as CSC inhibitor. Hyaluronic acid (HA), an endogenous anionic polysaccharide was coated on cationic liposomes for targeting CD44 receptors over expressed on CSCs. Liposomes were prepared by ethanol injection method with particle size below 100 nm and entrapment efficiency of more than 90% at 10% w/w drug loading. Liposomes were characterized by dynamic light scattering, transmission electron microscopy, ¹H nuclear magnetic resonance and scanning electron microscopy-energy dispersive x-ray spectroscopy. Liposomes were evaluated for their anticancer action in androgen independent human prostate cancer cell lines (PC-3 and DU-145). HA coated liposomes showed potential cytotoxicity over other groups with low IC₅₀, significantly inhibited cell migration and induced apoptosis. Synergistic cytotoxic effect was also observed with HA coated liposomes that resulted in colony formation inhibition and G2/M phase arrest. Proficient cytotoxicity against CD44⁺ cells (14.87 ± 0.41% in PC-3 and 33.95 ± 0.68% in DU-145 cells) indicated the efficiency of HA coated liposomes towards CSC targeting. Hence, the outcome of this combinational therapy with CD44 targeting indicates the suitability of HA coated CBX and SIL co-loaded liposomes as a potential approach for eradicating prostate cancer and herein might provide a insight for future studies.

Silibinin is a direct inhibitor of STAT3

We herein combined experimental and computational efforts to delineate the mechanism of action through which the flavonolignan silibinin targets STAT3. Silibinin reduced IL-6 inducible, constitutive, and acquired feedback activation of STAT3 at tyrosine 705 (Y705). Silibinin attenuated the inducible phospho-activation of Y705 in GFP-STAT3 genetic fusions without drastically altering the kinase activity of the STAT3 upstream kinases JAK1 and JAK2. A comparative computational study based on docking and molecular dynamics simulation over 14 different STAT3 inhibitors (STAT3i) predicted that silibinin could directly bind with high affinity to both the Src homology-2 (SH2) domain and the DNA-binding domain (DBD) of STAT3. Silibinin partially overlapped with the cavity occupied by other STAT3i in the SH2 domain to indirectly prevent Y705 phosphorylation, yet showing a unique binding mode. Moreover, silibinin was the only STAT3i predicted to establish direct interactions with DNA in its targeting to the STAT3 DBD. The prevention of STAT3 nuclear translocation, the blockade of the binding of activated STAT3 to its consensus DNA sequence, and the suppression of STAT3-directed transcriptional activity confirmed silibinin as a direct STAT3i. The unique characteristics of silibinin as a bimodal SH2- and DBD-targeting STAT3i make silibinin a promising lead for designing new, more effective STAT3i.

Effects of silibinin-loaded thermosensitive liposome-microbubble complex on inhibiting rabbit liver VX2 tumors in sub-hyperthermia fields

In the present study, the effects of silibinin-loaded thermosensitive liposome-microbubble complex (STLMC) on rabbit liver VX2 tumors in sub-hyperthermia fields were investigated using two-dimensional ultrasonography (2D US), contrast-enhanced US (CEUS), hematoxylin and eosin (H&E) staining, immunohistochemistry and ultrastructure observation. 50 rabbits with VX2 liver tumors were divided into five groups: Sub-hyperthermia microwave ablation group (SHM), STLMC injection group (STLMC), SHM ablation plus STLMC injection group (SHM + STLMC), microbubble injection group and blank control group without any treatment. Rabbits in each group were examined using 2D US and CEUS in order to evaluate the tumor volume and diameter before treatment and at day 7 and 21 after treatment. Morphology, expression of CD163 and CD206, and ultrastructure of the tumors were assessed. The average post-treatment volume of tumors in group SHM + STLMC was 1.17±0.88 cm³ at day 7 and 2.15±0.96 cm³ at day 21, which was significantly decreased compared with all other groups (P<0.05). H&E staining indicated that the number of disordered macrophages in the SHM + STLMC group significantly increased compared with the other groups (P<0.05). Immunohistochemical results demonstrated that in the SHM + STLMC, the expression of CD163 and CD206 significantly decreased compared with all other groups (P<0.05). These results suggested that STLMC has a potential function in preventing tumor growth, which may be due to its inhibitory effect on tumor-associated macrophages in the tumor microenvironment.

Suppression of endogenous lipogenesis induces reversion of the malignant phenotype and normalized differentiation in breast cancer

The correction of specific signaling defects can reverse the oncogenic phenotype of tumor cells by acting in a dominant manner over the cancer genome. Unfortunately, there have been very few successful attempts at identifying the primary cues that could redirect malignant tissues to a normal phenotype. Here we show that suppression of the lipogenic enzyme fatty acid synthase (FASN) leads to stable reversion of the malignant phenotype and normalizes differentiation in a model of breast cancer (BC) progression. FASN knockdown dramatically reduced tumorigenicity of BC cells and restored tissue architecture, which was reminiscent of normal ductal-like structures in the mammary gland. Loss of FASN signaling was sufficient to direct tumors to a reversed phenotype that was near normal when considering the development of polarized growth-arrested acinar-like structure similar to those formed by nonmalignant breast cells in a 3D reconstituted basement membrane in vitro. This process, in vivo, resulted in a low proliferation index, mesenchymal-epithelial transition, and shut-off of the angiogenic switch in FASN-depleted BC cells orthotopically implanted into mammary fat pads. The role of FASN as a negative regulator of correct breast tissue architecture and terminal epithelial cell differentiation was dominant over the malignant phenotype of tumor cells possessing multiple cancer-driving genetic lesions as it remained stable during the course of serial in vivo passage of orthotopic tumor-derived cells. Transient knockdown of FASN suppressed hallmark structural and cytosolic/secretive proteins (vimentin, N-cadherin, fibronectin) in a model of EMT-induced cancer stem cells (CSC). Indirect pharmacological inhibition of FASN promoted a phenotypic switch from basal- to luminal-like tumorsphere architectures with reduced intrasphere heterogeneity. The fact that sole correction of exacerbated lipogenesis can stably reprogram cancer cells back to normal-like tissue architectures might open a new avenue to chronically restrain BC progression by using FASN-based differentiation therapies.

Response of brain metastasis from lung cancer patients to an oral nutraceutical product containing silibinin

Despite multimodal treatment approaches, the prognosis of brain metastases (BM) from non-small cell lung cancer (NSCLC) remains poor. Untreated patients with BM have a median survival of about 1 month, with almost all patients dying from neurological causes. We herein present the first report describing the response of BM from NSCLC patients to an oral nutraceutical product containing silibinin, a flavonoid extracted from the seeds of the milk thistle. We present evidence of how the use of the silibinin-based nutraceutical Legasil^® resulted in significant clinical and radiological improvement of BM from NSCLC patients with poor performance status that progressed after whole brain radiotherapy and chemotherapy. The suppressive effects of silibinin on progressive BM, which involved a marked reduction of the peritumoral brain edema, occurred without affecting the primary lung tumor outgrowth in NSCLC patients. Because BM patients have an impaired survival prognosis and are in need for an immediate tumor control, the combination of brain radiotherapy with silibinin-based nutraceuticals might not only alleviate BM edema but also prove local control and time for either classical chemotherapeutics with immunostimulatory effects or new immunotherapeutic agents such as checkpoint blockers to reveal their full therapeutic potential in NSCLC BM patients. New studies aimed to illuminate the mechanistic aspects underlying the regulatory effects of silibinin on the cellular and molecular pathobiology of BM might expedite the entry of new formulations of silibinin into clinical testing for progressive BM from lung cancer patients.

E-Cadherin/β-Catenin Complex: A Target for Anticancer and Antimetastasis Plants/Plant-derived Compounds

Plants reputed to have cancer-inhibiting potential and putative active components derived from those plants have emerged as an exciting new field in cancer study. Some of these compounds have cancer-inhibiting potential in different clinical staging levels, especially metastasis. A few of them which stabilize cell-cell adhesions are controversial topics. This review article introduces some effective herbal compounds that target E-cadherin/β-catenin protein complex. In this article, at first, we briefly review the structure and function of E-cadherin and β-catenin proteins, Wnt signaling pathway, and its target genes. Then, effective compounds of the Teucrium persicum, Teucrium polium, Allium sativum (garlic), Glycine max (soy), and Brassica oleracea (broccoli) plants, which influence stability and cellular localization of E-cadherin/β-catenin complex, were studied. Based on literature review, there are some compounds in these plants, including genistein of soy, sulforaphane of broccoli, organosulfur compounds of garlic, and the total extract of Teucrium genus that change the expression of variety of Wnt target genes such as MMPs, E-cadherin, p21, p53, c-myc, and cyclin D1. So they may induce cell-cycle arrest, apoptosis and/or inhibition of Epithelial-Mesenchymal Transition (EMT) and metastasis.

Inhibition of T24 and RT4 Human Bladder Cancer Cell Lines by Heterocyclic Molecules

Background

Bladder cancer is a major widespread tumor of the genitourinary tract. Around 30% of patients with superficial cancers develop invasive and metastatic pathology.

Material/Methods

Some new heterocyclic 4-methyl coumarin derivatives were designed using molecular modeling studies to evaluate their potential against bladder cancer lines T24 and RT-4. The designed compounds that showed good binding affinity to T24 and RT4 were synthesized, with excellent yield. The synthesized compounds after structural evaluation were further evaluated for their antiproliferative activity by cell viability assay, cell cycle analysis, and apoptosis assay.

Results

The compound BC-14 exhibited the best cytotoxicity against T24 cells, but were not highly active against RT4 cells.

Conclusions

The results of the present study may suggest the selectivity pattern of the synthesized compounds. These results should be explored further with chemical modification for other cancer types.

STAT3-targeted treatment with silibinin overcomes the acquired resistance to crizotinib in ALK-rearranged lung cancer

The signal transducer and activator of transcription 3 (STAT3) has been suggested to play a prominent role in mediating non-small-cell lung cancer (NSCLC) resistance to some tyrosine kinase inhibitor (TKI)-mediated therapies. Using a model of anaplastic lymphoma kinase gene (ALK)-translocated NSCLC with acquired resistance to the ALK TKI crizotinib, but lacking amplifications or mutations in the kinase domain of ALK, we herein present evidence that STAT3 activation is a novel mechanism of crizotinib resistance that involves the upregulation of immune escape and epithelial to mesenchymal transition (EMT) signaling pathways. Taking advantage of the flavonolignan silibinin as a naturally occurring STAT3-targeted pharmacological inhibitor, we confirmed that STAT3 activation protects ALK-translocated NSCLC from crizotinib. Accordingly, silibinin-induced inhibition of STAT3 worked synergistically with crizotinib to reverse acquired resistance and restore sensitivity in crizotinib-resistant cells. Moreover, silibinin treatment significantly inhibited the upregulation of the immune checkpoint regulator PD-L1 and also EMT regulators (e.g., SLUG, VIM, CD44) in crizotinib-refractory cells. These findings provide a valuable strategy to potentially improve the efficacy of ALK inhibition by cotreatment with silibinin-based therapeutics, which merit clinical investigation for ALK TKI-resistant NSCLC patients.

Inhibition of Wnt Signaling by Silymarin in Human Colorectal Cancer Cells

Silymarin from milk thistle (Silybum marianum) has been reported to show an anti-cancer activity. In previous study, we reported that silymarin induces cyclin D1 proteasomal degradation through NF-κB-mediated threonine-286 phosphorylation. However, mechanism for the inhibition of Wnt signaling by silymarin still remains unanswered. Thus, we investigated whether silymarin affects Wnt signaling in human colorectal cancer cells to elucidate the additional anti-cancer mechanism of silymarin. Transient transfection with a TOP and FOP FLASH luciferase construct indicated that silymarin suppressed the transcriptional activity of β-catenin/TCF. Silymarin treatment resulted in a decrease of intracellular β-catenin protein but not mRNA. The inhibition of proteasome by MG132 and GSK3β inhibition by SB216763 blocked silymarin-mediated downregulation of β-catenin. In addition, silymarin increased phosphorylation of β-catenin and a point mutation of S33Y attenuated silymarin-mediated β-catenin downregulation. In addition, silymarin decreased TCF4 and increased Axin expression in both protein and mRNA level. From these results, we suggest that silymarin-mediated downregulation of β-catenin and TCF4 may result in the inhibition of Wnt signaling in human colorectal cancer cells.

Structure-activity relationship studies of 4-methylcoumarin derivatives as anticancer agents

CONTEXT

Cancer is a leading cause of death worldwide and novel chemotherapeutic agents with better efficacy and safety profiles are much needed. Coumarins are natural polyphenolic compounds with important pharmacological activities, which are present in many dietary plants and herbal remedies.

OBJECTIVES

The objective of this study is to investigate natural and synthetic coumarin derivatives with considerable anticancer capacity against three human cancer cell lines.

MATERIALS AND METHODS

We synthesized 27 coumarin derivatives (mostly having 4-methyl moiety) and examined their cytotoxic effect on three human cancer cell lines, K562 (chronic myelogenous leukemia), LS180 (colon adenocarcinoma), and MCF-7 (breast adenocarcinoma) by MTT reduction assay. Screened compounds included 7-hydroxy-4-methylcoumarins (7-HMCs), 7-acetoxy-4-methylcoumarins (7-AMCs), and different dihydroxy-4-methylcoumarin (DHMC) and diacetoxy-4-methylcoumarin (DAMC) derivatives. Some compounds with methoxy, amine, and bromine substitutions were also examined.

RESULTS

7,8-DHMCs bearing alkyl groups at C3 position were the most effective subgroup, and of which, the most potent is compound 11, with an n-decyl chain at C3, which had IC50 values of 42.4, 25.2, and 25.1 µM against K562, LS180, and MCF-7 cells, respectively. The second most active subgroup was 7,8-DAMCs containing ethoxycarbonylmethyl and ethoxycarbonylethyl moieties at C3 position. Compound 27 (6-bromo-4-bromomethyl-7-hydroxycoumarin), the only derivative containing bromine also showed reasonable cytotoxic activities (IC50 range: 32.7-45.8 µM).

DISCUSSION AND CONCLUSION

This structure-activity relationship (SAR) study of 4-methylcoumarins shows that further investigation of these derivatives may lead to the discovery of novel anticancer agents.

Silibinin and STAT3: A natural way of targeting transcription factors for cancer therapy

Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in many different types of cancer and plays a pivotal role in tumor growth and metastasis. Retrospective studies have established that STAT3 expression or phospho-STAT3 (pSTAT3 or activated STAT3) are poor prognostic markers for breast, colon, prostate and non-small cell lung cancer. Silibinin or silybin is a natural polyphenolic flavonoid which is present in seed extracts of milk thistle (Silybum marianum). Silibinin has been shown to inhibit multiple cancer cell signaling pathways in preclinical models, demonstrating promising anticancer effects in vitro and in vivo. This review summarizes evidence suggesting that silibinin can inhibit pSTAT3 in preclinical cancer models. We also discuss current strategies to overcome the limitations of oral administration of silibinin to cancer patients to translate the bench results to the bed side. Finally, we review the ongoing clinical trials exploring the role of silibinin in cancer.

Silymarin induces cyclin D1 proteasomal degradation via its phosphorylation of threonine-286 in human colorectal cancer cells

Silymarin from milk thistle (Silybum marianum) plant has been reported to show anti-cancer, anti-inflammatory, antioxidant and hepatoprotective effects. For anti-cancer activity, silymarin is known to regulate cell cycle progression through cyclin D1 downregulation. However, the mechanism of silymarin-mediated cyclin D1 downregulation still remains unanswered. The current study was performed to elucidate the molecular mechanism of cyclin D1 downregulation by silymarin in human colorectal cancer cells. The treatment of silymarin suppressed the cell proliferation in HCT116 and SW480 cells and decreased cellular accumulation of exogenously-induced cyclin D1 protein. However, silymarin did not change the level of cyclin D1 mRNA. Inhibition of proteasomal degradation by MG132 attenuated silymarin-mediated cyclin D1 downregulation and the half-life of cyclin D1 was decreased in the cells treated with silymarin. In addition, silymarin increased phosphorylation of cyclin D1 at threonine-286 and a point mutation of threonine-286 to alanine attenuated silymarin-mediated cyclin D1 downregulation. Inhibition of NF-κB by a selective inhibitor, BAY 11-7082 suppressed cyclin D1 phosphorylation and downregulation by silymarin. From these results, we suggest that silymarin-mediated cyclin D1 downregulation may result from proteasomal degradation through its threonine-286 phosphorylation via NF-κB activation. The current study provides new mechanistic link between silymarin, cyclin D1 downregulation and cell growth in human colorectal cancer cells.

New Therapeutic Potentials of Milk Thistle (Silybum marianum)

Silymarin is a bioflavonoid complex extract derived from dry seeds of Milk thistle [( Silybum marianum(L.) Gaernt. (Fam. Asteraceae/Compositaceae)] whose hepatoprotective effect has clinically been proved. Low toxicity, favorable pharmacokinetics, powerful antioxidant, detoxifying, preventive, protective and regenerative effects and side effects similar to placebo make silymarin extremely attractive and safe for therapeutic use. The medicinal properties of silymarin and its main component silibinin have been studied in the treatment of Alzheimer's disease, Parkinson's disease, sepsis, burns, osteoporosis, diabetes, cholestasis and hypercholesterolemia. Owing to its apoptotic effect, without cytotoxic effects, silymarin possesses potential applications in the treatment of various cancers. Silymarin is being examined as a neuro-, nephro- and cardio-protective in the damage of different etiologies due to its strong antioxidant potentials. Furthermore, it has fetoprotective (against the influence of alcohol) and prolactin effects and is safe to be used during pregnancy and lactation. Finally, the cosmetics industry is examining the antioxidant and UV-protective effects of silymarin. Further clinical studies and scientific evidence that silymarin and silibinin are effective in the therapy of various pathologies are indispensable in order to confirm their different flavonolignan pharmacological effects.

Stem cell-like ALDH(bright) cellular states in EGFR-mutant non-small cell lung cancer: a novel mechanism of acquired resistance to erlotinib targetable with the natural polyphenol silibinin

The enrichment of cancer stem cell (CSC)-like cellular states has not previously been considered to be a causative mechanism in the generalized progression of EGFR-mutant non-small cell lung carcinomas (NSCLC) after an initial response to the EGFR tyrosine kinase inhibitor erlotinib. To explore this possibility, we utilized a pre-clinical model of acquired erlotinib resistance established by growing NSCLC cells containing a TKI-sensitizing EGFR exon 19 deletion (ΔE746-A750) in the continuous presence of high doses of erlotinib. Genome-wide analyses using Agilent 44K Whole Human Genome Arrays were evaluated via bioinformatics analyses through GSEA-based screening of the KEGG pathway database to identify the molecular circuitries that were over-represented in the transcriptomic signatures of erlotinib-refractory cells. The genomic spaces related to erlotinib resistance included a preponderance of cell cycle genes (E2F1, - 2, CDC2, -6) and DNA replication-related genes (MCM4, - 5, - 6, - 7), most of which are associated with early lung development and poor prognosis. In addition, metabolic genes such as ALDH1A3 (a candidate marker for lung cancer cells with CSC-like properties) were identified. Thus, we measured the proportion of erlotinib-resistant cells expressing very high levels of aldehyde dehydrogenase (ALDH) activity attributed to ALDH1/3 isoforms. Using flow cytometry and the ALDEFLUOR® reagent, we confirmed that erlotinib-refractory cell populations contained drastically higher percentages (> 4500%) of ALDH(bright) cells than the parental erlotinib-responsive cells. Notably, strong decreases in the percentages of ALDH(bright) cells were observed following incubation with silibinin, a bioactive flavonolignan that can circumvent erlotinib resistance in vivo. The number of lung cancer spheres was drastically suppressed by silibinin in a dose-dependent manner, thus confirming the ability of this agent to inhibit the self-renewal of erlotinib-refractory CSC-like cells. This report is the first to show that: (1) loss of responsiveness to erlotinib in EGFR-mutant NSCLC can be explained in terms of erlotinib-refractory ALDH(bright) cells, which have been shown to exhibit stem cell-like properties; and (2) erlotinib-refractory ALDH(bright) cells are sensitive to the natural agent silibinin. Our findings highlight the benefit of administration of silibinin in combination with EGFR TKIs to target CSCs and minimize the ability of tumor cells to escape cell death in EGFR-mutant NSCLC patients.