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.

Nutritional Niches of Cancer Therapy-Induced Senescent Cells.

Therapy-induced senescence (TIS) is a state of stable proliferative arrest of both normal and neoplastic cells that is triggered by exposure to anticancer treatments. TIS cells acquire a senescence-associated secretory phenotype (SASP), which is pro-inflammatory and actively promotes tumor relapse and adverse side-effects in patients. Here, we hypothesized that TIS cells adapt their scavenging and catabolic ability to overcome the nutritional constraints in their microenvironmental niches. We used a panel of mechanistically-diverse TIS triggers (i.e., bleomycin, doxorubicin, alisertib, and palbociclib) and Biolog Phenotype MicroArrays to identify (among 190 different carbon and nitrogen sources) candidate metabolites that support the survival of TIS cells in limiting nutrient conditions. We provide evidence of distinguishable TIS-associated nutrient consumption profiles involving a core set of shared (e.g., glutamine) and unique (e.g., glucose-1-phosphate, inosine, and uridine) nutritional sources after diverse senescence-inducing interventions. We also observed a trend for an inverse correlation between the intensity of the pro-inflammatory SASP provoked by different TIS agents and diversity of compensatory nutritional niches utilizable by senescent cells. These findings support the detailed exploration of the nutritional niche as a new metabolic dimension to understand and target TIS in cancer.

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.

Extra-virgin olive oil contains a metabolo-epigenetic inhibitor of cancer stem cells.

Targeting tumor-initiating, drug-resistant populations of cancer stem cells (CSC) with phytochemicals is a novel paradigm for cancer prevention and treatment. We herein employed a phenotypic drug discovery approach coupled to mechanism-of-action profiling and target deconvolution to identify phenolic components of extra virgin olive oil (EVOO) capable of suppressing the functional traits of CSC in breast cancer (BC). In vitro screening revealed that the secoiridoid decarboxymethyl oleuropein aglycone (DOA) could selectively target subpopulations of epithelial-like, aldehyde dehydrogenase (ALDH)-positive and mesenchymal-like, CD44+CD24-/low CSC. DOA could potently block the formation of multicellular tumorspheres generated from single-founder stem-like cells in a panel of genetically diverse BC models. Pretreatment of BC populations with noncytotoxic doses of DOA dramatically reduced subsequent tumor-forming capacity in vivo. Mice orthotopically injected with CSC-enriched BC-cell populations pretreated with DOA remained tumor-free for several months. Phenotype microarray-based screening pointed to a synergistic interaction of DOA with the mTOR inhibitor rapamycin and the DNA methyltransferase (DNMT) inhibitor 5-azacytidine. In silico computational studies indicated that DOA binds and inhibits the ATP-binding kinase domain site of mTOR and the S-adenosyl-l-methionine (SAM) cofactor-binding pocket of DNMTs. FRET-based Z-LYTE™ and AlphaScreen-based in vitro assays confirmed the ability of DOA to function as an ATP-competitive mTOR inhibitor and to block the SAM-dependent methylation activity of DNMTs. Our systematic in vitro, in vivo and in silico approaches establish the phenol-conjugated oleoside DOA as a dual mTOR/DNMT inhibitor naturally occurring in EVOO that functionally suppresses CSC-like states responsible for maintaining tumor-initiating cell properties within BC populations.

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.

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.

Computer-aided discovery of biological activity spectra for anti-aging and anti-cancer olive oil oleuropeins.

Aging is associated with common conditions, including cancer, diabetes, cardiovascular disease, and Alzheimer's disease. The type of multi-targeted pharmacological approach necessary to address a complex multifaceted disease such as aging might take advantage of pleiotropic natural polyphenols affecting a wide variety of biological processes. We have recently postulated that the secoiridoids oleuropein aglycone (OA) and decarboxymethyl oleuropein aglycone (DOA), two complex polyphenols present in health-promoting extra virgin olive oil (EVOO), might constitute a new family of plant-produced gerosuppressant agents. This paper describes an analysis of the biological activity spectra (BAS) of OA and DOA using PASS (Prediction of Activity Spectra for Substances) software. PASS can predict thousands of biological activities, as the BAS of a compound is an intrinsic property that is largely dependent on the compound's structure and reflects pharmacological effects, physiological and biochemical mechanisms of action, and specific toxicities. Using Pharmaexpert, a tool that analyzes the PASS-predicted BAS of substances based on thousands of "mechanism-effect" and "effect-mechanism" relationships, we illuminate hypothesis-generating pharmacological effects, mechanisms of action, and targets that might underlie the anti-aging/anti-cancer activities of the gerosuppressant EVOO oleuropeins.

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 the primary active constituent of a crude extract (silymarin) from milk thistle plant (Silybum marianum) seeds. We explored the ability of an oral milk thistle extract formulation that was enriched with a water-soluble form of silibinin complexed with the amino-sugar meglumine to inhibit the growth of non-small-cell lung carcinoma (NSCLC) mouse xenografts. As a single agent, oral silibinin meglumine notably decreased the overall volumes of NSCLC tumors as efficiently as did the EGFR tyrosine kinase inhibitor (TKI) gefitinib. Concurrent treatment with silibinin meglumine impeded the regrowth of gefitinib-unresponsive tumors, resulting in drastic tumor growth prevention. Because the epithelial-to-mesenchymal transition (EMT) is required by a multiplicity of mechanisms of resistance to EGFR TKIs, we evaluated the ability of silibinin meglumine to impede the EMT in vitro and in vivo. Silibinin-meglumine efficiently prevented the loss of markers associated with a polarized epithelial phenotype as well as the de novo synthesis of proteins associated with the mesenchymal morphology of transitioning cells. Our current findings with this non-toxic, orally active, and water-soluble silibinin formulation might facilitate the design of clinical trials to test the administration of silibinin meglumine-containing injections, granules, or beverages in combination with EGFR TKIs in patients with EGFR-mutated NSCLC.