Entinostat reverses P-glycoprotein activation in snail-overexpressing adenocarcinoma HCC827 cells

Correlations of mRNA Levels among Efflux Transporters, Transcriptional Regulators, and Scaffold Proteins in Non-Small-Cell Lung Cancer

Multidrug resistance (MDR) due to enhanced drug efflux activity of tumor cells can severely impact the efficacy of antitumor therapies. We recently showed that increased activity of the efflux transporter P-glycoprotein (P-gp) associated with activation of Snail transcriptional regulators may be mediated mainly by moesin in lung cancer cells. Here, we aimed to systematically evaluate the relationships among mRNA expression levels of efflux transporters (P-gp, breast cancer resistance protein (BCRP), and multidrug resistance-associated protein 2 (MRP2)), scaffold proteins (ezrin (Ezr), radixin (Rdx), and moesin (Msn); ERM proteins), and SNAI family members (Snail, Slug, and Smac) in clinical lung cancer and noncancer samples. We found high correlations between relative (cancer/noncancer) mRNA expression levels of Snail and Msn, Msn and P-gp, Slug and MRP2, and Smuc and BCRP. These findings support our previous conclusion that Snail regulates P-gp activity via Msn and further suggest that Slug and Smuc may contribute to the functional regulation of MRP2 and BCRP, respectively, in lung cancer cells. This trial is registered with UMIN000023923.

Epigenetics Involvement in Oxaliplatin-Induced Potassium Channel Transcriptional Downregulation and Hypersensitivity

Peripheral neuropathy is the most frequent dose-limiting adverse effect of oxaliplatin. Acute pain symptoms that are induced or exacerbated by cold occur in almost all patients immediately following the first infusions. Evidence has shown that oxaliplatin causes ion channel expression modulations in dorsal root ganglia neurons, which are thought to contribute to peripheral hypersensitivity. Most dysregulated genes encode ion channels involved in cold and mechanical perception, noteworthy members of a sub-group of potassium channels of the K2P family, TREK and TRAAK. Downregulation of these K2P channels has been identified as an important tuner of acute oxaliplatin-induced hypersensitivity. We investigated the molecular mechanisms underlying this peripheral dysregulation in a murine model of neuropathic pain triggered by a single oxaliplatin administration. We found that oxaliplatin-mediated TREK-TRAAK downregulation, as well as downregulation of other K+ channels of the K2P and Kv families, involves a transcription factor known as the neuron-restrictive silencer factor (NRSF) and its epigenetic co-repressors histone deacetylases (HDACs). NRSF knockdown was able to prevent most of these K+ channel mRNA downregulation in mice dorsal root ganglion neurons as well as oxaliplatin-induced acute cold and mechanical hypersensitivity. Interestingly, pharmacological inhibition of class I HDAC reproduces the antinociceptive effects of NRSF knockdown and leads to an increased K+ channel expression in oxaliplatin-treated mice.

Rapid Increase of Gastrointestinal P-Glycoprotein Functional Activity in Response to Etoposide Stimulation

We previously reported that exposure of human colon adenocarcinoma (Caco-2) cells to the bitter substance phenylthiocarbamide (PTC) rapidly enhanced the transport function of P-glycoprotein (P-gp). In this study, we investigated the short-term effect of etoposide, another bitter-tasting P-gp substrate, on P-gp transport function in the same cell line. We found that etoposide exposure significantly increased both the P-gp protein level in the plasma membrane fraction and the efflux rate of rhodamine123 (Rho123) in Caco-2 cells within 10 min. The efflux ratio (ratio of the apparent permeability coefficient in the basal-to-apical direction to that in the apical-to-basal direction) of Rho123 in etoposide-treated cells was also significantly increased compared with the control. These results indicated that etoposide rapidly enhances P-gp function in Caco-2 cells. In contrast, P-gp expression in whole cells at both the mRNA and protein level was unchanged by etoposide exposure, compared with the levels in non-treated cells. Furthermore, etoposide increased the level of phosphorylated ezrin, radixin and moesin (P-ERM) proteins in the plasma membrane fraction of Caco-2 cells within 10 min. P-gp functional changes were blocked by YM022, an inhibitor of cholecystokinin (CCK) receptor. These results suggest that etoposide induces release of CCK, causing activation of the CCK receptor followed by phosphorylation of ERM proteins, which recruit intracellular P-gp for trafficking to the gastrointestinal membrane, thereby increasing the functional activity of P-gp.

Functional Alterations of Multidrug Resistance-Associated Proteins 2 and 5, and Breast Cancer Resistance Protein upon Snail-Induced Epithelial-Mesenchymal Transition in HCC827 Cells

Our previous report indicated that Snail-induced epithelial-mesenchymal transition (EMT) enhanced P-glycoprotein (P-gp) function and drug resistance to P-gp substrate anticancer drug in a human non-small cell lung cancer (NSCLC) cell line, HCC827. Our objective is to evaluate the changes in the mRNA and protein expression levels and the functions of multidrug resistance-associated protein (MRP) 2, MRP5 and breast cancer resistance protein (BCRP). Snail-expressing HCC827 cells showed increased mRNA levels of Snail and a mesenchymal marker vimentin, and decreased mRNA levels of an epithelial marker E-cadherin after transduction, indicating that Snail had induced EMT consistent with our previous reports. The mRNA level of MRP2 was significantly decreased, while that of MRP5 remained unchanged, in Snail-expressing cells. The expression levels of MRP2 and MRP5 proteins in whole-cell homogenate were unchanged in Snail-expressing cells, but MRP5 protein showed significantly increased membrane localization. Snail-transduction increased the efflux transport of 5-(and-6)-carboxy-2',7'-dichlorofluorescein (CDCF), a substrate of MRP2, 3 and 5. This increase was blocked by MK571, which inhibits MRP1, 2, and 5. Toxicity of cisplatin, a substrate of MRP2 and 5, was significantly decreased in Snail-expressing cells. BCRP mRNA and protein levels were both decreased in Snail-expressing cells, which showed an increase in the intracellular accumulation of 7-ethyl-10-hydroxycamptothecin (SN-38), a BCRP substrate, resulting in reduced viability. These results suggested that MRP5 function appears to be increased via an increase in membrane localization, whereas the BCRP function is decreased via a decrease in the expression level in HCC827 cells with Snail-induced EMT.

Gastrointestinal absorption of pimozide is enhanced by inhibition of P-glycoprotein

Drug-drug interaction was suggested to have played a role in the recent death due to cardiac arrest of a patient taking pimozide, sertraline and aripiprazole antipsychotic/antidepressant combination therapy. Here, we investigated the possible involvement of P-glycoprotein (P-gp)-mediated interaction among these drugs, using in vitro methods. ATPase assay confirmed that pimozide is a P-gp substrate, and might act as a P-gp inhibitor at higher concentrations. The maximum transport rate (J_max) and half-saturation concentration (K_t) for the carrier-mediated transport estimated by means of pimozide efflux assay using P-gp-overexpressing LLC-GA5-CoL150 cells were 84.9 ± 8.9 pmol/min/mg protein, and 10.6 ± 4.7 μM, respectively. These results indicate that pimozide is a good P-gp substrate, and it appears to have the potential to cause drug-drug interactions in the digestive tract at clinically relevant gastrointestinal concentrations. Moreover, sertraline or aripiprazole significantly decreased the efflux ratio of pimozide in LLC-GA5-CoL150 cells. Transport studies using Caco-2 cell monolayers were consistent with the results in LLC-GA5-CoL150 cells, and indicate that P-gp-mediated drug-drug interaction may occur in the gastrointestinal tract. Thus, P-gp inhibition by sertraline and/or aripiprazole may increase the gastrointestinal permeability of co-administered pimozide, resulting in an increased blood concentration of pimozide, which is known to be associated with an increased risk of QT prolongation, a life-threatening side effect.

Role of Exosomal miRNAs and the Tumor Microenvironment in Drug Resistance

Tumor microenvironment (TME) is composed of different cellular populations, such as stromal, immune, endothelial, and cancer stem cells. TME represents a key factor for tumor heterogeneity maintenance, tumor progression, and drug resistance. The transport of molecules via extracellular vesicles emerged as a key messenger in intercellular communication in the TME. Exosomes are small double-layered lipid extracellular vesicles that can carry a variety of molecules, including proteins, lipids, and nucleic acids. Exosomal miRNA released by cancer cells can mediate phenotypical changes in the cells of TME to promote tumor growth and therapy resistance, for example, fibroblast- and macrophages-induced differentiation. Cancer stem cells can transfer and enhance drug resistance in neighboring sensitive cancer cells by releasing exosomal miRNAs that target antiapoptotic and immune-suppressive pathways. Exosomes induce drug resistance by carrying ABC transporters, which export chemotherapeutic agents out of the recipient cells, thereby reducing the drug concentration to suboptimal levels. Exosome biogenesis inhibitors represent a promising adjunct therapeutic approach in cancer therapy to avoid the acquisition of a resistant phenotype. In conclusion, exosomal miRNAs play a crucial role in the TME to confer drug resistance and survivability to tumor cells, and we also highlight the need for further investigations in this promising field.

Regulation of breast cancer resistance protein and P-glycoprotein by ezrin, radixin and moesin in lung, intestinal and renal cancer cell lines

Objectives

Ezrin (Ezr), radixin (Rdx) and moesin (Msn) (ERM) proteins anchor other proteins to the cell membrane, serving to regulate their localization and function. Here, we examined whether ERM proteins functionally regulate breast cancer resistance protein (BCRP) and P-glycoprotein in cell lines derived from lung, intestinal and renal cancers.

Methods

ERM proteins were each silenced with appropriate siRNA. BCRP and P-gp functions were evaluated by means of efflux and uptake assays using 7-ethyl-10-hydroxycamptothecin (SN-38) and rhodamine123 (Rho123) as specific substrates, respectively, in non-small cell lung cancer HCC827 cells, intestinal cancer Caco-2 cells and renal cancer Caki-1 cells.

Key findings

In HCC827 cells, the efflux rates of SN-38 and Rho123 were significantly decreased by knockdown of Ezr or Msn, but not Rdx. However, BCRP function was unaffected by Ezr or Rdx knockdown in Caco-2 cells, which do not express Msn. In Caki-1 cells, Rdx knockdown increased the intracellular SN-38 concentration, while knockdown of Ezr or Msn had no effect.

Conclusions

Our findings indicate that regulation of BCRP and P-gp functions by ERM proteins is organ-specific. Thus, if the appropriate ERM protein(s) are functionally suppressed, accumulation of BCRP or P-gp substrates in lung, intestine or kidney cancer tissue might be specifically increased.

Implication for Cancer Stem Cells in Solid Cancer Chemo-Resistance: Promising Therapeutic Strategies Based on the Use of HDAC Inhibitors

Resistance to therapy in patients with solid cancers represents a daunting challenge that must be addressed. Indeed, current strategies are still not effective in the majority of patients; which has resulted in the need for novel therapeutic approaches. Cancer stem cells (CSCs), a subset of tumor cells that possess self-renewal and multilineage differentiation potential, are known to be intrinsically resistant to anticancer treatments. In this review, we analyzed the implications for CSCs in drug resistance and described that multiple alterations in morphogenetic pathways (i.e., Hippo, Wnt, JAK/STAT, TGF-β, Notch, Hedgehog pathways) were suggested to be critical for CSC plasticity. By interrogating The Cancer Genome Atlas (TCGA) datasets, we first analyzed the prevalence of morphogenetic pathways alterations in solid tumors with associated outcomes. Then, by highlighting epigenetic relevance in CSC development and maintenance, we selected histone deacetylase inhibitors (HDACi) as potential agents of interest to target this subpopulation based on the pleiotropic effects exerted specifically on altered morphogenetic pathways. In detail, we highlighted the role of HDACi in solid cancers and, specifically, in the CSC subpopulation and we pointed out some mechanisms by which HDACi are able to overcome drug resistance and to modulate stemness. Although, further clinical and preclinical investigations should be conducted to disclose the unclear mechanisms by which HDACi modulate several signaling pathways in different tumors. To date, several lines of evidence support the testing of novel combinatorial therapeutic strategies based on the combination of drugs commonly used in clinical practice and HDACi to improve therapeutic efficacy in solid cancer patients.