Proteasome inhibitors can alter the signaling pathways and attenuate the P-glycoprotein-mediated multidrug resistance

A new combination strategy to enhance apoptosis in cancer cells by using nanoparticles as biocompatible drug delivery carriers

Some experimental and clinical studies have been conducted for the usage of chemotherapeutic drugs encapsulated into nanoparticles (NPs). However, no study has been conducted so far on the co-encapsulation of doxorubicin (Dox) and epoxomicin (Epo) into NPs as biocompatible drug delivery carriers. Therefore, we investigated if co-encapsulation of doxorubicin (Dox) and/or epoxomicin (Epo) into NPs enhance their anticancer efficiency and prevent drug resistance and toxicity to normal cells. We synthesized Dox and/or Epo loaded poly (lactic-co-glycolic acid) (PLGA) NPs using a multiple emulsion solvent evaporation technique and characterized them in terms of their particle size and stability, surface, molecular, thermal, encapsulation efficiency and in vitro release properties. We studied the effects of drug encapsulated NPs on cellular accumulation, intracellular drug levels, oxidative stress status, cellular viability, drug resistance, 20S proteasome activity, cytosolic Nuclear Factor Kappa B (NF-κB-p65), and apoptosis in breast cancer and normal cells. Our results proved that the nanoparticles we synthesized were thermally stable possessing higher encapsulation efficiency and particle stability. Thermal, morphological and molecular analyses demonstrated the presence of Dox and/or Epo within NPs, indicating that they were successfully loaded. Cell line assays proved that Dox and Epo loaded NPs were less cytotoxic to single-layer normal HUVECs than free Dox and Epo, suggesting that the NPs would be biocompatible drug delivery carriers. The apoptotic index of free Dox and Epo increased 50% through their encapsulation into NPs, proving combination strategy to enhance apoptosis in breast cancer cells. Our results demonstrated that the co-encapsulation of Dox and Epo within NPs would be a promising treatment strategy to overcome multidrug resistance and toxicity to normal tissues that can be studied in further in vivo and clinical studies in breast cancer.

[Role of protein kinase D1 in regulating the growth, apoptosis and drug sensitivity of oral squamous carcinoma cells]

OBJECTIVE

This study aimed to investigate the role of protein kinase D (PKD)1 in regulating the growth, apop-tosis, and drug sensitivity of the squamous carcinoma cell line SCC-25.

METHODS

The SCC-25 cell line was transfected with either the control-shRNA or PKD1-shRNA plasmids. The stable transfected cells were selected, and the efficiency of PKD1 knockdown was detected by Western blot. The growth and apoptosis of SCC-25 were analyzed with a cell counting kit-8 (CCK8) and flow cytometry. The 50% inhibitory concentrations (IC50) of paclitaxel in the control and PKD1 knockdown cell lines were detected by CCK-8. The expression levels of Bax, Bcl-2, and P-gp were detected by Western blot.

RESULTS

PKD1 was constitutively expressed and phosphorylated in various cancer cell lines. Inhibiting the expression of PKD1 in SCC-25 cells by RNA interference could inhibit the growth and promote the apoptosis of SCC-25 cells via downregulating Bcl-2 expression. Additionally, inhibiting PKD1 expression could downregulate the expression of P-gp, thereby decreasing both the IC50 and resistance index of paclitaxel.

CONCLUSIONS

PKD1 plays an important role in regulating the biobehavior of SCC-25. It is a potential therapeutic target for oral squamous carcinoma.

MiR-199a-3p enhances cisplatin sensitivity of cholangiocarcinoma cells by inhibiting mTOR signaling pathway and expression of MDR1

Several studies have reported reduced miRNA-199a-3p (miR-199a-3p) in different human malignancies, however, little is known about miR-199a-3p in cholangiocarcinoma cells. In this study, we demonstrate the essential role and mechanism of miR-199a-3p in regulating cisplatin sensitivity in cholangiocarcinoma cell lines. Using a CCK-8 cell counting assay we found that expression of miR-199a-3p was positively correlated with cisplatin sensitivity in cholangiocarcinoma cell lines. MiR-199a-3p overexpression could decrease the proliferation rate and increase apoptosis of cholangiocarcinoma cells in the presence of cisplatin, while miR-199a-3p inhibition had the opposite effect. Further study demonstrated that mTOR was the target gene of miR-199a-3p, and that miR-199a-3p mimics could inhibit expression of mTOR, which consequently reduced the phosphorylation of its downstream proteins 4EBP1 and p70s6k. Rescue experiments proved that miR-199a-3p could increase the cisplatin sensitivity of cholangiocarcinoma cell lines by regulating mTOR expression. Moreover, we also found that miR-199a-3p overexpression could reduce cisplatin induced MDR1 expression by decreasing the synthesis and increasing the degradation of MDR1, thus enhancing the effectiveness of cisplatin in cholangiocarcinoma. In conclusion, miR-199a-3p could increase cisplatin sensitivity of cholangiocarcinoma cell lines by inhibiting the activity of the mTOR signaling pathway and decreasing the expression of MDR1.

E-cadherin expression increases cell proliferation by regulating energy metabolism through nuclear factor-κB in AGS cells

β-Catenin is a central player in Wnt signaling, and activation of Wnt signaling is associated with cancer development. E-cadherin in complex with β-catenin mediates cell-cell adhesion, which suppresses β-catenin-dependent Wnt signaling. Recently, a tumor-suppressive role for E-cadherin has been reconsidered, as re-expression of E-cadherin was reported to enhance the metastatic potential of malignant tumors. To explore the role of E-cadherin, we established an E-cadherin-expressing cell line, EC96, from AGS cells that featured undetectable E-cadherin expression and a high level of Wnt signaling. In EC96 cells, E-cadherin re-expression enhanced cell proliferation, although Wnt signaling activity was reduced. Subsequent analysis revealed that nuclear factor-κB (NF-κB) activation and consequent c-myc expression might be involved in E-cadherin expression-mediated cell proliferation. To facilitate rapid proliferation, EC96 cells enhance glucose uptake and produce ATP using both mitochondria oxidative phosphorylation and glycolysis, whereas AGS cells use these mechanisms less efficiently. These events appeared to be mediated by NF-κB activation. Therefore, E-cadherin re-expression and subsequent induction of NF-κB signaling likely enhance energy production and cell proliferation.

Targeting autophagy augments the activity of DHA-E3 to overcome p-gp mediated multi-drug resistance

Multidrug resistance (MDR) is a major obstacle for successful chemotherapy treatment. Searching for effective MDR modulators and combining them with anticancer drug therapies has been a promising strategy against clinical MDR. In our previous study, we have found that DHA-E3, a synthetic derivative of DHA, has the ability to modulate the function of P-glycoprotein (P-gp) and reverse MDR in cancer cells. In this study, we further evaluated the reversal effect of DHA-E3 on MDR and explored its mechanism of action in vitro. Our findings showed that DHA-E3 significantly potentiated the cytotoxicity of vincristine(VCR) and adriamycin(ADR) in the P-gp over-expressing KB/VCR and A02 cells. The mechanistic study found that DHA-E3 increased the intracellular accumulation of ADR and rhodamine-123 by directly inhibiting the drug-transport activity of P-gp. In the present study, we found that DHA-E3 not only reversed MDR, but also induced autophagy in MDR cancer cells. To determine whether DHA-E3-induced autophagy is an adaptive survival response or contributes to cell death, we manipulated autophagic activity using autophagy inhibitor 3-MA or siRNA targeting Beclin1. We found that the reversal activity of DHA-E3 was significantly exacerbated in the presence of 3-MA or blocking the expression of Beclin1. These results suggest that DHA-E3 is capable of reversing MDR, induction of autophagy represents a defense mechanism and inhibiting this process may be an effective strategy to augment the reversal activity of reversal agents.

Wnt pathway activation and ABCB1 expression account for attenuation of proteasome inhibitor-mediated apoptosis in multidrug-resistant cancer cells

Multiple drug resistance (MDR) is a major obstacle to attenuating the effectiveness of chemotherapy to many human malignancies. Proteasome inhibition induces apoptosis in a variety of cancer cells and is recognized as a novel anticancer therapy approach. Despite its success, some multiple myeloma patients are resistant or become refractory to ongoing treatment by bortezomib suggesting that chemoresistant cancer cells may have developed a novel mechanism directed against the proteasome inhibitor. The present study aimed to investigate potential mechanism(s) of attenuation in a MDR cell line, MES-SA/Dx5. We found that compared to the parental human uterus sarcoma cell line MES-SA cells, MES-SA/Dx5 cells highly expressed the ABCB1 was more resistant to MG132 and bortezomib, escaping the proteasome inhibitor-induced apoptosis pathway. The resistance was reversed by co-treatment of MG132 and the ABCB1 inhibitor verapamil. The data indicated that ABCB1 might play a role in the efflux of MG132 from the MES-SA/Dx5 cells to reduce MG132-induced apoptosis. Furthermore, the canonical Wnt pathway was found activated only in the MES-SA/Dx5 cells through active β-catenin and related transactivation activities. Western blot analysis demonstrated that Wnt-targeting genes, including c-Myc and cyclin D1, were upregulated and were relevant in inhibiting the expression of p21 in MES-SA/Dx5 cells. On the other hand, MES-SA cells expressed high levels of p21 and downregulated cyclin D1 and caused cell cycle arrest. Together, our study demonstrated the existence and participation of ABCB1 and the Wnt pathway in an MDR cell line that attenuated proteasome inhibitor-induced apoptosis.

Selective intracellular delivery of proteasome inhibitors through pH-sensitive polymeric micelles directed to efficient antitumor therapy

The ubiquitin-proteasome system is central in the regulation of cellular proteins controlling cell cycle progression and apoptosis, drawing much interest for developing effective targeted cancer therapies. Herein, we developed a novel pH-responsive polymeric-micelle-based carrier system to effectively deliver the proteasome inhibitor MG132 into cancer cells. MG132 is covalently bound to the block copolymer composed of polyethylene glycol (PEG) and polyaspartate through an acid-labile hydrazone bond. This bond is stable at physiological condition, but hydrolytically degradable in acidic compartments in the cell, such as late-endosomes and lysosomes, and thus, it was used for controlled release of MG132 after EPR-mediated preferential accumulation of the micelles into the tumor. MG132-loaded micelles have monodispersed size distribution with an average diameter of 45nm, and critical micelle concentration is well below 10(-7)M. In vitro studies against several cancer cell lines confirmed that MG132-loaded micelles retained the cytotoxic effect, and this activity was indeed due to the inhibition of proteasome by released MG132 from the micelles. Real-time in vitro confocal-microscopy experiments clearly indicated that MG132-conjugated micelles disintegrated only inside the target cells. By intravital confocal micro-videography, we also confirmed the prolonged circulation of MG132 loaded micelles in the bloodstream, which lead to tumor specific accumulation of micelles, as confirmed by in vivo imaging 24h after injection. These micelles showed significantly lower in vivo toxicity than free MG132, while achieving remarkable antitumor effect against a subcutaneous HeLa-luc tumor model. Our findings create a paradigm for future development of polymeric-micelle-based carrier system for other peptide aldehyde type proteasome inhibitors to make them effective cohort of the existing cancer therapeutic regiments.

Targeting tumor ubiquitin-proteasome pathway with polyphenols for chemosensitization

The development of tumor drug resistance is one of the biggest obstacles on the way to achieve a favorable outcome of chemotherapy. Among various strategies that have been explored to overcome drug resistance, the combination of current chemotherapy with plant polyphenols as a chemosensitizer has emerged as a promising one. Plant polyphenols are a group of phytochemicals characterized by the presence of more than one phenolic group. Mechanistic studies suggest that polyphenols have multiple intracellular targets, one of which is the proteasome complex. The proteasome is a proteolytic enzyme complex responsible for intracellular protein degradation and has been shown to play an important role in tumor growth and the development of drug resistance. Therefore, proteasome inhibition by plant polyphenols could be one of the mechanisms contributing to their chemosensitizing effect. Plant polyphenols that have been identified to possess proteasome-inhibitory activity include (-)-epigallocatechins-3-gallate (EGCG), genistein, luteolin, apigenin, chrysin, quercetin, curcumin and tannic acid. These polyphenols have exhibited an appreciable effect on overcoming resistance to various chemotherapeutic drugs as well as multidrug resistance in a broad spectrum of tumors ranging from carcinoma and sarcoma to hematological malignances. The in vitro and in vivo studies on polyphenols with proteasome-inhibitory activity have built a solid foundation to support the idea that they could serve as a chemosensitizer for the treatment of cancer. In-depth mechanistic studies and identification of optimal regimen are needed in order to eventually translate this laboratory concept into clinical trials to actually benefit current chemotherapy.

The interaction of bortezomib with multidrug transporters: implications for therapeutic applications in advanced multiple myeloma and other neoplasias

PURPOSE

Bortezomib is an important agent in multiple myeloma treatment, but resistance in cell lines and patients has been described. The main mechanisms of resistance described in cancer fall into one of two categories, pharmacokinetic resistance (PK), e.g. over expression of drug efflux pumps and pharmacodynamic resistance, e.g. apoptosis resistance or altered survival pathways, where the agent reaches an appropriate concentration, but this fails to propagate an appropriate cell death response. Of the known pump mechanisms, P-glycoprotein (P-gp) is the best studied and considered to be the most important in contributing to general PK drug resistance. Resistance to bortezomib is multifactorial and there are conflicting indications that cellular overexpression of P-gp may contribute to resistance agent. Hence, better characterization of the interactions of this drug with classical resistance mechanisms should identify improved treatment applications.

METHODS

Cell lines with different P-gp expression levels were used to determine the relationship between bortezomib and P-gp. Coculture system with stromal cells was used to determine the effect of the local microenvironment on the bortezomib-elacridar combination. To further assess P-gp function, intracellular accumulation of P-gp probe rhodamine-123 was utilised.

RESULTS

In the present study, we show that bortezomib is a substrate for P-gp, but not for the other drug efflux transporters. Bortezomib activity is affected by P-gp expression and conversely, the expression of P-gp affect bortezomib's ability to act as a P-gp substrate. The local microenvironment did not alter the cellular response to bortezomib. We also demonstrate that bortezomib directly affects the expression and function of P-gp.

CONCLUSIONS

Our findings strongly support a role for P-gp in bortezomib resistance and, therefore, suggest that combination of a P-gp inhibitor and bortezomib in P-gp positive myeloma would be a reasonable treatment combination to extend efficacy of this important drug.

Paclitaxel-induced apoptosis is BAK-dependent, but BAX and BIM-independent in breast tumor

Paclitaxel (Taxol)-induced cell death requires the intrinsic cell death pathway, but the specific participants and the precise mechanisms are poorly understood. Previous studies indicate that a BH3-only protein BIM (BCL-2 Interacting Mediator of cell death) plays a role in paclitaxel-induced apoptosis. We show here that BIM is dispensable in apoptosis with paclitaxel treatment using bim^−/− MEFs (mouse embryonic fibroblasts), the bim^−/− mouse breast tumor model, and shRNA-mediated down-regulation of BIM in human breast cancer cells. In contrast, both bak^−/− MEFs and human breast cancer cells in which BAK was down-regulated by shRNA were more resistant to paclitaxel. However, paclitaxel sensitivity was not affected in bax^−/− MEFs or in human breast cancer cells in which BAX was down-regulated, suggesting that paclitaxel-induced apoptosis is BAK-dependent, but BAX-independent. In human breast cancer cells, paclitaxel treatment resulted in MCL-1 degradation which was prevented by a proteasome inhibitor, MG132. A Cdk inhibitor, roscovitine, blocked paclitaxel-induced MCL-1 degradation and apoptosis, suggesting that Cdk activation at mitotic arrest could induce subsequent MCL-1 degradation in a proteasome-dependent manner. BAK was associated with MCL-1 in untreated cells and became activated in concert with loss of MCL-1 expression and its release from the complex. Our data suggest that BAK is the mediator of paclitaxel-induced apoptosis and could be an alternative target for overcoming paclitaxel resistance.

Reversion of Multidrug-Resistance by Proteasome Inhibitor Bortezomib in K562/DNR Cell Line

OBJECTIVE

To observe the reversion of multi-drug resistance by proteasome inhibitor bortezomib in K562/DNR cell line and to analyze the possible mechanism of reversion of multidrug-resistance.

METHODS

MTT method was used to determine the drug resistance of K562/DNR cells and the cellular toxicity of bortezomib. K562/DNR cells were cultured for 12 hours, 24 hours and 36 hours with 100 μg/ml DNR only or plus 4 μg/L bortezomib. The expressions of NF-κB, IκB and P-gp of K562/DNR were detected with Western blot method, the activity of NF-κB was tested by ELISA method and the apoptosis rate was observed in each group respectively.

RESULTS

The IC50 of DNR on cells of K562/S and K562/DNR groups were 1.16 μg/ml and 50.43 μg/mL, respectively. The drug-resistant fold was 43.47. The IC10 of PS-341 on Cell strain K562/DNR was 4 μg/L. Therefore, 4 μg/L was selected as the concentration for PS-341 to reverse drug-resistance in this study. DNR induced down-regulation of IκB expression, up-regulation of NF-κB and P-gp expression. After treatment with PS-341, a proteasome inhibitor, the IκB degradation was inhibited, IκB expression increased, NF-κB and P-gp expression decreased in a time dependent manner. Compared to DNR group, the NF-κB p65 activity of DNR+PS-341 group was decreased. Compared to corresponding DNR group, DNR induced apoptosis rate increases after addition of PS-341 in a time dependent manner.

CONCLUSION

Proteasome inhibitor bortezomib can convert the leukemia cell drug resistance. The mechanism may be that bortezomib decreases the degradation of IκB and the expression of NF-κB and P-gp, therefore induces the apoptosis of multi-drug resistant cells.

Enhancement of cellular uptake and cytotoxicity of curcumin-loaded PLGA nanoparticles by conjugation with anti-P-glycoprotein in drug resistance cancer cells

AIM

To compare the anti-cancer activity and cellular uptake of curcumin (Cur) delivered by targeted and non-targeted drug delivery systems in multidrug-resistant cervical cancer cells.

METHODS

Cur was entrapped into poly (DL-lactide-co-glycolide) (PLGA) nanoparticles (Cur-NPs) in the presence of modified-pluronic F127 stabilizer using nano-precipitation technique. On the surface of Cur-NPs, the carboxy-terminal of modified pluronic F127 was conjugated to the amino-terminal of anti-P-glycoprotein (P-gp) (Cur-NPs-APgp). The physical properties of the Cur-NPs, including particle size, zeta potential, particle morphology and Cur release kinetics, were investigated. Cellular uptake and specificity of the Cur-NPs and Cur-NPs-APgp were detected in cervical cancer cell lines KB-V1 (higher expression of P-gp) and KB-3-1 (lower expression of P-gp) using fluorescence microscope and flow cytometry, respectively. Cytotoxicity of the Cur-NPs and Cur-NPs-APgp was determined using MTT assay.

RESULTS

The particle size of Cur-NPs and Cur-NPs-APgp was 127 and 132 nm, respectively. The entrapment efficiency and actual loading of Cur-NPs-APgp (60% and 5 μg Cur/mg NP) were lower than those of Cur-NPs (99% and 7 μg Cur/mg NP). The specific binding of Cur-NPs-APgp to KB-V1 cells was significantly higher than that to KB-3-1 cells. Cellular uptake of Cur-NPs-APgp into KB-V1 cells was higher, as compared to KB-3-1 cells. However, the cellular uptake of Cur-NPs and Cur-NPs-IgG did not differ between the two types of cells. Besides, the cytotoxicity of Cur-NPs-APgp in KB-V1 cells was higher than those of Cur and Cur-NPs.

CONCLUSION

The results demonstrate that Cur-NPs-APgp targeted to P-gp on the cell surface membrane of KB-V1 cells, thus enhancing the cellular uptake and cytotoxicity of Cur.

Spindle poisons and cell fate: a tale of two pathways

Spindle poisons, such as paclitaxel and vinblastine, exert their potent anti-neoplastic effects through activation of the spindle assembly checkpoint (SAC), thereby arresting cells in mitosis. Unfortunately, only certain cancers are susceptible to these drugs, and many patients fail to respond to treatment. We review the pathways that are triggered by spindle poisons and highlight recent studies that describe the great variability of tumor cells in responding to these drugs. We also describe the recent identification of an apoptotic pathway that is activated by mitotic arrest in response to spindle poisons. Emerging from these studies is not only a greater understanding of how these classic antimitotic agents bring about cell death, but also a wealth of potential new targets of anticancer therapeutics.

Proteomic analysis of anti-tumor effects by tetrandrine treatment in HepG2 cells

Tetrandrine (TET), a bis-benzylisoquinoline alkaloid isolated from the root of Hang-Fang-Chi (Stephenia tetrandra S Moore), exhibits broad pharmacological effects, including anti-tumor activity. Recently, the beneficial effects of TET on cytotoxicity towards tumor cells, radiosensitization, circumventing multidrug resistance, normal tissue radioprotection, and antiangiogenesis have been examined extensively. To explore the potential molecular mechanism of the anti-tumor effect of TET, we applied proteomic tools to profile the proteins in HepG2 cells subjected to TET treatment. The levels of 39 proteins in cells exposed to TET (IC₅₀=5±0.6 μg/ml) for 48 h were observed to undergo significant alterations. Six proteins were identified by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) using peptide fingerprinting from 10 protein spots (density difference >1.5-fold between the control and TET-treated group). Among them, 5 proteins were downregulated (proteasome activator complex subunit 3, 40S ribosomal protein S12, phosphoglycerate mutase 1, destrin, transaldolase) and 1 protein was upregulated (guanylate kinase 1) by TET treatment in HepG2 cells as determined by spot volume (P<0.05). Most of the identified proteins were associated with tumor growth, migration, and anti-tumor drug resistance. These data will be helpful in elucidating the molecular mechanism of TET's anti-tumor effect in HepG2 cells.

The clinically approved proteasome inhibitor PS-341 efficiently blocks influenza A virus and vesicular stomatitis virus propagation by establishing an antiviral state

Recently it has been shown that the proinflammatory NF-kappaB pathway promotes efficient influenza virus propagation. Based on these findings, it was suggested that NF-kappaB blockade may be a promising approach for antiviral intervention. The classical virus-induced activation of the NF-kappaB pathway requires proteasomal degradation of the inhibitor of NF-kappaB, IkappaB. Therefore, we hypothesized that inhibition of proteasomal IkappaB degradation should impair influenza A virus (IAV) replication. We chose the specific proteasome inhibitor PS-341, which is a clinically approved anticancer drug also known as Bortezomib or Velcade. As expected, PS-341 treatment of infected A549 cells in a concentration range that was not toxic resulted in a significant reduction of progeny virus titers. However, we could not observe the proposed suppression of NF-kappaB-signaling in vitro. Rather, PS-341 treatment resulted in an induction of IkappaB degradation and activation of NF-kappaB as well as the JNK/AP-1 pathway. This coincides with enhanced expression of antiviral genes, such as interleukin-6 and, most importantly, MxA, which is a strong interferon (IFN)-induced suppressor of influenza virus replication. This suggests that PS-341 may act as an antiviral agent via induction of the type I IFN response. Accordingly, PS-341 did not affect virus titers in Vero cells, which lack type I IFN genes, but strongly inhibited replication of vesicular stomatitis virus (VSV), a highly IFN-sensitive pathogen. Thus, we conclude that PS-341 blocks IAV and VSV replication by inducing an antiviral state mediated by the NF-kappaB-dependent expression of antivirus-acting gene products.

Depression of MAD2 inhibits apoptosis and increases proliferation and multidrug resistance in gastric cancer cells by regulating the activation of phosphorylated survivin

Mitotic arrest-deficient 2 (MAD2) is one of the essential mitotic spindle checkpoint regulators, and it can protect cells from aberrant chromosome segregation. The Mad2 gene is very rarely mutated in many kinds of human cancer, but aberrantly reduced expression of MAD2 has been correlated with defective mitotic checkpoints in several human cancers. We have previously found that the MAD2 expression level is also shown to be associated with the multidrug resistance of tumour cells. In this study, we constructed a small interfering RNA (siRNA) eukaryotic expression vector of MAD2 and downregulated MAD2 expression in the gastric cancer cell line SGC7901 by transfection of MAD2-siRNA. SGC7901 cells stably transfected with the MAD2-siRNA exhibited significantly increased expression of phosphorylated survivin protein and enhanced drug resistance. Furthermore, MAD2-siRNA suppressed the proliferation of SGC7901 cells and inhibited tumour formation in athymic nude mice. This study clearly reveals that downregulation of MAD2 could regulate the cell cycle, increase proliferation, and improve the drug resistance of gastric cancer cells by regulating the activation of phosphorylated survivin. It also suggests both that MAD2 might play an important role in the development of human gastric cancer and that silencing the MAD2 gene may help to deal with the multidrug resistance of gastric cancer cells.

PYRIN domain of NALP2 inhibits cell proliferation and tumor growth of human glioblastoma

NACHT leucine-rich domain and pyrin-containing protein 2 (NALP2) plays a crucial role in inflammation through regulation of NF-kappaB activity. The N-terminal PRYIN domain of NALP2 (PYD) functions similarly in inhibiting NF-kappaB activity. To investigate if NALP2 or PYD regulates cell proliferation or tumor growth of glioblastoma, lentiviruses carrying PYD (Lenti-PYD-Flag) was successfully packaged. Lenti-PYD-Flag is able to transduce tumor cells with high efficiency and mediate high expression of peptide PYD-Flag. Transduction with Lenti-PYD-Flag significantly inhibited cell proliferation and tumor growth of U-87 MG, but not other cell lines tested. PYD inhibited nuclear accumulation of endogenous p65. These findings imply that: (i) our pRRL-based lentiviral system can transduce tumor cells with high transduction efficiency, and mediate high level expression of, at least 1.8 kb, foreign genes; (ii) PYD inhibits cell proliferation and tumor growth of glioblastoma possibly through the inhibition of NF-kappaB activity, and PYD appears to be a promising candidate for the development of targeted therapy for glioblastoma.

Proteasome inhibition: a new therapeutic strategy to cancer treatment

The ubiquitin-proteasome system is a major pathway for protein degradation. Targeting this pathway using proteasome inhibitors represents a novel approach for the treatment of cancer. Proteasome inhibitors lower cell proliferation and induce apoptosis in solid and hematologic malignancies through multiple mechanisms, including stabilization of cell cycle regulators and pro-apoptotic factors, stimulation of bone morphogenetic protein signaling, inhibition of protein translation, and sensitization to ligand-induced apoptosis. In this connection, proteasome inhibition activates macroautophagy, a compensatory protein degradation system, as well as other pro-survival signaling pathways. Inhibition of these auto-protective responses sensitizes cancer cells to the anti-proliferative effects of proteasome inhibitors.

Increased expression of enolase alpha in human breast cancer confers tamoxifen resistance in human breast cancer cells

Enolase-alpha (ENO-1) is a key glycolytic enzyme that has been used as a diagnostic marker to identify human lung cancers. To investigate the role of ENO-1 in breast cancer diagnosis and therapy, the mRNA levels of ENO-1 in 244 tumor and normal paired tissue samples and 20 laser capture-microdissected cell clusters were examined by quantitative real-time PCR analysis. Increased ENO-1 mRNA expression was preferentially detected in estrogen receptor-positive (ER+) tumors (tumor/normal ratio >90-fold) when compared to ER-negative (tumor/normal ratio >20-fold) tumor tissues. The data presented here demonstrate that those patients whose tumors highly expressed ENO-1 had a poor prognosis with greater tumor size (>2 cm, *P = .017), poor nodal status (N > 3, *P = .018), and a shorter disease-free interval (<==1 year, *P < .009). We also found that higher-expressing ENO-1 tumors confer longer distance relapse (tumor/normal ratio = 82.8-92.4-fold) when compared to locoregional relapse (tumor/normal ratio = 43.4-fold) in postsurgical 4-hydroxy-tamoxifen (4-OHT)-treated ER+ patients (*P = .014). These data imply that changes in tumor ENO-1 levels are related to clinical 4-OHT therapeutic outcome. In vitro studies demonstrated that decreasing ENO-1 expression using small interfering RNA (siRNA) significantly augmented 4-OHT (100 nM)-induced cytotoxicity in tamoxifen-resistant (Tam-R) breast cancer cells. These results suggest that downregulation of ENO-1 could be utilized as a novel pharmacological approach for overcoming 4-OHT resistance in breast cancer therapy.

Role of combination bortezomib and pegylated liposomal doxorubicin in the management of relapsed and/or refractory multiple myeloma

The first in class proteasome inhibitor bortezomib (B) received its initial regulatory approval for therapy of patients with multiple myeloma (MM) in the relapsed/refractory setting. Modulation of proteasome function, however, is also a rational strategy for chemosensitization, and a variety of agents have shown synergistic activity with bortezomib pre-clinically, including anthracyclines. This formed the basis for evaluation of a regimen of bortezomib with pegylated liposomal doxorubicin (PLD). PLD+B, in a phase I study, induced a predictable and manageable toxicity profile, and showed encouraging anti-MM activity. In a recent international, randomized phase III trial, PLD+B demonstrated a superior overall response rate and response quality compared to bortezomib alone, as well as a longer time to progression, duration of response, progression-free survival, and overall survival. Sub-analyses revealed benefits in almost all clinically relevant subgroups, including several which would be considered to have high-risk disease. These findings have led to the establishment of the PLD+B regimen as one of the standards of care for patients with relapsed and/or refractory myeloma. Efforts are now underway to build on this combination further by adding other active anti-myeloma agents. In this review, we will discuss the role of PLD+B as an important addition to our therapeutic armamentarium for patients with MM.

Gamma-linolenic acid modulates the response of multidrug-resistant K562 leukemic cells to anticancer drugs

Gamma-linolenic acid (GLA) is known to have selective tumoricidal action. It is also reported that GLA may increase the cytotoxic activity of cancer chemotherapeutic agents in some cancer cells. The present study examined whether GLA pretreatment could modulate the response of multidrug-resistant K562/ADM leukemic cells to anticancer drugs. The cell viability assay results showed that GLA at 10 microg/ml enhanced cell growth inhibition induced by the MDR-type drugs doxorubicin, etoposide and vincristine, but could not enhance or even attenuated cell growth inhibition induced by the non-MDR-type drug cisplatin, mitomycin and fluorouracil in K562/ADM cells. Further flow cytometry results showed that GLA decreased the expression of P-glycoprotein, enhanced the accumulation of doxorubicin and rhodamine 123 in K562/ADM cells and inhibited the efflux of rhodamine 123 from K562/ADM cells, lowered the efflux rate. These results suggest that GLA could modulate the response to anti-cancer agents in P-gp overexpressing multidrug-resistant cells, and the mechanism may be by decreasing the P-gp expression and inhibiting P-gp function.

Fractionated irradiation can induce functionally relevant multidrug resistance gene and protein expression in human tumor cell lines

The molecular basis of radiotherapy-related multidrug resistance (MDR) is still unclear. Here we report on a study investigating the effect of fractionated irradiation on expression of the MDR-associated proteins P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), and lung resistance-related protein (LRP), the respective mRNAs, and the functional consequences. Cells of six colon and five breast cancer cell lines were irradiated with a total dose of 27 Gy, five fractions of 1.8 Gy per week. The mRNA expression was measured by quantitative RT-PCR, protein levels and drug sensitivity to cisplatin, doxorubicin and bendamustine were assessed by flow cytometry. Breast cancer cell lines showed enhancement of the mRNAs encoding for P-gp, MRP1 and LRP in comparison to nonirradiated cells. No up-regulation of the three mRNA species was observed in the colon cancer cell lines. After irradiation, three breast cancer cell lines showed an up-regulation of LRP, one line an up-regulation of MRP1, and four lines a small up-regulation of P-gp. In the colon cancer cell lines, radiation induced significant enhancement of all three proteins. In comparison to controls, the irradiated cells lines showed a significant resistance to cisplatin, doxorubicin and bendamustine. This study confirms the prior reports of enhancement of P-gp and MRP1 after irradiation, which is accompanied by a multidrug resistance phenomenon, but in addition proposes a novel mechanism in the appearance of MDR after radiation-induced enhancement of LRP.

REIC/Dkk-3 overexpression downregulates P-glycoprotein in multidrug-resistant MCF7/ADR cells and induces apoptosis in breast cancer

The overexpression of reduced expression in immortalized cells (REIC)/Dickkopf-3 (Dkk-3), a tumor suppressor gene, induced apoptosis in human prostatic and testicular cancer cells. The aim of this study is to examine the potential of REIC/Dkk-3 as a therapeutic target against breast cancer. First, the in vitro apoptotic effect of Ad-REIC treatment was investigated in breast cancer cell lines and the adenovirus-mediated overexpression of REIC/Dkk-3 was thus found to lead to apoptotic cell death in a c-Jun-NH(2)-kinase (JNK) phosphorylaion-dependent manner. Moreover, an in vivo apoptotic effect and MCF/Wt tumor growth inhibition were observed in the mouse model after intratumoral Ad-REIC injection. As multidrug resistance (MDR) is a major problem in the chemotherapy of progressive breast cancer, the in vitro effects of Ad-REIC treatment were investigated in terms of the sensitivity of multidrug-resistant MCF7/ADR cells to doxorubicin and of the P-glycoprotein expression. Ad-REIC treatment in MCF7/ADR cells also downregulated P-glycoprotein expresssion through JNK activation, and sensitized its drug resistance against doxorubicin. Therefore, not only apoptosis induction but also the reversal of anticancer drug resistance was achieved using Ad-REIC. We suggest that REIC/Dkk-3 is a novel target for breast cancer treatment and that Ad-REIC might be an attractive agent against drug-resistant cancer in combination with conventional antineoplastic agents.

A phase I study of bortezomib, etoposide and carboplatin in patients with advanced solid tumors refractory to standard therapy

PURPOSE

To evaluate the toxicity, pharmacological, and biological properties of the combination of bortezomib, etoposide, and carboplatin in adults with advanced solid malignancies.

PATIENTS AND METHODS

Patients received escalating doses of bortezomib, etoposide, and carboplatin every 21 days. Surrogate markers of angiogenesis were evaluated.

RESULTS

Twenty-four patients received 64 courses of therapy. The most common treatment-related adverse events were myelosuppression. Dose-limiting grade 3 and 4 neutropenia and thrombocytopenia were observed when bortezomib was given on days 1, 4, 8, 11. With revised dosing, the maximum tolerated dose (MTD) of bortezomib 0.75 mg/m(2) (days 1, 8), etoposide 75 mg/m(2) (days 1-3), and carboplatin AUC 5 (day 1) was well tolerated, and are the recommended doses for further studies with this combination. No objective responses were observed, however stable disease was noted for greater or equal to four cycles in nine highly refractory patients.

Three-dimensional cellular microarray for high-throughput toxicology assays

We have developed a miniaturized 3D cell-culture array (the Data Analysis Toxicology Assay Chip or DataChip) for high-throughput toxicity screening of drug candidates and their cytochrome P450-generated metabolites. The DataChip consists of human cells encapsulated in collagen or alginate gels (as small as 20 nl) arrayed on a functionalized glass slide for spatially addressable screening against multiple compounds. A single DataChip containing 1,080 individual cell cultures, used in conjunction with the complementary human P450-containing microarray (the Metabolizing Enzyme Toxicology Assay Chip or MetaChip), simultaneously provided IC(50) values for nine compounds and their metabolites from CYP1A2, CYP2D6, and CYP3A4 and a mixture of the three P450s designed to emulate the human liver. Similar responses were obtained with the DataChip and conventional 96-well plate assays, demonstrating that the near 2,000-fold miniaturization does not influence the cytotoxicity response. The DataChip may therefore enable toxicity analyses of drug candidates and their metabolites at throughputs compatible with the availability of compounds at early-stage drug discovery.

Apoptotic pathways in tumor progression and therapy

Apoptosis is a cell suicide program that plays a critical role in development and tissue homeostasis. The ability of cancer cells to evade this programmed cell death (PCD) is a major characteristic that enables their uncontrolled growth. The efficiency of chemotherapy in killing such cells depends on the successful induction of apoptosis, since defects in apoptosis signaling are a major cause of drug resistance. Over the past decades, much progress has been made in our understanding of apoptotic signaling pathways and their dysregulation in cancer progression and therapy. These advances have provided new molecular targets for proapoptotic cancer therapies that have recently been used in drug development. While most of those therapies are still at the preclinical stage, some of them have shown much promise in the clinic. Here, we review our current knowledge of apoptosis regulation in cancer progression and therapy, as well as the new molecular targeted molecules that are being developed to reinstate cancer cell death.

Antitumor effects and drug interactions of the proteasome inhibitor bortezomib (PS341) in gastric cancer cells

The proteasome inhibitor bortezomib (PS341) inhibits the function of the 26S proteasome and has been extensively investigated in the clinical setting of hematologic malignancies. Remarkable efficacy has been reported in the treatment of multiple myeloma, but there have been few studies of its use in the treatment of gastrointestinal malignancy, especially gastric cancer. Here, we demonstrate its efficacy, both alone and in combination with other cytotoxic agents, in gastric cancer cell lines. The human gastric cancer cell lines AZ521, MKN45 and NUGC3 were used as experimental models. Bortezomib produced significant growth inhibition in these cells (mean IC50 values: 1.26, 9.44 and 8.63 micromol/l, respectively) and was also observed to decrease the activity of the extracellular signal-regulated kinase 1/2 and Akt signal pathways, increasing the accumulation of p21. Cell-cycle analysis revealed that a low concentration of bortezomib (10-100 nmol/l) increased accumulation in the G1 phase. Moreover, bortezomib showed synergistic growth inhibition in combination with the conventional cytotoxic agents 5-fluorouracil, paclitaxel, doxorubicin and SN-38, and also downregulates the activity of nuclear factor -kappaB, which is induced by these agents. Our results demonstrate that bortezomib could be an effective antitumor agent in the treatment of gastric cancer, both as single-agent therapy and in combination with conventional chemotherapeutic agents.

Pathogenesis of colorectal carcinoma and therapeutic implications: the roles of the ubiquitin-proteasome system and Cox-2

Pathways of the molecular pathogenesis of colorectal carcinoma have been extensively studied and molecular lesions during the development of the disease have been revealed. High up in the list of colorectal cancer lesions are APC (adenomatous polyposis coli), K-ras, Smad4 (or DPC4-deleted in pancreatic cancer 4) and p53 genes. All these molecules are part of important pathways for the regulation of cell proliferation and apoptosis and as a result perturbation of these processes lead to carcinogenesis. The ubiquitin-proteasome system (UPS) is comprised of a multi-unit cellular protease system that regulates several dozens of cell proteins after their ligation with the protein ubiquitin. Given that among these proteins are regulators of the cell cycle, apoptosis, angiogenesis, adhesion and cell signalling, this system plays a significant role in cell fate and carcinogenesis. UPS inhibition has been found to be a pre-requisite for apoptosis and is already clinically exploited with the proteasome inhibitor bortezomib in multiple myeloma. Cyclooxygenase-2 (Cox-2) is the inducible form of the enzyme that metabolizes the lipid arachidonic acid to prostaglandin H2, the first step of prostaglandins production. This enzyme is up-regulated in colorectal cancer and in several other cancers. Inhibition of Cox-2 by aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) has been found to inhibit proliferation of colorectal cancer cells and in epidemiologic studies has been shown to reduce colon polyp formation in genetically predisposed populations and in the general population. NSAIDs have also Cox-independent anti-proliferative effects. Targeted therapies, the result of increasingly understanding carcinogenesis in the molecular level, have entered the field of anti-neoplastic treatment and are used by themselves and in combination with chemotherapy drugs. Combinations of targeted drugs have started also to be investigated. This article reviews the molecular pathogenesis of colorectal cancer, the roles of UPS and Cox-2 in it and puts forward a rational for their combined inhibition in colorectal cancer treatment.

Emerging Data on the Use of Anthracyclines in Combination with Bortezomib in Multiple Myeloma

Since the inception of infusional vincristine/doxorubicin/pulsed dexamethasone (VAD) for the treatment of multiple myeloma, anthracyclines have remained an important class of antimyeloma agents. More recently, the introduction of pegylated liposomal doxorubicin with improved pharmacokinetic characteristics has led to the development of newer anthracycline-containing regimens with improved toxicity profiles. Bortezomib, a first in class reversible inhibitor of the proteasome, has also emerged as an important novel agent for the treatment of multiple myeloma and is currently approved for patients with relapsed/refractory disease progressing after 1 previous therapy. Although both classes of agents have potent proapoptotic activity, they also induce activation of an antiapoptotic prosurvival program that limits their own efficacy, a process known as inducible chemotherapy resistance. Importantly, in preclinical studies, each of these drugs has been shown to attenuate chemotherapy resistance induced by the other, and combinations of the 2 have demonstrated striking synergistic activity. Furthermore, early phase I/II clinical trials have shown impressive activity of pegylated liposomal doxorubicin and conventional doxorubicin in combination with bortezomib in patients with newly diagnosed and relapsed/refractory myeloma. Phase II/III clinical trials evaluating these regimens in patients with newly diagnosed and relapsed/refractory disease have recently completed accrual and will better define the role of these combinations in myeloma therapy. Herein, we review the preclinical data supporting the use of bortezomib with anthracyclines and the promising clinical data with these combinations.

Development of resistance to chemotherapeutic drugs in human osteosarcoma cell lines largely depends on up-regulation of Clusterin/Apolipoprotein J

Clusterin/Apolipoprotein J (CLU) is differentially regulated during in vivo cancer progression. We have addressed the role of CLU during the acquisition and maintenance of human cancer cells resistance to chemotherapeutic drugs. We used two osteosarcoma (OS) cell lines, namely U-2 OS and KH OS, and selected three generations of doxorubicin (DXR)-resistant cells (R1, R2 and R3; resistant to 0.0035, 0.035 and 0.35 microM DXR, respectively) by continuous exposure to increasing, clinically relevant, DXR concentrations. Our studies showed that the DXR-resistant OS cell lines were cross-resistant to a variety of unrelated cytotoxic agents. Analysis of the CLU mRNA and protein expression levels revealed a minimal CLU up-regulation in the U-2 OS R2 cells and a significant, more than 4-fold, induction in the KH OS R2 and R3 cells. Antibody-mediated neutralization of the extracellular CLU, or silencing of CLU gene expression via small interfering RNA (siRNA) partially sensitized KH OS R2 cells to the drugs assayed. Moreover, siRNA-mediated CLU knock down in the absence of DXR induced high levels of endogenous spontaneous apoptosis in both the parental and R2 OS cell lines. This effect was enhanced by more than 60% in the KH OS R2 cells as compared to their parental counterparts, indicating that the high CLU levels in the KH OS R2 cells are essential for survival. Overall, we suggest that CLU up-regulation in the multi-drug resistant OS cells relates to enhanced drug resistance. Therefore, CLU may represent a predictive marker, which correlates to response of cancer cells to chemotherapy.

Beyond single-agent bortezomib: combination regimens in relapsed multiple myeloma

PURPOSE OF REVIEW

Bortezomib-based combinations are being investigated in relapsed or refractory multiple myeloma with the aim of improving outcomes. This review presents recent data from clinical trials of these combinations and discusses their implications.

RECENT FINDINGS

Preclinical findings indicating additive or synergistic activity of bortezomib plus conventional and novel agents for multiple myeloma appear to be supported by clinical studies of bortezomib-based combinations. Bortezomib combined with a broad set of active agents results in enhanced response rates, including high complete response rates. Encouraging responses to bortezomib and its combinations are also seen in elderly patients, patients with adverse prognostic factors such as refractory disease and increased beta2-microglobulin, patients with cytogenetic abnormalities such as chromosome 13 deletion, advanced bone disease, extramedullary involvement, and patients with renal impairment, including patients with renal failure requiring dialysis. Toxicities are predictable and manageable and comparable to those seen with bortezomib monotherapy.

SUMMARY

Bortezomib-based combinations show promising activity in relapsed or refractory multiple myeloma, including reversal of chemoresistance to previously used agents. As high complete and overall response rates translate into longer survival, bortezomib-based combinations appear likely to have a significant impact on the multiple myeloma treatment algorithm and on the course of the disease itself.

Targeting the ubiquitin-proteasome pathway in breast cancer therapy

The ubiquitin-proteasome pathway (UPP) is the major eukaryotic mechanism for regulated intracellular proteolysis. Targeting this pathway with proteasome inhibitors has been validated as a rational strategy against hematologic malignancies, but for most solid tumor populations, including breast cancer, such agents have not shown encouraging activity. However, there is an increasing body of evidence showing that UPP dysregulation plays an important role in mammary tumorigenesis. Moreover, modulation of ubiquitin-proteasome function is emerging as a rational strategy to enhance chemosensitivity and overcome chemoresistance. Taken together, these facts suggest that we are only beginning to appreciate the relevance of this pathway for the current and future therapy of patients with breast cancer. This review provides an overview of the biology of the UPP, its role in the malignant process, the current state of knowledge regarding clinical heat shock protein and proteasome inhibition, and some likely future directions that may enhance our ability to exploit this pathway therapeutically.

Down-regulation of ABCB1 transporter by atorvastatin in a human hepatoma cell line and in human peripheral blood mononuclear cells

PURPOSE

The effect of atorvastatin, an HMG-CoA reductase inhibitor, on expression and activity of the drug transporter ABCB1 in HepG2 cells and peripheral blood mononuclear cells (PBMCs) was examined.

METHODS

Localization and expression of ABCB1 in hepatocytes was examined by indirect immunofluorescence. Expression of ABCB1 mRNA and ABCB1 activity were examined in atorvastatin-treated and control cells and PBMCs using real-time PCR and Rhodamine 123 efflux assay.

RESULTS

Immunohistochemical analysis revealed that ABCB1 is located at the apical membrane of the bile canaliculi. Atorvastatin at 10 and 20 microM up-regulated ABCB1 expression resulting in a significant 1.4-fold increase of the protein levels. Treatment of HepG2 cells with 20 microM atorvastatin caused a 60% reduction on mRNA expression (p<0.05) and a 41% decrease in ABCB1-mediated efflux of Rhodamine123 (p<0.01) by flow cytometry. Correlation was found between ABCB1 mRNA levels and creatine kinase (r=0.30; p=0.014) and total cholesterol (r=-0.31; p=0.010). CONCLUSIONS. Atorvastatin leads to decreased ABCB1 function and modulates ABCB1 synthesis in HepG2 cells and in PBMCs. ABCB1 plays a role in cellular protection as well as in secretion and/or disposition, therefore, inhibition of ABCB1 synthesis may increase the atorvastatin efficacy, leading to a more pronounced reduction of plasma cholesterol.

Altering protein turnover in tumor cells: New opportunities for anti-cancer therapies

The promising effects of the proteasome inhibitor bortezomib (Velcade, PS-341) in the treatment of certain types of cancer have fired up the interest on this multicatalytic proteolytic machinery. A number of recent reviews thoroughly describe various aspects of the ubiquitin-proteasome system and its importance in the control of cell growth and tumorigenesis. Here, we will focus on recent data unveiling a link between the proteasome and some elements of the apoptotic machinery including Bcl-2 members, caspases, IAPs and IAP antagonists. Perturbing their turnover significantly contributes to the apoptotic response and the anti-neoplastic activity of proteasome inhibitors.