The PI3K inhibitor LY294002 blocks drug export from resistant colon carcinoma cells overexpressing MRP1

Modification of sialylation is associated with multidrug resistance in human acute myeloid leukemia

Aberrant cell surface sialylation patterns have been shown to correlate with tumor progression and metastasis. However, the role of sialylation regulation of cancer multidrug resistance (MDR) remains poorly understood. This study investigated sialylation in modification on MDR in acute myeloid leukemia (AML). Using mass spectrometry (MS) analysis, the composition profiling of sialylated N-glycans differed in three pairs of AML cell lines. Real-time PCR showed the differential expressional profiles of 20 sialyltransferase (ST) genes in the both AML cell lines and bone marrow mononuclear cells (BMMCs) of AML patients. The expression levels of ST3GAL5 and ST8SIA4 were detected, which were overexpressed in HL60 and HL60/adriamycin-resistant (ADR) cells. The altered levels of ST3GAL5 and ST8SIA4 were found in close association with the MDR phenotype changing of HL60 and HL60/ADR cells both in vitro and in vivo. Further data demonstrated that manipulation of these two genes' expression modulated the activity of phosphoinositide-3 kinase (PI3K)/Akt signaling pathway and its downstream target thus regulated the proportionally mutative expression of P-glycoprotein (P-gp) and MDR-related protein 1 (MRP1), both of which are known to be involved in MDR. Blocking the PI3K/Akt pathway by its specific inhibitor LY294002 or by Akt small interfering RNA resulted in the reduced chemosensitivity of HL60/ADR cells. Therefore, this study indicated that sialylation involved in the development of MDR of AML cells probably through ST3GAL5 or ST8SIA4 regulating the activity of PI3K/Akt signaling and the expression of P-gp and MRP1.

Reversal effect of ST6GAL 1 on multidrug resistance in human leukemia by regulating the PI3K/Akt pathway and the expression of P-gp and MRP1

β-galactoside α2, 6-sialyltransferse gene (ST6GAL) family has two members, which encode corresponding enzymes ST6Gal I and ST6Gal II. The present atudy was to investigate whether and how ST6GAL family involved in multidrug resistance (MDR) in human leukemia cell lines and bone marrow mononuclear cells (BMMC) of leukemia patients. Real-time PCR showed a high expression level of ST6GAL1 gene in both MDR cells and BMMCs (*P<0.05). Alternation of ST6GAL1 levels had a significant impact on drug-resistant phenotype changing of K562 and K562/ADR cells both in vitro and in vivo. However, no significant changes were observed of ST6GAL2 gene. Further data revealed that manipulation of ST6GAL1 modulated the activity of phosphoinositide 3 kinase (PI3K)/Akt signaling and consequently regulated the expression of P-glycoprotein (P-gp, *P<0.05) and multidrug resistance related protein 1 (MRP1, *P<0.05), which are both known to be associated with MDR. Therefore we postulate that ST6GAL1 is responsible for the development of MDR in human leukemia cells probably through medicating the activity of PI3K/Akt signaling and the expression of P-gp and MRP1.

Isorhamnetin suppresses colon cancer cell growth through the PI3K‑Akt‑mTOR pathway

Isorhamnetin, a flavonoid isolated from the fruits of herbal medicinal plants, such as Hippophae rhamnoides L., exerts anticancer effects similar to other flavonoids. However, the effect of isorhamnetin on colorectal cancer (CRC) and the underlying molecular mechanism are unclear. This study aimed to determine the effect of isorhamnetin on the proliferation of cells from the human CRC cell lines, HT‑29, HCT116 and SW480. It was demonstrated that isorhamnetin suppressed the proliferation of cells from all three cell lines, induced cell cycle arrest at the G2/M phase and suppressed cell proliferation by inhibiting the PI3K‑Akt‑mTOR pathway. Isorhamnetin also reduced the phosphorylation levels of Akt (ser473), phosph‑p70S6 kinase and phosph‑4E‑BP1 (t37/46) protein, and enhanced the expression of Cyclin B1 protein. Therefore, this compound was revealed to be a selective PI3K‑Akt‑mTOR pathway inhibitor, and may be a potent anticancer agent for the treatment of CRC, as it restrains the proliferation of CRC cells.

FUT family mediates the multidrug resistance of human hepatocellular carcinoma via the PI3K/Akt signaling pathway

The fucosyltransferase (FUT) family is the key enzymes in cell-surface antigen synthesis during various biological processes such as tumor multidrug resistance (MDR). The aim of this work was to analyze the alteration of FUTs involved in MDR in human hepatocellular carcinoma (HCC) cell lines. Using mass spectrometry (MS) analysis, the composition profiling of fucosylated N-glycans differed between drug-resistant BEL7402/5-FU (BEL/FU) cells and the sensitive line BEL7402. Further analysis of the expressional profiles of the FUT family in three pairs of parental and chemoresistant human HCC cell lines showed that FUT4, FUT6 and FUT8 were predominant expressed in MDR cell lines. The altered levels of FUT4, FUT6 and FUT8 were responsible for changed drug-resistant phenotypes of BEL7402 and BEL/FU cells both in vitro and in vivo. In addition, regulating FUT4, FUT6 or FUT8 expression markedly modulated the activity of the phosphoinositide 3 kinase (PI3K)/Akt signaling pathway and MDR-related protein 1 (MRP1) expression. Inhibition of the PI3K/Akt pathway by its specific inhibitor wortmannin, or by Akt small interfering RNA (siRNA), resulted in decreased MDR of BEL/FU cells, partly through the downregulation of MRP1. Taken together, our results suggest that FUT4-, FUT6- or FUT8-mediated MDR in human HCC is associated with the activation of the PI3K/Akt pathway and the expression of MRP1, but not of P-gp, indicating a possible novel mechanism by which the FUT family regulates MDR in human HCC.

Transport mechanisms for soy isoflavones and microbial metabolites dihydrogenistein and dihydrodaidzein across monolayers and membranes

Isoflavone data concerning the metabolism and permeability on intestinal epithelial cells are scarce, particularly for microbial isoflavone metabolites. This study evaluates the absorption mechanisms for the isoflavones, genistein and daidzein, and their microbial metabolites, dihydrogenistein (DHG) and dihydrodaidzein (DHD). The permeability characteristics of isoflavones were compared by using the Caco-2 human colon adenocarcinoma cell line for a parallel artificial membrane permeability assay, and comparing their physicochemical properties. The data suggest that genistein, DHG and DHD were efficiently transported by passive diffusion according to the pH-partition hypothesis. Genistein was conjugated by phase II metabolizing enzymes and acted as a substrate of the breast cancer resistance protein (BCRP). Daidzein was not conjugated but did act as a substrate for BCRP, multidrug resistance-associated proteins, and P-glycoprotein. In contrast, DHG and DHD were markedly more permeable than their parent isoflavones; they were therefore difficult to transport by the efflux effect, and glucuronidation/sulfation was limited by the flux time.

Regulation of YAP through an Akt-dependent process by 3, 3'-diindolylmethane in human colon cancer cells

Cancer development is a complex process governed by the interaction of several signaling pathways. The Hippo and PI3K/Akt pathways have been shown to play a critical role in controlling tissue growth involved in the regulation of cell proliferation. 3, 3'-diindolylmethane (DIM) is a natural compound that selectively kills cancer cells without causing toxicity to normal cells. This study aims to investigate whether DIM has an effect on the Hippo signaling pathway mediated via the PI3K/Akt signaling pathway in colon cancer cells. Our study provides new insights into the mechanisms of crosstalk between Hippo signaling and the Akt pathway controlling cell proliferation by PI3K inhibitor and DIM treatment in colon cancer cells. DIM strongly potentiates the lethality of LY294002 in HCT116 cells and inhibits proliferation of colon cancer cells via inactivation of Akt and YAP. Thus, DIM has dramatic therapeutic effects when it is combined with the PI3K inhibitor in the treatment of colon cancer cells. These findings highlight the potential usefulness of DIM and can help develop therapeutic strategies for the prevention and treatment of colon cancer.

Targeting multidrug resistance protein 1 (MRP1, ABCC1): past, present, and future

The human ATP-binding cassette transporter multidrug resistance protein 1 (MRP1), encoded by ABCC1, was initially identified because of its ability to confer multidrug resistance in lung cancer cells. It is now established that MRP1 plays a role in protecting certain tissues from xenobiotic insults and that it mediates the cellular efflux of the proinflammatory cysteinyl leukotriene C4 as well as a vast array of other endo- and xenobiotic organic anions. Many of these are glutathione (GSH) or glucuronide conjugates, the products of Phase II drug metabolism. MRP1 also plays a role in the cellular efflux of the reduced and oxidized forms of GSH and thus contributes to the many physiological and pathophysiological processes influenced by these small peptides, including oxidative stress. In this review, the pharmacological and physiological aspects of MRP1 are considered in the context of the current status and future prospects of pharmacological and genetic modulation of MRP1 activity.

Vascular endothelial growth factor induces multidrug resistance-associated protein 1 overexpression through phosphatidylinositol-3-kinase /protein kinase B signaling pathway and transcription factor specificity protein 1 in BGC823 cell line

Multidrug resistance (MDR) is one of the most important causes of chemotherapy failure and carcinoma recurrence. But the roles of the MDR-associated protein MRP1 in MDR remain poorly understood. Vascular endothelial growth factor (VEGF), one of the most active and specific vascular growth factors, plays a significant role in proliferation, differentiation, and metastasis of cancers. To explore the effect of VEGF on the expression of MRP1, we used recombinant human VEGF to stimulate K562 and BGC-823 cell lines. Quantitative real-time polymerase chain reaction and western blot analysis showed that the expression of MRP1 at both mRNA and protein levels was increased. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide results also showed that VEGF significantly enhanced the IC50 of the cells treated with adriamycin. To explore the underlying regulatory mechanisms, we constructed MRP1 promoter and the luciferase reporter gene recombinant vector. The luciferase reporter gene assay showed that the activity of the MRP1 promoter was markedly increased by VEGF stimulation, while LY294002, an inhibitor of the phosphatidylinositol-3-kinase (PI3K)/protein kinase B (Akt) signaling pathway, reduced this effect. Transcription factor specificity protein 1 (SP1) binding site mutation partially blocked the up-regulation of MRP1 promoter activity by VEGF. In summary, our results demonstrated that VEGF enhanced the expression of MRP1, and the PI3K/Akt signaling pathway and SP1 may be involved in this modulation.

Versatile inhibitory effects of the flavonoid-derived PI3K/Akt inhibitor, LY294002, on ATP-binding cassette transporters that characterize stem cells

Stem cells are undifferentiated cells capable of proliferation, self-renewal, and production of a large number of differentiated progeny. Stem cells exist even in malignancies. They are called cancer stem cells, which may represent the origin of these tumors and may be one of the reasons of chemoresistance. The phosphatidylinositol-3-kinase (PI3K)/Akt pathway is important for the maintenance of pluripotency in stem cells. Flow cytometry assay for identifying stem cells defines a side population of cells that displays low fluorescent dye and is highly enriched for stem cells. The dye efflux is attributed to expression of ATP-binding cassette transporters such as P-glycoprotein and breast cancer resistance protein (BCRP)/ABCG2, which also transport a variety of anticancer drugs. The PI3K/Akt pathway can modulate functions of ABC transporters through various mechanisms. Reportedly, inhibition of the PI3K/Akt pathway caused BCRP translocation in hematopoietic stem cells and glioma stem-like cells. On the other hand, a PI3K inhibitor, LY294002, reversed multidrug resistance in cancer cells that overexpress BCRP not by affecting BCRP translocation but putatively as a competitive inhibitor. Other PI3K inhibitors, wortmannin and PI-103, did not reverse BCRP-mediated drug resistance. Since LY294002 is a derivative of quercetin that is a naturally occurring flavonoid, its chemical structure is similar to those of a group of flavonoids but those of wortmannin and PI-103 are quite different. It is known that many flavonoids are inhibitors of BCRP and PI3K. LY294002 has also been reported to exert inhibitory effects on multidrug resistance-associated protein 1 (MRP1) function via dual mechanisms, competitive block of substrate transport and modulation of expression. Furthermore, LY294002 has been found to antagonize transport activity of P-glycoprotein without influencing its expression. Taken together, LY294002 can inhibit all BCRP, P-glycoprotein, and MRP1, which are three major ABC transporters that are highly expressed in stem cells and cause multidrug resistance. Due to its versatile effects, LY294002 could be a lead compound for developing more effective and tolerable reagents for cancer treatment.

Collagen/β1 integrin signaling up-regulates the ABCC1/MRP-1 transporter in an ERK/MAPK-dependent manner

Collagen/β1 integrin/extracellular signal-regulated kinase signaling up-regulates the expression and function of ABCC1 transporter. This suggests that its activation could represent an important pathway in cancer chemoresistance.

The mechanisms by which β1 integrins regulate chemoresistance of cancer cells are still poorly understood. In this study, we report that collagen/β1 integrin signaling inhibits doxorubicin-induced apoptosis of Jurkat and HSB2 leukemic T-cells by up-regulating the expression and function of the ATP-binding cassette C 1 (ABCC1) transporter, also known as multidrug resistance–associated protein 1. We find that collagen but not fibronectin reduces intracellular doxorubicin content and up-regulates the expression levels of ABCC1. Inhibition and knockdown studies show that up-regulation of ABCC1 is necessary for collagen-mediated reduction of intracellular doxorubicin content and collagen-mediated inhibition of doxorubicin-induced apoptosis. We also demonstrate that activation of the extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase signaling pathway is involved in collagen-induced reduction of intracellular doxorubicin accumulation, collagen-induced up-regulation of ABCC1 expression levels, and collagen-mediated cell survival. Finally, collagen-mediated up-regulation of ABCC1 expression and function also requires actin polymerization. Taken together, our results indicate for the first time that collagen/β1 integrin/ERK signaling up-regulates the expression and function of ABCC1 and suggest that its activation could represent an important pathway in cancer chemoresistance. Thus simultaneous targeting of collagen/β1 integrin and ABCC1 may be more efficient in preventing drug resistance than targeting each pathway alone.

miR-126 enhances the sensitivity of non-small cell lung cancer cells to anticancer agents by targeting vascular endothelial growth factor A

Increasing evidence suggests that hsa-miR-126 (miR-126) is down-regulated in non-small cell lung cancer (NSCLC) cell lines and the restoration of miR-126 impairs tumor cell proliferation, migration, invasion, and survival by targeting specific molecules. Here, we reported for the first time that miR-126 was involved in regulating the response of NSCLC cells to cancer chemotherapy. After transfected A549 cells with miR-126 mimic or inhibitor, we found that an elevated level of miR-126 was significantly associated with a decreased half maximal inhibitory concentration of adriamycin (ADM) and vincristine, an increased accumulation of ADM, down-regulation of vascular endothelial growth factor A (VEGFA) and multidrug resistance-associated protein 1 (MRP1), and inactivation of the Akt signaling pathway. Furthermore, enhanced expression of miR-126 suppressed the growth of A549 xenograft and inhibited the expression of VEGFA and MRP1. miR-126 could efficiently down-regulate VEGFA expression through the interaction with the VEGFA 3'-untranslated region, whereas restoration of VEGFA could partially attenuate the suppression of MRP1 by miR-126. However, LY294002, an inhibitor of the PI3K/Akt signaling pathway, diminished this effect, suggesting that enhanced expression of miR-126 increased the sensitivity of NSCLC cells to anticancer agents through negative regulation of a VEGF/PI3K/Akt/MRP1 signaling pathway.

PI3-kinase and mTOR inhibitors differently modulate the function of the ABCG2 multidrug transporter

The ATP-binding cassette (ABC) transporter ABCG2 plays an important role in tissue detoxification and confers multidrug resistance to cancer cells. Identification of expressional and functional cellular regulators of this multidrug transporter is therefore intensively pursued. The PI3-kinase/Akt signaling axis has been implicated as a key element in regulating various cellular functions, including the expression and plasma membrane localization of ABCG2. Here we demonstrate that besides inhibiting their respective target kinases, the pharmacological PI3-kinase inhibitor LY294002 and the downstream mTOR kinase inhibitor rapamycin also directly inhibit ABCG2 function. In contrast, wortmannin, another commonly used pharmacological inhibitor of PI3-kinase does not interact with the transporter. We suggest that direct functional modulation of ABCG2 should be taken into consideration when pharmacological agents are applied to dissect the specific role of PI3-kinase/Akt/mTOR signaling in cellular functions.

15-Deoxy-Δ12,14-prostaglandin J₂ modulates manganese-induced activation of the NF-κB, Nrf2, and PI3K pathways in astrocytes

Excessive exposure to manganese (Mn) increases levels of oxidative stressors and proinflammatory mediators, such as cyclooxygenase-2 and prostaglandin E(2). Mn also activates nuclear factor-κB (NF-κB), an important mediator of inflammation. The signaling molecule 15-deoxy-Δ12,14-prostaglandin J(2) (15 d-PGJ(2)) is an anti-inflammatory prostaglandin. Here, we tested the hypothesis that 15 d-PGJ(2) modulates Mn-induced activation of astrocytic intracellular signaling, including NF-κB and nuclear factor erythroid 2-related factor (Nrf2), a master regulator of antioxidant transcriptional responses. The results establish that 15 d-PGJ(2) suppresses Mn-induced NF-κB activation by interacting with several signaling pathways. The PI3K/Akt pathway, which is upstream of NF-κB, plays a role in this activation, because (i) pretreatment with 15 d-PGJ(2) (10 μM for 1h) significantly (p<0.01) inhibited Mn (500 μM)-induced PI3K/Akt activation and (ii) inhibition of the PI3K/Akt pathway with LY29004 significantly (p<0.05) decreased NF-κB activation. 15 d-PGJ(2) also significantly (p<0.05) attenuated Mn-induced astrocytic NF-κB activation by inhibiting the Mn-induced phosphorylation of IκB kinase and subsequent IκB-α degradation. Because Mn-induced oxidative stress is also associated with Nrf2 activation, additional studies addressed the ability of 15 d-PGJ(2) to modulate the Nrf2 pathway. 15 d-PGJ(2) significantly (p<0.01) increased Nrf2 expression in whole-cell lysates. Consistent with its pro-oxidant properties, Mn also increased Nrf2 expression. Nevertheless, cotreatment of whole-cell lysates with both Mn and 15 d-PGJ(2) partially suppressed (p<0.01) the 15 d-PGJ(2)-induced increase in astrocytic Nrf2 protein expression. Mn treatment also decreased (p<0.001) expression of DJ-1, a Parkinson disease-associated protein and a stabilizer of Nrf2, and 15 d-PGJ(2) attenuated Mn-induced astrocytic inhibition of DJ-1 expression. Collectively, these results demonstrate that 15d-PGJ(2) exerts a protective effect in astrocytes against Mn-induced inflammation and oxidative stress by modulating the activation of the NF-κB and Nrf2 signaling pathways.

Starvation, detoxification, and multidrug resistance in cancer therapy

The selection of chemotherapy drugs is based on the cytotoxicity to specific tumor cell types and the relatively low toxicity to normal cells and tissues. However, the toxicity to normal cells poses a major clinical challenge, particularly when malignant cells have acquired resistance to chemotherapy. This drug resistance of cancer cells results from multiple factors including individual variation, genetic heterogeneity within a tumor, and cellular evolution. Much progress in the understanding of tumor cell resistance has been made in the past 35 years, owing to milestone discoveries such as the identification and characterization of ABC transporters. Nonetheless, the complexity of the genetic and epigenetic rewiring of cancer cells makes drug resistance an equally complex phenomenon that is difficult to overcome. In this review, we discuss how the remarkable changes in the levels of glucose, IGF-I, IGFBP-1 and in other proteins caused by fasting have the potential to improve the efficacy of chemotherapy against tumors by protecting normal cells and tissues and possibly by diminishing multidrug resistance in malignant cells.

Targeted therapies and predictive markers in epithelial malignancies of the gastrointestinal tract

CONTEXT

In recent years, there has been a tremendous amount of interest in the development of targeted therapies for the treatment of human cancers. Increased understanding of the specific molecular pathways and driver mutations critical to cancer cell growth have allowed the development of these advanced therapeutics. Among these, inhibitors of the epidermal growth factor receptor and HER2/neu pathways now play a major role in the management of gastrointestinal cancers in addition to other solid malignancies. In colorectal and gastric cancers, the use of epidermal growth factor receptor inhibitors and HER2/neu inhibitors has increased the available treatment options for patients with advanced disease.

OBJECTIVE

To focus on the current targeted therapies and predictors of response in malignancies of the gastrointestinal tract.

DATA SOURCES

Medical literature searchable on PubMed (US National Library of Medicine) as well as older studies revealed by the literature review were used as the source of data.

CONCLUSION

Gene testing of critical elements of the pathways targeted by these agents (such as KRAS mutational analysis in colorectal tumors and HER2/neu testing in gastric cancers) allows the ability to predict which patients will respond to these treatments. As the molecular profiling of tumors and our understanding of cancer genomics and epigenetic alterations continues to grow, it is expected that these personalized targeted therapies will form one of the mainstays of gastrointestinal cancer treatment.

Stem-like cells and therapy resistance in squamous cell carcinomas

Cancer stem cells (CSCs) within squamous cell carcinomas (SCCs) are hypothesized to contribute to chemotherapy and radiation resistance and represent potentially useful pharmacologic targets. Hallmarks of the stem cell phenotype that may contribute to therapy resistance of CSCs include quiescence, evasion of apoptosis, resistance to DNA damage, and expression of drug transporter pumps. A variety of CSC populations within SCCs of the head and neck and esophagus have been defined tentatively, based on diverse surface markers and functional assays. Stem-like self-renewal and differentiation capacities of these SCC subpopulations are supported by sphere formation and clonogenicity assays in vitro as well as limiting dilution studies in xenograft models. Early evidence supports a role for SCC CSCs in intrinsic therapy resistance, while detailed mechanisms by which these subpopulations evade treatment remain to be defined. Development of novel SCC therapies will be aided by pursuing such mechanisms as well as refining current definitions for CSCs and clarifying their relevance to hierarchical versus dynamic models of stemness.

The phosphoinositide 3-kinase inhibitor LY294002, decreases aminoacyl-tRNA synthetases, chaperones and glycolytic enzymes in human HT-29 colorectal cancer cells

The proposed anticancer drug LY294002, inhibits phosphoinositide-3 kinase (PI3K) that initiates a signalling pathway often activated in colorectal cancer (CRC). The effects of LY294002 (10 μM, 48 h) on the cytosolic, mitochondrial and nuclear proteomes of human HT-29 CRC cells have been determined using iTRAQ (isobaric tag for relative and absolute quantitation) and tandem mass spectrometry (MS/MS). Analysis of cells treated with LY294002 identified 26 differentially abundant proteins that indicate several mechanisms of action. The majority of protein changes were directly or indirectly associated with Myc and TNF-α, previously implicated in CRC progression. LY294002 decreased the levels of 6 aminoacyl-tRNA synthetases (average 0.39-fold) required for protein translation, 5 glycolytic enzymes (average 0.37-fold) required for ATP synthesis, and 3 chaperones required for protein folding. There was a 3.2-fold increase in lysozyme C involved in protein-glycoside hydrolysis. LY294002 increased cytosolic p53 with a concomitant decrease in nuclear p53, suggesting transfer of p53 to the cytosol where apoptosis might be initiated via the intrinsic mitochondrial pathway. Protein changes described here suggest that the anti-angiogenic effects of LY294002 may be related to p53; the mutational status of p53 in CRC may be an important determinant of the efficacy of PI3K inhibitors for treatment.

Development of a double-layer microfluidic chip with flow medium for chemotherapy resistance analysis of lung cancer

Integration and miniaturization are main advantages of microchip-based systems. Vertical integration of the multiple operations within a multiple-layer chip is expected to satisfy the urgent demand for high-throughput and large-scale applications. This study aimed at establishing a double-layer chip to integrate the operations including the cell culture, the identification of the protein and the detection of the cell viability onto a platform systematically and supplied with flow fresh medium continuously via a syringe pump to mimic the microenvironment in vivo. With this device, human non-small cell lung cancer cell line (SPCA-1) was cultured well; the expression and the activity of multidrug resistance-associated protein (MRP1) were detected by immunofluorescence assay for the cells pretreated with or without MK-571, a known inhibitor of MRP1; apoptosis percentages were assayed for the cells after being treated by the anticancer drug etoposide (VP-16). The results demonstrated that the function of the MRP1 was inhibited by MK-571, and the percentage of apoptotic for the cells pretreated with MK-571 was higher than that of the control (38.2±2.5% versus 12.3±0.85%, p<0.005). All these indicated that the new device could provide a suitable condition for cell culture and functional analysis in biomedical research, and MK-571 is an effective inhibitor of MRP1 associated with the viability of SPCA-1 cell line treated by VP-16.

EGFR related mutational status and association to clinical outcome of third-line cetuximab-irinotecan in metastatic colorectal cancer

Background

As supplement to KRAS mutational analysis, BRAF and PIK3CA mutations as well as expression of PTEN may account for additional non-responders to anti-EGFR-MoAbs treatment. The aim of the present study was to investigate the utility as biomarkers of these mutations in a uniform cohort of patients with metastatic colorectal cancer treated with third-line cetuximab/irinotecan.

Methods

One-hundred-and-seven patients were prospectively included in the study. Mutational analyses of KRAS, BRAF and PIK3CA were performed on DNA from confirmed malignant tissue using commercially available kits. Loss of PTEN and EGFR was assessed by immunohistochemistry.

Results

DNA was available in 94 patients. The frequency of KRAS, BRAF and PIK3CA mutations were 44%, 3% and 14%, respectively. All were non-responders. EGF receptor status by IHC and loss of PTEN failed to show any clinical importance. KRAS and BRAF were mutually exclusive. Supplementing KRAS analysis with BRAF and PIK3CA indentified additional 11% of non-responders. Patient with any mutation had a high risk of early progression, whereas triple-negative status implied a response rate (RR) of 41% (p < 0.001), a disease control (DC) rate of 73% (p < 001), and a significantly higher PFS of 7.7(5.1-8.6 95%CI) versus 2.3 months (2.1-3.695%CI) (p < 0.000).

Conclusion

Triple-negative status implied a clear benefit from treatment, and we suggest that patient selection for third-line combination therapy with cetuximab/irinotecan could be based on triple mutational testing.

Rhabdastrellic acid-A induced autophagy-associated cell death through blocking Akt pathway in human cancer cells

Background

Autophagy is an evolutionarily conserved protein degradation pathway. A defect in autophagy may contribute to tumorigenesis. Autophagy inducers could have a potential function in tumor prevention and treatment.

Methodology/Principal Findings

Our results showed that Rhabdastrellic acid-A, an isomalabaricane triterpenoid isolated from the sponge Rhabdastrella globostellata, inhibited proliferation of human cancer cell lines Hep3B and A549 and induced caspase-independent cell death in both the cell lines. Further investigation showed that Rhabdastrellic acid-A induced autophagy of cancer cells determined by YFP-LC3 punctation and increased LC3-II. The pretreatment with autophagy inhibitor 3-MA inhibited Rhabdastrellic acid-A-induced cell death. Knockdown of autophagy-related gene Atg5 inhibited Rhabdastrellic acid-A-induced cell death in A549 cells. Also, phospho-Akt and its downstream targets significantly decreased after treatment with Rhabdastrellic acid-A in both cancer cell lines. Transfection of constitutive active Akt plasmid abrogated autophagy and cell death induced by Rhabdastrellic acid-A.

Conclusions/Significance

These results suggest that Rhabdastrellic acid-A could induce autophagy-associated cell death through blocking Akt pathway in cancer cells. It also provides the evidence that Rhabdastrellic acid-A deserves further investigation as a potential anticancer or cancer preventive agent.

Aromatic 2-(thio)ureidocarboxylic acids as a new family of modulators of multidrug resistance-associated protein 1: synthesis, biological evaluation, and structure-activity relationships

Four series of aromatic carboxylic acids were prepared with a urea or thiourea moiety at the neighboring position to the carboxyl group and benzene or thiophene as aromatic scaffold. Using a calcein AM assay, these compounds were evaluated as inhibitors of multidrug resistance-associated protein 1 (MRP1) and selected compounds were examined toward P-glycoprotein (P-gp) as well as breast cancer resistance protein (BCRP) to assess selectivity for MRP1. Two 2-thioureidobenzo[b]thiophene-3-carboxylic acids (48, 49) were identified as particularly potent inhibitors of MRP1, with IC50 values of around 1 microM. The structural features of this new family of nontoxic MRP1 inhibitors include a (thio)urea disubstituted with preferentially two alkyl groups at the terminal nitrogen and an additional fused aromatic ring.

PIK3CA mutation is associated with poor prognosis among patients with curatively resected colon cancer

PURPOSE

PIK3CA mutation and subsequent activation of the AKT pathway play an important role in colorectal carcinogenesis. However, little is known about the prognostic role of PIK3CA mutation in colon cancer.

PATIENTS AND METHODS

Using 450 resectable colon cancers (stage I to III) in two independent prospective cohorts, we detected PIK3CA mutation in 82 tumors (18%) by pyrosequencing. Cox proportional hazards models were used to calculate hazard ratios (HRs) of colon cancer-specific and overall mortalities, adjusted for patient characteristics and tumoral molecular features, including the CpG island methylation phenotype, microsatellite instability (MSI), LINE-1 hypomethylation, and p53, CIMP, KRAS and BRAF mutation.

RESULTS

Compared with patients with PIK3CA wild-type tumors, those with PIK3CA-mutated tumors experienced an increase in colon cancer-specific mortality according to univariate analysis (HR = 1.64; 95% CI, 0.95 to 2.86), which persisted after adjusting for other known or potential risk factors for cancer recurrence (including MSI; multivariate HR = 2.23; 95% CI, 1.21 to 4.11). The effect of PIK3CA mutation on cancer survival seemed to differ according to KRAS mutational status. Among patients with KRAS wild-type tumors, the presence of PIK3CA mutation was associated with a significant increase in colon cancer-specific mortality (HR = 3.80; 95% CI, 1.56 to 9.27). In contrast, PIK3CA mutation conferred no significant effect on mortality among patients with KRAS-mutated tumors (HR = 1.25; 95% CI, 0.52 to 2.96).

CONCLUSION

Among patients who undergo a curative resection of colon cancer, PIK3CA mutation is associated with shorter cancer-specific survival. The adverse effect of PIK3CA mutation may be potentially limited to patients with KRAS wild-type tumors.

Akt as a therapeutic target in cancer

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/v-akt murine thymoma viral oncogene homolog (Akt)/mammalian target of rapamycin (mTOR) pathway is central in the transmission of growth regulatory signals originating from cell surface receptors.

OBJECTIVE

This review discusses how mutations occur that result in elevated expression the PI3K/PTEN/Akt/mTOR pathway and lead to malignant transformation, and how effective targeting of this pathway may result in suppression of abnormal growth of cancer cells.

METHODS

We searched the literature for articles which dealt with altered expression of this pathway in various cancers including: hematopoietic, melanoma, non-small cell lung, pancreatic, endometrial and ovarian, breast, prostate and hepatocellular.

RESULTS/CONCLUSIONS

The PI3K/PTEN/Akt/mTOR pathway is frequently aberrantly regulated in various cancers and targeting this pathway with small molecule inhibitors and may result in novel, more effective anticancer therapies.

PI3K/Akt inhibition modulates multidrug resistance and activates NF-kappaB in murine lymphoma cell lines

Upregulation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway has been described in some tumors related to multidrug resistance (MDR). The aim of this work was to analyze the relationship between PI3K/Akt, MDR and NF-kappaB in murine lymphoma cell lines resistant to vincristine (LBR-V160) and doxorubicin (LBR-D160) as well as in the sensitive line (LBR-). PI3K/Akt activity, analyzed by phosphatidylinositol trisphosphate production and phosphorylated Akt (p-Akt) expression, was higher in the resistant cell lines than in the sensitive one and inhibition with wortmannin or LY294002 improved apoptosis in the resistant cell lines. Vincristine but not doxorubicin increased p-Akt expression whereas co-treatment with PI3K inhibitors and vincristine increased apoptosis in the three cell lines. Wortmannin and LY294002 inhibited P-glycoprotein (Pgp) function and also increased NF-kappaB activity. We concluded that the PI3K/Akt pathway is involved in MDR in lymphoma cell lines and PI3K/Akt inhibition correlates down-regulation of NF-kappaB activity and inhibition Pgp function.

Development of inhibitors of ATP-binding cassette drug transporters: present status and challenges

BACKGROUND

Multi-drug resistance (MDR) of cancer cells is an obstacle to effective chemotherapy of cancer. The ATP-binding cassette (ABC) transporters, including P-glycoprotein (ABCB1), MRP1 (ABCC1) and ABCG2, play an important role in the development of this resistance. An attractive approach to overcoming MDR is the inhibition of the pumping action of these transporters. Several inhibitors/modulators of ABC transporters have been developed, but cytotoxic effects and adverse pharmacokinetics have prohibited their use. The ongoing search for such inhibitors/modulators that can be applied in the clinic has led to three generations of compounds. The most recent inhibitors are more potent and less toxic than first-generation compounds, yet some are still prone to adverse effects, poor solubility and unfavorable changes in the pharmacokinetics of the anticancer drugs.

OBJECTIVE

This review provides an update of the published work on the development of potent modulators to overcome MDR in cancer cells, their present status in clinical studies and suggestions for further improvement to obtain better inhibitors.

METHODS

This review summarizes recent advances in the development of less toxic modulators, including small molecules and natural products. In addition, a brief overview of other novel approaches that can be used to inhibit ABC drug transporters mediating MDR has also been provided.

CONCLUSION

The multifactorial nature of MDR indicates that it may be important to develop modulators that can simultaneously inhibit both the function of the drug transporters and key signaling pathways, which are responsible for development of this phenomenon.

STX140 is efficacious in vitro and in vivo in taxane-resistant breast carcinoma cells

PURPOSE

The aim of these studies was to characterize the action of STX140 in a P-glycoprotein-overexpressing tumor cell line both in vitro and in vivo. In addition, its efficacy was determined against xenografts derived from patients who failed docetaxel therapy.

EXPERIMENTAL DESIGN

The effects of STX140, Taxol, and 2-methoxyestradiol (2-MeOE2) on cell proliferation, cell cycle, and apoptosis were assessed in vitro in drug-resistant cells (MCF-7(DOX)) and the parental cell line (MCF-7(WT)). Mice bearing an MCF-7(DOX) tumor on one flank and an MCF-7(WT) tumor on the other flank were used to assess the in vivo efficacy. Furthermore, the responses to STX140 of three xenografts, derived from drug-resistant patients, were assessed.

RESULTS

In this study, STX140 caused cell cycle arrest, cyclin B1 induction, and subsequent apoptosis of both MCF-7(DOX) and MCF-7(WT) cells. Taxol and 2-MeOE2 were only active in the MCF-7(WT) parental cell line. Although both STX140 and Taxol inhibited the growth of xenografts derived from MCF-7(WT) cells, only STX140 inhibited the growth of tumors derived from MCF-7(DOX) cells. 2-MeOE2 was ineffective at the dose tested against both tumor types. Two out of the three newly derived docetaxel-resistant xenografts, including a metastatic triple-negative tumor, responded to STX140 but not to docetaxel treatment.

CONCLUSIONS

STX140 shows excellent efficacy in both MCF-7(WT) and MCF-7(DOX) breast cancer xenograft models, in contrast to Taxol and 2-MeOE2. The clinical potential of STX140 was further highlighted by the efficacy seen in xenografts recently derived from patients who had failed on taxane therapy.

Rhabdastrellic acid-A inhibited PI3K/Akt pathway and induced apoptosis in human leukemia HL-60 cells

Increasing evidence suggests that aberrant activation of PI3K/Akt is involved in many human cancers, and that inhibition of the PI3K/Akt pathway might be a promising strategy for cancer treatment. Our investigation indicates that Rhabdastrellic acid-A, an isomalabaricane triterpenoid isolated from the sponge, Rhabdastrella globostellata, inhibits proliferation of HL-60 cells with an IC(50) value of 0.68mug/ml, and induces apoptosis. Rhabdastrellic acid-A also induces cleavage of the death substrate poly (ADP-ribose) polymerase (PARP) and caspase-3. Pretreatment of HL-60 cells with the caspase-3 specific inhibitor, DEVD-CHO, prevents Rhabdastrellic acid-A-induced DNA fragmentation and PARP cleavage. Activated PI3K and Akt significantly decreases after treatment with Rhabdastrellic acid-A in HL-60 cells. Expression levels of protein bcl-2, bax remain unchanged in response to Rhabdastrellic acid-A treatment in HL-60 cells. These results suggest that Rhabdastrellic acid-A inhibits PI3K/Akt pathway and induces caspase-3 dependent-apoptosis in HL-60 human leukemia cells.

Exploring the specificity of the PI3K family inhibitor LY294002

The PI3Ks (phosphatidylinositol 3-kinases) regulate cellular signalling networks that are involved in processes linked to the survival, growth, proliferation, metabolism and specialized differentiated functions of cells. The subversion of this network is common in cancer and has also been linked to disorders of inflammation. The elucidation of the physiological function of PI3K has come from pharmacological studies, which use the enzyme inhibitors Wortmannin and LY294002, and from PI3K genetic knockout models of the effects of loss of PI3K function. Several reports have shown that LY294002 is not exclusively selective for the PI3Ks, and could in fact act on other lipid kinases and additional apparently unrelated proteins. Since this inhibitor still remains a drug of choice in numerous PI3K studies (over 500 in the last year), it is important to establish the precise specificity of this compound. We report here the use of a chemical proteomic strategy in which an analogue of LY294002, PI828, was immobilized onto epoxy-activated Sepharose beads. This affinity material was then used as a bait to fish-out potential protein targets from cellular extracts. Proteins with high affinity for immobilized PI828 were separated by one-dimensional gel electrophoresis and identified by liquid chromatography-tandem MS. The present study reveals that LY294002 not only binds to class I PI3Ks and other PI3K-related kinases, but also to novel targets seemingly unrelated to the PI3K family.

Anti-Cripto Mab inhibit tumour growth and overcome MDR in a human leukaemia MDR cell line by inhibition of Akt and activation of JNK/SAPK and bad death pathways

Doxorubicin (DOX) selection of CCRF-CEM leukaemia cell line resulted in multidrug resistance (MDR) CEM/A7R cell line, which overexpresses MDR, 1 coded P-glycoprotein (Pgp). Here, we report for the first time that oncoprotein Cripto, a founding member of epidermal growth factor-Cripto-FRL, 1-Criptic family is overexpressed in the CEM/A7R cells, and anti-Cripto monoclonal antibodies (Mab) inhibited CEM/A7R cell growth both in vitro and in an established xenograft tumour in severe combined immunodeficiency mice. Cripto Mab synergistically enhanced sensitivity of the MDR cells to Pgp substrates epirubicin (EPI), daunorubicin (DAU) and non-Pgp substrates nucleoside analogue cytosine arabinoside (AraC). In particular, the combination of anti-Cripto Mab at less than 50% of inhibition concentrations with noncytotoxic concentrations of EPI or DAU inhibited more than 90% of CEM/A7R cell growth. Cripto Mab slightly inhibited Pgp expression, and had little effect on Pgp function, indicating that a mechanism independent of Pgp was involved in overcoming MDR. We demonstrated that anti-Cripto Mab-induced CEM/A7R cell apoptosis, which was associated with an enhanced activity of the c-Jun N-terminal kinase/stress-activated protein kinase and inhibition of Akt phosphorylation, resulting in an activation of mitochondrial apoptosis pathway as evidenced by dephosphorylation of Bad at Ser136, Bcl-2 at Ser70 and a cleaved caspase-9.

Multidrug resistance-associated protein 1 expression is under the control of the phosphoinositide 3 kinase/Akt signal transduction network in human acute myelogenous leukemia blasts

A high incidence of relapses following induction chemotherapy is a major hindrance to patient survival in acute myelogenous leukemia (AML). There is strong evidence that activation of the phosphoinositide 3 kinase (PI3K)/Akt signaling network plays a significant role in rendering AML blasts drug resistant. An important mechanism underlying drug resistance is represented by overexpression of membrane drug transporters such as multidrug resistance-associated protein 1 (MRP1) or 170-kDa P-glycoprotein (P-gp). Here, we present evidence that MRP1, but not P-gp, expression is under the control of the PI3K/Akt axis in AML blasts. We observed a highly significant correlation between levels of phosphorylated Akt and MRP1 expression in AML cells. Furthermore, incubation of AML blasts with wortmannin, a PI3K pharmacological inhibitor, resulted in lower levels of phosphorylated Akt, downregulated MRP1 expression, and decreased Rhodamine 123 extrusion in an in vitro functional dye efflux assay. We also demonstrate that wortmannin-dependent PI3K/Akt inhibition upregulated p53 protein levels in most AML cases, and this correlated with diminished MRP1 expression and enhanced phosphorylation of murine double minute 2 (MDM2). Taken together, these data suggest that PI3K/Akt activation may lead to the development of chemoresistance in AML blasts through a mechanism involving a p53-dependent suppression of MRP1 expression.

The role of multidrug resistance efflux transporters in antifolate resistance and folate homeostasis

Members of the ATP-binding cassette (ABC) transporters including P-glycoprotein (Pgp/ABCB1), multidrug resistance proteins (MRPs/ABCC) as well as breast cancer resistance protein (BCRP/ABCG2) function as ATP-dependent drug efflux transporters, which form a unique defense network against multiple chemotherapeutic drugs and cellular toxins. Among antitumor agents is the important group of folic acid antimetabolites known as antifolates. Antifolates such as methotrexate (MTX), pemetrexed and raltitrexed exert their cytotoxic activity via potent inhibition of folate-dependent enzymes essential for purine and pyrimidine nucleotide biosynthesis and thereby block DNA replication. Overexpression of MRPs and BCRP confers resistance upon malignant cells to various hydrophilic and lipophilic antifolates. Apart from their central role in mediating resistance to antifolates and other anticancer drugs, MRPs and BCRP have been recently shown to transport naturally occurring reduced folates. This was inferred from various complementary systems as follows: (a) Cell-free systems including ATP-dependent uptake of radiolabeled folate/MTX into purified inside-out membrane vesicles from stable transfectants and/or cells overexpressing these transporters, (b) Decreased accumulation of radiolabeled folate/MTX in cultured tumor cells overexpressing these transporters, as well as (c) In vivo rodent models such as Eisi hyperbillirubinemic rats (EHBR) that hereditarily lack MRP2 in their canalicular membrane and thereby display a bile that is highly deficient in various reduced folate cofactors and MTX, when compared with wild type Sprague-Dawley (SD) rats. In all cases, these folate/antifolate transporters functioned as high capacity, low affinity ATP-driven exporters. While the mechanism of cellular retention of (anti)folates is mediated via (anti)folylpolyglutamylation, certain efflux transporters including MRP5 (ABCC5) and BCRP were shown to transport both mono-, di- as well as triglutamate derivatives of MTX and folic acid. Furthermore, overexpression of MRPs and BCRP has been shown to result in decreased cellular folate pools, whereas loss of ABC transporter expression brought about a significant expansion in the intracellular reduced folate pool. The latter finding has important implications to antifolate-based chemotherapy as an augmented cellular folate pool results in a significant level of resistance to certain antifolates. Hence, the aims of the present review are: (a) To summarize and discuss the cumulative evidence supporting a functional role for various multidrug resistance efflux transporters of the ABC superfamily which mediate resistance to hydrophilic and lipophilic antifolates, (b) To describe and evaluate the recent data suggesting a role for these efflux transporters in regulation of cellular folate homeostasis under folate replete and deplete conditions. Furthermore, novel developments and future perspectives regarding the identification of novel antifolate target proteins and mechanisms of action, as well as rationally designed emerging drug combinations containing antifolates along with receptor tyrosine kinase inhibitors are being discussed.

LY294,002, a specific inhibitor of PI3K/Akt kinase pathway, antagonizes P-glycoprotein-mediated multidrug resistance

The transmembrane transport pump P-glycoprotein (P-gp) causes the efflux of chemotherapeutic agents from cells and is an important system that secures multidrug resistance (MDR) of neoplastic cells. In the present study drug sensitive L1210 and multidrug resistant L1210/VCR mouse leukemic cell lines were used as an experimental model. We found that LY 294,002, a specific inhibitor of PI3K/Akt kinase pathway, reduced the degree of vincristine resistance in L1210/VCR cells significantly and in a concentration-dependent manner. This was accompanied by decrease in IC(50) value to vincristine from 3.195+/-0.447 to 1.898+/-0.676 micromol/l for 2 micromol/l, to 0.947+/-0.419 micromol/l for 4 micromol/l, and to 0.478+/-0.202 micromol/l for 8 micromol/l LY294,002. The IC(50) value of sensitive cells for vincristine was about 0.010 micromol/l. FACS analysis of the proportion of cells in apoptosis or necrosis by annexin-V apoptosis kit showed the following: (i) vincristine-induced apoptosis in resistant cell to a much lower extent than in sensitive cells; (ii) LY294,002 alone did not induce apoptosis or necrosis in both sensitive and resistant cells; (iii) LY294,002 applied together with vincristine significantly increased the number of apoptotic cells. Transport activity of P-gp in resistant cells was monitored using calcein/AM as substrate and was depressed by LY294,002 in a concentration dependent manner. Significant differences in calcein retention were not observed when cells were preincubated with LY294,002 at different times from 0.5 to 24h. Sensitive and resistant cells contain similar amounts of uncleaved (i.e., unactivated) caspase-3 but in latter cells the activation of caspase-3 by proteolytic cleavage was decreased. The reversal of vincristine resistance by LY294,002 was associated with marked activation of caspase-3. Western blot analysis revealed that the development of MDR phenotype in L1210/VCR cells was also associated with increased level of Bcl-2 protein. All the above findings point to the possible involvement of PI3K/Akt kinase pathway in modulation of P-gp mediated multidrug resistance in L1210/VCR mouse leukemic cell line. MDR reversal effect of LY294,002 is accompanied with this compound's influence on vincristine-induced apoptosis.

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Flunarizine induces Nrf2-mediated transcriptional activation of heme oxygenase-1 in protection of auditory cells from cisplatin

We investigated the cytoprotective mechanisms of flunarizine in cisplatin-induced death of auditory cells. Concomitant with an increase in viability, treatment with flunarizine resulted in a marked dissociation of Nrf2/Keap1 and subsequent intranuclear translocation of Nrf2, which was mediated by PI3K-Akt signaling. Overexpression of Nrf2 protected cells from cisplatin along with transcriptional activation of ARE to generate heme oxygenase-1 (HO-1). Pretreatment with flunarizine predominantly increased the transcriptional activity of HO-1 among Nrf2-driven transcripts, including HO-1, NQO1, GCLC, GCLM, GST micro-1, and GSTA4. Furthermore, both pharmacological inhibition and siRNA transfection of HO-1 completely abolished the flunarizine-mediated protection of HEI-OC1 cells and the primary rat (P2) organ of Corti explants from cisplatin. These results suggest that Nrf2-driven transcriptional activation of ARE through PI3K-Akt signaling augments the generation of HO-1, which may be a critically important determinant in cellular response toward cisplatin and the cytoprotective effect of flunarizine against cisplatin.