Sensitivity of myeloid leukemia cells to calcium influx blockade: application to bone marrow purging

Nutrient-sensitizing drug repurposing screen identifies lomerizine as a mitochondrial metabolism inhibitor of chronic myeloid leukemia

In chronic myeloid leukemia (CML), the persistence of leukemic stem cells (LSCs) after treatment with tyrosine kinase inhibitors (TKIs), such as imatinib, can lead to disease relapse. It is known that therapy-resistant LSCs rely on oxidative phosphorylation (OXPHOS) for their survival and that targeting mitochondrial respiration sensitizes CML LSCs to imatinib treatment. However, current OXPHOS inhibitors have demonstrated limited efficacy or have shown adverse effects in clinical trials, highlighting that identification of clinically safe oxidative pathway inhibitors is warranted. We performed a high-throughput drug repurposing screen designed to identify mitochondrial metabolism inhibitors in myeloid leukemia cells. This identified lomerizine, a US Food and Drug Administration (FDA)-approved voltage-gated Ca2+ channel blocker now used for the treatment of migraines, as one of the top hits. Transcriptome analysis revealed increased expression of voltage-gated CACNA1D and receptor-activated TRPC6 Ca2+ channels in CML LSCs (CD34+CD38-) compared with normal counterparts. This correlated with increased endoplasmic reticulum (ER) mass and increased ER and mitochondrial Ca2+ content in CML stem/progenitor cells. We demonstrate that lomerizine-mediated inhibition of Ca2+ uptake leads to ER and mitochondrial Ca2+ depletion, with similar effects seen after CACNA1D and TRPC6 knockdown. Through stable isotope-assisted metabolomics and functional assays, we observe that lomerizine treatment inhibits mitochondrial isocitrate dehydrogenase activity and mitochondrial oxidative metabolism and selectively sensitizes CML LSCs to imatinib treatment. In addition, combination treatment with imatinib and lomerizine reduced CML tumor burden, targeted CML LSCs, and extended survival in xenotransplantation model of human CML, suggesting this as a potential therapeutic strategy to prevent disease relapse in patients.

Dissecting exosome inhibitors: therapeutic insights into small-molecule chemicals against cancer

Intensive research in the field of cancer biology has revealed unique methods of communication between cells through extracellular vesicles called exosomes. Exosomes are released from a broad spectrum of cell types and serve as functional mediators under physiological or pathological conditions. Hence, blocking the release of exosome bio carriers may prove useful for slowing the progression of certain types of cancers. Therefore, efforts are being made to develop exosome inhibitors to be used both as research tools and as therapies in clinical trials. Thus, studies on exosomes may lead to a breakthrough in cancer research, for which new clinical targets for different types of cancers are urgently needed. In this review, we briefly outline exosome inhibitors and discuss their modes of action and potential for use as therapeutic tools for cancer.

Targeting CAMKK2 and SOC Channels as a Novel Therapeutic Approach for Sensitizing Acute Promyelocytic Leukemia Cells to All-Trans Retinoic Acid

Calcium ions (Ca²⁺) play important and diverse roles in the regulation of autophagy, cell death and differentiation. Here, we investigated the impact of Ca²⁺ in regulating acute promyelocytic leukemia (APL) cell fate in response to the anti-cancer agent all-trans retinoic acid (ATRA). We observed that ATRA promotes calcium entry through store-operated calcium (SOC) channels into acute promyelocytic leukemia (APL) cells. This response is associated with changes in the expression profiles of ORAI1 and STIM1, two proteins involved in SOC channels activation, as well as with a significant upregulation of several key proteins associated to calcium signaling. Moreover, ATRA treatment of APL cells led to a significant activation of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) and its downstream effector AMP-activated protein kinase (AMPK), linking Ca²⁺ signaling to autophagy. Pharmacological inhibition of SOC channels and CAMKK2 enhanced ATRA-induced cell differentiation and death. Altogether, our results unravel an ATRA-elicited signaling pathway that involves SOC channels/CAMKK2 activation, induction of autophagy, inhibition of cellular differentiation and suppression of cell death. We suggest that SOC channels and CAMKK2 may constitute novel drug targets for potentiating the anti-cancer effect of ATRA in APL patients.

Advances in the discovery of exosome inhibitors in cancer

Exosomes are small membrane vesicles released by most eukaryotic cells. They are considered to play an essential role in cell-to-cell communication, and It is also found that they serve as functional mediators in many severe diseases, including progression of various types of cancers. Inhibition of exosome release may slow the progression of some cancers; thus, exosome has been an attractive target for cancer treatment. Over the years, considerable efforts have been made to discover novel, highly potent and excellently selective exosome inhibitors. Most of these inhibitors are derived from synthetic compounds, some of which are currently existed drugs and found to have the potential to inhibit exosome release. In this review, we briefly discussed the development of exosome inhibitors that are currently discovered and provided guidance for the future development of inhibitors.

Ca2+ as a therapeutic target in cancer

Ca2+ is a ubiquitous and dynamic second messenger molecule that is induced by many factors including receptor activation, environmental factors, and voltage, leading to pleiotropic effects on cell function including changes in migration, metabolism and transcription. As such, it is not surprising that aberrant regulation of Ca2+ signals can lead to pathological phenotypes, including cancer progression. However, given the highly context-specific nature of Ca2+-dependent changes in cell function, delineation of its role in cancer has been a challenge. Herein, we discuss the distinct roles of Ca2+ signaling within and between each type of cancer, including consideration of the potential of therapeutic strategies targeting these signaling pathways.

Identification of a five-mRNA signature as a novel potential prognostic biomarker in pediatric Wilms tumor

Background

The aim of this study was to generate a prognostic model to predict survival outcome in pediatric Wilms tumor (WT).

Methods

The data including mRNA expression and clinical information of pediatric WT patients were downloaded from the Therapeutically Available Research to Generate Effective Treatments (TARGET) database. The differentially expressed genes were identified and a prognostic signature of pediatric WT was generated according to the results of univariate and multivariate Cox analysis. Receiver operating characteristic (ROC) curve was used to evaluate the five‐mRNA signature in pediatric Wilms tumor patients. Bootstrap test with 500 times was used to perform the internal validation.

Results

We identified 6,964 differentially expressed mRNAs associated with pediatric WT, including 3,190 downregulated mRNAs and 3,774 up‐regulated mRNAs. Univariate and multivariate Cox analysis identified five mRNAs (SPRY1, SPIN4, MAP7D3, C10orf71, and SPAG11A) to establish a predictive model. The risk score formula is as follows: Risk score = 0.3036*SPIN4 + 0.8576*MAP7D3 −0.1548*C10orf71 −0.7335*SPRY1 −0.2654*SPAG11A. The pediatric WT patients were divided into low‐risk group and high‐risk group based on the median risk score (value = 1.1503). The receiver operating characteristic (ROC) curve analysis revealed good performance of the 5‐mRNA prognostic model (the area under the curve [AUC] was 0.821). Bootstrap test (Bootstrap resampling times = 500) was used to perform the internal validation and revealed that the AUC was 0.822. REACTOME, KEGG, and BIOCARTA pathway analyses demonstrated that these survival‐related genes were mainly enriched in ErbB2 and ErbB3 signaling pathways, and calcium signaling pathway.

Conclusion

The five‐mRNA signature can predict the prognosis of patients with pediatric WT. It has significant implication in the understanding of therapeutic targets for pediatric WT patients. However, further study is needed to validate this five‐mRNA signature and uncover more novel diagnostic or prognostic mRNAs candidates in pediatric WT patients.

Inhibition of exosome release by ketotifen enhances sensitivity of cancer cells to doxorubicin

Exosomes released from cancer cells support metastasis and growth of recipient cells and increase their resistance to chemotherapy. Therapeutic targeting of exosomes is a promising area in cancer research. Our aim is to test the effect of the mast cell stabilizer ketotifen on exosomes release from cancer cells and how this can modify their response to doxorubicin. Exosomes release from three cancer cell lines (MCF7, HeLa and BT549) was assessed by scan electron microscope and exosomes quantification kit. Doxorubicin export within exosomes was monitored flurometrically and cellular sensitivity to doxorubicin ± ketotifen was measured by sulphorhodamine-B and colony formation assays. The three cell lines release different amounts of exosomes with the highest quantity released from BT549 followed by MCF7 and then HeLa. Ketotifen (10 µmol L^-1) reduced exosomes release in all three cell lines with different efficiency (HeLa>MCF7>BT549). Doxorubicin export via exosomes was highest in BT549, lower in HeLa and lowest in MCF7 cells. Pretreatment with ketotifen sensitized the cells to doxorubicin (HeLa>MCF7>BT549) with a sensitization factor of 27, 8 and 1.25 respectively. Increased sensitivity of cells to doxorubicin by ketotifen was proportional to its effect on exosomes release. Our data is the first report of ketotifen modulating exosomes release from cancer cells and opens the avenue for exosomes-targeting cancer therapy. The differential effects of ketotifen on doxorubicin exosomal export in the cell lines studied, suggests an opportunity of pharmacological enhancement of doxorubicin anti-tumor activity in some but not all cancer types.

Econazole induces increases in free intracellular Ca2+ concentrations in human osteosarcoma cells

Econazole is an antifungal drug with different in vitro effects. However, econazole's effect on osteoblast like cells is unknown. In human MG63 osteosarcoma cells, the effect of econazole on intracellular Ca2+ concentrations ([Ca2+]i) was explored by using fura-2. At a concentration of 0.1 μM, econazole started to cause a rise in [Ca2+]i in a concentration-dependent manner. Econazole-induced [Ca2+]i rise was reduced by 74% by removal of extracellular Ca2+. The econazole-induced Ca2+ influx was mediated via a nimodipine-sensitive pathway. In Ca2+ free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+ ATPase, caused a [Ca2+]i rise, after which the increasing effect of econazole on [Ca2+]i was abolished. Pretreatment of cells with econazole to deplete Ca2+ stores totally prevented thapsigargin from releasing Ca2+. U73122, an inhibitor of phospholipase C, abolished histamine (an inositol 1,4,5-trisphosphate dependent Ca2+ mobilizer)-induced, but not econazoleinduced, [Ca2+]i rise. Econazole inhibited 76% of thapsigargin-induced store-operated Ca2+ entry. These findings suggest that in MG63 osteosarcoma cells, econazole increases [Ca2+]i by stimulating Ca2+ influx and Ca2+ release from the endoplasmic reticulum via a phospholipase C-independent manner. In contrast, econazole acts as a potent blocker of store-operated Ca2+ entry.

Potentiation of the store-operated calcium entry (SOCE) induces phytohemagglutinin-activated Jurkat T cell apoptosis

Store-operated Ca(2+) entry (SOCE) is the main Ca(2+) entry pathway of non-excitable cells. In the past decade, the activation of this entry has been unveiled, with STIM1, a protein of the endoplasmic reticulum able to sense the intraluminal Ca(2+) content, and Orai1, the pore-forming unit of the Ca(2+) release activated Ca(2+) (CRAC) channels. When Ca(2+) ions are released from the endoplasmic reticulum, STIM1 proteins oligomerize and directly interact with Orai1 proteins, allowing the opening of the CRAC channels and a massive Ca(2+) ion influx known as SOCE. As Ca(2+) is involved in various cellular processes, the discovery of new drugs acting on the SOCE should be of interest to control the cell activity. By testing analogs of 2-aminoethyl diphenylborinate (2-APB), a well known, though not so selective effector of the SOCE, we identified methoxy diethylborinate (MDEB), a molecule able to potentiate the SOCE in three leukocyte and two breast cancer cell lines by increasing the Ca(2+) influx amplitude. Unlike 2-APB, MDEB does not affect the Ca(2+) pumps or the Ca(2+) release from the endoplasmic reticulum. MDEB could therefore represent the first member of a new group of molecules, specifically able to potentiate SOCE. Although not toxic for non-activated Jurkat T cells, it could induce the apoptosis of phytohemagglutinin-stimulated cells.

Novel Suppressive Effects of Ketotifen on Migration and Invasion of MDA-MB-231 and HT-1080 Cancer Cells

The high mortality rates associated with cancer reflect the metastatic spread of tumor cells from the site of their origin. Metastasis, in fact, is the cause of 90% of cancer deaths. Therefore, considerable effort is being made to inhibit metastasis. In the present study, we screened ketotifen for anti-migratory and anti-invasive activities against MDA-MB-231 breast cancer and HT-1080 fibrosarcoma cancer cells. Cancer cell migration and invasion were measured using multi-well chambers. Additionally, western blots were used to examine the effects of ketotifen on the expressions of CDC42, Rho, Rac, and matrix metalloproteinase 9 (MMP-9). The results showed that ketotifen dose-dependently suppressed the migration and invasion of MDA-MB-231 and HT-1080 cells. Ketotifen also suppressed the expressions of CDC42, Rac, and Rho, which, significantly, are involved in MDA-MB-231 and HT-1080 cancer cell migration. Moreover, ketotifen suppressed the expression and activity of MMP-9, which is involved in degradation of the extracellular matrix leading to invasion. The overall data suggested that ketotifen suppresses the migration and invasion of MDA-MB-231 and HT-1080 cancer cells via inhibition of CDC42, Rac, Rho, and MMP-9 expression.

Store-operated Ca2+ entry is remodelled and controls in vitro angiogenesis in endothelial progenitor cells isolated from tumoral patients

BACKGROUND

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain tumor vascularisation and promote the metastatic switch. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca(2+) entry (SOCE), which is activated by a depletion of the intracellular Ca(2+) pool, regulates the growth of human EPCs, where is mediated by the interaction between the endoplasmic reticulum Ca(2+)-sensor, Stim1, and the plasmalemmal Ca(2+) channel, Orai1. As oncogenesis may be associated to the capability of tumor cells to grow independently on Ca(2+) influx, it is important to assess whether SOCE regulates EPC-dependent angiogenesis also in tumor patients.

METHODOLOGY/PRINCIPAL FINDINGS

The present study employed Ca(2+) imaging, recombinant sub-membranal and mitochondrial aequorin, real-time polymerase chain reaction, gene silencing techniques and western blot analysis to investigate the expression and the role of SOCE in EPCs isolated from peripheral blood of patients affected by renal cellular carcinoma (RCC; RCC-EPCs) as compared to control EPCs (N-EPCs). SOCE, activated by either pharmacological (i.e. cyclopiazonic acid) or physiological (i.e. ATP) stimulation, was significantly higher in RCC-EPCs and was selectively sensitive to BTP-2, and to the trivalent cations, La(3+) and Gd(3+). Furthermore, 2-APB enhanced thapsigargin-evoked SOCE at low concentrations, whereas higher doses caused SOCE inhibition. Conversely, the anti-angiogenic drug, carboxyamidotriazole (CAI), blocked both SOCE and the intracellular Ca(2+) release. SOCE was associated to the over-expression of Orai1, Stim1, and transient receptor potential channel 1 (TRPC1) at both mRNA and protein level The intracellular Ca(2+) buffer, BAPTA, BTP-2, and CAI inhibited RCC-EPC proliferation and tubulogenesis. The genetic suppression of Stim1, Orai1, and TRPC1 blocked CPA-evoked SOCE in RCC-EPCs.

CONCLUSIONS

SOCE is remodelled in EPCs from RCC patients and stands out as a novel molecular target to interfere with RCC vascularisation due to its ability to control proliferation and tubulogenesis.

Elevated calpain activity in acute myelogenous leukemia correlates with decreased calpastatin expression

Calpains are intracellular cysteine proteases that have crucial roles in many physiological and pathological processes. Elevated calpain activity has been associated with many pathological states. Calpain inhibition can be protective or lethal depending on the context. Previous work has shown that c-myc transformation regulates calpain activity by suppressing calpastatin, the endogenous negative regulator of calpain. Here, we have investigated calpain activity in primary acute myelogenous leukemia (AML) blast cells. Calpain activity was heterogeneous and greatly elevated over a wide range in AML blast cells, with no correlation to FAB classification. Activity was particularly elevated in the CD34+CD38− enriched fraction compared with the CD34+CD38+ fraction. Treatment of the cells with the specific calpain inhibitor, PD150606, induced significant apoptosis in AML blast cells but not in normal equivalent cells. Sensitivity to calpain inhibition correlated with calpain activity and preferentially targeted CD34+CD38− cells. There was no correlation between calpain activity and p-ERK levels, suggesting the ras pathway may not be a major contributor to calpain activity in AML. A significant negative correlation existed between calpain activity and calpastatin, suggesting calpastatin is the major regulator of activity in these cells. Analysis of previously published microarray data from a variety of AML patients demonstrated a significant negative correlation between calpastatin and c-myc expression. Patients who achieved a complete remission had significantly lower calpain activity than those who had no response to treatment. Taken together, these results demonstrate elevated calpain activity in AML, anti-leukemic activity of calpain inhibition and prognostic potential of calpain activity measurement.

Inhibition of bone resorption by econazole in rat osteoclast-like cells through suppressing TRPV5

Osteoclasts are primary bone resorption cells and intervention in osteoclast activation is considered an effective therapeutic approach to treatment of bone diseases involving osteoclasts. TRPV5 was detected in osteoclasts and it has been thought to take part in the transportation of the degraded calcium in the resorption lacuna, which is essential for bone resorption. The aim of the present study was to examine the effects of a modulator of calcium dynamics, econazole, on the expression of TRPV5 and bone resorption activity in rat osteoclast-like cells (OLCs). OLCs were obtained by co-culturing rat bone marrow cells with osteoblasts and then culturing with different concentrations of econazole (0.01, 0.1, 1.0, 10.0 μmol/L). Cell counting and staining protocols were used to determine whether econazole influenced the survival of OLCs. Expression of TRPV5 in response to econazole treatment was assessed by western blotting. Bone resorption activity of OLCs was determined by measuring the resorption area of dentin slices with a microscope and a digital image analysis system. Additionally, Ca(2+) inside OLCs was tested. We found that econazole inhibited expression of TRPV5 in a dose dependent manner while it had no influence on the survival of OLCs and it therefore inhibited bone resorption activity in rat OLCs. Ca(2+) inside OLCs increased, suggesting a limited compensatory mechanism to make up for inhibition of TRPV5 effects.

WT1/EGR1-mediated control of STIM1 expression and function in cancer cells

There have been numerous publications linking Ca(2+) signaling and cancer, however, a clear explanation for this link has remained elusive. We recently identified the oncogenes/tumor suppressors Wilms Tumor Suppressor 1 (WT1) and Early Growth Response 1 (EGR1) as regulators of the expression of STIM1, an essential regulator of Ca(2+) entry in non-excitable cells. The current review focuses on the literature defining both differential Ca(2+) signaling and WT1/EGR1 expression patterns in 6 specific cancer subtypes: Acute Myeloid Leukemia, Wilms Tumor, breast cancer, ovarian cancer, glioblastoma and prostate cancer. For each tumor-type, we have assessed how specific changes in WT1 and EGR1 expression might contribute to aberrant Ca(2+) homeostasis as well as the therapeutic potential of these observations.

Oleic acid versus linoleic and α-linolenic acid. different effects on Ca2+ signaling in rat thymocytes

BACKGROUND

Oleic acid is the principal fatty acid of olive oil composition and is reported to play a crucial role in its healthy aspects. However, the detailed mechanism of action is poorly understood.

AIMS

This study aims to elucidate the role of oleic acid in calcium signaling in rat thymocytes, in comparison to linoleic and linolenic acid.

METHODS

Fatty acids were applied to thymocytes isolated from wistar rats and loaded with Fura-2 to measure calcium signals.

RESULTS

The main results showed a concentration-dependent increase in [Ca(2+)](i) induced by the 3 fatty acids. Raising the number of unsaturations resulted in greater increases. Two different pathways contributed to the increase induced by the polyunsaturated fatty acids: an IP(3)- independent release from the thapsigargin-sensitive stores and an extracellular calcium entry by econazole and nifedipine-insensitive channels. However, the OA-induced increases in [Ca(2+)](i) seemed to be due mostly to the Ca(2+) recruited from the intracellular stores.

CONCLUSION

This study demonstrates that the fatty acids tested induce increases in [Ca(2+)](i) in rat thymocytes, with differences in close relation to the degree of unsaturation. Such differences could be responsible for their different physiological action.

ABC50 modulates sensitivity of HL60 leukemic cells to endoplasmic reticulum (ER) stress-induced cell death

ABC50 (aka ABCF1) is a member of the ATP Binding Cassette protein family. ABC50 stimulates complex formation between eIF2, GTP and Met-tRNA implicating it in translation initiation. Econazole (Ec) is an imidazole anti-fungal that induces endoplasmic reticulum (ER) stress in mammalian cells by promoting ER Ca(2+) depletion and sustained protein synthesis inhibition. HL60 cells selected for Ec resistance were found to exhibit a multi-drug resistance phenotype associated specifically with ER stress. Differential Display was used to identify ABC50 as an overexpressed gene in resistant cells. ABC50 knockdown (KD) in Ec-resistant HL60 cells partially restored Ec sensitivity. In parental HL60 cells, ABC50 KD increased sensitivity to Ec, thapsigargin and tunicamycin but not to serum withdrawal or etoposide. ABC50 overexpression (OE) partially and specifically decreased sensitivity to ER stress agents. ABC50 KD or OE had no effect on ROS generation by Ec, ER Ca(2+) stores or thapsigargin-stimulated influx. Increased eIF2α phosphorylation in response to ER stress was observed in the KD cells while decreased phosphorylation was observed in the OE cells. Ribosomal content was reduced in ABC50 KD cells and increased in OE cells. Knockdown suppressed protein synthesis while OE increased it. Protein synthesis was sustained in ABC50 OE cells exposed to Ec. ABC50 OE promoted ER stress resistance and increased antibody production in the hybridoma GK1.5 suggesting it may be useful for the overproduction of specific proteins. Taken together, these results indicate that ABC50 modulates sensitivity to Ec and other ER stress agents primarily through its effects on protein synthesis.

Transcriptional mechanisms regulating Ca(2+) homeostasis

Ca(2+) is a dynamic cellular secondary messenger which mediates a vast array of cellular responses. Control over these processes is achieved via an extensive combination of pumps and channels which regulate the concentration of Ca(2+) within not only the cytosol but also all intracellular compartments. Precisely how these pumps and channels are regulated is only partially understood, however, recent investigations have identified members of the Early Growth Response (EGR) family of zinc finger transcription factors as critical players in this process. The roles of several other transcription factors in control of Ca(2+) homeostasis have also been demonstrated, including Wilms Tumor Suppressor 1 (WT1), Nuclear Factor of Activated T cells (NFAT) and c-myc. In this review, we will discuss not only how these transcription factors regulate the expression of the major proteins involved in control of Ca(2+) homeostasis, but also how this transcriptional remodeling of Ca(2+) homeostasis affects Ca(2+) dynamics and cellular responses.

Wilms tumor suppressor 1 (WT1) and early growth response 1 (EGR1) are regulators of STIM1 expression

Store-operated calcium entry (SOCE) is a key evolutionarily conserved process whereby decreases in endoplasmic reticulum Ca(2+) content lead to the influx of Ca(2+) across the plasma membrane. How this process is regulated in specific tumor cell types is poorly understood. In an effort to address this concern, we obtained and tested primary Wilms tumor cells, finding no detectable SOCE in this cell type. Analysis of the expression levels of STIM1 and ORAI1 (the molecular mediators of SOC) revealed poor STIM1 expression. Analysis of the STIM1 promoter using the TESS search system (University of Pennsylvania) revealed four putative response elements to the zinc-finger proteins WT1 (Wilms tumor suppressor 1) and EGR1 (early growth response 1). Either overexpression of WT1 or knockdown of EGR1 resulted in loss of STIM1 expression and a resultant decrease in SOCE. Furthermore, examination of Egr1 knock-out animals revealed loss of STIM1 expression in multiple tissues. Finally, using chromatin immunoprecipitation, we reveal direct binding of both WT1 and EGR1 to putative response elements located within 500 bp of the transcriptional start site of STIM1. Considering that WT1 and EGR1 are well described oncogenes and tumor suppressors, these observations may reveal new mechanisms responsible for distinct Ca(2+) signals in cancer cells.

Mitochondrial regulation by c-Myc and hypoxia-inducible factor-1 alpha controls sensitivity to econazole

Econazole is an azole antifungal with anticancer activity that blocks Ca(2+) influx and stimulates endoplasmic reticulum (ER) Ca(2+) release through the generation of mitochondrial reactive oxygen species (ROS), resulting in sustained depletion of ER Ca(2+) stores, protein synthesis inhibition, and cell death. c-Myc, a commonly activated oncogene, also promotes apoptosis in response to growth factor withdrawal and a variety of chemotherapeutic agents. We have investigated the role of c-myc in regulating sensitivity to econazole. Here, we show that c-myc-negative cells are profoundly resistant to econazole. c-Myc-negative rat fibroblasts failed to generate mitochondrial ROS in response to econazole and consequently failed to deplete the ER of Ca(2+). HL60 cells knocked down for c-myc expression also displayed decreased ROS generation and decreased econazole sensitivity. Addition of H(2)O(2) restored sensitivity to econazole in both c-myc-negative rat fibroblasts and c-myc knocked-down HL60 cells, supporting a role for ROS in cell death induction. c-Myc-negative cells and HL60 cells knocked down for c-myc have reduced mitochondrial content compared with c-myc-positive cells. The hypoxia sensor, hypoxia-inducible factor-1alpha (HIF-1alpha), interacts antagonistically with c-myc and also regulates mitochondrial biogenesis. Knockdown of HIF-1alpha in c-myc-negative cells increased mitochondrial content restored ROS generation in response to econazole and increased sensitivity to the drug. Taken together, these results show that c-myc and HIF-1alpha regulate sensitivity to econazole by modulating the ability of the drug to generate mitochondrial ROS.

Effects of carboxyamidotriazole on in vitro models of imatinib-resistant chronic myeloid leukemia

Although imatinib mesylate (IM) has revolutionized the treatment of chronic myeloid leukemia (CML), some patients develop resistance with progression of leukemia. Alternative or additional targeting of signaling pathways deregulated in bcr-abl-driven CML cells may provide a feasible option for improving clinical response and overcoming resistance. In this study, we show that carboxyamidotriazole (CAI), an orally bioavailable calcium influx and signal transduction inhibitor, is equally effective in inhibiting the proliferation and bcr-abl dependent- and independent-signaling pathways in imatinib-resistant CML cells. CAI inhibits phosphorylation of cellular proteins including STAT5 and CrkL at concentrations that induce apoptosis in IM-resistant CML cells. The combination of imatinib and CAI also down-regulated bcr-abl protein levels. Since CAI is already available for clinical use, these results suggest that it may be an effective addition to the armamentarium of drugs for the treatment of CML.

A parenteral econazole formulation using a novel micelle-to-liposome transfer method: in vitro characterization and tumor growth delay in a breast cancer xenograft model

PURPOSE

The purpose of this study was to develop a parenteral liposomal formulation of econazole, a poorly water-soluble compound not previously available in an intravenous form. We are investigating econazole as an anticancer agent based on its unique mechanism of action to which cancer cells are preferentially sensitive. An intravenous formulation of econazole was desired for preclinical toxicity and efficacy studies of econazole.

METHODS

Liposomal econazole was prepared using a novel micelle exchange technique to incorporate the drug into the lipid bilayer of pre-formed liposomes using a poly(ethylene) glycol-linked phospholipid, distearoyl phosphatidylethanolamine (DSPE-PEG). This method allowed for stable and efficient drug incorporation into DPPC and DMPC liposomes at a final drug:lipid ratio of 0.05 (w/w) and increased solubility in saline from <0.1 to 5 mg/ml.

RESULTS

Stability over 14 days at 4 degrees C in buffer was demonstrated as well as in vitro plasma stability at 37 degrees C. Plasma elimination studies of micelle-loaded liposomal econazole showed a half-life of approximately 35 min and plasma AUC of 281 microg/ml min. In MCF-7 human breast cancer xenografts in Rag2M mice. Liposomal econazole did not induce significant hepatoxicity, renal toxity or weight loss compared to empty liposomes. Tumor growth was slightly delayed in liposomal econazole-treated mice, with approximately 10-day lag time to reach 300 mm(3) compared to vehicle controls.

CONCLUSIONS

The micelle transfer method provided an efficient means of preparing liposomal econazole suitable for intravenous administration. Liposomal econazole was successfully administered to tumor bearing mice at 50 mg/kg, and no significant toxicities attributable to econazole were observed.

A Parenteral Econazole Formulation Using a Novel Micelle-to-Liposome Transfer Method: In Vitro Characterization and Tumor Growth Delay in a Breast Cancer Xenograft Model

PURPOSE

The aim of the study is to develop modified, branched versions of the Noyes-Whitney and the Weibull equations, including explicitly the solubility/dose parameter, for the analysis of dissolution data, which reach the plateau either at infinite or finite time.

METHODS

The modified Weibull function is applied to the analysis of experimental and literature dissolution data. To demonstrate the usefulness of the mathematical models, two model drugs are used: one highly soluble, metoprolol, and one relatively insoluble, ibuprofen.

RESULTS

The models were fitted successfully to the data performing better compared with their classic versions. The advantages of the use of the models presented are several. They fit better to a large range of datasets, especially for fast dissolution curves that reach complete dissolution at a finite time. Also, the modified Weibull presented can be derived from differential equations, and it has a physical meaning as opposed to the purely empirical character of the original Weibull equation. The exponent of the Weibull equation can be attributed to the heterogeneity of the process and can be explained by fractal kinetics concepts. Also, the solubility/dose ratio is present explicitly as a parameter and allows to obtain estimates of the solubility even when the dissolution data do not reach the solubility level.

CONCLUSION

The use of the developed branched equations gives better fittings and specific physical meaning to the dissolution parameters. Also, the findings underline the fact that even in the simplest, first-order case, the speed of the dissolution process depends on the dose, a fact of great importance in biopharmaceutic classification for regulatory purposes.

Inhibition of Ca2+ influx is required for mitochondrial reactive oxygen species-induced endoplasmic reticulum Ca2+ depletion and cell death in leukemia cells

Disturbances of endoplasmic reticulum (ER) Ca2+ homeostasis or protein processing can lead to ER stress-induced cell death. Increasing evidence suggests that oxidative stress (OS) plays an important role in a variety of cell death mechanisms. To investigate the role of OS in ER stress, we measured OS in response to three ER stress agents: econazole (Ec), which stimulates ER Ca2+ release and blocks Ca2+ influx; thapsigargin (Tg), a sarco(endo)plasmic reticulum Ca2+ ATPase inhibitor that releases ER Ca2+ and stimulates Ca2+ influx; and tunicamycin (Tu), a glycosylation inhibitor that causes protein accumulation in the ER. Ec, but not Tg or Tu, caused a rapid increase in OS. Reactive oxygen species (ROS) generation was observed within mitochondria immediately after exposure to Ec. Furthermore, Ec hyperpolarized the mitochondrial membrane and inhibited adenine nucleotide transport in cell-free mitochondria, suggesting a mitochondrial target. Antimycin A, an inhibitor of complex III in electron transport, reversed mitochondrial hyperpolarization, OS generation, ER Ca2+ depletion, and cell death by Ec, suggesting complex III dependence for these effects. Antioxidants butylated hydroxytoluene and N-Acetyl-L-cysteine prevented ER Ca2+ depletion and cell death by Ec. However, inhibition of Ca2+ influx by Ec was unaffected by either antimycin A or the antioxidants, suggesting that this target is distinct from the mitochondrial target of Ec. Atractyloside, an adenine nucleotide transport inhibitor, generated ROS and stimulated ER Ca2+ release, but it did not block Ca2+ influx, deplete the ER or induce cell death. Taken together, these results demonstrate that combined mitochondrial ROS generation and Ca2+ influx blockade by Ec is required for cell death.

Growth, differentiation, and malignant transformation of pre-B cells mediated by inducible activation of v-Abl oncogene

The nonreceptor tyrosine kinase, encoded by the v-Abl oncogene of Abelson murine leukemia virus induces transformation of progenitor B cells. The v-Abl oncogene promotes cell cycle progression and inhibits pre-B cell differentiation. The temperature-sensitive form of Abelson murine leukemia virus offers a reversible model to study the role of v-Abl in regulating growth and differentiation. Inactivation of v-Abl elevates p27 and Foxo3a levels and activates NF-kappaB/Rel, which leads to G1 arrest and induction of Ig L chain gene rearrangement, respectively. In turn, v-Abl reactivation reduces p27 and Foxo3a levels, thus permitting G1-arrested cells to reenter the cell cycle. However, the cell lines derived from SCID mice that are defective in the catalytic subunit of DNA-dependent protein kinase retain elevated levels of p27 and Foxo3a proteins despite reactivation of v-Abl. Consequently, these cells are locked in the G1 phase for an extended period of time. The few cells that manage to bypass the G1 arrest become tumorigenic and fail to undergo pre-B cell differentiation induced by v-Abl inactivation. Deregulation of p27, Foxo3a, c-myc, and NF-kappaB/Rel was found to be associated with the malignant transformation of SCID temperature-sensitive form of Abelson murine leukemia virus pre-B cells.

Tyrosine kinase modulation of protein kinase C activity regulates G protein-linked Ca2+ signaling in leukemic hematopoietic cells

We have used a recombinant mouse pre-B cell line (TonB210.1, expressing Bcr/Abl under the control of an inducible promoter) and several human leukemia cell lines to study the effect of high tyrosine kinase activity on G protein-coupled receptor (GPCR) agonist-stimulated cellular Ca(2+) release and store-operated Ca(2+) entry (SOCE). After induction of Bcr/Abl expression, GPCR-linked SOCE increased. The effect was reverted in the presence of the specific Abl inhibitor imatinib (1microM) and the Src inhibitor PP2 (10microM). In leukemic cell lines constitutively expressing high tyrosine kinase activity, Ca(2+) transients were reduced by imatinib and/or PP2. Ca(2+) transients were enhanced by specific inhibitors of PKC subtypes and this effect was amplified by tyrosine kinase inhibition in Bcr/Abl expressing TonB210.1 and K562 cells. Under all conditions Ca(2+) transients were essentially blocked by the PKC activator PMA. In Bcr/Abl expressing (but not in native) TonB210.1 cells, tyrosine kinase inhibitors enhanced PKCalpha catalytic activity and PKCalpha co-immunoprecipitated with Bcr/Abl. Unlike native TonB210.1 cells, Bcr/Abl expressing cells showed a high rate of cell death if Ca(2+) influx was reduced by complexing extracellular Ca(2+) with BAPTA. Our data suggest that tonic inhibition of PKC represents a mechanism by which high tyrosine kinase activity can enhance cellular Ca(2+) transients and thus exert profound effects on the proliferation, apoptosis and chemotaxis of leukemic cells.

Econazole attenuates cytotoxicity of 1-methyl-4-phenylpyridinium by suppressing mitochondrial membrane permeability transition

Defects in mitochondrial function have been shown to participate in the induction of neuronal cell injury. The effect of econazole against the cytotoxicity of 1-methyl-4-phenylpyridinium (MPP(+)) in differentiated PC12 cells was assessed in relation to the mitochondrial membrane permeability changes. Treatment of PC12 cells with MPP(+) resulted in the nuclear damage, decrease in the mitochondrial transmembrane potential, cytosolic accumulation of cytochrome c, activation of caspase-3, increase in the formation of reactive oxygen species (ROS) and depletion of GSH. Econazole (0.25-2.5 microM) inhibited the cytotoxicity of MPP(+) or rotenone. The addition of econazole (0.5 microM) significantly attenuated the MPP(+)-induced mitochondrial damage, elevation of intracellular Ca(2+) level and cell death. However, because of the cytotoxicity, econazole at 5 microM did not attenuate the toxicity of MPP(+). The results show that econazole at the low concentrations may reduce the MPP(+)-induced viability loss in PC12 cells by suppressing the mitochondrial permeability transition, leading to activation of caspase-3 and the elevation of intracellular Ca(2+) levels, which are associated with the increased formation of ROS and depletion of GSH.

Molecular mechanisms of econazole-induced toxicity on human colon cancer cells: G0/G1 cell cycle arrest and caspase 8-independent apoptotic signaling pathways

Econazole (Eco), a potent broad-spectrum anti-fungal agent, has been used in the treatment of superficial mycosis. Eco is a store-operated Ca2+ channel antagonist which induces cytotoxic cell death of leukemia. However, little is known about its cytotoxic effect upon solid tumor cells. The purpose of this study is to investigate both the in vitro and in vivo molecular mechanisms of Eco-induced toxicity on colon cancer cells. We used COLO 205 cell line and nude mice xenograft model to investigate the cytotoxic effect of Eco. We demonstrated that lower doses Eco (5-20 microM) arrested human colon cancer cells at the G0/G1 phase of the cell cycle. The protein levels of p53, p21/Cip1, and p27/Kip1 were significantly elevated while CDK2 and CDK4 kinase activity were significantly suppressed by Eco treatment in COLO 205 cells. At higher doses (40-60 microM), Eco induced COLO 205 cells apoptosis evidenced by ladder formation in DNA fragmentation assay and sub-G1 peak in flow cytometry analysis. Western blot analysis showed that caspases 3, 9 but not 8 were activated by high dose Eco treatment to the COLO 205 cells accompanied with cytochrome c and apoptosis-inducing factor (AIF) translocation. Significant anti-tumorigenesis effect was further demonstrated in vivo by treating nude mice bearing COLO 205 tumor xenografts with Eco 50 mg/kg intraperitoneally. Our findings highlight the molecular mechanisms underlying the Eco-induced toxicity on colon cancer cells.

EFFECTS OF ECONAZOLE ON Ca2+ LEVELS IN AND THE GROWTH OF HUMAN PROSTATE CANCER PC3 CELLS

1. Econazole is used clinically as an antifungal drug with many different in vitro effects. However, the effects of econazole on prostate cancer cells are unknown. The effects of econazole on intracellular Ca2+ concentrations ([Ca2+]i) in and the proliferation of human PC3 prostate cancer cells was explored in the present study using fura-2 and tetrazolium as fluorescent dyes. 2. At a concentration of 0.1 micromol/L, econazole started to increase [Ca2+]i in a concentration-dependent manner. The econazole-induced increase in [Ca2+]i was reduced by 48% by removal of extracellular Ca2+, suggesting that the econazole-induced increase in [Ca2+]i was composed of extracellular Ca2+ influx and intracellular Ca2+. 3. This econazole-induced Ca2+ influx was via an L-type Ca2+ channel-like pathway. In Ca2+-free medium, 1 micromol/L thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, caused a monophasic increase in [Ca2+]i, after which the effect of econazole to increase [Ca2+]i was substantially inhibited. Conversely, pretreatment with 5 micromol/L econazole to deplete intracellular Ca2+ stores totally prevented thapsigargin from releasing more Ca2+. 4. The phospholipase C (PLC) inhibitor U73122 (2 micromol/L) abolished the increase in [Ca2+]i induced by 10 micromol/L ATP (a Ca2+ mobilizer that needs inositol 1,4,5-trisphosphate). 5. Overnight incubation with 1-30 micromol/L econazole inhibited proliferation of PC3 cells in a concentration-dependent manner. 6. These findings suggest that, in PC3 cells, econazole increases [Ca2+]i by stimulating Ca2+ influx into cells and Ca2+ release from the endoplasmic reticulum via a PLC-independent mechanism. Econazole is cytotoxic at submicromolar concentrations.

Changes in intracellular Ca2+and pH in response to thapsigargin in human glioblastoma cells and normal astrocytes

Despite extensive work in the field of glioblastoma research no significant increase in survival rates for this devastating disease has been achieved. It is known that disturbance of intracellular Ca2+([Ca2+]i) and intracellular pH (pHi) regulation could be involved in tumor formation. The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a major regulator of [Ca2+]i. We have investigated the effect of inhibition of SERCA by thapsigargin (TG) on [Ca2+]iand pHiin human primary glioblastoma multiforme (GBM) cells and GBM cell lines, compared with normal human astrocytes, using the fluorescent indicators fura-2 and BCECF, respectively. Basal [Ca2+]iwas higher in SK-MG-1 and U87 MG but not in human primary GBM cells compared with normal astrocytes. However, in tumor cells, TG evoked a much larger and faster [Ca2+]iincrease than in normal astrocytes. This increase was prevented in nominally Ca2+-free buffer and by 2-APB, an inhibitor of store-operated Ca2+channels. In addition, TG-activated Ca2+influx, which was sensitive to 2-APB, was higher in all tumor cell lines and primary GBM cells compared with normal astrocytes. The pHiwas also elevated in tumor cells compared with normal astrocytes. TG caused acidification of both normal and all GBM cells, but in the tumor cells, this acidification was followed by an amiloride- and 5-( N, N-hexamethylene)-amiloride-sensitive recovery, indicating involvement of a Na+/H+exchanger. In summary, inhibition of SERCA function revealed a significant divergence in intracellular Ca2+homeostasis and pH regulation in tumor cells compared with normal human astrocytes.

Flowing cells through pulsed electric fields efficiently purges stem cell preparations of contaminating myeloma cells while preserving stem cell function

Autologous stem cell transplantation, in the setting of hematologic malignancies such as lymphoma, improves disease-free survival if the graft has undergone tumor purging. Here we show that flowing hematopoietic cells through pulsed electric fields (PEFs) effectively purges myeloma cells without sacrificing functional stem cells. Electric fields can induce irreversible cell membrane pores in direct relation to cell diameter, an effect we exploit in a flowing system appropriate for clinical scale. Multiple myeloma (MM) cell lines admixed with human bone marrow (BM) or peripheral blood (PB) cells were passed through PEFs at 1.35 kV/cm to 1.4 kV/cm, resulting in 3- to 4-log tumor cell depletion by flow cytometry and 4.5- to 6-log depletion by tumor regrowth cultures. Samples from patients with MM gave similar results by cytometry. Stem cell engraftment into nonobese diabetic-severe combined immunodeficient (NOD/SCID)/beta2m-/- mice was unperturbed by PEFs. Flowing cells through PEFs is a promising technology for rapid tumor cell purging of clinical progenitor cell preparations.

Increased calcium influx and ribosomal content correlate with resistance to endoplasmic reticulum stress-induced cell death in mutant leukemia cell lines

Cell clones were derived by treatment of HL-60 cells with stepwise increasing concentrations of econazole (Ec), an imidazole antifungal that blocks Ca2+ influx and induces endoplasmic reticulum (ER) stress-related cell death in multiple mammalian cell types. Clones exhibit 20- to more than 300-fold greater resistance to Ec. Unexpectedly, they also display stable cross-resistance to tunicamycin, thapsigargin, dithiothreitol, and cycloheximide but not doxorubicin, etoposide, or Fas ligand. Phenotypic analysis indicates that the cells display increased store-operated calcium influx and resistance to ER Ca2+ store depletion by Ec. E2R2, the most resistant clone, was observed to maintain protein synthesis levels after treatment with Ec or thapsigargin. Expression of GRP78, an ER-based chaperone, was induced by these ER stress treatments but to equal degrees in HL-60 and E2R2 cells. By using microarray analysis, at least 15 ribosomal protein genes were found to be overexpressed in E2R2 compared with HL-60 cells. We also found that ribosomal protein content was increased by 30% in E2R2 as well as other clones. The resistance phenotype was partially reversed by the ribosome-inactivating protein saporin. Therefore, increased store-operated calcium influx, resistance to ER Ca2+ store depletion, and overexpression of ribosomal proteins define a novel phenotype of ER stress-associated multidrug resistance.

Ketotifen reverses MDR1-mediated multidrug resistance in human breast cancer cells in vitro and alleviates cardiotoxicity induced by doxorubicin in vivo

PURPOSE

To investigate the effect of the antihistamine ketotifen on multidrug resistance in human breast cancer cells and doxorubicin toxicity in mice.

METHODS

Clonogenicity assays were used to test the effect of ketotifen on human multidrug resistant breast cancer cell lines exposed to chemotherapeutic agents. Flow cytometry was used to measure accumulation of doxorubicin in cells. Fluorimetry was used to measure accumulation of doxorubicin in cardiac tissues. Histological analysis and toxicity studies in mice were used to test the effect of ketotifen on doxorubicin-induced toxicity.

RESULTS

Ketotifen was found to restore the sensitivity of P-glycoprotein-overexpressing multidrug-resistant MCF-7/adr cells to doxorubicin, mitoxantrone, VP-16 and vinblastine, but not to methotrexate or camptothecin. Ketotifen, however, was unable to restore sensitivity of BCRP-overexpressing MCF-7/mx cells or MRP-overexpressing MCF-7/vp cells to mitoxantrone or VP-16, respectively. In vivo, pretreatment of mice with ketotifen caused an increased accumulation of doxorubicin in cardiac tissue, consistent with a block in drug clearance. However, unlike verapamil, ketotifen pretreatment did not enhance doxorubicin toxicity but in fact provided protection, both at the level of cardiac tissue damage and in terms of survival.

CONCLUSIONS

Taken together, these observations show that ketotifen is unique in its ability both to reverse multidrug resistance due to P-glycoprotein overexpression and to provide cardioprotection to doxorubicin.