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The introduction of novel frontline agents in multiple myeloma (MM), like immunomodulatory drugs and proteasome inhibitors, has improved the overall survival of patients. Yet, MM is still not curable, and drug resistance (DR) remains the main challenge. To improve the understanding of DR in MM, we established a resistant cell line (MOLP8/R). The exploration of DR mechanisms yielded an overexpression of HIF1α, due to impaired proteasome activity of MOLP8/R. We show that MOLP8/R, like other tumor cells, overexpressing HIF1α, have an increased resistance to the immune system. By exploring the main target genes regulated by HIF1α, we could not show an overexpression of these targets in MOLP8/R. We, however, show that MOLP8/R cells display a very high overexpression of LCP1 gene (l-Plastin) controlled by HIF1α, and that this overexpression also exists in MM patient samples. The l-Plastin activity is controlled by its phosphorylation in Ser5. We further show that the inhibition of l-Plastin phosphorylation restores the sensitivity of MOLP8/R to immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs). Our results reveal a new target gene of DR, controlled by HIF1α.

Clinical trials have shown activity of the isotype-selective histone deacetylase (HDAC) inhibitor MGCD0103 in different hematologic malignancies. There are data to support the use of HDAC inhibitors in association with other cancer therapies. To propose a rational combination therapy, it is necessary to depict the molecular basis behind the cytotoxic effect of MGCD0103. In this study, we found that MGCD0103 was substantially more toxic in neoplastic B cells relative to normal cells, and we described the death pathways activated by MGCD0103 in B-cell chronic lymphocytic leukemia (CLL) cells from 32 patients. MGCD0103 decreased the expression of Mcl-1 and induced translocation of Bax to the mitochondria, mitochondrial depolarization, and release of cytochrome c in the cytosol. Caspase processing in the presence of the caspase inhibitor Q-VD-OPh and time course experiments showed that caspase-9 was the apical caspase. Thus, MGCD0103 induced the intrinsic pathway of apoptosis in CLL cells. Moreover, MGCD0103 treatment resulted in the activation of a caspase cascade downstream of caspase-9, caspase-dependent amplification of mitochondrial depolarization, activation of calpain, and Bax cleavage. We propose a model whereby the intrinsic pathway of apoptosis triggered by MGCD0103 in CLL is associated with a mitochondrial death amplification loop. Mol Cancer Ther; 9(5); 1349–60. ©2010 AACR.

The main challenge in using chemotherapy to treat multiple myeloma (MM) is drug resistance. In order to evaluate the anti-neoplastic properties of a new drug combination in MM, two clinically available drugs, valproic acid (VPA) a histone deacetylase (HDAC) inhibitor and pioglitazone, a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, were tested in vitro on MM cell lines and MM patient cells. The sensitivity towards VPA alone was observed on several MM cell lines tested and also on primary myeloma cells and peripheral blood mononuclear cells from healthy donors. Importantly, the addition of a PPARgamma agonist to the VPA treatment increased the cytotoxic effect of VPA in a synergistic/additive manner on the different MM cell lines and MM patient cells. This effect was observed at the physiological range of VPA used to treat epileptic patients. The mechanisms underlying this increase induced a cell cycle arrest and caspase-dependent apoptosis. The potentiation of the effect of VPA by pioglitazone was mediated by higher acetylation levels of histones H3 and H4 compared to levels induced by HDAC inhibitors alone. This association reveals a new promising chemotherapeutic combination to be tested in MM.

Epigenetic modifications play a major role in the development of multiple myeloma. We have previously reported that the PPARγ agonist pioglitazone (PIO) enhances, in-vitro, the cytotoxic effect of the Histone deacetylase inhibitor (HDACi), valproic acid (VPA), on multiple myeloma cells. Here, we described the development of a new multiple myeloma mouse model using MOLP8 cells, in order to evaluate the effect of VPA/PIO combination on the progression of myeloma cells, by analyzing the proliferation of bone marrow plasma cells. We showed that VPA/PIO delays the progression of the disease and the invasion of myeloma cells in the bone marrow. Mechanistically, we demonstrated that VPA/PIO increases the cleavage of caspase 3 and PARP, and induces the acetylation of Histone 3 (H3). Furthermore, we provided evidence that PPARγ agonist is able to enhance the action of other HDACi such as Vorinostat or Mocetinostat. Using PPARγ antagonist or siPPARγ, we strongly suggest that, as described during adipogenesis, PIO behaves as an epigenetic regulator by improving the activity of HDACi. This study highlights the therapeutic benefit of PIO/VPA combination, compared to VPA treatment as a single-arm therapy on multiple myeloma and further highlights that such combination may constitute a new promising treatment strategy which should be supported by clinical trials.

We examined the involvement of sphingosine kinase-1, a critical regulator of the sphingolipid balance, in susceptibility to antineoplastic agents of either sensitive or multidrug-resistant acute myeloid leukemia cells. Contrary to parental HL-60 cells, doxorubicin and etoposide failed to trigger apoptosis in chemoresistant HL-60/Doxo and HL-60NP16 cells overexpressing MRP1 and MDR1, respectively. Chemosensitive HL-60 cells displayed sphingosine kinase-1 inhibition coupled with ceramide generation. In contrast, chemoresistant HL-60/ Doxo and HL-60/VP16 had sustained sphingosine kinase-1 activity and did not produce ceramide during treatment. Enforced expression of sphingosine kinase-1 in chemosensitive HL-60 cells resulted in marked inhibition of apoptosis that was mediated by blockade of mitochondrial cytochrome c efflux hence suggesting a control of apoptosis at the pre-mitochondrial level. Incubation with cell-permeable ceramide of chemoresistant cells led to a sphingosine kinase-1 inhibition and apoptosis both prevented by sphingosine kinase-1 over-expression. Furthermore, F-12509a, a new sphingosine kinase inhibitor, led to ceramide accumulation, decrease in sphingosine 1-phosphate content and caused apoptosis equally in chemosensitive and chemoresistant cell lines that is inhibited by adding sphingosine 1-phosphate or overexpressing sphingosine kinase-1. F-12509a induced classical apoptosis hallmarks namely nuclear fragmentation, caspase-3 cleavage as well as downregulation of antiapoptotic XIAP, and release of cytochrome c and SMAC/Diablo.

Ligands that stabilize the telomeric G-rich single-stranded DNA overhang into G-quadruplex can be considered as potential antitumor agents that block telomere replication. Ligand 12459, a potent G-quadruplex ligand that belongs to the triazine series, has been previously shown to induce both telomere shortening and apoptosis in the human A549 cell line as a function of its concentration and time exposure. We show here that A549 clones obtained after mutagenesis and selected for resistance to the short term effect of ligand 12459 frequently displayed hTERT transcript overexpression (2-6-fold). Overexpression of hTERT was also characterized in two resistant clones (JFD10 and JFD18) as an increase in telomerase activity, leading to an increase in telomere length. An increased frequency of anaphase bridges was also detected in JFD10 and JFD18, suggesting an alteration of telomere capping functions. Transfection of either hTERT or DN-hTERT cDNAs into A549 cells did not confer resistance or hypersensitivity to the short term effect of ligand 12459, indicating that telomerase expression is not the main determinant of the antiproliferative effect of ligand 12459. In contrast, transfection of DN-hTERT cDNA into resistant JFD18 cells restored sensitivity to apoptotic concentrations of ligand 12459, suggesting that telomerase does participate in the resistance to this G-quadruplex ligand. This work provides evidence that telomerase activity is not the main target for the 12459 G-quadruplex ligand but that hTERT functions contribute to the resistance phenotype to this class of agents.

Using the monoclonal antibodies JIM 5 and 7, pectin was immunolocalized and quantitatively assayed in three anther compartments of Lilium hybrida during pollen development. Pectin levels in both the anther wall and the loculus increased following meiosis, were maximal during the early microspore stages and declined during the remainder of pollen ontogenesis. In the microspores/pollen grains, pectin was detectable at low levels during the microspore stages but accumulated significantly during pollen maturation. During early microspore vacuolation, esterified pectin epitopes were detected both in the tapetum cytoplasm and vacuoles. In the anther loculus, the same epitopes were located simultaneously in undulations of the plasma membrane and in the locular fluid. At the end of microspore vacuolation, esterified pectin epitopes were present within the lipids of the pollenkitt, and released in the loculus at pollen mitosis. Unesterified pectin epitopes were hardly detectable in the cytoplasm of the young microspore but were as abundant in the primexine matrix as in the loculus. During pollen maturation, both unesterified and esterified pectin labelling accumulated in the cytoplasm of the vegetative cell, concurrently with starch degradation. In the mature pollen grain, unesterified pectin epitopes were located in the proximal intine whereas esterified pectin epitopes were deposited in the distal intine. These data suggest that during early microspore development, the tapetum secretes pectin, which is transferred to the primexine matrix via the locular fluid. Further, pectin is demonstrated to constitute a significant component of the pollen carbohydrate reserves in the mature grain of Lilium.

International audience; The selection pressure for resistance to chemotherapy is accompanied by the enhanced expression of ABC proteins and increased cellular glycosphingolipid content. Thus, a possible connection between glycosphingolipid metabolism and ABC proteins in drug resistance has been suggested. In the present study, we established two human multidrug-resistant (MDR) cell lines derived from MESSA sarcoma cells by culturing with increasing concentrations of doxorubicin (DX5 cells) or doxorubicin together with cyclosporin A (GARF cells). Both resistant cell lines overexpressed the MDR1 gene and the wild-type P-glycoprotein at the same level. The cyclosporin derivative PSC833, a potent inhibitor of P-glycoprotein, sensitized DX5 but not GARF cells to the cytotoxic effects of daunorubicin. Moreover, PSC833 increased the nuclear accumulation of daunorubicin and the cellular accumulation of [3H]vinblastine in the DX5 but not in the GARF cells. The cellular incorporation of [3H]-cyclosporin A was lower in DX5 cells compared to MESSA and GARF cells, which incorporated the same level of [3H]-cyclosporin A. Sphingolipid analysis showed that the lactosylceramide level was 2.5- and 5-fold higher in DX5 and GARF cells, respectively, than in MESSA cells. Whereas the pharmacological inhibition of lactosylceramide synthesis was able to reverse only partially the resistance of GARF cells to daunorubicin without significant increase in nuclear accumulation of the drug, the same treatment before the co-treatment with PSC833 and daunorubicin increased the cytotoxic effect of daunorubicin and its nuclear accumulation. These data suggest a possible relationship between lactosylceramide levels and the resistance of P-glycoprotein to modulation by MDR modulators.

The main challenge in using chemotherapy to treat multiple myeloma (MM) is drug resistance. In order to evaluate the anti-neoplastic properties of a new drug combination in MM, two clinically available drugs, valproic acid (VPA) a histone deacetylase (HDAC) inhibitor and pioglitazone, a peroxisome proliferator-activated receptor gamma (PPARgamma) agonist, were tested in vitro on MM cell lines and MM patient cells. The sensitivity towards VPA alone was observed on several MM cell lines tested and also on primary myeloma cells and peripheral blood mononuclear cells from healthy donors. Importantly, the addition of a PPARgamma agonist to the VPA treatment increased the cytotoxic effect of VPA in a synergistic/additive manner on the different MM cell lines and MM patient cells. This effect was observed at the physiological range of VPA used to treat epileptic patients. The mechanisms underlying this increase induced a cell cycle arrest and caspase-dependent apoptosis. The potentiation of the effect of VPA by pioglitazone was mediated by higher acetylation levels of histones H3 and H4 compared to levels induced by HDAC inhibitors alone. This association reveals a new promising chemotherapeutic combination to be tested in MM.

Multiple myeloma (MM) is an incurable hematological disorder characterized by dysregulated proliferation of terminally differentiated plasma cells. Aberrant histone acetylation has been observed in the development of numerous malignancies. Histone deacetylase inhibitors such as valproic acid (VPA) are promising drugs for cancer therapy since they have been reported to have antiproliferative effects and to induce differentiation in carcinoma and leukemic cells. Considering the advantage of being already in clinical use for epilepsy treatment, valproic acid might be a promising therapeutic candidate drug in the management of multiple myeloma. In this study, we show that the short fatty acid VPA has a time and dose-dependent cytotoxic effect on the MM cell lines OPM2, RPMI and U266. The influence of VPA on cell cycle and apoptosis have been evaluated by flow cytometry. Our results show that the three cell lines are blocked in G 0 /G 1 phase. The observed sensitivity to VPA can be partially explained by late apoptosis. Since caspase 3 is activated in all tested cell lines after VPA treatment, a caspase-dependent pathway seems to be involved but not activated by the classic apoptotic pathways. We have also studied another mechanism of cell death, the senescence-like phenotype, but did not find any evidence for its implication. Thus, treatment with VPA may imply other alternative cell death mechanisms.

The molecular mechanisms induced by G-quadruplex ligands to trigger senescence in mammalian cells are still unknown, although the critical role of telomerase is highly suspected. JFA2 cells selected for resistance to senescence induced by the G-quadruplex ligand 12459 presented an overexpression of hTERT transcript that correlated to a functional increase in telomerase activity and telomere length. Consistently, treatment with 12459 failed to trigger senescence and telomere shortening in JFA2 cells. Resistant cells also presented cross-resistance for senescence induction to telomestatin, another G-quadruplex ligand from a different series, but not to other anticancer agents, indicating the selectivity of the resistance mechanism. We, thus, provide evidence that telomerase activity and telomere length are key cellular determinants of the resistance to G-quadruplex ligands.

Previous studies have demonstrated that doxorubicin (DOX) encapsulated in polyisohexylcyano-acrylate nanospheres (NS-DOX) circumvented the resistance of breast cancer cells overexpressing P-glycoprotein (Pgp). Another protein is involved in multidrug resistance phenotype, the multidrug resistance associated protein (MRP1). We report that NS-DOX overcomes multidrug resistance in breast cancer cells overexpressing MRP1. Taking into account that anthracyclines are conjugated to or co-transported with glutathione by MRP1, these data suggest that probably due to ion pair formation (NS-DOX), MRP1 could not transport the anthracycline. Pgp is probably able to transport the ion pair drug complex and the mechanisms of drug resistance reversion in Pgp expressing cells need to be further elucidated.

Multidrug-resistant (MDR) cancer cells have been shown to have an accumulation of glucosylceramide (GlcCer). In this study, we aim at localizing, at subcellular level, where these lipids accumulate. Neutral lipids and phospholipid containing organelles have been identified using confocal fluorescence microscopy and microspectrofluorometry by monitoring the emission of the fluorescent probe Nile-red. Data from confocal fluorescence microscopy analysis shows accumulation of neutral lipids in cytoplasmic droplets of MDR human carcinoma MCF7R cells. Microspectrofluorometric measurements show an increase of the gold-yellow emission intensity in MCF7R cells, corresponding to neutral lipids. Similar observations were made in human MDR vincristine-HL60 and doxorubicin-KB selected cells. Total cellular glucosylceramide (GlcCer) measurements using [(3)H]-palmitic acid and thin layer chromatography show a significant increase of GlcCer in MCF7R cells. Moreover, MCF7R cells treated with fluorescent GlcCer-bodipy exhibit an accumulation of this lipid in cytoplasmic droplets. Treatment of MCF7R cells with 1-phenyl-2-palmitoylamino-3-morpholino-1-propanolol (PPMP), a potent inhibitor of GlcCer synthase, attenuates the Nile-red fluorescence emission emanating from these structures and reverses MDR. Moreover, Golgi compartments stained with fluorescent PPMP-bodipy, show an increase in the Golgi compartments density. Treatment of MCF7R cells with cyclosporine A (CSA), tamoxifen (TMX) and 3'-azido-3'deoxythymidine (AZT) leads to the same effect observed in the presence of PPMP. Treatment of MCF7 and MCF7R with the beta-glucosidase inhibitor conduritol beta-epoxide (CBE) significantly increases resistance to daunorubicin only in MCF7R cells. These data demonstrate also that: (i) CSA, an inhibitor of MDR, has an additional target in addition to P-glycoprotein; and (ii) TMX (used in breast cancer treatment and prevention) and AZT (used in the treatment of HIV) could have side effects by disturbing lipid metabolism and inhibiting many cellular functions required in normal cells.

Background Chronic lymphocytic leukemia (CLL) cells are often affected by genomic aberrations targeting key regulatory genes. Although fludarabine is the standard first line therapy to treat CLL, only few data are available about the resistance of B cells to this purine nucleoside analog in vivo. Here we sought to increase our understanding of fludarabine action and describe the mechanisms leading to resistance in vivo. We performed an analysis of genomic aberrations, gene expression profiles, and microRNAs expression in CLL blood B lymphocytes isolated during the course of patients' treatment with fludarabine. Results In sensitive patients, the differentially expressed genes we identified were mainly involved in p53 signaling, DNA damage response, cell cycle and cell death. In resistant patients, uncommon genomic abnormalities were observed and the resistance toward fludarabine could be characterized based on the expression profiles of genes implicated in lymphocyte proliferation, DNA repair, and cell growth and survival. Of particular interest in some patients was the amplification of MYC (8q) observed both at the gene and transcript levels, together with alterations of myc-transcriptional targets, including genes and miRNAs involved in the regulation of cell cycle and proliferation. Differential expression of the sulfatase SULF2 and of miR-29a, -181a, and -221 was also observed between resistant and sensitive patients before treatment. These observations were further confirmed on a validation cohort of CLL patients treated with fludarabine in vitro. Conclusion In the present study we identified genes and miRNAs that may predict clinical resistance of CLL to fludarabine, and describe an interesting oncogenic mechanism in CLL patients resistant to fludarabine by which the complete MYC-specific regulatory network was altered (DNA and RNA levels, and transcriptional targets). These results should prove useful for understanding and overcoming refractoriness to fludarabine and also for predicting the clinical outcome of CLL patients before or early during their treatment.