Inhibition of P-glycoprotein activity in human leukemic cells by mifepristone

Mifepristone as a Potential Therapy to Reduce Angiogenesis and P-Glycoprotein Associated With Glioblastoma Resistance to Temozolomide

Glioblastoma, the most common primary central nervous system tumor, is characterized by extensive vascular neoformation and an area of necrosis generated by rapid proliferation. The standard treatment for this type of tumor is surgery followed by chemotherapy based on temozolomide and radiotherapy, resulting in poor patient survival. Glioblastoma is known for strong resistance to treatment, frequent recurrence and rapid progression. The aim of this study was to evaluate whether mifepristone, an antihormonal agent, can enhance the effect of temozolomide on C6 glioma cells orthotopically implanted in Wistar rats. The levels of the vascular endothelial growth factor (VEGF), and P-glycoprotein (P-gp) were examined, the former a promoter of angiogenesis that facilitates proliferation, and the latter an efflux pump transporter linked to drug resistance. After a 3-week treatment, the mifepristone/temozolomide regimen had decreased the level of VEGF and P-gp and significantly reduced tumor proliferation (detected by PET/CT images based on 18F-fluorothymidine uptake). Additionally, mifepristone proved to increase the intracerebral concentration of temozolomide. The lower level of O6-methylguanine-DNA-methyltransferase (MGMT) (related to DNA repair in tumors) previously reported for this combined treatment was herein confirmed. After the mifepristone/temozolomide treatment ended, however, the values of VEGF, P-gp, and MGMT increased and reached control levels by 14 weeks post-treatment. There was also tumor recurrence, as occurred when administering temozolomide alone. On the other hand, temozolomide led to 100% mortality within 26 days after beginning the drug treatment, while mifepristone/temozolomide enabled 70% survival 60–70 days and 30% survived over 100 days, suggesting that mifepristone could possibly act as a chemo-sensitizing agent for temozolomide.

Specific reversal of multidrug resistance to colchicine in CEM/VLB(100) cells by Gynostemma pentaphyllum extract

P-glycoprotein (P-gp)-mediated multiple drug resistance (MDR) is perhaps the most thoroughly studied cellular mechanism of cytotoxic drug resistance. Its efflux function can be circumvented by a wide range of pharmacological agents in vitro and in vivo. Most of these agents are pharmaceuticals used clinically for conditions other than cancer. However, their use in alleviating MDR is limited because the concentrations required for inhibition of the pump surpass their dose-limiting toxicity. The aim of this research is to study the role of gypenosides, isolated from Gynostemma pentaphyllum, as modulators of P-gp-mediated MDR in tumor cells, at both cellular and plasma membrane level. In the presence of total gypenoside preparation (0.1 mg/ml), an approximately 15-fold reversal of colchicine (COL) resistance was observed in P-gp-overexpressed CEM/VLB(100) cells. However, the gypenoside sample showed no reversal effect in cells treated with vinblastine and taxol. A purified gypenoside sample (gypenoside fraction 100) exhibited even more significant reversal of COL resistance (approximately 42-fold) in the CEM/VLB(100) cells. Further examination of the reversal effect of fraction 100 in membrane vesicles derived from CEM/VLB(100) cells using the continuous fluorescence method found that gypenoside fraction 100 at 0.1 mg/ml completely abolished the transport of fluorescein-COL.

Chronic suppressive therapy with calcium channel antagonists for refractory meningiomas

✓In this article, the authors review the research supporting the use of calcium channel antagonists (CCAs) in the treatment of recurrent or unresectable meningiomas. Calcium channel antagonists (for example, diltiazem and verapamil) are known to augment the effects of chemotherapy drugs (for example, vincristine) in multiple cancers. Although it was initially thought that this occurred by interference with calcium-dependent secondary messenger systems, it appears that other mechanisms account for this effect. The authors' initial work in this field was based on the then-emerging data that meningiomas are receptor positive for growth factor receptors (for example, platelet-derived growth factor [PDGF]), which are known to trigger calcium-dependent secondary messenger pathways. In fact, they were able to show that CCAs block the growth stimulatory effects of multiple growth factors, including PDGF, in vitro and augment the growth inhibitory effects of hydroxyurea and RU486 (mifepristone). The authors have shown similar in vivo growth inhibition by these agents. In addition, diltiazem- and verapamil-treated meningiomas are less vascular and smaller, with decreased cell proliferation and increased apoptosis. The use of CCAs is attractive as an adjunct treatment for unresectable or recurrent meningiomas because they are safe drugs with well-known side effect profiles that lend themselves to long-term chronic therapy.

Computational models to assign biopharmaceutics drug disposition classification from molecular structure

PURPOSE

We applied in silico methods to automatically classify drugs according to the Biopharmaceutics Drug Disposition Classification System (BDDCS).

MATERIALS AND METHODS

Models were developed using machine learning methods including recursive partitioning (RP), random forest (RF) and support vector machine (SVM) algorithms with ChemDraw, clogP, polar surface area, VolSurf and MolConnZ descriptors. The dataset consisted of 165 training and 56 test set molecules.

RESULTS

RF model 3, RP model 1, and SVM model 1 can correctly predict 73.1, 63.6 and 78.6% test compounds in classes 1, 2 and 3, respectively. Both RP and SVM models can be used for class 4 prediction. The inclusion of consensus analysis resulted in improved test set predictions for class 2 and 4 drugs.

CONCLUSIONS

The models can be used to predict BDDCS class for new compounds from molecular structure using readily available molecular descriptors and software, representing an area where in silico approaches could aid the pharmaceutical industry in speeding drugs to the patient and reducing costs. This could have significant applications in drug discovery to identify molecules that may have future developability issues.

Calcium Channel Antagonists Augment Hydroxyurea- And Ru486-Induced Inhibition Of Meningioma Growth In Vivo And In Vitro

OBJECTIVE

Although the chemotherapy drug hydroxyurea (HU) and the antiprogesterone mifepristone (RU486) have been used to treat meningiomas for which surgical and radiation therapies have failed, results have been disappointing. The addition of calcium channel antagonists (CCAs) to chemotherapeutic drugs enhances tumor growth inhibition in other tumor types, and the authors demonstrated that CCAs can block meningioma growth in vitro and in vivo. The purpose of this study was to test the effects of the addition of a CCA to HU or RU486 on meningioma growth.

METHODS

Primary and malignant (IOMM-Lee) meningioma cell lines were treated with HU, RU486, or either of these plus diltiazem or verapamil. Assays for cell growth, apoptosis, and fluorescent-activated cell sorting were performed on in vitro cultures. Similar cell lines were implanted into nude mice and were treated with HU or RU486, in combination with a CCA. Tumors were analyzed by light microscopy, MIB-1, and factor VIII immunohistochemical staining studies.

RESULTS

The addition of diltiazem or verapamil to HU or RU486 augmented meningioma growth inhibition by 20 to 60% in vitro. In vivo, tumors treated with combination drugs were smaller; and immunohistochemical analysis of the IOMM-Lee tumors showed a 10% decrease in the MIB-1 ratio (from 0.41 to 0.30) and an approximate 75% decrease in microvascular density.

CONCLUSION

The addition of diltiazem or verapamil to HU or RU486 augments meningioma growth inhibition in vitro by inducing apoptosis and G1 cell-cycle arrest. The combination of HU and diltiazem inhibited the growth of meningiomas in vivo by decreasing proliferation and microvascular density. These results suggest a possible role for these drugs as an additional adjuvant therapy for recurrent or unresectable meningiomas.

Modification of OATP2B1-mediated transport by steroid hormones

The family of the organic anion transporting polypeptides forms an increasing group of uptake transport proteins with a wide substrate spectrum. Although the expression of some members of this group, such as organic anion transporting polypeptide (OATP)-A or C, is limited to special tissues (such as liver or brain), the organic anion transporting polypeptide 2B1 (OATPB/SLCO2B1) is expressed in many organs, including liver, placenta, mammary gland, brain, and intestine. However, little is known about its function in those tissues because only a limited number of compounds, such as dehydroepiandrosterone-sulfate (DHEAS) and estrone-3-sulfate (E3S), have been characterized as OATP2B1 substrates. To further elucidate the role of OATP2B1 on steroid transport, we examined the influence of steroid hormones on OATP2B1-mediated E3S and DHEAS uptake using OATP2B1-overexpressing Madin-Darby canine kidney II cells. We identified unconjugated androgens (e.g., testosterone) as potent inhibitors for OATP2B1. In contrast, gestagenes such as progesterone enhanced E3S uptake in a concentration-dependent manner to up to 300% of the control, accompanied by a significant decrease in the OATP2B1 K(m) value for E3S (control, K(m) = 14 microM; in the presence of 31.6 muM progesterone, K(m) = 3.6 microM). Moreover, we demonstrated that testosterone and progesterone are not substrates of OATP2B1, indicating an allosteric mechanism for the observed effects. Furthermore, we showed that progesterone enhances the OATP2B1-dependent pregnenolone sulfate transport. Taken together, the results indicate functional modification of OATP2B1-mediated E3S and DHEAS as well as pregnenolone sulfate transport through steroid hormones such as progesterone. These effects can have physiological consequences for the organ-specific uptake of steroids.

ABC transporters as multidrug resistance mechanisms and the development of chemosensitizers for their reversal

One of the major problems related with anticancer chemotherapy is resistance against anticancer drugs. The ATP-binding cassette (ABC) transporters are a family of transporter proteins that are responsible for drug resistance and a low bioavailability of drugs by pumping a variety of drugs out cells at the expense of ATP hydrolysis. One strategy for reversal of the resistance of tumor cells expressing ABC transporters is combined use of anticancer drugs with chemosensitizers. In this review, the physiological functions and structures of ABC transporters, and the development of chemosensitizers are described focusing on well-known proteins including P-glycoprotein, multidrug resistance associated protein, and breast cancer resistance protein.

Potassium antimonyl tartrate induces caspase- and reactive oxygen species-dependent apoptosis in lymphoid tumoral cells

The metalloid salt potassium antimonyl tartrate (PAT), previously used as an antiparasitic agent, has recently been shown to exert cytotoxicity towards acute promyelocytic leukaemia cells like arsenical compounds. In this study, we have investigated its effects towards human lymphoid malignant cells and compared them with those of arsenic trioxide (As2O3). Like As2O3, PAT was found to inhibit cell growth of various lymphoid cell lines, deriving from either acute lymphoid leukaemias (Jurkat, Molt-4 and Nalm-6) or lymphomas (Daudi, Raji and Rec1). PAT toxicity was linked, at least in part, to induction of apoptosis in both Daudi and Jurkat cells, which was dependent on caspase activity. This apoptotic process was also associated, similarly to that triggered by As2O3, with loss of mitochondrial potential and enhanced cellular production of reactive oxygen-related species. It was enhanced by co-treatment with the pro-oxidant buthionine sulphoximine and abolished in response to the antioxidant N-acetylcysteine, thus underlining that PAT toxicity, similarly to that of As2O3, is probably modulated by the redox status of the cells. PAT, used at concentrations in the micromolar range that are thought to be clinically achievable, was also demonstrated to markedly decrease the viability of primary cultured tumoral B cells that originated from 18 patients suffering from chronic lymphoid leukaemia whereas normal lymphocytes were less sensitive. These data therefore suggest that PAT may deserve to be evaluated in the treatment of some lymphoid malignancies.

Influence of ceramide metabolism on P-glycoprotein function in immature acute myeloid leukemia KG1a cells

Previous studies have emphasized the role of glucosylceramide (Glu-Cer) synthase in multidrug resistance (MDR) regulation. However, the mechanism by which the inhibition of this enzyme results in increased drug retention and cytotoxicity remains unclear. In this study, we investigated the respective role of ceramide (Cer) accumulation and Glu-Cer derivatives depletion in MDR reversal effect of 1-phenyl-2-decanoylamino-3-morpholino-1-propanolol (PDMP), a Glu-Cer synthase inhibitor. We show here that treatment with PDMP resulted in increased rhodamine 123 (Rh123) retention and potent chemosensitization of P-glycoprotein (P-gp)-expressing cells, including KG1a cells, KG1a/200 cells, K562/138 cells, and K562/mdr-1 cells. Metabolic studies revealed that PDMP induced not only time-dependent Cer accumulation but also reduction of all glycosylated forms of Cer, including Glu-Cer, lactosylceramide (Lac-Cer), monosialo ganglioside (GM3) and disialo ganglioside (GD3). The influence of these metabolites on P-gp function was investigated by measuring Rh123 retention in PDMP-treated cells. P-gp function was found to be stimulated only by the addition of gangliosides in all resistant cell lines, whereas Glu-Cer, Lac-Cer, and Cer had no effect. Moreover, in KG1a/200 cells, GD3 and, to a lesser extent, GM3 were found to phosphorylate P-gp on serine residues. Altogether, these results suggest that, at least in leukemic cells, gangliosides depletion accounts for PDMP-mediated MDR reversal effect, and that gangliosides are important P-gp regulators perhaps through their capacity to modulate P-gp phosphorylation.

Reversal of MRP-mediated multidrug resistance in human lung cancer cells by the antiprogestatin drug RU486

Multidrug resistance-associated protein (MRP) and P-glycoprotein (P-gp) are drug efflux pumps conferring multidrug resistance to tumor cells. RU486, an antiprogestatin drug known to inhibit P-gp function, was examined for its effect on MRP activity in MRP-overexpressing lung tumor GLC4/Sb30 cells. In such cells, the antihormone compound was found to increase intracellular accumulation of calcein, a fluorescent compound transported by MRP, in a dose-dependent manner, through inhibition of cellular export of the dye; in contrast, it did not alter calcein levels in parental GLC4 cells. RU486, when used at 10 microM, a concentration close to plasma concentrations achievable in humans, strongly enhanced the sensitivity of GLC4/Sb30 cells towards two known cytotoxic substrates of MRP, the anticancer drug vincristine and the heavy metal salt potassium antimonyl tartrate. Vincristine accumulation levels were moreover up-regulated in RU486-treated GLC4/Sb30 cells. In addition, such cells were demonstrated to display reduced cellular levels of glutathione which is required for MRP-mediated transport of some anticancer drugs. These findings therefore demonstrate that RU486 can down-modulate MRP-mediated drug resistance, in addition to that linked to P-gp, through inhibition of MRP function.

Antiprogestin pharmacodynamics, pharmacokinetics, and metabolism: implications for their long-term use

Antiprogestins represent a relatively new and promising class of therapeutic agents that could have significant impact on human health and reproduction. In the present work, the pharmacodynamics, pharmacokinetics, and metabolism of mifepristone (MIF), lilopristone (LIL), and onapristone (ONA) in humans are reviewed, and characteristics bearing important clinical implications are discussed. Although MIF has gained notoriety as an "abortion pill," antiprogestins may more importantly prove effective in the treatment of endometriosis, uterine leiomyoma, meningioma, cancers of the breast and prostate, and as contraceptive agents. MIF pharmacokinetics display nonlinearities associated with saturable plasma protein (alpha 1-acid glycoprotein, AAG) binding and characterized by lack of dose dependency for parent drug plasma concentrations (for doses greater than 100 mg) and a zero-order phase of elimination. LIL and ONA pharmacokinetics are less well characterized but ONA does not appear to bind AAG and displays a much shorter t1/2 than the other agents. The three antiprogestins are substrates of cytochrome P450 (CYP) 3A4, an enzyme exceedingly important in human xenobiotic metabolism. Even more implicative of likely drug-drug interactions subsequent to their long-term administration are recent data from our laboratory indicating that they inactivate CYP3A4 in a cofactor- and time-dependent manner, suggesting that complexation and induction of the enzyme may occur in vivo via protein stabilization. Moreover, it has been demonstrated that MIF increases CYP3A4 mRNA levels in human hepatocytes in primary culture, indicative of message stabilization and/or transcriptional activation of CYP3A4 expression. Finally, MIF has also been shown to inhibit P-glycoprotein function. Whether LIL and ONA share these latter two characteristics with MIF has not yet been determined but they illustrate properties that, in addition to diminished antiglucocorticoid activities and altered pharmacokinetic characteristics, warrant consideration during the development of these and never antiprogestational agents.