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

SIAH1 ubiquitination-modified HMGCR inhibits lung cancer progression and promotes drug sensitivity through cholesterol synthesis

BACKGROUNDS

Lung cancer is one of the most frequently diagnosed cancers and the leading cause of cancer-related deaths worldwide. Deep understanding of chemoresistance will lead to remarkable progress in lung cancer treatment strategy. Cholesterol accumulation was associated with cisplatin resistance in lung cancer treatment. And we found the degree of cisplatin resistance was correlated with the expression of the cholesterol synthesis HMGCR.

METHODS

We analyzed a group of 42 lung cancer patients who received cisplatin treatment after lung resection surgery. The expression of HMGCR and its correlation with cholesterol in lung cancer cell lines were determined by qRT-PCR and ELISA analyses. We focus on the function and mechanism of HMGCR in lung cancer and reveal that knockdown of HMGCR expression inhibits the proliferation, colony formation, and migration of lung cancer cell lines in vitro or in vivo and dramatically enhances the efficacy of cisplatin.

RESULTS

Through mechanism studies, we illustrate that SIAH1, an E3 ubiquitin-protein ligase, ubiquitination modifies HMGCR and inhibits efflux protein activity via regulating cholesterol synthesis. In vivo experiments showed that SIAH1 overexpression or using HMGCR knockdown retard tumor growth and enhanced the efficacy of cisplatin. In summary, HMGCR affects cholesterol metabolism by regulating key enzymes in cholesterol synthesis, thereby reducing drug sensitivity.

CONCLUSION

This study indicates that lung cancer patients with lower HMGCR levels may lead to a better prognosis and provide a potential treatment by SIAH1 overexpression for lung cancer patients with cisplatin resistance.

Dexamethasone enhances the efficacy of atorvastatin in inhibiting excessively inflammation-induced abnormal angiogenesis by regulating macrophages

BACKGROUND

We have recently showed that atorvastatin (ATO) combined with low dose of dexamethasone (DEX) was more efficacious in treating patients with chronic subdural haematoma (CSDH) than ATO monotherapy. This study was designed to investigate the underlying mechanisms of the improved efficacy of this combined therapy.

METHODS

Mass spectrometry was performed to quantitatively detect drugs in haematoma fluids and serum samples from CSDH patients and also in cultured macrophages after treatment with either ATO alone or in combination with DEX. The differentiation and apoptosis of macrophages were evaluated using flow cytometry. The expression of cytokines, chemokines and angiogenesis-related proteins was evaluated using proteome profile arrays, immunoblots and ELISA, respectively.

RESULTS

ATO was detected in haematoma fluids and serum samples, whose levels were increased significantly in samples collected from patients treated with both ATO and DEX. ATO was also increased in cultured macrophages treated with ATO and DEX. The numbers of M1-polarized macrophages were higher than the M2 phenotype in the haematoma fluids of patients. Cultured macrophages treated with ATO and DEX had reduced numbers of M1-polarized macrophages, increased numbers of M2-polarized macrophages as compared to monotherapies, and decreased rate of apoptosis induced by high-dose DEX. DEX enhanced the anti-inflammatory and anti-angiogenic activity of ATO by suppressing VEGFA and other inflammatory angiogenic factors. Consistent with the finding, patients responded well to the drug treatments had lower serum levels of VEGFA.

CONCLUSIONS

We have shown for the first time that ATO given orally was detected in CSDH haematoma fluids. DEX enhances the anti-inflammatory and anti-angiogenic effects of ATO, primarily by increasing the presence of ATO in haematoma and macrophages and by regulating the functions of macrophages.

Does atorvastatin therapy change the anti-Xa activity in xabans-treated patients with atrial fibrillation?

Atorvastatin and direct oral factor Xa inhibitors (xabans) are frequently co‐administrated in patients with atrial fibrillation (AF). However, no studies investigating the possibility of the pharmacologic interaction between these agents have been conducted. The aim of this prospective observational study was to determine the impact of atorvastatin therapy on anti‐Xa activity in xabans‐treated patients with AF. We enrolled 115 AF patients on long‐term rivaroxaban (52 patients) and long‐term apixaban (63 patients) therapy. Long‐term atorvastatin (40 mg once daily) was administrated to 28 rivaroxaban‐treated patients and to 28 apixaban‐treated patients. Trough and peak samples were tested for anti‐Xa activity with drug‐specific anti‐Xa chromogenic analysis. For rivaroxaban, there were no significant differences in trough activity (45.5 ± 39.5 ng/ml vs. 46.2 ± 30.1 ng/ml; p = .34) and peak anti‐Xa activity (179.2 ± 108.8 ng/ml vs. 208.1 ± 104.1 ng/ml; p = .94) between atorvastatin‐treated patients and those without atorvastatin. Similarly, atorvastatin did not impact the trough activity (127.7 ± 71.1 ng/ml vs. 100.8 ± 61.1 ng/ml; p = .12) or peak anti‐Xa activity (213.8 ± 103.6 ng/ml vs. 179.3 ± 72.9 ng/ml; p = .14) among apixaban‐treated patients with AF. This observational study did not show a significant impact of atorvastatin on trough and peak anti‐Xa activity in xabans‐treated patients with AF.

Simvastatin enhances the efficacy of nilotinib in chronic myeloid leukaemia by post-translational modification and drug transporter modulation

The resistance of chronic myeloid leukaemia (CML) to tyrosine kinase inhibitors (TKIs) remains a significant clinical problem. Targeting alternative pathways, such as protein prenylation, is known to be effective in overcoming resistance. Simvastatin inhibits 3-hydroxy-3-methylglutaryl-CoA reductase (a key enzyme in isoprenoid-regulation), thereby inhibiting prenylation. We demonstrate that simvastatin alone effectively inhibits proliferation in a panel of TKI-resistant CML cell lines, regardless of mechanism of resistance. We further show that the combination of nilotinib and simvastatin synergistically kills CML cells via an increase in apoptosis and decrease in prosurvival proteins and cellular proliferation. Mechanistically, simvastatin inhibits protein prenylation as shown by increased levels of unprenylated Ras and rescue experiments with mevalonate resulted in abrogation of synergism. The combination also leads to an increase in the intracellular uptake and retention of radio-labelled nilotinib, which further enhances the inhibition of Bcr-Abl kinase activity. In primary CML samples, this combination inhibits clonogenicity in both imatinib-naive and resistant cells. Such combinatorial effects provide the basis for utilising these Food and Drug Administration-approved drugs as a potential clinical approach in overcoming resistance and improving CML treatment.

Comedications influence immune infiltration and pathological response to neoadjuvant chemotherapy in breast cancer

Immunosurveillance plays an important role in breast cancer (BC) prognosis and progression, and can be geared by immunogenic chemotherapy. In a cohort of 1023 BC patients treated with neoadjuvant chemotherapy (NAC), 40% of the individuals took comedications mostly linked to aging and comorbidities. We systematically analyzed the off-target effects of 1178 concurrent comedications (classified according to the Anatomical Therapeutic Chemical (ATC) Classification System) on the density of tumor-infiltrating lymphocytes (TILs) and pathological complete responses (pCR). At level 1 of the ATC system, the main anatomical classes of drugs were those targeting the nervous system (class N, 39.1%), cardiovascular disorders (class C, 26.6%), alimentary and metabolism (class A, 16.9%), or hormonal preparations (class H, 6.5%). At level 2, the most frequent therapeutic classes were psycholeptics (N05), analgesics (N02), and psychoanaleptics (N06). Pre-NAC TIL density in triple-negative BC (TNBC) was influenced by medications from class H, N, and A, while TIL density in HER2⁺ BC was associated with the use of class C. Psycholeptics (N05) and agents acting on the renin-angiotensin system (C09) were independently associated with pCR in the whole population of BC or TNBC, and in HER2-positive BC, respectively. Importantly, level 3 hypnotics (N05C) alone were able to reduce tumor growth in BC bearing mice and increased the anti-cancer activity of cyclophosphamide in a T cell-dependent manner. These findings prompt for further exploration of drugs interactions in cancer, and for prospective drug-repositioning strategies to improve the efficacy of NAC in BC.

Atorvastatin modulates drug transporters and ameliorates nicotine-induced testicular toxicity

We studied the changes in mRNA expressions of influx and efflux transporters, blood-testis-barrier proteins (BTB) and key apoptotic genes in the testis of rats coadministered with nicotine and atorvastatin. Rats were divided into four groups: (i) control, (ii) atorvastatin (10 mg/kg b.wt), (iii) nicotine (0.6 mg/kg b.wt) and (iv) atorvastatin (10 mg/kg b.wt) + nicotine (0.6 mg/kg b.wt). Atorvastatin was given by oral intubation and nicotine by intraperitoneal injection. After 60 days of treatment, expressions of key apoptotic genes involved in both intrinsic and extrinsic pathways; solute carrier influx transporters SLCOB1, SLC22A1 and efflux transporter ABCB1 associated with transport of atorvastatin and nicotine, and proteins of BTB were assayed. Nicotine administration activated apoptosis and downregulated SLCOB1, which transport atorvastatin. Atorvastatin administration suppressed apoptotic pathway and downregulated SLC22A1, transporter of nicotine. Coadministration of atorvastatin with nicotine downregulated expressions of apoptotic genes. The combined administration of atorvastatin and nicotine reduced the influx of both atorvastatin and nicotine and enhanced the efflux of these drugs thereby altering the microenvironment of testis and improving testicular function. We conclude that atorvastatin-mediated alterations of BTB and drug transporters might have played a significant role in ameliorating nicotine-induced testicular toxicity.

7-ketocholesterol and 27-hydroxycholesterol decreased doxorubicin sensitivity in breast cancer cells: estrogenic activity and mTOR pathway

Hypercholesterolemia is one of the risk factors for poor outcome in breast cancer therapy. To elucidate the influence of the main circulating oxysterols, cholesterol oxidation products, on the cell-killing effect of doxorubicin, cells were exposed to oxysterols at a subtoxic concentration. When cells were exposed to oxysterols in fetal bovine serum-supplemented medium, 7-ketocholesterol (7-KC), but not 27-hydroxycholesterol (27-HC), decreased the cytotoxicity of doxorubicin in MCF-7 (high estrogen receptor (ER)α/ERβ ratio) cells and the decreased cytotoxicity was restored by the P-glycoprotein inhibitor verapamil. 7-KC stimulated the efflux function of P-glycoprotein and reduced intracellular doxorubicin accumulation in MCF-7 but not in ERα(-) MDA-MB-231 and the resistant MCF-7/ADR cells. In MCF-7 cells, 7-KC increased the mRNA and protein levels of P-glycoprotein. The 7-KC-suppressed doxorubicin accumulation was restored by the fluvestrant and ERα knockdown. In a yeast reporter assay, the ERα activation by 7-KC was more potent than 27-HC. 7-KC, but not 27-HC, stimulated the expression of an ER target, Trefoil factor 1 in MCF-7 cells. When charcoal-stripped fetal bovine serum was used, both 7-KC and 27-HC induced Trefoil factor 1 expression and reduced doxorubicin accumulation in MCF-7 cells. 7-KC-reduced doxorubicin accumulation could be reversed by inhibitors of phosphatidylinositol 3-kinase, Akt, and mammalian target of rapamycin (mTOR). These findings demonstrate that 7-KC decreases the cytotoxicity of doxorubicin through the up-regulation of P-glycoprotein in an ERα- and mTOR-dependent pathway. The 7-KC- and 27-HC-elicited estrogenic effects are crucial in the P-glycoprotein induction in breast cancer cells.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

Atorvastatin attenuation of ABCB1 expression is mediated by microRNA miR-491-3p in Caco-2 cells

AIM

Atorvastatin, a HMG-CoA reductase inhibitor, used in the treatment of hypercholesterolemia, has been previously shown to regulate ABCB1 expression in vivo and in vitro. We hypothesized that the statin could regulate gene expression of ABCB1 transporter via microRNAs.

METHODS

Expression of microRNAs and ABCB1 mRNA was examined in atorvastatin-treated and control cells using real-time PCR. miR-491-3P mimic and inhibitor were transfected in Caco-2 and ABCB1 expression was monitored by western blot and real-time PCR.

RESULTS

In HepG2 cells, none of the microRNAs predicted to target ABCB1 3'UTR was regulated by atorvastatin treatment. In agreement with this, ABCB1 3'UTR activity was not modulated in HepG-2 cells after 48h-treatment as measured by luciferase assay. In Caco-2 cells, atorvastatin treatment provoked a decrease in luciferase activity and, accordingly, miR-491-3p was upregulated about 2.7 times after 48h-statin treatment. Luciferase analysis of miR-491-3p with a mimetic or inhibitor of miR-491-3p revealed that this microRNA could target ABCB1 3'UTR, as after miR-491-3p inhibition, ABCB1 levels were increased by two-fold, and miR-491-3p superexpression decreased ABCB1 3'UTR activity. Finally, functional analysis revealed that treatment with miR-491-3p inhibitor could reverses atorvastatin attenuation of ABCB1 (Pg-p) protein levels.

CONCLUSION

Our results suggest atorvastatin control ABCB1 expression via miR-491-3p in Caco-2 cells. This finding may be an important mechanism of statin drug-drug interaction, since common concomitant drugs used in the prevention of cardiovascular diseases are ABCB1 substrates.

Influence of genetic polymorphisms of multidrug and toxin extrusion protein 1 on its mRNA expression in peripheral blood cells

This study aimed to determine the effect of multidrug and toxin extrusion protein 1 (MATE1) genetic variants on its transcript expression in peripheral blood cells. Consistent with previous in vitro findings, MATE1 mRNA levels were significantly higher in subjects carrying rs2453579, but not rs2252281, compared to those without either of these promoter variants. In addition, the mRNA levels did not differ between subjects with both variants and those with neither allele. Thus, this study reveals that the influence of MATE1 genetic variants on its mRNA expression can be detected in vivo using peripheral blood.

In vitro and in vivo downregulation of the ATP binding cassette transporter B1 by the HMG-CoA reductase inhibitor simvastatin

Extrusion of chemotherapeutics by ATP-binding cassette (ABC) transporters like ABCB1 (P-glycoprotein) represents a crucial mechanism of multidrug resistance in cancer therapy. We have previously shown that the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin directly inhibits ABCB1, alters the glycosylation of the transporter, and enhances the intracellular accumulation of doxorubicin with subsequent anti-cancer action. Here, we show that simvastatin reduces endogenous dolichol levels and ABCB1 in human neuroblastoma SH-SY5Y cells. Coapplication with dolichol prevents the downregulation of the ABCB1 transporter. Importantly, dolichol also attenuated simvastatin-induced apoptosis, unmasking involvement of unfolded protein response. Direct monitoring of the fluorescent fusion protein YFP-ABCB1 further confirms concentration-dependent reduction of ABCB1 in HEK293 cells by simvastatin. In simvastatin-treated murine xenografts, ABCB1 was also reduced in the liver and rhabdomyosarcoma but did not reach significance in neuroblastoma. Nevertheless, the in vivo anti-cancer effects of simvastatin are corroborated by increased apoptosis in tumor tissues. These findings provide experimental evidence for usage of simvastatin in novel chemotherapeutic regimens and link dolichol depletion to simvastatin-induced anti-cancer activity.

Calcium and P-glycoprotein independent synergism between schweinfurthins and verapamil

Schweinfurthins are intriguing natural products with anti-cancer activities and as yet incompletely understood mechanisms of action. We investigated whether inhibitors of P-glycoprotein (Pgp), in a manner analogous to other natural products, might enhance schweinfurthins' growth inhibitory actions by increasing intracellular schweinfurthin levels. Both the schweinfurthin-sensitive glioblastoma multiforme cell line SF-295 and relatively insensitive lung carcinoma cell line A549 were treated with 2 schweinfurthin analogs: 3-deoxyschweinfurthin B-p-nitro bis-stilbene (3dSB-PNBS) and 5'-methylschweinfurthin G (methyl-G). There was a synergistic enhancement of growth inhibition with the combination of the Pgp inhibitor verapamil and both analogs in SF-295 cells. Methyl-G, verapamil, and the combination did not result in alterations to intracellular calcium concentration. Verapamil increased the intracellular concentration of 3dSB-PNBS in both SF-295 and A549 cells in a Pgp-independent manner. Methyl-G, verapamil, and the combination do not result in increased ER stress. Methyl-G increased the intracellular concentration of a known Pgp substrate, Rhodamine 123 in SF-295 cells. Reduction of cellular cholesterol leads to the accumulation of Pgp substrates, as Pgp requires cholesterol for proper function. Since 3dSB enhances lovastatin-induced upregulation of the cholesterol efflux pump ABCA1, it is intriguing that co-treatment with cholesterol rescued the methyl-G-induced increase in Rhodamine 123 intracellular concentration. These studies support the hypothesis that verapamil potentiates the schweinfurthin growth inhibitory effect by increasing its intracellular concentration.

Expression and activity of ABCG2, but not ABCB1 or OATP1B1, are associated with cholesterol levels: evidence from in vitro and in vivo experiments

Aim: This study investigated whether cholesterol levels influence the expression and function of drug transporters and whether statin treatments could alter this by reducing plasma low-density lipoprotein cholesterol levels. Patients & methods: The mRNA expression and function of OATP1B1, ABCB1 and ABCG2 were assessed in peripheral blood mononuclear cells (PBMCs) of healthy subjects and from patients with familial hypercholesterolemia (FH) before and after statin treatment by real-time PCR and flow cytometric assay, respectively. The effects of statin exposure and cholesterol depletion in PBMCs and in cell lines were assessed. Results: ABCG2 expression and activity in PBMCs in patients with FH were 2-fold and 26-fold higher, respectively, than those of the healthy subjects (p < 0.001 for both). Statin treatment decreased ABCG2 expression and function in patients with FH. Depletion of cholesterol ex vivo reduced ABCG2 expression in PBMCs and reduced ABCG2 activity in liver and colon cells. Conclusion: This study suggested that statins may downregulate ABCG2 expression and function through reducing low-density lipoprotein cholesterol levels.

Original submitted 25 November 2013; Revision submitted 21 March 2014

Interference of flavonoids with fluorescent intracellular probes: methodological implications in the evaluation of the oxidative burst by flow cytometry

The evaluation of oxidative burst is particularly relevant in many pathological and subclinical conditions. Flow cytometry provides quick and accurate measures of the reactive oxygen species production by leukocytes in most situations. However, spurious results, related to probes' efflux may be observed in several instances. Many factors affect the evaluation of the oxidative burst with fluorescent probes that require intracellular deacetylation and could be substrate of the multidrug resistance proteins (MDR). After discussing the implications of the efflux of fluorophores in the normalization strategies in flow cytometry assays, we have pointed out the possible interference of flavonoids with fluorescet probes' staining and signal. We have also reviewed the results from human intervention studies regarding the evaluation of oxidative burst with these probes. In vitro, at concentrations close to post-ingestion circulating levels, some flavonoids and their metabolites could interfere with probes' staining and fluorescence signal through different mechanisms, such as the inhibition of esterases, the modulation of the MDR-mediate efflux of probe and the inhibition of the oxidation of probe. These effects may explain the contrasting results obtained by human intervention studies. Finally, also inflammatory state or the use of drugs substrate of MDR proteins could affect the evaluation of the oxidative burst with intracellular probes.

Do MDR1 and SLCO1B1 polymorphisms influence the therapeutic response to atorvastatin? A study on a cohort of Egyptian patients with hypercholesterolemia

BACKGROUND

Statins are among the most prescribed drugs worldwide to reduce the risk of cardiovascular events. Interindividual variability in drug response is a major clinical problem and is of concern during drug development. Statins, such as atorvastatin, are taken orally and access to their site of action in the liver is greatly facilitated by both intestinal and hepatic transporters.

OBJECTIVE

To examine the impact of polymorphisms of the multidrug resistance 1(MDR1) and solute carrier organic anion transporter 1B1 (SLCO1B1) genes on the therapeutic response to atorvastatin as well as the presence of gender-gene interaction.

METHODS

Serum lipid levels were determined at baseline and 4 weeks following 40 mg/day atorvastatin treatment in 50 Egyptian hypercholesterolemic patients (27 males and 23 females). Identification of MDR1 C3435T and SLCO1B1 A388G gene polymorphisms was performed using a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

Treatment with atorvastatin resulted in a mean reduction of total cholesterol (TC), low density lipoprotein cholesterol (LDL-C), and triglyceride (TG) of 8.7 %, 9.2 %, and 4.1 %, respectively, and a mean increase of high density lipoprotein cholesterol (HDL-C) of 1 %. Baseline and post-treatment HDL-C levels were statistically significantly higher in the MDR 1 TT homozygotes when compared with the CC wild type. The percentage change in TC, LDL-C, TG, and HDL-C did not show any statistically significant difference when compared among the different MDR 1 C3435T or SLCO1B1 A388G genotypes. The SLCO1B1 GG homozygotes showed a decrease in TG, whereas there was an increase in TG following atorvastatin treatment in AA and AG carriers in females; however, males did not show any statistically significant difference. There was no statistically significant association between either the coronary artery disease (CAD) risk factors (family history of CAD, hypertension, diabetes mellitus, smoking) or concomitant medications with the percentage change in different lipid parameters.

CONCLUSION

MDR1 C3435T was associated with baseline and post-treatment HDL-C variation. SLCO1B1 A388G showed gender-related effects on TG change following atorvastatin treatment. None of the comorbidities or the concomitant medications influenced the percentage change of lipid parameters following atorvastatin treatment. The results of this study may lead to an improved understanding of the genetic determinants of lipid response to atorvastatin treatment.

ABCB1 haplotypes are associated with P-gp activity and affect a major molecular response in chronic myeloid leukemia patients treated with a standard dose of imatinib

Despite the high efficacy of imatinib mesylate (IM) treatment for chronic myeloid leukemia (CML) patients, some individuals develop resistance due to impaired bioavailability. It has been previously demonstrated that the haplotypes for ATP-binding cassette subfamily B member 1 (ABCB1)with c.1236C>T, c.3435C>T and c.2677G>T/A polymorphisms markedly affect the secondary structure of ABCB1 mRNA and its activity. These modifications may affect efflux transporter activity and response to treatment with IM. The aim of the present study was to investigate the influence of ABCB1 haplotypes on P-glycoprotein (P-gp) activity, IM plasma levels and IM response. In total, 28 chronic-phase CML patients treated with a standard dose of IM (400 mg/day) were studied. The patients were selected according to the haplotypes of ABCB1, with c.1236C>T, c.3435C>T and c.2677G>T polymorphisms, and were classified into two groups based on the presence of the mutated allele in each genotype for the three ABCB1 polymorphisms. In addition, expression of P-gp and breakpoint cluster region-abelson 1 (BCR-ABL1), ABCB1 and solute carrier family 22 member 1 (SLC22A1) mRNA were evaluated. The P-gp activity in the wild-type group was found to be higher than that in the mutated group (59.1 vs. 38.3%; P=0.001). Furthermore, the patients who did not achieve major molecular response (MMR) showed a higher rate of efflux mediated by P-gp when compared with individuals who achieved MMR (64.7 vs. 45.7%; P=0.001). All patients without MMR demonstrated effluxes of >60%. In addition, patients without MMR exhibited lower plasma concentrations of IM compared with those with MMR (0.51 vs. 1.42 μg/ml; P=0.001). Higher levels of SLC22A1 mRNA were observed in patients who achieved MMR and complete molecular response (P<0.05). In conclusion, the ABCB1 1236CT/3435CT/2677GT and 1236TT/3435TT/2677TT haplotypes are associated with reduced P-gp activity and MMR in chronic-phase CML patients treated with a standard dose of IM.

7-Ketocholesterol induces P-glycoprotein through PI3K/mTOR signaling in hepatoma cells

7-Ketocholesterol (7-KC) is found at an elevated level in patients with cancer and chronic liver disease. The up-regulation of an efflux pump, P-glycoprotein (P-gp) leads to drug resistance. To elucidate the effect of 7-KC on P-gp, P-gp function and expression were investigated in hepatoma cell lines Huh-7 and HepG2 and in primary hepatocyte-derived HuS-E/2 cells. At a subtoxic concentration, 48-h exposure to 7-KC reduced the intracellular accumulation and cytotoxicity of P-gp substrate doxorubicin in hepatoma cells, but not in HuS-E/2 cells. In Huh-7 cells, 7-KC elevated efflux function through the activation of phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway. 7-KC activated the downstream protein synthesis initiation factor 4E-BP1 and induced P-gp expression post-transcriptionally. The stimulation of efflux was reversible and could not be prevented by N-acetyl cysteine. Total cellular ATP content remained the same, whereas the lactate production was increased and fluorescence lifetime of protein-bound NADH was shortened. These changes suggested a metabolic shift to glycolysis, but glycolytic inhibitors did not eliminate 7-KC-mediated P-gp induction. These results demonstrate that 7-KC induces P-gp through PI3K/mTOR signaling and decreased the cell-killing efficacy of doxorubicin in hepatoma cells.

Atorvastatin treatment induces uptake and efflux transporters in human liver

The metabolism and disposition of statins are highly dependent on different cytochrome P450 enzymes, such as CYP3A4 and CYP2C9, as well as membrane transporters SLCO1B1, SLCO2B1, ABCB1, and ABCG2. Interindividual gene expression differences among these enzymes may explain part of the variability in tolerance and effect for statin treatment. The aim of the present study was to investigate the effect of statin treatment on these genes in human liver tissue. Levels of CYP3A4, CYP2C9, SLCO1B1, SLCO2B1, ABCB1, and ABCG2 mRNA in liver tissue from a previously performed clinical trial in 29 patients randomized to treatment with placebo, 80 mg/day of atorvastatin, or 20 mg/day of fluvastatin for 4 weeks were measured using quantitative polymerase chain reaction. Treatment with atorvastatin (n = 10), but not with fluvastatin (n = 10), resulted in 3-fold higher expression of SLCO2B1 compared with placebo-treated patients (n = 9) (P < 0.05). Atorvastatin increased the expression of both ABCB1 and ABCG2 by more than 2-fold (P < 0.05). No difference was found in CYP2C9, CYP3A4, or SLCO1B1 mRNA expression in patients administered statins or those administered placebo. Premenopausal women (n = 8) had higher expression of CYP3A4 (P < 0.05) and lower expression of CYP2C9 (P < 0.05) compared with postmenopausal women (n = 10) and men (n = 11), respectively. Here we show for the first time that atorvastatin treatment leads to increased expression of the membrane transporters SLCO2B1, ABCB1, and ABCG2 in human liver tissue, which potentially may counteract the efficacy of the treatment, and our findings may cast light on the mechanisms of clinical problems with adverse reactions and drug interactions in statin treatment.

Using genetic and clinical factors to predict tacrolimus dose in renal transplant recipients

AIMS

Tacrolimus has a narrow therapeutic window and shows significant interindividual difference in dose requirement. In this study we aim to first identify genetic factors that impact tacrolimus dose using a candidate gene association approach, and then generate a personalized algorithm combining identified genetic and clinical factors to predict individualized tacrolimus dose.

MATERIALS & METHODS

We screened 768 SNPs in 15 candidate genes in metabolism, transport and calcineurin inhibition pathways of tacrolimus, for association with tacrolimus dose in a discovery cohort of 96 patients.

RESULTS

Four polymorphisms in CYP3A5 and one polymorphism in CYP3A4 were identified to be significantly associated with tacrolimus stable dose (p < 8.46 × 10(-5)). The same SNPs were identified when dose-normalized trough tacrolimus concentration was analyzed. The CYP3A5*1 allele was associated with significantly higher stable dose, bigger dose increase, higher risk of being underdosed and lower incidence of post-transplant hyperlipidemia. ABCB1 polymorphisms were not associated with stable dose. No significant difference was found between CYP3A5 expressers and nonexpressers in incidence of acute rejection and time to first rejection. Age, ethnicity and CYP3A inhibitor use could predict 30% of tacrolimus dosing variability. Adding the identified genetic polymorphisms to the algorithm increased the predictability to 58%. In two validation cohorts of 77 and 64 patients, the algorithm containing both genetic and clinical factors produced correlation coefficients of 0.63 and 0.42, respectively. This algorithm gave a prediction of the stable doses closer to the actual doses when compared with another algorithm based only on the CYP3A5 genotype.

CONCLUSION

CYP3A5 genotype is the most significant genetic factor that impacts tacrolimus dose among the genes studied. This study generated the first pharmacogenomics model that predicts tacrolimus stable dose based on age, ethnicity, genotype and comedication use. Our results highlight the importance of incorporating both genetic and clinical, demographic factors into dose prediction.

Effects of lipid-lowering drugs on reverse cholesterol transport gene expressions in peripheral blood mononuclear and HepG2 cells

AIMS

The ATP-binding cassette transporters, ABCA1 and ABCG1, are LXR-target genes that play an important role in reverse cholesterol transport. We examined the effects of inhibitors of the cholesterol absorption (ezetimibe) and synthesis (statins) on expression of these transporters in HepG2 cells and peripheral blood mononuclear cells (PBMCs) of individuals with primary (and nonfamilial) hypercholesterolemia (HC).

MATERIALS & METHODS

A total of 48 HC individuals were treated with atorvastatin (10 mg/day/4 weeks) and 23 were treated with ezetimibe (10 mg/day/4 weeks), followed by simvastatin (10 mg/day/8 weeks) and simvastatin plus ezetimibe (10 mg of each/day/4 weeks). Gene expression was examined in statin- or ezetimibe-treated and control HepG2 cells as well as PBMCs using real-time PCR.

RESULTS

In PBMCs, statins and ezetimibe downregulated ABCA1 and ABCG1 mRNA expression but did not modulate NR1H2 (LXR-β) and NR1H3 (LXR-α) levels. Positive correlations of ABCA1 with ABCG1 and of NR1H2 with NR1H3 expressions were found in all phases of the treatments. In HepG2 cells, ABCA1 mRNA levels remained unaltered while ABCG1 expression was increased by statin (1.0-10.0 µM) or ezetimibe (5.0 µM) treatments. Atorvastatin upregulated NR1H2 and NR1H3 only at 10.0 µM, meanwhile ezetimibe (1.0-5.0 µM) downregulated NR1H2 but did not change NR1H3 expression.

CONCLUSION

Our findings reveal that lipid-lowering drugs downregulate ABCA1 and ABCG1 mRNA expression in PBMCs of HC individuals and exhibit differential effects on HepG2 cells. Moreover, they indicate that the ABCA1 and ABCG1 transcript levels were not correlated directly to LXR mRNA expression in both cell models treated with lipid-lowering drugs.

Structure and function of ABCG2-rich extracellular vesicles mediating multidrug resistance

Multidrug resistance (MDR) is a major impediment to curative cancer chemotherapy. The ATP-Binding Cassette transporters ABCG2, ABCB1 and ABCC2 form a unique defense network against multiple structurally and functionally distinct chemotherapeutics, thereby resulting in MDR. Thus, deciphering novel mechanisms of MDR and their overcoming is a major goal of cancer research. Recently we have shown that overexpression of ABCG2 in the membrane of novel extracellular vesicles (EVs) in breast cancer cells results in mitoxantrone resistance due to its dramatic sequestration in EVs. However, nothing is known about EVs structure, biogenesis and their ability to concentrate multiple antitumor agents. To this end, we here found that EVs are structural and functional homologues of bile canaliculi, are apically localized, sealed structures reinforced by an actin-based cytoskeleton and secluded from the extracellular milieu by the tight junction proteins occludin and ZO-1. Apart from ABCG2, ABCB1 and ABCC2 were also selectively targeted to the membrane of EVs. Moreover, Ezrin-Radixin-Moesin protein complex selectively localized to the border of the EVs membrane, suggesting a key role for the tethering of MDR pumps to the actin cytoskeleton. The ability of EVs to concentrate and sequester different antitumor drugs was also explored. Taking advantage of the endogenous fluorescence of anticancer drugs, we found that EVs-forming breast cancer cells display high level resistance to topotecan, imidazoacridinones and methotrexate via efficient intravesicular drug concentration hence sequestering them away from their cellular targets. Thus, we identified a new modality of anticancer drug compartmentalization and resistance in which multiple chemotherapeutics are actively pumped from the cytoplasm and highly concentrated within the lumen of EVs via a network of MDR transporters differentially targeted to the EVs membrane. We propose a composite model for the structure and function of MDR pump-rich EVs in cancer cells and their ability to confer multiple anticancer drug resistance.

The expression of efflux and uptake transporters are regulated by statins in Caco-2 and HepG2 cells

AIM

Statin disposition and response are greatly determined by the activities of drug metabolizing enzymes and efflux/ uptake transporters. There is little information on the regulation of these proteins in human cells after statin therapy. In this study, the effects of atorvastatin and simvastatin on mRNA expression of efflux (ABCB1, ABCG2 and ABCC2) and uptake (SLCO1B1, SLCO2B1 and SLC22A1) drug transporters in Caco-2 and HepG2 cells were investigated.

METHODS

Quantitative real-time PCR was used to measure mRNA levels after exposure of HepG2 and Caco-2 cells to statins.

RESULTS

Differences in mRNA basal levels of the transporters were as follows: ABCC2>ABCG2>ABCB1>SLCO1B1>>>SLC22A1>SLC O2B1 for HepG2 cells, and SLCO2B1>>ABCC2>ABCB1>ABCG2>>>SLC22A1 for Caco-2 cells. While for HepG2 cells, ABCC2, ABCG2 and SLCO2B1 mRNA levels were significantly up-regulated at 1, 10 and 20 micromol/L after 12 or 24 h treatment, in Caco-2 cells, only the efflux transporter ABCB1 was significantly down-regulated by two-fold following a 12 h treatment with atorvastatin. Interestingly, whereas treatment with simvastatin had no effect on mRNA levels of the transporters in HepG2 cells, in Caco-2 cells the statin significantly down-regulated ABCB1, ABCC2, SLC22A1, and SLCO2B1 mRNA levels after 12 or 24 h treatment.

CONCLUSION

These findings reveal that statins exhibits differential effects on mRNA expression of drug transporters, and this effect depends on the cell type. Furthermore, alterations in the expression levels of drug transporters in the liver and/or intestine may contribute to the variability in oral disposition of statins.Acta Pharmacologica Sinica (2009) 30: 956-964; doi: 10.1038/aps.2009.85; published online 22 June 2009.

Impact of cholesterol on ABC and SLC transporters expression and function and its role in disposition variability to lipid-lowering drugs

This report focuses on the effects of cholesterol on the expression and function of the ATP-binding cassette (ABCB1, ABCG2 and ABCC2) and solute-linked carrier (SLCO1B1 and SLCO2B1) drug transporters with a particular focus on the potential impact of cholesterol on lipid-lowering drug disposition. Statins are the most active agents in the treatment of hypercholesterolemia. However, considerable interindividual variation exists in the response to statin therapy. Therefore, it would be huge progress if factors were identified that reliably differentiate between responders and nonresponders. Many studies have suggested that plasma lipid concentrations can affect drug disposition of compounds, such as ciclosporin and amphotericin B. Both compounds are able to affect the expression and function of ABC transporters. Although still speculative, these effects might be owing to the regulation of drug transporters by plasma cholesterol levels. Studies with normo- and hyper-cholesterolemic individuals, before and after atorvastatin treatment, have demonstrated that plasma cholesterol levels are correlated with drug transporter expression, as well as being related to atorvastatin’s cholesterol-lowering effect. The mechanism influencing the correlation between cholesterol levels and the expression and function of drug transporters remains unclear. Some studies provide strong evidence that nuclear receptors, such as the pregnane X receptor and the constitutive androstane receptor, mediate this effect. In the near future, pharmacogenomic studies with individuals in a pathological state should be performed in order to identify whether high plasma cholesterol levels might be a factor contributing to interindividual oral drug bioavailability.

ABCB1 and ABCC1 expression in peripheral mononuclear cells is influenced by gene polymorphisms and atorvastatin treatment

This study investigated the effects of atorvastatin on ABCB1 and ABCC1 mRNA expression on peripheral blood mononuclear cells (PBMC) and their relationship with gene polymorphisms and lowering-cholesterol response. One hundred and thirty-six individuals with hypercholesterolemia were selected and treated with atorvastatin (10 mg/day/4 weeks). Blood samples were collected for serum lipids and apolipoproteins measurements and DNA and RNA extraction. ABCB1 (C3435T and G2677T/A) and ABCC1 (G2012T) gene polymorphisms were identified by polymerase chain reaction-restriction (PCR)-RFLP and mRNA expression was measured in peripheral blood mononuclear cells by singleplex real-time PCR. ABCB1 polymorphisms were associated with risk for coronary artery disease (CAD) (p<0.05). After atorvastatin treatment, both ABCB1 and ABCC1 genes showed 50% reduction of the mRNA expression (p<0.05). Reduction of ABCB1 expression was associated with ABCB1 G2677T/A polymorphism (p=0.039). Basal ABCB1 mRNA in the lower quartile (<0.024) was associated with lower reduction rate of serum low-density lipoprotein (LDL) cholesterol (33.4+/-12.4%) and apolipoprotein B (apoB) (17.0+/-31.3%) when compared with the higher quartile (>0.085: LDL-c=40.3+/-14.3%; apoB=32.5+/-10.7%; p<0.05). ABCB1 substrates or inhibitors did not affect the baseline expression, while ABCB1 inhibitors reversed the effects of atorvastatin on both ABCB1 and ABCC1 transporters. In conclusion, ABCB1 and ABCC1 mRNA levels in PBMC are modulated by atorvastatin and ABCB1 G2677T/A polymorphism and ABCB1 baseline expression is related to differences in serum LDL cholesterol and apoB in response to atorvastatin.

Induction of P-glycoprotein expression and function in human intestinal epithelial cells (T84)

Intestinal induction of Pgp is known to limit the oral availability of certain drug compounds and give rise to detrimental drug-drug interactions. We have investigated the induction of P-glycoprotein (Pgp; MDR1) activity in a human intestinal epithelial cell line (T84) following pre-exposure to a panel of drug compounds, reported to be Pgp substrates, inhibitors or inducers. Human MDR1-transfected MDCKII epithelial monolayers were used to assess Pgp substrate interactions and inhibition of digoxin secretion by the selected drug compounds. The T84 cell line was used to assess induction of Pgp-mediated digoxin secretion following pre-exposure to the same compounds. Changes in gene expression (MDR1, MRP2, PXR and CAR) were determined by quantitative RT-PCR. Net transepithelial digoxin secretion was increased (1.3 fold, n=6, P<0.05) following pre-exposure to the PXR activator hyperforin (100nM, 72h), as was MDR1 mRNA expression (3.0 fold, n=4, P<0.05). A number of Pgp substrates (quinidine, amprenavir, irinotecan, topotecan, atorvastatin and erythromycin) induced net digoxin secretion, as did the non-Pgp substrate artemisinin. Various non-Pgp substrates demonstrated inhibition of digoxin secretion (verapamil, mifepristone, clotrimazole, mevastatin, diltiazem and isradipine) but did not induce Pgp-mediated digoxin secretion. Of the compounds that increased Pgp secretion, quinidine, topotecan, atorvastatin and amprenavir pre-exposure also elevated MDR1 mRNA levels, whereas erythromycin, irinotecan and artemisinin displayed no change in transcript levels. This indicates possible post-translational regulation of digoxin secretion. Finally, a strong correlation between drug modulation of MRP2 and PXR mRNA expression levels was evident.

Atorvastatin effects on SREBF1a and SCAP gene expression in mononuclear cells and its relation with lowering-lipids response

BACKGROUND

The transcription factors SREBP1 and SCAP are involved in intracellular cholesterol homeostasis. Polymorphisms of these genes have been associated with variations on serum lipid levels and response to statins that are potent cholesterol-lowering drugs. We evaluated the effects of atorvastatin on SREBF1a and SCAP mRNA expression in peripheral blood mononuclear cells (PBMC) and a possible association with gene polymorphisms and lowering-cholesterol response.

METHODS

Fifty-nine hypercholesterolemic patients were treated with atorvastatin (10 mg/day for 4 weeks). Serum lipid profile and mRNA expression in PBMC were assessed before and after the treatment. Gene expression was quantified by real-time PCR using GAPD as endogenous reference and mRNA expression in HepG2 cells as calibrator. SREBF1 -36delG and SCAP A2386G polymorphisms were detected by PCR-RFLP.

RESULTS

Our results showed that transcription of SREBF1a and SCAP was coordinately regulated by atorvastatin (r=0.595, p<0.001), and that reduction in SCAP transcription was associated with the 2386AA genotype (p=0.019). Individuals who responded to atorvastatin with a downregulation of SCAP had also a lower triglyceride compared to those who responded to atorvastatin with an upregulation of SCAP.

CONCLUSION

Atorvastatin has differential effects on SREBF1a and SCAP mRNA expression in PBMC that are associated with baseline transcription levels, triglycerides response to atorvastatin and SCAP A2386G polymorphism.

P-glycoprotein is downregulated in KG1a-primitive leukemia cells by LDL cholesterol deprivation and by HMG-CoA reductase inhibitors

OBJECTIVE

P-glycoprotein (pgp) is a membrane transporter encoded by the multidrug resistance (MDR1, ABCB1) gene. Pgp is a poor prognostic factor in elderly patients with acute myeloid leukemia (AML). In addition to its role in drug efflux, pgp has been implicated in cellular cholesterol homeostasis. We investigated the effects of exogenous cholesterol removal on pgp expression and function.

METHODS

KG1a drug-naïve, primitive leukemia cells were cultured in serum-free medium with or without the addition of low-density lipoprotein (LDL) cholesterol. After 72 hours, pgp expression and function was assessed by flow cytometry and total cholesterol content of the KG1a cells was determined by the Amplex Red cholesterol assay. The addition of clinically available cholesterol-lowering agents, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors to KG1a cells was also assessed.

RESULTS

There was a 39% (SEM = 8.3%; p = 0.03) decrease in pgp protein expression after 3 days of serum-free culture. The decrease was also observed at the message and functional levels. In the presence of low-density lipoprotein cholesterol, pgp expression was restored to 86% of the basal value. Addition of a HMG-CoA reductase inhibitor to KG1a cells resulted in an additional 26% (lovastatin, p = 0.03) and 16% (pravastatin, p = 0.05) reduction in pgp, respectively. Furthermore, toxicity of the pgp substrate drug daunorubicin was enhanced following lovastatin preculture (p = 0.04).

CONCLUSION

LDL cholesterol contributes to pgp expression and chemoresistance in primitive leukemia cells. Use of HMG-CoA reductase inhibitors may be of clinical value in lowering pgp expression in AML.