Molecular Characteristics of Everolimus-resistant Renal Cell Carcinoma Cells Generated by Continuous Exposure to Everolimus.

BACKGROUND/AIM: Mammalian target of rapamycin (mTOR) inhibitors represent the standard of care for metastatic renal cell carcinoma (RCC). However, treatment outcomes are relatively poor, suggesting a potential problem with tolerating mTOR inhibitors. The aim of this study was to establish everolimus-resistant sublines and to compare their molecular characteristics with those of their counterparts. MATERIALS AND METHODS: Human-derived RCC, Caki-2, and 786-O cells were continuously exposed to everolimus at 1 µM, and the established resistant sublines were designated as Caki/EV and 786/EV, respectively. Cellular characteristics were compared between both cells. RESULTS: Caki/EV and 786/EV cells showed a decrease in sensitivity to everolimus as well as other mTOR inhibitors. Expression of mTOR and its effectors exhibited no alteration in resistant sublines and their counterparts. However, phosphorylation of S6K, an index of mTOR activity, decreased in resistant sublines. PCR array analysis of mTOR signaling pathway-related factors indicated that the expression of INSR, TP53, and IGFBP3 increased in Caki/EV cells, whereas that of TELO2, HRAS, and SGK1 was up-regulated in 786/EV cells. The levels of DDIT4, DEPTOR, HIF1A, and PLD1 mRNAs decreased in both cell lines. CONCLUSION: The novel everolimus-resistant Caki/EV and 786/EV cells exhibited cross-resistance to other mTOR inhibitors and decreased mTOR activity. Furthermore, down-regulation of DDIT4, DEPTOR, HIF1A, and PLD1 may contribute to everolimus resistance.

Induction of Cross-resistance to ABCB1 Substrates in Venetoclax-resistant Human Leukemia HL60 Cells.

BACKGROUND/AIM: Resistance to venetoclax, a selective inhibitor of BCL2 apoptosis regulator (BCL2), is regarded as a clinical problem. However, it is unclear whether resistance to venetoclax induces cross-resistance to other drugs. MATERIALS AND METHODS: Venetoclax-resistant HL60/VEN cells were newly established through continuous exposure of human acute promyelocytic leukemia HL60 cells to venetoclax, and drug sensitivity, apoptotic activity, and mRNA expression were compared between HL60 and HL60/VEN cells. RESULTS: HL60/VEN cells displayed approximately 3-fold resistance to venetoclax, maintained their ability to synthesize DNA and had low apoptotic activity. HL60/VEN cells also exhibited diverse sensitivity to cytotoxic drugs, especially resistance to ATP binding cassette subfamily B member 1 (ABCB1) substrates, and up-regulation of ABCB1 mRNA. However, the sensitivity of HL60/VEN cells to venetoclax was not restored by ABCB1 inhibitor. ABCB1-overexpressing cells did not show resistance to venetoclax. CONCLUSION: HL60/VEN cells exhibited up-regulation of ABCB1 in addition to an alteration in apoptotic activity, and cross-resistance to ABCB1 substrates was clarified. However, sensitivity to venetoclax was hardly affected by ABCB1.

[Analysis of Time-to-onset and Onset-pattern of Interstitial Lung Disease after the Administration of Monoclonal Antibody Agents].

The aim of this study has been to investigate the time-to-onset and onset-pattern of drug-induced interstitial lung disease (DILD) after the administration of monoclonal antibodies through the use of the spontaneous adverse reaction reporting system of the Japanese Adverse Drug Event Report database. DILD datasets for adalimumab, bevacizumab, cetuximab, denosumab, golimumab, infliximab, nivolumab, panitumumab, pembrolizumab, tocilizumab, and trastuzumab were used to calculate the median time-to-onset of DILD, as well as the Weibull distribution parameters. The median time-to-onset of DILD for pembrolizumab and infliximab was within 1 month. The median time-to-onset of DILD for cetuximab, nivolumab, panitumumab, bevacizumab, golimumab, trastuzumab, and tocilizumab ranged from 1 to 2 months. The median time-to-onset of DILD for denosumab and adalimumab was more than 2 months. Infliximab, trastuzumab and tocilizumab, and denosumab were estimated to fit the early failure type profile of the Weibull distribution parameters. Cetuximab, nivolumab, panitumumab, bevacizumab, golimumab, and adalimumab were estimated to fit the random failure type profile. Pembrolizumab was estimated to fit the wear out failure type profile. Cluster analysis was performed to classify the time-to-onset patterns of DILD. Hierarchical cluster analysis showed 3 clusters. The findings of this study established both the most likely time period and onset-pattern of DILD that can occur in patients after the administration of monoclonal antibody agents.

Pharmacokinetic Interaction Between Tacrolimus and Fentanyl in Patients Receiving Allogeneic Hematopoietic Stem Cell Transplantation.

BACKGROUND Tacrolimus and fentanyl are well-known cytochrome P450 (CYP) 3A4 substrates with a narrow therapeutic range. However, the pharmacokinetic interaction between tacrolimus and fentanyl is unclear. The aim of this study was to determine whether drug interaction exists between tacrolimus and fentanyl. MATERIAL AND METHODS A retrospective study was performed in 6 patients who had received allogeneic hematopoietic stem cell transplantation between April 2010 and March 2015. The patients received continuous intravenous infusion of fentanyl with concomitant use of tacrolimus, and the blood concentrations of tacrolimus were evaluated using fluorescence polarization immunoassay. RESULTS The clearance (CL) of tacrolimus decreased significantly from 1.28 to 0.68 mL/min/kg with concomitant use of fentanyl. The CL changed with time and dose of fentanyl administration. In addition, the CL of tacrolimus was reverted by stopping fentanyl infusion. Horn's drug interaction probability scale indicated a probable category or possible category, suggesting a drug interaction between tacrolimus and fentanyl. No patient showed a difference in hepatic or renal function before and after fentanyl administration. No additional administration of other CYP3A4 inhibitors was observed, suggesting that the drug interaction was mediated by CYP3A4. CONCLUSIONS The influence of fentanyl on the pharmacokinetics of tacrolimus was demonstrated to be of clinical importance. It is proposed that the dose of tacrolimus be reduced by 40% when used in combination with fentanyl.

Combination of lenalidomide and low-dose dexamethasone therapy promotes the anticoagulant activity of warfarin in patients with immunoglobulin light-chain amyloidosis.

The present study aimed to evaluate the drug interactions between warfarin and combination chemotherapy with lenalidomide and low-dose dexamethasone in immunoglobulin light-chain (AL) amyloidosis patients with unstable international normalized ratios (INR). The changes to INR values over time in 3 AL amyloidosis patients treated with warfarin and a combination of lenalidomide and low-dose dexamethasone between March 2011 and February 2015 were analyzed retrospectively. The mean INR value was 1.52 prior to the combination chemotherapy, and the value increased 1.7-fold during treatment. The median time to reach maximum values was 17 days. Horn's drug Interaction Probability Scale indicated a possible interaction between lenalidomide and warfarin. These patients exhibited no marked alterations in hepatic function or serum albumin concentrations prior to and following combination chemotherapy and no additional administration of CYP2C9 inhibitors or vitamin K supplements was conducted. In addition, no patient experienced chemotherapy-induced nausea or appetite loss. These findings suggest that the total clearance or protein binding of warfarin remained unchanged. Therefore, the combination of warfarin and lenalidomide may cause a pharmacodynamic interaction, more likely by inhibiting the production of interleukin-6. In conclusion, clinically important interactions between warfarin and lenalidomide and low-dose dexamethasone therapy were observed in AL amyloidosis patients, where INR values signi ficantly increased. Therefore, close and regular monitoring of patients during the course of treatment is important, and the dose of warfarin should be reduced if required.

The interaction between oral melphalan and gastric antisecretory drugs: Impact on clinical efficacy and toxicity.

The aim of the present study was to clarify whether gastric antisecretory drugs affect the clinical efficacy and toxicity of orally administered melphalan in patients with multiple myeloma. A total of 10 patients receiving bortezomib plus oral melphalan and prednisolone (VMP) therapy between December 2011 and November 2014 were analyzed retrospectively. The patients were divided into a control group (seven patients) and a concomitant group (three patients, who were also administered with gastric antisecretory drugs). The gastric antisecretory drugs included rabeprazole sodium (two patients) and famotidine (one patient). No significant differences between the groups were observed in either the characteristics of the patients or the VMP regimen. The levels of monoclonal protein (M protein) in the control group tended to decrease (with a VMP cycle-dependency), although they were primarily stable in the concomitant group. During the second and third VMP cycles, the levels of M protein were markedly lower in the control group compared with the concomitant group. All the patients in the control group achieved a partial response, whereas those in the concomitant group exhibited stable disease. Hematological toxicity levels were revealed to be comparable between the two groups, whereas gastrointestinal toxicity was more prevalent in the control group. In conclusion, the results of the present study suggested that the clinical efficacy of melphalan may be reduced by the co-administration of gastric antisecretory drugs. This interaction may result in decreased toxicity and clinical efficacy of melphalan.

Quantitative interactome analysis reveals a chemoresistant edgotype.

Chemoresistance is a common mode of therapy failure for many cancers. Tumours develop resistance to chemotherapeutics through a variety of mechanisms, with proteins serving pivotal roles. Changes in protein conformations and interactions affect the cellular response to environmental conditions contributing to the development of new phenotypes. The ability to understand how protein interaction networks adapt to yield new function or alter phenotype is limited by the inability to determine structural and protein interaction changes on a proteomic scale. Here, chemical crosslinking and mass spectrometry were employed to quantify changes in protein structures and interactions in multidrug-resistant human carcinoma cells. Quantitative analysis of the largest crosslinking-derived, protein interaction network comprising 1,391 crosslinked peptides allows for 'edgotype' analysis in a cell model of chemoresistance. We detect consistent changes to protein interactions and structures, including those involving cytokeratins, topoisomerase-2-alpha, and post-translationally modified histones, which correlate with a chemoresistant phenotype.

Induction of epithelial-mesenchymal transition via activation of epidermal growth factor receptor contributes to sunitinib resistance in human renal cell carcinoma cell lines.

Sunitinib is widely used for treating renal cell carcinoma (RCC). However, some patients do not respond to treatment with this drug. We aimed to study the association between sunitinib sensitivity and epithelial-mesenchymal transition (EMT) regulation via epidermal growth factor receptor (EGFR) signaling, which is a mechanism of resistance to anticancer drugs. Three RCC cell lines (786-O, ACHN, and Caki-1) were used, and then we evaluated cell viability, EMT regulatory proteins, and signal transduction with sunitinib treatment. Cell viability of 786-O cells was maintained after treatment with sunitinib. After treatment with sunitinib, EGFR phosphorylation increased in 786-O cells, resulting in an increase in the phosphorylation of extracellular signal-regulated kinase, nuclear translocation of ß-catenin, and expression of mesenchymal markers. These results suggest that sunitinib induced EMT via activation of EGFR in 786-O cells, but not in ACHN and Caki-1 cells. Caki-1/SN cells, a resistant cell line generated by continuous exposure to sunitinib, displayed increased phosphorylation of EGFR. Cell viability in the presence of sunitinib was decreased by erlotinib, as the selective inhibitor of EGFR, treatment in 786-O and Caki-1/SN cells. Similarly, erlotinib suppressed sunitinib-induced EGFR activation and upregulated mesenchymal markers. Thus, we postulate that resistance to sunitinib in RCC may be associated with EMT caused by activation of EGFR.

Factors affecting the sensitivity of human-derived esophageal carcinoma cell lines to 5-fluorouracil and cisplatin.

Effective chemotherapy against esophageal carcinoma is considered achievable with a combination of 5-fluorouracil (5-FU) and cisplatin (CDDP). However, chemo-therapy remains ineffective in certain patients. The aim of this study was to clarify the factors which affect sensitivity to 5-FU and CDDP. The effects of factors known to influence sensitivity to 5-FU and CDDP, namely transporters, DNA repair enzymes and metabolic enzymes, were examined. mRNA levels of four transporters, SLC22A2, SLC23A2, ABCB1 and ABCC2, two DNA repair-related enzymes, Rad51 and MSH2, and one metabolic enzyme, dihydropyrimidine dehydrogenase (DPYD), showed a strong correlation (|r|>0.7) with IC(50) values for 5-FU. In addition, the mRNA levels of ABCC2, MSH2 and DPYD showed a strong correlation (|r|>0.7) with the IC(50) values for CDDP. Gimeracil, a DPYD inhibitor, enhanced the sensitivity of some cells to 5-FU but decreased the sensitivity of all the cells to CDDP. The inhibitory effects of ABCC2 with MK571 did not correspond to those observed in the correlation analysis. In conclusion, mRNA levels of SLC22A2, SLC23A2, ABCB1, ABCC2, Rad51, MSH2 and DPYD were confirmed to be strongly correlated with IC50 values for 5-FU, and mRNA levels of ABCC2, MSH2 and DPYD were confirmed to be strongly correlated with IC(50) values for CDDP. In addition, the inhibition of DPYD appeared to affect the cytotoxicity of CDDP.

Effect of dexamethasone on extracellular secretion of cystatin C in cancer cell lines.

The aim of the present study was to investigate dexamethasone (DEX)-induced secretion of cystatin C (Cys C) and the effect of cisplatin (CDDP) and 5-fluorouracil (5-FU) on Cys C secretion in human cancer cell lines. KYSE150, A549 and Caki-2 human cancer cell lines were cultured on plastic dishes and treated with DEX (100 nM) for 24, 48 and 72 h. KYSE150 cells were co-treated with DEX, CDDP (10 µM), and 5-FU (2 µM). The effects of DEX, CDDP and 5-FU on cell viability were evaluated. Results showed Cys C secretion levels in the culture medium of DEX-treated KYSE150 cells to be 1.8- to 2.3-fold higher compared to those in the culture medium of control cells. A similar tendency was observed in A549 cells at all the time points, whereas a significant increase in the Cys C secretion by Caki-2 cells was observed only 24 h after DEX treatment. Regarding KYSE150 cells, the secretion of Cys C was also enhanced by co-treatment of CDDP or 5-FU with DEX, although it was not affected by the co-administration of DEX and mifepristone, a glucocorticoid receptor antagonist. At concentrations that are typically used in esophageal cancer chemotherapy, CDDP and 5-FU demonstrated a moderate level of cytotoxicity in KYSE150 cells in contrast to DEX. These findings suggested that DEX has the potential to enhance the extracellular secretion of Cys C in esophageal cancer cells, possibly due to the transcriptional regulation mediated by glucocorticoid receptor activity.

Effects of α-adrenoceptor antagonists on ABCG2/BCRP-mediated resistance and transport.

Acquired resistance of cancer cells to various chemotherapeutic agents is known as multidrug resistance, and remains a critical factor in the success of cancer treatment. It is necessary to develop the inhibitors for multidrug resistance. The aim of this study was to examine the effects of eight α-adrenoceptor antagonists on ABCG2/BCRP-mediated resistance and transport. Previously established HeLa/SN100 cells, which overexpress ABCG2/BCRP but not ABCB1/MDR1, were used. The effects of the antagonists on sensitivity to mitoxantrone and the transport activity of Hoehst33342, both substrates for ABCG2/BCRP, were evaluated using the WST-1 assay and cellular kinetics, respectively. ABCG2/BCRP mRNA expression and the cell cycle were also examined by real-time RT-PCR and flow cytometry, respectively. Sensitivity to mitoxantrone was reversed by the α-adrenoceptor antagonists in a concentration-dependent manner, although such effects were also found in the parental HeLa cells. Levels of ABCG2/BCRP mRNA expression were not influenced by the antagonists. The transport activity of Hoechst33342 was decreased by doxazosin and prazosin, but unaffected by the other antagonists. In addition, doxazosin and prazosin increased the proportion of S phase cells in the cultures treated with mitoxantrone, whereas the other α-adrenoceptor antagonists increased the percentage of cells in G(2)/M phase. These findings suggested that doxazosin and prazosin reversed resistance mainly by inhibiting ABCG2/BCRP-mediated transport, but the others affected sensitivity to mitoxantrone via a different mechanism.

Treatment schedule-dependent effect of 5-fluorouracil and platinum derivatives in colorectal cancer cells.

AIM: Combination chemotherapy for treating cancer often is superior in clinical efficacy to monotherapy. The aim of this study was to investigate the schedule-dependent effect of 5-fluorouracil (5-FU) and platinum derivatives (cisplatin or oxaliplatin) in colorectal cancer (CRC) cell lines, and to explore factors affecting it. METHODS: Two human CRC-derived cell lines, DLD-1 and HCT116, were used. Three treatment schedules were tested, and growth inhibitory effects were evaluated with a WST-1 assay. Combined effects were assessed with isobolograms and a combination index. Cellular accumulation and DNA-binding of platinum were measured with inductively coupled plasma mass spectrometry. RESULTS: Exposure to 5-FU followed by cisplatin produced synergistic effects in DLD-1 cells, and the amount of platinum bound to DNA was substantially increased as compared with that for other schedules. 5-FU and oxaliplatin also tended to be synergistic when 5-FU was given first, but no significant change in the cellular kinetics of platinum was observed. On the other hand, in HCT116 cells, the combined effects of 5-FU and platinum derivatives were comparable among the three schedules. CONCLUSION: Exposure to 5-FU followed by cisplatin had a synergistic effect in DLD-1 cells, suggesting that the amount of platinum bound to DNA contributes to this result. Also, the effect was dependent on the type of platinum derivative and cell.

Differential effects of calcium antagonists on ABCG2/BCRP-mediated drug resistance and transport in SN-38-resistant HeLa cells.

The effects of 9 calcium antagonists on ABCG2/BCRP-mediated resistance and transport were examined in HeLa and SN-38-resistant HeLa (HeLa/SN100) cells, overexpressing ABCG2/BCRP. Sensitivity to mitoxantrone, an ABCG2/BCRP substrate, in HeLa/SN100 cells was significantly reversed by the coexistence of the calcium antagonists, except for diltiazem and verapamil. The accelerated transport activity of Hoechst33342, an ABCG2/BCRP substrate, in HeLa/SN100 cells was significantly decreased by the presence of the calcium antagonists, except for diltiazem, nifedipine or verapamil, returning to the level of HeLa cells. The present study classifies the calcium antagonists into 3 categories: strong (benidipine, felodipine, nicardipine, nisoldipine and nitrendipine), moderate (amlodipine and nifedipine) and weak (diltiazem and verapamil) inhibitors of ABCG2/BCRP.

Quantitative proteomic and interaction network analysis of cisplatin resistance in HeLa cells.

Cisplatin along with other platinum based drugs are some of the most widely used chemotherapeutic agents. However drug resistance is a major problem for the successful chemotherapeutic treatment of cancer. Current evidence suggests that drug resistance is a multifactorial problem due to changes in the expression levels and activity of a wide number of proteins. A majority of the studies to date have quantified mRNA levels between drug resistant and drug sensitive cell lines. Unfortunately mRNA levels do not always correlate with protein expression levels due to post-transcriptional changes in protein abundance. Therefore global quantitative proteomics screens are needed to identify the protein targets that are differentially expressed in drug resistant cell lines. Here we employ a quantitative proteomics technique using stable isotope labeling with amino acids in cell culture (SILAC) coupled with mass spectrometry to quantify changes in protein levels between cisplatin resistant (HeLa/CDDP) and sensitive HeLa cells in an unbiased fashion. A total of 856 proteins were identified and quantified, with 374 displaying significantly altered expression levels between the cell lines. Expression level data was then integrated with a network of protein-protein interactions, and biological pathways to obtain a systems level view of proteome changes which occur with cisplatin resistance. Several of these proteins have been previously implicated in resistance towards platinum-based and other drugs, while many represent new potential markers or therapeutic targets.

Inhibitory effects of uraemic toxins 3-indoxyl sulfate and p-cresol on losartan metabolism in vitro.

OBJECTIVES: The purpose of this study was to clarify the cause of decreased metabolic clearance of losartan in patients with end-stage renal failure. The influence of serum from haemodialysis patients (uraemic serum) and uraemic toxins on the metabolism of losartan to EXP-3174 was investigated in vitro. METHODS: The formation of EXP-3174 was estimated using pooled human liver microsomes. 3-Carboxy-4-methyl-5-propyl-2-furanpropanoic acid, hippuric acid, indole-3-acetic acid, 3-indoxyl sulfate and p-cresol were used as uraemic toxins. KEY FINDINGS: Uraemic serum potently decreased the formation of EXP-3174 in pooled human liver microsomes. In addition, 3-indoxyl sulfate and p-cresol significantly decreased the formation of EXP-3174 in a concentration-dependent manner. Furthermore, normal serum (10% v/v) with both 3-indoxyl sulfate and p-cresol (both 20 micromol/l) significantly decreased the formation of EXP-3174 by 46%, which was similar to the level of inhibition with uraemic serum (10% v/v). CONCLUSIONS: These results suggest that decreased the metabolic clearance of losartan in patients with end-stage renal failure is partly due to high concentrations of 3-indoxyl sulfate and p-cresol.

Characterization, in vitro cytotoxicity and cellular accumulation of paclitaxel-loaded lipid nano-emulsions.

Lipid nano-emulsions (LNEs) having a mean droplet size of approximately 50 nm were investigated as drug carriers for paclitaxel (TXL) to achieve its satisfactory loadings and to develop a pharmaceutically acceptable alternative to the current formulation, Taxol. TXL was incorporated into the LNEs at 2.0 mg/ml without changes in particle size or drug precipitation. In the cytotoxicity study, TXL-loaded LNEs had cytotoxicity to HeLa cells equivalent to that of TXL alone; the 50% growth inhibitory concentrations (IC(50)) of TXL-loaded LNEs and TXL alone were 1.53 +/- 0.23 nM and 1.76 +/- 0.08 nM, respectively. However, a cellular accumulation study using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a fluorescent probe showed that the accumulation of DPH-loaded LNEs in HeLa cells was remarkably lower than that of DPH alone. These results indicated that LNEs were a useful vehicle for TXL, even though LNEs themselves could not be efficiently accumulated in HeLa cells.

Effects of nonsteroidal anti-inflammatory drugs on the expression and function of P-glycoprotein/MDR1 in Caco-2 cells.

The aim of this study was to examine the effects of 16 kinds of nonsteroidal anti-inflammatory drugs (NSAIDs) on P-glycoprotein/MDR1 in Caco-2 cells as an intestinal epithelial cell model. Cells were treated with NSAIDs for 24 hours, and then, the expression of MDR1 mRNA was evaluated by reverse-transcriptase polymerase chain reaction. The function of MDR1 in cells pretreated with NSAIDs for 48 hours was evaluated by measuring the cellular amount of rhodamine123, which is a substrate of MDR1. The expression of MDR1 mRNA was increased by diclofenac, fenbufen, indomethacin, and nimesulide and the tended to be increased by meloxicam, mepirizole, and sulindac. However, pretreatment for 48 hours with diclofenac, indomethacin, or nimesulide, but not fenbufen, resulted in a significant increase in the amount of rhodamine123 accumulated. Although NSAIDs without effects on the expression of MDR1 mRNA altered the accumulation of rhodamine123 significantly, the efflux of rhodamine123 from cells was unchanged. In conclusion, the expression of MDR1 mRNA in Caco-2 cells was demonstrated to be increased by treatment with some NSAIDs, although the transport function of MDR1 was unchanged. These findings imply that the NSAIDs did not cause the drug interaction via MDR1 induction.

[Equalization of breast cancer chemotherapy at general hospital( II )-evaluation of safety in FEC and TC regimens].

The safety of epirubicin (75 mg/m(2)), 5-fluorouracil (500 mg/m(2)) plus cyclophosphamide (500 mg/m(2)) (FEC75 therapy) and docetaxel (75 mg/m(2)) plus cyclophosphamide (600 mg/m(2)) (TC therapy) every three weeks as neoadjuvant or adjuvant chemotherapy was evaluated. Six or 9 patients received FEC75 or TC therapy, respectively. The nadir of white blood cells and neutrocyte counts in FEC75 and TC therapy were after 11-15 days and 8-11 days of chemotherapy, respectively. On the other hand, those of monocyte and reticulocyte counts were after 8-11 and 4-8 days for FEC75 and TC therapy, respectively. This suggests that there is a lag time in these parameters for the evaluation of myelosuppression in each chemotherapy regimen, resulting in the prediction of the degree of myelotoxicity by these profiles. Although 2 patients who received TC therapy encountered febrile neutropenia, the symptoms were improved by quinolones, and so granulocyte colony-stimulating factor was not needed. In addition, remarkable non-hematological side effects were not observed, and, therefore, almost all chemotherapy was performed as scheduled. From these results, FEC75 and TC therapy are considered to be safe.

Effects of alpha-adrenoceptor antagonist doxazosin on MDR1-mediated multidrug resistance and transcellular transport.

The purpose of this study is to examine the effects of doxazosin, an alpha-adrenoceptor antagonist, on P-glycoprotein/MDR1-mediated multidrug resistance (MDR) and the transport of anticancer drugs. The effects of doxazosin, prazosin, and terazosin on MDR1-mediated MDR were assessed in human cervical carcinoma HeLa cells and the MDR1-overexpressing derivative Hvrl00-6, established by stepwise increases of the vinblastine concentration in the culture medium. The effects of doxazosin on the transcellular transport and intracellular accumulation of [3H]vinblastine, [3H]daunorubicin, and [3H]digoxin, all MDR1 substrates, were evaluated using LLC-GA5-COL150 cell monolayers, established by transfection of human MDR1 cDNA into porcine kidney epithelial LLC-PK1 cells. The sensitivity to vinblastine and paclitaxel of Hvrl00-6 cells was increased at 3.4- and 17.5-fold, respectively, by the addition of 1 microM doxazosin, whereas prazosin and terazosin had weaker or no such effects. Prazosin at 1 microM had a reversal effect on the sensitivity to vinblastine, whereas terazosin had no effect. In transport experiments, doxazosin concentration dependently increased the apical-to-basal transport of radiolabeled drugs in LLC-GA5-COL150 cells, but did not show remarkable effects on the basal-to-apical transport. In addition, doxazosin restored the intracellular accumulation in a concentration-dependent manner in LLC-GA5-COL150 cells. Doxazosin may partly reverse MDR by inhibiting MDR1-mediated transport, making it a candidate lead compound in the development of a reversing agent for MDR.

The structure-activity correlation on the inhibitory effects of flavonoids on cytochrome P450 3A activity.

Flavonoids are divided into flavones, flavonols, flavanones, and isoflavones etc. according to their basal structure, and are known to include compounds with physiological and pharmacological effects such as anti-oxidant, anti-tumor, and anti-inflammation activities. The ingestion of flavonoids may induce pharmacokinetic interactions through the co-administration of drugs. In this study, we investigated the inhibitory potentials on cytochrome P450 (CYP) 3A activity of 23 flavonoids using human liver microsomes, and tried to identify the molecular features that cause the inhibition of CYP3A. The activity of testosterone 6beta-hydroxylate was evaluated to quantify CYP3A activity. We analyzed Quantification Theory I, in which extreme values of the inhibitory effects of CYP3A activity were tested with flavonoids supplied at a level of 10 microM. The inhibitory effects of flavonoids ranged widely from 1.5 microM to more than 100 microM for the half maximal inhibitory concentration. Because the inhibitory effects were only weakly correlated with the pK(a) value, the inhibitory effects could not be accounted for by the molecular characteristics of the flavonoids. On the other hand, flavones with the basal structure and hydroxylation at positions 7 and 4' showed significantly increased inhibitory effects on CYP3A activity. In addition, the hydroxylation of position 2' and 3', methoxylation of position 4', and the isoflavone basal structure significantly decreased the inhibitory effects on CYP3A activity. In conclusion, the basal structure and the substituents of flavonoids are important in the inhibitory effects of flavonoids on CYP3A activity.