Reduction of doxorubicin and oracin and induction of carbonyl reductase in human breast carcinoma MCF-7 cells

Esterase-Responsive Fluorogenic Prodrugs of Aldose Reductase Inhibitor Epalrestat: An Innovative Strategy toward Enhanced Anticancer Activity

In addition to the conventional chemotherapeutic drugs, potent inhibitors of key enzymes that are differentially overexpressed in cancer cells and associated with its progression are often considered as the drugs of choice for treating cancer. Aldose reductase (AR), which is primarily associated with complications of diabetes, is known to be closely related to the development of cancer and drug resistance. Epalrestat (EPA), an FDA-approved drug, is a potent inhibitor of AR and exhibits anticancer activity. However, its poor pharmacokinetic properties limit its bioavailability and therapeutic benefits. We report herein the first examples of esterase-responsive turn-on fluorogenic prodrugs for the sustained release of EPA to cancer cells with a turn-on fluorescence readout. Carboxylesterases are known to be overexpressed in several organ-specific cancer cells and help in selective uncaging of drug from the prodrugs. The prodrugs were synthesized using a multistep organic synthesis and successfully characterized. Absorption and emission spectroscopic studies indicated successful activation of the prodrugs in the presence of porcine liver esterase (PLE) under physiological condition. HPLC studies revealed a simultaneous release of both the drug and the fluorophore from the prodrugs over time with mechanistic insights. While the inhibitory potential of EPA released from the prodrugs toward the enzyme AR was validated in the aqueous medium, the anticancer activity of the prodrugs was studied in a representative cervical cancer cell line. Interestingly, our results revealed that the development of the prodrugs can significantly enhance the anticancer potential of EPA. Finally, the drug uncaging process from the prodrugs by the intracellular esterases was studied in the cellular medium by measuring the turn-on fluorescence using fluorescence microscopy. Therefore, the present study highlights the rational development of the fluorogenic prodrugs of EPA, which will help enhance its anticancer potential with better therapeutic potential.

AKR1B1 inhibition using NARI-29-an Epalrestat analogue-alleviates Doxorubicin-induced cardiotoxicity via modulating Calcium/CaMKII/MuRF-1 axis

The clinical use of doxorubicin (Dox) is narrowed due to its carbonyl reduction to doxorubicinol (Doxol) implicating resistance and cardiotoxicity. Hence, in the present study we have evaluated the cardioprotective effect of AKR1B1 (or aldose reductase, AR) inhibitor NARI-29 (epalrestat (EPS) analogue) and its effect in the Dox-modulated calcium/CaMKII/MuRF1 axis. Initially, the breast cancer patient survival associated with AKR1B1 expression was calculated using Kaplan Meier-plotter (KM-plotter). Further, breast cancer, cardiomyoblast (H9c2), and macrophage (RAW 264.7) cell lines were used to establish the in vitro combination effect of NARI-29 and Dox. To develop the cardiotoxicity model, mice were given Dox 2.5 mg/kg (i.p.), biweekly. The effect of AKR1B1 inhibition using NARI-29 on molecular and cardiac functional changes was measured using echocardiography, fluorescence-imaging, ELISA, immunoblotting, flowcytometry, High-Performance Liquid Chromatography with Fluorescence Detection (HPLC-FD) and cytokine-bead array methods. The bioinformatics data suggested that a high expression of AKR1B1 is associated with significantly low survival of breast cancer patients undergoing chemotherapy; hence, it could be a target for chemo-sensitization and chemo-prevention. Further, in vitro studies showed that AKR1B1 inhibition with NARI-29 has increased the accumulation and sensitized Dox to breast cancer cell lines. However, treatment with NARI-29 has alleviated the Dox-induced toxicity to cardiomyocytes and decreased the secretion of inflammatory cytokines from RAW 264.7 cells. In vivo studies revealed that the NARI-29 (25 and 50 mg/kg) has prevented the functional, histological, biochemical, and molecular alterations induced by Dox treatment. Moreover, we have shown that NARI-29 has prevented the carbonyl reduction of Dox to Doxol in the mouse heart, which reduced the calcium overload, prevented phosphorylation of CaMKII, and reduced the expression of MuRF1 to protect from cardiac injury and apoptosis. Hence in conclusion, AKR1B1 inhibitor NARI-29 could be used as an adjuvant therapeutic agent with Dox to prevent cardiotoxicity and synergize anti-breast cancer activity.

Aldose reductase and cancer metabolism: The master regulator in the limelight

It is strongly established that metabolic reprogramming mediates the initiation, progression, and metastasis of a variety of cancers. However, there is no common biomarker identified to link the dysregulated metabolism and cancer progression. Recent studies strongly advise the involvement of aldose reductase (AR) in cancer metabolism. AR-mediated glucose metabolism creates a Warburg-like effect and an acidic tumour microenvironment in cancer cells. Moreover, AR overexpression is associated with the impairment of mitochondria and the accumulation of free fatty acids in cancer cells. Further, AR-mediated reduction of lipid aldehydes and chemotherapeutics are involved in the activation of factors promoting proliferation and chemo-resistance. In this review, we have delineated the possible mechanisms by which AR modulates cellular metabolism for cancer proliferation and survival. An in-depth understanding of cancer metabolism and the role of AR might lead to the use of AR inhibitors as metabolic modulating agents for the therapy of cancer.

Pathophysiological roles of autophagy and aldo-keto reductases in development of doxorubicin resistance in gastrointestinal cancer cells

Here, we show that incubation of three human gastrointestinal cancer cell lines (HCT15, LoVo and MKN45) with doxorubicin (DOX) provokes autophagy through facilitating production of reactive oxygen species (ROS). HCT15 cell treatment with DOX resulted in up-regulation of Beclin1, down-regulation of Bcl2, activation of AMPK and JNK, and Akt inactivation, all of which were restored by pretreating with an antioxidant N-acetyl-l-cysteine. These data suggest that all the autophagy-related alterations evoked by DOX result from the ROS production. In the DOX-resistant cancer cells, degree of autophagy elicited by DOX was milder than the parental cells, and DOX treatment hardly activated the ROS-dependent apoptotic signals [formation of 4-hydroxy-2-nonenal (HNE), cytochrome-c release into cytosol, and activation of JNK and caspase-3], inferring an inverse correlation between cellular antioxidant capacity and autophagy induction by DOX. Monitoring of expression levels of aldo-keto reductases (AKRs) in the parental and DOX-resistant cells revealed an up-regulation of AKR1B10 and/or AKR1C3 with acquiring the DOX resistance. Knockdown and inhibition of AKR1B10 or AKR1C3 in these cells enhanced DOX-elicited autophagy. Measurement of DOX-reductase activity and HNE-sensitivity assay also suggested that both AKR1B10 (via high HNE-reductase activity) and AKR1C3 (via low HNE-reductase and DOX-reductase activities) are involved in the development of DOX resistance. Combination of inhibitors of autophagy and the two AKRs overcame DOX resistance and cross-resistance of gastrointestinal cancer cells with resistance development to DOX or cis-diamminedichloroplatinum. Therefore, concomitant treatment with the inhibitors may be effective as an adjuvant therapy for elevating DOX sensitivity of gastrointestinal cancer cells.

Synergistic anticancer activity of doxorubicin and piperlongumine on DU-145 prostate cancer cells - The involvement of carbonyl reductase 1 inhibition

One of the causes of therapeutic failure of chemotherapy is cancer cell resistance. In the case of anthracyclines, many resistance mechanisms have been described. One of them assumes the role of carbonyl reductase 1 (CBR1), a cytosolic enzyme that is responsible for the biotransformation process of anthracyclines to less active, undesirable metabolites. Therefore, CBR1 inhibitors are considered for use as a chemosensitizing agents. In the present study, piperlongumine (PL), a Piper longum L. alkaloid that has previously been described as a CBR1 inhibitor, was investigated for its chemosensitizing properties in co-treatment with doxorubicin (DOX). The biotransformation process of DOX in the presence of PL was tracked using human cytosol fraction and LC-MS, then a molecular modeling study was conducted to predict the interaction of PL with the active site of the CBR1. The biological interaction between DOX and PL was investigated using DU-145 prostate cancer cells. Cytotoxic and antiproliferative properties of DOX and PL were examined, and the type and potency of interaction was quantified by Combination Index. The mechanism of the cell death induced by the agents was investigated by flow cytometry and the anti-invasive properties of the drugs were determined by monitoring the movement of individual cells. PL showed dose-dependent inhibition of DOX metabolism in cytosol, which resulted in less doxorubicinol (DOXol) metabolite being formed. The possible mechanism of CBR1 inhibition was explained through molecular modeling studies by prediction of PL's binding mode in the active site of the enzyme's crystal structure-based model. DOX and PL showed a synergistic antiproliferative and proapoptotic effect on cancer cells. Significant anti-invasive properties of the combination of DOX and PL were found, but when the drugs were used separately they did not alter the cancer cells' motility. Cell motility inhibition was accompanied by significant changes in cytoskeleton architecture. DOX and PL used in co-treatment showed significant synergistic anticancer properties. Inhibition of DOX metabolism by PL was found to be a mechanism that was likely to be responsible for the observed interaction.

Inhibition of Carbonyl Reductase 1 Safely Improves the Efficacy of Doxorubicin in Breast Cancer Treatment

AIMS

Doxorubicin (DOX) is a chemotherapeutic drug that is used to treat many cancers, but its use is limited by cardiotoxic side effect. Carbonyl reductase 1 (CBR1) is an NADPH-dependent oxidoreductase that reduces DOX to doxorubicinol (DOXOL), a less potent derivative that is responsible for DOX cardiotoxicity. Thus, we aimed to demonstrate that inhibition of CBR1 enhances the chemotherapeutic efficacy of DOX and attenuates cardiotoxicity.

RESULTS

Pharmacological or genetic inhibition of CBR1 improved the anticancer effects of DOX in preclinical models of breast cancer. RNA interference or chemical inhibition of CBR1 improved the anticancer effect of DOX in breast cancer. Moreover, CBR1 overexpression enabled breast cancer cells to obtain chemotherapeutic resistance to DOX treatment. Intriguingly, inhibition of CBR1 decreased DOX-induced cardiotoxicity in animal model. Innovation and Conclusions: Inhibition of CBR1 increases chemotherapeutic efficacy of DOX and reduces cardiotoxicity by blocking DOX reduction to DOXOL. Therefore, we offer preclinical proof-of-concept for a combination strategy to safely leverage the efficacy of doxorubicin by blunting its cardiotoxic effects that limit use of this cytotoxic agent used widely in the oncology clinic. Antioxid. Redox Signal. 26, 70-83.

Emerging role of NRF2 in chemoresistance by regulating drug-metabolizing enzymes and efflux transporters

Chemoresistance is a disturbing barrier in cancer therapy, which always results in limited therapeutic options and unfavorable prognosis. Nuclear factor E2-related factor 2 (NRF2) controls the expression of genes encoding cytoprotective enzymes and transporters that protect against oxidative stress and electrophilic injury to maintain intrinsic redox homeostasis. However, recent studies have demonstrated that aberrant activation of NRF2 due to genetic and/or epigenetic mutations in tumor contributes to the high expression of phase I and phase II drug-metabolizing enzymes, phase III transporters, and other cytoprotective proteins, which leads to the decreased therapeutic efficacy of anticancer drugs through biotransformation or extrusion during chemotherapy. Therefore, a better understanding of the role of NRF2 in regulation of these enzymes and transporters in tumors is necessary to find new strategies that improve chemotherapeutic efficacy. In this review, we summarized the recent findings about the chemoresistance-promoting role of NRF2, NRF2-regulated phase I and phase II drug-metabolizing enzymes, phase III drug efflux transporters, and other cytoprotective genes. Most importantly, the potential of NRF2 was proposed to counteract drug resistance in cancer treatment.

Inhibition of human anthracycline reductases by emodin - A possible remedy for anthracycline resistance

The clinical application of anthracyclines, like daunorubicin and doxorubicin, is limited by two factors: dose-related cardiotoxicity and drug resistance. Both have been linked to reductive metabolism of the parent drug to their metabolites daunorubicinol and doxorubicinol, respectively. These metabolites show significantly less anti-neoplastic properties as their parent drugs and accumulate in cardiac tissue leading to chronic cardiotoxicity. Therefore, we aimed to identify novel and potent natural inhibitors for anthracycline reductases, which enhance the anticancer effect of anthracyclines by preventing the development of anthracycline resistance. Human enzymes responsible for the reductive metabolism of daunorubicin were tested for their sensitivity towards anthrachinones, in particular emodin and anthraflavic acid. Intense inhibition kinetic data for the most effective daunorubicin reductases, including IC50- and Ki-values, the mode of inhibition, as well as molecular docking, were compiled. Subsequently, a cytotoxicity profile and the ability of emodin to reverse daunorubicin resistance were determined using multiresistant A549 lung cancer and HepG2 liver cancer cells. Emodin potently inhibited the four main human daunorubicin reductases in vitro. Further, we could demonstrate that emodin is able to synergistically sensitize human cancer cells towards daunorubicin at clinically relevant concentrations. Therefore, emodin may yield the potential to enhance the therapeutic effectiveness of anthracyclines by preventing anthracycline resistance via inhibition of the anthracycline reductases. In symphony with its known pharmacological properties, emodin might be a compound of particular interest in the management of anthracycline chemotherapy efficacy and their adverse effects.

Analysis of doxorubicin distribution in MCF-7 cells treated with drug-loaded nanoparticles by combination of two fluorescence-based techniques, confocal spectral imaging and capillary electrophoresis

The intracellular distribution of the antiancer drug doxorubicin (DOX) was followed qualitatively by fluorescence confocal spectral imaging (FCSI) and quantitatively by capillary electrophoresis (CE). FCSI permits the localization of the major fluorescent species in cell compartments, with spectral shifts indicating the polarity of the respective environment. However, distinction between drug and metabolites by FCSI is difficult due to their similar fluorochromes, and direct quantification of their fluorescence is complicated by quantum yield variation between different subcellular environments. On the other hand, capillary electrophoresis with fluorescence detection (CE-LIF) is a quantitative method capable of separating doxorubicin and its metabolites. In this paper, we propose a method for determining drug and metabolite concentration in enriched nuclear and cytosolic fractions of cancer cells by CE-LIF, and we compare these data with those of FCSI. Significant differences in the subcellular distribution of DOX are observed between the drug administered as a molecular solution or as a suspension of drug-loaded iron oxide nanoparticles coated with polyethylene glycol. Comparative analysis of the CE-LIF vs FCSI data may lead to a tentative calibration of this latter method in terms of DOX fluorescence quantum yields in the nucleus and more or less polar regions of the cytosol.

Aldo-keto reductase 1C3 (AKR1C3) is associated with the doxorubicin resistance in human breast cancer via PTEN loss

Aldo-keto reductase 1C3 (AKR1C3), one member of the aldo-keto reductase superfamily, is involved in a variety of cancers. Recently, AKR1C3 has been demonstrated to be related with the doxorubicin (DOX) resistance in human breast cancer. Here, we attempted to explore the resistance mechanism mediated by AKR1C3. First, one DOX resistant breast cancer cell line MCF-7/DOX was successfully established and an increased level of AKR1C3 was observed in the MCF-7/DOX cells compared to the parental MCF-7 cells. To investigate the contribution of AKR1C3 in the DOX resistance, we further established an AKR1C3 overexpression cell line, referred to MCF-7/AKR1C3. In the MCF-7/AKR1C3 cells, the DOX induced cytotoxicity, detected by CCK-8 cell viability assay and DAPI staining, was greatly reduced (3.2-fold increase in the IC50 value). Interestingly, a loss of tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10) was observed when AKR1C3 was overexpressed. Secondary to the PTEN loss, the activated Akt also markedly increased. In addition, the AKR1C3 mediated DOX resistance can be conquered by the Akt inhibitor (LY294002). Furthermore, we found that the expression levels of AKR1C3 and PTEN had a negative relationship in the human breast tumor tissues (the standard correlation coefficient=-0.71; P=0.048). In conclusion, our data suggested that the AKR1C3 mediated DOX resistance might be resulted from the activation of anti-apoptosis PTEN/Akt pathway via PTEN loss. AKR1C3 may present a potential therapeutic target in addressing DOX resistance in breast cancer.

In vivo effect of oracin on doxorubicin reduction, biodistribution and efficacy in Ehrlich tumor bearing mice

BACKGROUND

The limitation of carbonyl reduction represents one possible way to increase the effectiveness of anthracycline doxorubicin (DOX) in cancer cells and decrease its toxicity in normal cells. In vitro, isoquinoline derivative oracin (ORC) inhibited DOX reduction and increased the antiproliferative effect of DOX in MCF-7 breast cancer cells. Moreover, ORC significantly decreases DOX toxicity in non-cancerous MCF-10A breast cells and in hepatocytes. The present study was designed to test in mice the in vivo effect of ORC on plasma and tissue concentrations of DOX and its main metabolite DOXOL. The effect of ORC on DOX efficacy in mice bearing solid Ehrlich tumors (EST) was also studied.

METHODS

DOX and DOX + ORC combinations were iv administered to healthy mice. Blood samples, livers and hearts were collected during the following 48 h. DOX and DOXOL concentrations were assayed using HPLC. The mice with inoculated EST cells were treated repeatedly iv with DOX and DOX + ORC combinations, and the growth of tumors was monitored.

RESULTS

ORC in combination with DOX significantly decreased DOXOL plasma concentrations during four hours after administration, but this significantly affected neither DOX plasma concentrations nor DOX or DOXOL concentrations in the liver and heart at any of intervals tested. In EST bearing mice, ORC did not significantly affect DOX efficacy on tumor growth. However, EST was shown to be an improper model for the testing of ORC efficacy in vivo, as ORC did not inhibit DOXOL formation in EST.

CONCLUSIONS

In vivo, ORC was able to retard DOXOL formation but was not able to improve DOX efficacy in EST-bearing mice.

Enhancement of docetaxel-treated MCF-7 cell death by 900-MHz radiation

The aim of the study was to investigate the effect of high-frequency electromagnetic field of 900 MHz at 8 W input power on metabolic activity of human breast adenocarcinoma MCF-7 cells. With the aid of the colorimetric MTT assay, it was shown that there is significant change in cell culture survival exposed to docetaxel in field-free conditions in comparison with cells treated with docetaxel simultaneously exposed to high-frequency electromagnetic field.

Role of aldo-keto reductases and other doxorubicin pharmacokinetic genes in doxorubicin resistance, DNA binding, and subcellular localization

Background

Since proteins involved in chemotherapy drug pharmacokinetics and pharmacodynamics have a strong impact on the uptake, metabolism, and efflux of such drugs, they likely play critical roles in resistance to chemotherapy drugs in cancer patients.

Methods

To investigate this hypothesis, we conducted a whole genome microarray study to identify difference in the expression of genes between isogenic doxorubicin-sensitive and doxorubicin-resistant MCF-7 breast tumour cells. We then assessed the degree of over-representation of doxorubicin pharmacokinetic and pharmacodynamic genes in the dataset of doxorubicin resistance genes.

Results

Of 27,958 Entrez genes on the array, 7.4 per cent or 2,063 genes were differentially expressed by ≥ 2-fold between wildtype and doxorubicin-resistant cells. The false discovery rate was set at 0.01 and the minimum p value for significance for any gene within the “hit list” was 0.01. Seventeen and 43 per cent of doxorubicin pharmacokinetic genes were over-represented in the hit list, depending upon whether the gene name was identical or within the same gene family, respectively. The most over-represented genes were within the 1C and 1B families of aldo-keto reductases (AKRs), which convert doxorubicin to doxorubicinol. Other genes convert doxorubicin to other metabolites or affect the influx, efflux, or cytotoxicity of the drug. In further support of the role of AKRs in doxorubicin resistance, we observed that, in comparison to doxorubicin, doxorubincol exhibited dramatically reduced cytotoxicity, reduced DNA-binding activity, and strong localization to extra nuclear lysosomes. Pharmacologic inhibition of the above AKRs in doxorubicin-resistant cells increased cellular doxorubicin levels, restored doxorubicin cytotoxicity and re-established doxorubicin localization to the nucleus. The properties of doxorubicinol were unaffected.

Conclusions

These findings demonstrate the utility of using curated pharmacokinetic and pharmacodynamic knowledge bases to identify highly relevant genes associated with doxorubicin resistance. The induction of one or more of these genes was found to be correlated with changes in the drug’s properties, while inhibiting one specific class of these genes (the AKRs) increased cellular doxorubicin content and restored drug DNA binding, cytotoxicity, and subcellular localization.

Effect of quercetin on impaired immune function in mice exposed to irradiation

Radiation used in cancer treatment may cause side effects such as inflammation. Quercetin is a polyphenol that reduces inflammation. This study evaluated the recovery efficacy of quercetin on impaired immune function in irradiation-induced inflammatory mice. Quercetin administered at two concentrations of 10 and 40 mg/kg body weight was initiated 2 weeks before irradiation and was continued 30 days after irradiation. The animals exposed/not exposed to radiation were sacrificed on radiation days 10 and 30. Splenocyte proliferation, which was diminished after irradiation, was enhanced significantly by quercetin supplementation after 30 days of irradiation. Cytokine secretion increased in the radiation group compared to that in the non-radiation control group. After 30 days of radiation, interleukin (IL)-1β and IL-6 secretion decreased significantly in the radiation-quercetin groups. When quercetin was administered for 44 days, it showed a possible protective effect against irradiation-induced inflammation in mice. Quercetin could be beneficial in the recovery of irradiation-induced increases in cytokine secretion.

The influence of oracin on reduction and toxicity of doxorubicin in hepatocytes and mammary epithelial cells MCF-10A

The ways, how to increase effectiveness of doxorubicin (DOX) in cancer cells and decrease its toxicity in normal cells, have been intensively studied. In breast cancer cells MCF-7, isoquinoline derivative oracin (ORC) inhibited DOX reduction and increased DOX antiproliferative effect. The aim of this study was to test the influence of ORC on the reduction of DOX and its toxicity in hepatocytes and non-tumourous breast cells. The kinetics of DOX reduction was measured in cytosols from rat liver, human liver and human mammary epithelial cells MCF-10A. Activity and expression of carbonyl reductase 1 (CBR1) were assayed using menadione as a substrate and western blot analysis. End-point tests of viability served for study of cytotoxicity of DOX, ORC and DOX+ORC combinations in rat hepatocytes and MCF-10A cells. The inhibitory effect of ORC on DOX reductases was almost none in MCF-10A cells and mild in liver. CBR1 expression and activity was lower in non-tumourous MCF-10A cells than in cancer MCF-7 cells. Cytotoxicity tests showed that DOX+ORC combinations had significantly lower toxicity than DOX alone in MCF-10A cells as well as in hepatocytes. ORC significantly decreases DOX toxicity in MCF-10A and in hepatocytes. Therefore, concomitant use of ORC and DOX may protect normal cells against DOX toxicity.

DNA and histone deacetylases as targets for neuroblastoma treatment

Neuroblastoma, a tumor of the peripheral sympathetic nervous system, is the most frequent solid extra cranial tumor in children and is a major cause of death from neoplasia in infancy. Still little improvement in therapeutic options has been made, requiring a need for the development of new therapies. In our laboratory, we address still unsettled questions, which of mechanisms of action of DNA-damaging drugs both currently use for treatment of human neuroblastomas (doxorubicin, cis-platin, cyclophosphamide and etoposide) and another anticancer agent decreasing growth of neuroblastomas in vitro, ellipticine, are predominant mechanism(s) responsible for their antitumor action in neuroblastoma cell lines in vitro. Because hypoxia frequently occurs in tumors and strongly correlates with advanced disease and poor outcome caused by chemoresistance, the effects of hypoxia on efficiencies and mechanisms of actions of these drugs in neuroblastomas are also investigated. Since the epigenetic structure of DNA and its lesions play a role in the origin of human neuroblastomas, pharmaceutical manipulation of the epigenome may offer other treatment options also for neuroblastomas. Therefore, the effects of histone deacetylase inhibitors on growth of neuroblastoma and combination of these compounds with doxorubicin, cis-platin, etoposide and ellipticine as well as mechanisms of such effects in human neuroblastona cell lines in vitro are also investigated. Such a study will increase our knowledge to explain the proper function of these drugs on the molecular level, which should be utilized for the development of new therapies for neuroblastomas.

AKR1B10 induces cell resistance to daunorubicin and idarubicin by reducing C13 ketonic group

Daunorubicin, idarubicin, doxorubicin and epirubicin are anthracyclines widely used for the treatment of lymphoma, leukemia, and breast, lung, and liver cancers, but tumor resistance limits their clinical success. Aldo-keto reductase family 1 B10 (AKR1B10) is an NADPH-dependent enzyme overexpressed in liver and lung carcinomas. This study was aimed to determine the role of AKR1B10 in tumor resistance to anthracyclines. AKR1B10 activity toward anthracyclines was measured using recombinant protein. Cell resistance to anthracycline was determined by ectopic expression of AKR1B10 or inhibition by epalrestat. Results showed that AKR1B10 reduces C13-ketonic group on side chain of daunorubicin and idarubicin to hydroxyl forms. In vitro, AKR1B10 converted daunorubicin to daunorubicinol at V(max) of 837.42±81.39nmol/mg/min, K(m) of 9.317±2.25mM and k(cat)/K(m) of 3.24. AKR1B10 showed better catalytic efficiency toward idarubicin with V(max) at 460.23±28.12nmol/mg/min, K(m) at 0.461±0.09mM and k(cat)/K(m) at 35.94. AKR1B10 was less active toward doxorubicin and epirubicin with a C14-hydroxyl group. In living cells, AKR1B10 efficiently catalyzed reduction of daunorubicin (50nM) and idarubicin (30nM) to corresponding alcohols. Within 24h, approximately 20±2.7% of daunorubicin (1μM) or 23±2.3% of idarubicin (1μM) was converted to daunorubicinol or idarubicinol in AKR1B10 expression cells compared to 7±0.9% and 5±1.5% in vector control. AKR1B10 expression led to cell resistance to daunorubicin and idarubicin, but inhibitor epalrestat showed a synergistic role with these agents. Together our data suggest that AKR1B10 participates in cellular metabolism of daunorubicin and idarubicin, resulting in drug resistance. These data are informative for the clinical use of idarubicin and daunorubicin.

Cadmium-induced up-regulation of aldo-keto reductase 1C3 expression in human nasal septum carcinoma RPMI-2650 cells: Involvement of reactive oxygen species and phosphatidylinositol 3-kinase/Akt

Cadmium is a well-known toxic metal and occupational exposure to it is associated with lung cancer. In probing the possible non-genotoxic molecular targets of cadmium-induced nasal toxicity, we performed an mRNA differential display analysis for cadmium-treated human nasal septum carcinoma RPMI-2650 cells. Cadmium (≥ 0.5 μM) inhibited the cell proliferation. The intracellular ROS levels were induced by cadmium treatment. In addition, cadmium elicited the AKR1C3 expression. The cadmium-induced increase in AKR1C3 protein levels was suppressed by N-acetylcysteine (NAC) and, to a lesser extent, PI3K inhibitor (Ly294002). Cells pretreated with Ly294002 were more resistant to cadmium toxicity than control. The increase in AKR1C3 protein level was accompanied by an increase in the nuclear transcription factor Nrf2. Overall, our data suggest that cadmium-induced ROS cause up-regulation of AKR1C3 expression, at least partially via the activation of PI3K-related intracellular signaling pathways, and Nrf2 activation, thereby contributing to an adaptive intracellular response to cadmium toxicity.

Stereospecific reduction of a potent kinesin spindle protein (KSP) inhibitor in human tissues

Compound A, 1-{(3R,3aR)-3-[3-(4-acetylpiperazin-1-yl)propyl]-7-fluoro-3-phenyl-3a,4-dihydro-3H-pyrazolo[5,1-c][1,4]benzoxazin-2-yl}ethanone, is a novel and potent inhibitor of the mitotic kinesin spindle protein. Metabolism studies with human hepatocytes showed that Compound A underwent significant ketone reduction to its biologically active metabolite M1. Here, we describe the studies that characterized the metabolic interconversion between Compound A and M1 in vitro in human tissues. LC-MS/MS analysis showed that the ketone reduction was stereospecific for M1 with no diastereomer of M1 detected in incubations with human hepatocytes. Interestingly, such stereospecific ketone reduction was not observed with Compound B, the enantiomer of Compound A. No reductive products were observed when Compound B was incubated with human hepatocytes. Studies with human liver subcellular fractions showed that Compound A was reduced to M1 primarily by human liver cytosol with little contribution from human liver microsomes and mitochondria. NADPH was the preferred cofactor for the reduction reaction. Reverse oxidation of M1 back to Compound A was also observed, preferentially in human liver cytosol with NADP(+) as the cofactor. The interconversion between Compound A and M1 in human liver cytosol was inhibited significantly by flufenamic acid and phenolphthalein (potent inhibitors for aldo-keto reductase 1Cs, p<0.05), but not by menadione, a selective inhibitor for carbonyl reductase. In addition to the liver, S9 from human lung and kidney was also capable of catalyzing this interconversion. Collectively, the results implicated the aldo-keto reductase 1Cs as the most likely enzymes responsible for the metabolic interconversion of Compound A and its active metabolite M1.

Direct sampling from human liver tissue cross sections for electrophoretic analysis of doxorubicin

After chemoembolization of the liver with doxorubicin (Dox), this drug and its metabolites are not homogeneously distributed in this organ. The distribution cannot be easily measured making it difficult to assess how the drug performs in different tissue regions. Here we report a technique for sampling tissue cross sections that can analyze the contents of micrometer size regions. The tissue cross sections were from the explanted liver of a hepatocellular carcinoma patient. Samples were directly aspirated from a 5 microm thick tissue cross section into a 50 microm i.d. capillary where the tissue was solubilized with a separation buffer containing sodium dodecyl sulfate. Upon sample dissolution, Dox and natively fluorescent compounds were separated and detected by micellar electrokinetic chromatography with laser-induced fluorescence detection. Sampling reproducibility and recovery were assessed using 10% (w/v) gelatin as tissue mimic. Sampling from gelatin slices containing Dox revealed a relative standard deviation of 13%, which was comparable to that of sampling from solution. Dox recovery was 82% +/- 16% (n = 5). When sampling tumor and nontumor tissue regions, samples could be taken from the same region 100 microm apart. Atomic force microscopy was used to determine that each sample was 8.4 +/- 1.0 pL in volume which made it possible to determine Dox concentrations in the ranges of 0.4-1.3 and 0.3-0.5 microM for the samples taken from tumor and nontumor regions, respectively. The results demonstrated the feasibility of sampling, detection, and quantification of Dox in micrometer size regions, which could be a useful resource for analyzing the Dox concentration and distribution in highly heterogeneous tissues.