Idarubicin, an Anthracycline, Induces Oxidative DNA Damage in the Presence of Copper (II).

BACKGROUND/AIM: The aim of the present study was to investigate whether idarubicin (IDR) induces oxidative DNA damage in the presence of copper (II). MATERIALS AND METHODS: DNA damage was evaluated by pBR322 plasmid DNA cleavage. The formation of oxidative stress markers [O2 •- and 8-hydroxy-2'-deoxyguanosine (8-OHdG)] was analysed. RESULTS: IDR induced DNA damage and O2 •- and 8-OHdG generation in the presence of copper (II). CONCLUSION: IDR induced oxidative DNA damage in the presence of copper (II). Since it has been reported that the concentration of copper in the serum of cancer patients is higher than that in healthy groups, IDR-induced oxidative DNA damage in the presence of copper (II) may play an important role in anticancer therapeutic strategies.

Functional Analysis of the Role of Equilibrative Nucleobase Transporter 1 (ENBT1/SLC43A3) in Adenine Transport in HepG2 Cells.

Equilibrative nucleobase transporter 1 (ENBT1/SLC43A3) has recently been identified as a purine-selective nucleobase transporter. Although it is highly expressed in the liver, its role in nucleobase transport has not been confirmed yet in hepatocytes or any relevant cell models. We, therefore, examined its role in adenine transport in the HepG2 cell line as a human hepatocyte model. The uptake of [3H]adenine in HepG2 cells was highly saturable, indicating the involvement of carrier-mediated transport. The carrier-mediated transport component, for which the Michaelis constant was estimated to be 0.268 µM, was sensitive to decynium-22, an ENBT1 inhibitor, with the half maximal inhibitory concentration of 2.59 µM, which was comparable to that of 2.30 µM for [3H]adenine uptake by ENBT1 in its transient transfectant human embryonic kidney 293 cells. Although equilibrative nucleoside transporter 1 (ENT1/SLC29A1) and ENT2/SLC29A2 are also known to be able to transport adenine, [3H]adenine uptake in HepG2 cells was not inhibited by the ENT1/2-specific inhibitor of either dipyridamole or nitrobenzylthioinosine. Finally, [3H]adenine uptake was extensively reduced by silencing of ENBT1 by RNA interference in the hepatocyte model. All these results, taken together, suggest the predominant role of ENBT1 in the uptake of adenine in HepG2 cells.

Oxidative DNA Damage and Apoptosis Induced by Aclarubicin, an Anthracycline: Role of Hydrogen Peroxide and Copper.

BACKGROUND/AIM: This study aimed to investigate aclarubicin (ACR)-induced oxidative DNA damage and apoptosis. MATERIALS AND METHODS: ACR-induced apoptosis was analyzed using HL-60 leukemia cells and HP100 cells, hydrogen peroxide (H2O2)-resistant cells derived from HL-60 cells. ACR-induced DNA damage was analyzed using plasmid DNA. RESULTS: HL-60 cells were more sensitive to ACR than HP100 cells. In HP100 cells, DNA ladder formation and caspase-3/7 activity induced by ACR were suppressed or delayed in comparison to those in HL-60 cells. ACR-induced DNA damage occurred in the presence of Cu(II), and scavenger experiments showed that the reactive species causing DNA damage appeared to be generated from H2O2 and Cu(I). Moreover, we detected intracellular Cu(I) induced by ACR in HL-60 cells, using CopperGREEN™, a fluorescent probe for detection of Cu(I) ion specifically. CONCLUSION: ACR-induced DNA damage and apoptosis can be accounted for by the involvement of H2O2 and Cu(I).

Urate transport function of rat sodium-dependent nucleobase transporter 1.

Sodium-dependent nucleobase transporter 1 (SNBT1) is a nucleobase-specific transporter identified in our recent study. In an attempt to search for its potential substrates other than nucleobases in this study, we could successfully find urate, a metabolic derivative of purine nucleobases, as a novel substrate, as indicated by its specific Na+ -dependent and saturable transport, with a Michaelis constant of 433 µmol/L, by rat SNBT1 (rSNBT1) stably expressed in Madin-Darby canine kidney II cells. However, urate uptake was observed only barely in the everted tissue sacs of the rat small intestine, in which rSNBT1 operates for nucleobase uptake. These findings suggested that urate undergoes a futile cycle, in which urate transported into epithelial cells is immediately effluxed back by urate efflux transporters, in the small intestine. In subsequent attempts to examine that possibility, such a futile urate cycle was demonstrated in the human embryonic kidney 293 cell line as a model cell system, where urate uptake induced by transiently introduced rSNBT1 was extensively reduced by the co-introduction of rat breast cancer resistance protein (rBCRP), a urate efflux transporter present in the small intestine. However, urate uptake was not raised in the presence of Ko143, a BCRP inhibitor, in the everted intestinal tissue sacs, suggesting that some other transporter might also be involved in urate efflux. The newly found urate transport function of SNBT1, together with the suggested futile urate cycle in the small intestine, should be of interest for its evolutional and biological implications, although SNBT1 is genetically deficient in humans.

Oxidative DNA Damage Induced by Pirarubicin, an Anthracycline Anticancer Agent, in the Presence of Copper(II).

BACKGROUND/AIM: One mechanism of the anticancer action of anthracyclines is believed to be oxidative DNA damage. Previously, we reported that doxorubicin induced oxidative DNA damage in the presence of Cu(II). However, the mechanism of pirarubicin-induced oxidative DNA damage has not been well clarified. MATERIALS AND METHODS: DNA damage by pirarubicin in the presence of Cu(II) was analyzed using pBR322 plasmid DNA. O2•- derived from pirarubicin in the presence of Cu(II) was detected by cytochrome c reduction. RESULTS: Pirarubicin induced DNA damage in the presence of Cu(II). Scavenger experiments suggest that reactive species are generated from H2O2 and Cu(I). Pirarubicin induced O2•- production in the presence of Cu(II). CONCLUSION: These findings suggest that pirarubicin plus Cu(II) induces oxidative DNA damage in a similar manner to doxorubicin, and Cu(II)-mediated oxidative DNA damage may serve as a common mechanism for antitumor effects of anthracyclines.

Role of Equilibrative Nucleobase Transporter 1/SLC43A3 as a Ganciclovir Transporter in the Induction of Cytotoxic Effect of Ganciclovir in a Suicide Gene Therapy with Herpes Simplex Virus Thymidine Kinase.

A suicide gene therapy using herpes simplex virus thymidine kinase (HSV-TK) with ganciclovir (GCV) has been under development as a tumor-targeted therapy; however, the mechanism of cellular GCV uptake, which is prerequisite in the therapy, has not been clarified. In an attempt to resolve this situation and gain information to optimize HSV-TK/GCV system for cancer therapy, we found that human equilibrative nucleobase transporter 1 (ENBT1) can transport GCV with a Michaelis constant of 2.75 mM in Madin-Darby canine kidney II (MDCKII) cells stably transfected with this transporter. In subsequent experiments using green fluorescent protein (GFP)-tagged ENBT1 (GFP-ENBT1) and HSV-TK, the uptake of GCV (30 µM), which was minimal in MDCKII cells and unchanged by their transfection with HSV-TK alone, was increased extensively by their transfection with GFP-ENBT1, together with HSV-TK. Accordingly, cytotoxicity, which was assessed by the WST-8 cell viability assay after the treatment of those cells with GCV (30 µM) for 72 hours, was induced in those transfected with GFP-ENBT1, together with HSV-TK but not in those transfected with HSV-TK alone. These results suggest that ENBT1 could facilitate GCV uptake and thereby enhance cytotoxicity in HSV-TK/GCV system. We also identified Helacyton gartleri (HeLa) and HepG2 as cancer cell lines that are rich with ENBT1 and A549, HCT-15 and MCF-7 as those poor with ENBT1. Accordingly, the HSV-TK/GCV system was effective in inducing cytotoxicity in the former but not in the latter. Thus, ENBT1 was found to be a GCV transporter that could enhance the performance of HSV-TK/GCV suicide gene therapy.

Characteristic Analysis of Intestinal Transport in Enterocyte-Like Cells Differentiated from Human Induced Pluripotent Stem Cells.

We previously demonstrated that differentiated enterocytes from human induced pluripotent stem (iPS) cells exhibited drug-metabolizing activities and cytochrome P450 CYP3A4 inducibility. The aim of this study was to apply human iPS cell-derived enterocytes in pharmacokinetic studies by investigating the characteristics of drug transport into enterocyte-like cells. Human iPS cells cultured on feeder cells were differentiated into endodermal cells using activin A. These endodermal-like cells were then differentiated into intestinal stem cells by fibroblast growth factor 2. Finally, epidermal growth factor and small-molecule compounds induced the maturation of the intestinal stem cell-like cells. After differentiation, we performed transepithelial electrical resistance (TEER) measurements, immunofluorescence staining, and transport studies. TEER values increased in a time-dependent manner and reached approximately 100 Ω × cm(2) Efflux transport of Hoechst 33342, a substrate of breast cancer resistance protein (BCRP), was observed and inhibited by the BCRP inhibitor Ko143. The uptake of peptide transporter 1 substrate glycylsarcosine was also confirmed and suppressed when the temperature was lowered to 4°C. Using immunofluorescence staining, villin and Na(+)-K(+) ATPase were expressed. These results suggest that human iPS cell-derived enterocytes had loose tight junctions, polarity, as well as uptake and efflux transport functions. In addition, the rank order of apparent membrane permeability coefficient (Papp) values of these test compounds across the enterocyte-like cell membrane corresponded to the fraction absorbance (Fa) values. Therefore, differentiated enterocytes from human iPS cells may provide a useful comprehensive evaluation model of drug transport and metabolism in the small intestine.

Functional identification of SLC43A3 as an equilibrative nucleobase transporter involved in purine salvage in mammals.

The purine salvage pathway plays a major role in the nucleotide production, relying on the supply of nucleobases and nucleosides from extracellular sources. Although specific transporters have been suggested to be involved in facilitating their transport across the plasma membrane in mammals, those which are specifically responsible for utilization of extracellular nucleobases remain unknown. Here we present the molecular and functional characterization of SLC43A3, an orphan transporter belonging to an amino acid transporter family, as a purine-selective nucleobase transporter. SLC43A3 was highly expressed in the liver, where it was localized to the sinusoidal membrane of hepatocytes, and the lung. In addition, SLC43A3 expressed in MDCKII cells mediated the uptake of purine nucleobases such as adenine, guanine, and hypoxanthine without requiring typical driving ions such as Na(+) and H(+), but it did not mediate the uptake of nucleosides. When SLC43A3 was expressed in APRT/HPRT1-deficient A9 cells, adenine uptake was found to be low. However, it was markedly enhanced by the introduction of SLC43A3 with APRT. In HeLa cells, knock-down of SLC43A3 markedly decreased adenine uptake. These data suggest that SLC43A3 is a facilitative and purine-selective nucleobase transporter that mediates the cellular uptake of extracellular purine nucleobases in cooperation with salvage enzymes.

Functional characteristics of two human MATE transporters: kinetics of cimetidine transport and profiles of inhibition by various compounds.

PURPOSE: Human multidrug and toxin extrusion protein 1 (hMATE1) and hMATE2-K are organic cation/H+ antiporters that have recently been identified and suggested to be involved in the renal brush border secretion of various organic cations. Information about functional characteristics of them has been accumulating, but still insufficient to fully understand their functions and respective roles. The present study was conducted to help clarify them. METHODS: The cDNA of hMATE1 was isolated from human brain cDNA by RT-PCR and hMATE2-K cDNA was from human kidney cDNA. HEK293 cells were stably transfected with hMATE1 and hMATE2-K, and the cellular uptakes of [3H]cimetidine and [14C]tetraethylammonium (TEA) were evaluated. RESULTS: It was first found that both hMATE1 and hMATE2-K can transport cimetidine with high affinities, indicated by small Michaelis constants of 8.00 mM and 18.18 mM, respectively. These were much smaller than those for TEA (366 mM and 375 mM, respectively, for hMATE1 and hMATE2-K). Subsequent investigation using cimetidine as a probe substrate into the profiles of inhibition of the two hMATEs by various compounds indicated that they are similar in principle but different to some extent in substrate recognition, reflecting the modest differences in amino acid sequences between them. In fact, cimetidine transport by hMATE1 was correlated to that by hMATE2-K, which is 65% similar to hMATE1, but not as good as to that by rat MATE1, which is 86% similar. CONCLUSIONS: Cimetidine was demonstrated to be a high affinity substrate of both hMATEs. Subsequent evaluation of the inhibition of hMATEs by various compounds indicated no major difference in function or role between hMATE1 and hMATE2-K.