Selectively induced high MRP gene expression in multidrug-resistant human HL60 leukemia cells

Pharmacological Activity of Cepharanthine

Cepharanthine, a natural bisbenzylisoquinoline (BBIQ) alkaloid isolated from the plant Stephania Cephalantha Hayata, is the only bisbenzylisoquinoline alkaloid approved for human use and has been used in the clinic for more than 70 years. Cepharanthine has a variety of medicinal properties, including signaling pathway inhibitory activities, immunomodulatory activities, and antiviral activities. Recently, cepharanthine has been confirmed to greatly inhibit SARS-CoV-2 infection. Therefore, we aimed to describe the pharmacological properties and mechanisms of cepharanthine, mainly including antitumor, anti-inflammatory, anti-pathogen activities, inhibition of bone resorption, treatment of alopecia, treatment of snake bite, and other activities. At the same time, we analyzed and summarized the potential antiviral mechanism of cepharanthine and concluded that one of the most important anti-viral mechanisms of cepharanthine may be the stability of plasma membrane fluidity. Additionally, we explained its safety and bioavailability, which provides evidence for cepharanthine as a potential drug for the treatment of a variety of diseases. Finally, we further discuss the potential new clinical applications of cepharanthine and provide direction for its future development.

Targeting multidrug resistance-associated protein 1 (MRP1)-expressing cancers: Beyond pharmacological inhibition

Resistance to chemotherapy remains one of the most significant obstacles to successful cancer treatment. While inhibiting drug efflux mediated by ATP-binding cassette (ABC) transporters is a seemingly attractive and logical approach to combat multidrug resistance (MDR), small molecule inhibition of ABC transporters has so far failed to confer clinical benefit, despite considerable efforts by medicinal chemists, biologists, and clinicians. The long-sought treatment to eradicate cancers displaying ABC transporter overexpression may therefore lie within alternative targeting strategies. When aberrantly expressed, the ABC transporter multidrug resistance-associated protein 1 (MRP1, ABCC1) confers MDR, but can also shift cellular redox balance, leaving the cell vulnerable to select agents. Here, we explore the physiological roles of MRP1, the rational for targeting this transporter in cancer, the development of small molecule MRP1 inhibitors, and the most recent developments in alternative therapeutic approaches for targeting cancers with MRP1 overexpression. We discuss approaches that extend beyond simple MRP1 inhibition by exploiting the collateral sensitivity to glutathione depletion and ferroptosis, the rationale for targeting the shared transcriptional regulators of both MRP1 and glutathione biosynthesis, advances in gene silencing, and new molecules that modulate transporter activity to the detriment of the cancer cell. These strategies illustrate promising new approaches to address multidrug resistant disease that extend beyond the simple reversal of MDR and offer exciting routes for further research.

Although c‑MYC contributes to tamoxifen resistance, it improves cisplatin sensitivity in ER‑positive breast cancer

Tamoxifen (TAM) resistance is a major challenge in the treatment of estrogen receptor‑positive (ER+) breast cancer. To date, to the best of our knowledge, there are only a few studies available examining the response of patients with TAM‑resistant breast cancer to chemotherapy, and the guidelines do not specify recommended drugs for these patients. In the present study, TAM‑resistant cells were shown to exhibit increased proliferation and invasion compared with the parent cells, and the increased expression of c‑MYC was demonstrated to play an important role in TAM resistance. Furthermore, the TAM‑resistant cells were significantly more sensitive to cisplatin compared with the parent cells, and the silencing of c‑MYC expression desensitized the cells to cisplatin through the inhibition of the cell cycle. An increased c‑MYC expression was observed in 28 pairs of primary and metastatic tumors from patients treated with TAM, and the clinical remission rate of cisplatin‑based chemotherapy was significantly higher compared with other chemotherapy‑based regimens in 122 patients with TAM resistant breast cancer. Taken together, the data of the present study demonstrated that although c‑MYC was involved in TAM resistance, it increased the sensitivity of ER+ breast cancer to cisplatin. Thus, cisplatin may be a preferred chemotherapeutic agent for the treatment of patients with TAM‑resistant breast cancer, particularly in patients where the rapid control of disease progression is required.

The RNA/DNA-binding protein PSF relocates to cell membrane and contributes cells' sensitivity to antitumor drug, doxorubicin

Cell surface proteins play an important role in multidrug resistance (MDR). However, the identification involving chemoresistant features for cell surface proteins is a challenge. To identify potential cell membrane markers in hematologic cancer MDR, we used a cell- and antibody-based strategy of subtractive immunization coupled with cell surface comparative screening of leukemia cell lines from sensitive HL60 and resistant HL60/DOX cells. Fifty one antibodies that recognized the cell surface proteins expressed differently between the two cell lines were generated. One of them, the McAb-5D12 not only recognizes its antigen but also block its function. Comparative analysis of immunofluorescence, flow cytometry, and mass spectrum analysis validated that the membrane antigen of McAb-5D12 is a nucleoprotein-polypyrimidine tract binding protein associated splicing factor, PSF. Our results identified that PSF overexpressed on the membrane of sensitive cells compared with resistant cells and its relocation from the nuclear to the cell surface was common in hematological malignancy cell lines and marrow of leukemia patients. Furthermore, we found that cell surface PSF contributed to cell sensitivity by inhibiting cell proliferation. The results represent a novel and potentially useful biomarker for MDR prediction. The strategy enables the correlation of expression levels and functions of cell surface protein with some cell-drug response traits by using antibodies.

Molecular mechanisms of cisplatin resistance

Platinum-based drugs, and in particular cis-diamminedichloroplatinum(II) (best known as cisplatin), are employed for the treatment of a wide array of solid malignancies, including testicular, ovarian, head and neck, colorectal, bladder and lung cancers. Cisplatin exerts anticancer effects via multiple mechanisms, yet its most prominent (and best understood) mode of action involves the generation of DNA lesions followed by the activation of the DNA damage response and the induction of mitochondrial apoptosis. Despite a consistent rate of initial responses, cisplatin treatment often results in the development of chemoresistance, leading to therapeutic failure. An intense research has been conducted during the past 30 years and several mechanisms that account for the cisplatin-resistant phenotype of tumor cells have been described. Here, we provide a systematic discussion of these mechanism by classifying them in alterations (1) that involve steps preceding the binding of cisplatin to DNA (pre-target resistance), (2) that directly relate to DNA-cisplatin adducts (on-target resistance), (3) concerning the lethal signaling pathway(s) elicited by cisplatin-mediated DNA damage (post-target resistance) and (4) affecting molecular circuitries that do not present obvious links with cisplatin-elicited signals (off-target resistance). As in some clinical settings cisplatin constitutes the major therapeutic option, the development of chemosensitization strategies constitute a goal with important clinical implications.

Update information on drug metabolism systems--2009, part II: summary of information on the effects of diseases and environmental factors on human cytochrome P450 (CYP) enzymes and transporters

The present paper is an update of the data on the effects of diseases and environmental factors on the expression and/or activity of human cytochrome P450 (CYP) enzymes and transporters. The data are presented in tabular form (Tables 1 and 2) and are a continuation of previously published summaries on the effects of drugs and other chemicals on CYP enzymes (Rendic, S.; Di Carlo, F. Drug Metab. Rev., 1997, 29(1-2), 413-580., Rendic, S. Drug Metab. Rev., 2002, 34(1-2), 83-448.). The collected information presented here is as stated by the cited author(s), and in cases when several references are cited the latest published information is included. Inconsistent results and conclusions obtained by different authors are highlighted, followed by discussion of the major findings. The searchable database is available as an Excel file, for information about file availability contact the corresponding author.

SKP2 siRNA inhibits the degradation of P27kip1 and down-regulates the expression of MRP in HL-60/A cells

S-phase kinase-associated protein 2 (SKP2) gene is a tumor suppressor gene, and is involved in the ubiquitin-mediated degradation of P27kip1. SKP2 and P27kip1 affect the proceeding and prognosis of leukemia through regulating the proliferation, apoptosis and differentiation of leukemia cells. In this study, we explored the mechanism of reversing of HL-60/A drug resistance through SKP2 down-regulation. HL-60/A cells were nucleofected by Amaxa Nucleofector System with SKP2 siRNA. The gene and protein expression levels of Skp2, P27kip1, and multi-drug resistance associated protein (MRP) were determined by reverse transcription-polymerase chain reaction and western blot analysis, respectively. The cell cycle was analyzed by flow cytometry. The 50% inhibitory concentration value was calculated using cytotoxic analysis according to the death rate of these two kinds of cells under different concentrations of chemotherapeutics to compare the sensitivity of the cells. HL-60/A cells showed multi-drug resistance phenotype characteristic by cross-resistance to adriamycin, daunorubicin, and arabinosylcytosine, due to the expression of MRP. We found that the expression of SKP2 was higher in HL-60/A cells than in HL-60 cells, but the expression of P27kip1 was lower. The expression of SKP2 in HL-60/A cells nucleofected by SKP2 siRNA was down-regulated whereas the protein level of P27kip1 was up-regulated. Compared with the MRP expression level in the control group (nucleofected by control siRNA), the mRNA and protein expression levels of MRP in HL-60/A cells nucleofected by SKP2 siRNA were lower, and the latter cells were more sensitive to adriamycin, daunorubicin, and arabinosylcytosine. Down-regulating the SKP2 expression and arresting cells in the G0/G1 phase improve drug sensitivity of leukemia cells with down-regulated MRP expression.

Combined Fourier transform infrared and Raman spectroscopic approach for identification of multidrug resistance phenotype in cancer cell lines

Cancer cells escape cytotoxic effects of anticancer drugs by a process known as multidrug resistance (MDR). Identification of cell status by less time-consuming methods can be extremely useful in patient management and treatment. This study aims at evaluating the potentials of vibrational spectroscopic methods to perform cell typing and to differentiate between sensitive and resistant human cancer cell lines, in particular those that exhibit the MDR phenotype. Micro-Raman and Fourier transform infrared (FTIR) spectra have been acquired from the sensitive promyelocytic HL60 leukemia cell line and two of its subclones resistant to doxorubicin (HL60/DOX) and daunorubicin (HL60/DNR), and from the sensitive MCF7 breast cancer cell line and its MDR counterpart resistant to verapamil (MCF7/VP). Principal components analysis (PCA) was employed for spectral comparison and classification. Our data show that cell typing was feasible with both methods, giving two distinct clusters for HL60- and MCF7-sensitive cells. In addition, phenotyping of HL60 cells, i.e., discriminating between the sensitive and MDR phenotypes, was attempted by both methods. FTIR could not only delineate between the sensitive and resistant HL60 cells, but also gave two distinct clusters for the resistant cells, which required a two-step procedure with Raman spectra. In the case of MCF7 cell lines, both the sensitive and resistant phenotypes could be differentiated very efficiently by PCA analysis of their FTIR and Raman point spectra. These results indicate the prospective applicability of FTIR and micro-Raman approaches in the differentiation of cell types as well as characterization of the cell status, such as the MDR phenotype exhibited in resistant leukemia cell lines like HL60 and MCF7.

VEGF inhibition and cytotoxic effect of aplidin in leukemia cell lines and cells from acute myeloid leukemia

BACKGROUND

Aplidine (APL) is a marine depsipeptide isolated from the Mediterranean tunicate Aplidium albicans that is under clinical phase II development. In contrast to the lack of bone marrow toxicity reported in phase I/II studies, it has been shown to induce cytotoxicity at very low concentration against lymphoblastic leukemia blast, as well as having an impact in the vascular endothelial growth factor (VEGF)/VEGF receptor 1 loop.

PATIENTS AND METHODS

To confirm these findings we investigated APL-related VEGF inhibition and its cytotoxic effect on myeloid leukemic cells lines (K-562, HEL and HL60) and fresh leukemia blasts derived from 30 patients with acute myeloid leukemia (AML). The conventional active 4-demetoxi-daunorubicin (idarubicin; IDA) was included as a positive control.

RESULTS

APL was found to be significantly (P<0.001) more active than IDA in obtaining 50% growth-inhibition in K-562, HEL and HL60 cell lines. Results obtained with AML blast cells were super imposible. ID(50) ranged from 0.024 to 0.610 microM for IDA (0.200+/-0.176) and from 0.001 to 0.108 microM for APL (0.020+/-0.031). Annexin V tests and cell cycle analysis performed on cell lines confirmed the stronger citotoxic capability of APL as apoptotic inducer and as a G(1) blocker. The inhibitory effects of APL on VEGF release and secretion have been confirmed by ELISA tests performed on HEL: the VEGF concentration in cell surnatant was reduced from 169 to 36 pg/ml after 24 h of exposure to a pharmacological concentration of APL.

CONCLUSIONS

APL harbors a strong in vitro antileukemic activity at a concentration achievable in patients at non-myelotoxic doses. Our data also support the notion of an impact on VEGF secretion. Clinical studies with this new marine-derived compound in relapsed/resistant leukemia are underway.

In vitro antileukemic effect of a new anthracycline analogue, MEN 11079

The biological activity of MEN 11079, a new daunorubucin analogue with a fluorine atom in C(8) of ring A, was investigated in the human leukemic cell lines K-562 and in mononuclear cells (MNCs) of 40 patients with acute myeloid leukemia (AML) and the activity compared to two well-characterized anthracyclines, idarubicin (IDA) and doxorubicin (DOXO). IDA and MEN 11079 were more active than DOXO in cytotoxicity tests (WST-1 assay). IDA and MEN 11079 ID(50) values were also significantly different from each other (K-562: P=0.038; MNCs: P=0.003). Moreover, the range was 0.002-4.300 microM for IDA and 0.002-0.670 microM for MEN 11079, in the MNCs. Therefore, the latter appeared to assure a smaller variability of response in the AML cells. Apoptosis assays (performed using Annexin-V assay and propidium iodide) and cell cycle studies demonstrated that the MEN 11079 effective concentration was 10-fold lower than the DOXO and IDA ones. MDR (Pgp and MRP1 proteins), as measured by semiquantitative RT-PCR, cytofluorimetric and functional analysis of proteins, was similarly elicited by IDA and MEN 11079. In conclusion, the response of the cells to the new anthracycline indicates that there is greater cytotoxic activity of this molecule than IDA and DOXO. Its narrower ID(50) range may allow for a more predictable response in the clinical setting.

Mechanism of 5-fluorouracil required resistance in human hepatocellular carcinoma cell line Bel7402

AIM: To investigate the resistance mechanism of 5-fluorouracil (5-FU) in Bel₇₄₀₂/5-FU cells which was established in our lab by in vitro continuous stepwise exposure of human hepatocellular carcinoma (HCC) cell line Bel₇₄₀₂ to 5-FU.

METHODS: The expression of multidrug resistance-associated protein (MRP) and thymidylate synthase (TS) in Bel₇₄₀₂ cells was detected by immonocytochemistry. The fluorescein (FLU) accumulation, an index of MRP functional activity, was determined by flow cytometry. The distribution of FLU was observed by confocal laser scanning microscope. The spectrofluorometry was used to show the intracelluar content of glutathione (GSH). Cell growth inhibition was determined by MTT assay. The activity of glutathione S-transferases (GSTs) was determined by spectrophotometry.

RESULTS: A higher expression of MRP in the Bel₇₄₀₂/5-FU cells was observed by using monoclonal mouse anti-MRP antibody, MRPr-1, in comparison with Bel₇₄₀₂ cells. Bel₇₄₀₂/5-FU cells also showed a significant decrease of FLU accumulation. FLU mainly accumulated in the nucleus with a high nuclear/cytoplasmic ratio in Bel₇₄₀₂ cells, whereas there was no difference of FLU accumulation between the nucleus and cytoplasm in Bel₇₄₀₂/5-FU cells. The intracellular GSH content in Bel₇₄₀₂/5-FU cells was almost 3 folds higher than that in Bel₇₄₀₂ cells. Addition of D, L-buthione-S, R-sulfoximine (BSO) dose-dependently reduced the GSH content in Bel₇₄₀₂/ 5-FU cells, however, only a weak enhancement on the cytotoxicity of 5-FU and doxorubicin (Dox) to Bel₇₄₀₂/5-FU cells was observed. Bel₇₄₀₂/5-FU cells also exhibited 29.1% higher total GSTs activity than Bel₇₄₀₂ cells. Immunocytochemical staining by using anti-TS monoclonal antibody TS 106 showed that the level of TS in Bel₇₄₀₂/5-FU cells elevated markedly as compared with Bel₇₄₀₂ cells.

CONCLUSION: The continuous exposure of Bel₇₄₀₂ cells to 5-FU led to overexpression of TS and MRP, as well as increased intracellular GSH content and total GST activity.

Subcellular daunorubicin distribution and its relation to multidrug resistance phenotype in drug-resistant cell line SMMC-7721/R

AIM: To investigate the correlation between subcellular daunorubicin distribution and the multidrug resistance phenotype in drug-resistant cell line SMMC-7721/R.

METHODS: The multidrug resistant cell line SMMC-7721/R, a human hepatocellular carcinoma cell line, was established. Antisense oligonucleotides (AS-ODN) were used to obtain different multidrug resistance phenotypes by inhibiting the expression of mdr1 gene and/or multidrug resistance-related protein gene (mrp) using Lipofectamine as delivery agent. Expression of mdr1 and mrp genes was evaluated by RT-PCR and Western blotting. Intracellular daunorubicin (DNR) concentration was measured by flow cytometry. Subcellular DNR distribution was analyzed by confocal laser scanning microscopy. Adriamycin (ADM) and DNR sensitivity was examined by MTT method.

RESULTS: Low level expression of mdr1 and mrp mRNAs and no expression of P-Glycoprotein (P-gp) and multidrug resistance-related protein (P₁₉₀) were detected in parental sensitive cells SMMC-7721/S, but over-expression of these two genes was observed in drug-resistant cell SMMC-7721/R. The expression of mdr1 and mrp genes in SMMC-7721/R cells was down-regulated to the level in the SMMC-7721/S cells by AS-ODN. Intracellular DNR concentration in SMMC-7721/S cells was 10 times higher than that in SMMC-7721/R cells. In SMMC7721/S cells intracellular DNR distributed evenly in the nucleus and cytoplasm, while in SMMC-7721/R cells DNR distributed in a punctate pattern in the cytoplasm and was reduced in the nucleus. DNR concentration in SMMC-7721/R cells co-transfected with AS-ODNs targeting to mdr1 and mrp mRNAs recovered to 25 percent of that in SMMC7721/S cells. Intracellular DNR distribution pattern in drug-resistant cells treated by AS-ODN was similar to drug-sensitive cell, and the cells resistance index (RI) to DNR and ADM decreased at most from 88.0 and 116.0 to 4.0 and 2.3, respectively. Co-Transfection of two AS-ODNs showed a stronger synergistic effect than separate transfection.

CONCLUSIONS: P-gp and P₁₉₀ are two members mediating MDR in cell line SMMC7721/R. Intracellular drug concentration increase and subcellular distribution change are two important factors in multidrug resistance (MDR) formation. The second factor, drugs transport by P-gp and P₁₉₀ from cell nucleus to organell in cytoplasm, may play a more important role.

High cellular accumulation of sulphoraphane, a dietary anticarcinogen, is followed by rapid transporter-mediated export as a glutathione conjugate

Sulphoraphane (SF), a naturally occurring isothiocyanate, is a potent anticarcinogen in animal experiments. The mechanism of action of sulphoraphane includes induction of Phase 2 detoxification enzymes, inhibition of carcinogen-activating Phase 1 enzymes, induction of apoptosis and cell cycle arrest, and anti-inflammation. We have recently found that it was accumulated in mammalian cells by up to several hundred-fold over the extracellular concentration, primarily by conjugation with intracellular GSH. The intracellular accumulation levels of SF can reach millimolar concentrations. The anticarcinogenic activity of SF is at least partly dependent on its accumulation levels in cells. Here we show, however, that the accumulated SF was rapidly exported mainly in the form of GSH conjugate (GS-SF) in cultured human cells. It appeared that to sustain the intracellular accumulation levels required a continuous uptake of SF to offset the rapid export of SF/GS-SF. These findings may have important implications for the development of an effective dosing regimen for SF. Moreover, the export was temperature-sensitive and was inhibited by known inhibitors of membrane pumps, suggesting the involvement of such a pump in exporting accumulated SF/GS-SF. Indeed, studies with human leukemia cells (HL60) with or without overexpression of multidrug resistance associated protein-1(MRP-1) and human myeloma cells (8226) with or without overexpression of P-glycoprotein-1 (Pgp-1) indicated that both MRP-1 and Pgp-1 are involved in the export of intracellular SF/GS-SF.

Biochemical changes associated with a multidrug-resistant phenotype of a human glioma cell line with temozolomide-acquired resistance

Temozolomide (TMZ) is a newly approved alkylating agent for the treatment of malignant gliomas. To investigate resistance mechanisms in a multidrug therapeutic approach, a TMZ-resistant human glioma cell line, SF188/TR, was established by stepwise exposure of human SF188 parental cells to TMZ for approximately 6 months. SF188/TR showed 6-fold resistance to TMZ and cross-resistance to a broad spectrum of other anticancer agents that included 3-5-fold resistance to melphalan (MEL), gemcitabine (GEM), paclitaxel (PAC), methotrexate (MTX), and doxorubicin (DOX), and 1.6-2-fold resistance to cisplatin (CDDP) and topotecan (TPT). Alkylguanine alkyltransferase (AGT) activity was increased significantly in the resistant cell line compared with the parental cell line (P<0.05), whereas no significant differences occurred in the cellular uptake of TMZ and PAC between resistant and parental cells. Depletion of AGT by O(6)-benzylguanine significantly increased the cytotoxicity of TMZ in both the sensitive and resistant cell lines, but did not influence the cytotoxicity of the other drugs tested. Treatment with TMZ caused SF188 cells to accumulate in S phase, whereas SF188/TR cells were unaffected. Expression of Bcl-2 family members in SF188/TR cells compared with SF188 cells indicated that the pro-apoptotic proteins (i.e. Bad, Bax, Bcl-X(S)) were reduced 2-4-fold in the resistant cell line, whereas the anti-apoptotic proteins Bcl-2 and Bcl-X(L) were expressed at similar levels in both cell lines. In conclusion, the mechanism of resistance of SF188/TR cells to TMZ involved increased activity of AGT, a primary resistance mechanism, whereas the broad cross-resistance pattern to other anticancer drugs was due to a common secondary resistance mechanism related to alterations in the relative expression of the pro-apoptotic and anti-apoptotic proteins.

NOD/SCID repopulating cells but not LTC-IC are enriched in human CD34+ cells expressing the CCR1 chemokine receptor

Human haemopoietic stem and progenitor cells may be distinguished by the pattern of cell surface markers they display. The cells defined as 'stem' cells are heterogeneous and lack specific markers for their detection. However, they may be identified in in vitro assays such as the long-term culture initiating cell (LTC-IC) and in transplant assays involving immunosuppressed NOD/SCID mice. It is still not clear to what extent, if any, these cell populations overlap. The chemokine macrophage inflammatory protein-1alpha (MIP-1alpha) prolongs survival of LTC-IC in suspension cultures and we now show that in longterm bone marrow cultures (LTBMC) maintenance of haemopoiesis was significantly better from the CD34+ cells which possess MIP-1alpha receptors (P < 0.006). We examined one MIP-1alpha receptor, CCR1, which is present on CD34+ cells from haemopoietic tissues. In LTBMC the production of GM-CFC from CD34+CCR1- cells was significantly higher (P < 0.02) than that from CD34+CCR1+ cultures and the incidence of LTC-IC was 3- to 6-fold higher in the CD34+CCR1- cell fraction. In contrast, the cells responsible for high levels of engraftment in NOD/SCID mice were contained in the CD34+CCR1+ cell fraction. The CD34+CCR1+ cells engrafted to high levels in NOD/SCID and generated large numbers of progenitor cells. Therefore, we conclude that LTC-IC and SRC may be distinguished on the basis of expression of the chemokine receptor CCR1.

Anthracycline drug targeting: cytoplasmic versus nuclear--a fork in the road

The anthracycline antibiotics doxorubicin (Adriamycin; DOX) and daunorubicin (DNR) continue to be essential components of first-line chemotherapy in the treatment of a variety of solid and hematopoietic tumors. The overall efficacies of DOX and DNR are, however, impeded by serious dose-limiting toxicities, including cardiotoxicity, and the selection of multiple mechanisms of cellular drug resistance. These limitations have necessitated the development of newer anthracyclines whose structural and functional modifications circumvent these impediments. In this review, we will present recent strategies in anthracycline design and assess their potential therapeutic merits. Current anthracycline design has diverged to target either cytoplasmic or nuclear sites. Nuclear targets have been broadened to include not only topoisomerase II (topo II) inhibition through ternary complex stabilization and catalytic inhibition, but also topoisomerase I (topo I) inhibition and transcriptional inhibition. In contrast, cytoplasmic targeting focuses on anthracycline binding to protein kinase C (PKC) regulatory domain with consequent modulation of activity.

Mechanism of resistance to oxidative stress in doxorubicin resistant cells

Doxorubicin (DOX) is an anthracycline drug widely used in chemotherapy for cancer patients, but it often gives rise to multidrug resistance in cancer cells. The purpose of this work was to study the effect of hydrogen peroxide in DOX-sensitive mouse P388/S leukemia cells and in the DOX-resistant cell line. Hydrogen peroxide induced a significant increase in dose- and time-response cell death in cultured P388/S cells. The degree of cell death in P388/DOX cells induced by hydrogen peroxide was less than that in P388/S cells treated with hydrogen peroxide. Parent cells exposed to 3 mM of hydrogen peroxide showed a loss of mitochondrial membrane potential correlated with cell death. Hydrogen peroxide at a concentration greater than 0.3 mM increased the intracellular Ca2+ of P388/S cells dose-dependently; however, no change following addition of hydrogen peroxide (0.3-1 mM) was observed in the resistant cells. Hydrogen peroxide (0.1 and 1 mM) treatment also induced the production of intracellular ROS in P388/S cells, while no such increase was produced by this substance in P388/DOX cells. Resistant cells also showed a significant level of glutathione (GSH) compared with the parent cells. In addition, N-acetyl-L-cysteine and reduced GSH antioxidants abolished death of P388/S cells caused by hydrogen peroxide. Therefore, it is believed that the reduced effect of oxidative stress towards the resistant cells may be related to an increase in intracellular GSH level.

Technetium-99m-tetrofosmin would be a substrate for multidrug resistance-associated protein (MRP): comparison between a leukemia cell line with high MRP gene expression and its parental cell line

The kinetics of cellular accumulation and retention of technetium-99m-tetrofosmin (99mTc-TF) were investigated in wild type HL60/WT cell line and in its doxorubicin-resistant HL60/DOX cell line with multidrug resistance-associated protein (MRP), but without P-gp overexpression, to determine whether 99mTc-TF is a substrate for MRP.

METHODS

The accumulation and washout of 99mTc-TF were observed in both cell lines at 37 degrees C. The effect of verapamil on the kinetics was also assessed.

RESULTS

99mTc-TF net accumulation was significantly lower in HL60/DOX (1.35 +/- 0.23%) than in HL60/WT (12.79 +/- 0.47%) at 60 min (P < 0.001). Three minutes after exchanging the incubation solution to the tracer-free medium, only 18.20 +/- 0.34% of 99mTc-TF remained in HL60/DOX, whereas 84.74 +/- 0.65% did in HL60/WT (P < 0.001). In the presence of 10 microM verapamil, 99mTc-TF net accumulation in HL60/DOX was 302% of the control and the washout was significantly delayed.

CONCLUSION

99mTc-TF would be a substrate for MRP and 99mTc-TF may be used as a functional imaging agent of MRP in vivo.