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Biomedical subjects

Susan E Bates

Publications and source records attributed to Susan E Bates.

51 records · Page 3Linked to original sources
PubMed2003

Differential effects of the breast cancer resistance protein on the cellular accumulation and cytotoxicity of 9-aminocamptothecin and 9-nitrocamptothecin.

Breast cancer resistance protein (BCRP)/MXR/ABCG2 is a new member of the family of ATP-dependent drug efflux proteins. Whereas overexpression of another member of this family, P-glycoprotein, minimally affects the cytotoxicity of camptothecins (CPTs), overexpression of wild-type as well as certain mutant BCRPs confers resistance to CPT analogues that are used clinically, including topotecan and irinotecan. Relatively little is known regarding the effects of BCRP on other CPT analogues. We now report studies of 9-aminocamptothecin (9-AC) and 9-nitrocamptothecin (9-NC) using mammalian cells stably transfected with constructs expressing a variety of efflux proteins, including wild-type BCRP and a mutant BCRP that contains a threonine rather than an arginine at position 482 (R482T). The results indicate that overexpression of either P-glycoprotein, multidrug resistance protein type 1, or multidrug resistance protein type 2 has little effect on the cytotoxicity of 9-NC or 9-AC. By contrast, overexpression of either wild-type or R482T BCRP confers resistance to 9-AC, but not to 9-NC. Furthermore, overexpression of wild-type or mutant BCRP is associated with reduced intracellular accumulation of 9-AC, but not 9-NC. In addition, immunoblotting studies indicate that whereas increased BCRP expression is evident in cells selected for resistance to irinotecan, BCRP expression is not detectable in two different cell lines selected for resistance to 9-NC. Taken together, these findings suggest that wild-type as well as R482T BCRP mediates cellular efflux of 9-AC but not 9-NC. Furthermore, the results suggest that polar groups at the 9 or 10 position of the CPT A ring facilitate interaction with BCRP and have implications for the clinical development of new CPT analogues.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2003

The role of ABC transporters in clinical practice.

Drug resistance remains one of the primary causes of suboptimal outcomes in cancer therapy. ATP-binding cassette (ABC) transporters are a family of transporter proteins that contribute to drug resistance via ATP-dependent drug efflux pumps. P-glycoprotein (P-gp), encoded by the MDR1 gene, is an ABC transporter normally involved in the excretion of toxins from cells. It also confers resistance to certain chemotherapeutic agents. P-gp is overexpressed at baseline in chemotherapy-resistant tumors, such as colon and kidney cancers, and is upregulated after disease progression following chemotherapy in malignancies such as leukemia and breast cancer. Other transporter proteins mediating drug resistance include those in the multidrug-resistance-associated protein (MRP) family, notably MRP1, and ABCG2. These transporters are also involved in normal physiologic functions. The expressions of MRP family members and ABCG2 have not been well worked out in cancer. Increased drug accumulation and drug resistance reversal with P-gp inhibitors have been well documented in vitro, but only suggested in clinical trials. Limitations in the design of early resistance reversal trials contributed to disappointing results. Despite this, three randomized trials have shown statistically significant benefits with the use of a P-gp inhibitor in combination with chemotherapy. Improved diagnostic techniques aimed at the selection of patients with tumors that express P-gp should result in more successful outcomes. Further optimism is warranted with the advent of potent, nontoxic inhibitors and new treatment strategies, including the combination of new targeted therapies with therapies aimed at the prevention of drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

MS-27-275, an inhibitor of histone deacetylase, has marked in vitro and in vivo antitumor activity against pediatric solid tumors.

The antitumor efficacy of the synthetic benzamide derivative MS-27-275 (MS-275), an inhibitor of histone deacetylation [T. Suzuki et al., J. Med. Chem., 42: 3001-3003, 1999], was evaluated in a series of pediatric solid tumor cell lines, including neuroblastoma, rhabdomyosarcoma, Ewing's sarcoma (EWS), retinoblastoma, medulloblastoma, undifferentiated sarcoma (US), osteosarcoma, and malignant rhabdoid tumors. Treatment with MS-275 results in an increase in acetylation of histones within 4 h of drug exposure. The cell lines were treated with various concentrations of MS-275 for 3 days and incubated with [(3)H]thymidine for 20 h before cell harvest. MS-275 inhibited [(3)H]thymidine uptake in a dose-dependent manner in all tumor cell lines examined. The IC(50) ranged from 50 nm in the D283 medulloblastoma cell line to 1.3 micro M in the US. A common feature of MS-275 treatment of pediatric tumor cell lines was induction of p21mRNA. However, the effects on cell cycle were diverse because in some cases MS-275 induced an increase in G(1) or G(2), whereas in others, there was an induction of apoptosis. In EWS, the EWS/fli chimeric transcription factor created by the t(11;22) suppresses transforming growth factor (TGF) betaRII transcription, however, MS-275 was able to induce an increase in TGF-betaRII mRNA and restore TGF-beta signaling. Using xenograft orthotopic models of US, EWS, and neuroblastoma, we find that the growth of established tumors is inhibited in mice treated with MS-275.

Acetylation↗
PubMed2002

Use of peptide antibodies to probe for the mitoxantrone resistance-associated protein MXR/BCRP/ABCP/ABCG2.

Recent studies have characterized the ABC half-transporter associated with mitoxantrone resistance in human cancer cell lines. Encoded by the ABCG2 gene, overexpression confers resistance to camptothecins, as well as to mitoxantrone. We developed four polyclonal antibodies against peptides corresponding to four different epitopes on the mitoxantrone resistance-associated protein, ABCG2. Three epitopes localized on the cytoplasmic region of ABCG2 gave rise to high-affinity antibodies, which were demonstrated to be specific for ABCG2. Western blot analysis of cells with high levels of ABCG2 showed a single major band of the expected 72-kDa molecular size of ABCG2 under denaturing conditions. Immunoblot analysis performed under non-reducing conditions and after treatment with cross-linking reagents demonstrated a molecular weight shift from 72 kDa to several bands of 180 kDa and higher molecular weight, suggesting detection of dimerization products of ABCG2. Evidence of N-linked glycosylation was also obtained using tunicamycin and N-glycosidase F. Finally, both by light, fluorescence and electron microscopic immunohistochemical staining, we demonstrate cytoplasmic and predominantly plasma membrane localization of ABCG2 in cell lines with high levels of expression. Plasma membrane staining was observed on the surface of the chorionic villi in placenta. These results support the hypothesis that ABCG2 is an ABC half-transporter that forms dimers in the plasma membrane, functioning as an ATP-dependent outward pump for substrate transport.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2002

Expression and activity of breast cancer resistance protein (BCRP) in de novo and relapsed acute myeloid leukemia.

Overexpression of the breast cancer resistance protein (BCRP) efflux pump in human cancer cell lines results in resistance to a variety of cytostatic agents. The aim of this study was to analyze BCRP protein expression and activity in acute myeloid leukemia (AML) samples and to determine whether it is up-regulated due to clonal selection at relapse/refractory disease. BCRP protein expression was measured flow cytometrically with the monoclonal antibodies BXP-34 and BXP-21 in 20 paired samples of de novo and relapsed/refractory AML. BXP-34/immunoglobulin G1 ratios were observed of 1.6 +/- 0.5 (mean +/- SD, range 0.8-2.7) and BXP-21/immunoglobulin G2a ratios of 4.9 +/- 3.0 (range 1.1-14.5) in the patient samples versus 9.8 +/- 6.8 and 6.5 +/- 2.4, respectively, in the MCF-7 cell line. BCRP activity was determined flow cytometrically by measuring mitoxantrone accumulation in absence and presence of the inhibitor fumitremorgin C. Mitoxantrone accumulation, expressed as mean fluorescence intensity (MFI), varied between 44 and 761 MFI (227 +/- 146 MFI) and correlated inversely with BCRP expression (r = -0.58, P <.001). Addition of fumitremorgin C showed a small increase in mitoxantrone accumulation (11 +/- 29 MFI, n = 40) apart from the effect of PSC833 and MK-571. No consistent up-regulation of BCRP expression or activity was observed at relapse/refractory disease; some cases showed an increase and other cases a decrease at relapse. Relatively high BCRP expression correlated with immature immunophenotype, as determined by expression of the surface marker CD34 (r = 0.54, P =.001). In conclusion, this study shows that BCRP protein is expressed at low but variable levels in AML, especially in immature CD34(+) cells. BCRP was not consistently up-regulated in relapsed/refractory AML.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2002

Impact of BCRP/MXR, MRP1 and MDR1/P-Glycoprotein on thermoresistant variants of atypical and classical multidrug resistant cancer cells.

The impact of the ABC transporters breast cancer resistance protein/mitoxantrone resistance associated transporter (BCRP/MXR), multidrug resistance-associated protein 1 (MRP1) and multidrug resistance gene-1/P-glycoprotein (MDR1/PGP) on the multidrug resistance (MDR) phenotype in chemoresistance and thermoresistance was investigated in the parental human gastric carcinoma cell line EPG85-257P, the atypical MDR subline EPG85-257RNOV, the classical MDR subline EPG85-257RDB and their thermoresistant counterparts EPG85-257P-TR, EPG85-257RNOV-TR and EPG85-257RDB-TR. Within the atypical MDR subline EPG85-257RNOV expression of BCRP/MXR and of MRP1 were clearly enhanced (vs. parental and classical MDR lines). MDR1/PGP expression was distinctly elevated in the classical MDR subline EPG85-257RDB (vs. parental and atypical MDR sublines). In all thermoresistant counterparts basal expression of BCRP/MXR, MRP1 and MDR1/PGP was increased relative to thermosensitive sublines. Although it could be shown that the overexpressed ABC transporters were functionally active, however, no decreased drug accumulations of doxorubicin, mitoxantrone and rhodamine 123 were observed. Thus, expression of BCRP/MXR, MRP1 and MDR1/PGP was found to be dependent on the appropriate type of chemoresistance; correlating with a classical or atypical MDR phenotype. Within the thermoresistant variants, however, the increase in ABC transporter expression did obviously not influence the MDR phenotype.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Differential sensitivity of cancer cells to inhibitors of the epidermal growth factor receptor family.

Clinical responses to the HER1 (EGF receptor) inhibitors and HER2/neu/ErbB2 inhibitors correlate with high levels of receptor expression. However, a significant subset of patients with high receptor levels appear to be refractory to treatment. We have observed similar results in the 60 cell lines of the NCI Anti-Cancer Drug Screen using a panel of 11 selective HER1 inhibitors. As expected, low HER1-expressing cell lines were insensitive to HER1 inhibitors. In cell lines with high HER1 expression, low concentrations of HER1 inhibitors potently inhibit both HER1 phosphorylation and the mitogen-activated protein kinase (MAPK) pathway. However, this inhibition did not always correlate with cellular arrest. High HER1-expressing cell lines can be subdivided into two groups based on their sensitivity to HER1 inhibitors. In the sensitive group, receptor and growth inhibition was concordant and occurred at sub-micromolar concentrations of HER1 inhibitors. In the insensitive group, receptor inhibition occurred at a low concentration (< 1 microM) but concentrations that were ten times or higher were required for growth inhibition. Also, neither induction of p21 and cyclin D1 nor p53 status could explain the difference between sensitive and insensitive cells. Although EGF activated the MAPK pathway in all cell lines, only drug-sensitive cell lines responded to EGF (accelerated entry from G1 to S) and to HER1 inhibitors (G1 arrest) by changes in cell cycling. Furthermore, an EGF-dependent immortalized mammary epithelial cell line was extremely sensitive to a panel of HER1 inhibitors. We infer that independence from mitogen-mediated signaling confers insensitivity to HER1 inhibitors in a large subset of cancer cell lines.

Cell Cycle↗
PubMed2002

Multidrug resistance in cancer: role of ATP-dependent transporters.

Chemotherapeutics are the most effective treatment for metastatic tumours. However, the ability of cancer cells to become simultaneously resistant to different drugs--a trait known as multidrug resistance--remains a significant impediment to successful chemotherapy. Three decades of multidrug-resistance research have identified a myriad of ways in which cancer cells can elude chemotherapy, and it has become apparent that resistance exists against every effective drug, even our newest agents. Therefore, the ability to predict and circumvent drug resistance is likely to improve chemotherapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Phase I trial of the histone deacetylase inhibitor, depsipeptide (FR901228, NSC 630176), in patients with refractory neoplasms.

PURPOSE: The primary objectives of this trial were to define the maximum tolerated dose (MTD) and to characterize the toxicities and pharmacokinetics of depsipeptide (FR901228) given on a day-1 and day-5 schedule every 21 days. A secondary objective of the trial was to seek evidence of antineoplastic activity. PATIENTS AND METHODS: Patients with advanced or refractory neoplasms received depsipeptide by a 4-h i.v. infusion on days 1 and 5 of a 21-day cycle. On the basis of preclinical data suggesting that depsipeptide may have significant cardiac toxicity, patients were treated while receiving continuous cardiac monitoring and were followed with serial cardiac enzyme determinations, electrocardiograms (ECGs), and nuclear ventriculograms (MUGA scans). The starting dose of the trial was 1 mg/m(2), and dose escalations proceeded through a total of eight dose levels to a maximum of 24.9 mg/m(2). Toxicities were graded using the National Cancer Institute common toxicity criteria, and pharmacokinetics were determined using a liquid chromatography/tandem mass spectrometry method. RESULTS: Patients (37) received a total of 88 cycles of treatment on study (range: one to eight cycles). Dose-limiting toxicity (DLT) was observed, and the MTD exceeded at a dose of 24.9 mg/m(2). The DLTs included grade-3 fatigue (3 patients), grade-3 nausea and vomiting (1 patient), grade-4 thrombocytopenia (2 patients), and grade-4 cardiac arrhythmia (1 patient, atrial fibrillation). The MTD was defined at the seventh dose level (17.8 mg/m(2)). Reversible ST/T changes and mild reversible dysrhythmias were observed on the post-treatment ECG. There were no clinically significant changes in left ventricular ejection fraction. One patient achieved a partial response. The plasma disposition of depsipeptide was well described by a first-order, two-compartment model. The mean volume of distribution, clearance, t(1/2alpha) and t(1/2beta) at a dose of 17.8 mg/m(2) was: 8.6 liters/m(2), 11.6 liters/h/m(2), 0.42 h, and 8.1 h, respectively. The mean maximum plasma concentration at the MTD was 472.6 ng/ml (range: 249-577.8 ng/ml). Biological assays showed that the serum levels achieved could cause the characteristic cell cycle effects of this agent when serum was added to PC3 cells in culture, as well as increased histone acetylation in patient-derived peripheral blood mononuclear cells. CONCLUSION: The MTD of depsipeptide given on a day-1 and -5 schedule every 21 days is 17.8 mg/m(2). The DLTs are fatigue, nausea, vomiting, and transient thrombocytopenia and neutropenia. Whereas cardiac toxicity was anticipated based on preclinical data, there was no evidence of myocardial damage. However, reversible ECG changes with ST/T wave flattening were regularly observed. Biologically active serum concentrations were achieved, and 1 patient obtained a partial response. The recommended Phase II dose is 17.8 mg/m(2) administered on day 1 and 5 of a 21-day cycle.

Adult↗
PubMed2002

ABC transporters and inhibitors: new targets, new agents.

P-glycoprotein (P-gp), a plasma membrane pump associated with multidrug resistance (MDR), is a member of the superfamily of ATP-binding cassette (ABC) transporters. The discovery that inhibitors of drug efflux can increase drug accumulation and reverse drug resistance in the laboratory has led to the clinical development of a number of P-gp inhibitors. Initial studies were performed with agents already in use in the clinic for other indications, the 'first generation' studies. Second generation inhibitors were taken into clinical trials in leukemia, breast cancer, ovarian cancer and sarcoma, malignancies for which there is evidence that P-gp is expressed, and in some cases, associated with a poorer therapeutic outcome. One major limitation of these trials, however, was the reduction in anticancer drug doses that was required with concurrent administration of inhibitor. The reduction in drug dose needed in these combination studies, may have confounded the results and contributed to disappointing outcomes. Functional assays to verify the role of P-gp inhibition in MDR, such as sestamibi imaging are proving helpful in assessing the development of improved inhibitors that are providing hope for the future. This review focuses on attempts aimed at overcoming resistancemediated by ABC transporters and evaluates the prospects for addition of new inhibitors to the anticancer armamentarium.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2002

Histone deacetylase inhibitors all induce p21 but differentially cause tubulin acetylation, mitotic arrest, and cytotoxicity.

By preventing deacetylation of histones, histone deacetylase inhibitors (HDIs) transcriptionally induce p21. Here we show that the HDIs sodium butyrate (Bu), trichostatin A (TSA) and depsipeptide (FR901228) all induced p21, but only TSA and FR901228 caused mitotic arrest (in addition to arrest in G1 and G2). The ability to cause mitotic arrest correlated with the higher cytotoxicity of these compounds. Although causing mitotic arrest, TSA and FR901228 (unlike paclitaxel) did not affect tubulin polymerization. Unlike FR9012208, TSA caused acetylation of tubulin at lysine 40; both soluble tubulin and microtubules were acetylated. Whereas the induction of p21 reached a maximum by 8 h, tubulin was maximally acetylated after only 1 h of TSA treatment. Tubulin acetylation was detectable after treatment with 12-25 ng/ml TSA although acetylation plateaued at 50 ng/ml TSA, coinciding with G2-M arrest, appearance of cells with a sub-2N DNA content, poly(ADP-ribose) polymerase cleavage, and rapid cell death. We conclude that HDIs have differential effects on non-histone deacetylases and that rapid acetylation of tubulin caused by TSA is a marker of nontranscriptional effects of TSA.

Anesthetics, Intravenous↗
PubMedDate not supplied

Single-nucleotide polymorphism (SNP) analysis in the ABC half-transporter ABCG2 (MXR/BCRP/ABCP1).

Variations in the amino acid sequence of ABC transporters have been shown to impact substrate specificity. We identified two acquired mutations in ABCG2, the ABC half-transporter overexpressed in mitoxantrone-resistant cell lines. These mutations confer differences in substrate specificity and suggest that naturally occurring variants could also affect substrate specificity. To search for the existence of single nucleotide polymorphisms (SNPs) in ABCG2, we sequenced 90 ethnically diverse DNAs from the Single Nucleotide Polymorphism Discovery Resource representing the spectrum of human genotypes. We identified 3 noncoding SNPs in the untranslated regions, 3 nonsynonymous and 2 synonymous SNPs in the coding region and 7 SNPs in the intron sequences adjacent to the sixteen ABCG2 exons. Nonsynonymous SNPs at nucleotide 238 (V12M; exon 2) and nucleotide 625 (Q141K; exon 5) showed a greater frequency of heterozygosity (22.2% and 10%) than the SNP at 2062 (D620N; exon 16). Heterozygous changes at nucleotide 238 are in linkage disequilibrium with an SNP observed 36 bases downstream from the end of exon 2. No polymorphism at amino acid 482 was identified to correspond to the R to G or R to T mutations previously found in two drug resistant cell lines. Among 23 drug resistant sublines for which sequence at position 482 was determined, no additional mutations were found. Heterozygosity at amino acid 12 allowed us to identify overexpression of a single allele in a subset of drug resistant cell lines, a feature that could be exploited clinically in evaluating the significance of ABCG2 expression in malignancy. We conclude that ABCG2 is well conserved and that described amino acid polymorphisms seem unlikely to alter transporter stability or function.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMedDate not supplied

Low and high concentrations of the topo II inhibitor daunorubicin in NIH3T3 cells: reversible G2/M versus irreversible G1 and S arrest.

Daunorubicin (DNR) blocks the cell cycle by interfering with synthesis and repair of DMA. In both drug-sensitive 3T3 cells and drug-resistant 3T3 cells (NIH-MDR-6185, created by transfection with a human MDR1 cDNA), low concentrations of DNR (up to 80 ng/ml in sensitive cells, 1600 ng/ml in resistant cells) initially slowed S-phase progression for 2 to 3 hours, but the treated cells then continued in progression at a steady rate, close to that of untreated cells, and accumulated in G(2)/M. The 2 to 3 h lag period represents the time taken for fully establishing the G(2)/M block. The time required to bring about cessation of proliferation is the sum of this lag period and the time taken to travel through the cell cycle. This low concentration effect is cytostatic, and fully reversible on washing out the daunorubicin. At higher drug concentrations (above 160 ng/ml in sensitive cells, 3200 ng/ml in resistant cells) the cells became blocked in both G] and S, and did not reach G(2)/M. The high concentration effect was cytotoxic and irreversible, and was followed by cell death. Only cells that were in S phase were subject to this block in S, since cells that had accumulated in G(2)/M by using a low concentration (60 ng/ml DNR for 20 h) were not blocked in S, and did not die, when subsequently treated with high drug concentrations (320 ng/ml, 30 h). The low concentration effect occurred at the same maximal rate (4 %/h) in sensitive or resistant cells, but the external drug concentration required to produce half the maximal rate was, appropriately, twenty-fold higher in the resistant cells (20 ng/ml and 400 ng/ml, respectively).

Antineoplastic Agents↗
PubMedDate not supplied

MDR1 (ABCB1) gene polymorphism C3435T is associated with P-glycoprotein activity in B-cell chronic lymphocytic leukemia.

Functional single nucleotide polymorphism (SNP) C3435T in exon 26 of the MDR1 ( ABCB1 ) gene encoding the xenobiotic transporter P-glycoprotein (P-gp, MDR1, ABCB1) may influence susceptibility to several diseases as well as clinical outcome of treatment with P-gp substrates. Exposure to environmental chemicals is thought to be involved in the pathogenesis of B-cell chronic lymphocytic leukemia (B-CLL) and P-gp-transported drugs are used in its treatment; however, little is known about the impact of the C3435T MDR1 SNP in B-CLL. In this study, 110 Caucasian B-CLL patients and 201 healthy controls were genotyped for the MDR1 C3435T SNP. Additionally, P-gp activity was assessed in malignant lymphocytes of 22 untreated B-CLL patients. We observed a higher frequency of carriers of at least one 3435T allele (3435CT and 3435TT genotypes) among B-CLL patients as compared to normal individuals (76% vs . 63%, p=0.027). The genotypes 3435CT and 3435TT were associated with B-CLL, (odds ratio=1.8, 95% confidence interval = 1.1-3.0). Moreover, P-gp activity in B-CLL cells depended on MDR1 genotype, with the highest P-gp activity in 3435CC homozygotes, intermediate in 3435CT heterozygotes and the lowest in 3435TT homozygotes (p=0.042). P-gp activity was also significantly lower in carriers of the T-allele (3435CT/TT genotype) as compared to the non-carriers (3435CC genotype), (p=0.029). Taken together, these data indicate that the MDR1 C3435T SNP may carry an increased risk of developing B-CLL, possibly by virtue of decreased protection against P-gp-substrate carcinogens. The differences in P-gp activity in B-CLL tumor cells related to MDR1 genotype may have implications to the response to chemotherapy with P-gp transported anticancer agents.

ATP Binding Cassette Transporter, Subfamily B, Mem↗