Chromosomal location of human P-glycoprotein gene sequences

A Comprehensive Review of Alzheimer's Association with Related Proteins: Pathological Role and Therapeutic Significance

Alzheimer's is an insidious, progressive, chronic neurodegenerative disease which causes the devastation of neurons. Alzheimer's possesses complex pathologies of heterogeneous nature counting proteins as one major factor along with enzymes and mutated genes. Proteins such as amyloid precursor protein (APP), apolipoprotein E (ApoE), presenilin, mortalin, calbindin-D28K, creactive protein, heat shock proteins (HSPs), and prion protein are some of the chief elements in the foremost hypotheses of AD like amyloid-beta (Aβ) cascade hypothesis, tau hypothesis, cholinergic neuron damage, etc. Disturbed expression of these proteins results in synaptic dysfunction, cognitive impairment, memory loss, and neuronal degradation. On the therapeutic ground, attempts of developing anti-amyloid, anti-inflammatory, anti-tau therapies are on peak, having APP and tau as putative targets. Some proteins, e.g., HSPs, which ameliorate oxidative stress, calpains, which help in regulating synaptic plasticity, and calmodulin-like skin protein (CLSP) with its neuroprotective role are few promising future targets for developing anti-AD therapies. On diagnostic grounds of AD C-reactive protein, pentraxins, collapsin response mediator protein-2, and growth-associated protein-43 represent the future of new possible biomarkers for diagnosing AD. The last few decades were concentrated over identifying and studying protein targets of AD. Here, we reviewed the physiological/pathological roles and therapeutic significance of nearly all the proteins associated with AD that addresses putative as well as probable targets for developing effective anti-AD therapies.

Association of ABCB1, β tubulin I, and III with multidrug resistance of MCF7/DOC subline from breast cancer cell line MCF7

Docetaxel is a first-line chemotherapeutic agent for treating advanced breast cancer. The development of chemoresistance or multidrug resistance (MDR), however, results in breast cancer chemotherapy failure. This study aims to explore the molecular mechanisms underlying docetaxel-resistance in treatment of breast cancer. The docetaxel-resistant subline MCF7/DOC, derived from the parental sensitive breast cancer cell line MCF7, was established by intermittent exposure to moderate concentrations of docetaxel, followed by examination of its phenotypes. The MCF7/DOC subline showed cross resistance against paclitaxel, doxorubicin, methotrexate, and 5-Fu. Compared to the parental MCF7, MCF7/DOC cells were enlarged with heterogeneous sizes and a cobblestone and polygonal appearance. They were arrested at G2/M phase and proliferated slowly. The colony formation potential of MCF7/DOC in soft agar was significantly increased. MCF7/DOC cells showed reduced intracellular accumulation and increased efflux of rhodamine 123. The mRNA expression level of adenosine triphosphate binding cassette (ABC) transporter family, i.e., ABCB1, ABCC1, ABCC2, ABCG2, and β tubulin isotypes were characterized by quantitative PCR. High-level expression of ABCB1, βI, and βIII tubulin mRNA in MCF7/DOC was detected. Downregulation of ABCB1, βI, and βIII tubulin mediated by three combined siRNAs resulted in stronger growth inhibition of MCF7/DOC than inhibition of the expression of individual genes. ABCB1, βI, and βIII tubulin might contribute to the MDR of MCF7/DOC and be potential therapeutic targets for overcoming MDR of breast cancer.

Taxane resistance in breast cancer: mechanisms, predictive biomarkers and circumvention strategies

BACKGROUND

Taxanes are established in the treatment of metastatic breast cancer (MBC) and early breast cancer (EBC) as potent chemotherapy agents. However, their therapeutic usefulness is limited by de-novo refractoriness or acquired resistance, which are common drawbacks to most anti-cancer cytotoxics. Considering that the taxanes will remain principle chemotherapeutic agents for the treatment of breast cancer, we reviewed known mechanisms of resistance in with an outlook of optimizing their clinical use.

METHODS

We searched the PubMed and MEDLINE databases for articles (from inception through to 9th January 2012; last search 10/01/2012) and journals known to publish information relevant to taxane chemotherapy. We imposed no language restrictions. Search terms included: cancer, breast cancer, response, resistance, taxane, paclitaxel, docetaxel, taxol. Due to the possibility of alternative mechanisms of resistance all combination chemotherapy treated data sets were removed from our overview.

RESULTS

Over-expression of the MDR-1 gene product Pgp was extensively studied in vitro in association with taxane resistance, but data are conflicting. Similarly, the target components microtubules, which are thought to mediate refractoriness through alterations of the expression pattern of tubulins or microtubule associated proteins and the expression of alternative tubulin isoforms, failed to confirm such associations. Little consensus has been generated for reported associations between taxane-sensitivity and mutated p53, or taxane-resistance and overexpression of Bcl-2, Bcl-xL or NFkB. In contrary sufficient in vitro data support an association of spindle assembly checkpoint (SAC) defects with resistance. Clinical data have been limited and inconsistent, which relate to the variety of methods used, lack of standardization of cut-offs for quantitation, differences in clinical endpoints measured and in methods of tissue collection preparation and storage, and study/patient heterogeneity. The most prominent finding is that pharmaceutical down-regulation of HER-2 appears to reverse the taxane resistance.

CONCLUSIONS

Currently no valid practical biomarkers exist that can predict resistance to the taxanes in breast cancer supporting the principle of individualized cancer therapy. The incorporation of several biomarker analyses into prospectively designed studies in this setting are needed.

Molecular mechanisms of drug resistance in acute myeloid leukaemia

Resistance to chemotherapy in acute myeloid leukaemia is a major obstacle to a successful outcome for many patients. Often, there is resistance against a broad range of drugs due to multiple, simultaneously active processes. These mechanisms include effects on drug influx and efflux, drug activation/inactivation, DNA repair mechanisms, altered response of end targets, an altered haematopoietic microenvironment and dysfunctional apoptotic pathways. This article reviews the factors that determine leukaemic cell chemosensitivity and discusses the potential for rationally guided therapy.

Implications of genetic polymorphisms in drug transporters for pharmacotherapy

Drug transporters are increasingly recognized as a key determinant of drug disposition and response. It is now widely appreciated that expression of the ATP-dependent efflux transporter, MDR1 (ABCB1, P-glycoprotein), in organs such as the gastrointestinal tract, liver and kidney significantly alters the extent of drug absorption and excretion. Moreover, expression of MDR1 at the level of the blood-brain barrier limits the entry of many drugs into the central nervous system. Given such an important role of MDR1 in the drug disposition process, it is not surprising to see increasing focus on the role of single nucleotide polymorphisms (SNPs) in this transporter as a potential determinant of interindividual variability in drug disposition and pharmacological response. However, drug transport is often the result of the concerted action of efflux and uptake pumps located both in the basolateral and apical membranes of epithelial cells. A growing list of membrane-spanning proteins involved in the in- or outward transport of a large variety of drugs has been recognized and characterized over the past few years in almost all tissues, including organic anion and cation transporters (OAT, OCT, solute carrier family SLC22A), organic anion transport proteins (OATP, solute carrier family SLCO, formerly SLC21A), and MRPs (ABCCs), other members of the ATP-binding cassette family. We are just beginning to appreciate their role for drug delivery and disposition and the contribution of genetic polymorphisms in these transport proteins to interindividual variability in the efficacy and safety for pharmacotherapy. This review summarizes the consequences of inherited differences in drug transport for pharmacotherapy. With the main focus on ABCB1, an update of recent advances is given and clinically relevant examples are used to illustrate how heritable differential drug transport can help to explain individual variability in drug response. The pharmacogenetics of other transporters is briefly introduced.

Similar chromosomal changes in cisplatin and oxaliplatin-resistant sublines of the H69 SCLC cell line are not associated with platinum resistance

Small cell lung cancer (SCLC) initially responds well to DNA damaging drugs such as cisplatin, however this is transitory as resistance normally develops. To investigate whether changes in chromosomal copy number caused by platinum drug treatment contributes to platinum resistance, we have analyzed H69 SCLC cells and two low-level platinum-resistant sublines, H69CIS200 and H69OX400, derived by cisplatin and oxaliplatin treatment, respectively. Affymetrix 10K SNP array showed that cisplatin and oxaliplatin have independently caused similar changes including loss of segments 6q21-qter and 13pter-13q.14.11 and duplication of chromosome 21. Interestingly, despite using equally cytotoxic doses of drug in the development of the cell lines, oxaliplatin caused three times more chromosomal changes than cisplatin. The resistant cell lines lose their resistant phenotype after 3 months of drug-free culture. The revertant cell lines, denoted H69CIS200-S and H69OX400-S, were also analyzed by Affymetrix array to determine if chromosomal changes associated with resistance remain after the resistant phenotype is lost. In the H69OX400-S many of the changes observed in the resistant cells were absent suggesting that they contributed to the resistant phenotype including: loss of 1q23.3-qter, 10q11.23, and 19q13.12-q13.2 and duplication of segments 6p21.2-p12.3, 16q12.1-16q13, 16q21-q23.1, and 19q12. However, out of the similar changes induced by cisplatin and oxaliplatin, both the loss of 6q21-qter and gain of 21 were still present in the H69CIS200-S and H69OX400-S cells. This suggests that cisplatin and oxaliplatin induced similar changes due to inherent vulnerabilities in the H69 cells rather than changes associated with platinum resistance.

ABC transporters as multidrug resistance mechanisms and the development of chemosensitizers for their reversal

One of the major problems related with anticancer chemotherapy is resistance against anticancer drugs. The ATP-binding cassette (ABC) transporters are a family of transporter proteins that are responsible for drug resistance and a low bioavailability of drugs by pumping a variety of drugs out cells at the expense of ATP hydrolysis. One strategy for reversal of the resistance of tumor cells expressing ABC transporters is combined use of anticancer drugs with chemosensitizers. In this review, the physiological functions and structures of ABC transporters, and the development of chemosensitizers are described focusing on well-known proteins including P-glycoprotein, multidrug resistance associated protein, and breast cancer resistance protein.

Parallel phase I studies of daunorubicin given with cytarabine and etoposide with or without the multidrug resistance modulator PSC-833 in previously untreated patients 60 years of age or older with acute myeloid leukemia: results of cancer and leukemia group B study 9420

PURPOSE

The Cancer and Leukemia Group B conducted parallel phase I trials of cytarabine, daunorubicin, and etoposide (ADE) with or without PSC-833 (P), a modulator of p-glycoprotein-mediated multidrug resistance.

PATIENTS AND METHODS

One hundred ten newly diagnosed patients > or = 60 years of age with de novo acute myeloid leukemia (AML) were treated. All patients received cytarabine by continuous infusion for 7 days at 100 mg/m(2)/d. The starting dose of daunorubicin was 30 mg/m(2)/d for 3 days. Etoposide was administered at a dose of 100 mg/m(2)/d for 3 days, except in the last cohort administered ADEP, who received 60 mg/m(2). PSC-833 was given intravenously with a loading dose of 1.5 mg/kg over 2 hours and a simultaneous continuous infusion of 10 mg/kg/d continued until 24 hours after the last dose of daunorubicin or etoposide.

RESULTS

There was no toxicity attributed to the PSC-833. Dose-limiting toxicity was primarily gastrointestinal (diarrhea, mucositis in the ADEP group). The estimated maximum-tolerated doses, calculated using a logistic regression model, were daunorubicin 40 mg/m(2)/d for 3 days with etoposide 60 mg/m(2) for 3 days in the ADEP group and daunorubicin 60 mg/m(2)/d for 3 days and etoposide 100 mg/m(2)/d for 3 days in the ADE group. Twenty-one (48%) of 44 patients achieved complete remission with ADE, compared with 29 (44%) of 66 patients treated with ADEP.

CONCLUSION

It is necessary to decrease the doses of daunorubicin and etoposide when they are administered with PSC-833, presumably because of the effect of the modulator on the pharmacokinetics of these agents. A phase III trial comparing the regimens derived from this phase I trial has recently begun.

Molecular dissection of the human multidrug resistance P-glycoprotein

The human multidrug resistance P-glycoprotein is an ATP-dependent drug pump that extrudes a broad range of cytotoxic agents from the cell. Its physiological role may be to protect the body from endogenous and exogenous cytotoxic agents. The protein has clinical importance because it contributes to the phenomenon of multidrug resistance during chemotherapy. In this review, we discuss some of the results obtained by using molecular biology and protein chemistry techniques for studying this important and intriguing protein.Key words: P-glycoprotein, ABC transporters, drug transport, dibromobimane, mutagenesis, disulfide crosslinking, metal-chelate chromatography, ATPase activity.

Is aggressive chemotherapy the best choice for patients with acute nonlymphocytic leukemia after myelodysplastic syndromes?

Myelodysplastic syndromes (MDS) evolve in overt acute nonlymphocytic leukemia (ANLL) in about 40% of patients: the treatment of ANLL-MDS is not yet well clarified. To identify the role for aggressive and conservative approaches in ANLL-MDS, we evaluated retrospectively 78 patients in a 7-year period. Thirty-one patients (16 males and 15 females, median age 57.5 years, median MDS duration 5.5 months) were eligible for aggressive chemotherapy; 17 patients (54.8%) achieved complete remission (CR), 10 (32.3%) were resistant and 4 (12.9%) died during induction from infective complications. All patients that achieved CR relapsed, with a median CR duration of 6 months (range 2-28 months); median survival of the whole group was 8.5 months, while median survival of responders was 9 months. No prognostic factor revealed a statistical significance in the outcome, due to the small number of patients in each subgroup. Forty-seven patients (27 male and 20 female, median age 71.8 years, median MDS duration 10.1 months) were not eligible for aggressive chemotherapy; 16 patients (34.2%) received supportive care only, 31 patients (65.8%) needed conservative chemotherapy for disease progression. Median survival of the conservatively treated group was 5.5 months, without statistical difference from the aggressively treated group; 10/47 conservatively treated patients (21%) survived for longer than 12 months. In conclusion, aggressive chemotherapy may play a role only in a selected population of ANLL-MDS patients, while further studies could be helpful to identify the optimal conservative approach.

Myelodysplastic syndromes (refractory anemia). A perspective of the biologic, clinical, and therapeutic issues

The myelodysplastic syndromes (MDS) are a diverse group of hematologic disorders that have an abnormality in differentiation of the hematopoietic stem cell resulting in varying degrees of peripheral blood cytopenias. The author reviews the hematologic and clinical aspects of MDS, summarizes the recent pertinent aspects of the advances in our understanding of the disease, and explores the current approaches in the new treatment programs.

Characterization by somatic cell genetics of a monoclonal antibody to the MDR1 gene product (P-glycoprotein): determination of P-glycoprotein expression in multi-drug-resistant KB and CEM cell variants

We isolated an IgG2a murine monoclonal antibody (MAb) termed MAb57, specifically reactive with multi-drug-resistant (MDR) human cells. Its specificity toward the MDRI gene product (P-glycoprotein) has been demonstrated by the concordant segregation of the MAb57 epitope with the MDRI gene in interspecific mouse x human cell hybrids, and the reactivity of several different MDRI gene-expressing cells with MAb57, particularly insect cells acutely infected with a baculovirus encoding the MDRI gene. MAb57 can be used to detect, by flow cytometry, variations in the relative drug-resistance levels of several MDR KB and CEM cell variants. This immunological probe has also proven useful in selectively destroying MDR target cells in an antibody-dependent cell-mediated (ADCC) assay system as well as in detecting P-glycoprotein expression in normal and malignant tissues and cells.

Absence of structural alterations of the multidrug resistance genes in transitional cell carcinoma

Tumor DNA from 27 patients with treated or untreated transitional cell carcinomas of the urinary tract was screened for genomic alterations of the multidrug resistance genes in order to determine whether structural changes of these genes are important in primary urothelial tumors. None of the tumors showed evidence of amplification or rearrangements of either mdr1 or mdr2. The lack of amplification or rearrangements observed in these tumors suggests that structural alterations of the mdr1 and mdr2 genes are not important mediators of drug resistance in TCC.

Murine monoclonal antibody recognizing a 90-kDa cell-surface determinant selectively lost by multi-drug-resistant variants of CEM cells

We describe a murine IgG1 monoclonal antibody (MAb56), specific for a cell-surface protein structure (MC56 determinant) expressed by the human CEM cell line. A large band of approximately 90 kDa was identified as the main specific component of the MC56 determinant. Such a 90-kDa protein is significantly associated with the drug-sensitive phenotype, its expression being progressively reduced quantitatively in multi-drug-resistant (MDR) variants of CEM cells, according to the extent of drug resistance. In addition, the MC56 determinant is expressed de novo in drug-sensitive revertant cell lines derived from MDR cells and unreactive with the MAb56. The MAb56 shows a high affinity towards the immunizing drug-sensitive CEM cell line (Ka = 1.86 x 10(9) L/mole) while not binding to MDR cell variants. The expression of the MC56 molecule on a variety of human cells and tissues makes such a cellular determinant a candidate as a marker for studying the MDR phenomenon both in vivo and in vitro.

Amplification and expression of a multidrug resistance gene in human glioma cell lines

Two human glioma cell lines were examined for multidrug resistance (MDR). A vincristine (VCR)-resistant glioma cell line showed a cross resistance to Adriamycin (doxorubicin, ADR) and etoposide (VP-16) to varying extents, suggesting the presence of MDR; the resistance to VCR was considerably decreased by calcium entry blockers. On the other hand, another VCR-sensitive glioma cell line exhibited no cross resistance to ADR or VP-16. Double minute chromosomes and homogeneously staining regions as well as clonal aberrations of chromosome 7 were not observed in cytogenetic studies of multidrug-resistant and multidrug-sensitive glioma cell lines. In Northern and Southern blot analyses, MDR gene 1 (MDR1) messenger ribonucleic acid (mRNA) was shown to be overexpressed without any amplification of the MDR1 gene in multidrug-resistant glioma cell lines as compared to multidrug-sensitive glioma cell lines. It would be reasonable to suggest that amplification of the MDR1 gene may not be a sine qua non for acquisition of MDR and that the MDR1 mRNA level may be correlated with the extent of MDR.

Expression of the multidrug resistance gene in myeloid leukemias

The human multidrug-resistance gene (MDR1) encodes an energy-dependent multidrug efflux protein responsible for the cross-resistance of cultured cells to natural product chemotherapeutic agents such as the anthracyclines and vinca alkaloids. RNA transcript levels were measured in leukemia cells obtained from 15 adult acute nonlymphocytic leukemia (ANLL) cases and 15 cases of chronic myelogenous leukemia (CML). Expression of MDR1 RNA was common in ANLL, and appears to be most frequent in leukemic cells of patients with the poorest response to chemotherapy. Expression of the MDR1 gene was not detectable in the peripheral white blood cells of any of the CML cases during the chronic phase, but was detectable in the immature cells present during this phase of the disease. The cells of the three blastic crisis patients contained detectable levels of MDR1 RNA. These studies support the idea that expression of the MDR1 gene contributes to drug resistance in ANLL, and may play a role in some instances in the drug-resistance of CML in blastic crisis. In contrast, studies of the level of expression of anionic glutathione transferase and DNA polymerase B failed to show any relationship between the RNA transcript levels of these enzymes and responsiveness to chemotherapy.

Cytogenetic and molecular studies in patients with chronic myeloid leukemia and variant Philadelphia translocations

Out of 105 Philadelphia (Ph) positive chronic myeloid leukemia patients analyzed, six (5.7%) carried a variant Ph translocation, namely t(6;9;9;10;22)(q24;p13;q34;p15;q11); t(9;13;22)(q34;q21;q11);der(2)(2pter----2q31::9q21---- 9q34::22q11----22qter) and der(9)t(2;9) (9pter----9q21::2q31----2qter);t(7;9;22)(q11;q34 ;q11), 14q + ;t(7;9;22)(q35;q34;q11), and t(9;11;22) (q34;q13;q11), respectively. Five of these patients were analyzed with Southern blotting. Three of them showed an atypical molecular pattern; namely, the patient with t(9;13;22) showed no rearrangement in the breakpoint cluster region (bcr), the patient with t(7;9;22)(q35;q34;q11) showed a 3' deletion, and the patient with t(7;9;22), 14q + showed a bcr rearrangement 3' to the exon 4 of the M-BCR. Chromosome in situ hybridization studies demonstrated that in patient one, a two-step translocation occurred: the first step moved the 3' bcr from chromosome 22 to chromosome 9, and the second moved the terminal part of 22q, carrying the c-sis protooncogene, to 10p. Variant Ph translocations appear to be associated with atypical molecular breakpoints.

The gene for prolactin-inducible protein (PIP), uniquely expressed in exocrine organs, maps to chromosome 7

The hormonally responsive prolactin-inducible protein (PIP) gene is expressed in benign and malignant breast tumor tissues and in such normal exocrine organs as sweat, salivary, and lacrimal glands. In this communication we report the regional chromosome localization of the PIP gene locus to chromosome 7 by Southern hybridization to DNA from human-hamster somatic cell hybrids, and to 7q32-36 by in situ hybridization.

Malignant cell glycoproteins and glycolipids

The cell surface is involved in cell growth and division, cell-cell interaction, communication, differentiation and migration, and other processes likely to be involved in malignant transformation and/or the metastatic spread of cancer. Although there are many alterations of glycoproteins and glycolipids on the malignant cell surface, it is unclear whether these alterations are epiphenomena or an integral part of the malignancy process. This article reviews the recent literature and some earlier studies relevant for understanding emerging concepts and trends with respect to malignant cell glycoconjugates. Emphasis is on structural alterations of the carbohydrate portions of malignant cell glycoproteins and glycolipids and on the enzymes (glycosyltransferases and glycosidases) involved in their metabolism. Practical applications derived from malignant cell glycoconjugate studies are discussed briefly with respect to the diagnosis, staging, monitoring, and treatment of malignant disease. The review concludes by indicating which research areas on malignant cell glycoconjugates are likely to be fruitful in increasing our basic understanding of, and ability to deal effectively with, malignant disease.

Increased epidermal growth factor receptor in multidrug-resistant human neuroblastoma cells

Multidrug-resistant human neuroblastoma cell lines obtained by selection with vincristine or actinomycin D from two independent clonal lines, SH-SY5Y and MC-IXC, have 3- to 30-fold more cell surface epidermal growth factor (EGF) receptors than the drug-sensitive parental cells as indicated by EGF binding assays and immunoprecipitation, affinity-labeling, and phosphorylation studies. Reversion to drug sensitivity in one line was accompanied by a return to the parental level of EGF receptor. SH-EP cells, a clone derived from the same neuroblastoma cell line as SH-SY5Y but which displays melanocyte rather than neuronal lineage markers, also express significantly more EGF receptor than SH-SY5Y cells. By nucleic acid hybridization analysis with a molecularly cloned probe, increased receptor level in multidrug-resistant cells was shown to be the result of higher levels of EGF receptor mRNA in drug-resistant than in drug-sensitive cells. The increased steady state amount of specific RNA did not result from amplification of receptor-encoding genes. A small difference was observed in the electrophoretic mobility under denaturing conditions of EGF receptor immunoprecipitated from drug-resistant and drug-sensitive cells. Quantitative and qualitative modulation of the EGF receptor might reflect alterations in the transformation and/or differentiation phenotype of the resistant cells or might result from unknown selective pressures associated with the development of multidrug resistance.