Effect of S9788 on the efficiency of doxorubicin in vivo and in vitro in medullary thyroid carcinoma xenograft

In medullary carcinoma of the thyroid (MTC), drug resistance remains the major obstacle to effective chemotherapy. In this work, we studied the effect of S9788 on doxorubicin (DOX) efficiency in a MTC cell line (TT cells) injected in nude mice. After two passages, TT cells were injected in 40 nude mice divided into four groups [controls and groups receiving DOX alone (10 mg/kg), S9788 alone (50 mg/kg) or both DOX + S9788]. The weight of the mice, tumoral volume (TV), doubling time (DT) of the tumor and survival time of mice were evaluated in each group. In addition, the efficiency of DOX with or without S9788 was assessed by the inhibition of tumoral growth and specific growth delay. In vitro, glycoprotein P 170 (P-gp) was detected on tissular sections and on tumoral cells by immunocytochemistry or flow cytometry with several monoclonal antibodies: JSB1, MRK 16, C219 and UIC2. In vivo the weight of the mice decreased slightly with DOX and dropped dramatically with DOX + S9788. The DT of the tumors increased with DOX over controls (22.5 +/- 8.5/12.7 +/- 3.9 days) and showed a higher value with DOX + S9788 (29.2 +/- 11.4 days). Inhibition of tumoral growth, 89% with DOX, fell to 47.6% with DOX + S9788. Specific growth delay increased with the double treatment (130 versus 75% with DOX alone). In vitro, P-gp was not detected on tissular sections and cells whatever the method and the antibody used. In conclusion, S9788 potentiates the efficiency of DOX treatment in vivo. The absence of P-gp may result from the absence of translation of the MDR1 gene. The reversal effect of S9788 may involve another resistance mechanism such as the MDR Sister of MRP.     

Confocal scanning microspectrofluorometry reveals specific anthracyline accumulation in cytoplasmic organelles of multidrug-resistant cancer cells

We used confocal microspectrofluorometry to investigate intracellular distribution of pirarubicin or THP-DOX in parental K562, CEM, and LR73 tumor cells and their corresponding multidrug-resistant (MDR) strains. Each spectrum of a recorded image was considered as a combination of cell autofluorescence and fluorescence of the drug. In the cytoplasm of parental K562, CEM, and LR73 cells, THP-DOX fluorescence emission profile was similar to that of free drug in aqueous buffer. The (I550nm/I600nm) ratio was 0. 50 +/- 0.1. However, in the cytoplasm of resistant cells the 550-nm band profile was modified. The I550nm/I600nm ratio was 0.85 +/- 0.2 in MDR K562 cells, which is significantly different from the ratio in sensitive cells (p<0.01). This appeared first to correspond to accumulation and self-oligomerization of THP-DOX in cytoplasmic organelles of MDR cells. Transfection of LR73 cells with the mdr1 gene conferred this characteristic on the resistant LR73R cells. Bodipy-ceramide, a trans-Golgi probe, was co-localized with the typical fluorescence emission peak at 550 nm observed in the cytoplasm of MDR cells. This organelle has been shown to be more acidic in MDR cells. Moreover, this specific pattern was similar to that observed when anthracycline is complexed with sphingomyelin. The typical fluorescence emission peak at 550 nm decreased in MDR cells incubated simultaneously in the presence of the drug and quinine, verapamil, or S9788. Growth inhibitory effect and nuclear accumulation of THP-DOX data obtained on LR73R and LR73D cell lines showed that only during reversion of resistance by verapamil and S9788 was an increase of nuclear THP-DOX accumulation observed. Our data suggest that characteristics of molecular environment, such as higher pH gradient or lipid structures, would be potential mechanisms of multidrug-resistance via the sequestration of anthracyclines.     

Antibody affinity maturation using bacterial surface display

A drug-resistant cell line (EAC/Dox) was developed by repeated exposure of Ehrlich ascites carcinoma cells to Doxorubicin (Dox) in vivo in male albino Swiss mice (6-8 weeks old). The weekly i.p. injections of Dox to mice (2 or 4 mg/kg/week for 4 months) gave rise to Dox-resistant cell line EAC/Dox, which displayed typical multidrug resistant (MDR) features of cross-resistance to a number of structurally and functionally unrelated drugs like doxorubicin, vinblastine and cisplatin. Moreover, the EAC/Dox cell line had lower drug accumulation than drug-sensitive (EAC/S) cells. Study of Western blots and immunofluorescence revealed that P-glycoprotein 170 kDa (P-gp) was absent in EAC/Dox cells. The drug resistance appeared to be due to the presence of a higher level of reduced glutathione (GSH) and glutathione S-transferase (GST) in EAC/Dox cells than in drug-sensitive (EAC/S) cells. The two structurally similar hydroxamic acid derivatives, i.e. oxalyl bis(N-phenyl)hydroxamic acid (X1) and succinyl bis(N-phenyl)hydroxamic acid (X2), having very low in vitro toxicity (IC50 value 250 microg/ ml), were investigated for their efficacy to reverse MDR. The compound X1 was able to reverse the effect of MDR and reduce GST in EAC/Dox cells. The compound X2 had no ability to reverse the effect of MDR. Further study on the mechanism of glutathione depletion and the resistance modifying property of X1 on other cell lines is warranted.     

Comparison between technetium-99m-sestamibi and hydrogen-3-daunomycin myocardial cellular retention in vitro

This study was undertaken to verify whether 99mTc-sestamibi uptake parallels that of 3H-daunomycin in cells treated with multidrug resistance (MDR) reversing agents. Since we have detected in a previous work a moderate typical MDR phenotype in rat cardiac cells, a model of cultured myocardial cells was used. METHODS: Newborn-rat cultured myocardial cells were incubated 120 min with the MDR-reversing agent verapamil 50 microM, PSC833 1 microM or S9788 10 microM alone or in combination, and the cellular retention of 3H-daunomycin and 99mTc-sestamibi was counted. RESULTS: Hydrogen-3-daunomycin cellular accumulation was never modified by more than 15% when compared to control values, while 99mTc-sestamibi decreased to 75% +/- 32% (m +/- s.d.) of controls in the presence of S9788 and to 44% +/- 19% when S9788 was associated with verapamil. CONCLUSION: The variations of 99mTc-sestamibi and 3H-daunomycin cellular accumulation induced by MDR-reversing agents in cultured myocardial cells can be dramatically different. While some MDR-reversing agents can significantly increase the 3H-daunomycin retention in cardiac cells, they have unexpected effects on that of 99mTc-sestamibi.     

The multidrug resistance in human leukemias. Minireview

Leukemia/lymphoma cells, clinically refractory to therapy are often associated with expression of P-glycoprotein (P-gp), which is encoded by the multidrug resistance (MDR) gene, mdr1. Cell lines expressing mdr1 exhibit resistance to several structurally unrelated lipophilic drugs, such as anthracyclines, vinca alkaloids, and epopodophyllotoxins. This MDR can be conferred to drug-sensitive cells mdr1 cDNA transfer. In resistant cells, MDR is characterized by overexpression of P-gp and by the enhanced efflux, and P-gp fluorescence probe, rhodamine 123 (Rh 123). This can be circumvented by addition of certain non-cytotoxic drugs, such as verapamil and cyclosporin A.     

Nitric oxide synthesis inhibition retards surgical reversal of one-kidney Goldblatt hypertension in rats

We investigated the cellular drug resistance to aclarubicin (Acla), cytosine arabinoside (Ara-C), daunorubicin (Dau), doxorubicin (Dox), etoposide (Etop) and mitoxantrone (Mitox) using the MTT assay at time of disease presentation in 93 cases of acute myeloid leukaemia (AML). In 31 cases we concomitantly investigated MDR1 (multiple drug resistance 1 gene) expression (semi-quantitative competitive RT-PCR) of the leukaemic cells. Drug resistance towards Dau, Dox and Etop was correlated to the MDR1 expression of the AML cells (P<0.05) with high MDR1 expression being associated with high drug resistance towards these drugs. Although the data did not allow firm conclusions to be drawn on the correlation between MDR1 expression and drug resistance towards Ara-C and Mitox, the drug resistance towards Acla clearly was not correlated to, or dependent on, the MDR1 expression level of the AML blast cells. In addition, when examining the cross-activities among the six drugs distinct patterns emerged. Thus, high to very high degrees of cross-activity were found to exist between Dau, Dox, Etop and Mitox, whereas Ara-C had moderate cross-activity with the other drugs except Acla, which showed absent to moderate cross-activity with the other drugs. We conclude that MDR1 gene expression is of significance for cellular drug resistance towards specific (MDR1-related) drugs in AML, whereas it is not of significance regarding drug resistance towards other drugs, which is the case with the anthracycline Acla. We suggest that in the place of other more or less complicated ways to circumvent MDR1-mediated drug resistance, Acla may be used to replace Dau, Dox and other MDR1-related drugs if proven as potent as the drug it is to substitute.     

In vitro effect of GF120918, a novel reversal agent of multidrug resistance, on acute leukemia and multiple myeloma cells

Resistance to chemotherapy in multiple myeloma (MM) and acute myeloid leukemia (AML) is frequently caused by multiple drug resistance (MDR), characterized by a decreased intracellular drug accumulation. MDR is associated with expression of P-glycoprotein (P-gp). GF120918, an acridine derivative, enhances doxorubicin cell kill in resistant cell lines. In this study, the effect of GF120918 on MDR cell lines and fresh human leukemia and myeloma cells was investigated. The reduced net intracellular rhodamine-123 (Rh-123) accumulation in the MDR cell lines RPMI 8226/Dox1, /Dox4, /Dox6 and /Dox40 as compared with wild-type 8226/S was reversed by GF120918 (0.5-1.0 microM), and complete inhibition of rhodamine efflux was achieved at 1-2 microM. This effect could be maintained in drug-free medium for at least 5 h. GF120918 reversal activity was significantly reduced with a maximum of 70% in cells incubated with up to 100% serum. GF120918 significantly augmented Rh-123 accumulation in vitro in CD34-positive acute leukemia (AML) blasts and CD38-positive myeloma (MM) plasma cells obtained from 11/27 de novo AML and 2/12 refractory MM patients. A significant correlation was observed between a high P-gp expression and GF120918 induced Rh-123 reversal (P=0.0001). Using a MRK16/IgG2a ratio > or = 1.1, samples could be identified with a high probability of GF120918 reversal of Rh-123 accumulation. In conclusion, GF120918 is a promising MDR reversal agent which is active at clinically achievable serum concentrations.     

Semi-automated PCR method for quantitating MDR1 expression

The MDR1 gene is involved in drug resistance in many hematopoietic and solid tumors. The Quantitative PCR System 5000 (QPCR-5000; Perkin-Elmer) is a new instrument system that uses electrochemiluminescence to automatically quantitate polymerase chain reaction (PCR) products. A comparative study between radioactively labeled PCR (32P-PCR) and QPCR was performed to analyze the MDR1 gene expression in the drug-resistant (Doxorubicin) cell lines Dox40, Dox6, the parental cell line 8226/S, CEM Dox1 and three acute myeloid leukemia (AML) patient samples. Using the Dox40 and Dox6 resistant cell lines, we compared the sensitivities of QPCR and 32P-PCR. A strong signal was obtained from QPCR at 20 to 25 cycles (which is in the linear range for quantitation), while a weak signal was obtained using 32P-PCR at the same cycle number. Dilution experiments gave better precision with the QPCR than with the radioactive method. AML samples were studied with the MDR1-specific MAbs MRK16 and 4E3, and the efflux function was analyzed using Rh-123 retention in the absence or presence of verapamil. The three samples showed high (D = 0.79), medium (D = 0.52) and negative (D = 0.08) p-glycoprotein (P-gp) levels and correlated with efflux function. The MDR1/beta 2-M mRNA ratios for 32P-PCR were 0.41, 0.40 and 0.12, respectively, and were 0.127, 0.097 and 0.028, respectively, for QPCR. There were significant differences between the samples with high and medium P-gp levels comparing the two methods. Very low levels of MDR1 in CEM Dox1 cells could be detected only by QPCR. In conclusion, QPCR was found to be more reproducible, accurate and sensitive than 32P-PCR.     

Development and characterisation of novel human multidrug resistant mammary carcinoma lines in vitro and in vivo

Clinical chemotherapy of breast carcinomas must be considered insufficient, mainly due to the appearance of drug resistance. The multidrug resistance (MDR) phenotype, either intrinsically occurring or acquired, e.g., against a panel of different antineoplastic drugs, is discussed in relation to several MDR-associated genes such as the MDR-gene mdr1 encoding the P-glycoprotein (PGP), the MRP gene (multidrug resistance protein) encoding an MDR-related protein or the LRP gene encoding the lung resistance protein. Numerous experimental and clinical approaches aiming at reversing resistance require well-characterised in vitro and in vivo models. The aim of our work was to develop multidrug resistant sublines from human xenotransplanted breast carcinomas, in addition to the broadly used line MCF-7 and its multidrug resistant subline MCF-7/AdrR. MDR was induced in vitro with increasing concentrations of Adriablastin (ADR) for several weeks, resulting in a 3.5- to 35-fold increase in IC50 values using the MTT-test. Cell lines were cross-resistant toward another MDR-related drug, vincristine, but remained sensitive to non-MDR-related compounds such as cisplatin and methotrexate. The resistance toward Adriamycin and vincristine was confirmed in vivo by a lack of tumour growth inhibition in the nude mouse system. Gene expression data for the mdr1/PGP, MRP/MRP and LRP/LRP on both the mRNA (RT-PCR) and the protein levels (immunoflow cytometry) demonstrated that induction of mdr1 gene expression was responsible for the acquired MDR phenotype. Rhodamine efflux data, indicated by PGP overexpression, underlined the development of this MDR mechanism in the newly established breast carcinoma lines MT-1/ADR, MT-3/ADR and MaTu/ADR.     

Co-ordinate loss of protein kinase C and multidrug resistance gene expression in revertant MCF-7/Adr breast carcinoma cells

The aim of this study was to investigate the link between protein kinase C (PKC) and multidrug resistance (mdr) phenotype. The expression of both was studied in doxorubicin-resistant MCF-7/Adr cells as they reverted to the wild-type phenotype when cultured in the absence of drug. The following parameters were measured in cells 4, 10, 15, 20 and 24 weeks after removal of doxorubicin; (1) sensitivity of the cells towards doxorubicin; (2) levels of P-glycoprotein (P-gp) and MDR1 mRNA; (3) levels and cellular localization of PKC isoenzyme proteins alpha, theta and epsilon; and (4) gene copy number of PKC-alpha and MDR1 genes. Cells lost their resistance gradually with time, so that by week 24 they had almost completely regained the drug sensitivity seen in wild-type MCF-7 cells. P-gp levels measured by Western blot mirrored the change in doxorubicin sensitivity. By week 20, P-gp had decreased to 18% of P-gp protein levels at the outset, and P-gp was not detectable at week 24. Similarly, MDR1 mRNA levels had disappeared by week 24. MCF-7/Adr cells expressed more PKCs-alpha and -theta than wild-type cells and possessed a different cellular localization of PKC-epsilon. The expression and distribution pattern of these PKCs did not change for up to 20 weeks, but reverted back to that seen in wild-type cells by week 24. MDR1 gene amplification remained unchanged until week 20, but then was lost precipitously between weeks 20 and 24. The PKC-alpha gene was not amplified in MCF-7/Adr cells. The results suggest that MCF-7/Adr cells lose MDR1 gene expression and PKC activity in a co-ordinate fashion, consistent with the existence of a mechanistic link between MDR1 and certain PKC isoenzymes.     

Doxorubicin cellular pharmacokinetics plays no role in chemosensitizing effect of verapamil on Swiss-3T3 cells

AIM: To find whether or not the doxorubicin (Dox) cellular pharmacokinetics plays a role in chemosensitizing effect of verapamil (Ver) on drug sensitive cells. METHODS: Cytotoxicity and cellular Dox contents (during accumulation and retention periods) were measured in the absence and presence of verapamil in Swiss-3T3 cells and compared with those in multidrug resistant (MDR) MCF-7Adr cells and drug sensitive MCF-7WT cells. mdr-1 mRNA expression in Swiss-3T3 cells was analyzed. RESULT: Dox cytotoxicity was enhanced 2.0-fold in Swiss-3T3 cells by Ver (3 mumol.L-1) and 3.6-fold in MCF-7Adr cells by Ver (6 mumol.L-1), but not in MCF-7WT cells (Ver 6 mumol.L-1). Cellular accumulation of equi-effective concentrations of Dox increased at 6-h incubation in the presence of Ver in Swiss-3T3 (1.5-fold)i and MCF-7WT cells (2.1-fold) but decreased rapidly in MCF-7Adr cells by 20% to 50% compared to that in the absence of Ver. Cellular retention of Dox decreased after 10-min increase in the presence of Ver in Swiss-3T3 cells compared to that in the absence of Ver, that was similar to that in MCF-7WT cells, while the retention was augmented by Ver in MCF-7Adr cells. Slot blot analysis of RNA revealed no mdr-1 gene expression in Swiss-3T3 cells. CONCLUSION: Changes in cellular accumulation and retention of Dox did not account for the chemosensitizing effect of Ver on Swiss-3T3 cells.     

Cytotoxic and antitumor activity of MEN 10710, a novel alkylating derivative of distamycin

MEN 10710 is a new synthetic distamycin derivative possessing four pyrrole rings and a bis-(2-chloroethyl)aminophenyl moiety linked to the oligopyrrole backbone by a flexible butanamido chain. Its biological properties have been investigated in comparison with the structurally related compound, tallimustine (FCE24517), and the classical alkylating agent, melphalan (L-PAM). Cytotoxic potency of MEN 10710 was increased from 10- to 100-fold, as compared to tallimustine or L-PAM in murine L1210, human LoVo and MCF7 tumor cell lines. MEN 10710 was still active against L1210/L-PAM leukemic cells, while a partial cross-resistance was observed in LoVo/DX and in MCF7/DX cells selected for resistance to doxorubicin and expressing a MDR phenotype. Treatment with verapamil (VRP) reduced the resistance to tallimustine, but not to MEN 10710, in MCF7/DX cells. The cytotoxic effects reflect in vivo antitumor potency and toxicity in the treatment of human tumor xenografts. MEN 10710 was more effective in A2780/DDP, an ovarian carcinoma selected for resistance to cisplatin. On the other hand, the IC30 for inhibiting murine granulocyte/macrophage colony formation was 50 times higher for MEN 10710 than for tallimustine, suggesting a lower myelotoxic potential. In conclusion, the particular biological profile of MEN 10710 characterized by a marked cytotoxic potency, an interesting antitumor efficacy and a reduced in vitro myelosuppressive action may represent a further improvement in the rational design of a novel distamycin-related alkylating compound.     

Functional assay of multidrug resistant cells using JC-1, a carbocyanine fluorescent probe

Multidrug resistance (MDR) is characterized by a decrease in the efficiency of chemotherapeutic agents correlated with the expression and activity of a membrane protein: the permeability-glycoprotein (Pgp 170). Clinically, detection of MDR can be performed by functional tests based on the accumulation of fluorescent compounds such as rhodamine 123. With the aim of improving the sensitivity of such analysis, we have evaluated JC-1, a fluorescent lipophilic carbocyanine dye. Above a critical concentration, JC-1 aggregates in a 'liquid crystal' form. Aggregates display a specific red emission band centered at 597 nm whereas the monomers display a green emission band centered at 540 nm. JC-1 was avidly accumulated in sensitive K562 cells where it displayed both a green cytoplasmic and red mitochondrial fluorescence. In contrast, JC-1 was poorly accumulated in resistant K562 cells, which displayed only a slight green fluorescence. The level of JC-1 accumulation was correlated with the level of Pgp expression detected by MRK16 and UIC2 antibodies on a set of K562 subclones with increasing resistance levels. The specific fluorescence properties of JC-1 allow accurate discrimination between low-level resistant cells and sensitive cells. Chemosensitizers such as verapamil, cyclosporine A or S9788 restored JC-1 accumulation in resistant cells. The fluorescence properties of JC-1 could therefore be used for monitoring the effects of reversing agents.     

In vitro and in vivo reversal of multidrug resistance by GF120918, an acridonecarboxamide derivative

N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]- phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) has been selected from a chemical program aimed at identifying an optimized inhibitor of multidrug resistance (MDR). The potency of GF120918 is assessed by dose-dependent sensitization of CHRC5, OV1/DXR and MCF7/ADR cells to the cytotoxicity of doxorubicin and vincristine respectively: GF120918 fully reverses multidrug resistance at 0.05 to 0.1 microM and is half maximally active at 0.02 microM. The spectrum of drugs sensitized by GF120918 coincides with those having the classical MDR phenotype. In CHRC5 cells, 0.01-0.1 microM GF120918 enhances the uptake of [3H]daunorubicin and blocks the efflux from preloaded cells. It is also shown that GF120918 is still active several hours after being taken away from the culture medium showing that it is not, like verapamil, effluxed rapidly by P-glycoprotein. GF120918 effectively competes with [3H]azidopine for binding P-glycoprotein, pointing to this transport membrane protein as its likely site of action. After i.v. administration to mice, GF120918 penetrates thoroughly various organs that have a tissue level/blood level ratio above 10. It is eliminated from organs and blood with a half-time of approximately 2.7 h. It is well absorbed after p.o. administration. In mice implanted i.p. with the MDR P388/Dox tumor, a single i.v. or p.o. dose of GF120918 restores sensitivity of the tumor to a single i.p. dose (5 mg/kg) of doxorubicin administered 1 h later. A statistically significant effect is observed at 1 mg/kg GF120918 i.v. and maximal effect is reached at 5 mg/kg. Similarly, whereas neither drug alone is effective, GF120918 (10 mg/kg i.p.) associated with doxorubicin (5 mg/kg i.p.) inhibits the growth of the moderately MDR C26 tumor implanted s.c. as assessed by tumor size at day 19. GF120918 does not modify significantly the distribution or the elimination of doxorubicin in mice ruling out the possibility that the antitumor effects seen might be explained by pharmacokinetic interactions.     

The small heat shock protein hsp27 is correlated with growth and drug resistance in human breast cancer cell lines

An emerging body of evidence suggests that the heat shock proteins (hsp) may be involved in drug resistance. When hsp are induced by elevated temperatures, resistance to doxorubicin (Dox), but not to other commonly used chemotherapeutic agents, is induced in breast cancer cells. To evaluate the role of hsp27 in this phenomenon, we have transfected MDA-MB-231 breast cancer cells, which normally express low levels of hsp27, with a full-length hsp27 construct. These hsp27-overexpressing cells now display a 3-fold elevated resistance to Dox. Anchorage-dependent proliferation and anchorage-independent growth were also increased 2-4-fold in these transfectants. We have also derived a MCF-7 breast cancer cell line with amplified endogenous hsp27 which is highly resistant to Dox. When these cells are transfected with an antisense hsp27 construct, they are rendered sensitive to Dox (3-fold) with anchorage-dependent as well as anchorage-independent growth, similarly decreased. These results suggest that hsp27 specifically confers Dox resistance in human breast cancer cells and, furthermore, that hsp27 may be involved in the regulation of cell growth.     

Multidrug resistance gene expression in rodents and rodent hepatocytes treated with mitoxantrone

Overexpression of P-glycoprotein in tumor cells can represent a severe drawback for cancer chemotherapy. P-glycoprotein acts as an efflux transporter for a variety of chemotherapeutic agents. It is encoded by multidrug resistance (mdr) genes of the subfamily 1 in humans (MDR1) and rodents (mdr1a and 1b). Because mdr1 gene expression is inducible in cultured rat hepatocytes and in rat liver with chemical carcinogens such as 2-acetylaminofluorene or aflatoxin B1, which form DNA-binding electrophiles during their metabolism, we investigated whether the DNA-damaging chemotherapeutic drug mitoxantrone may induce multidrug resistance in rodents and in hepatocytes in primary culture. In H4IIE rat hepatoma cells stably transfected with a luciferase construct containing the rat mdr1b promoter, mitoxantrone caused a concentration-dependent increase in promoter activity. Mdr1 gene expression in cultured rat hepatocytes was enhanced at mitoxantrone concentrations greater than or equal to 0.1 microM and in mouse hepatocytes at 5 microM. In hepatocytes from both species, a correlation was found between mdr1 induction and the inhibition of protein synthesis. In vivo, mitoxantrone was a very powerful inducer of mdr1 gene expression in rat liver and small intestine. In rat kidney, induction of mRNA was lower, and a marginal effect was seen in lung. In contrast with rats, no significant induction of mdr1 gene expression was obtained in mouse liver. Probably as a consequence of inhibition of protein synthesis, mitoxantrone did not lead to a pronounced elevation of P-glycoprotein levels in rat liver and kidney.     

Clinico-epidemiologic profile of Chagas disease patients attending an ambulatory referral center and proposal of a model of care for the Chagas patient under the perspective of a comprehensive health care

A significant number of patients with acute leukaemias fail in their treatment as a result of the development of resistance to chemotherapy. Several evidences indicate that the expression of a mdr 1 gen, which codifies for P glycoprotein (PgP), contributes to this resistance in leukaemic cells. PgP functions as an energy-dependent efflux pump transporting a variety of unrelated drugs to the outside of the cells. It is possible to modulate this efflux using a number of drugs known as multidrug resistance (MDR) reversors or modulating agents. The present paper discusses some of the methods used for detecting the MDR phenotype, although the most reliable results are the ones that take into account an association of various methods. Despite the existence of disagreements regarding which method presents the greatest sensitivity or specificity the majority of authors agrees that the MDR phenotype, in isolation, affects the prognosis of leukaemias. The, coexpression of PgP with the molecule CD34 confers the worst prognosis in acute leukaemias. The authors demonstrate using cell cultures testing chemotherapeutic agents, alone or associated to modulating agents, that this line of research may allow in the future to elaborate an individualized clinical treatment. They emphasize the necessity of integration between haematologists and basic research as this may lead to a new therapeutic option for refractory patients to conventional treatment.