Ultra-short course sirolimus contributes to effective GVHD prophylaxis after reduced-intensity allogeneic hematopoietic cell transplantation.

Reduced-intensity conditioning (RIC) allo-SCT is a potentially curative treatment approach for patients with relapsed Hodgkin's or non-Hodgkin's lymphoma. In the present study, 37 patients underwent RIC allo-SCT after induction treatment with EPOCH-F(R) using a novel form of dual-agent immunosuppression for GVHD prophylaxis with CsA and sirolimus. With a median follow-up of 28 months among survivors, the probability for OS at 3 and 5 years was 56%. Treatment-related mortality was 16% at day +100 and 30% after 1 year of transplant. Acute GVHD grades II-IV developed in 38% of patients, suggesting that the regimen consisting of CsA and an ultra-short course of sirolimus is effective in the prevention of acute GVHD.

A prospective study of neuropsychological functioning in testicular cancer patients.

BACKGROUND: Whether systemic chemotherapy has a negative effect on cognitive function in patients, concern oncologists. In testicular cancer patients (TCPs) treated with cisplatin-based chemotherapy, only few cross-sectional studies have addressed this concern. We prospectively studied neuropsychological functioning in TCPs. PATIENTS AND METHODS: In a consecutive sampling, 122 TCPs were examined at baseline (after orchidectomy, before any additional treatment) and then at follow-up at a median of 12 months after end of treatment. The examinations included a neuropsychological test battery, interview on background variables and questionnaires on mental distress, fatigue and neurotoxic symptoms. Changes in neuropsychological functioning from baseline to follow-up were compared between three treatments groups: no chemotherapy (N = 31), one cycle of chemotherapy (N = 38) and two or more cycles of chemotherapy (N = 53). Variables associated with a decline in neuropsychological test performance from baseline to follow-up were explored. RESULTS: No statistically significant differences in proportions of TCPs with a decline in neuropsychological test performance were observed between the three treatment groups. Decline in neuropsychological test performance was not associated with demographic variables, distress, fatigue or with chemotherapy. CONCLUSION: No negative effect of systemic chemotherapy on neuropsychological test performance in TCPs at 1-year follow-up was found in this study.

Oral administration of a new soluble branched beta-1,3-D-glucan is well tolerated and can lead to increased salivary concentrations of immunoglobulin A in healthy volunteers.

The soluble branched yeast beta-1,3-D-glucan (SBG) belongs to a group of carbohydrate polymers known to exert potent immunomodulatory effects when administered to animals and humans. A new oral solution of SBG has been developed for local application to the oropharyngeal and oesophageal mucosa in order to strengthen the defence mechanisms against microbial and toxic influences. In the present study oral administration of SBG has been investigated primarily for assessment of safety and tolerability in an early phase human pharmacological study (phase I). Eighteen healthy volunteers were included among non-smoking individuals. The study was an open 1:1:1 dose-escalation safety study consisting of a screening visit, an administration period of 4 days and a follow-up period. Groups of six individuals received SBG 100 mg/day, 200 mg/day or 400 mg/day, respectively, for 4 consecutive days. The dose increase was allowed after a careful review of the safety data of the lower dose group. No drug-related adverse event, including abnormalities in vital signs, was observed. By inspection of the oral cavity only minor mucosal lesions not related to the study medication were seen in seven subjects. Repeated measurements of beta-glucan in serum revealed no systemic absorption of the agent following the oral doses of SBG. In saliva, the immunoglobulin A concentration increased significantly for the highest SBG dose employed. SBG was thus safe and well tolerated by healthy volunteers, when given orally once daily for 4 consecutive days at doses up to 400 mg.

The cyclosporin PSC 833 increases survival and delays engraftment of human multidrug-resistant leukemia cells in xenotransplanted NOD-SCID mice.

Circumvention of chemoresistance in cancer may involve several modulator drugs with high affinity for the multidrug transporter P-glycoprotein (Pgp), which is expressed in a number of multi-resistant malignancies. Pgp acts as a membrane efflux pump with broad substrate specificity including antineoplastic drugs and endogenous substances such as certain cytokines and sphingolipids. Therefore, the consequence of Pgp blockade could be far more complex than intracellular drug retention. In the present study exposure of the Pgp inhibitor, PSC 833 (1200 ng/ml), to Pgp expressing KG1a/200 human leukemia cells provoked cell cycle arrest and apoptosis in vitro. This finding was put to test in vivo using a xenotransplant model of KG1a/200 human cells intravenously inoculated into non-obese diabetic severe combined immunodeficient (NOD-SCID) mice. The animals were randomly allocated to receive treatment with PSC 833 (n = 32) or placebo (n = 24). PSC 833 (30 mg/kg) was subcutaneously injected six or 12 times separated by 48-96 h. The overall mean whole blood concentration of PSC 833 was 1191 +/- 60 ng/ml (s.e.m.) at 20 h after administration. Tumor engraftment was significantly reduced in the treatment group (P = 0.037), which also had prolonged survival compared to control animals (P = 0.0016). This is the first study that demonstrates antileukemic effects of a Pgp inhibitor as single agent therapy in vivo, and the present data raise the possibility of alternative exploitation of modulators in cancer chemotherapy.

Differential expression of the efflux pumps P-glycoprotein and multidrug resistance-associated protein in human monocyte-derived dendritic cells.

P-glycoprotein (P-gp), an ATP-binding cassette (ABC) drug efflux pump, has been recently shown to play an important role in the physiology of Langherans cells, a subtype of dendritic cells (DC) found in the skin. The present study was designed to investigate expression and activity of P-gp and of multidrug resistance-associated protein (MRP), another ABC efflux pump sharing numerous substrates with P-gp, in human monocyte-derived DC. Immunolabeling experiments and dye efflux assays indicated that such cells displayed elevated levels of MRP activity and expression when compared to those present in parental monocytes. Generation of DC from monocytes in the presence of the MRP inhibitor indomethacin did not, however, alter the capacity of DC to stimulate allogeneic T cells proliferation in mixed lymphocyte reaction. In addition, indomethacin did not inhibit the up-regulation of the CD1a, a marker occurring during the differentiation of monocytes into DC. In contrast to that of MRP, functional expression of P-gp was not detected in monocyte-derived DC. Such antigen presenting cells that constitute a promising tool for antitumor vaccinal therapy therefore display differential expression of the efflux pumps P-gp and MRP.

Phase I/II trial of the multidrug-resistance modulator valspodar combined with cisplatin and doxorubicin in refractory ovarian cancer.

PURPOSE: To determine the maximum-tolerated dose (MTD) of doxorubicin when given in combination with cisplatin and the multidrug-resistance (MDR) modulator valspodar and the remission rate induced by this combination in patients with platinum- and anthracycline-resistant ovarian cancer. PATIENTS AND METHODS: Fifty-nine patients who had failed prior platinum- and anthracycline-based chemotherapy were enrolled. During the dose-finding phase, patients received a loading dose of valspodar (1.5 or 2 mg/kg) via 2-hour intravenous (IV) infusion on day 1 and continuous IV infusion (CIVI) of valspodar (2, 4, or 10 mg/kg/d) over 3 days. Doxorubicin (starting from 20 up to 50 mg/m(2)) and cisplatin (50 mg/m(2)) were administered via 15- to 20-minute IV infusions on day 3. During the efficacy phase, patients received at least two treatment cycles unless toxicity was unacceptable, and responding patients and those with stable disease received four to six cycles. RESULTS: All patients completed at least one cycle of combined treatment. The MTD of doxorubicin was determined to be 35 mg/m(2) when administered with valspodar at 2 mg/kg loading dose and 10 mg/kg/d CIVI plus 50 mg/m(2) cisplatin. At these doses, valspodar blood concentrations known to reverse MDR in vitro were reached in all patients. Valspodar was well tolerated at all dose levels. Dose-limiting toxicities of the combination were primarily hematologic and included febrile neutropenia and prolonged leucopenia. The addition of valspodar to the treatment did not worsen cisplatin-related toxicity. Among 33 patients treated at the MTD for doxorubicin, one (3%) had a complete response, and four (12%) had a partial response. An additional seven patients experienced a stabilization of their previously progressive disease. The survival rates at 6 and 12 months were 59% and 19%, respectively. CONCLUSION: Valspodar can be safely coadministered with doxorubicin and cisplatin. Although the regimen used in this trial produced renewed responses in patients with heavily pretreated, refractory ovarian cancer, the value of valspodar in reversing resistance mediated by P-glycoprotein remains to be determined.

Multidrug resistance protein (MRP) activity in normal mature leukocytes and CD34-positive hematopoietic cells from peripheral blood.

Multidrug resistance proteins (MRPs) such as MRP1, MRP2 and MRP3 are membrane efflux pumps involved in multidrug resistance and handling organic anions. In the present study, MRP activity was investigated in normal mature leucocytes and CD34-positive hematopoietic cells from peripheral blood using the flow cytometric carboxy-2',7'-dichlorofluorescein (CF) efflux assay. Basal and similar cellular exports of CF, an anionic fluorescent dye substrate for MRP1 and MRP2 transporters, were evidenced in lymphocytes whatever their subsets (CD3, CD4, CD8, CD20 and CD56 cells), in CD14 monocytes and in CD15 granulocytes whereas higher CF efflux was found in CD34 cells. Such outwardly-directed transports of CF were inhibited by known blockers of MRP function such as probenecid whereas the P-glycoprotein modulator verapamil did not alter the retention of the dye in the blood leukocytes. Peripheral mature blood leukocytes were moreover found to express MRP1 mRNAs and MRP1 protein as assessed by Northern-blot and Western-blot analyses, whereas MRP2 and MRP3 transcripts were not present or only at very low levels. Mature leukocytes therefore display basal constitutive MRP-related transport activity regardless of cell lineage and likely related to MRP1 expression whereas higher MRP-related efflux can be detected in peripheral CD34 hematopoietic cells.

Diverse effects of P-glycoprotein inhibitory agents on human leukemia cells expressing the multidrug resistance protein (MRP).

UNLABELLED: Multidrug resistance (MDR) to cancer chemotherapy is frequently associated with decreased drug accumulation in cancer cells due to drug expulsion by multidrug transporters such as P-glycoprotein (Pgp) and multidrug resistance protein (MRP). The novel resistance modifying agents PSC 833, 280-446, and LY 335979 are primarily targeted at inhibition of Pgp, and their MRP inhibitory potential is largely unknown. OBJECTIVE: In the present study we addressed the effect of these agents on MRP-derived drug resistance. MATERIALS: Drug-resistant human leukemia cells with Pgp+/MRP- (KG1a/200, K562/150) and Pgp-/MRP+ (HL60/130) phenotypes were maintained in suspension cultures for experimental studies of drug accumulation and drug sensitization by Pgp inhibitors. METHODS: Intracellular accumulation of the fluorescent anthracycline daunorubicin was measured by flow cytometry and fluorescence detection. Daunorubicin dose-response curves were generated by non-linear regression of electronically measured cell counts of 72- - 96-h cultures. The half-maximal growth inhibitory dose (GI50) was used as measure of growth inhibition. RESULTS: All MDR phenotypes studied exercised significant resistance to daunorubicin. PSC 833, 280-446 and LY335979 were equal in sensitizing Pgp+/MRP- cells to daunorubicin-induced growth inhibition (p < 0.0001). The Pgp-/MRP+ cells responded to PSC 833 and 280-446 by increased accumulation of daunorubicin (p = 0.0022 and p = 0.0005, respectively) and sensitization to the drug (p = 0.0009 and p = 0.0007, respectively). Conversely, LY335979 did not affect accumulation of daunorubicin in Pgp-/MRP+ cells nor sensitize these cells to daunorubicin. CONCLUSION: Pgp inhibitory agents have differential effects on MRP-derived drug resistance which could be exploited in treatment of multidrug resistance in cancer patients.

P-glycoprotein as a drug target in the treatment of multidrug resistant cancer.

Multidrug resistance (MDR) is a major obstacle to successful cancer chemotherapy. One important mechanism of MDR involves the multidrug transporter, P-glycoprotein (Pgp), which confers upon cancer cells the ability to resist lethal doses of certain cytotoxic drugs by pumping the drugs out of the cells and thus reducing their cytotoxicity. Pgp belongs to the ATP-binding cassette (ABC) family of transporter molecules which require hydrolysis of ATP to run the transport mechanism. The substrates of Pgp may be endogenous (steroid hormones, cytokines) or exogenous (cytostatic drugs). A number of studies have demonstrated a negative correlation between Pgp expression levels and chemosensitivity or survival in a range of human malignancies. In principle, Pgp mediated drug resistance can be circumvented by treatment regimens that either exclude Pgp substrate drugs or include Pgp inhibitory agents. Experimental studies have demonstrated that certain structural modifications of anthracyclines confer the ability to escape Pgp transport. The therapeutic benefit of Pgp inhibitors as chemosensitizers is currently being explored in phase III clinical trials, and the first promising results have already been reported. Another therapeutic option for Pgp inhibitors has recently evolved as several Pgp inhibitors, many of which are generally low-toxic substances, by themselves constrain proliferation and cause cell death by apoptosis in certain MDR cancer cell lines. The dual effect of Pgp inhibitors, targeting MDR cancer cells selectively, may translate into improved efficacy of cancer chemotherapy and perhaps new and less toxic drug treatment strategies in human MDR cancer.

Growth inhibition, cytokinesis failure and apoptosis of multidrug-resistant leukemia cells after treatment with P-glycoprotein inhibitory agents.

The multidrug transporter P-glycoprotein (Pgp), which is frequently overexpressed in multidrug resistant leukemia, has many proposed physiological functions including involvement in transmembraneous transport of certain growth-regulating cytokines. Therefore, we studied cell growth of three pairs of drug resistant and sensitive leukemia cell lines (KG1a, K562 and HL60) exposed to three different inhibitors of Pgp. The resistant KG1a and K562 sublines, which expressed high levels of Pgp, responded to low doses of the cyclosporin SDZ PSC 833, the cyclopeptolide SDZ 280-446, and the cyclopropyldibenzosuberane LY335979 with a dose-dependent growth inhibition. In the resistant variants of KG1a and K562 cells the mean half-maximal growth inhibitory doses (GI50) of SDZ PSC 833 were 312 (SE 41) and 414 (SE 50) nM, those of SDZ 280-446 were 685 (SE 51) and 578 (SE 54) nM, and those of LY335979 were 66 (SE 1) and 48 (SE 8) nM, respectively. Exposure to 1 microM SDZ PSC 833 resulted in tetraploidization, cytokinesis failure and apoptosis of the KG1a and K562 MDR variants. Conversely, parental cells with no or low levels of Pgp and the non-Pgp resistant variant of HL60 cells were not receptive to these cytotoxic effects. We conclude that inhibition of Pgp may exercise selective cytotoxicity in Pgp-rich leukemia cells indicating a possible therapeutic target in multiresistant leukemia.

Challenging drug resistance in cancer therapy--review of the First Nordic Conference on Chemoresistance in Cancer Treatment, October 9th and 10th, 1997.

The First Nordic Conference on Chemoresistance in Cancer Treatment was held in the Danish town of Helsingør on October 9th and 10th, 1997, under the auspices of the Nordic Cancer Chemoresistance Group (NCCG). The meeting focused on biochemical chemoresistance in a multidisciplinary approach. There were 19 oral and 15 poster presentations documenting recent advances in experimental and clinical research of drug transport mechanisms, DNA repair systems, detoxifying enzymes, drug target regulation, in vitro sensitivity tests, apoptosis inhibition, and strategies to circumvent chemoresistance. In the present paper we review the main issues that were addressed and discuss the findings with reference to the current literature in the field. The meeting demonstrated the plurality and the complexity of chemoresistance, which is a major obstacle to successful chemotherapy in cancer patients. The new insights to mechanisms of drug resistance and sensitization represent a useful basis for further development of strategies to circumvent chemoresistance in clinical practice.

Human hepatoma cells rich in P-glycoprotein display enhanced in vitro invasive properties compared to P-glycoprotein-poor hepatoma cells.

Whether the phenotypes of drug resistance and metastatic activity in cancer are dependent on each other or not is controversial. We compared in vitro invasive properties of human hepatoma cells resistant to epirubicin and rich in P-glycoprotein (Pgp) (HB8065/R) with the parental epirubicin-sensitive, Pgp-poor cells (HB8065/S). The HB8065/R cells displayed elevated capacity to migrate in a transwell chamber assay (three- to fourfold compared to the HB8065/S cells), both in the absence and presence of a reconstituted basement membrane extract (Matrigel). In the presence of the P-gp inhibitor PSC 833 (1.5 micrograms/ml) the capacity of the HB8065/R cells to cross Matrigel-coated filters was attenuated by approximately 25%. Compared to the HB8065/S cells, the resistant cell line expressed higher level of plasminogen activator inhibitor (PAI)-1 mRNA (approximately threefold), which was reflected by a approximately fivefold increase in secreted PAI-1 immunoactivity (approximately 50 ng/10(6) HB8065/R cells). Furthermore, treatment with PSC 833 was associated with upregulation of PAI-1 mRNA (approximately 3.5-fold) and immunoactivity (approximately twofold) in the HB8065/R cells. Level of tissue inhibitor of metalloproteinases (TIMP)-1 was also significantly increased in the HB8065/R cells compared to the HB8065/S cells, whereas both cell lines showed low constitutive expression of TIMP-2. Levels of TIMPs were not altered by PSC 833. These data suggest that overexpression of Pgp in these hepatoma cells may covariate with the phenotypes of both enhanced in vitro invasiveness and high PAI-1 expression, whether randomly acquired or not.

Cytotoxic effect of the cyclosporin PSC 833 in multidrug-resistant leukaemia cells with increased expression of P-glycoprotein.

Multidrug resistance (MDR) to anti-cancer agents is frequently associated with overexpression of the drug efflux transporter P-glycoprotein (Pgp) in cancer cells, ensuing drug expulsion and maintenance of tolerable intracellular levels of certain cytotoxic drugs. Pgp may also be present in normal tissue, providing protection against toxic substances, but the physiological role of Pgp is not fully understood. Recently, it was shown that Pgp also takes part in the transport of certain growth-regulating cytokines (Drach et al, 1996; Raghu et al, 1996). Therefore, we studied the effect of the highly potent Pgp inhibitor PSC 833 on proliferation of three pairs of MDR and parental human cell lines (HB8065 hepatoma cells, KG1a and K562 leukaemia cells). The MDR phenotypes were characterized by Pgp overexpression, which was demonstrated by flow cytometry using the anti-Pgp antibody MRK16. Electronic cell counting of 72-96 h cultures revealed a dose-dependent antiproliferative effect of PSC 833 in the resistant KG1a/200 and K562/150 cells. The half-maximal growth inhibitory concentrations (GI50) were 0.2 microM and 0.7 microM respectively. Exposure to PSC 833 induced cell death by apoptosis in both cell types, as revealed by flow cytometry and detection of 3'-hydroxy ends of DNA (the result of DNA fragmentation associated with apoptosis), by terminal transferase-mediated dUTP-biotin nick end-labelling (TUNEL). Similar effects were not found in the hepatoma cell lines or the parental leukaemia lines. These results demonstrated a discriminating cytotoxicity of PSC 833 in two human leukaemia MDR variants, representing a possible therapeutic indication which warrants consideration during the ongoing clinical evaluation of this drug.

Increased potency and decreased elimination of lamifiban, a GPIIb-IIIa antagonist, in patients with severe renal dysfunction.

Activation of the platelet membrane receptor glycoprotein (GP) IIb-IIIa is essential for thrombus formation. The novel nonpeptide GPIIb-IIIa antagonist, lamifiban, represents a promising approach for antiplatelet therapy in patients with cardiovascular disease. Since renal impairment frequently occurs in these patients, we designed a phase I study to assess the tolerability, pharmacodynamics and pharmacokinetics of lamifiban in patients with renal impairment. Four healthy volunteers (Group 1) with creatinine clearance (CLCR) >75 ml/min, eight patients (Group 2) with mild to moderately impaired renal function (CLCR 30-74 ml/min) and eight patients (Group 3) with severe renal impairment (CLCR 10-29 ml/min) were studied. They received stepwise increased doses of lamifiban intravenously (i.v.). There was a linear relationship between the systemic clearance of the drug and renal function (R2 = 0.86). The mean plasma concentration required for half-maximal inhibition of thrombin-receptor agonist peptide (TRAP) induced platelet aggregation (EC50) ex vivo was 21, 28 and 11 ng/ml in Groups 1, 2 and 3. The patients in Group 3 were sensitized to the antiplatelet effect allowing an 18-fold dosage reduction without compromising the pharmacodynamics. In conclusion, the decreased clearance of lamifiban may act in concert with increased potency of the drug in patients with severe renal impairment, and the drug dosage should be reduced accordingly.

Human hepatoma cells rich in P-glycoprotein are sensitive to aclarubicin and resistant to three other anthracyclines.

Drug resistance is a major obstacle to successful chemotherapy of primary liver cancer, which is associated with high expression of the multidrug resistance (MDR) gene product P-glycoprotein (Pgp), a multidrug efflux transporter. The most effective single agents in treatment of primary liver carcinoma belong to the anthracycline family, yet several anthracyclines are known to be substrates for Pgp. In the present study, we compared four anthracyclines with respect to cell growth inhibition, intracellular accumulation and cellular efflux using the HB8065/R human hepatoma cell line which is rich in Pgp, and the Pgp-poor parental line HB8065/S. The anthracyclines were also administered in conjunction with the Pgp-modifying agents verapamil and SDZ PSC 833 to assess modulation of resistance. The HB8065/R cells were sensitive to aclarubicin (ACL) and highly resistant to epirubicin (EPI), doxorubicin (DOX) and daunorubicin (DNR). SDZ PSC 833 enhanced accumulation, decreased efflux and increased cytotoxicity of EPI, DOX and DNR in the HB8065/R cells, but none of these effects was seen with ACL. In conclusion, ACL is apparently not transported by Pgp and retains its activity in a multidrug-resistant human hepatoma cell line; such properties can be exploited for clinical purposes.

P-glycoprotein is not expressed in a majority of colorectal carcinomas and is not regulated by mutant p53 in vivo.

Overexpression of the MDR1 product, P-glycoprotein (Pgp), has been shown to be one of the mechanisms underlying the development of multidrug resistance (MDR). Recently, one mutant p53 has been shown to stimulate the MDR1 gene promoter in vitro, whereas wild-type p53 repressed this activity. We measured Pgp and p53 expression by immunoblotting in 34 colorectal tumours, and performed mutation analyses on the p53-positive tumours to confirm the presence of mutant p53 protein. Tumour DNA indices (DIs) were also measured using flow cytometry. Pgp was detected in 44% (15/34) of the tumours and in 100% (13/13) of the normal mucosas (P = 0.0005), with highest levels of expression seen in normal mucosa, suggesting that initial drug resistance in colorectal tumours is not caused by Pgp. Highly DNA aneuploid tumours demonstrated the lowest levels of Pgp expression relative to moderately aneuploid and diploid colorectal tumours. p53 protein was detected in 53% (18/34) of the tumours, and 12 of 14 p53-positive tumours had p53 gene mutations, p53-negative tumours had approximately twice the level of Pgp expression of p53-positive tumours. Pgp expression was not associated with either p53 expression (P = 0.73) or incidence of p53 gene mutation (P = 0.70), suggesting that mutant p53 does not induce Pgp overexpression in colorectal carcinomas.

Clinical and biochemical long-term toxicity after postoperative cisplatin-based chemotherapy in patients with low-stage testicular cancer.

In this case-control study the long-term chemotherapy-related morbidity was assessed in testicular cancer patients (> or = 5 years after treatment). The case group consisted of 47 patients with nonseminomatous testicular cancer who had undergone retroperitoneal surgery and 3-4 cycles of conventional-dose cisplatin-based chemotherapy (accumulated cisplatin dose: 300-400 mg/m2), also containing vinblastine and bleomycin. The results of the clinical and biochemical investigations and the patients' responses to a questionnaire were compared to similar observations from a control group comprising 47 patients treated with surgery only. In the case group the serum magnesium values and the levels of FVIIvWF were significantly lower (but within the normal range) than in the control group. Serum cholesterol values were distributed similarly in both groups. About 40% of the patients from the chemotherapy group still suffered from Raynaud-like phenomena and/or sensoric neurotoxicity as compared to 10% of the patients from the control group. Chemotherapy resulted in a significant elevation of serum LH within the normal range, probably associated with a slight subclinical Leydig cell dysfunction. Serum FSH levels were similar in the case and control groups, indicating an absence of long-term disturbance of spermatogenesis after chemotherapy. No increased cardiovascular morbidity was observed as a result of chemotherapy. Raynaud-like phenomena and sensoric neurotoxicity represent the principal clinical long-term side effects after 3-4 cycles of cisplatin-based chemotherapy containing vinblastine and bleomycin. Serum LH is slightly elevated after chemotherapy, whereas long-term spermatogenesis seems to be unaffected.

Binding diversity of antibodies against external and internal epitopes of the multidrug resistance gene product P-glycoprotein.

P-glycoprotein (Pgp) is a trans-membraneous protein that is associated with multidrug resistance (MDR) in human cancer, including hepatocellular carcinomas and leukemias. There is no consensus regarding methods of choice for analysis of Pgp expression, and development of reliable analytical methods is now essential. We have studied the the Pgp expression in human hepatoma and leukemia cell lines using flow cytometry. The aim of the study was to compare binding properties of anti-Pgp antibodies reacting with surface (MRK16, UIC2) and cytoplasmic (C219, JSB-1) epitopes to assess which antibody performed best with respect to fluorescence discrimination. By histogram subtraction the fractions of resistant human hepatoma cells positive for Pgp were 99% (MRK16), 97% (UIC2), 77% (JSB-1), and 51% (C219), demonstrating variations in antibody reactivity. The resolution in detecting decreasing levels of Pgp in hepatoma cells was superior for the externally binding antibodies, showing that there is a correlation between antibody reactivity and fluorescence discrimination. Similar results were obtained for parental and resistant KG1a human leukemia cell lines. The Pgp epitopes remained reactive to the anti-Pgp MAbs after methanol fixation and cryopreservation. By dual parameter flow cytometry it was shown that Pgp expression in viable cells may be assessed together with uptake of epirubicin, which was low in cells expressing high levels of Pgp and vice versa. In conclusion, all tested antibodies proved useful for flow cytometric detection of high levels of Pgp, but the externally binding ones were superior in detection of low and variable levels of Pgp.