Immunohistochemical detection of multidrug resistance associated P-glycoprotein in tumour and stromal cells of human cancers

Future perspectives for the development of P-glycoprotein modulators

Resistance to chemotherapeutic agents constitutes one of the major obstacles to the successful treatment of cancer. While several mechanisms underlying drug resistance have been elucidated, the most widely studied mechanism involves the efflux of antineoplastic drugs from cancer cells by P-glycoprotein, the 170 kD glycoprotein product of the MDR-I gene. The observation that several compounds are able to inhibit P-glycoprotein in vitro created optimism that the problem of multidrug resistance in cancer could be quickly resolved by moving these compounds into the clinic. However, despite a large number of clinical trials with several different putative Pgp modulators, the value of Pgp modulation in clinical oncologic practice remains unresolved. While these initial trials have not answered the question of whether Pgp is an important mechanism of resistance in human cancers, or whether modulation of Pgp is likely to positively impact on the treatment of cancer, they have provided insights regarding the problems inherent in conducting trials of this nature. These clinical insights, along with knowledge gained from continued basic research on drug resistance mediated by Pgp and related transporters, will form a strong foundation for future research into the role of Pgp and Pgp modulation in the treatment of cancer. The ubiquitous nature of transporters and the high prevalence of transporter substrates among antineoplastic drugs, compel the development of modulators that can be used to prevent or reverse drug resistance.

IIVP Salvage Regimen Induces High Response Rates in Patients With Relapsed Lymphoma Before Autologous Stem Cell Transplantation

Patients with relapsed lymphoma can be cured with high-dose chemotherapy and autologous hematopoietic stem cell transplantation (HSCT). New therapeutic approaches with better cytoreductive capacity are needed for relapsed patients to keep their chance for cure with transplantation. We report 30 patients with relapsed lymphoma, median age 43 years, treated with IIVP salvage regimen consisting of ifosfamide, mesna, idarubicin, and etoposide for 2 or 3 cycles. Seventeen patients had non-Hodgkin lymphoma (NHL) and 13 patients had Hodgkin disease (HD). Fourteen (47%) patients were at their first relapse. Overall response rate was 86.6% (n = 26) with 19 patients (63.3%) achieving complete response. Overall response rate was 92% in patients with HD and 82% in NHL. The most frequent side effects observed were grade III-IV neutropenia (87%) and thrombocytopenia (73%). IIVP regimen is a highly effective salvage therapy for patients with relapsed HD or NHL who are candidates for autologous HSCT. Close follow up is necessary because of the high incidence of grade III-IV hematologic toxicity.

Pharmacogenomics of MDR and MRP subfamilies

Drug-metabolizing enzymes, drug transporters and drug targets play significant roles as determinants of drug efficacy and toxicity. Their genetic polymorphisms often affect the expression and function of their products and are expected to become surrogate markers to predict the response to drugs in individual patients. With the sequencing of the human genome, it has been estimated that approximately 500–1200 genes code for drug transporters and, recently, there have been significant and rapid advances in the research on the relationships between genetic polymorphisms of drug transporters and interindividual variation of drug disposition. At present, the clinical studies of multi-drug resistance protein 1 (MDR1, P-glycoprotein, ABCB1), which belongs to the ATP-binding cassette (ABC) superfamily, are the most comprehensive among the ABC transporters, but clinical investigations on other drug transporters are currently being performed around the world. MDR1 can be said to be the most important drug transporter, since clinical reports have suggested that it regulates the disposition of various types of clinically important drugs, but in vitro investigations or animal experiments have strongly suggested that the members of the multi-drug resistance-associated protein (MRP) subfamily can also become key molecules for pharmacotherapy. In addition to those, breast cancer resistance protein (BCRP, ABCG2), another ABC transporter, is well known as a key molecule of multi-drug resistance to several anticancer agents. However, this review focuses on the latest information on the pharmacogenetics of the MDR and MRP subfamilies, and its impact on pharmacotherapy is discussed.

Liposome-Encapsulated Doxorubicin in Combination With Standard Agents (cyclophosphamide, vincristine, prednisone) in Patients With Newly Diagnosed AIDS-Related Non-Hodgkin's Lymphoma: Results of Therapy and Correlates of Response

Purpose

To evaluate the safety and efficacy of liposomal doxorubicin (Myocet; Medeus Pharma Ltd, Herts,UK) when substituted for doxorubicin in the CHOP regimen (cyclophosphamide, doxorubicin, vincristine, prednisone) in patients with newly diagnosed AIDS-related non-Hodgkin's lymphoma (AIDS-NHL). Secondary objectives were to assess the impact of HIV viral control on response and survival, and to correlate MDR-1 expression with outcome.

Patients and Methods

Liposomal doxorubicin at doses of 40, 50, 60, and 80 mg/m2was given with fixed doses of cyclophosphamide, vincristine, and prednisone every 21 days. All patients received concurrent highly active antiretroviral therapy. NHL tissues were evaluated for multidrug resistance (MDR-1) expression.

Results

Twenty-four patients were accrued. 67% had high or high-intermediate International Prognostic Index scores; the median CD4 lymphocyte count was 112/mm3(range, 19/mm3to 791/mm3). No dose-limiting toxicities were observed at any level, with myelosuppression being the most frequent toxicity. Overall response rate was 88%, with 75% complete responses (CRs), and 13% partial responses. The median duration of CR was 15.6+ months (range, 1.7 to 43.5+ months). Effective HIV viral control during chemotherapy was associated with significantly improved survival (P = .027), but CRs were attained independent of HIV viral control. MDR-1 expression did not correlate with response, suggesting that the liposomal doxorubicin may evade this resistance mechanism.

Conclusion

Liposomal doxorubicin in combination with cyclophosphamide, vincristine, and prednisone is active in AIDS-NHL, with complete remissions achieved in 75% independent of HIV viral control or tissue MDR-1 expression. HIV viral control is associated with a significant improvement in survival. Additional studies are warranted.

Increased myelotoxicity of idarubicin: is there a pharmacological basis? Results of a pharmacokinetic and an in vitro cytotoxicity study

BACKGROUND

Clinical trials evaluating idarubicin (IDA) in acute myeloid leukemia, multiple myeloma and non-Hodgkin's lymphoma (NHL) have provided some evidence for an increased myelotoxicity of IDA compared to other anthracyclines. IDA is known to be less sensitive towards multidrug resistance mediated by P-glycoprotein (P-gp). This phenotype is a major impediment to successful antineoplastic treatment, but P-gp is also expressed on hematopoietic stem cells (HSC).

METHODS

We investigated the pharmacokinetics of IDA and etoposide (ETO) in seven previously untreated patients with aggressive NHL. The patients received a CHOP-derived protocol (CIVEP) in which doxorubicin (DOX) was substituted by IDA 11-16 mg/m(2) and ETO 3 x 100 mg/m(2) was added. Furthermore, we evaluated in vitro the impact of P-gp expression on the cytotoxicity of DOX and IDA in cells from three parental chemosensitive leukemia and lymphoma cell lines (HL60, U937, CCRF) and their resistant sublines, as well as in CD34-positive HSC.

RESULTS

The peak plasma levels (C(max)), terminal elimination half-life (t(1/2)) and area under the concentration curve (AUC) both for IDA and for ETO did not differ from published data. In cell line models the numbers of viable cells in a P-gp-expressing resistant CCRF-VCR100 subline were significantly more reduced by IDA ( P<0.001), but there was no difference in the cytotoxicities of IDA and DOX in chemosensitive CCRF cells and in the (non-P-gp-expressing) resistant U937 and HL60 sublines. Cytotoxicity against HSC was more pronounced after incubation with IDA than after treatment with DOX ( P=0.014), even when a tenfold higher concentration of DOX than of IDA was used. The addition of cyclosporin A increased the cytotoxic effect of DOX but not that of IDA in HSC.

CONCLUSIONS

The pharmacokinetics of IDA and its main metabolite idarubicinol in CHOP-derived protocols were not different from data obtained with other combinations or monotherapy. The increased myelotoxicity of IDA may be a consequence of P-gp expression in CD34-positive HSC.

Resistance in the anti-angiogenic era: nay-saying or a word of caution?

The hope that anti-angiogenic therapy might be the panacea for cancer has not yet been realized. There are many possible reasons for this, including endothelial and tumor cell heterogeneity, the presence of survival factors within the tumor micro-environment, the problem of defining the best dose and schedule for anti-angiogenic therapies, and angiogenesis-independent regrowth of tumors. Once these problems are understood, we can begin to evaluate approaches to thwarting them. These could include combining anti-angiogenic therapies with chemotherapy, with other anti-angiogenic agents or with other biological therapies. Another approach would be to employ a particular agent or combination of agents that target processes crucial to the survival of a particular cancer.

The Snark is a Boojum: the continuing problem of drug resistance in the antiangiogenic era

If your Snark be a Snark, that is right: Fetch it home by all means-you may serve it with greens, And it's handy for striking a light. "But oh, beamish nephew, beware of the day, If your Snark be a Boojum! For then You will softly and suddenly vanish away, And never be met with again!" Lewis Carroll The Hunting of the Snark

Multidrug resistance (MDR-1) expression in AIDS-related lymphomas

P-glycoprotein is a product of the multidrug resistance (MDR-1) gene. In non-Hodgkin's lymphoma, less than 20% of untreated de novo lymphomas express MDR-1 compared with approximately 50% after failure of chemotherapy. We wished to study the expression of MDR-1 in AIDS-related non-Hodgkin's lymphoma (AIDS-NHL). Tissue biopsies from 50 patients with newly diagnosed AIDS-NHL were studied by immunohistochemical analysis using C494, a monoclonal antibody specific for the MDR-1 isoform of P-gp. MDR-1 expression was correlated with patient demographics, lymphoma characteristics, response to chemotherapy, and survival. Forty-six males and four females with a median age of 38 years (range 26-63) were studied. A prior AIDS-defining opportunistic infection was reported in 35 patients (70%). The median CD4+ lymphocyte count was 69/mm(3) (range 0-920). Thirty-two patients (63%) had received prior anti-HIV therapy, including a protease inhibitor in five (10%). Pathologic types consisted of diffuse large cell in 13 (26%), immunoblastic in 13 (26%), small non-cleaved in 22 (44%), and high grade not otherwise specified in two (4%). The majority of patients (76%) had stage III/IV disease. Pre-treatment lymphoma tissues from 33 patients (66%) stained positively for MDR-1. MDR-1 positive patients had a significantly lower complete remission rate compared to MDR-1 negative patients (33 versus 65%, P=0.042). Duration of complete response was significantly longer in MDR-1 negative patients compared with MDR-1 positive patients (not reached versus 9.9 months, P=0.003). Strategies to overcome MDR-1 expression may be important for initial treatment in patients with AIDS-NHL.

Chemotherapy resistance in acute myeloid leukaemia

The development of refractory disease in acute myeloid leukaemia (AML) is frequently associated with the expression of one or several multidrug resistance (MDR) genes. MDR1, MRP1 and LRP have been identified as important adverse prognostic factors in AML. Recently it has become possible to reverse clinical multidrug resistance by blocking P-glycoprotein-mediated drug efflux. The potential relevance of MDR and new approaches to treat refractory disease, are discussed.

High expression of MDR-1 gene and P-glycoprotein in initial and re-biopsy specimens of relapsed B-cell lymphoma

AIMS

Multidrug resistance (MDR) is a major obstacle in the treatment of lymphoma. The expression of MDR-1 mRNA and P-glycoprotein (MDR-1/P-gp) has been linked to MDR. We aimed to investigate the expression of MDR-1/P-gp in B-cell lymphoma.

METHODS AND RESULTS

Samples at diagnosis and relapse from 10 patients with B-cell lymphoma were obtained. We also obtained 14 unselected control cases of B-cell lymphoma at diagnosis. The expression of mRNA and protein were determined semiquantitatively by RT-PCR and immunohistochemistry. High MDR-1 and P-gp expressions were found in seven and seven of 10 samples obtained at diagnosis, eight and eight of 10 samples obtained at relapse, and three and four of 14 control cases at diagnosis, respectively. The results of RT-PCR paralleled those of immunohistochemistry. Concordance of high MDR-1/P-gp expression was noted in 27 of 34 samples (r = 0.73, P = 0.001). There were no significant changes in MDR-1/P-gp expression in all cases at relapse and during the clinical course following chemotherapy. In the 14 control cases, the average survival time was 12.7 months in MDR-1/P-gp positive cases and 29.0 months in the MDR-1/P-gp negative cases (P = 0.20).

CONCLUSIONS

Our results showed that at least some B-cell lymphomas express MDR-1/P-gp, which could be detected by different methods, and suggested that high MDR-1/P-gp expression in tumour cells may be associated with a high probability of relapse and poor prognosis.

P-glycoprotein expression and multidrug resistance in cutaneous T-cell lymphoma

Advanced-stage cutaneous T-cell lymphoma (CTCL) is generally resistant to standard chemotherapy. Because P-glycoprotein (P-gp) has been detected in other types of resistant solid tumors, leukemias, and lymphomas, we analyzed P-gp expression in CTCL. Twenty-seven patients with CTCL and circulating Sezary cells in the peripheral blood as observed on a peripheral smear treated at the Yale Photopheresis Center between 1987 and 1993 were identified. Twenty-five of these patients had skin biopsies evaluated for expression of P-gp using JSB-1 (Accurate Chemical), MRK-16 (gift of T. Tsuruo), and UIC-2 (gift of E. Metchner). P-gp expression was considered present if immunoreactivity was noted with two of the three antibodies. Eighteen of 25 patients (72%) evaluated exhibited expression. The patients were treated with various combinations of drugs consisting of topical and systemic steroids electron beam therapy, psoralens in combination with UV light A (PUVA), systemic chemotherapy, and photopheresis before testing the tissue for P-gp expression. Treatment with systemic chemotherapy in P-gp-positive patients produced responses in 3 and no responses in 11 patients (4 were lost to follow-up). Seven patients did not express P-gp: One patient responded to treatment, five did not respond, and one patient was lost to follow-up. These results demonstrate that P-gp is frequently expressed in CTCL. P-gp expression in our study was not a useful predictor of drug resistance.

Redefining the target: chemotherapeutics as antiangiogenics

Angiogenesis, or new blood vessel formation, is now known to play an important role in both growth and metastasis of many cancers. The central importance of angiogenesis and the understanding of how new blood vessels are formed, has led to novel therapies designed to interrupt this process. Though specific antiangiogenic compounds have only recently entered the clinic, they herald a new era, one in which biology is the basis for therapy. The intense interest in angiogenesis has also lead to a re-examination of the activity of many established cytotoxic agents. Claims of antiangiogenic activity abound, unfortunately, with no common criteria and often little evidence of clinical relevance. What are we to think? Have oncologists unknowingly been administering antiangiogenic therapy all these years? If chemotherapeutics are really antiangiogenics in disguise, why have they failed to cure most solid tumors? Might the hard-learned lessons of chemotherapy resistance pertain to the novel antiangiogenics as well? Though we can offer no certain answers to these important questions, we do offer a framework on which to order the rapidly burgeoning literature. We suggest criteria by which a cytotoxic agent might reasonably be considered to have meaningful antiangiogenic activity. Finally, we describe potential mechanisms of resistance to antiangiogenic chemotherapies-some of which may apply to the pure antiangiogenics currently in development.

The management of adult aggressive non-Hodgkin's lymphomas

Aggressive non-Hodgkin's lymphona include diffuse large B-cell lymphoma, anaplastic large cell lymphona, and different peripheral T-cell lymphomas. An international prognostic index has been developed including age, serum LDH, performance status, and extranodal involvement. For localized aggressive lymphoma, the preferred treatment is 3-4 CHOP and radiation therapy, with a cure rate of 70-80%. For disseminated aggressive lymphoma, current regimens have a cure rate of less than 40%. Innovative strategies, including dose escalation, autologus stem cell support, new drugs, and immunotherapy are being explored to improve these results.

Multidrug resistance in haematological malignancies

The development of refractory disease in acute myeloid or lymphoblastic leukaemias (AML, ALL) and multiple myeloma (MM) is frequently associated with the expression of one or several multidrug resistance (MDR) genes. MDR1, MRP1 and LRP have been identified as important adverse prognostic factors in AML, T-ALL and MM. Recently, it has become possible to reverse clinical multidrug resistance by blocking P-glycoprotein-mediated drug efflux. The potential relevance of these reversal agents of MDR and potential new approaches to treat refractory disease are discussed.

Clinical significance of P-glycoprotein (P-gp) expression in childhood acute lymphoblastic leukemia. Results of a 6-year prospective study

P-glycoprotein (P-gp), a cellular drug-efflux pump is thought to be one of the major causes of multidrug resistance in malignancies. Since therapeutic strategies are being developed to circumvent drug resistance by inhibiting P-gp, prospective studies concerning the clinical relevance of P-gp in childhood leukemia are warranted.

METHODS

P-gp was studied in 102 consecutive cases of de novo childhood ALL and in 34 relapsed patients. An immunocytochemical technique with two monoclonal antibodies (C219,4E3) was used on bone marrow and blood smears.

RESULTS

12/34 (35%) children were scored positive at relapse compared to 12/102 (12%) children with newly diagnosed ALL (p = 0.006). No correlation between P-gp expression and clinical and hematological parameters was seen. All patients were treated according to the EORTC-CLCG protocols (survival at 5 years = 85%). 20/102 patients relapsed. The mortality rate in the P-gp positive group was significantly worse (Logrank P = 0.009) than in the P-gp negative patients. In the relapsed patient population 10/12 P-gp positive cases experienced an unfavourable outcome compared with 10/22 P-gp negative patients [Risk Ratio 2.21 (0.90-5.45)].

CONCLUSIONS

P-glycoprotein expression in newly diagnosed childhood ALL is an independent prognostic parameter for dismal outcome. P-gp positivity at relapse tends towards an adverse clinical outcome compared to the P-gp negative relapsed population.

High expression of multidrug resistance-1 (MDR-1) and its relationship with multiple prognostic factors in gastric carcinomas in patients in Turkey

Drug resistance remains a major problem in the treatment of gastric cancer. In Turkey, gastric carcinoma is the second most common cancer and, because the rate of early diagnosis is low, chemotherapy plays an important role in the treatment of the disease. We aimed to investigate expression of the multidrug resistance-1 gene (MDR-1) and its relationship with multiple prognostic factors in gastric cancers. Between 1996 and 1998, a total of 55 patients (37 men and 19 women; median age 55 years) were studied. Sections from specimens of gastric carcinomas were immunohistochemically stained to detect P-glycoprotein (which is associated with MDR-1 expression). We found MDR-1 expression in 48 (87%) of the patients. None of the multiple prognostic factors, including histological type of tumour, correlated with expression of MDR-1. Patients who had low MDR-1 expression had better survival. We conclude that the expression of MDR-1 in gastric cancer is high in Turkey, and this may be related to poor prognosis.

ATPase activity of purified multidrug resistance-associated protein

Human multidrug resistance protein (MRP) was expressed at high levels in stably transfected baby hamster kidney (BHK-21) cells. These cells exhibited a pattern of cross-resistance to several different drugs typical of an MRP-mediated phenotype despite the addition of 10 histidine residues at the C terminus to facilitate purification. Consistent with this functional evidence of the presence of MRP at the surface of these transfectants, strong signals were detected by immunoblotting and immunofluorescence using a specific monoclonal antibody to MRP. There was intense uniform staining of the cell surface as well as weaker staining of intracellular membranes. MRP-containing membranes were solubilized in 1% N-dodecyl-beta-D-maltoside in the presence of 0.4% sheep brain phospholipids. Two sequential affinity purification steps on Ni-NTA agarose and wheat germ agglutinin agarose provided substantial enrichment, and contaminating bands were not detected. ATPase activity of the purified protein was assayed in the presence of the phospholipids, which had been maintained throughout all purification steps. ATP was hydrolyzed in proportion to the amount of purified protein assayed, and typical Michaelis-Menten behavior was exhibited, yielding estimations of Km of approximately 3.0 mM and Vmax of 0.46 micromol mg-1 min-1. This activity was moderately stimulated by the drugs that others have shown to be transported by MRP-containing membrane vesicles. This stimulation was enhanced by reduced glutathione as is its drug transport, and oxidized glutathione, itself a substrate for transport, caused a strong stimulation. These data describe the first purification of MRP and provide the first direct evidence that the molecule possesses drug-stimulated ATPase activity.

The role of MDR-1 in refractory lymphoma

Although lymphoma is one of the few solid tumours for which chemotherapy can be curative, the treatment of refractory lymphoma remains a major clinical problem. P-glycoprotein (Pgp), the drug efflux pump encoded by the MDR-1 gene is associated with multidrug resistance in several laboratory models of drug resistance, and a number of investigators have attempted to establish a role for Pgp in refractory lymphoma. Despite a considerable variability in the results of these studies investigating Pgp expression in lymphoma, the preponderance of the data suggests that Pgp may at least in part account for drug resistance in this disease. Several clinical trials using Pgp modulating compounds have attempted to reverse the drug resistant phenotype of refractory lymphoma. These studies, although difficult to interpret because of the effect of Pgp modulators on chemotherapeutic drug pharmacokinetics, also suggest a role for Pgp in mediating drug resistance in a subset of patients with refractory lymphoma. Studies with newer Pgp modulating agents with phase III designs will be needed before Pgp modulation can be considered for incorporation into routine oncologic practice.

A new mdr-1 encoded P-170 specific monoclonal antibody: (6/1C) on paraffin wax embedded tissue without pretreatment of sections

AIMS

The generation and characterisation of a monoclonal antibody that specifically recognises the mdr-1 encoded protein, P-glycoprotein (P-170), on routinely processed formalin fixed, paraffin wax embedded tissue sections.

METHODS

The monoclonal antibody, designated 6/1C, was produced following a combination of in vivo and in vitro immunisation regimens in Balb/c mice with a synthetic 12 amino acid peptide that corresponds to amino acids 21-32 (believed to be intracellularly located) of P-170 and has insignificant homology with the mdr-3 encoded P-170. Antibody 6/1C was characterised by western blotting and immunocytochemistry on cytospins of paired multidrug resistant or sensitive cell lines, including mdr-1 and mdr-3 transfected cells, and by immunohistochemistry on normal and malignant formalin fixed paraffin wax embedded tissue sections.

RESULTS

Antibody 6/1C showed a single band at 170 kDa on western blots of multidrug resistant cell lysates and mdr-1 transfected cell lysates that was absent on similar preparations of drug sensitive cells and mdr-3 transfected cells. Immunocytochemical studies on cytospins of multidrug resistant cells and mdr-1 transfected cells revealed strong inner plasma membrane/cytoplasmic staining. Staining was negligible on drug sensitive cells and cells transfected with the mdr-3 gene. Immunohistochemical studies on formalin fixed, paraffin wax embedded normal adult kidney, liver, and breast tissue and a range of fetal tissues exhibited staining patterns of a variety of secretory surfaces consistent with documented mdr-1 specific staining. Specific staining of malignant cells in similarly treated sections of breast tumours was seen also with antibody 6/1C. Staining on paraffin wax embedded tissue with this antibody did not require any pretreatment of tissue sections.

CONCLUSIONS

This new monoclonal antibody, chosen for its specificity with the mdr-1 encoded P-170 and its reactivity on routinely fixed paraffin wax embedded tissue samples without pretreatment, appears to be useful for the investigation of P-170 in archival material. It is especially useful for retrospective studies on pretreatment and post-treatment tissue sections, and could help establish when and how rapidly mdr-1 associated drug resistance develops during chemotherapeutic regimens. Immunohistochemical assessment of P-170 expression in many cancers has potential for diagnostic purposes and may influence the choice of chemotherapeutic drugs used in the treatment of refractory tumours.

Reverse transcriptase-polymerase chain reaction amplification of MDR1 gene expression in adult soft tissue sarcomas

Expression of the multidrug resistance gene MDR1 is reported to be an important determinant of the response to chemotherapy and survival in some cancers. We compared three methods for determining the intrinsic MDR1 expression in soft tissue sarcomas. We studied MDR1 gene expression in 39 samples from 33 cases of soft tissue sarcomas comprising 11 liposarcomas, nine malignant fibrous histiocytomas, six leiomyosarcomas, four malignant schwannomas, three fibrosarcomas, three synovial sarcomas, and three epithelioid sarcomas, and seven cases of benign soft tissue tumors in adult patients. To detect MDR1 mRNA, reverse transcriptase-polymerase chain reaction (RT-PCR) was performed in all samples. Furthermore, RNA dot-blot analysis with digoxigenin-labeled RNA probe and immunohistochemistry with JSB-1 and C-219 antibodies for P-glycoprotein were employed in 34 and 37 samples in soft tissue sarcomas, respectively. We compared these three detection techniques. Of the 39 specimens, 18 (46%) showed MDR1 PCR products. Liposarcomas (six of 11), malignant fibrous histiocytomas (six of nine), leiomyosarcomas (four of six), fibrosarcomas (two of three) revealed high or intermediate MDR1 expression at high frequency. No MDR1 expression was detectable in malignant schwannomas, synovial sarcomas, or epithelioid sarcomas. Of seven benign soft tissue tumors, one ganglioneuroma and one lipomatosis showed low levels of MDR1 expression. By RNA dot-blot analysis, MDR1 transcripts were detectable in 12 of 34 specimens (35%). Four samples were negative by dot blot despite positivity with RT-PCR. Concordance between MDR1 expression by RNA level with RT-PCR and dot blot and at the protein level with immunohistochemistry using C-219 was found in 16 (47%) of the 34 comparable specimens. Eight samples showed positive immunoreactivity for C-219 despite negative results in RT-PCR and dot-blot analysis. The intrinsic MDR1 expression in soft tissue sarcoma seemed to depend on certain tumor types, such as liposarcoma, malignant fibrous histiocytoma, leiomyosarcoma, and fibrosarcoma. For the evaluation of MDR1 expression, RT-PCR is useful because of its relative simplicity and sensitivity. However, the clinical significance of such low levels of MDR1 expression detected only by RT-PCR must be discussed within systematically treated patient groups.

Detection of the multidrug resistance marker P-glycoprotein by immunohistochemistry in malignant lung tumours

BACKGROUND

The multidrug resistance marker P-glycoprotein (P-gp) was studied immunohistochemically in 78 primary malignant lung tumours. P-gp is a 170 kD transmembrane ATP dependent drug efflux pump which has been shown to be important in the resistance of some tumours to chemotherapy. Certain normal tissues express P-gp and tumours derived from these tissues are often insensitive to cytotoxic agents, showing raised P-gp levels innately or following chemotherapy or radiotherapy.

METHODS

Samples from 78 patients undergoing surgery for primary malignant lung tumours were snap frozen and stained immunohistochemically using the monoclonal antibody C219 which reacts with a P-gp epitope. None of the study group had received chemotherapy or radiotherapy before surgery was performed.

RESULTS

Twenty seven of the 78 lung tumours (34.6%) showed immunohistochemically detectable levels of P-gp which varied with tumour type; 17 of 54 squamous cell carcinomas (31.5%), seven of 15 adenocarcinomas (46.7%), and neither of two small cell carcinomas showing positive staining. In six of seven cases normal respiratory epithelium present showed the presence of P-gp.

CONCLUSIONS

P-gp is immunohistochemically detectable in frozen tissue from a proportion of malignant lung tumours before exposure to radiotherapy or drugs associated with multidrug resistance. It may have a role in tumour resistance to cytotoxic drugs, but further clinical studies will be required to evaluate any correlation between P-gp levels and response to treatment.

Multidrug resistance in pediatric oncology

Cancer survival among children and adolescents has improved markedly due to evolution of multimodal treatment that incorporates combination chemotherapy, radiation therapy and/or surgery. However, 20-30% of children with malignancies will succumb to their disease or complications associated with their disease or treatment. A major limiting factor to improvement in survival among these patients is the occurrence of intrinsic and/or acquired resistance to our treatment interventions, chemotherapy and radiotherapy. Among these mechanisms, multidrug resistance, the focus of this review, is a well-documented phenomenon whose biochemistry, pharmacology and molecular biology has been extensively studied. A role for multidrug resistance in chemoresistance and therapeutic failure in childhood malignancies is suggested by the observation of clinical resistance to treatment regimes containing agents that are known substrates of multidrug resistance mechanisms. With the current results from studies in rhabdomyosarcoma, neuroblastoma, osteosarcoma, Ewing's sarcoma, leukemia and retinoblastoma, the role of multidrug resistance is still unclear. Earlier studies attempted to define a role for P-glycoprotein-mediated multidrug resistance; however, a limited number of reports suggest that the multidrug-associated resistance protein may play an active role in neuroblastoma. Further studies will be necessary using standardized and uniform approaches for the analyses of these mechanisms. Clinical trials directed toward reversal of multidrug resistance are premature since the exact role of P-glycoprotein is controversial in pediatric malignancies, the role of other mechanisms of multidrug resistance must be assessed and selective inhibitors of multidrug resistance have yet to be developed.

MDR1 gene expression: evaluation of its use as a molecular marker for prognosis and chemotherapy of bone and soft tissue sarcomas

Successful chemotherapeutic treatment of malignant tumours is often limited by the intrinsic or acquired multidrug resistance (MDR). The classical MDR phenotype is characterised by reduced drug accumulation within the cell, caused by overexpression of the MDR1 gene encoded P-glycoprotein. Some reports have been published evaluating MDR1 expression as a molecular marker for response to chemotherapy in human bone and soft tissue sarcomas. In this review, an attempt is made to summarise the accuracy of the measurement of MDR1 expression for use in prognosis, as well as in decisions on chemotherapeutic treatment of sarcomas. In addition, general problems for the performance of such studies is discussed.

Is P-glycoprotein a sufficient marker for multidrug resistance in vivo? Immunohistochemical staining for P-glycoprotein in children and adult leukemia: correlation with clinical outcome

Seventy-eight patients: 45 children, 33 adults and 27 normal healthy donors were enrolled in the study. Expression of P-glycoprotein (P-gp) was evaluated with three monoclonal antibodies (MAb's) directed to intra-(C219, JSB-1) and extra-cellular (MRK-16) epitopes of P-gp and immunocytochemical (IC) APAAP staining method. Twenty-seven healthy donors peripheral blood mononuclear cells (PBMC) were investigated by means of IC and FACScan analysis. Positive staining for P-gp was detected in 31% children's and 33% adults' leukemia samples. No reactivity of three MAb's was observed with peripheral blood mononuclear cells (PBMC) by means of IC. Flow cytometry analysis with C219 MAb revealed staining for P-gp present on sub-population of lymphocytes and monocytes. P-gp (+) as well as P-gp (-) cases were compared in respect to clinical outcome, FAB classification and blood group. Complete remission (CR) was achieved in 12/14 (85%) children's and 9/11 (81%) adults' P-gp (+) leukemia cases. Within the P-gp (-) leukemia cases CR was observed in 24/29 (82%) and 18/22 (81%), respectively. Partial remission, relapse, resistance and death were noticed in 14% children's and 18% adults' P-gp (+) samples. In P-gp (-) cases these parameters were observed in 17% and 18%, respectively. These results raise the question whether the expression of P-gp can be used as single prognostic marker to detect multidrug resistance (MDR phenomenon) in vivo?

Expression of P-glycoprotein in high-grade osteosarcomas in relation to clinical outcome

BACKGROUND

Increased levels of P-glycoprotein occur in some osteosarcomas. In this study we determined the relation between P-glycoprotein status and outcome in patients with high-grade osteosarcoma.

METHODS

P-glycoprotein status was determined immunohistochemically in specimens of osteosarcoma of the extremities (stage II) from 92 patients who were treated with surgery and chemotherapy. The P-glycoprotein status was analyzed in relation to the length of event-free survival.

RESULTS

The presence of increased levels of P-glycoprotein in the osteosarcoma was significantly associated with a decreased probability of remaining event-free after diagnosis (P = 0.002). In a multivariate analysis, P-glycoprotein status (P = 0.001) and the extent of tumor necrosis after preoperative chemotherapy (P = 0.04) were independent predictors of clinical outcome. The risk of adverse events was increased substantially (rate ratio, 3.37; 95 percent confidence interval, 1.60 to 7.10) among patients with increased levels of P-glycoprotein in tumor cells, as compared with patients who did not have increased levels of P-glycoprotein in tumor cells.

CONCLUSIONS

In patients with high-grade osteosarcoma treated with surgery and chemotherapy, the presence of increased levels of P-glycoprotein in tumor cells is associated with a significantly increased risk of adverse events and is independent of the extent of necrosis after preoperative chemotherapy.

P-glycoprotein expression in primary and metastatic malignant melanoma

Metastatic malignant melanoma is notoriously resistant to chemotherapeutic agents, but the exact mechanisms involved in this drug resistance are unknown. One recently defined major mechanism of multidrug resistance involves the overexpression of P-glycoprotein on cell membranes. In order to evaluate the significance of this putative drug efflux pump for chemoresistance of malignant melanoma, five different antibodies were employed to examine P-glycoprotein expression on tissue from 33 primary malignant melanomas and 35 metastases, before and after chemotherapy, using immunohistological techniques. The expression of P-glycoprotein was low on primary cutaneous melanomas (three of 33), and on metastases (one of 35). Normal tissue in and around the melanoma showed reactivity of endothelial cells, stromal cells and eccrine sweat glands with several antibodies tested. Chemotherapy with drugs commonly used in metastatic melanoma, including agents known to induce P-glycoprotein expression in other tumours (vindesine, cisplatin) had no effect on P-glycoprotein expression in human melanoma metastases. The high chemoresistance of human melanoma cells in vitro and in vivo is probably not mediated via P-glycoprotein, and other possible mechanisms involved will have to be explored in future studies.

Overexpression of P-glycoprotein in adenomatous hyperplasia of human liver with cirrhosis

Adenomatous hyperplasia in the human liver with cirrhosis is similar to the hyperplastic nodule in rat hepato-carcinogenesis in that the mdr gene or its product P-glycoprotein is overexpressed. We immunohistochemically stained archival formalin-fixed, paraffin-embedded sections of 15 adenomatous hyperplasias with or without hepatocellular carcinoma in livers with cirrhosis, using the avidin-biotin-complex method and the JSB-1 monoclonal antibody which specifically binds the cytoplasmic epitope of P-glycoprotein. Of 15 cases with adenomatous hyperplasia, four were found solely in livers with cirrhosis. In six cases, adenomatous hyperplasia and hepatocellular carcinoma were found in the same liver separately. Hepatocellular carcinoma was discovered within adenomatous hyperplasia in five cases. All 15 livers with cirrhosis and those with adenomatous hyperplasia were positively stained for P-glycoprotein. When the grade of staining was compared between adenomatous hyperplasia and the surrounding liver, P-glycoprotein was overexpressed in 12 of 15 cases with adenomatous hyperplasia. P-glycoprotein was also stained more strongly in well-differentiated hepatocellular carcinoma than in the liver, but the staining grade of hepatocellular carcinoma was weaker than that of adenomatous hyperplasia. Moreover, the glycoprotein expression was less when the tumor was less differentiated.

P-glycoprotein and glutathione S-transferase pi in childhood acute lymphoblastic leukaemia

Blast cells obtained from 104 children with untreated acute lymphoblastic leukaemia were analysed for the expression of P-glycoprotein (P-170) and glutathione S-transfer pi (GST-pi) using immunohistochemistry. Expression of P-170 was detected in 36 of 104 patients (35%) and increased GST-pi was seen in 52 patients (50%). Coexpression of both resistance proteins was observed in 22 leukaemias (21%), whereas no evidence of the resistance markers was found in 38 cases (37%). In patients with P-170-positive leukaemic cells, a significantly lower probability of remaining in first continuous complete remission (CCR) was observed when compared with patients with P-170-negative tumours (P < 0.05). However, only a trend for a more frequent expression of P-170 was found in the leukaemic cells of patients who experienced relapses (P = 0.099). Overexpression of GST-pi was correlated with a higher relapse rate (P = 0.001) and a lower probability of remaining in first CCR (P = 0.01). Expression of P-170 and GST-pi was independent of sex, FAB type, immunological subtype and initial blast cell count. The multivariate analysis indicated that only the expression of P-170 is an unfavourable prognostic factor for children with acute lymphoblastic leukaemia in addition to the prognostic clinical factors.

Parallel assessment of glutathione-based detoxifying enzymes, O6-alkylguanine-DNA alkyltransferase and P-glycoprotein as indicators of drug resistance in tumor and normal lung of patients with lung cancer

The levels of several potential indicators of drug resistance were measured in tumor and corresponding normal tissue of 55 untreated patients with lung cancer. The resistance parameters include glutathione (GSH) level, activities of the enzymes glutathione transferase (GST), glutathione peroxidase (GPx) and O6-alkylguanine-DNA alkyltransferase (ATase), as well as expression of P-glycoprotein (Pgp). Median values of GSH, GST and GPx were significantly higher in tumor than in normal tissue of non-small-cell lung cancer (NSCLC) or of small-cell lung cancer (SCLC), whereas ATase was elevated in tumor tissue of NSCLC only. Pgp expression as determined by Western blotting was significantly lower in tumor than in normal tissue of NSCLC. Resistance-parameter expression did not correlate with stage of disease or age of the patients. We found a negative correlation between smoking intensity and GSH level in normal tissue. Our findings indicate that the fundamental differences in chemosensitivity between SCLC and NSCLC cannot be explained by differences in the GSH-system or in the expression of Pgp. However, the level of ATase activity may be one of the factors responsible for the difference in chemosensitivity.

S100-positive histiocytes in T-cell-dependent area in human lymph nodes express P-glycoprotein

In the present study, we examined P-glycoprotein (P-gp)-expressing cells in human lymph nodes (LN) from patients with reactive lymph adenitis and various malignant lymphomas (ML). MDR1 mRNA was detected in all reactive LN and in 8 of 10 ML samples examined by reverse transcription polymerase chain reaction (RT-PCR). The signal intensity of the bands was stronger in samples from T-cell ML LN than in those from LN of reactive lymph adenitis and B-cell ML. Immunohistochemistry also showed positive reactivity with cellular components in the LN. The P-gp-positive cells, detected by UIC2, in reactive lymph adenitis and ML samples were large in size in the T-cell-dependent paracortical area in LN. Further, morphological characteristics were similar in UIC2-positive cells between reactive and ML LN. Double staining with UIC2 and a hematopoietic cell lineage-specific monoclonal antibody showed that UIC2-positive cell co-expressed S-100, but not other lymphocyte- and ML cell-specific antigens, indicating that these cells correspond to histiocytes in the T-cell-dependent paracortical area. Our results show that P-gp was expressed in histiocytes but not ML cells in LN, and suggest that this molecule may play an important role in the biological function of histiocytes and/or for maintenance of homeostatic levels in T-cell ML LN.

Immunohistochemical evaluation of P-glycoprotein in human malignancies by monoclonal antibody MC57

P-glycoprotein expression was analyzed on 137 formalin-fixed, paraffin-embedded human tumours by monoclonal antibody (MAb) MC57. This MAb recognizes an extracellular human specific P-glycoprotein epitope and defines their multidrug resistance (MDR) phenotype by its binding on cells. Immunohistochemistry indicated that this MAb reacted in human cells and tissues in the same pattern as that found with other MAbs to P-glycoprotein. However, the present extensive study demonstrated that MAb MC57 is a highly specific reagent for the evaluation of an extracellular P-glycoprotein epitope preserved after fixation procedures and that this MAb is available to assess P-glycoprotein expression in routinely processed human tumour specimens.

Modulation of tumor cell response to chemotherapy by the organ environment

The outcome of cancer metastasis depends on the interaction of metastatic cells with various host factors. The implantation of human cancer cells into anatomically correct (orthotopic) sites in nude mice can be used to ascertain their metastatic potential. While it is clear that vascularity and local immunity can retard or facilitate tumor growth, we have found that the organ environment also influences tumor cell functions such as production of degradative enzymes. The organ microenvironment can also influence the response of metastases to chemotherapy. It is not uncommon to observe the regression of cancer metastases in one organ and their continued growth in other sites after systemic chemotherapy. We demonstrated this effect in a series of experiments using a murine fibrosarcoma, a murine colon carcinoma, and a human colon carcinoma. The tumor cells were implanted subcutaneously or into different visceral organs. Subcutaneous tumors were sensitive to doxorubicin (DXR), whereas lung or liver metastases were not. In contrast, sensitivity to 5-FU did not differ between these sites of growth. The differences in response to DXR between s.c. tumors (sensitive) and lung or liver tumors (resistant) were not due to variations in DXR potency or DXR distribution. The expression of the multidrug resistance-associated P-glycoprotein as determined by flow cytometric analysis of tumor cells harvested from lesions in different organs correlated inversely with their sensitivity to DXR: increased P-glycoprotein was associated with overexpression of mdr1 mRNA. However, the organ-specific mechanism for upregulating mdr1 and P-glycoprotein has yet to be elucidated.

Stage-specific distribution of P-glycoprotein in first-trimester and full-term human placenta

The distribution of P-glycoprotein in human placenta has been examined by immunohistochemistry using a battery of monoclonal antibodies (MRK-16, C219 and JSB-1). P-glycoprotein was located on the syncytiotrophoblast microvillus border in first-trimester placentas and some of the placental macrophages (Hofbauer cells) showed weak cytoplasmic staining. In term placentas, however, staining was not observed in the trophoblast but most of the Hofbauer cells displayed strong cytoplasmic staining. In situ hybridization with specific gene probes suggested that both human multidrug resistance genes were expressed in the placenta, although only the multidrug resistance-1 gene product would have been detected by the MRK and JSB-1 antibodies. These results point to distinct functions for P-glycoprotein during the different stages of placental development and indicate that its expression may be under developmental control.

Multidrug resistance gene (MDR 1) expression in neuro-axial tumours of children and young adults

Drug resistance in many cancers outside the CNS has been associated with over-expression of the multidrug resistance gene (MDR1), which codes for the transmembrane efflux pump P-glycoprotein (Pgp). To determine whether tumours of the neuroaxis over-express MDR1 and to identify the site of Pgp expression we examined 50 tumour specimens from 46 children and young adults using immunocytochemistry. Pgp was not expressed by any neoplastic cells, but was detected in the endothelium of tumour blood vessels in 35 of the 50 samples (70%). 11/35 (31%) were Pgp positive in the majority of vessels, 11/35 (31%) in a proportion, but < 50% of vessels, and 13/35 (37%) in one or two vessels. Pgp was also detected in surrounding normal brain capillaries. MDR1 may play a role in the chemoresistance of neuro-axial tumours either by its expression in the normal blood-brain barrier or by forming a blood-tumour barrier. The proportion of vessels expressing Pgp may determine the degree of resistance.

Expression of the multidrug-resistance gene product in untreated human breast cancer and its relationship to prognostic markers

The immunohistochemical expression of the 170-kDa permeability glycoprotein (P-gp) was investigated in 41 primary untreated breast carcinomas, using the monoclonal antibodies C219 and MRK16. DNA ploidy by flow cytometry and estrogen (ER) and progesterone receptor (PgR) contents were also determined. P-gp expression, as revealed by C219 or MRK16, was observed in 6 (14%) of the investigated cancers. P-gp expression had a tendency to occur in non-diploid, high-grade tumors as well as in patients with lymph node negative disease. However, except for lymph node status, these associations were not statistically significant. No positive statistical relationships were observed between other prognostic parameters (age, tumor size, and receptor status) and P-gp expression. Considering the great heterogeneity observed in previous studies and the low expression of P-gp observed hereby, the utility of P-gp immunostaining as a guide for therapy planning in patients with breast cancer remains uncertain.

Expression of MDR1/P glycoprotein in human sarcomas

Conflicting reports of MDR1 gene expression in human tumours are observed according to whether studies are performed at the mRNA or P-glycoprotein level. We have investigated this expression in 22 clinically drug-resistant sarcomas at the mRNA level by Northern blot (NB), Dot blot (DB), in situ hybridisation (ISH), and at the protein level by immunohistochemistry (IHC) using three monoclonal antibodies (MoAbs): C219, JSB1, MRK16. Increased MDR1 mRNA expression was detected by NB, DB, and ISH in 1/22 sarcoma (an Ewing's sarcoma). ISH was perfectly correlated with DB hybridisation and confirmed the expression of tumoral cells alone. Specific staining of 100% of tumoral cells was obtained with the three MoAbs in the same sarcoma. Expression in tumoral cells of 12 other sarcomas was detected with MRK16, and positive staining of stromal cells with both C219 (1/22) and MRK16 (8/22) was observed. This study confirms that MDR1 overexpression occurs in human sarcomas but is not the principal mechanism of drug-resistance. Furthermore, positivity with one antibody does not necessarily imply the presence of P glycoprotein (P-gp) and a disparity may exist between the levels of P-gp and its mRNA in the same sample. So care must be taken in interpreting results and more sensitive techniques such as the polymerase chain reaction (PCR) could prove useful.

Staining with Hoechst 33342 and rhodamine 123: an attempt to detect multidrug resistant phenotype cells in leukemia

Development of resistance is the major cause of failure in chemotherapeutic treatments. We have previously shown that the level of labeling with Hoechst 33342 and rhodamine 123 in established cell lines was decreased in cells with 'classic' MDR phenotype. This functional test was carried out using fluorescence image cytometry on living cells. We applied this protocol to patients with chronic lymphocytic leukemia. Although a large variability of the labeling is observed in cells from healthy donors, this approach seems to be useful for early detection of P-gp-dependent resistance in leukemia cells and for identification of new reversing agents on patient lymphocytes.

Evaluation of flow cytometry for multidrug resistance detection in low resistance K562 cells using daunorubicin and monoclonal antibodies

We compared the effectiveness of two flow cytometric methods for the detection of the multidrug resistance (MDR) phenotype. The sensitivity of both methods depended on the ability to discriminate low resistance cells from sensitive ones. Therefore, K562 cells with decreasing vinblastine (VLB) resistance levels were examined, the lowest resistance level being nonmeasurable with a colorimetric MTT assay. The fluorescent drug daunorubicin (DNR) was measured in combination with two modulators of MDR, cyclosporin-A (CsA) and verapamil (Vp) in a functional flow cytometric assay. When compared to sensitive cells, DNR uptake levels at steady state were reduced in all resistant cell lines, except for the lowest resistant cell line. The effect of modulator, CsA, on DNR uptake was seen in all resistant sublines, compared to sensitive cells, except for the lowest resistant cells. In another assay, the P-glycoprotein (Pgp) expression was analysed with monoclonal antibodies, MRK16 and C219. MRK16 was found to be the most sensitive antibody to screen for MDR+ cells, since we could show Pgp hyperexpression in all resistant cells. C219 reactivity became evident in cells possessing resistance factors higher than 5. These results indicate that both the functional assay and the Pgp assay are sensitive to be used for screening of MDR+ cells.