P-glycoprotein expression as a predictor of the outcome of therapy for neuroblastoma

Characterization of a novel bisacridone and comparison with PSC 833 as a potent and poorly reversible modulator of P-glycoprotein

Novel compounds, composed of two acridone moieties connected by a propyl or butyl spacer, were synthesized and tested as potential modulators of P-glycoprotein (P-gp)-mediated multidrug resistance. The propyl derivative 1,3-bis(9-oxoacridin-10-yl)-propane (PBA) was extremely potent and, at a concentration of 1 microM, increased steady state accumulation of vinblastine (VLB) approximately 9-fold in the multidrug-resistant cell line KB8-5. In contrast to the readily reversible effects of VRP and cyclosporin A on VLB uptake and similar to the effects of the cyclosporin analog PSC 833, this modulation by PBA was not fully reversed 6-8 hr after transfer of cells to PBA-free medium. Continuous exposure to 3 microM PBA was nontoxic and could completely reverse VLB resistance in KB8-5 cells. Consistent with its effects on VLB transport, the drug resistance-modulating effect of PSC 833 was significantly more persistent than that of VRP. However, the effect of PBA was, like that of VRP, rapidly reversed once the modulator was removed from the extracellular environment. PBA was able to compete with radiolabeled azidopine for binding to P-gp and to stimulate P-gp ATPase activity. However, both the steady state accumulation of PBA and the rate of efflux of PBA were similar in drug-sensitive KB3-1 and drug-resistant KB8-5 cells, suggesting that this compound is not efficiently transported by P-gp. These results indicate that PBA represents a new class of potent and poorly reversible synthetic modulators of P-gp-mediated VLB transport.

P-glycoprotein expression: critical determinant in the response to osteosarcoma chemotherapy

BACKGROUND

Fewer than 20% of patients with bone cancer who are treated with surgery alone are cured. Even with the best current treatment, surgery combined with chemotherapy, only 60%-80% of patients with nonmetastatic bone cancer and 10% of patients with metastatic bone cancer are cured. Thus far, the reason for treatment failure in the nonresponding subset has not been identified. It has been hypothesized that P-glycoprotein, which confers multidrug resistance, might be the cause. We sought to determine whether the expression of P-glycoprotein is associated with poor treatment outcome in osteosarcoma.

METHODS

In a retrospective study, we correlated P-glycoprotein expression with the outcome of conventional chemotherapy in 62 consecutive, clinically staged patients diagnosed as having osteosarcoma between 1980 and 1989.

RESULTS

P-glycoprotein was overexpressed in 27 patients but not in another 34 patients, and expression was ambiguous in the sample from one patient. At a median follow-up of 8.9 years, the 34 patients whose tumors did not express P-glycoprotein had significantly better relapse-free rates than the 27 subjects whose tumors expressed the protein (87% versus 0%; P<.00001) and had improved survival rates (94% versus 35%; P<.00001). Among the 46 patients who received chemotherapy before surgery, the 23 whose tumors were negative for P-glycoprotein showed significantly better long-term outcomes (P<.00002), although differences in tumor necrosis in response to therapy were only of borderline significance (P = .057).

CONCLUSIONS

P-glycoprotein expression does correlate with treatment failure in patients with osteosarcoma. This correlation raises the possibility that inhibiting the action of P-glycoprotein as part of therapy for this disease would improve outcome.

Expression of the MDR1 gene product P-glycoprotein in childhood neuroblastoma

BACKGROUND

In cancer treated with chemotherapy, multidrug resistance is characterized by increased genetic expression of P-glycoprotein (P-gp), which acts as an ATP-dependent drug-efflux pump. However, the clinical significance of the expression of the multidrug resistance gene (MDR1) product P-gp in neuroblastoma (NB) is still a matter of debate. In this study, the role of the expression of P-gp in NB was evaluated.

METHODS

NB tumor imprints and NB positive bone marrow smears from 23 children before and after multidrug chemotherapy were examined for P-gp expression by antialkaline phosphatase immunocytochemical analysis.

RESULTS

Before chemotherapy, only 10% of the NB samples showed positivity for P-gp. At diagnosis, no difference in P-gp expression was found between primary tumor cells and NB cells from metastases to bone marrow. P-gp positivity was only observed in patients with nonlocalized disease. P-gp positivity was never found in tumor cells that were histologically well differentiated. No clear correlation of P-gp positivity with poor prognostic parameters, such as chromosome 1p deletion or MYCN amplification, were found. Multidrug chemotherapy did not induce enhanced expression of P-gp in the neuroblasts. However, at clinical recurrence, P-gp expression was found in the metastatic NB cells of five of seven bone marrow samples examined.

CONCLUSIONS

The prognostic relevance of P-gp expression in NB was not clear from the results of this study. To resolve the uncertainties, a standardization of the methodology and more prospective studies are needed to determine whether routine analysis of P-gp is worth adding to the other prognostic parameters that are evaluated in NB patients. The finding that metastatic cells are capable of expressing MDR1, in contrast to the NB cells of the primary tumor, would certainly be an interesting topic for further study as work directed at understanding the progression to metastasis continues.

The prognostic value of MDR1 gene expression in primary untreated neuroblastoma

The contribution of MDR1 gene expression to the biology of childhood neuroblastoma is unclear. To clarify the role of MDR1 in this malignancy, we examined the relationship between MDR1 expression and patient outcome in subsets of 60 primary untreated neuroblastomas for which MYCN gene copy number and expression of the multidrug resistance-associated-protein (MRP) gene had been previously characterised. In contrast to MRP gene expression, MDR1 expression was lower in tumours with MYCN gene amplification compared with those without amplification. Strong correlations between MDR1 and MRP gene expression, and between MDR1 and MYCN gene expression, were observed in tumours lacking MYCN gene amplification (P < 0.0005). In these single-copy tumours, very high MDR1 gene expression was significantly associated with poor outcome (P < 0.05). Very high MDR1 expression was also strongly predictive of poor outcome in older children (P < 0.0001), but not in infants. These findings suggest a clinical role for the MDR1 gene in specific subgroups of primary neuroblastoma.

Correlation between morphologic and nonmorphologic prognostic markers of neuroblastoma

Morphologic (Shimada classification--SC, original and modified histologic grades--OHG and MHG) and nonmorphologic (serum LDH, 1 p del, DNA index, N-myc copy number, telomerase activity, and expression of MRP, MDR1, and TRK) prognostic markers for NB have been reviewed. The functional role of these nonmorphologic markers in the development and progression of this disease include abnormal cell proliferation, resistance to chemotherapeutic agents, and induction of apoptosis. A statistically significant association between high OHG/MHG (grade 3), DNA index of 1 (diploidy), > 1 copy of N-myc per haploid genome and serum LDH of > or = 1500 IU/1 (p < 0.001 for each) has been described. In SC, undifferentiated histology and high MKI are associated with N-myc amplification. However, a lack of correlation between morphology and N-myc amplification has been found in localized NB. Confirmation of these observations must now be obtained on larger numbers of prospectively studied cases. Data on correlation for various prognostic markers could provide guidelines for identification of subsets of NB having strongly significant, readily determinable, reproducible, and relatively inexpensive prognostic markers that could ultimately be used to design an algorithm for risk-specific therapy.

Standardization of a single-cell assay for sensitive detection of multidrug resistance protein expression in normal and malignant cells in archival clinical samples

Multidrug resistance protein (MRP), like P170, confers multidrug resistance, but its clinical relevance is uncertain, whereas P170 is an accepted cause of chemotherapy failure for which ongoing reversal trials are being conducted. Because such trials have been only modestly successful, we must investigate alternative drug resistance mechanisms such as MRP, which is poorly blocked by P170 inhibitors. The significance of MRP has remained undefined because MRP mRNA is difficult to assay in archival material, does not necessarily reflect MRP levels, and is widely expressed in normal or hematopoietic cells within tumors and bone marrow. Because conventional immunoblot or immunocytochemistry may not be sensitive enough to detect low or heterogeneous MRP expression in clinical samples, we elected to score MRP in single tumor cells by modifying our P170 assays that have proven valuable for correlating P170 expression with the outcome of pediatric cancer chemotherapy. We enhanced the signal-to-noise ratio with several peroxidase-tagged secondary antibody layers and staining refinements, standardizing the assay with MRP-negative and MRP-positive but P170-negative transfected or drug-selected controls in which MRP was quantified by immunoblot. We confirmed sensitivity by staining a very low MRP-expressing revertant line and "mixed" samples containing small numbers of positive cells; we confirmed specificity by applying two antibodies directed against separate MRP epitopes. We examined neuroblastoma, osteosarcoma, rhabdomyosarcoma, and retinoblastoma samples, identifying MRP-positive malignant cells, which were distinguishable from MRP-positive normal cells. This assay may be valuable for early diagnosis of low but potentially important MRP expression, which would allow timely application of alternative therapy, perhaps with MRP-specific blockers.

Expression of P-glycoprotein and p53 in advanced hepatocellular carcinoma treated by single agent chemotherapy: clinical correlation

Hepatocellular carcinoma (HCC), a chemoresistant tumour, is the most common fatal cancer in Taiwan. Hepatocellular carcinoma frequently expresses a high level of P-glycoprotein (P-gp), which is a specific phenotype of a multidrug-resistance gene, and harbours mutations of the tumour suppressor gene p53. A modulatory relationship between p53 and P-gp has been reported. In this study, we analysed the expression of P-gp in relation to chemotherapeutic response and p5353 protein expression in advanced HCC. Prechemotherapeutic tumour samples were obtained from 25 patients with HCC which had been treated with either etoposide (VP-16) or doxorubicin. P-glycoprotein and p53 in HCC were visualized by immunohistochemical staining using the monoclonal antibodies JSB-1 and DO1, respectively. We investigated the correlation of P-gp expression with chemotherapeutic responses, clinicopathological features and p53 protein expression. In our study, seven cases achieved partial remission, and the remaining 18 cases had a poor response to chemotherapy. Expression of P-gp was observed in 13 tumours (52%). Positive P-gp protein expression was significantly associated with non-responders (8% or 1/13 vs 50% or 6/12, P = 0.03). Thus, P-gp expression inversely correlated with chemotherapeutic response. Expression of p53 protein was seen in 12 cases and did not correlate with chemosensitivity or P-gp expression. In summary, P-gp expression correlates with the chemosensitivity of HCC that has been treated with VP-16 or doxorubicin and p 53 mutations do not appear to be a major determinant of P-gp expression in advanced HCC.

Biology and treatment of neuroblastoma

Neuroblastoma is an enigmatic tumor that has the highest rate of spontaneous regression of all human malignant neoplasms, yet has one of the poorest outcomes when occurring as disseminated disease in children. The emergence of neuroblastoma tumor biology, coupled with age and stage of diagnosis, has allowed more accurate routing of patients to risk-related therapy and refining of such therapy to minimize treatment for those with low risk for recurrent disease and searching out new treatment strategies for patients with high-risk disease. Continued assessment of tumor biologic features in all patients will provide new insights into tumorigenesis, cell differentiation, and death pathways, resulting in the potential for developing newer therapies for patients with high-risk disease.

MDR1 RNA transcripts do not indicate long-term prognosis in colorectal carcinomas

Because P-glycoprotein expression might be associated with a more aggressive behaviour of colorectal carcinomas (Weinstein et al., Cancer Res, 1991, 51, 2720-2726), we determined the relationship between MDR1 RNA expression of the carcinomas and the survival of the patients. At a median duration of follow-up of 86 months, event-free survival of patients with MDR1 RNA-negative tumours (n = 35) was not significantly different to that of patients with MDR1 RNA positive tumours (n = 67). Among the different tumour stages, event-free survival of the patients was also independent of MDR1 gene expression of the tumours. Thus, these findings do not support the hypothesis that local aggressiveness of P-glycoprotein positive tumour cells translates into worse clinical outcome.

Neuroblastoma

The neuroblastic tumours, derived from primordial neural crest cells which ultimately populate the sympathetic ganglia, adrenal medulla and other sites, (Brodeur GM and Castleberry RP. Neuroblastoma. In Pizzo PA, Poplack DG, eds, Principles and Practice of Pediatric Oncology. Philadelphia, J. B. Lippincott Co., 1997, 761-797) are an enigmatic group of neoplasms which have the highest rate of spontaneous regression of all human malignant neoplasms yet one of the poorest outcomes when occurring as disseminated disease in children. Significant advances in understanding and predicting the natural history of neuroblastoma have resulted from translational studies coupling tumour biology and clinical features to form prognostic strata and allowing more accurate routeing of patients to risk-related management. While this strategy has clarified the management for lower risk tumours, little improvement in survival for higher risk disease has been realised. Ironically, this latter patient subset, for which the most innovative therapeutic strategies are needed, is also the one from which the least tumour biology is gleaned owing to inadequate tissue sampling. This update will summarise the evolving biology of neuroblastoma and its relationship to current risk-related therapy and future management strategies. Throughout this report, prognostic grouping by age will be infants (< 1 year) versus children (> or = 1 year) since the change of risk according to age seems most distinct at this cut-off point.

P-glycoprotein expression in cartilaginous tumors

BACKGROUND AND OBJECTIVES

Malignant cartilage tumors demonstrate chemotherapeutic resistance through undetermined mechanisms. P-glycoprotein is the protein product of the multiple drug resistance gene 1 (MDR-1) and confers multidrug chemotherapeutic resistance in a variety of malignancies.

METHODS

MDR-1 expression was examined in 55 benign and malignant cartilage tumor specimens by immunohistochemistry using C219, C494, and JSB-1 antibodies, and by in situ hybridization with an MDR-1 specific oligonucleotide cDNA probe.

RESULTS

Constitutive expression of P-glycoprotein was observed in all benign and malignant cartilage tumor specimens with a similar pattern of immunohistochemical staining present with all three antibodies. In benign tumors and low grade chondrosarcomas, the staining pattern was weak to intermediate and localized to clusters of cells. However, higher grade-tumors (Grade II and III) expressed P-glycoprotein in a higher percentage of cells and with more intense staining. P-glycoprotein expression was absent in normal human articular cartilage, but was focally present in costal and growth plate cartilage. The immunohistochemistry results were confirmed by in situ hybridization in 10 cases.

CONCLUSIONS

P-glycoprotein is expressed constitutively in cartilaginous tumors, with greatest expression in high grade malignancies. The findings may account for the resistance of cartilage tumors to chemotherapeutic agents.

DNA elements recognizing NF-Y and Sp1 regulate the human multidrug-resistance gene promoter

Regulation of the human multidrug resistance gene (hMDR1) was studied by mapping DNA elements in the proximal promoter necessary for efficient transcription. Transient transfection analysis in tumor cell lines (HCT116, HepG2, and Saos2) of promoter deletions identified several regulatory domains. These cell lines expressed hMDR1 mRNA. Removal of an element between +25 and +158 reduced promoter activity by 2-3-fold, whereas deletion of sequences from approximately -5000 to -138 base pairs gave a approximately 2-fold increase. The activity of the hMDR1 promoter (-137 to +25) was comparable in activity to the SV40 early promoter and enhancer combination. Deletion of the hMDR1 promoter between -86 and -44 reduced activity by 5-10-fold, identifying an important regulatory region. This minimal region (-88 to -37) activated transcription when inserted upstream of a synthetic promoter, suggesting that it acts independently of other regulatory sequences. Two DNA elements within 85 base pairs of the transcriptional start site were required to confer efficient gene expression. A double-point mutation in the Y box (inverted CCAAT box) between -70 and -80 reduced activity of the promoter by 5-10-fold, and a single-point mutation at -52 within a GC-rich element reduced activity by 3-fold. Thus, both the Y-box and GC elements must each remain intact for optimal promoter activity. DNA-binding analyses suggest that the transcription factor NF-Y, but not YB-1 or c/EBP, is most likely responsible for controlling the activity of the Y-box element in these tumor cell lines. DNA-binding analyses also suggest that Sp1, alone or in combination with other nuclear factors, likely controls the activity of the GC element.

Expression of drug resistance proteins in breast cancer, in relation to chemotherapy

Drug resistance plays an important role in chemotherapy failure in breast cancer. We studied the expression of MDR1, MRP, LRP, DNA topoisomerases, p53 and Ki-67 in different groups of breast cancer patients in relation to chemotherapy. Tissues from 6 normal breasts and 20 primary operable, 40 locally advanced and 10 anthracycline-resistant metastatic breast cancers were assessed. Sequential samples of the same patient were available from 17 patients with locally advanced breast cancer undergoing neo-adjuvant chemotherapy and in 7 metastatic patients undergoing paclitaxel treatment. Protein expression was investigated by immunohistochemistry. Significantly higher protein expression was observed for Pgp, Ki-67 and p53 in the locally advanced breast cancers than in primary operable breast cancers. No other significant differences in protein expression were found among the 3 breast cancer groups. Expression of none of the markers that could be assessed (Pgp, MRP, LRP, p53 and Ki-67) in locally advanced breast cancer had predictive value for pathological response. Interestingly, after chemotherapy a significant decrease in percentage of Ki-67 positive tumor cells was observed, whereas the other markers did not vary substantially. Furthermore, considering all breast cancer samples, a cumulative dose of doxorubicin >400 mg/m2 inversely correlated with Ki-67 positivity. However, 2 patients with a pathological complete remission had only 5-10% Ki67-positive tumor cells before chemotherapy, indicating that Ki67 negativity itself is not responsible for chemoresistance. In conclusion, none of the known proteins related to multidrug resistance predicted response to chemotherapy in breast cancer, and resistant clones left behind generally had a low proliferation rate.

P-glycoprotein mediated multidrug resistance and its implications for pathology

The discovery of P-glycoprotein has revealed a fundamental mechanism by which cancer cells evade chemotherapy and this principle has proven relevant to general cellular defence mechanisms in normal physiology. To date this knowledge has promised to improve current cancer chemotherapy through the manipulation of drug combinations according to the P-glycoprotein status of the tumor. Furthermore, the discovery of inhibitors of the protein may provide new therapeutic tools in the treatment of multidrug resistant neoplasia, provided the benefits are deemed greater than the potential detrimental side effects. When looking towards future therapies, however, we must also consider additional mechanisms which undoubtedly contribute to clinical drug resistance. Complete elucidation of this complex cellular defence network will hopefully translate into therapeutic opportunities to circumvent all mechanisms of multidrug resistance, thus positively impacting on patient survival.

Annamycin circumvents resistance mediated by the multidrug resistance-associated protein (MRP) in breast MCF-7 and small-cell lung UMCC-1 cancer cell lines selected for resistance to etoposide

Annamycin (Ann) is a highly lipophilic anthracycline antibiotic that has been shown to circumvent MDR-1 both in vitro and in vivo. A liposomal formulation of Ann is currently in phase I clinical trials. The multidrug resistance-associated protein (MRP) has been found to be over-expressed in some human leukemias at relapse and to be a poor prognostic factor in neuroblastoma. We studied the in vitro cytotoxicity and the cellular uptake and efflux of Ann and doxorubicin (Dox) in 2 pairs of human cell lines, breast carcinoma MCF7 and small-cell lung cancer UMCC-1, and their MRP-expressing counterparts, MCF-7/VP and UMCC-1/VP. Resistance indexes were 1.1 and 1.4 for Ann vs. 6.9 and 11.6 for Dox. Ann cellular accumulation was 3- to 5-fold higher than that of Dox in both sensitive and resistant cells. No changes in drug efflux between sensitive and resistant cells were observed in the case of Ann, while Dox efflux at 1 hr was 20-25% higher in resistant than in sensitive cells. By confocal microscopy, the subcellular distribution of Ann was identical in sensitive and resistant cells, localizing mostly in the perinuclear structures, while that of Dox was exclusively nuclear in sensitive cells and nuclear and in the cell membrane in resistant cells. There was a good correlation between the extent of DNA breaks induced by each drug in the different cell lines and cytotoxic effect. Our results indicate that Ann may be effective in the treatment of malignancies in which MRP is a relevant mechanism of clinical resistance.

Expression of multidrug resistance-related P-glycoprotein shows good prognosis in neuroblastoma

Expression of P-glycoprotein was studied in formalin-fixed tissue sections from 75 materials with an immunoperoxidase (ABC) method using the monoclonal antibody MRK-16. Specimens examined were from three monkey fetuses, eight autopsy cases, and 64 neuroblastoma patients, 25 of whom were underwent mass screening for diagnosis. P-glycoprotein test results were positive in fetal lung alveolar tissue and in the adrenal medulla of three of seven adult autopsy cases. Expression of P-glycoprotein was demonstrated in 22 of 35 cases (63%) in a group of neuroblastoma patients younger than 12 months of age, as compared with 9 of 20 (31%) who were older than 12 months of age at diagnosis. P-glycoprotein positivity was higher in patients who were alive (25 of 40, 63%) than in those who had died (6 of 24, 25%). Previous studies on P-glycoprotein expression in neuroblastoma were carried out using specimens mainly from older children, and the results were not analyzed with reference to the findings in normal tissues. The present study has clearly shown that positive P-glycoprotein expression in neuroblastoma patients should be evaluated carefully in infant cases because it stains frequently in normal adrenal glands.

Biology and genetics of human neuroblastomas

PURPOSE

Neuroblastomas have a variety of clinical behaviors, from spontaneous regression or differentiation to early metastasis and death. We have examined a variety of genetic variables that might explain or predict the clinical behavior.

PATIENTS AND METHODS

We have studied DNA or RNA from a number of children enrolled in clinical trials with the major pediatric oncology cooperative groups.

RESULTS

We propose that neuroblastomas may be classified into three subsets with distinct biological features and clinical behavior. The first subset consists of those tumors with hyperdiploid modal karyotypes and high TRK-A expression. Patients with these tumors are usually infants with low stages of disease and a very favorable outcome. The second group consists of tumors that have a near-diploid DNA content, usually with 1p allelic loss or other structural changes, but they lack MYCN amplification, and TRK-A expression is low. The patients are generally older, with advanced stages of disease and an intermediate outcome. The third group is characterized by tumors with MYCN amplification, 1p allelic loss, and low or absent TRK-A expression. The patients are 1-5 years of age and have advanced stages of disease, rapid tumor progression, and a very poor prognosis. Current evidence suggests the tumor types are genetically distinct, and one type seldom if ever evolves into another.

CONCLUSIONS

Identification of these genetic and clinical subsets permits a more accurate prediction of outcome. This, in turn, allows more appropriate selection of therapeutic intensity to minimize side effects in those with a favorable outcome but optimize the chance of cure in those requiring aggressive treatment.

In vivo detection of multidrug-resistant (MDR1) phenotype by technetium-99m sestamibi scan in untreated breast cancer patients

Technetium-99m sestamibi is a transport substrate recognised by the multidrug-resistant P-glycoprotein (Pgp). To test whether 99mTc-sestamibi efflux is enhanced in breast carcinomas overexpressing Pgp, we determined the efflux rates of 99mTc-sestamibi and Pgp levels in tumours from 30 patients with untreated breast carcinoma. Patients were intravenously injected with 740 MBq of 99mTc-sestamibi and underwent a 15-min dynamic study followed by the acquisition of static planar images at 0.5, 1, 2 and 4 h. Tumour specimens were obtained from each patient 24 h after 99mTc-sestamibi scan and Pgp levels were determined using 125I-MRK16 monoclonal antibody and in vitro quantitative autoradiography. All breast carcinomas showed high uptake of 99mTc-sestamibi and data from region of interest analysis on sequential images were fitted with a monoexponential function. The efflux rates of 99mTc-sestamibi, calculated from decay-corrected time-activity curves, ranged between 0.00121 and 0.01690 min-1 and were directly correlated with Pgp levels measured in the same tumours (r=0.62; P<0.001). Ten out of 30 breast carcinomas (33%) contained 5 times more Pgp than benign breast lesions and showed a mean concentration of 5.73+/- 1.63 pmol/g of tumour (group A). The remaining 20 breast carcinomas had a mean Pgp concentration of 1.29+/-0.64 pmol/g (group B), equivalent to that found in benign breast lesions. 99mTc-sestamibi efflux from tumours of group A was 2.7 times higher than that observed in tumours of group B (0.00686+/-0.00390 min-1 vs 0.00250+/-0.00090 min-1, P<0.001). The in vivo functional test with 99mTc-sestamibi showed a sensitivity and a specificity of 80% and 95%, respectively. In conclusion, the efflux rate of 99mTc-sestamibi may be used for the in vivo identification of the multidrug resistant (MDR1) phenotype in untreated breast cancer patients.

Expression of MDR1/p-glycoprotein and multidrug resistance-associated protein in childhood solid tumours

We evaluated the expression of MDR1/p-glycoprotein in paediatric tumours using reverse transcriptase polymerase chain reaction (RT-PCR), RNA dot blot analysis, and immunohistochemistry on formalin fixed paraffin-embedded material with JSB-1 and C-219 monoclonal antibodies, and compared these three techniques. The expression of multidrug resistance-associated protein (MRP) gene was examined by RT-PCR assay. We studied MDR1/p-glycoprotein and MRP expression in 13 samples from 10 neuroblastoma patients, 11 samples from 10 nephroblastoma patients, 2 rhabdomyosarcomas, 1 adrenocortical carcinoma and 10 benign tumours or tumour-like lesions. Eleven of 13 neuroblastomas, 7 of 11 nephroblastomas, 2 rhabdomyosarcomas, 1 adrenocortical carcinoma, and 7 of 10 benign tumours or tumour-like lesions showed MDR1 PCR products. By RNA dot blot analysis, MDR1 transcripts were detectable in 11 of 34 specimens. Immunohistochemically, we detected positive reaction products for JSB-1 in 26 of 36 samples. There was a significant correlation between the immunoreactivity for JSB-1 and the expression of MDR1 mRNA expression by RT-PCR (P = 0.0001). However, the presence of p-glycoprotein immunostaining does not correlate with the MDR1 expression shown by RT-PCR in every case. As for MRP mRNA expression, 9 of 13 neuroblastomas and 10 of 11 nephroblastomas revealed PCR products.

Reversal of P-glycoprotein-associated multidrug resistance by ivermectin

P-Glycoprotein (P-gp) causes a multidrug resistance (MDR) phenotype in tumour cells. In some cancers, the expression of P-gp has been correlated with low clinical response to chemotherapy and survival of patients. Previous studies have shown that certain lipophilic drugs bind to P-gp and reverse the MDR phenotype of tumour cells. In this study, we extend that list of compounds and present evidence for the capacity of a potent and clinically safe anthelmintic, ivermectin (IVM), as an MDR-reversing drug. Using a highly drug-resistant human cell line, we compared IVM with other MDR-reversing agents and showed that IVM is 4- and 9-fold more potent than cyclosporin A and verapamil, respectively. The capacity of IVM to inhibit iodoaryl-azidoprazosin photolabeling of P-gp is consistent with direct binding to P-gp. Studies showed that [3H]IVM binding to membranes from resistant cells is specific and saturable with KD and Bmax values of 10.6 nM and 19.8 pmol/mg, respectively. However, while cyclosporin A or vinblastine inhibited [3H]IVM binding to membranes from drug-resistant but not drug-sensitive cells, neither verapamil nor colchicine had any effect. Furthermore, both IVM and cyclosporin A and, to a lesser extent, verapamil also inhibited [3H]vinblastine binding to membranes from drug-resistant cells. Drug transport studies showed that [3H]IVM is a substrate for the P-gp drug efflux pump. However, it was transported less efficiently by P-gp than [3H]vinblastine. Moreover, only cyclosporin A was effective in potentiating the accumulation of [3H]IVM in drug-resistant cells. Taken together, the high efficiency of MDR reversal by IVM combined with its low toxicity are consistent with the properties of an ideal MDR-reversing agent.

Synovial sarcoma: immunohistochemical expression of P-glycoprotein and glutathione S transferase-pi and clinical drug resistance

Our purpose was to study the role of the expression of P-glycoprotein (Pgp) and glutathione S transferase-pi (GST-pi) in predicting the response to chemotherapy, relapse-free interval, and survival of patients with synovial sarcoma (SS). Thirty-seven cases of primary SS, without regional lymph node or distant metastases, were studied. There were 17 females and 20 males, ranging in age from 7 to 81 years (median, 31 years) with tumors located in the lower extremity (n = 24) upper extremity (n = 5) and trunchus (n = 8). The cases were retrospectively studied without knowledge of clinical course to compare the immunohistochemical expression of Pgp and GST-pi, flow cytometry parameters (ploidy and % of cells in S+G2 phases), and PCNA and Ki-67 labeling of primary tumors before any therapy, with that observed in local recurrences and metastases after chemotherapy. The relationship of the aforementioned parameters with clinicopathological features (gender, age, and histo-blood group of the patients, size, location, histological subtype. TNM stage, and clinical response to chemotherapy of the tumors) was also evaluated. Results revealed that Pgp and GST-pi were expressed in 29.7% and 40.5% of the cases, respectively. In 48.6% of the tumors there was expression of a least one of the drug resistance markers. The markers were coexpressed in 25.0% of the tumors. The prevalence of Pgp expression was lower, but not significantly, in stage I-II (17.6%) than in stage III (40.0%) tumors, and also in cases without clinical progression (16.7%), than in cases with (36.0%). No such differences were observed for GST-pi expression. Pgp and GST-pi expressions were significantly associated with biphasic SS and were particularly noticeable in solid/glandular areas of biphasic SS. The expression of the drug resistance markers was not significantly associated with gender, age, and histo-blood group of the patients, dimension, location, and proliferative activity of the tumors; it was also not significantly related to relapse-free interval and survival of the patients. The expression of Pgp and GST-pi was not significantly associated either to response to chemotherapy or influenced by chemotherapy. We conclude that Pgp and GST-pi expressions are not good predictors response to of the chemotherapy in patients with localized SS. Other drug resistance mechanisms may be active in SS.

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.

Monoclonal antibody C219 immunohistochemistry against P-glycoprotein: sequential analysis and predictive ability in dogs with lymphoma

In the present study, the prevalence of positive staining for P-glycoprotein using C219 monoclonal antibody was assessed in 58 tissue samples of high-grade lymphoma from dogs before initiation of chemotherapy. Samples were also evaluated at relapse in 22 dogs, at necropsy in 34 dogs, and at all 3 times in 15 dogs. The frequency of positive staining was significantly higher than that found prior to the initiation of chemotherapy at the following times: relapse (P = .0001), necropsy (P < .0001), and both relapse and necropsy (P < .001, sequential data). The frequency of positive staining prior to the initiation of chemotherapy was significantly inversely related to remission (P < .001) and survival times (P = .0012). Similarly, when populations below and above the median initial C219 score were compared with respect to remission and survival times, the population with scores greater than the median had significantly lower remission (P < .001) and survival (P = .008) times, respectively. The frequency of positive staining determined at relapse was significantly inversely related to the time from relapse to death (P = .0102). Similarly, when populations below and above the median relapse C219 score were compared with respect to the time from relapse to death, the population with C219 scores greater than the median had a significantly lower time from relapse to death (P = .006). It appears that this immunohistochemical methodology may be used as a predictor of remission time, survival time, and the time from relapse to death. Additional studies are required to confirm the usefulness of C219 as a true marker of P-glycoprotein and to evaluate P-glycoprotein as a useful prognostic factor in dogs with lymphoma.

Secondary and tertiary structure changes of reconstituted P-glycoprotein. A Fourier transform attenuated total reflection infrared spectroscopy analysis

The structure of purified P-glycoprotein functionally reconstituted into liposomes was investigated by attenuated total reflection Fourier transform infrared spectroscopy. A quantitative evaluation of the secondary structure and a kinetic of 2H/H exchange of the P-glycoprotein were performed both in the presence and in the absence of MgATP, MgATP-verapamil, and MgADP. This approach was previously shown to be a useful tool to detect tertiary structure changes resulting from the interaction between a protein and its specific ligands, as established for the Neurospora crassa H+-ATPase. 2H/H exchange measurements provided evidence that a large fraction of the P-glycoprotein is poorly accessible to the aqueous medium. Addition of MgATP induced an increased accessibility to the solvent of a population of amino acids, while addition of MgATP-verapamil resulted in a subtraction of a part of the protein from access to the aqueous solvent. No significant changes were observed upon addition of MgADP or verapamil alone. The secondary structure of P-glycoprotein was not affected by addition of ligands. The variations observed in the 2H/H exchange rate when P-glycoprotein interacted with the above ligands therefore represented tertiary structure changes. Fluorescence quenching experiments confirmed that MgATP-induced changes are to be found in the tertiary structure of the enzyme.

mdm2 gene mediates the expression of mdr1 gene and P-glycoprotein in a human glioblastoma cell line

The overexpression of the multidrug resistance (mdr1) gene and its product, P-glycoprotein (P-gp), is thought to limit the successful chemotherapy of human tumours. The mechanism by which mdr1 gene and P-gp are overexpressed in human tumours, however, is not yet clear. In this report, we show that the mdm2 (murine double minute 2) gene induced the expression of the mdr1 gene and P-gp in human glioblastoma U87-MG cells, which did not express the MDM2 protein or P-gp. The mdm2 gene, in addition, conferred the resistance of U87-MG cells to the apoptotic cell death induced by etoposide (VP-16) or doxorubicin. Furthermore, treatment with mdm2 antisense oligonucleotides inhibited the expression of P-gp in MDM2-expressing U87-MG cells. These findings suggest that the mdm2 gene may play an important role in the development of MDR phenotype in human tumours.

Quantitative analysis of multidrug resistance gene expression in human osteosarcomas

We evaluated the MDR1 expression levels in 77 osteosarcomas and investigated whether MDR1 mRNA expression in osteosarcomas varies with location within the tumour, following chemotherapy, or after metastasis. We modified the semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) assay to determine accurately the levels of MDR1 mRNA expression in clinical specimens. We show that specimens collected from multiple locations in six tumours revealed very little variation in MDR1 expression suggesting that the levels of MDR1 in these tumours do not vary greatly with location within the tumour mass. In a comparison of pre and post-chemotherapy specimens it was found that MDR1 levels did not change appreciably following chemotherapy in 16 of 20 cases. In addition, in eight of ten specimens obtained before and after metastasis, the amount of MDR1 mRNA was found to remain relatively constant despite metastatic spread. Thus, many osteosarcomas exhibited intrinsic expression of MDR1 mRNA before multidrug regimens which invariably included doxorubicin and, in most cases, MDR1 expression was not induced following chemotherapeutic treatment. Our results suggest that some osteosarcoma patients may have primary tumours which are resistant to doxorubicin. These individuals may benefit from different chemotherapeutic regimens, e.g. the addition of MDR reversal agents.

Immunohistochemical detection of P-glycoprotein in formalin-fixed and paraffin-embedded normal and neoplastic canine tissues

Expression of P-glycoprotein, a phylogenetically conserved integral plasma membrane protein, is implicated as one of the most important factors contributing to tumor cell multidrug resistance. Formalin-fixed, paraffin-embedded normal and neoplastic canine tissues were studied using an avidin-biotin complex technique employing three murine monoclonal antibodies (C494, C219, JSB-1) to different epitopes of the P-glycoprotein molecule. Evaluation of immunostaining of normal canine tissues revealed positive labeling detected by each antibody in the liver, proximal renal tubular epithelium, adrenal cortex, colonic epithelium, and capillary endothelial cells of the brain. A total of 166 tumors of epithelial or mesenchymal origin were evaluated for P-glycoprotein immunoreactivity. Hepatomas (4/4), colorectal adenomas (7/7), colorectal carcinomas (4/4), adrenal cortical adenomas (3/3), hemangiopericytomas (15/15), apocrine gland adenocarcinomas (4/5, 80%), and transitional cell carcinomas (2/2) consistently labeled with at least one of the antibodies. Histiocytomas (0/10), cutaneous plasma cell tumors (0/10), fibromas (0/3), fibrosarcomas (0/4), and leiomyomas (0/4) were uniformly negative with all antibodies. Malignant lymphomas (6/22, 27.3%), malignant melanomas (4/13, 30.8%), leiomyosarcomas (3/6, 50%), mammary gland carcinomas (12/19, 63.2%), mammary gland adenomas (3/9, 33.3%), squamous cell carcinomas (8/10, 80%), basal cell tumors (5/7, 71.4%), apocrine gland adenomas (1/2, 50%), cholangiocarcinomas (2/3, 66.7%), and thyroid gland carcinomas (2/4, 50%) gave variable results. The antibodies C494, JSB-1, and C219 labeled 66/166 (39.8%), 53/166 (31.9%), and 38/166 (22.9%) of all tumors studied, respectively. A total of 26/166 (15.7%), 22/166 (13.3%), and 37/166 (22.6%) of tumors were labeled by all three, just two, or one antibody alone, respectively. The antibody C494 was the only antibody labeling 28/166 (16.9%) of the cases. JSB-1 alone labeled 9/166 (5.4%) of the tumors. C219 failed to label any tumors not also labeled by either C494 or JSB-1. Labeling by C494 was more intense and specific than labeling by the other two antibodies. Results indicate that P-glycoprotein can be detected in routinely processed canine tissues. The detection of P-glycoprotein within canine liver, kidney, adrenal gland, and colon and within tumors arising from these tissues is consistent with that reported in the literature for human tissues. Variable labeling results of other tumors such as malignant lymphoma and mammary gland carcinomas also is consistent with reports of human studies. Detection of multidrug resistance markers such as P-glycoprotein in canine tissues may provide additional information upon which to base a prognosis or to design treatment regimens for canine tumors.

Therapeutic activity of CPT-11, a DNA-topoisomerase I inhibitor, against peripheral primitive neuroectodermal tumour and neuroblastoma xenografts

The anti-tumour activity of CPT-11, a topoisomerase I inhibitor, was evaluated in four human neural-crest-derived paediatric tumour xenografts; one peripheral primitive neuroectodermal tumour (pPNET) (SK-N-MC) and three neuroblastomas. Two models, SK-N-MC and IGR-N835, were established in athymic mice from a previously established in vitro cell line. Two new neuroblastoma xenograft models, IGR-NB3 and IGR-NB8, were derived from previously untreated non-metastatic neuroblastomas. They exhibited the classic histological features of immature neuroblastoma along with N-myc amplification, paradiploidy, chromosome 1p deletions and overexpression of the human mdr 1 gene. These tumour markers have been shown to be poor prognostic factors in children treated for neuroblastoma. CPT-11 was tested against advanced stage subcutaneous tumours. CPT-11 was administered i.v. using an intermittent (q4d x 3) and a daily x 5 schedule. The optimal dosage and schedule was 40 mg kg-1 daily for 5 days. At this highest non-toxic dose, CPT-11 induced 100% tumour-free survivors on day 121 in mice bearing the pPNET SK-N-MC xenograft. For the three neuroblastoma xenografts, 38-100% complete tumour regressions were observed with a tumour growth delay from 38 to 42 days, and anti-tumour activity was clearly sustained at a lower dosage (27 mg kg-1 day-1). The efficacy of five anti-cancer drugs commonly used in paediatric oncology or in clinical development was evaluated against SK-N-MC and IGR-N835. The sensitivity of these two xenografts to cyclophosphamide, thiotepa and cisplatin was of the same order of magnitude as that of CPT-11, but they were refractory to etoposide and taxol. In conclusion, CPT-11 demonstrated significant activity against pPNET and neuroblastoma xenografts. Further clinical development of CPT-11 in paediatric oncology is warranted.

Characterization and epitope mapping of several new anti-P-glycoprotein monoclonal antibodies

Monoclonal antibodies (MAbs) were raised against partially purified Class I P-glycoprotein from multidrug-resistant Chinese hamster ovary CHRB30 cells. Fifteen stable monoclonal hybridoma cell lines were established, and the secreted antibodies were classified into 8 groups on the basis of banding pattern on immunoblots of P-glycoprotein digested with cyanogen bromide or partially digested with proteases. One representative of each group was tested further for several activities. Six of the 8 recognized human P-glycoprotein in the multidrug-resistant SKVLBI cell line. None of the antibodies recognized P-glycoprotein in unfixed cells, suggesting that all recognize cytoplasmic epitopes or extracellular epitopes not accessible in native P-glycoprotein. All 8 antibodies were able to immunoprecipitate P-glycoprotein from non-denaturing detergent solution. The linear epitopes of the antibodies were mapped to 11-27 amino acids. Two of the antibodies had epitopes in the linker region, 3 in the N-terminal nucleotide binding domain, 2 in the C-terminal nucleotide binding domain and 1 in the predicted cytoplasmic loop between predicted transmembrane helices 8 and 9. These antibodies, with known epitopes, could have uses for P-glycoprotein detection, structure/function studies, purification and quantitation.

p53 and P-glycoprotein are often co-expressed and are associated with poor prognosis in breast cancer

Expression of both P-glycoprotein (P-gp) and mutant p53 have recently been reported to be associated with poor prognosis of breast cancer. The expression of P-gp is associated in vitro and in vivo with cross-resistance to several anti-cancer drugs. p53 plays a regulatory role in apoptosis, and mutant p53 has been suggested to be involved in drug resistance. Interestingly, in vitro experiments have shown that mutant p53 can activate the promoter of the MDR1 gene, which encodes P-gp. We investigated whether p53 and P-gp are simultaneously expressed in primary breast cancer cells and analysed the impact of the co-expression on patients prognosis. Immunohistochemistry was used to investigate P-gp expression (JSB-1, C219) and nuclear p53 accumulation (DO-7) in 20 operable chemotherapy untreated and 30 locally advanced breast cancers undergoing neoadjuvant chemotherapy with doxorubicin and cyclophosphamide. Double immunostaining showed that P-gp expression and nuclear p53 accumulation often occur concomitantly in the same tumour cells. A correlation between p53 and P-gp expression was found in all 50 breast cancers (P = 0.003; Fisher's exact test). P-gp expression, nuclear p53 accumulation, and co-expression of p53 and P-gp were more frequently observed in locally advanced breast cancers than in operable breast cancers (P = 0.0004, P = 0.048; P = 0.002 respectively. Fisher's exact test). Co-expression of p53 and P-gp was the strongest prognostic factor for shorter survival by multivariate analysis (P = 0.004) in the group of locally advanced breast cancers (univariate analysis: P = 0.0007). Only 3 out of 13 samples sequentially taken before and after chemotherapy displayed a change in P-gp or p53 staining. In conclusion, nuclear p53 accumulation is often associated with P-gp expression in primary breast cancer, and simultaneous expression of p53 and P-gp is associated with shorter survival in locally advanced breast cancer patients. Co-expression of P-gp and mutant p53 belong to a series of molecular events resulting in a more aggressive phenotype, drug resistance and poor prognosis.

Molecular mechanisms of multidrug resistance in cancer chemotherapy

The occurrence of multidrug resistance (MDR) is one of the main obstacles in the successful chemotherapeutic treatment of cancer. MDR cell lines are resistant to the so-called naturally occurring anti-cancer drugs, such as anthracyclines, Vinca alkaloids and epipodophyllotoxins, but are not cross-resistant to alkylating agents, antimetabolites and cisplatin. So far, three separate forms of MDR have been characterized in more detail: classical MDR, non-Pgp MDR and atypical MDR. Although all three MDR phenotypes have much in common with respect to cross-resistance patterns, the underlying mechanisms certainly differ. Atypical MDR is associated with quantitative and qualitative alterations in topoisomerase II alpha, a nuclear enzyme that actively participates in the lethal action of cytotoxic drugs. Atypical MDR cells do not overexpress P-glycoprotein, and are unaltered in their ability to accumulate drugs. In this review we will focus on classical and non-Pgp MDR. The molecular mechanism of classical and non-Pgp MDR is transcriptional activation of membrane-bound transport proteins. These transport proteins belong to the ATP-binding cassette (ABC) superfamily of transport systems. The classical MDR phenotype is characterized by a reduced ability to accumulate drugs, due to activity of an energy-dependent uni-directional, membrane-bound, drug-efflux pump with broad substrate specificity. The classical MDR drug pump is composed of a transmembrane glycoprotein (P-glyco-protein-Pgp) with a molecular weight of 170 kD, and is, in man, encoded by the so-called multidrug resistance (MDR1) gene. Typically, non-Pgp MDR has no P-gly-coprotein expression, yet has about the same cross-resistance pattern as classical MDR. This non-Pgp MDR phenotype is caused by overexpression of the multidrug resistance-associated protein (MRP) gene, which encodes a 190 kD membrane-bound glycoprotein (MRP). MRP probably works by direct extrusion of cytotoxic drugs from the cell and/or by mediating sequestration of the drugs into intracellular compartments, both leading to a reduction in effective intracellular drug concentrations. For the classical MDR phenotype, evidence is accumulating that it plays a role indeed, in clinical drug resistance, especially in some hematological malignancies (acute myeloid leukemia, multiple myeloma and non-Hodgkin's lymphoma) and solid tumors (soft tissue sarcomas and neuroblastoma). The association of MRP with clinical drug resistance has not been elaborated, yet, and studies on MRP expression in human cancer have just begun. We found that overexpression of MRP, as determined by RNase protection assay as well as by immunohistochemistry, occurs in several human cancers, among which are cancer of the lung, esophagus, breast and ovary, and leukemias. Further studies are indicated to establish whether elevated MRP expression at diagnosis is an unfavorable prognostic factor for clinical outcome of chemotherapy.

Immunohistochemical localization of P-glycoprotein and expression of the multidrug resistance-1 gene in human pancreatic cancer: relevance to indicator of better prognosis

We investigated immunohistochemical localization of P-glycoprotein (P-gp) on paraffin-embedded sections from 103 cases of previously untreated pancreatic tumors and also analyzed multidrug resistance-1 (MDR1) gene expression by polymerase chain reaction after reverse transcription in 35 cases. High positive staining for P-gp was observed in 72.8% of pancreatic tumors and in 73.2% of ductal adenocarcinoma. In ductal adenocarcinoma, immunoreactivity of P-gp was inversely correlated with biological aggressiveness of tumors determined by histologic grading (P<0.01), tumor size (P < 0.01), retroperitoneal invasion (P < 0.01) and portal invasion (P < 0.05). Expression of the MDR1 gene was detected in all the pancreatic tumors examined and was significantly higher than that in normal pancreas (P < 0.05). The levels of MDR1 mRNA showed a moderate correlation with those of P-gp (r=0.62, P<0.0001). Higher expression levels of MDR1/P-gp significantly correlated with better prognosis of patients with ductal carcinoma (P < 0.05). Among patients with ductal carcinoma, the high staining group for P-gp revealed a 3.5-fold better prognosis compared with the low staining group (HR=3.47, 95% CI=1.62, 7.45; P=0.0016). In conclusion, MDR1 gene/P-gp expression in pancreatic cancer without chemotherapy inversely correlates with biological aggressiveness and is an independent indicator of favorable prognosis.

Serum can inhibit reversal of multidrug resistance by chemosensitisers

The purpose of this study was to evaluate to what extent the ability of various chemosensitisers (CS) to reverse P-glycoprotein-associated multidrug resistance (MDR) is reduced when tested in physiological serum protein concentrations. Utilising drug sensitivity and accumulation assays, the CS were tested in medium containing 10% fetal bovine serum and in 100% horse or human serum. Two RPMI 8226 human myeloma sublines were used which express different levels of P-glycoprotein. The CS were tested at various concentrations, including clinically achievable blood levels. When using the CS at high doses, wide differences were observed in the extent CS activity was diminished by serum. Verapamil, cyclosporin A and quinine were not affected, quinidine and medroxyprogesterone acetate were moderately inhibited, and amiodarone and trifluoperazine were largely inactivated. When the CS were used at concentrations achievable in humans, the activity of all agents except quinine was markedly reduced by serum. With respect to the extent to which CS activity was diminished by serum, good statistical correlation (r > 0.90, P < 0.001) was found between the use of cytotoxicity and drug accumulation assays, horse and human serum or cell lines with high and low levels of P-glycoprotein, respectively. These studies demonstrated that physiological serum protein concentrations can profoundly diminish the MDR reversing activity of particular CS. Some drugs, such as amiodarone and trifluoperazine, are largely inactivated by serum when used at a wide range of concentrations. Other agents, such as verapamil and cyclosporin A, are essentially unaffected when used at high doses but markedly inhibited at concentrations achievable in humans. These data suggest that in vitro studies of CS in medium containing low serum protein concentrations can result in misleading conclusions regarding the potential clinical activity of such agents.

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.

Experimental models for the study of drug resistance in osteosarcoma: P-glycoprotein-positive, murine osteosarcoma cell lines

P-glycoprotein is an adenosine triphosphate-dependent drug-efflux pump that extrudes drugs from cells and causes drug-resistance. P-glycoprotein is believed to mediate drug-resistance in a wide variety of tumors. In this study, we developed two P-glycoprotein-positive, murine osteosarcoma cell lines that were resistant to Adriamycin (doxorubicin) (MOS/ADR1 and MOS/ADR2). We created the cell lines by short-term pulse exposures of the parent cell line to Adriamycin followed by single-cell cloning. The MOS/ADR1 and MOS/ADR2 cells were sevenfold and eighteenfold more resistant to Adriamycin than the cells from the parent line. Expression of P-glycoprotein, as examined with an immunofluorescence method, was detected in most of the MOS/ADR1 and MOS/ADR2 cells but not in the parent cells. After the cells had been incubated with Adriamycin for one hour, there was less accumulation of the drug in the resistant cell lines than in the parent cell line. The reduced accumulation was due to the increased efflux of Adriamycin. The Adriamycin-resistant cell lines demonstrated greater alkaline phosphatase activity than the parent cell line and produced more differentiated osteoblastic sarcomas in mice. Dose survival studies with use of a tetrazolium colorimetric assay showed that the MOS/ADR1 cells were cross-resistant to vincristine, vinblastine, etoposide, bleomycin, mitomycin C, and actinomycin D but not to dacarbazine, cisplatin, carboplatin, cytosine arabinoside, carmustine, cyclophosphamide, ifosfamide, methotrexate, and 5-fluorouracil. Although the MOS/ADR2 cells exhibited a similar spectrum of cross-resistance, they were more resistant than the MOS/ADR1 cells. We also tested the effect of three different resistance-modifying agents on the reversal of resistance to Adriamycin. We found that verapamil and trifluoperazine substantially reversed resistance to Adriamycin in the P-glycoprotein positive cell lines, whereas cyclosporin A was relatively ineffective. Because these cell lines retain the histological and biochemical features of bone-producing sarcomas and display the multidrug-resistant phenotype, they may be useful models for additional investigations of drug resistance in osteosarcoma.

HMG-CoA reductase mediates the biological effects of retinoic acid on human neuroblastoma cells: lovastatin specifically targets P-glycoprotein-expressing cells

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, involved in de novo cholesterol synthesis and cell-cycle progression, was identified as a potential mediator of the growth inhibitory effects of retinoic acid on human neuroblastoma. Lovastatin, a nonreversible inhibitor of HMG-CoA reductase, induced extensive cytotoxicity that was restricted to drug-resistant P-glycoprotein-expressing neuroblastoma cell lines. This response was potentiated by dibutyryl cyclic AMP but not retinoic acid. Patients with advanced-stage metastatic neuroblastoma often display an acquired chemoresistant phenotype, which may in part be mediated by P-glycoprotein. Our studies support the application or use of HMG-CoA reductase inhibitors as potential therapeutic agents in the treatment of these patients who are refractory to chemotherapy.

Metastatic neuroblastoma in children older than one year: prognostic significance of the initial metaiodobenzylguanidine scan and proposal for a scoring system

BACKGROUND

Metaiodobenzylguanidine (mIBG) is a guanethidine analog that has demonstrated a high sensitivity and specificity in detecting bone metastases in about 90% of metastatic neuroblastomas. However, the predictive value of initial mIBG scan in neuroblastoma patients older than 1 year of age regarding response to initial chemotherapy has yet to be ascertained. Therefore, a scoring system for grading the positivity of mIBG scans was devised and applied in a retrospective study in an attempt to determine whether this score had a prognostic value in neuroblastoma patients older than 1 year of age at diagnosis.

METHODS

Eighty-six children, older than 1 year of age, with metastatic neuroblastomas were homogeneously treated and had a mIBG scan performed at diagnosis and following the induction regimen to assess bone metastases. Each mIBG scan was assigned a reproducible score and the predictive value of the initial mIBG score was assessed in order to evaluate response to induction regimen.

RESULTS

The relative risk of failing to achieve complete remission after four courses of induction therapy was 6.9 times higher in patients who had more than four mIBG spots at diagnosis. A multivariate analysis including the established prognostic factors revealed that the initial mIBG score was the only significant factor (P < 0.001).

CONCLUSIONS

The initial mIBG scan is of prognostic significance to predict response to chemotherapy for metastatic neuroblastoma in children older than 1 year of age. A prospective study comparing this initial mIBG score with other recently established prognostic factors is warranted.

Expression of the gene for multidrug-resistance-associated protein and outcome in patients with neuroblastoma

BACKGROUND

Overexpression of the gene for the multidrug-resistance-associated protein (MRP) has been linked with resistance to chemotherapeutic agents (multidrug resistance) in vitro. The expression of MRP by neuroblastoma cells correlates with N-myc oncogene amplification, a well-established prognostic indicator in patients with neuroblastoma.

METHODS

To relate MRP gene expression to established prognostic markers and the clinical outcome of neuroblastoma, we analyzed MRP expression in specimens of primary tumors from 60 patients with neuroblastoma.

RESULTS

Levels of MRP gene expression were significantly higher in tumors with N-myc amplification than in tumors without such amplification (P < 0.001). High levels of MRP expression were strongly associated with reductions in both survival and event-free survival (P < 0.001) in the overall study population and in subgroups of patients without N-myc amplification and patients with localized disease. For the overall study population, the five-year cumulative survival rates in the groups with high and low levels of MRP expression were 57 percent (95 percent confidence interval, 37 to 78 percent) and 94 percent (95 percent confidence interval, 86 to 100 percent), respectively. In contrast, expression of the MDR1 multi-drug-resistance gene was not predictive of survival or event-free survival. After adjustment by multivariate analysis for the effects of N-myc amplification and other prognostic indicators, high levels of MRP expression retained significant prognostic value for poor survival (relative hazard, 14.9; P = 0.01) and poor event-free survival (relative hazard, 9.7; P = 0.004), whereas N-myc amplification had no prognostic value.

CONCLUSIONS

High levels of MRP gene expression in patients with neuroblastoma correlate strongly with poor outcome. The findings suggest that expression of this multidrug-resistance gene accounts for the association between N-myc amplification and reduced survival.

Sequential assessment of multidrug resistance phenotype and measurement of S-phase fraction as predictive markers of breast cancer response to neoadjuvant chemotherapy

BACKGROUND

The authors examined the relevance of S-phase fraction (SPF) and multidrug resistance (MDR) phenotype as predictive tests of breast cancer response in a series of patients treated by conventional doses of neoadjuvant chemotherapy with (FAC) or without (FTC) doxorubicin.

METHODS

Fine needle samplings of tumors were used to measure SPF by flow cytometry before treatment (Day 0), and to assess the MDR phenotype using semiquantified reverse transcriptase polymerase chain reaction and immunocytochemistry, before and after (Days 8 and 28) the first cycle of chemotherapy.

RESULTS

Measurement of SPF before treatment was significantly associated with clinical response, but sequential assessment of MDR phenotype identified three groups of tumors with distinct outcomes: (1) tumors with a positive and constant expression of MDR1, in which prediction of resistance was restricted to patients treated by FAC; (2) tumors without any detectable expression, in which resistance to FAC or FTC treatments was rarely observed; and (3) tumors with an early (Day 8) acquired or increased MDR1 gene expression, which were always resistant to therapy to both treatment regimens. These results were confirmed at the protein level.

CONCLUSIONS

Sequential assessment of MDR phenotype is a relevant tool for monitoring breast cancer response in neoadjuvant chemotherapy.

Modulation of multidrug resistance with antisense oligodeoxynucleotide to mdr1 mRNA

BACKGROUND

P-glycoprotein (pgp), a 170-kDa adenosine triphosphate-dependent membrane drug efflux pump encoded by the mdr1 gene, mediates cross-resistance in tumor cells to structurally unrelated cancer drugs. We investigated the capacity for modulating multidrug resistance by selectively inhibiting synthesis of Pgp using an antisense oligodeoxynucleotide complementary to the initiation codon of mdr1 messenger RNA.

METHODS

By continuous culture of K562 in 100 nM vincristine, a resistant cell line, K562/VCR100, was derived with high expression of Pgp (95.9% of cells) and an IC50 40-fold greater than that of the parental cell line. The K562/VCR100 cells were treated with 10 microM of 15-mer antisense and sense phosphorothioate oligodeoxynucleotides. Modulation of multidrug resistance was analyzed using a daunorubicin/tritiated thymidine incorporation assay and flow cytometric assessment of cellular rhodamine 123 accumulation.

RESULTS

Treatment of K562/VCR100 with the antisense oligodeoxynucleotide led to a doubling in daunorubicin growth inhibition at 1 microgram/ml and a tripling of growth inhibition at 0.6 micrograms/ml (p < 0.0023); a 58% reduction in the daunorubicin IC50 (p < 0.02); and an increased rate of rhodamine-123 accumulation (p = 0.02) compared with treatment with sense oligodeoxynucleotide or media controls.

CONCLUSIONS

These results suggest that antisense oligodeoxynucleotides may serve as a useful adjunct in the treatment and prevention of multidrug resistance during cancer chemotherapy.

p-Glycoprotein expression as a predictor of breast cancer recurrence

BACKGROUND

Many new prognostic factors for breast cancer have been described, and yet the ability to predict patient outcomes remains poor. Overexpression of p-glycoprotein (p-gp), the multidrug resistance efflux pump, confers a worse prognosis to patients with certain leukemias and other tumors. The purpose of this study was to analyze the potential usefulness of p-gp expression as a prognostic factor in patients with breast cancer.

METHODS

Paraffin blocks were obtained from 55 previously untreated patients who underwent surgery between 1987 and 1988. To determine p-gp expression, tumor cell suspensions were incubated with the p-gp-specific C219 monoclonal antibody and analyzed using an indirect immunofluorescent flow cytometric assay.

RESULTS

Twenty-four (44%) of the tumors were p-gp positive and 31 (56%) were p-gp negative. Among the p-gp positive patients, 65% had recurrence of their disease, whereas only 13% of the p-gp negative patients experienced recurrence (p = 0.0001). The 5-year disease-free rate for p-gp positive patients was 39% compared with 83% for p-gp negative patients (p = 0.0001). In univariate analysis examining 10 different variables, significant predictors of recurrence were p-gp, stage, and tumor size. Multivariate analysis using Cox Proportional Hazards regression showed that only p-gp and stage were significant independent predictors of recurrence (p = 0.0002).

CONCLUSIONS

p-gp is frequently expressed in patients with untreated breast cancer, with p-gp-positive patients being at significantly greater risk for disease recurrence. p-gp appears to be a useful prognostic factor in breast cancer and could potentially help guide management.