Reactivity of P-Glycoprotein Monoclonal Antibodies in Childhood Cancers

P-glycoprotein expression, tumor weight, age, and relapse in patients with stage I and II favorable-histology Wilms' tumor

Fifteen percent of patients with Wilms' tumor (WT) experience relapse. It has been suggested that weight and age may affect the chances of relapse. Few studies have investigated the role, if any, between P-glycoprotein (P-gp) and relapse. The authors assessed the prognostic value of tumor weight and age at diagnosis and asked whether some other potential biological markers, specifically P-gp protein expression, had a prognostic value in favorable-histology WT. No association between age and relapse could be found. Patients with tumor weight ≥550 g were 6 times more likely to relapse, whereas P-gp expression was positive in 18/40 (45%) of the patients, of which 10/12 (83.3%) relapsed and 8/28 (28.6%) did not. Further studies are necessary to elucidate whether or not P-gp is related to relapse in patients with histologically favorable Wilms' tumor. If confirmed, the protein may be used in the future as a target for new drugs and treatments for this group of patients.

Pharmacokinetic interactions of cyclosporine with etoposide and mitoxantrone in children with acute myeloid leukemia

The purpose of this study was to assess the effect of the multidrug resistance modulator cyclosporine (CsA) on the pharmacokinetics of etoposide and mitoxantrone in children with de novo acute myeloid leukemia (AML). Serial blood samples for pharmacokinetic studies were obtained in 38 children over a 24-h period following cytotoxin treatment with or without CsA on days 1 and 4. Drug concentrations were quantitated using validated HPLC methods, and pharmacokinetic parameters were determined using compartmental modeling with an iterative two-stage approach, implemented on ADAPT II software. Etoposide displayed a greater degree of interindividual variability in clearance and systemic exposure than mitoxantrone. With CsA treatment, etoposide and mitoxantrone mean clearance declined by 71% and 42%, respectively. These effects on clearance, in combination with the empiric 40% dose reduction for either cytotoxin, resulted in a 47% and 12% increases in the mean AUC for etoposide and mitoxantrone, respectively. There were no differences in the rates of stomatitis or infection between the two groups. CsA treatment resulted in an increased incidence of hyperbilrubinemia, which rapidly reversed upon conclusion of drug therapy. The variability observed in clearance, combined with the empiric 40% dose reduction of the cytotoxins, resulted in statistically similar systemic exposure and similar toxicity.

Nephroblastoma: multidrug-resistance P-glycoprotein expression in tumor cells and intratumoral capillary endothelial cells

The development of chemoresistance in a variety of cancers seems related to overexpression of the P-glycoprotein (P-gp) drug pump. Nephroblastoma, the most common malignant renal tumor of childhood, usually is responsive to treatment, and prognosis is favorable in most cases. However, the disease in a subset of patients is refractory to treatment, and the disease follows an aggressive course. To study P-gp expression in this tumor and its correlation with outcome, tumor samples from 93 patients were examined by immunohistochemical analysis. P-gp expression was determined separately in both tumor cells and intratumoral capillary endothelium. The likelihood ratio test, the Kaplan-Meier method, and the log-rank test were used to evaluate its association with clinical course, grade, stage, and administration of preoperative chemotherapy. The results for the majority of nephroblastomas were variably positive; in 43 (46%) of them, newly formed capillary endothelial cells also stained positive. While no association of P-gp expression in tumor cells with clinical course, stage, and grade could be demonstrated, positivity in endothelial cells correlated significantly with unfavorable outcome, suggesting that chemoresistance depended on an active blood-tumor barrier. Previous chemotherapy induced P-gp overexpression in tumor cells.

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.

Multiple drug resistance mediated by P-glycoprotein is not a major factor in a slow response to therapy in childhood ALL

In childhood acute lymphoblastic leukemia (ALL), early response to treatment is an important prognostic factor and drug resistance is a major cause of poor outcome. One of the most investigated resistance mechanisms is P-glycoprotein (P-gp)-mediated multiple drug resistance (MDR). We analyzed P-gp using flow cytometry with monoclonal antibody JSB1 in a series of 118 children with ALL, 103 at diagnosis and 15 at relapse. Increased P-gp expression was found in 55 (53%) patients at diagnosis and in 11 (73%) at relapse. We also analyzed the bone marrow aspirate slides for early response to treatment in a central review. No correlation was found between P-gp and early response. Patients with T-ALL had higher P-gp levels than the others, 5.3% versus 1.0% (P = .002). We conclude that P-gp-mediated multiple drug resistance is not a factor in a slow response to ALL induction therapy.

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.

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.

Expression of resistance-related proteins in nephroblastoma after chemotherapy

Tumor tissues of untreated and cytostatic-agent-treated patients with nephroblastomas were investigated for expression of resistance-related proteins (P-glycoprotein, glutathione S-transferase-pi, glutathione peroxidase and topoisomerase II) to ascertain whether resistance proteins are changed after treatment. Tumor tissue was analyzed by means of mRNA. Twenty-three children were treated with actinomycin D and vincristine for 4 to 8 weeks. Eight children received no preoperative chemotherapy. In untreated patients, no expression of P-glycoprotein was seen, whereas, in the patients who were treated with actinomycin D and vincristine, 12 out of 23 tumors showed increased P-glycoprotein expression (> mean value). Although we found no difference between treated and untreated tumors for glutathione S-transferase-pi, we found significant differences in the expression of glutathione peroxidase. In the 8 untreated patients, 7 tumors showed low glutathione peroxidase (< mean value) and one high (> mean value) glutathione-peroxidase-mRNA content. With treatment, 11 tumors expressed low levels and 12 tumors high levels of mRNA. A significant positive correlation between P-glycoprotein and glutathione peroxidase was found. In addition, of the 8 untreated patients, 2 had low topoisomerase-II expression, and 6 high expression. With treatment, the expression was reduced in 18 tumors, and only 5 tumors had high levels of this protein. These results were confirmed by PCR and immunohistochemistry.

Expression of mdr1/P-glycoprotein and p110 in neuroblastoma

Overexpression of the multidrug resistance gene, mdr1, and its product, P-glycoprotein (Pgp), has been associated with cross-resistance to structurally unrelated compounds in cell lines and tumours. Recently, a non-Pgp-mediated form of drug resistance has been described, due to the overexpression of p110, a transport protein. Thirty formalin-fixed, paraffin-embedded neuroblastoma samples from 21 cases were examined for overexpression of mdr1 and Pgp using newly established non-radioactive in situ hybridization and sensitive immunocytochemical techniques. Tumours were examined from patients with all the stages of disease and from primary and metastatic sites. Paired tumour samples (pre-chemotherapy and post-chemotherapy) were available from cases with stage 2 (n = 1) and stage 4 disease (n = 8). Immunoreactivity to p110 was also tested on all the samples. Mdr1 mRNA was expressed in 16/21 cases and in all the stages. Pgp immunoreactivity was detected in all the cases. Weak cytoplasmic immunoreactivity to p110 was seen in the ganglion cells in 12/21 cases. The expression of mdr1, Pgp, and p110 showed a statistically significant (two-sided Fisher exact test, P = 0.04, 0.03, 0.04, respectively) correlation with differentiation (Beckwith and Martin grading) but there was no correlation with survival. Pgp immunoreactivity also showed a significant correlation with favourable clinical variables: age less than 1 year at diagnosis and stages 1, 2, and 4 s (two-sided Fisher exact test, P = 0.01, 0.005, respectively).

P-glycoprotein status of favorable-histology Wilms' tumor predicts treatment outcome

Patients with advanced-stage favorable-histology (FH) Wilms' tumor have a 4-year relapse-free survival rate of 70% to 90% after resection and chemotherapy of actinomycin D, vincristine, and doxorubicin. These three agents are actively pumped out of cells by P-glycoprotein (Pgp). The authors studied whether Wilms' tumor expresses Pgp and if the degree of Pgp expression correlates with treatment outcome. At the time of diagnosis, eight blinded paraffin-embedded FH and four anaplastic (ANA) Wilms' tumor sections were immunogold-labeled with a Pgp monoclonal antibody (17F9). Four of the FH-tumor patients had had relapse (FH+) according to the National Wilms' Tumor Study-3 protocol. Negative-relapse FH-tumor patients (FH-) had at least 6 years of follow-up. All 12 Wilms' tumors stained positive for Pgp. Both differentiated tubular structures and blastemal elements expressed Pgp. By the pathologist's score and the computerized cell image analysis, the degree of Pgp staining was greater at the time of diagnosis in FH+ tumors than in FH- tumors (P < .03; Mann-Whitney test). There was no statistically significant difference between ANA and FH+ or FH- tumors. These results show that both FH and ANA Wilms' tumors express Pgp, with higher levels of Pgp expression found in FH patients who had relapse. Current chemotherapeutic protocols, using Pgp-sensitive agents, may not be optimal for all FH Wilms' tumor patients.