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

N-myc over-expression downregulates alpha3beta1 integrin expression in human Saos-2 osteosarcoma cells

Alterations in adhesion to the extracellular matrix mediated by integrin receptors are commonly observed in a wide variety of transformed/tumor classes. Reductions in the expression of several integrin subunits have been documented in human neuroblastoma cell lines that over-express the neuroblastoma-associated oncogene N-myc. Neuroblastoma cells transfected with a cDNA encoding N-myc on a high-expression plasmid exhibit greatly reduced levels of alpha2, alpha3 and beta1 integrin subunits with concomitant rounding of cells on substrata. In the current studies, we examined whether integrin downregulation by N-myc is cell-type specific by transfecting a human N-myc cDNA into Saos-2 human osteosarcoma cells and evaluating integrin expression. Several N-myc-expressing cell lines were isolated which exhibit reduced levels of beta1 integrin subunit protein and significant alteration in cell morphology - these cell lines resemble N-myc-over-expressing neuroblastoma cells. In addition to reduced beta1 subunit levels, the osteosarcoma-derived N-myc transfectants exhibit little or no alpha3beta1 integrin complexes, either intracellular or at the cell surface. Finally, reduced amounts of alpha3 integrin subunit in these cell lines occur at the level of alpha3 integrin mRNA, although post-transcriptional mechanisms may also be involved, particularly with inability of pre-beta1 protein to mature. These results confirm our previous studies demonstrating integrin downregulation by an N-myc-dependent process and, in addition, demonstrate lack of cell-type specificity in the action of N-myc on integrin extracellular matrix receptor expression when comparing neural precursor (neuroblastoma) cells with connective tissue (osteosarcoma) cells.

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.

Genetic staging of unresectable or metastatic neuroblastoma in infants: a Pediatric Oncology Group study

BACKGROUND

Current staging systems for unresectable or metastatic neuroblastoma do not reliably predict responses to chemotherapy in infants under 1 year of age. Previous studies have indicated that the DNA content, or ploidy, of malignant neuroblasts can discriminate between good and poor responders in this group of patients, but the clinical utility of ploidy assessment has remained in question.

PURPOSE

We tested, in a prospective nonrandomized study, the hypothesis that neuroblast ploidy could be used as the sole guide for treatment selection in infants with unresectable or metastatic tumors and could differentiate between those who would respond to our previous standard regimen and those who would benefit from an immediate switch to another therapy.

METHODS

One hundred seventy-seven infants were enrolled in this trial. Five of these infants were subsequently excluded (two ineligible, two lacking ploidy information, and one protocol violation); therefore, 172 patients were included in the study. One hundred thirty infants with hyperdiploid tumors (DNA index > 1.0; better prognosis in retrospective studies) were treated with a well-tolerated regimen of cyclophosphamide (150 mg/m2 per day orally or intravenously on days 1-7) and doxorubicin (35 mg/m2 intravenously on day 8). Forty-two infants with diploid tumors (DNA index = 1.0; worse prognosis in retrospective studies) received cisplatin (90 mg/m2 intravenously on day 1) and teniposide (100 mg/ m2 intravenously on day 3) after an initial course of cyclophosphamide plus doxorubicin. Statistical end points were response and long-term survival. In addition, we assessed within each ploidy group (i.e., patients with hyperdiploid tumors and those with diploid tumors) the prognostic significance of NMYC gene copy number, tumor stage, and other variables commonly measured in this disease.

RESULTS

Of the 127 assessable infants with hyperdiploid tumors, 115 (91%) had complete responses--85 after receiving five courses of cyclophosphamide plus doxorubicin and 30 after receiving further therapy including cisplatin plus teniposide. The 3-year survival estimate for the entire hyperdiploid group was 94% (95% confidence interval [CI] = 89%-98%). Nineteen (46%) of 41 assessable infants with diploid tumors were complete responders. The overall 3-year survival estimate for this group was 55% (95% CI = 39%-70%). Prognostic factor analysis indicated that NMYC gene amplification and an elevated serum lactate dehydrogenase level were statistically significant markers of higher risk disease within the diploid group (two-sided P values of .005 and .003, respectively). Only NMYC was predictive in the hyperdiploid group (P = .003).

CONCLUSION

Use of a prognostic staging system based on tumor cell ploidy, augmented with the NMYC gene copy number and serum level of lactate dehydrogenase, would very likely improve the treatment of infants with unresectable or metastatic neuroblastoma. Patients with diploid tumors characterized by an amplified NMYC locus represent a particularly unfavorable risk group that may benefit from innovative new therapies.

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 drug-selectable genes: a new concept in gene therapy

Chemoresistance genes, initially considered to be a major impediment to the successful treatment of cancer, may become useful tools for gene therapy of cancer and of genetically determined disorders. Various target cells are rendered resistant to anticancer drugs by transfer of chemoresistance genes encoding P-glycoprotein, the multidrug resistance-associated protein-transporter, dihydrofolate reductase, glutathione-S-transferase, O6-alkylguanine DNA alkyltransferase, or aldehyde reductase. These genes can be used for selection in vivo because of the pharmacology and pharmacokinetics of their substrates. In contrast, several other selectable marker genes conferring resistance to substrates like neomycin or hygromycin can only be utilized in tissue culture. Possible applications for chemoresistance genes include protection of bone marrow and other organs from adverse effects caused by the toxicity of chemotherapy. Strategies have also been developed to introduce and overexpress nonselectable genes in target cells by cotransduction with chemoresistance genes. Thereby expression of both transgenes can be increased following selection with drugs. Moreover, treatment with chemotherapeutic agents should restore transgene expression when or if expression levels decrease after several weeks or months. This approach may improve the efficacy of somatic gene therapy of hematopoietic disorders which is hampered by low or unstable gene expression in progenitor cells. In this article we review preclinical studies in tissue culture and animal models, and ongoing clinical trials on transfer of chemoresistance genes to hematopoietic precursor cells of cancer patients.

Expression of the multidrug resistance-associated protein (MRP) gene in colorectal carcinomas

To determine the clinical significance of MRP in patients with colorectal carcinomas, we have studied the expression of the MRP gene by reverse transcription-polymerase chain reaction (RT-PCR) (n = 105) and by immunohistochemistry (n = 30). MRP mRNA expression was observed in 92 (88%) tumour specimens. Positive MRP staining with monoclonal antibodies QCRL-1 and QCRL-3 was detected in all samples studied with strong staining in seven (23%) and weak staining in 23 (77%) specimens. Strong MRP staining in these samples did not appear to be related to the age and sex of the patients, localization of the primary tumour, histological grade, tumour size, lymph node metastasis, distant metastasis and tumour stage. Strong MRP staining was not associated with MDR1 RNA or P-glycoprotein (P-gp) expression. Kaplan-Meier curves revealed that overall survival of patients with strong MRP-staining tumours was similar to the survival of patients with weak-staining tumours. These data indicate that the MRP gene is expressed in primary colorectal carcinomas but is neither related to known prognostic factors nor a prognostic factor by itself.

Expression of the multidrug resistance-associated protein (MRP) gene in urothelial carcinomas

The intrinsic or acquired resistance of urothelial cancer to chemotherapy is one major obstacle to successful treatment. Generally, the expression level of P-glycoprotein in urothelial cancer is low, so we accordingly investigated the expression of multidrug resistance-associated protein (MRP). We examined the expression of MRP mRNA by means of slot-blotting samples of 11 renal pelvic and/or ureteral tumors, 33 bladder tumors, one lung metastasis from a ureter tumor, 7 non-cancerous urothelia from patients with transitional-cell carcinoma (TCC) and one urothelium from a patient with renal-cell carcinoma (RCC). We also estimated, by Southern blotting, whether or not the MRP gene was amplified in clinical specimens that overexpressed MRP mRNA. MRP was detected immunohistochemically using a polyclonal antibody against MRP. In all, 5 of 11 renal pelvic and/or ureter tumors (45.5%), 17 of 33 bladder tumors (51.5%) and 4 of 7 non-cancerous urothelia of TCC patients (57.1%) expressed more than 2-fold the MRP mRNA levels of drug-sensitive human KB cells. There was no significant difference in the MRP mRNA level between primary and recurrent tumors. Low-grade urothelial carcinomas (G1 and G2 TCCs) expressed significantly higher levels of MRP mRNA than the high-grade G3 TCC. The MRP gene was not amplified in urothelial carcinomas, irrespective of their expression levels of MRP mRNA. Immunohistochemically, MRP was located mainly on the plasma membrane, but also detected on the cytoplasm of cancer cells. MRP may be one mechanism responsible for intrinsic drug resistance in low-grade urothelial cancer.

Multidrug resistance in ocular melanoma

AIMS/BACKGROUND

Metastatic disease in patients with ocular melanoma is resistant to chemotherapy. One of the main mechanisms of modulating multidrug resistance is the expression of the multidrug resistance gene 1 (MDR1) product (p-glycoprotein) by tumour cells. The purpose of this study was to evaluate the frequency of expression of the MDR1 gene in ocular melanoma whose primary treatment was surgical excision or enucleation.

METHODS

Twelve recent ocular melanomas were received fresh, snap frozen and cryostat sections of tumour were analysed for expression of MDR1 by immunohistochemistry using a well characterised monoclonal antibody to MDR1. Tumour explants were established in short term tissue culture from four tumours and cell blocks were examined by immunohistochemistry.

RESULTS

MDR1 expression was present in five of 12 ocular melanomas. Upregulation of protein expression was found in four cell lines established in short term culture from tumour explants. A recurrent tumour, initially treated by local excision and radioactive plaque, showed overexpression of MDR1 mRNA.

CONCLUSIONS

These results suggest that significant level of MDR1 may be intrinsically present in ocular melanomas before exposure to drugs involved in multidrug resistance, and indicate the possible importance of MDR1 in modulating chemoresistance in ocular melanoma. Chemosensitisation may be of potential value in planning adjuvant chemotherapy for patients with metastatic disease.

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.