Malignant phenotype correlating with drug resistance in two human neuroblastoma cell lines

Reduced expression of plakoglobin correlates with adverse outcome in patients with neuroblastoma

Plakoglobin and its homologue beta-catenin are cytoplasmic proteins that mediate adhesive functions by interacting with cadherin receptors and signaling activities by interacting with transcription factors. It has been suggested that plakoglobin can suppress tumorigenicity whereas beta-catenin can act as an oncogene. We investigated the correlation between the expression pattern of N-cadherin, beta-catenin, and plakoglobin and tumor behavior in primary tumors of 20 neuroblastoma patients of all stages and in 11 human neuroblastoma cell lines. N-cadherin and beta-catenin were detected in 9 of 11 and 11 of 11 cell lines, respectively, whereas plakoglobin was undetectable or severely reduced in 6 of 11 cell lines. Tumor cells from 16 of 20 patients expressed N-cadherin and 20 of 20 patients expressed beta-catenin at levels similar to those of normal ganglion cells. Plakoglobin was undetectable in 9 of 20 tumors. Plakoglobin deficiency in the primary tumors was significantly associated with adverse clinical outcome. Five of the patients with plakoglobin-negative tumors died whereas four patients are alive without evident disease. In contrast, all patients with plakoglobin-positive tumors are alive; 2 of 11 are alive with the disease and 9 of 11 are alive without evident disease. These results suggest that down-regulation of plakoglobin may be of prognostic value for neuroblastoma patients as predictor of poor outcome.

Cell membrane fluidity and adriamycin retention in a tumor progression model of AKR lymphoma

Counteraction of drug resistance is a major challenge in cancer therapy, particularly in advanced stages. The main mechanism of multidrug resistance is related to an increased drug efflux. In the present study we examined the effect of modifying cell membrane lipid fluidity on uptake of adriamycin (ADR) in cells of AKR lymphoma malignancy variants. Modification of cell membrane fluidity, either by lecithin or by lecithin-cholesterol mixtures, induced in a high proportion of cells of all variants a higher capacity to accumulate ADR. The chemosensitizing effect, for lecithin in particular, was proportional to the degree of malignancy of the lymphoma variants. The increased ADR uptake was up to 1.4-fold in the variant of lowest malignancy and up to 5-fold in the one of highest aggressiveness. This tendency correlates with our previous studies and is of particular value since highly-malignant tumors are often drug resistant. The cholesterol-lecithin mixture, induced, however, in part of the variants the appearance of a small subpopulation with very low ADR permeability. Cell membrane rigidification is of value for exposing tumor cell cryptic antigens but may be deleterious when used in conjunction with chemotherapy.

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.