Study On The Mechanisms Of Multidrug Resistance In Orbital Rhabdomyosarcoma

OBJECTIVESIn the present study, we established an in vitro resistance model of rhabdomyosarcoma, detected two-drug resistance-associated markers-mdrl and mrp, studied the expression and clinical significance of the P-glycoprotein (P-gp) and the multidrug resistance-associated protein (MRP) in orbital rhabdomyosarcoma. These can provide the theoretical information and clinical reference for elucidating the mechanisms of multidrug resistance (MDR), improving the chemotherapy scheme, evaluating the prognosis and reserving the MDR in orbital rhabdomyosarcoma.METHODS1. The resistance cell line, RD/VCR, was induced in the RD cell line in vitro by progressive concentrations of vincristine (VCR), a drug of choice in the treatment of rhabdomyosarcoma.2. The growth curves, drug sensitivity and morphological changes in the parental and resistant cell lines were investigated by cell counting, MTT assay, light microscope and electron microscope respectively. The expression of mdrl and mrp gene, P-gp and MRP protein were detected by RT-PCR and immunohistochemistry analysis respectively.3. The expression of P-gp and MRP in 42 cases of orbital rhabdomyosarcoma and 10 cases of normal orbital were detected by immunohistochemistry analysis.RESULTS1. RD/VCR cell line was cross-resistant to vincristine (VCR), adriamycin (ADM), etoposide (VP16) and actinomycin D (DAC), but not resistant to fluorouracil (5-FU) and cisplatin (DDP). There was no significant difference in the doubling time between RD cell line and RD/VCR cell line. However, morphological changes were found in the ultra structure.2. In RD/VCR cell line, the expression of mdrl and mrp mRNA was relatively higher while P-gp and MRP were positive. In RD cell line, the expression of mdrl mRNA was lower; mrp mRNA, P-gp and MRP were undetectable.3. P-gp and MRP expression percentage were 38.10% and 54.76% respectively in orbital rhabdomyosarcoma and were higher than in normal orbital tissue (p., =0.0495, p2=0.0004). There was no significant correlation between expression of P-gp or MRP and age, sex, histological type and stage. The positive rate of P-gp or MRP expression in recurrent tumor group was higher than in primary tumor group (p,=0.0078, p2=0.0186). No significant correlation between the expression of P-gp and MRP was found.CONCLUSIONS1. Exposing to VCR can induce MDR in rhabdomyosarcoma; its mechanism might be associated with the expression of mdrl/P-gp and mrp/MRP. Electron microscope played an important role in the morphological study.2. P-gp and MRP overexpression were participated in the acquired MDR in orbital rhabdomyosarcoma, but the ways were different. P-gp and MRP detection were of great value in prognosis evaluation.