Mechanisms And Reversal Of Resistance To Alkylating Agent Melphalan (Mel)

Two Mel-resistant variants of the leukemic cell lines (L1210/Mel and K562/Me1).which are stably 9.9-fold and 8.0-fold resistant to Mel, have been developed in vitro by continuous exposure to Mel.Both cell lines are also cross-resistant to nitrogen mustards and thiophosphoramide,but not to carmustine and doxorabicin.A comparison of some cell biological properties indicated that the sensitive and Mel resistant sublines of K562 and LI210 proliferated in vitro with a similar doubling time.Electronmicroscopy examinations indicated that resistant sublines maintained leukemic cell morphology in cell shape and dimensions. Cytogenetic analysis of K562/Me12 revealed that K562 specific ph chromosome was maintained but chromosome 6 turned abnormal. Surface antigens of K562/Mel2 and K562/S were proved to be similar by using indirect immunofluorescence assay with monoclonal antibodies.One Mel resistant subline(L1210/Mel mouse), which is stably 10 fold resistant to Mel, was implanted in the DBA/2 mouse acute lymphocytic leukemia model.Biopsy examination indicated that there were leukemic cells infiltrating in solid tumor,lung,spleen,bone marrow and diuretics,but not in liver. Primary data revealed that L1210/Mel mouse is resistant to Mel in vivo.This enhanced drug resistance is associated with increase in the level of expression of GST a gene and total GST,but not with increase in the level of expression of GST π, μ gene and Top-II gene. L1210/Mel cell line decreased DNA interstrand cross-link and enhanced removal when treated with 10uM Mel.Intracellular accumulation of DNR in K562/Me12 was as high as that in K562/S. P-glycoprotein was negative by immunohistochemistry assay.According to dot blot and RT-PCR analysis, in Mel-resistant cell-lines, the MDR-1 mRNA level was as high as that in sensitive cell lines.Interferon a at 500IU/ml is nontoxic to both...