Drug resistance continues to be a serious problem in cancer therapy. We investigated whether indomethacin, which inhibited cyclooxygenases, would overcome doxorubicin resistance in K562/ADR leukemia cells. Indomethacin at 10 muM increased the cytotoxicity of doxorubicin, as well as vincristine in K562/ADR. Both multi-drug resistant protein1 (MRP1) and P-glycoprotein were overexpressed in K562/ADR cells when compared with K562 parent cells (K562/P). Expression of MRP1 mRNA and protein, but not P-glycoprotein, was significantly decreased in K562/ADR cells after indomethacin treatment. Indomethacin treatment increased 5(6)-carboxyfluorescein diacetate (CFDA) efflux, as well as decreased accumulation in K562/ADR cells. The activity of the MRP1 promoter decreased after indomethacin treatment in Hela cells. These data strongly suggest that the cyclooxygenase inhibitor, indomethacin, increased the cytotoxicity of doxorubicin with decreasing expression of MRP1 through inhibition of MRP1 promoter activity.

Drug resistance continues to be a serious problem in cancer therapy. We investigated whether indomethacin, which inhibits cyclooxygenases, is able to overcome doxorubicin resistance in K562/ADR leukemia cells. Indomethacin at 10 microM increased the cytotoxicity of doxorubicin and vincristine in K562/ADR cells. Intracellular glutathione content was elevated in K562/ADR cells. Indomethacin treatment decreased glutathione content and glutathione-conjugates in K562/ADR cells. Increased expression of gamma-glutamylcysteine synthetase (gamma-GCS) was observed in K562/ADR cells, but this expression was decreased by indomethacin treatment. The activity of the gamma-GCS promoter from K562/ADR cells decreased after indomethacin treatment in MDA231 cells. These data strongly suggest that the cyclooxygenase inhibitor indomethacin increases the cytotoxicity of doxorubicin by decreasing the intracellular contents of glutathione and its conjugates with decreasing expression of gamma-GCS by inhibiting gamma-GCS promoter activity.

Metachromatic leukodystrophy (MLD) is an autosomal recessive, inherited, lysosomal storage disease caused by a deficiency in arylsulfatase A (ASA). This disease is characterized by progressive demyelination leading to severe neurological symptoms. Allogenic bone marrow transplantation at an early stage of clinical course is only effective treatment currently available. Accordingly the corrective transfer of the ASA gene into hematopoietic stem cells is thought to be an important option for curative treatment for MLD. We have recently developed a selectable vector system based on ex vivo sorting of transduced cells (Migita et al. 1995). In this study, we applied this selectable system for development of MLD gene therapy. A bicistronic retroviral vector containing ASA cDNA and CD24 cDNA as a selectable marker gene was constructed. This vector was successfully transduced on fibroblasts from MLD patients, ASA activity was increased 7-fold compared to normal untransduced cells. PCR Southern analysis of hematopoietic colonies showed that transduction efficiency of CD34+ cells was 11-22%. However, after fluorescenceactivated cell sorting using anti-CD24 antibody, 75-100% of colonies became vector positive. The sorting raised the ASA activity several fold compared to untransduced CD34+ progenitors. These results suggest that a bicistronic ASA vector containing a CD24 selectable marker could be a useful component of gene therapy for MLD.