Doxorubicin (Dox) is one of the most useful chemotherapeutic agents for patients with advanced neuroblastoma (NB). A series of Dox analogs with bulky substitutions at the C-4′ at amino-sugar have been designed to impair interactions between the drug and P-glycoprotein (P-gp), a multidrug drug resistance (MDR) transporter. Two analogs, WP744 and WP769, were selected and their biological properties were compared with Dox and the daunorubicin-based bisintercalator WP631. These novel Dox analogs may have antitumor activity beyond MDR evasion. MTT assays were used to determine the potency of three structurally altered Dox analogs against a panel of NB cell lines with and without amplification of the MYCN oncogene. Flow cytometry (FCM) was used to analyze apoptosis and cell death and phenotype cell lines for surface expression of the MDR protein P-gp. The 4′-O-benzylated Dox analogs WP744 and WP769 were 2 to 36 times more cytotoxic than Dox for the NB cell lines tested. The bis-intercalator WP631, despite its significantly greater affinity for DNA (>10,000-fold), was generally less potent against NB than Dox. In Tet21N cells, which conditionally express MYCN, greatly enhanced (nearly 6-fold) sensitivity to WP744 killing was seen when this oncogene was induced, while enhanced sensitivity to Dox was more modest (2-fold) under MYCN-induced conditions. Treatment with WP744 also resulted in enhanced apoptosis. Apoptosis, but not cell death, in response to either WP744 or Dox was inhibited by caspase inhibition, suggesting that cell death was not completely dependent upon apoptosis. P-gp expression was detectable on five NB cell lines. WP744 was more cytotoxic than Dox against both P-gp + and P-gp - cells. These findings demonstrate that 4′-O-benzylation of the anthracycline molecule significantly enhances potency against NB independent of MYCN status, caspase activation, and MDR phenotype. However, WP744 demonstrated a unique synergy with MYCN for cell killing when this oncogene was specifically induced. WP744 may be more useful than conventional agents for the treatment of tumor clones that harbor defects in apoptotic pathways, in those with MYCN amplification, and in those with drug-resistant tumors.
- cell death
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