Cancer research
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Clinical Trial
A phase I trial of amifostine (WR-2721) and melphalan in children with refractory cancer.
Melphalan has a steep dose-response curve, but the use of high doses results in unacceptable myelosuppression. Strategies to circumvent this dose-limiting myelosuppression would allow for the administration of higher, more effective doses of melphalan. Amifostine (WR-2721) has been shown in preclinical studies to protect the bone marrow from the myelotoxicity of melphalan, and in clinical trials, to protect from the myelotoxicity of other alkylating agents. ⋯ Although no dose-limiting (grade 3 or 4) toxicity was attributed to amifostine, significant anxiety and reversible urinary retention occurred at the two highest amifostine dose levels. A dose of 1650 mg/m2 for pediatric Phase II trials is recommended. High doses of amifostine, however, do not appear to allow for escalation of melphalan beyond its single agent MTD of 35 mg/m2.
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We have previously described a mitoxantrone-resistant human breast carcinoma cell line, MCF7/MX, in which resistance was associated with a defect in the energy-dependent accumulation of mitoxantrone in the absence of P-glycoprotein overexpression (M. Nakagawa et al., Cancer Res. 52: 6175-6181, 1992). We now report that this cell line is highly cross-resistant to the camptothecin analogues topotecan (180-fold), 9-aminocamptothecin (120-fold), CPT-11 (56-fold), and SN38 (101-fold), but is only mildly cross-resistant to the parent compound camptothecin (3.2-fold) and 10,11-methylenedioxy-camptothecin (2.9-fold). ⋯ No overexpression of the multidrug resistance-associated protein was detected compared to parental MCF7/WT cells. Furthermore, both sensitive MCF7/WT and mitoxantrone-resistant MCF7/MX cells contain equal amounts of DNA topoisomerase I protein, and DNA relaxation activities were equal in both cell lines and inhibited to the same extent by topotecan and camptothecin. Thus, these results suggest a novel mechanism of resistance to topoisomerase I inhibitors in cancer cells.