Combination cytotoxic-differentiation therapy of mouse erythroleukemia cells with 5-fluorouracil and hexamethylene bisacetamide.
The effects of 5-fluorouracil (5-FUra), in combination with various differentiation inducers on the growth and differentiation of mouse erythroleukemia (MEL) cells were investigated. The cells were first treated with 5-FUra, washed, and then treated with various concentrations of differentiation inducers: hexamethylene bisacetamide (HMBA), dimethyl sulfoxide (DMSO), and N-methylformamide. Pretreatment with 5-FUra, shown here to be a weak inducer of MEL cell differentiation, enhanced the subsequent HMBA induction of differentiation. The three inducers of differentiation markedly inhibited cell growth and increased cell death in a dose- and time-dependent manner if given immediately after cells were exposed to 5-FUra. In contrast, 5-FUra at similar concentrations inhibited cell growth, but only slightly increased cell death, while inducers without 5-FUra had little effect on cell growth or viability. When placed in fresh drug-free medium for 6 days following drug treatments, the cells completely recovered from the growth inhibition of 5-FUra as a single agent, whereas in cells previously treated with only HMBA there was a inhibition of cell growth without loss of viability. In contrast, a profound and prolonged growth inhibition with 98% cell death occurred in cells previously treated with 5-FUra followed by HMBA. The enhancement of 5-FUra cytotoxicity appeared to be directly related to the degree of differentiation and to biochemical events that occur during the commitment to terminal cell division induced by N-methylformamide, DMSO, or HMBA. An increase in Okazaki fragments was found in MEL cells treated with HMBA or DMSO when committed to terminal cell division. DNA breaks also follow 5-FUra treatment (A. Yoshioka et al., J. Biol. Chem., 262: 8235-8241, 1987) and may be the events that lead to cell death. The marked increase in cell death resulting from 5-FUra/HMBA treatment may be, at least partly, a consequence of increased DNA breaks due to 5-FUra followed by inhibition of DNA repair which is known to occur following the HMBA or DMSO induction of differentiation and commitment to terminal cell division. This combined sequential cytotoxic-differentiation therapy resulting in synergistic cytotoxicity and differentiation may be the basis of a new approach to cancer therapy and may aid in reducing the amounts of chemotherapeutic agents required for effective treatment, while maintaining or even increasing their therapeutic effects.
Waxman
S
S
Rochell Belfer Chemotherapy Foundation Laboratory, Department of Medicine, Mount Sinai Medical Center, New York, New York 10029.
Scher
B M
BM
Hellinger
N
N
Scher
W
W
D000081:Acetamides / Q000627:therapeutic use*; D000818:Animals; D002452:Cell Count / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D004273:DNA, Neoplasm / Q000096:biosynthesis / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D005472:Fluorouracil / Q000627:therapeutic use*; D005559:Formamides / Q000494:pharmacology; D002955:Leucovorin / Q000494:pharmacology; D004915:Leukemia, Erythroblastic, Acute / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D013997:Time Factors; D014407:Tumor Cells, Cultured
D000081:Acetamides; D004273:DNA, Neoplasm; D005559:Formamides; D003907:Dexamethasone; C014026:hexamethylene bisacetamide; D002955:Leucovorin; D005472:Fluorouracil; C002950:methylformamide; D004121:Dimethyl Sulfoxide