Comparisons between sensitive and resistant human tumor cell lines regarding effects of polyamine depletion on chloroethylnitrosourea efficacy.
We have reported that 2-difluoromethylornithine (DFMO)-induced polyamine (PA) depletion sensitized five chloroethylnitrosourea (CENU)-resistant, O6-alkylguanine repair-proficient (Mer+) human tumor cell lines to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), but failed to alter BCNU efficacy in a single CENU-sensitive, repair-deficient (Mer-) line. Further, alkaline elution assays of DNA interstrand cross-links (ISC) found no BCNU-induced ISC in either PA-depleted or control Mer+ cells, suggesting that targets other than ISC may be involved in the DFMO/BCNU drug interaction. To verify that DFMO-induced enhancement of BCNU action segregates with Mer phenotype, we tested three additional Mer- lines for effects of DFMO pretreatment on BCNU efficacy. We found no potentiation of BCNU by PA depletion in any of our human Mer- lines. We also used streptozotocin (STZ) to deplete the repair capacity of Mer+ cell lines, thus converting their BCNU sensitivity to near that of Mer- cells. Combined pretreatment with DFMO then STZ did enhance BCNU cell kill relative to STZ pretreatment alone. Exogenous putrescine restored BCNU sensitivity of (DFMO plus STZ)-pretreated cells to that of cells pretreated with STZ alone. Measurements of O6-alkylguanine DNA alkyltransferase activity verified that in at least one of the Mer+ lines (HT-29), STZ did deplete repair capacity to below detectable limits. These results suggest that in HT-29 cells, STZ and DFMO probably act via differing mechanisms to potentiate BCNU. Our observations also imply that targets for CENUs may differ between Mer+ and Mer- cells, with importance of ISC possibly limited to Mer- cells. Our data further suggest that PA depletion may potentiate CENUs only at targets critical in Mer+ cells. We also noted that 48-h treatments with DFMO markedly reduced clonogenicity of Mer- cells. Exogenous putrescine restored Mer- cell survival after DFMO to near that of controls. In contrast, Mer+ cells showed little, if any, effect of DFMO treatment on plating efficiency. These results suggest that PA depletion may be cytocidal to some Mer- cells.
Seidenfeld
J
J
Department of Pharmacology, Northwestern University Medical School, Chicago, Illinois 60611.
Sprague
W S
WS
D002330:Carmustine / Q000008:administration & dosage*; D002470:Cell Survival / Q000187:drug effects; D004260:DNA Repair; D004357:Drug Synergism; D000518:Eflornithine / Q000008:administration & dosage*; D006801:Humans; D066298:In Vitro Techniques; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D019853:O(6)-Methylguanine-DNA Methyltransferase; D011073:Polyamines / Q000378:metabolism*; D011700:Putrescine / Q000494:pharmacology; D013311:Streptozocin / Q000008:administration & dosage; D014407:Tumor Cells, Cultured / Q000187:drug effects*
D011073:Polyamines; D013311:Streptozocin; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine; D011700:Putrescine; D000518:Eflornithine