Human CD34+ hematopoietic progenitors have low, cytokine-unresponsive O6-alkylguanine-DNA alkyltransferase and are sensitive to O6-benzylguanine plus BCNU.
Human bone marrow (BM) cells contain low levels of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase, which may explain their susceptibility to nitrosourea-induced cytotoxicity and the development of secondary leukemia after nitrosourea treatment. Isolated CD34+ myeloid progenitors were also found to have low levels of alkyltransferase activity. The level of alkyltransferase in CD34+ cells or in mononuclear BM cells did not increase after incubation with granulocyte-macrophage colony-stimulating factor, interleukin-3, stem cell factor, the combination, or 5637 conditioned medium. BCNU sensitivity remained unchanged as well. In addition, O6-benzylguanine depleted alkyltransferase activity in BM cells at concentrations as low as 1.5 mumol/L after a 1-hour exposure. O6-benzylguanine pretreatment markedly sensitized hematopoietic progenitor colony-forming cells to BCNU, resulting in a reduction in the dose of drug (termed the dose-modification factor) required to inhibit 50% of the colony formation (IC50) of threefold to fivefold. Since, unlike many other cell types, proliferating early (CD34+) hematopoietic precursors do not induce alkyltransferase, myelosuppression may be the dose-limiting toxicity of the combination of O6-benzylguanine plus BCNU in clinical trials.
Gerson
S L
SL
Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
Phillips
W
W
Kastan
M
M
Dumenco
L L
LL
Donovan
C
C
D000328:Adult; D018952:Antigens, CD34 / Q000032:analysis; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000633:toxicity; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology / Q000633:toxicity; D001854:Bone Marrow Cells; D002330:Carmustine / Q000494:pharmacology* / Q000633:toxicity; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects; D004351:Drug Resistance; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000633:toxicity; D004921:Erythropoietin / Q000494:pharmacology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D006147:Guanine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000633:toxicity; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D008780:Methyltransferases / Q000032:analysis* / Q000037:antagonists & inhibitors; D019853:O(6)-Methylguanine-DNA Methyltransferase; D011994:Recombinant Proteins / Q000494:pharmacology; D019089:Stem Cell Factor / Q000494:pharmacology
D018952:Antigens, CD34; D000970:Antineoplastic Agents; D018906:Antineoplastic Agents, Alkylating; D017077:Culture Media, Conditioned; D004791:Enzyme Inhibitors; D007377:Interleukin-3; D011994:Recombinant Proteins; D019089:Stem Cell Factor; C064976:O(6)-benzylguanine; D004921:Erythropoietin; D006147:Guanine; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine