MGMT expression in murine bone marrow is a major determinant of animal survival after alkylating agent exposure.
Myelosuppression is commonly observed after alkylating agent chemotherapy due to low levels of O(6)-alkylguanine DNA alkyltransferase protein (AGT) in hematopoietic progenitors. Mice that lack AGT in all organs, O(6)-methylguanine-DNA methyltransferase gene knockout (MGMT(-/-)) mice are extremely hypersensitive to the methylating agent N-methyl-N-nitrosourea (MNU) and exhibit a 10-fold reduction in the LD(90). To determine whether bone marrow damage was the cause of the increased lethality, we transplanted 1 x 10(6) wild-type marrow into MGMT(-/-) mice and MGMT(-/-) marrow into wild-type mice and observed survival after MNU. Lethally irradiated MGMT(-/-) mice given > or = 25 mg/kg MNU 3 weeks after transplant of wild-type cells survived > 30 days (n = 11), whereas this dose was lethal to control MGMT(-/-) mice 9-12 days post treatment (n = 5). Conversely, lethally irradiated wild-type mice transplanted with MGMT(-/-) cells died after only 20-60 mg/kg MNU within 8-12 days (n = 6). No significant toxicities were found in other organs. Additionally, in an in vivo post transplant competition model, wild-type long-term repopulating cells had a > 200-fold competitive survival advantage over MGMT(-/-) cells, and after MNU treatment completely repopulated the mouse when transplanted at only one-tenth the cell number. We also observed a strong selection for transplanted marrow-derived wild-type stromal elements in the MGMT(-/-) background after drug treatment. These data indicate that alkylating agent hypersensitivity of MGMT(-/-) mice results from hematopoietic damage at the stem level. Thus, DNA repair involving AGT in hematopoietic cells is required for normal host survival following exposure to methylating and chloroethylating agents.
Division of Hematology/Oncology, Case Western Reserve University and University Hospitals, Ireland Cancer Center, Cleveland, OH 44106, USA.
J S
JS
Reese
X
X
Qin
C B
CB
Ballas
M
M
Sekiguchi
S L
SL
Gerson
D000477:Alkylating Agents / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001853:Bone Marrow / Q000378:metabolism*; D016026:Bone Marrow Transplantation; D004260:DNA Repair / Q000187:drug effects; D006410:Hematopoiesis / Q000187:drug effects / Q000235:genetics; D008770:Methylnitrosourea / Q000008:administration & dosage / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D015996:Survival Rate
D000477:Alkylating Agents; D008770:Methylnitrosourea; D019853:O(6)-Methylguanine-DNA Methyltransferase