Tolerance of human MSH2 ^+/− lymphoblastoid cells to the methylating agent temozolomide

Abstract

Members of hereditary nonpolyposis colon cancer (HNPCC) familiesharboring heterozygous germline mutations in the DNA mismatch repair genes hMSH2 or hMLH1 present with tumors generally two to three decades earlier than individuals with nonfamilial sporadic colon cancer. We searched for phenotypic features that might predispose heterozygous cells from HNPCC kindreds to malignant transformation. hMSH2 ؉/؊ lymphoblastoid cell lines were found to be on average about 4-fold more tolerant than wild-type cells to killing by the methylating agent temozolomide, a phenotype that is invariably linked with impairment of the mismatch repair system. This finding was associated with an average 2-fold decrease of the steady-state level of hMSH2 protein in hMSH2 ؉/؊ cell lines. In contrast, hMLH1 ؉/؊ heterozygous cells were indistinguishable from normal controls in these assays. Thus, despite the fact that HNPCC families harboring mutations in hMSH2 or hMLH1 cannot be distinguished clinically, the early stages of the carcinogenic process in hMSH2 and hMLH1 mutation carriers may be different. Should hMSH2 ؉/؊ colonocytes and lymphoblasts harbor a similar phenotype, the increased tolerance of the former to DNA-damaging agents present in the human colon may play a key role in the initiation of the carcinogenic process.

The Effect ofO6-Alkylguanine-DNA Alkyltransferase and Mismatch Repair Activities on the Sensitivity of Human Melanoma Cells to Temozolomide, 1,3-bis(2-Chloroethyl)1-nitrosourea, and Cisplatin

“…Therefore, resistance to methylating agents can be linked either to high OGAT levels or to loss of MMR. When OGAT activity is attenuated, the number of O 6 -MeG/T mispairs increases and the efficiency of cell killing by methylating agents becomes predominantly a function of MMR (Dosch et al, 1998;Marra et al, 2001). This relationship holds also for the majority of the melanoma cell lines analyzed in this study.…”

Carmustine-Resistant Cancer Cells Are Sensitized to Temozolomide As A Result of Enhanced Mismatch Repair during the Development of Carmustine Resistance

“…8, Table 2). Several reports suggest that hMLH1 and hMSH2 may affect cells' sensitivity to TMZ differently (Marra et al, 2001;Sansom et al, 2001), which might explain the difference in the effects between CdCl 2 that may inhibit the process where hMSH2 is involved (Fig. 7, Table 1) and shRNA against hMLH1 (Fig.…”

Autocrine insulin-like growth factor-I signaling promotes growth and survival of human acute myeloid leukemia cells via the phosphoinositide 3-kinase/Akt pathway

“…For growth factor stimulations, cells were incubated overnight in Optimem medium (Life Technologies/Invitrogen) and washed with serum-free medium before incubation with growth factors. Immortalized B cells 31 were cultured in RPMI with 20% (v/v) FCS and penicillin/streptomycin/ L-glutamine. Heparinized peripheral blood or bone marrow samples were obtained from adult patients with AML.…”