PT  - JOURNAL ARTICLE
AU  - Bertrand J. Jean-Claude
AU  - Amir Mustafa
AU  - Amanda J. Watson
AU  - Zoe Damian
AU  - Daniela Vasilescu
AU  - Tak Hang Chan
AU  - Brian Leyland-Jones
TI  - Tetrazepinones Are Equally Cytotoxic to Mer+ and Mer− Human Tumor Cell Lines
DP  - 1999 Feb 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 484--489
VI  - 288
IP  - 2
4099  - http://jpet.aspetjournals.org/content/288/2/484.short
4100  - http://jpet.aspetjournals.org/content/288/2/484.full
SO  - J Pharmacol Exp Ther1999 Feb 01; 288
AB  - Human brain and colon tumor cell lines SF-188 (Mer+) and WiDR (Mer+), which express the DNA repair proteinO6-methylguanine-DNA methyl transferase (MGMT), were 3- to 30-fold less sensitive to temozolomide, mitozolomide, andN,N′-bis(2-chloroethyl)-N-nitrosourea (BCNU) than the MGMT-deficient tumor cells SF-126 (Mer−) and BE (Mer−). This differential sensitivity was not observed when these cells were exposed to the novel tetrazepinones PYRZ, NIME, QUINCL, and PYRCL, which contain, like temozolomide and mitozolomide, a ureido-triazene moiety. Flow cytometric studies revealed that temozolomide induced G2-M arrest in the Mer− cells, but exerted a minor effect on the cycle of the Mer+ cells. Similarly, mitozolomide (25–100 μM) induced a stronger S-phase arrest in the SF-126 cells than in the SF-188 cells. In the same dose range (25–100) BCNU induced a significant cell cycle accumulation in G22-M in the SF-126 cells but little in the SF-188 cell line. In contrast, the cell cycle effects of the tetrazepinones were independent of the cell phenotypes. When O6-benzylguanine (O6-BG) was used to deplete MGMT activity in the SF brain tumor cell lines, significant potentiation of temozolomide (67-fold), mitozolomide (7-fold), and BCNU (3-fold) was observed in the SF-188 cell line. By contrast, O6-BG did not potentiate PYRZ, PYRCL, QUINCL, and NIME. Moreover, an MGMT inhibitory assay showed that all the tetrazepinones were capable of inactivating MGMT in the SF-188 cell line, the strongest inhibitor being PYRCL. The results suggest that, unlike temozolomide, mitozolomide, and BCNU, the cytotoxicity of the tetrazepinones does not correlate with the alkylation of the O6 position of guanine and that the mechanism of MGMT inactivation by tetrazepinones may differ from that of hitherto known inhibitors. The American Society for Pharmacology and Experimental Therapeutics