title: Temozolomide induces senescence but not apoptosis in human melanoma cells.
abstract: Temozolomide (TMZ), a DNA alkylating agent used in the treatment of melanoma, is believed to mediate its effect by addition of a methyl group to the O(6) position of guanine in DNA. Resistance to the agent may be in part due to the activity of O(6)-methylguanine-DNA methyl transferase (MGMT). In the present study, we show that sensitivity of melanoma cells to TMZ was dependent on their p53 status and levels of MGMT. Analysis of the mechanisms underlying reduced viability showed no evidence for induction of apoptosis even though marked levels of apoptosis was seen in TK6 lymphoma cells. Sensitivity of melanoma cells was associated with p53-dependent G2/M cell cycle arrest and induction of senescence. To verify the role of p53, the assays were repeated in presence of pifithrin-alpha, an inhibitor of p53. This resulted in increased viability of melanoma cells with wild-type p53 and reversed G2/M cell cycle arrest. Paradoxically, apoptosis was increased in melanoma but decreased as expected in TK6 lymphoma cells. These results are consistent with the view that TMZ is relatively ineffective against melanoma due to defective apoptotic signalling resulting from activation of p53. The nature of the defects in apoptotic signalling remains to be explored.
authors.affiliation: 1Immunology and Oncology Unit, Room 443, David Madison Building, Newcastle, New South Wales, Australia.
authors.forename: N M
authors.initials: NM
authors.lastname: Mhaidat
authors.forename: X D
authors.initials: XD
authors.lastname: Zhang
authors.forename: J
authors.initials: J
authors.lastname: Allen
authors.forename: K A
authors.initials: KA
authors.lastname: Avery-Kiejda
authors.forename: R J
authors.initials: RJ
authors.lastname: Scott
authors.forename: P
authors.initials: P
authors.lastname: Hersey
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D052160:Benzothiazoles / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects* / Q000502:physiology; D016922:Cellular Senescence / Q000187:drug effects*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016195:G2 Phase / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D008223:Lymphoma / Q000188:drug therapy; D008545:Melanoma / Q000378:metabolism / Q000473:pathology*; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000378:metabolism; D000077204:Temozolomide; D014050:Toluene / Q000031:analogs & derivatives / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D018906:Antineoplastic Agents, Alkylating; D052160:Benzothiazoles; D016159:Tumor Suppressor Protein p53; D014050:Toluene; D003606:Dacarbazine; C121565:pifithrin; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000077204:Temozolomide