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-a, 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.

Temozolomide- and fotemustine-induced apoptosis in human malignant melanoma cells: response related to MGMT, MMR, DSBs, and p53

“…Apoptosis was accompanied by caspase-7 and -3 activation and PARP cleavage. This is in contrast to a recent report stating that TMZ induces senescence, but not apoptosis in melanoma cells (Mhaidat et al, 2007). The failure to observe apoptosis in that study might be explained by the different postexposure times that were used.…”

“…In a recent study it was reported that TMZ does not induce apoptosis, but senescence in human melanoma cells (Mhaidat et al, 2007), which is surprising in view of the fact that other cell systems such as malignant gliomas undergo apoptosis very efficiently in response to TMZ (Roos et al, 2007a). For fotemustine, it has been shown that melanoma cells are killed by apoptosis (Passagne et al, 2003;Kissel et al, 2006), but detailed studies on the mode of cell death by this drug in melanoma cells are not available.…”

“…The failure to observe apoptosis in that study might be explained by the different postexposure times that were used. Thus, in the study by Mhaidat et al (2007) the expression of apoptosis marker such as caspase-3 and the cleaved PARP fragment was analysed 24 -72 h after TMZ treatment. This seems to be a too short time period for apoptosis activation because TMZ-induced apoptosis is a late response that needs the passage of cells through at least two cell cycles after treatment .…”

HSP90 Inhibition Enhances the Anti-Tumor Efficacy of Combination Chemo Immunotherapy Targeting DNA Repair Proteins

“…As a consequence, despite the known inherent resistance of human melanomas to TMZ [28][29][30], which we also observed in vivo in B16 models ( Figure 1B), this chemotherapeutic agent can be used to "accumulate" higher levels of DNA-RP to serve as conditional supply of immunogenic peptides when used in combination with HSP90i such as STA9090. This tumor conditioning effect was not restricted to TMZ, as we also observed that the genotoxic anthracycline doxorubicin [31,32], but not the BRAFi dabrafenib, was also able to promote elevated expression of DNA-RP in treated melanoma cells that were consequently susceptible to HSP90i-induced degradation ( Figure S1).…”

ENHANCED p53-DEPENDENT GROWTH INHIBITION OF HUMAN GLIOBLASTOMA CELLS BY COMBINATORIAL TREATMENT OF TEMOZOLOMIDE AND NOVEL PURIFIED NATURAL CARBOHYDRATE OF PLEUROTUS FLORIDA

“…Further, O6-methylguanine lesions induced by alkylating agents activate the p53-controlled DNA damage response pathway. TMZ treatment is also known to result in G2/M phase arrest in some cancer cells [9][10][11]. According to Uzzaman et al, the average survival of patients with glioblastoma after TMZ treatment is 22 mo, which has not rendered the drug entirely satisfactory for therapy [12].…”