Poly(ADP‐ribose) polymerase inhibitor increases growth inhibition and reduces G₂/M cell accumulation induced by temozolomide in malignant glioma cells

Abstract

Temozolomide (TZM) is a novel methylating agent currently under investigation for treatment of recurrent high-grade gliomas. Although TZM generates a wide spectrum of methyl adducts, its cytotoxicity has been attributed to mismatch repair (MR)-mediated processing of O(6)-methylguanine:T mispairs. N3-methyladenine and N7-methylguanine adducts are promptly repaired by the base excision repair system, unless a poly(ADP-ribose) polymerase (PARP) inhibitor is combined to TZM. In this case, the repair process of N-methylpurines cannot be completed and the deriving DNA strand breaks contribute to cytotoxicity. In this study, we investigated the influence on cell growth and cell cycle of treatment with TZM + PARP inhibitor in glioma cells characterized by different susceptibility to TZM. The results indicated that PARP inhibitor increases growth inhibition induced by TZM in either p53-wild-type or p53-mutant glioblastoma cells, as early as 24 h after drug exposure. The enhancing effect exerted by PARP inhibitor was particularly evident in glioma cells characterized by a defective expression of MR, since these cells are tolerant to O(6)-methylguanine damage and show low sensitivity to TZM. In O(6)-alkylguanine-DNA alkyltransferase (OGAT)-deficient and MR-proficient tumor cells bearing wild-type p53, the drug combination markedly reduced cell accumulation in the G(2)/M phase of cell cycle and induction of the G(2) checkpoint regulator Chk1 kinase. In short-term cultures of glioma cells derived from surgical specimens, PARP inhibitor enhanced chemosensitivity to TZM and this effect was especially evident in OGAT-proficient tumors. Thus, a pharmacological strategy based on the interruption of N-methylpurine repair might represent a novel strategy to restore or increase glioma sensitivity to TZM.

Poly(ADP-ribose) Polymerase Activity Prevents Signaling Pathways for Cell Cycle Arrest after DNA Methylating Agent Exposure

“…1A). Potentiation of TMZ-induced cytotoxicity by PARP inhibitors has been reported previously (32,33). For each of these agents, exposure to 4-AN resulted in a larger potentiation of cytotoxicity in ␤-pol null compared with wild-type cells (Figs.…”

“…4B). Clearly, in our cell lines as well as in others (32,33,36), the repair of N-methyl DNA adducts by BER is an important determinant of TMZ-mediated cytotoxicity.…”

The selective poly(ADP-ribose) polymerase-1(2) inhibitor, CEP-8983, increases the sensitivity of chemoresistant tumor cells to temozolomide and irinotecan but does not potentiate myelotoxicity

“…Using chemotherapy-resistant cell lines, the present study expanded on previous observations that PARP-1 inhibition results in the accumulation of tumor cells with DNA damage at the G 2 -M boundary of the cell cycle (7,27). PARP-1 inhibition with CEP-8983 in combination with SN38 or temozolomide resulted in a shift in the onset and magnitude of tumor cell accumulation at the G 2 -M boundary compared with SN38 or temozolomide treatment alone using HT29 and RH18 cells, respectively.…”

Hypersensitivity phenotypes associated with genetic and synthetic inhibitor-induced base excision repair deficiency

“…There is considerable interest in developing more potent nontoxic PARP inhibitors with the possibility for use in a clinical setting. As described above, PARP inhibition results in cellular sensitization to the chemotherapeutic methylating agent TMZ, particularly in MMR-deficient cells, just as it does to the model methylating agents MMS and MNU [66,90,[93][94][95][96]. Further, preclinical studies have demonstrated that novel PARP inhibitors can enhance the antitumor activity of TMZ against mouse tumors and human colon and glioma xenograft models [72,[97][98][99].…”