Evaluation of poly (ADP-ribose) polymerase inhibitor ABT-888 combined with radiotherapy and temozolomide in glioblastoma

Abstract

BackgroundThe cytotoxicity of radiotherapy and chemotherapy can be enhanced by modulating DNA repair. PARP is a family of enzymes required for an efficient base-excision repair of DNA single-strand breaks and inhibition of PARP can prevent the repair of these lesions. The current study investigates the trimodal combination of ABT-888, a potent inhibitor of PARP1-2, ionizing radiation and temozolomide(TMZ)-based chemotherapy in glioblastoma (GBM) cells.MethodsFour human GBM cell lines were treated for 5 h with 5 μM ABT-888 before being exposed to X-rays concurrently with TMZ at doses of 5 or 10 μM for 2 h. ABT-888′s PARP inhibition was measured using immunodetection of poly(ADP-ribose) (pADPr). Cell survival and the different cell death pathways were examined via clonogenic assay and morphological characterization of the cell and cell nucleus.ResultsCombining ABT-888 with radiation yielded enhanced cell killing in all four cell lines, as demonstrated by a sensitizer enhancement ratio at 50% survival (SER50) ranging between 1.12 and 1.37. Radio- and chemo-sensitization was further enhanced when ABT-888 was combined with both X-rays and TMZ in the O6-methylguanine-DNA-methyltransferase (MGMT)-methylated cell lines with a SER50 up to 1.44. This effect was also measured in one of the MGMT-unmethylated cell lines with a SER50 value of 1.30. Apoptosis induction by ABT-888, TMZ and X-rays was also considered and the effect of ABT-888 on the number of apoptotic cells was noticeable at later time points. In addition, this work showed that ABT-888 mediated sensitization is replication dependent, thus demonstrating that this effect might be more pronounced in tumour cells in which endogenous replication lesions are present in a larger proportion than in normal cells.ConclusionsThis study suggests that ABT-888 has the clinical potential to enhance the current standard treatment for GBM, in combination with conventional chemo-radiotherapy. Interestingly, our results suggest that the use of PARP inhibitors might be clinically significant in those patients whose tumour is MGMT-unmethylated and currently derive less benefit from TMZ.

Cancer stem cells in glioblastoma

“…A potential therapeutic strategy would be the use of PARP inhibitors to enhance apoptosis under genotoxic damage. When the PARP inhibitor ABT-888 was used in combination with TMZ and radiation in GBM cell lines, apoptosis increased, and cells were sensitized to therapy (Barazzuol et al 2013). GBMs thrive in harsh microenvironments characterized by hypoxia and limited nutrient availability.…”

Radiosensitization of glioblastoma cells using a histone deacetylase inhibitor (SAHA) comparing carbon ions with X-rays

“…The cells were cultured as previously described in Barazzuol et al (2013). The doubling time for both cell lines was approximately 24 hours, whereas the plating efficiency was 63 ± 2% for LN18 and 24 ± 2.6% for U251.…”

“…Patients with GBM are routinely treated with concomitant X-rays and temozolomide (TMZ), but prognosis still remains poor (Barazzuol et al 2010). Previously, we have shown that TMZ causes reproducible additive cytotoxicity when combined with radiation, regardless of the radiation types and only on 0 6 -methylguanine DNA methyltransferase (MGMT)-methylated GBM cell lines (Barazzuol et al 2011), while ABT-888 (a poly (ADP-ribose) polymerase (PARP) inhibitor) radiosensitises all tested cell lines regardless of their MGMT status (Barazzuol et al 2013). Despite advances in brain tumour treatment, it is clear that new therapies need to be developed to improve life expectancy.…”

PARP inhibitors: A new era of targeted therapy

“…These studies have led to clinical trials of PARP inhibitors in combination with chemotherapeutics that lead to DNA damage (Table 1), with the PARP inhibitor blocking the subsequent DNA repair mechanisms selectively in cancer cells. Some of the drugs being used with PARP inhibitors include platinum based DNA damaging agents such as cisplatin, carboplatin, oxaliplatin; alkylating agents like Temozolomide (TMZ) and topoisomerase inhibitors such as Camptothecin (CPT) and its derivatives (irinotecan and topotecan) [19][20][21][22][23][24][25]. TMZ therapy, when combined with radiation induces single stranded breaks (SSBs) and hence is the direct target of PARP inhibitors.…”