Inhibition of Poly(ADP-Ribose) Polymerase Enhances the Toxicity of ¹³¹I-Metaiodobenzylguanidine/Topotecan Combination Therapy to Cells and Xenografts That Express the Noradrenaline Transporter

Abstract

Targeted radiotherapy using 131 I-metaiodobenzylguanidine ( 131 I-MIBG) has produced remissions in some neuroblastoma patients. We previously reported that combining 131 I-MIBG with the topoisomerase I inhibitor topotecan induced long-term DNA damage and supraadditive toxicity to noradrenaline transporter (NAT)-expressing cells and xenografts. This combination treatment is undergoing clinical evaluation. This present study investigated the potential of poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP-1) inhibition, in vitro and in vivo, to further enhance 131 I-MIBG/topotecan efficacy. Methods: Combinations of topotecan and the PARP-1 inhibitor PJ34 were assessed for synergism in vitro by combination-index analysis in SK-N-BE(2c) (neuroblastoma) and UVW/NAT (NAT-transfected glioma) cells. Three treatment schedules were evaluated: topotecan administered 24 h before, 24 h after, or simultaneously with PJ34. Combinations of PJ34 and 131 I-MIBG and of PJ34 and 131 I-MIBG/topotecan were also assessed using similar scheduling. In vivo efficacy was measured by growth delay of tumor xenografts. We also assessed DNA damage by gH2A.X assay, cell cycle progression by fluorescence-activated cell sorting analysis, and PARP-1 activity in treated cells. Results: In vitro, only simultaneous administration of topotecan and PJ34 or PJ34 and 131 I-MIBG induced supraadditive toxicity in both cell lines. All scheduled combinations of PJ34 and 131 I-MIBG/topotecan induced supraadditive toxicity and increased DNA damage in SK-N-BE(2c) cells, but only simultaneous administration induced enhanced efficacy in UVW/NAT cells. The PJ34 and 131 I-MIBG/ topotecan combination treatment induced G 2 arrest in all cell lines, regardless of the schedule of delivery. In vivo, simultaneous administration of PJ34 and 131 I-MIBG/topotecan significantly delayed the growth of SK-N-BE(2c) and UVW/NAT xenografts, compared with 131 I-MIBG/topotecan therapy. Conclusion: The antitumor efficacy of topotecan, 131 I-MIBG, and 131 I-MIBG/ topotecan combination treatment was increased by PARP-1 inhibition in vitro and in vivo.

Preliminary evaluation of prostate-targeted radiotherapy using 131I-MIP-1095 in combination with radiosensitising chemotherapeutic drugs†

“…After 12 h, the cells were harvested by trypsinisation and fixed in 70% ethanol at −20 °C. LNCaP cells were stained with 20 μg/ml propidium iodide and 4 μg/ml RNAse A for at least 10 min prior to analysis using FACSCalibur (BD Biosciences, Mountain View, CA), as described previously …”

An evaluation in vitro of PARP-1 inhibitors, rucaparib and olaparib, as radiosensitisers for the treatment of neuroblastoma

“…PARP-1 inhibitors have shown great promise when used in combination with treatments that cause substantial DNA damage, including ionising radiation [ 20 – 23 ], DNA alkylating agents [ 20 , 24 ] and the topoisomerase-1 poisons topotecan or irinotecan [ 25 , 26 ]. Indeed, we have shown previously that the second generation PARP-1 inhibitor PJ34 enhanced the efficacy of 3-way modality treatment involving 131 I-MIBG and topotecan [ 22 ]. However, it has been suggested that PJ34 may be toxic to normal cells [ 27 , 28 ].…”

Association of PARP1 polymorphisms with response to chemotherapy in patients with high‐risk neuroblastoma

“…Indeed, the United States Food and Drug Administration (FDA) approved in March 2017, niraparib for maintenance therapy of recurrent gyneacologic cancers which are sensitive to previous platinum‐based chemotherapy irrespective of BRCA mutation and homologous recombination deficiency status . So far, encouraging results have been obtained from testing PARP inhibitors in NB pre‐clinical models in drug combination schemes . If the genetic association, here found, will be validated in prospective studies, in future novel guidelines for the treatment of patients with NB based on their SNPs in PARP1 might be generated.…”