Inhibition of poly(ADP-Ribose) polymerase enhances the toxicity of 131I-metaiodobenzylguanidine/topotecan combination therapy to cells and xenografts that express the noradrenaline transporter.
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 γH2A.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.


CONCLUSIONS
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.
Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom. anthony.mccluskey@strath.ac.uk
Anthony G
AG
McCluskey
Robert J
RJ
Mairs
Mathias
M
Tesson
Sally L
SL
Pimlott
John W
JW
Babich
Mark N
MN
Gaze
Sue
S
Champion
Marie
M
Boyd
D019797:3-Iodobenzylguanidine / Q000633:toxicity*; D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity*; D001932:Brain Neoplasms / Q000188:drug therapy / Q000532:radiotherapy / Q000628:therapy; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D002626:Chemistry, Pharmaceutical; D003131:Combined Modality Therapy; D053960:DNA Breaks / Q000187:drug effects / Q000528:radiation effects; D005260:Female; D005434:Flow Cytometry; D006657:Histones / Q000378:metabolism; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009447:Neuroblastoma / Q000188:drug therapy / Q000532:radiotherapy / Q000628:therapy; D050484:Norepinephrine Plasma Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D010766:Phosphorylation; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D019275:Radiopharmaceuticals / Q000633:toxicity*; D019772:Topotecan / Q000633:toxicity*; D014410:Tumor Stem Cell Assay
D000970:Antineoplastic Agents; C468783:H2AX protein, human; D006657:Histones; D050484:Norepinephrine Plasma Membrane Transport Proteins; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine; D019772:Topotecan; D011065:Poly(ADP-ribose) Polymerases