Preclinical selection of a novel poly(ADP-ribose) polymerase inhibitor for clinical trial

Abstract

Poly(ADP-ribose) polymerase (PARP)-1 (EC 2.4.2.30) is a nuclear enzyme that promotes the base excision repair of DNA breaks. Inhibition of PARP-1 enhances the efficacy of DNA alkylating agents, topoisomerase I poisons, and ionizing radiation. Our aim was to identify a PARP inhibitor for clinical trial from a panel of 42 potent PARP inhibitors (K i , 1.4 -15.1 nmol/L) based on the quinazolinone, benzimidazole, tricyclic benzimidazole, tricyclic indole, and tricyclic indole-1-one core structures. We evaluated chemosensitization of temozolomide and topotecan using LoVo and SW620 human colorectal cells; in vitro radiosensitization was measured using LoVo cells, and the enhancement of antitumor activity of temozolomide was evaluated in mice bearing SW620 xenografts. Excellent chemopotentiation and radiopotentiation were observed in vitro, with 17 of the compounds causing a greater temozolomide and topotecan sensitization than the benchmark inhibitor AG14361 and 10 compounds were more potent radiosensitizers than AG14361. In tumor-bearing mice, none of the compounds were toxic when given alone, and the antitumor activity of the PARP inhibitortemozolomide combinations was unrelated to toxicity. Compounds that were more potent chemosensitizers in vivo than AG14361 were also more potent in vitro, validating in vitro assays as a prescreen. These studies have identified a compound, AG14447, as a PARP inhibitor with outstanding in vivo chemosensitization potency at tolerable doses, which is at least 10 times more potent than the initial lead, AG14361. The phosphate salt of AG14447 (AG014699), which has improved aqueous solubility, has been selected for clinical trial. [Mol Cancer Ther 2007;6(3):945 -56]

Enhanced Killing of Cancer Cells by Poly(ADP-ribose) Polymerase Inhibitors and Topoisomerase I Inhibitors Reflects Poisoning of Both Enzymes

“…studies demonstrated that a variety of PARP inhibitors enhance the antiproliferative and cytotoxic effects of topo I poisons (23)(24)(25)(26)(27)(28)(29)(30)(31). Consistent with those earlier studies, we observed that treating various solid tumor cell lines, including A2780, SKOV3, Ovcar5, and A549 cells, with the PARP inhibitor veliparib (78) sensitized cells to the topo I poison topotecan (Fig.…”

“…A number of previous studies have demonstrated that small molecule PARP inhibitors selectively sensitize cells to topo I poisons in vitro and in vivo (23)(24)(25)(26)(27)(28)(29)(30)(31)(32). At least three explanations have been advanced to explain these observations.…”

An assay to measure poly(ADP ribose) glycohydrolase (PARG) activity in cells

“…Temozolomide (TMZ) is a DNA alkylating agent and is used as a standard-of-care treatment for patients with glioblastoma 13 . Here we used the colorectal cancer cell line SW620 that we knew was sensitive to alkylating agents ( Figure 5a) and which has been used in xenograft studies in combination with TMZ and the PARP inhibitors olaparib or AG014699 14, 15 . First we used the same assay conditions to determine whether increasing concentrations of TMZ induced PAR chains that could be maintained by inhibiting PARG with a potent inhibitor (compound 8 from Figure 3d).…”

Telomerase and its potential for therapeutic intervention

“…The PARP inhibitors were found to be potent chemosensitizers, and essentially lack single agent activity. PARP inhibitors under clinical investigation include ABT-888 (developed by Abbott Laboratories, Abbott Park, IL, USA and the USNational Cancer Institute, Bethesda, MD, USA) and AG14361 (developed by Pfizer, Cambridge, MA, USA and the University of Newcastle, Newcastle, UK) (Donawho et al, 2007;Thomas et al, 2007;No authors listed).…”