Abstract 5500: Inhibition of poly(ADP-ribose) polymerase in lung cancer cells with defective Fanconi anemia (FA) pathway
Authors: Gao Li , Duan Wenrui , Wu Xin , Otterson Gregory A. , Villalona-Calero Miguel A. 
Published: June 2012

The poly ADP-ribose polymerase (PARP) inhibitors are novel agents being developed with the hope of inhibiting base excision repair, a process that is of prime importance for tumors to survive genotoxic insult. BRCA gene homozygous deficiency has been identified as a potential predictor of response to PARP inhibitors. BRCA is involved in homologous recombination (HR), an example of double-strand break repair. Thus, inhibiting tumors which have lost one DNA repair pathway by targeting a second DNA repair pathway represents groundbreaking therapeutic strategy. BRCA is just one of many genes that collaborate in the same repair pathway, which has been named the Fanconi Anemia (FA) pathway. The FA pathway is a major mechanism of homologous recombination DNA repair in response to genotoxic insults. Deficiencies in FA pathway have been reported as a predictor of cisplatin and mitomycin C (MMC) sensitivity in cancer cells. Given that this pathway plays essential roles in response to the DNA damage, cancers with defective FA pathway are expected to be more sensitive to DNA cross-link based therapy, or to treatments in which additional repair mechanisms are targeted.

In order to preclinically evaluate the effect of PARP inhibition in lung cancer cells with spontaneously defective FA pathway, we utilized RNAi technology to create FANCD2 knockdown cancer cells. Lung cancer cells H1299 and A549 were transduced with FANCD2-specific shRNA-expressing and puromycin-resistant lentiviral particles, or control shRNA lentiviral particles to create stably transduced cells. Successful FANCD2 knockdown was confirmed by the Western blot by reduction in the FANCD2 protein. Cell viability was evaluated with MTT (Dimethylthiazolyl-2-5-diphenyltetrazolium bromide) analysis.

The FA defective H1299 and A549 lung cancer cells and the controls (transected with empty vectors) were treated with the PARP inhibitor ABT888 at a dose of 5µM. Then the treated cells were harvested at 24, 48 and 72 hours post treatment. MTT cell viability analysis showed that ABT888 alone was cytotoxic to the FA deficient lung cancer cells (H1299D2-down and A549D2-down) 72 hours post treatment. In both cell types, the FA defective lung cancer cells had less viable cells compared to controls 72 hours post treatment.

Recent clinical data confirmed the PARP inhibitors could be used not only as chemosensitizers but as well as single agents to selective kill tumors with BRCA-deficient breast cancers. Disruption of FA cascade has been reported in solid tumors. Given that the FA pathway plays an essential role in response to therapy-induced DNA interstrand cross-links, it is very plausible that cancers with defective FA pathway are more sensitive to cross-link based therapy and that treatments like PARP inhibitors in which an additional repair mechanism is targeted. A clinical trial to validate this hypothesis is under way.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5500. doi:10.1158/1538-7445.AM2011-5500