Abstract 2979: Combined cdk1 and PARP inhibition results in tumor regression in a KrasG12D p53L/L murine lung adenocarcinoma model
Authors: Johnson Neil , Li Yu-Chen , Walton Zandra , Li Danan , Moreau Lisa , Rodig Scott J. , D'Andrea Alan D. , Thomas Huw , Newell David R. , Curtin Nicola J. , Wong Kwok K. , Shapiro Geoffrey I. 
Published: June 2012

Abstract
Kras is one of the most commonly mutated oncogenes in non-small cell lung cancer (NSCLC), and targeted therapies are not available for this lung cancer subset. Consequently, there is an unmet need for improved therapies for patients with NSCLCs harboring Kras mutation. We previously demonstrated that cdk1 phosphorylates BRCA1, and is essential for efficient BRCA1 focus formation and activation of the S phase checkpoint in response to DNA damage in RAS mutant NSCLC cell lines (Johnson et al., Mol Cell 2009; 35: 327-39). PARP inhibition has been shown to selectively kill cancer cells that are unable to perform homologous recombination (HR)-mediated DNA repair. Furthermore, PARP inhibitors have provided clinical responses in patients with BRCA1 and BRCA2 mutations. We hypothesized that small molecule mediated cdk1 inhibition would disrupt BRCA1 function and sensitize BRCA-proficient, RAS mutant NSCLC cells to PARP inhibitors.
Using a gene conversion assay to directly measure HR, in which GFP expression indicates the occurrence of HR repair, we demonstrated that the small molecule cdk1 inhibitors RO-3306 and AG024322 reduced GFP expression 7.7-fold (p = 0.013) and 3.4 fold (p = 0.016), respectively, compared to vehicle. In colony forming assays, RO-3306 and AG024322 reduced the LC50 value of the PARP inhibitor AG014699 6.6-fold and 18.7-fold in Nras mutant, TP53-deleted NCI-H1299 cells. Similar results were observed with Kras mutant A549 cells. In contrast to transformed cells, non-transformed Retinal Pigment Epithelial (RPE) cells were less sensitive to combined RO-3306 and AG014699 treatment. Similarly, when NCI-H1299 xenograft-bearing mice were treated with both AG024322 and AG014699, tumor growth was significantly delayed compared to vehicle exposure or treatment with either compound alone. We further assessed the therapeutic efficacy of combined AG024322 and AG014699 treatment in the KrasG12Dp53L/L murine lung adenocarcinoma model. Mice treated with vehicle, AG024322 or AG014699 alone all demonstrated tumor growth by MRI. In contrast, 87.5% (14/16) treated with combined AG024322 and AG014699 had up to 70% reduction in tumor volume. Furthermore, combined AG024322 and AG014699 treatment resulted in a marked reduction in Ki67 staining and increased TUNEL staining in residual tumor compared to vehicle or individual treatments. No toxicity or damage to normal mouse tissues and organs was found after combination treatment by pathologic assessment. This approach provides the potential to extend well-tolerated PARP inhibition to treatment for BRCA-proficient Kras mutant NSCLC.
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 2979. doi:10.1158/1538-7445.AM2011-2979