Abstract 5212: Preclinical study of the cytotoxic effect of nutlin-3a as monotherapy or in combination with gemcitabine in non-small cell lung cancer cell lines.
Authors: Deben Christophe , Quix Céline , Wouters An , Baay Marc , Pauwels Patrick , Peeters Marc , Lardon Filip , Deschoolmeester Vanessa 
Published: August 2014

Abstract
Introduction: P53 is an important tumor suppressor protein, acting in response to cellular stress signals. In 50% of all tumors inactivating mutations in the p53 gene frequently disturb its function. Another mechanism that can suppress the p53 function is the overexpression of its negative regulator MDM2. Therefore, several small molecule inhibitors were developed which block the interaction between p53 and MDM2, leading to increased levels of p53 in the cell. Nutlin-3a is a very potent small molecule inhibitor, which binds the p53-binding pocket on MDM2, thus blocking their interaction. In this study, the effect of nutlin-3a was evaluated on a series of non-small cell lung cancer (NSCLC) cell lines when administrated alone or in combination with gemcitabine (dFdC).
Methods: Three human NSCLC cell lines (A549 (p53 wt), A549-LXSN (p53 wt), A549-E6 (p53 null) and CRL-5883 (p53 mut)) were treated with either nutlin-3a (0-30 μM) for 24 hours, or dFdC (0-100 nM) for 24 hours or with simultaneous or sequential exposure schedules (dFdC followed by nutlin-3a) in a concentration range of nutlin-3a and a fixed concentration of dFdC (IC20) for 24 hours. The resulting cell survival was assessed with the sulforhodamine B assay and IC50 values (representing the drug concentration reducing cell growth to 50%) were calculated.
Results: The observed IC50 values for nutlin-3a were clearly higher for p53 null or mutant cell lines, compared to p53 wt cell lines, with CRL-5883 showing the strongest resistance.
Cytotoxity of dFdC was comparable between A549, A549-LXSN and A549-E6, while the CRL-5883 cell line showed an IC50 almost twice as high.
When dFdC treatment was followed by nutlin-3a treatment, a slight to moderate synergistic effect was observed in all cell lines (0,80&lt;CI&lt;0,90) which was stronger when dFdC was combined with a lower concentration of nutlin-3a. Simultaneous treatment with dFdC and nutlin-3a showed an additive effect in all cell lines (0,96&lt;CI&lt;1,06).
Conclusion: Nutlin-3a induces a markedly higher cytotoxic effect in p53 wt cells than in p53 null/mutant cell lines, although the latter cell lines still experience some p53 independent cytotoxic effect. Further study will be necessary to determine which pathways are involved in this p53 independent response to nutlin-3a. The combination of nutlin-3a with dFdC was slightly to moderately synergistic in all cell lines after sequential exposure, but was stronger at low concentrations of nutlin-3a. When dFdC and nutlin-3a were administrated simultaneous no synergistic effect was observed. As only a low concentration of dFdC was used, further study with increased dFdC concentrations will be performed.
Citation Format: Christophe Deben, Céline Quix, An Wouters, Marc Baay, Patrick Pauwels, Marc Peeters, Filip Lardon, Vanessa Deschoolmeester. Preclinical study of the cytotoxic effect of nutlin-3a as monotherapy or in combination with gemcitabine in non-small cell lung cancer cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5212. doi:10.1158/1538-7445.AM2013-5212