Targeting the p53 pathway in non-small cell lung cancer: preclinical study on promising combination strategies in both TP53 wild type and TP53 mutant tumors
23 June 2016
UAntwerp - Campus Drie Eiken - Building Q - Promotiezaal - Universiteitsplein 1 - 2610 WILRIJK
Organization / co-organization:
Faculty of Medicine and Health Sciences
Prof P. Pauwels & Prof F. Lardon
PhD defence Christophe Deben - Faculty of Medicine and Health Sciences
The p53 protein is strongly involved in the cytotoxic response to DNA-damaging agents by acting as a transcription factor for genes regulating cell cycle distribution, senescence and apoptotic pathways. Consequently, disruption of p53’s normal function by either inactivating mutations in the TP53 gene or overexpression of its main negative regulator MDM2, has been associated with chemoresistance and poor survival.
In a patient-based study we showed the strong association between the presence of TP53 mutations and worse overall survival in non-small cell lung cancer (NSCLC) patients. Additionally, we demonstrated the relevance of the MDM2 SNP309 G-allele as a negative prognostic marker in TP53 wild type tumors. These data provide a logical rationale for targeting both wild type and mutant p53 in NSCLC to improve patient’s outcome.
Nutlin-3, an inhibitor of the MDM2-p53 interaction, induced a strong synergistic apoptotic response and cell cycle arrest when combined with cisplatin. This interaction was dependent on the presence of wild type p53 and was most efficient after sequential treatment of cisplatin, followed by nutlin-3. Interestingly, the synergistic effect of this combination strategy appeared to be stronger at low concentrations of both compounds, thereby possibly reducing unwanted side-effects.
Since p53 is mutated in over 50% of all NSCLC patients, our next goal was to restore mutant p53’s normal function using APR-246 to enhance the apoptotic response to cisplatin. We showed that APR-246 was able to overcome mutant p53 and hypoxia dependent resistance to cisplatin treatment in a synergistic manner. Translationally, this could greatly enhance clinical outcome in mutant p53 patients by overcoming chemoresistance.
Finally, APR-246 has been shown to induce oxidative stress by increasing intracellular reactive oxygen species (ROS) production. PARP-1 plays an important role in the repair of ROS induced DNA damage, which can be inhibited using the PARP-1 inhibitor olaparib. By combining both APR-246 and olaparib, this study has shown that intracellular ROS levels increased and DNA-damage accumulated in the cells leading to the induction of massive apoptosis.
In conclusion, this thesis shows the relevance of targeting the p53 pathway in NSCLC and provides preclinical evidence for several promising combination strategies.