Abstract 270: Synergistic effect with APR-246 and standard chemotherapy in small cell lung cancer cells carrying smoking-associated TP53 mutations
Authors: Mohell Nina , Fransson Åsa , Alfredsson Jessica , von Euler Mikael , Björklund Ulf , Abrahmsen Lars 
Published: July 2016

Abstract
Background: Although smoking increases risk for many tumor types, no malignancy is more closely linked to tobacco exposure than small cell lung cancer (SCLC); 90% of SCLC patients are smokers. Carcinogenic compounds in cigarettes increase cancer susceptibility due to formation of DNA adducts, leading to oncogenic mutations. Etoposide in combination with cisplatin or carboplatin is the standard chemotherapy for SCLC. However, most SCLC patients eventually die of chemotherapy-refractory disease. Mutation in the tumor suppressor gene TP53 is one of the main causes for resistance, and occurs in more than 70% of SCLC patients (http://p53.free.fr). APR-246 (PRIMA-1MET) is the first clinical-stage small molecule that reactivates mutant p53 by inducing its wild-type conformation triggering apoptosis. It has been tested in a First in Human clinical trial in hematological malignancies with encouraging results (Lehmann et al. J Clin Oncol 30, 2012), and a Phase Ib/II study in combination with platinum-based therapy in recurrent ovarian cancer is ongoing (AACR abstract #CT204, 2015). We have previously observed strong synergy with APR-246 and platinum compounds in TP53-mutant drug-resistant ovarian cancer cells (Mohell et al. Cell Death and Disease 6, 2015). The aim of the present study was to investigate whether APR-246 synergizes with standard chemotherapy in SCLC cells carrying smoking-associated and/or lung cancer-specific TP53 mutations. Methods: Cell viability was tested using CellTiter-Glo assay, TP53 status with Sanger sequencing and single strand conformation analysis, and p53 protein level with Western blotting. Combination Index (CI) was calculated according to Additive model. Results: We observed synergistic (CI&lt;0.8) or strong synergist effect (CI&lt;0.5) with APR-246 and cisplatin in SCLC cell lines carrying smoking-associated (often G&gt;T transversion) and/or lung cancer specific homozygous TP53 mutations, including NCI-H2195 (V157F, 4.3% of all SCLC tumors), NCI-H1048 (R273C, 1.78%) and NCI-H889 (C242S, 1.07%). Synergy was also observed in H196 cells with hotspot R175H mutation (2.14%), while additive effect (CI = 0.8-1.2) was found in NCI-H1882 (R273L, 1.78%) and NCI-H187 (S241C, 0.36%) cells. Synergy was also observed with etoposide in NCI-H2195 cells. Moreover, APR-246 sensitized the NCI-H2195 cells to cisplatin; the IC50 value decreased about 2-fold at clinically relevant concentration of APR-246. All tested SCLC cell lines had medium or high level of p53. Further studies with other conventional drugs are ongoing. Conclusions: Treatment with APR-246 in combination with cisplatin or etoposide resulted in synergy or strong synergy in SCLC cells carrying lung cancer-specific and/or smoking-related TP53 mutations. Our results suggest that combination treatment with APR-246 and standard chemotherapy can provide significantly improved treatment of TP53-mutant SCLC.
Citation Format: Nina Mohell, Åsa Fransson, Jessica Alfredsson, Mikael von Euler, Ulf Björklund, Lars Abrahmsen. Synergistic effect with APR-246 and standard chemotherapy in small cell lung cancer cells carrying smoking-associated TP53 mutations. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 270.