Abstract 3448: Strong synergistic effects with cisplatin and APR-246, a novel compound reactivating mutant p53, in ovarian cancer cell lines and primary cells from patients.

Abstract

Abstract Background: The tumor suppressor protein p53 is frequently mutated in cancer, and cancer cells carrying defects in p53 are generally more resistant to conventional chemotherapy. About 60% of patients with ovarian cancer have p53 mutations. Thus, restoration of wild type function of p53 is a promising strategy for cancer therapy. APR-246 (PRIMA-1MET) belongs to a class of small molecules (quinuclidinones) that reactivate mutated or otherwise non-functional p53 by promoting its correct wt folding thus triggering apoptosis (Lambert et al. Cancer Cell 15, 2009). In various in vitro, ex vivo and in vivo cancer models APR-246 has shown good antitumor activity and a unique pharmacological profile. In a Phase I/II clinical dose-finding study on hematological malignancies and prostate cancer APR-246 had a good safety profile, and both biological and clinical responses were observed (Lehmann et al. J Clin Oncol 30, 2012). A Phase II Proof of Concept study in p53 mutant ovarian cancer patients is currently under way. Here results from combination studies with APR-246 and platinum compounds in p53 mutant ovarian cancer cell lines, and primary cells from patients, are presented. Methods: Cell viability/proliferation was assessed with WST-1, MTT and/or FMCA assay. p53 gene status was determined with Sanger sequencing and single strand conformation analysis. p53 expression was determined with Western immunoblotting. Results: In the ovarian cancer cell line OVCAR-3, with homozygous “hot spot” p53 core domain mutation (R248Q), strong/outstanding synergistic effects with APR-246 and cisplatin were observed (CI < 0.5). This cell line was established from a patient resistant to clinically relevant concentrations of cisplatin, doxorubicin and melphalan. The OVCAR-3 cell line expresses a high level of p53. In the in vitro cisplatin resistant ovarian cancer cell lines (A2780-CP20, IGROV-1/CDDP, IGROV-1/Pt-1) harboring heterozygous frequently occurring p53 core domain mutations, synergistic (CI < 0.8) or strong synergistic effects were observed. Also these cell lines express p53 but at lower level. These resistant cell lines have been developed from parental cisplatin sensitive cell lines derived from untreated patients with wt p53, by chronic in vitro exposure to cisplatin. Carboplatin and doxorubicin showed cross-resistance in cisplatin resistant cell lines, while the sensitivity of APR-246 did not change. Primary ovarian cancer cells were also investigated and strong synergistic effect was found in all samples. In vivo efficacy (xenograft) combination studies using cisplatin resistant ovarian cancer cell lines in nude mice are ongoing. Conclusion: These results further support the Phase II Proof of Concept study of APR-246 in p53 mutated ovarian cancer patients who are candidates for further platinum-based chemotherapy. Citation Format: Nina Mohell, Jessica Alfredsson, Maria Uustalu, Åsa Fransson, Vladimir J.N. Bykov, Klas G. Wiman, Ulf Björklund. Strong synergistic effects with cisplatin and APR-246, a novel compound reactivating mutant p53, in ovarian cancer cell lines and primary cells from patients. [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 3448. doi:10.1158/1538-7445.AM2013-3448