Abstract 2784: Nutlin-3 induces cell cycle arrest in p53 wild-type ovarian carcinomas via upregulation of p21

Abstract

Abstract Despite the fact that ovarian epithelial ovarian cancer is a molecularly and histologically heterogeneous disease, standard treatment is the same for all subtypes. Most high-grade serous ovarian carcinomas (OCs) are responsive to initial platinum/taxane chemotherapy, but low-grade serous OCs and clear cell OCs are relatively chemoresistant with limited treatment options upon recurrence, and most patients succumb to the disease. It is therefore of interest to exploit the molecular differences between high-grade serous OCs and other histological types in order to develop novel therapeutics. Over 90% of high-grade serous OCs harbor p53 mutations, whereas low-grade serous OCs are p53 wild-type but more frequently contain KRAS and BRAF mutations. Similarly, ovarian clear cell carcinomas are p53 wild-type but more frequently contain PI3K mutations. Nutlin-3 functions via inhibition of MDM2, thereby activating wild-type p53 and inducing apoptosis. We therefore sought to validate nutlin-3 as a potential novel therapeutic compound for p53 wild-type ovarian carcinomas. Two low-grade serous OC cell lines (HOC-7, MPSC-1), two clear cell OC cell lines (TOV21G, OVAS), and one high-grade serous OC p53-null cell line (SKOV3) were treated with varying concentrations of nutlin-3 (0-70 µm) for 72 hours, and cellular proliferation assays were performed. The three serous OC cell lines were then treated with nutlin-3 (5 µm), and quantitative reaction real-time polymerase chain reaction (qRT-PCR) and Western blot (WB) were employed to quantify MDM2, p53, and p21 expression at 24, 48, and 72 hours after treatment. The MPSC-1 cell line was then sequenced for p53 mutations in exons 5, 6, 7, and 8. Nutlin-3 inhibited cellular proliferation in a dose-dependent manner in the clear cell and low-grade serous cell lines, but not the p53-null high-grade serous cell line, as expected. Both PI3K-mutant clear cell ovarian cancer cell lines exhibited decreased growth in response to nutlin-3, but to a lesser extent than the low-grade serous cell lines. HOC-7, which bears a KRAS mutation, was more sensitive to inhibition than BRAF-mutated MPSC-1. Sequencing for p53 mutation in MPSC-1 surprisingly revealed a heterozygous p53 40 bp deletion in exon 5, which accounted for the reduced sensitivity of MPSC-1 to nutlin-3. On qRT-PCR and WB, levels of p53 were slightly decreased after nutlin-3 treatment and were absent in SKOV3. MDM2 and p21 were initially upregulated, but returned to near-baseline levels after 72 hours. Nutlin-3 is a novel potential therapeutic agent for low-grade serous ovarian carcinoma, and is dependent on an intact p53 pathway. It appears to function via upregulation of p21 with subsequent cell cycle arrest. Further studies characterizing response to nutlin-3 according to tumor mutation status are underway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2784. doi:1538-7445.AM2012-2784