Abstract 2059: HO-3867-induced apoptosis in hypoxic ovarian cancer cells occurs via ubiquitin-dependent degradation of signal transducer and activator of transcription 3 (STAT3)

Abstract

Abstract Objectives: Hypoxia plays a role in tumorigenesis and the development of resistance to radio- and chemotherapy. We have shown that human xenograft tumors in mice are severely hypoxic and that hypoxic exposure increases the phosphorylation of STAT3 at the Tyr705 residue in A2780 cell lines and is associated with chemotherapeutic resistance. HO-3867, a novel curcumin analogue designed with our institution, induces cell cycle arrest and apoptosis via inhibition of the STAT3 signaling pathway. The goal of this study was to understand the mechanistic pathways involved. Methods: The study was performed using A2780 and SKOV3 human ovarian cancer cell lines grown under normoxic (21% O2) and hypoxic (1% O2) conditions for 24 hours. Hypoxia-exposed cells were subsequently treated with 10 or 20 uM of HO-3867 for 2 and 24 hours. The expression levels of pSTAT3, associated proteins, and apoptotic markers were evaluated by Western blot and RT-PCR. Quantification of apoptosis was performed by staining with Annexin V. We also examined cell viability and involvement of ubiquitin-dependent degradation of pSTAT3. Results: Treatment with HO-3867 under hypoxic conditions resulted in decreased protein expression of pSTAT3 Tyr705 and Ser727. Rapid downregulation of STAT3 correlated with accelerated ubiquitin-dependent degradation of Tyr705-phosphorylated STAT3. Treatment was associated with decreased levels of STAT3-targeting proteins VEGF, Bcl-2, Bcl-xL, and cyclin D1. RT-PCR revealed decreased BCL-2 mRNA expression with treatment. There was no change in expression of proteins upstream of STAT3 including pJAK1, JAK1, pTYK2, TYK2, SOCS1 and SOCS2. An induction in apoptosis contributed to inhibition of cell proliferation as HO-3867-exposed cells exhibited elevated levels of cleaved caspase-3, caspase-7, and PARP as well as an increase in apoptotic cell count measured by flow cytometry. Conclusion: Under hypoxic growth conditions, HO-3867 demonstrates cytotoxicity via inhibition of STAT3. The use of HO-3867 may be a potential adjunct in the treatment of hypoxia-mediated chemotherapy-resistant ovarian cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2059. doi:10.1158/1538-7445.AM2011-2059