Abstract 1783: Puupehenol natural product inhibits STAT3 signaling and induces antitumor cell effects in vitro against human glioblastoma cells

Abstract

Abstract Glioblastoma multiforme (GBM) is a malignant brain tumor that lacks effective therapeutics and has a high mortality rate. Constitutively-activated signal transducer and activator of transcription 3 (STAT3) protein is prevalent and implicated in GBM phenotype and represents a valid anti-GBM target. To discover novel STAT3 inhibitors suitable for GBM therapy, natural product extracts were investigated. Whole extracts from marine organisms were first screened for effects against cell viability using the human glioma model line, U251MG that harbors aberrantly-active STAT3 and normal fibroblasts that do not. The screening campaign identified the puupehenol, CC-1-2 from the whole extracts of leiodermatium sp as a bioactive compound that suppressed U251MG cell viability, with an IC50 4.1±0.1 µM, compared to an IC50 value of 7.3±0.3 µM against normal NIH3T3 mouse fibroblasts. Western blot analysis showed pSTAT3 levels in U251MG cells substantially decreased in a time-dependent manner in response to CC-1-2. Decreased pSTAT3 in treated cells occurred in parallel with partial suppression of both phospho- Janus kinase (Jak) 2 and pSrc levels and no induction of protein tyrosine phosphatase, PTP1B. Phosphorylated extracellular signal-regulated kinase (Erk) 1/2 levels also decreased in time-dependent manner, while pAkt remained unchanged in U251MG cells under the same treatment conditions. Furthermore, treatment of U251MG cells with CC-1-2 led to dramatic morphological changes that occurred in a dose- and time-dependent manner, compared to minimal changes observed for similarly-treated MCF-7 breast cancer cells that do not harbor aberrantly-active STAT3. Colony survival assay of U251MG cells revealed single treatment with 1-10 µM CC-1-2 decreased colony sizes and numbers in a dose-dependent manner, compared to moderate effects on MCF-7. In vitro wound-healing assay further showed reduced U251MG cell migration into the denuded area in response to CC-1-2 treatment. CC-1-2 further induced apoptosis in U251MG cells in a dose-dependent manner and suppressed the expression of c-Myc, Cyclin D1, and Bcl-2 levels, which are known STAT3-regulated genes. Studies together identify CC-1-2 as a natural product inhibitor of STAT3 that preferentially induces antitumor cell effects against human glioblastoma cells. Citation Format: Tyvette S. Hilliard, Christopher Chock, Philip Williams, James Turkson. Puupehenol natural product inhibits STAT3 signaling and induces antitumor cell effects in vitro against human glioblastoma cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1783. doi:10.1158/1538-7445.AM2014-1783