Abstract 2263: Biliverdin inhibits head and neck cancer cell growth via activation of retinoblastoma signaling pathway.

Head and neck cancer patients often present with advanced disease and, despite advances in chemoradiation treatment protocols, continue to have a poor prognosis while experiencing severe treatment induced toxicity. There is an increased demand for natural, and non-toxic agents for treatment, which can be either used alone or in combination with our therapies. In this study, we are using biliverdin (BV), an antioxidant bile pigment, which is oxidized from bilirubin. As a potent antioxidant, accumulating data from observations in experimental and human studies indicate that the BV may be protective against certain diseases, including cancer. Based on our own observations that BV suppresses cell proliferation in head and neck squamous cell carcinoma (HNSCC) cells and clinical observations finding a lesser incidence of cancer in healthy individuals with slightly elevated serum bilirubin levels, we hypothesized that BV might suppress tumor cell proliferation. The present study looks to evaluate whether BV treatment can suppress cell proliferation in HNSCC cells in vitro and in vivo, and to elucidate the potential mechanism through which it exerts this effect. HNSCC cell lines, with varying resistance to chemoradiation, and a mouse model with human HNSCC xenografts were used in this study. As potential effectors, we analyzed key proteins that are involved in apoptosis and cell cycle progression. In vitro, we investigated the effect of BV on five HNSCC cell lines and the signaling pathways involved in BV action on tumor cell proliferation using western blots. We also analyzed the antiproliferative effects of the BV by the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and cell cycle analysis where BV caused cell cycle arrest by hypophosphorylation (activating) of the retinoblastoma (Rb) tumor suppressor protein in HNSCC cells. Ex vivo, we found significant suppression of xenograft tumor growth in HNSCC cells pretreated with BV before intradermal injection in nude mice as compared to controls. In vivo, tumor growth was assessed in BALB/c nude mice bearing HNSCC xenografts that were treated with BV. The signaling pathway responsible for this action included dephosphorylation of epidermal growth factor receptor (EGFR), Akt, NF-κB, and hypophosphorylation of the Rb tumor suppressor protein as well as caspase activation. Our study provides a rationale for a novel therapeutic approach using exogenous BV, a nontoxic antioxidant product of heme catabolism, as an anti-cancer agent against HNSCC through its effect on the Rb/Akt/NF-κB signal transduction pathway. Our findings indicate that BV9s actions on these key tumorogenic pathways may extend its therapeutic potential to head and neck cancer. Citation Format: Jun Zheng, Danish A. Nagda, Shayanne A. Lajud, Sanjeev Kumar, Anas Mouchli, Orysia Bezpalko, Bert W. O9Malley, Daqing Li. Biliverdin inhibits head and neck cancer cell growth via activation of retinoblastoma signaling pathway. [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 2263. doi:10.1158/1538-7445.AM2013-2263