A Novel Role for BDNF-TrkB in the Regulation of Chemotherapy Resistance in Head and Neck Squamous Cell Carcinoma Junegoo Lee . , Tilahun Jiffar., Michael E. Kupferman* Department of Head and Neck Surgery, MD Anderson Cancer Center, University of Texas, Houston, Texas, United States of America Abstract Mechanisms of resistance for HNSCC to cisplatin (CDDP), the foundational chemotherapeutic agent in the treatment of this disease, remain poorly understood. We previously demonstrated that cisplatin resistance (CR) can be overcome by targeting Trk receptor. In the current study, we explored the potential mechanistic role of the BDNF-TrkB signaling system in the development of CDDP resistance in HNSCC. Utilizing an in vitro system of acquired CR, we confirmed a substantial up- regulation of both BDNF and TrkB at the protein and mRNA levels in CR cells, suggesting an autocrine pathway dysregulation in this system. Exogenous BDNF stimulation led to an enhanced expression of the drug-resistance and anti- apoptotic proteins MDR1 and XiAP, respectively, in a dose-dependently manner, demonstrating a key role for BDNF-TrkB signaling in modulating the response to cytotoxic agents. In addition, modulation of TrkB expression induced an enhanced sensitivity of cells to CDDP in HNSCC. Moreover, genetic suppression of TrkB resulted in changes in expression of Bim, XiAP, and MDR1 contributing to HNSCC survival. To elucidate intracellular signaling pathways responsible for mechanisms underlying BDNF/TrkB induced CDDP-resistance, we analyzed expression levels of these molecules following inhibition of Akt. Inhibition of Akt eliminated BDNF effect on MDR1 and Bim expression in OSC-19P cells as well as modulated expressions of MDR1, Bim, and XiAP in OSC-19CR cells. These results suggest BDNF/TrkB system plays critical roles in CDDP- resistance development by utilizing Akt-dependent signaling pathways. Citation: Lee J, Jiffar T, Kupferman ME (2012) A Novel Role for BDNF-TrkB in the Regulation of Chemotherapy Resistance in Head and Neck Squamous Cell Carcinoma. PLoS ONE 7(1): e30246. doi:10.1371/journal.pone.0030246 Editor: Kaustubh Datta, University of Nebraska Medical Center, United States of America Received August 10, 2011; Accepted December 15, 2011; Published January 20, 2012 Copyright: 2012 Lee et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work is supported by the following funding sources: NIH Grant K08-DE019185 (MEK), Joint American-College of Surgeons – Triological Society Grant (MEK), MD Anderson Cancer Center Physician-Scientist Program (MEK) and Sheila Newar Cancer Research Foundation. This research is also supported in part by the National Institutes of Health through M.D. Anderson’s Cancer Center Support Grant CA016672. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: mekupfer@mdanderson.org . These authors contributed equally to this work. Introduction As the sixth most common cancer worldwide, head and neck squamous cell carcinoma (HNSCC) is responsible for 5% percent of all cancers diagnosed in the United States [1]. The evolution of treatment for this disease has progressed to a greater emphasis on the use of cisplatin (CDDP)-based chemotherapy in the neoadju- vant and adjuvant settings. However, the clinical response to CDDP is associated with only a 10–15% improvement in local- regional control of disease, and marginal improvement in overall survival [2,3,4]. These sobering results suggest that resistance to CDDP (CR) is a fundamental biological property of this disease. Moreover, tumor recurrences or distant metastasis rarely respond to CDDP-based regimens. Therefore, understanding the mecha- nisms underlying CDDP resistance may provide strategic targets and promising treatments against HNSCC. Platinum-based chemotherapeutic agents, which include CDDP and carboplatinum, function therapeutically primarily by inducing DNA damage in rapidly dividing cells, thereby inducing apoptosis and cell death. Various mechanisms have been reported to contribute to the development of resistance against platinum- based chemotherapeutic agents including: (1) increased drug efflux; (2) decreased drug influx; (3) enhanced detoxification through GST-p activation; (4) suppressed apoptosis; and (5) enhanced DNA repair mechanisms [5,6]. Among these mecha- nisms, the Tyrosine Receptor Kinase B and Brain Derived neurotropic Factor (TrkB/BDNF) system has been reported to be responsible for chemoresistance, through Akt/PI-3K and MAPK signaling pathways, in selected models of cancer [7,8]. However, TrkB-mediated resistance to CDDP has not been studied in HNSCC. Although it is clearly evident that TrkB/BDNF system plays a role in tumor progression and metastasis, the molecular mechanisms underlying BDNF-induced chemoresistance develop- ment are not fully understood. The tropomyosin-related kinase B receptor (TrkB) belongs to receptor tyrosine kinase family and triggers its intracellular signals with its ligands, brain derived neurotrophic factor (BDNF) and neurotrophin 4 (NT4). TrkB has been shown to be over-expressed in various cancer types and is associated with poor prognosis [9,10]. Cumulative evidence indicates TrkB is responsible for tumor progression such as invasion, metastasis, angiogenesis, and resistance against therapeutic agents [11,12,13]. Mechanistically, the activation of TrkB by BDNF has shown to activate various intracellular signaling pathways including Akt, Src, or MAPK PLoS ONE | www.plosone.org 1 January 2012 | Volume 7 | Issue 1 | e30246