Tumor Tissue-Derived Formaldehyde and Acidic Microenvironment Synergistically Induce Bone Cancer Pain Zhiqian Tong 1 * . , Wenhong Luo2., Yanqing Wang3., Fei Yang 1 , Ying Han 1 , Hui Li2, Hongjun Luo 2 , Bo Duan 4 , Tianle Xu 4 , Qiliang Maoying 3 , Huangying Tan5, Jun Wang 6 , Hongmei Zhao7, Fengyu Liu1, You Wan1,8* 1 Neuroscience Research Institute, Peking University, Beijing, China, 2 The Central Laboratory, Shantou University Medical College, Shantou, China, 3 Department of Integrative Medicine and Neurobiology, State Key Laboratory of Medical Neurobiology, Shanghai Medical College, Fudan University, Shanghai, China, 4 Institute of Neuroscience and National Key Laboratory of Neuroscience, Chinese Academy of Sciences, Shanghai, China, 5 Department of TCM Oncology, China-Japan Friendship Hospital, Beijing, China, 6 Department of Thoratic Surgery, Peking University People’s Hospital, Beijing, China, 7 Department of General Surgery, Peking University Third Hospital, Beijing, China, 8 Key Laboratory for Neuroscience, Ministry of Education/Ministry of Public Health, Beijing, China Abstract Background: There is current interest in understanding the molecular mechanisms of tumor-induced bone pain. Accumulated evidence shows that endogenous formaldehyde concentrations are elevated in the blood or urine of patients with breast, prostate or bladder cancer. These cancers are frequently associated with cancer pain especially after bone metastasis. It is well known that transient receptor potential vanilloid receptor 1 (TRPV1) participates in cancer pain. The present study aims to demonstrate that the tumor tissue-derived endogenous formaldehyde induces bone cancer pain via TRPV1 activation under tumor acidic environment. Methodology/Principal Findings: Endogenous formaldehyde concentration increased significantly in the cultured breast cancer cell lines in vitro, in the bone marrow of breast MRMT-1 bone cancer pain model in rats and in tissues from breast cancer and lung cancer patients in vivo. Low concentrations (1,5 mM) of formaldehyde induced pain responses in rat via TRPV1 and this pain response could be significantly enhanced by pH 6.0 (mimicking the acidic tumor microenvironment). Formaldehyde at low concentrations (1 mM to 100 mM) induced a concentration-dependent increase of [Ca2+]i in the freshly isolated rat dorsal root ganglion neurons and TRPV1-transfected CHO cells. Furthermore, electrophysiological experiments showed that low concentration formaldehyde-elicited TRPV1 currents could be significantly potentiated by low pH (6.0). TRPV1 antagonists and formaldehyde scavengers attenuated bone cancer pain responses. Conclusions/Significance: Our data suggest that cancer tissues directly secrete endogenous formaldehyde, and this formaldehyde at low concentration induces metastatic bone cancer pain through TRPV1 activation especially under tumor acidic environment. Citation: Tong Z, Luo W, Wang Y, Yang F, Han Y, et al. (2010) Tumor Tissue-Derived Formaldehyde and Acidic Microenvironment Synergistically Induce Bone Cancer Pain. PLoS ONE 5(4): e10234. doi:10.1371/journal.pone.0010234 Editor: Hiroaki Matsunami, Duke University, United States of America Received November 25, 2009; Accepted March 24, 2010; Published April 21, 2010 Copyright: 2010 Tong 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 research was supported by grants from the National Natural Science Foundation of China (30700206, 30800332), the 111 Project of the Ministry of Education of China (B07001), the National Basic Research Program of the Ministry of Science and Technology of China (2007CB512501) and Beijing Outstanding Ph.D. Program Mentor Grant, Key Project of Chinese Ministry of Education (109003). 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: tzq88666883@sina.com (ZT); ywan@hsc.pku.edu.cn (YW) . These authors contributed equally to this work. Introduction Cancer pain is a severe clinical condition, and about 75,90% of advanced or terminal cancer patients experience chronic pain related to treatment failure and/or tumor progression or metastasis. Malignant bone tumors occur in patients with primary bone cancer, but are far more commonly found to be distant metastases from other primary cancers, notably breast, lung and prostate cancers. As such, bone is the most common site of origin of chronic pain in patients with metastatic lung, breast and prostate cancers and myeloma [1]. In the development of cancer, it is suggested that tumor tissues secrete different kinds of factors including cytokines such as TNF-a and IL-1 [2]. Clinical data have shown that formaldehyde concentration is elevated (2,8 fold) in the urine of patients with prostate and bladder cancer [3] and in the expired air from tumor-bearing mice and breast cancer patients [4]; and these patients frequently suffer from bone cancer pain [5,6]. Formaldehyde is considered to be a risk factor of cancer development [7], but for the most part knowledge about formaldehyde secretion by tumor tissue is PLoS ONE | www.plosone.org 1 April 2010 | Volume 5 | Issue 4 | e10234