Peripheral Contribution of BDNF/TrkB signaling in Mediating Oral Cancer Pain

Background: Oral cancer pain is debilitating and understanding mechanisms for it is critical to develop treatment strategies. Brain-derived neurotrophic factor (BDNF) signaling is elevated in oral tumor biopsies and has been reported to promote tumor progression. However, whether BDNF signaling in oral tumors contributes to cancer-induced pain is not known. Therefore, the current study evaluates a novel peripheral role of BDNF/TrkB signaling in oral cancer pain. Using an orthotopic mouse tongue cancer pain model, we determine BDNF levels and expression tumor-tongue and normal tongue tissues using ELISA and immunohistochemistry. Additionally, we evaluated the effect of local administration of BDNF neutralizing Ab as well as TrkB receptor antagonist (ANA12) in reversing pain-like behaviors in vivo. Further, we identified the sensory fiber type affected by local ANA12 treatment in tumor-bearing tongues using single-fiber tongue-nerve electrophysiology and characterized TrkB isoform expression in sensory neuronal subtypes innervating mouse tongue. Our data demonstrated that BDNF levels were up-regulated in superfusates and lysates of tumor tongues over normal tongues and that BDNF was expressed by the cancer cells within the tumor. Neutralization of BDNF or inhibition of TrkB activity (ANA12) within the tumor-bearing tongue reversed tongue-tumor induced pain-like behaviors. Single-fiber recordings of tongue-nerve preparations revealed that ANA12 reversed tumor-induced mechanical sensitivity of A-slow high threshold mechanoreceptors. Single-cell RTPCR of lingual neurons demonstrated expression of full-form TrkB and truncated TrkB in distinct neuronal subtypes. Our data suggests that BDNF is released from oral cancer cells at the site of tumor growth and activates TrkB-expressing lingual sensory fibers, thereby contributing to oral cancer pain. This is a novel finding and the first demonstration of a peripheral role for BDNF signaling in oral cancer pain. Targeting BDNF signaling peripherally may prove to be an effective treatment for cancer-induced pain as well as tumorigenesis.