IB4(+) and TRPV1(+) sensory neurons mediate pain but not proliferation in a mouse model of squamous cell carcinoma

Yi Ye,Scott Troob,Brian L Schmidt,Daniel Bernabé,Chi T Viet,Sam S Bae

doi:10.1186/1744-9081-10-5

Abstract

BackgroundCancer pain severely limits function and significantly reduces quality of life. Subtypes of sensory neurons involved in cancer pain and proliferation are not clear.MethodsWe produced a cancer model by inoculating human oral squamous cell carcinoma (SCC) cells into the hind paw of athymic mice. We quantified mechanical and thermal nociception using the paw withdrawal assays. Neurotoxins isolectin B4-saporin (IB4-SAP), or capsaicin was injected intrathecally to selectively ablate IB4(+) neurons or TRPV1(+) neurons, respectively. JNJ-17203212, a TRPV1 antagonist, was also injected intrathecally. TRPV1 protein expression in the spinal cord was quantified with western blot. Paw volume was measured by a plethysmometer and was used as an index for tumor size. Ki-67 immunostaining in mouse paw sections was performed to evaluate cancer proliferation in situ.ResultsWe showed that mice with SCC exhibited both mechanical and thermal hypersensitivity. Selective ablation of IB4(+) neurons by IB4-SAP decreased mechanical allodynia in mice with SCC. Selective ablation of TRPV1(+) neurons by intrathecal capsaicin injection, or TRPV1 antagonism by JNJ-17203212 in the IB4-SAP treated mice completely reversed SCC-induced thermal hyperalgesia, without affecting mechanical allodynia. Furthermore, TRPV1 protein expression was increased in the spinal cord of SCC mice compared to normal mice. Neither removal of IB4(+) or TRPV1(+) neurons affected SCC proliferation.ConclusionsWe show in a mouse model that IB4(+) neurons play an important role in cancer-induced mechanical allodynia, while TRPV1 mediates cancer-induced thermal hyperalgesia. Characterization of the sensory fiber subtypes responsible for cancer pain could lead to the development of targeted therapeutics.

Highlights

Cancer pain severely limits function and significantly reduces quality of life
Drugs were delivered into the subarachnoid space between the L4 and L5 vertebrae in the spinal cord via a 10 μl Hamilton syringe. 1.53 mM IB4saporin (IB4-SAP, 53% saporin/mole isolectin B4 (IB4)) or 0.81 mM saporin (SAP, Advanced Targeting Systems, San Diego, CA) was diluted with phosphate buffer saline (PBS) to a total volume of 8 μl, and were injected 2 weeks before squamous cell carcinoma (SCC) cell inoculation; as SAP has no method of cell entry on its own and does not change thermal or mechanical behaviours compared to naive mice [22], it was used as a control
SCC induced thermal hyperalgesia was mediated by TRPV1 To determine whether TRPV1 contributed to thermal hyperalgesia induced by SCC inoculation and isolectin B4-saporin (IB4-SAP) treatment, we quantified nociceptive behavior after intrathecal injection of capsaicin into IB4-SAP pre-treated mice during post SCC inoculation week 3

Summary

Introduction

Cancer pain severely limits function and significantly reduces quality of life. Subtypes of sensory neurons involved in cancer pain and proliferation are not clear. Cancer patients in pain suffer with a poor quality of life. One strategic approach to cancer pain drug development is targeted therapy against subtypes of nociceptors that control specific sensory modalities. It has been proposed that nonpeptidergic IB4(+) neurons and the peptidergic TRPV1(+) neurons represent two parallel neuronal pathways that selectively control mechanical and thermal pain, respectively [10,12]. Many other studies did not find complete segregation between the IB4(+) and TRPV1(+) neurons in mechanical vs thermal pain [15,16,17,18]. Some authors hypothesized that the two neuronal populations serve different functions in pathological pain conditions with IB4(+) neurons contributing to neuropathic pain while the TRPV1(+) neurons contribute to inflammatory pain [19,20]

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Discussion

Conclusion