Sensitization of Cutaneous Primary Afferents in Bone Cancer Revealed by In Vivo Calcium Imaging

Abstract

Cancer-induced bone pain (CIBP) is a complex condition, comprising components of inflammatory and neuropathic processes, but changes in the physiological response profiles of bone-innervating and cutaneous afferents remain poorly understood. We used a combination of retrograde labelling and in vivo calcium imaging of bone marrow-innervating dorsal root ganglia (DRG) neurons to determine the contribution of these cells in the maintenance of CIBP. We found a majority of femoral bone afferent cell bodies in L3 dorsal root ganglia (DRG) that also express the sodium channel subtype Nav1.8—a marker of nociceptive neurons—and lack expression of parvalbumin—a marker for proprioceptive primary afferents. Surprisingly, the response properties of bone marrow afferents to both increased intraosseous pressure and acid were unchanged by the presence of cancer. On the other hand, we found increased excitability and polymodality of cutaneous afferents innervating the ipsilateral paw in cancer bearing animals, as well as a behavioural phenotype that suggests changes at the level of the DRG contribute to secondary hypersensitivity. This study demonstrates that cutaneous afferents at distant sites from the tumour bearing tissue contribute to mechanical hypersensitivity, highlighting these cells as targets for analgesia.

Mechanisms of cancer pain

“…The cell lines used will vary across species and studies, e.g., for B6C3-Fe-a/a and C3H/HeJ mice, fibrosarcoma cells have been reported to be administered in the femur ( 26 , 27 ), humerus ( 28 ) and calcaneus bones ( 29 ). Lewis lung carcinoma cells are administered into the intramedullary space of the femur in C57BL/6 mice ( 30 ). In rats, MRMT1 mammary gland carcinoma cells are administered into the tibias of female Sprague–Dawley rats ( 31 ), and MDA-MB231 human breast cancer cells are injected into femoral arteries of nude rats ( 32 ) as well as R3327 prostate cancer cells ( 33 ).…”

“…Rodents exhibit pain-like behaviours within 2–3 weeks of intrafemoral inoculation with cancer cells in a dose-dependent manner ( 30 , 36 , 37 ). Non-evoked pain behaviours include reduced use of the affected limb, which can be quantified using a limb score, as well as a reduction in weight borne on the affected limb when tested by an incapacitance tester ( 30 , 36 – 38 ). Loss of bone mineral density or osteolysis can also be reliably detected with the progression of tumour growth ( 30 ).…”

Metformin Attenuates Bone Cancer Pain by Reducing TRPV1 and ASIC3 Expression

“…Previous studies have shown that 85% of patients with lung, breast and prostate cancer appear bone metastasis, and about one-third of them was accompanied with bone cancer pain (BCP) symptoms (Okui et al, 2021). Bone cancer pain (BCP) is a unique pain that includes features of nociceptive, neuropathic, and inflammatory pain (de Clauser et al, 2020). BCP can produce an excruciating pain, but current treatments strategies may be inadequate or have unacceptable side effects (Sindhi and Erdek, 2019;Yu et al, 2020;Chen et al, 2021).…”

Activation of GDNF-ERK-Runx1 signaling contributes to P2X3R gene transcription and bone cancer pain

“…Given that the cutaneous afferents innervating the hind paw rather than bone afferents themselves are sensitized in animals with bone cancer pain ( de Clauser et al., 2020 ; Kucharczyk et al., 2020 ), and the anti-P2X3 antibody only reverses cutaneous, but not skeletal pain hypersensitivity to these animals ( Guedon et al., 2016 ), it raises the possibility that bone afferents are probably not involved in the P2X3R-mediated mechanical hypersensitivity under bone cancer condition. It is suggested that cutaneous afferents at distant sites from the tumor-bearing bone might contribute to secondary mechanical hypersensitivity ( de Clauser et al., 2020 ; Kucharczyk et al., 2020 ). Further study is needed to determine the involved heterogeneous population of sensory neurons that contribute to nociceptive processing of bone cancer pain.…”