Effect of sex in the MRMT-1 model of cancer-induced bone pain

Sex differences in mechanisms of pain hypersensitivity

The introduction of sex-as-a-biological-variable policies at funding agencies around the world has led to an explosion of very recent observations of sex differences in the biology underlying pain. This review considers evidence of sexually dimorphic mechanisms mediating pain hypersensitivity, derived from modern assays of persistent pain in rodent animal models. Three well-studied findings are described in detail: the male-specific role of spinal cord microglia, the female-specific role of calcitonin gene-related peptide (CGRP), and the female-specific role of prolactin and its receptor. Other findings of sex-specific molecular involvement in pain are subjected to pathway analyses and reveal at least one novel hypothesis: that females may preferentially use Th1 and males Th2 T cell activity to mediate chronic pain.

Exosomal miR-19a and IBSP cooperate to induce osteolytic bone metastasis of estrogen receptor-positive breast cancer

Bone metastasis is an incurable complication of breast cancer. In advanced stages, patients with estrogen-positive tumors experience a significantly higher incidence of bone metastasis (>87%) compared to estrogen-negative patients (<56%). To understand the mechanism of this bone-tropism of ER+ tumor, and to identify liquid biopsy biomarkers for patients with high risk of bone metastasis, the secreted extracellular vesicles and cytokines from bone-tropic breast cancer cells are examined in this study. Both exosomal miR-19a and Integrin-Binding Sialoprotein (IBSP) are found to be significantly upregulated and secreted from bone-tropic ER+ breast cancer cells, increasing their levels in the circulation of patients. IBSP is found to attract osteoclast cells and create an osteoclast-enriched environment in the bone, assisting the delivery of exosomal miR-19a to osteoclast to induce osteoclastogenesis. Our findings reveal a mechanism by which ER+ breast cancer cells create a microenvironment favorable for colonization in the bone. These two secreted factors can also serve as effective biomarkers for ER+ breast cancer to predict their risks of bone metastasis. Furthermore, our screening of a natural compound library identifies chlorogenic acid as a potent inhibitor for IBSP-receptor binding to suppress bone metastasis of ER+ tumor, suggesting its preventive use for bone recurrence in ER+ patients.

The nociceptin/orphanin FQ receptor system as a target to alleviate cancer-induced bone pain in rats: Model validation and pharmacological evaluation

BACKGROUND AND PURPOSE

Cancer-induced bone pain remains inadequately controlled, and current standard of care analgesics is accompanied by several side effects. Nociceptin/orphanin FQ peptide (NOP) receptor agonists have demonstrated broad analgesic properties in rodent neuropathic and inflammatory pain models. Here, we investigate the analgesic potential of NOP receptor activation in a rodent cancer-induced bone pain model.

EXPERIMENTAL APPROACH

Model validation by intratibial inoculation in male Sprague Dawley rats was performed with varying MRMT-1/Luc2 cell quantities (0.5-1.5 × 106 ·ml-1 ) and a behavioural battery (>14 days post-surgery) including evoked and non-evoked readouts: paw pressure test, cold plate, von Frey, open field, and weight distribution. Anti-allodynic potential of the endogenous NOP receptor ligand nociceptin (i.t.) and NOP receptor agonist Ro65-6570 ( i.p.) was tested using von Frey filaments, followed by a combination experiment with Ro65-6570 and the NOP receptor antagonist J-113397 (i.p.). Plasma cytokine levels and NOP receptor gene expression in dorsal root ganglion (DRG, L4-L6) and bone marrow were examined.

KEY RESULTS

Inoculation with 1.5 × 106 ·ml-1 of MRMT-1/Luc2 cells resulted in a robust and progressive pain-related phenotype. Nociceptin and Ro65-6570 treatment inhibited cancer-induced mechanical allodynia. J-113397 selectively antagonized the effect of Ro65-6570. MRMT-1/Luc2-bearing animals demonstrated elevated plasma cytokine levels of IL-4, IL-5, IL-6 and IL-10 plus unaltered NOP-r gene expression in DRG and reduced expression in bone marrow.

CONCLUSION AND IMPLICATIONS

Nociceptin and Ro65-6570 selectively and dose-dependently reversed cancer-induced bone pain-like behaviour. The NOP receptor system may be a potential target for cancer-induced bone pain treatment.

LINKED ARTICLES

This article is part of a themed issue on The molecular pharmacology of bone and cancer-elated bone diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.9/issuetoc.

Modulation of Rat Cancer-Induced Bone Pain is Independent of Spinal Microglia Activity

The dissemination of cancer to bone can cause significant cancer-induced bone pain (CIBP), severely impairing the patient's quality of life. Several rodent models have been developed to explore the nociceptive mechanisms of CIBP, including intratibial inoculation of breast carcinoma cells in syngeneic Sprague Dawley rats. Using this model, we investigated whether resident spinal microglial cells are involved in the transmission and modulation of CIBP, a long-debated disease feature. Immunohistochemical staining of ionizing calcium-binding adaptor molecule 1 (Iba-1) and phosphorylated p38-mitogen-activated protein kinase (P-p38 MAPK) showed no spinal microglial reaction in cancer-bearing rats, independently of disease stage, sex, or carcinoma cell line. As a positive control, significant upregulation of both Iba-1 and P-p38 was observed in a rat model of neuropathic pain. Additionally, intrathecal administration of the microglial inhibitor minocycline did not ameliorate pain-like behaviors in cancer-bearing rats, in contrast to spinal morphine administration. Our results indicate that microglial reaction is not a main player in CIBP, adding to the debate that even within the same models of CIBP, significant variations are seen in disease features considered potential drug targets. We suggest that this heterogeneity may reflect the clinical landscape, underscoring the need for understanding the translational value of CIBP models.

Cancer-induced Bone Pain Impairs Burrowing Behaviour in Mouse and Rat

BACKGROUND

Cancer-induced bone pain remains a serious public health concern, with a need for translational behavioural tests in order to assess nociception in preclinical models of this condition. Burrowing is an innate, ethologically relevant rodent behaviour that has been proven sensitive to chronic pain conditions. Herein, we studied for the first time whether burrowing performance is altered in preclinical models of cancer-induced bone pain.

MATERIALS AND METHODS

Mice and rats were inoculated with syngeneic breast cancer cells. Bone degradation was radiographically evaluated and nociception was assessed in limb-use and burrowing tests.

RESULTS

Cancer-bearing rodents showed reduced relative bone density and limb-use scores, confirming disease development. Burrowing performance decreased over time in both rodent models.

CONCLUSION

Burrowing performance was reduced in both rodent models, indicating that the burrowing test is a relevant and reproducible behavioural test for assessing disease development in both mouse and rat models of cancer-induced bone pain.

The Src family kinase inhibitor dasatinib delays pain-related behaviour and conserves bone in a rat model of cancer-induced bone pain

Pain is a severe and debilitating complication of metastatic bone cancer. Current analgesics do not provide sufficient pain relief for all patients, creating a great need for new treatment options. The Src kinase, a non-receptor protein tyrosine kinase, is implicated in processes involved in cancer-induced bone pain, including cancer growth, osteoclastic bone degradation and nociceptive signalling. Here we investigate the role of dasatinib, an oral Src kinase family and Bcr-Abl tyrosine kinase inhibitor, in an animal model of cancer-induced bone pain. Daily administration of dasatinib (15 mg/kg, p.o.) from day 7 after inoculation of MRMT-1 mammary carcinoma cells significantly attenuated movement-evoked and non-evoked pain behaviour in cancer-bearing rats. Radiographic - and microcomputed tomographic analyses showed significantly higher relative bone density and considerably preserved bone micro-architecture in the dasatinib treated groups, suggesting a bone-preserving effect. This was supported by a significant reduction of serum TRACP 5b levels in cancer-bearing rats treated with 15 mg/kg dasatinib. Furthermore, immunoblotting of lumbar spinal segments showed an increased activation of Src but not the NMDA receptor subunit 2B. These findings support a role of dasatinib as a disease modifying drug in pain pathologies characterized by increased osteoclast activity, such as bone metastases.

Effect of sex in the MRMT-1 model of cancer-induced bone pain

An overwhelming amount of evidence demonstrates sex-induced variation in pain processing, and has thus increased the focus on sex as an essential parameter for optimization of in vivo models in pain research. Mammary cancer cells are often used to model metastatic bone pain in vivo, and are commonly used in both males and females. Here we demonstrate that compared to male rats, female rats have an increased capacity for recovery following inoculation of MRMT-1 mammary cells, thus potentially causing a sex-dependent bias in interpretation of the data.