A new rat model of bone cancer pain produced by rat breast cancer cells implantation of the shaft of femur at the third trochanter level

Advancing Pain Understanding and Drug Discovery: Insights from Preclinical Models and Recent Research Findings

Despite major advancements in our understanding of its fundamental causes, pain-both acute and chronic-remains a serious health concern. Various preclinical investigations utilizing diverse animal, cellular, and alternative models are required and frequently demanded by regulatory approval bodies to bridge the gap between the lab and the clinic. Investigating naturally occurring painful disorders can speed up medication development at the preclinical and clinical levels by illuminating molecular pathways. A wide range of animal models related to pain have been developed to elucidate pathophysiological mechanisms and aid in identifying novel targets for treatment. Pain sometimes drugs fail clinically, causing high translational costs due to poor selection and the use of preclinical tools and reporting. To improve the study of pain in a clinical context, researchers have been creating innovative models over the past few decades that better represent pathological pain conditions. In this paper, we provide a summary of traditional animal models, including rodents, cellular models, human volunteers, and alternative models, as well as the specific characteristics of pain diseases they model. However, a more rigorous approach to preclinical research and cutting-edge analgesic technologies may be necessary to successfully create novel analgesics. The research highlights from this review emphasize new opportunities to develop research that includes animals and non-animals using proven methods pertinent to comprehending and treating human suffering. This review highlights the value of using a variety of modern pain models in animals before human trials. These models can help us understand the different mechanisms behind various pain types. This will ultimately lead to the development of more effective pain medications.

OBSERVE: guidelines for the refinement of rodent cancer models

Existing guidelines on the preparation (Planning Research and Experimental Procedures on Animals: Recommendations for Excellence (PREPARE)) and reporting (Animal Research: Reporting of In Vivo Experiments (ARRIVE)) of animal experiments do not provide a clear and standardized approach for refinement during in vivo cancer studies, resulting in the publication of generic methodological sections that poorly reflect the attempts made at accurately monitoring different pathologies. Compliance with the 3Rs guidelines has mainly focused on reduction and replacement; however, refinement has been harder to implement. The Oncology Best-practices: Signs, Endpoints and Refinements for in Vivo Experiments (OBSERVE) guidelines are the result of a European initiative supported by EurOPDX and INFRAFRONTIER, and aim to facilitate the refinement of studies using in vivo cancer models by offering robust and practical recommendations on approaches to research scientists and animal care staff. We listed cancer-specific clinical signs as a reference point and from there developed sets of guidelines for a wide variety of rodent models, including genetically engineered models and patient derived xenografts. In this Consensus Statement, we systematically and comprehensively address refinement and monitoring approaches during the design and execution of murine cancer studies. We elaborate on the appropriate preparation of tumor-initiating biologicals and the refinement of tumor-implantation methods. We describe the clinical signs to monitor associated with tumor growth, the appropriate follow-up of animals tailored to varying clinical signs and humane endpoints, and an overview of severity assessment in relation to clinical signs, implantation method and tumor characteristics. The guidelines provide oncology researchers clear and robust guidance for the refinement of in vivo cancer models.

TRPV1 in dorsal root ganglion contributed to bone cancer pain

Tumor growth in situ or bone metastases in cancer patients all can induce bone cancer pain. It is frequently occurred in patients with breast, prostate, and lung cancer. Because of the lack of effective treatment, bone cancer pain causes depression, anxiety, fatigue, and sleep disturbances in cancer patients, disrupts the daily quality of life, and results in huge economic and psychological burden. Over the past years, transient receptor potential channels (TRPs), especially TRP vanilloid 1 (TRPV1) in dorsal root ganglion (DRG), have been considered to be involved in bone cancer pain. The characteristic of TRPV1 had been well studied. The mechanisms under TRPV1 regulation in DRG with bone cancer pain are complex, including inflammatory mediators, endogenous formaldehyde, and other mechanisms. In the present review, we summarize the role and potential mechanism of TRPV1 in DRG in bone cancer pain. As the primary sensory neurons, targeting the TRPV1 channel in DRG, might have fewer side effects than in central. We hope systematically understand of TRPV1 modulation in DRG will bring more effective strategy.

The spinal microglial IL-10/β-endorphin pathway accounts for cinobufagin-induced mechanical antiallodynia in bone cancer pain following activation of α7-nicotinic acetylcholine receptors

Background

Cinobufagin is the major bufadienolide of Bufonis venenum (Chansu), which has been traditionally used for the treatment of chronic pain especially cancer pain. The current study aimed to evaluate its antinociceptive effects in bone cancer pain and explore the underlying mechanisms.

Methods

Rat bone cancer model was used in this study. The withdrawal threshold evoked by stimulation of the hindpaw was determined using a 2290 CE electrical von Frey hair. The β-endorphin and IL-10 levels were measured in the spinal cord and cultured primary microglia, astrocytes, and neurons.

Results

Cinobufagin, given intrathecally, dose-dependently attenuated mechanical allodynia in bone cancer pain rats, with the projected E_max of 90% MPE and ED₅₀ of 6.4 μg. Intrathecal cinobufagin also stimulated the gene and protein expression of IL-10 and β-endorphin (but not dynorphin A) in the spinal cords of bone cancer pain rats. In addition, treatment with cinobufagin in cultured primary spinal microglia but not astrocytes or neurons stimulated the mRNA and protein expression of IL-10 and β-endorphin, which was prevented by the pretreatment with the IL-10 antibody but not β-endorphin antiserum. Furthermore, spinal cinobufagin-induced mechanical antiallodynia was inhibited by the pretreatment with intrathecal injection of the microglial inhibitor minocycline, IL-10 antibody, β-endorphin antiserum and specific μ-opioid receptor antagonist CTAP. Lastly, cinobufagin- and the specific α-7 nicotinic acetylcholine receptor (α7-nAChR) agonist PHA-543613-induced microglial gene expression of IL-10/β-endorphin and mechanical antiallodynia in bone cancer pain were blocked by the pretreatment with the specific α7-nAChR antagonist methyllycaconitine.

Conclusions

Our results illustrate that cinobufagin produces mechanical antiallodynia in bone cancer pain through spinal microglial expression of IL-10 and subsequent β-endorphin following activation of α7-nAChRs. Our results also highlight the broad significance of the recently uncovered spinal microglial IL-10/β-endorphin pathway in antinociception.

Anti-rheumatic drug iguratimod protects against cancer-induced bone pain and bone destruction in a rat model

The bone is one of the most common sites of metastasis in patients with cancer. Current treatments for bone metastases include bisphosphonates, denosumab, non-steroidal anti-inflammatory drugs and analgesics, but each of them has certain limitations. Cytokines and mediators released from various cells in the bone microenvironment may drive a vicious cycle of osteolytic bone metastases. Iguratimod (T-614), a novel disease-modifying anti-rheumatic drug, has demonstrated therapeutic effects by suppressing the production of inflammatory cytokines in rats and patients with rheumatoid arthritis. Therefore, the current study evaluated the hypothesis that iguratimod may protect against cancer-induced bone pain and bone metastasis in a rat model. For this purpose, rats inoculated with Walker 256 cells were treated with iguratimod from days 11–17 post-surgery. Mechanical paw withdrawal thresholds and expression levels of phosphorylated extracellular signal-related kinase (pERK) and c-Fos in the spinal cord were investigated to detect changes in bone pain. Bone destruction levels were detected using X-rays, hematoxylin and eosin and tartrate-resistant acid phosphatase staining. The results revealed that mechanical paw withdrawal thresholds and the expression levels of pERK and c-Fos declined in a dose-dependent manner in rats treated with iguratimod, and bone destruction severity was also reduced. These findings may provide important new insights into the treatment of bone metastasis symptoms.

The Walker 256 Breast Cancer Cell- Induced Bone Pain Model in Rats

The majority of patients with terminal breast cancer show signs of bone metastasis, the most common cause of pain in cancer. Clinically available drug treatment options for the relief of cancer-associated bone pain are limited due to either inadequate pain relief and/or dose-limiting side-effects. One of the major hurdles in understanding the mechanism by which breast cancer causes pain after metastasis to the bones is the lack of suitable preclinical models. Until the late twentieth century, all animal models of cancer induced bone pain involved systemic injection of cancer cells into animals, which caused severe deterioration of animal health due to widespread metastasis. In this mini-review we have discussed details of a recently developed and highly efficient preclinical model of breast cancer induced bone pain: Walker 256 cancer cell- induced bone pain in rats. The model involves direct localized injection of cancer cells into a single tibia in rats, which avoids widespread metastasis of cancer cells and hence animals maintain good health throughout the experimental period. This model closely mimics the human pathophysiology of breast cancer induced bone pain and has great potential to aid in the process of drug discovery for treating this intractable pain condition.

Fufang Kushen injection inhibits sarcoma growth and tumor-induced hyperalgesia via TRPV1 signaling pathways

Cancer pain is a deleterious consequence of tumor growth and related inflammation. Opioids and anti-inflammatory drugs provide first line treatment for cancer pain, but both are limited by side effects. Fufang Kushen injection (FKI) is GMP produced, traditional Chinese medicine used alone or with chemotherapy to reduce cancer-associated pain. FKI limited mouse sarcoma growth both in vivo and in vitro, in part, by reducing the phosphorylation of ERK and AKT kinases and BAD. FKI inhibited TRPV1 mediated capsaicin-induced ERK phosphorylation and reduced tumor-induced proinflammatory cytokine production. Thus, FKI limited cancer pain both directly by blocking TRPV1 signaling and indirectly by reducing tumor growth.

Evidence for involvement of spinal RANTES in the antinociceptive effects of triptolide, a diterpene triepoxide, in a rat model of bone cancer pain

It has been shown that triptolide has beneficial effects in the treatment of neuropathic pain, but its effects on bone cancer pain (BCP) remain unclear. In this study, we aimed to explore the potential role of spinal regulated activation of normal T cell expressed and secreted (RANTES) in the antinociceptive effects of triptolide on BCP. A BCP model was induced by injecting Walker 256 mammary gland carcinoma cells into the intramedullary space of rat tibia. Intrathecal administration of triptolide (0.5, 1, 2 μg) could dose-dependently alleviate mechanical hyperalgesia and spontaneous pain. In addition, there were also concomitant decreases in RANTES mRNA and protein expression levels in spinal dorsal horn. These results suggest that the antinociceptive effects of triptolide are related with inhibition of spinal RANTES expression in BCP rats. The findings of this study may provide a promising drug for the treatment of BCP.