CXCR3: latest evidence for the involvement of chemokine signaling in bone cancer pain

The CXCL10/CXCR3 axis regulates Th1 cell differentiation and migration in experimental autoimmune prostatitis through the PI3K/AKT pathway

OBJECTIVE

To investigate the mechanism of the CXCL10/CXCR3 axis regulating Th1 cell differentiation and migration through the PI3K/AKT pathway in chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS).

METHODS

Experimental autoimmune prostatitis (EAP) model, a well-described and validated animal model of CP/CPPS, was used in our study. After treatment with CXCL10, the severity of EAP and Th1 cell proportion were respectively measured by HE stains, immunohistochemistry, and flow cytometry. Then, the protein expression of the PI3K/AKT pathway in CXCL10/CXCR3-regulated Th1 cell differentiation and migration was evaluated by western blotting. Additionally, by the CXCR3 antagonist AMG487 and the PI3K inhibitor LY294002 applications, the effects of CXCL10/CXCR3 through PI3K/AKT pathway on the Th1 cell differentiation and migration were further assessed.

RESULTS

The EAP model was successfully built. CXCL10 increased the proportion of Th1 cells in EAP mice, accompanied by upregulation of the PI3K/AKT pathway. Additionally, the PI3K/AKT pathway was found to be involved in CXCL10/CXCR3 axis-mediated Th1 cell differentiation and migration.

CONCLUSIONS

Our investigations indicate that the CXCL10/CXCR3 axis regulates Th1 cell differentiation and migration in EAP through the PI3K/AKT pathway, which provides a new perspective on the immunological mechanisms of CP/CPPS.

Oxaliplatin inhibits colorectal cancer progression by inhibiting CXCL11 secreted by cancer-associated fibroblasts and the CXCR3/PI3K/AKT pathway

PURPOSE

Colorectal cancer (CRC) is a malignant tumor. Oxaliplatin (OXA) can inhibit cancer-associated fibroblasts (CAFs)-induced cancer progression. This study sought to explore the mechanism of OXA in CAFs-induced CRC development.

METHODS

CRC cell lines (Caco-2, SW620), normal fibroblasts (NFs), and CAFs were treated with OXA. NFs and CAFs were cultured. CAFs were treated with/without OXA (0.4 mM), and the supernatant was extracted as the conditioned medium (CM) to culture CRC cells. Cell malignant episodes, E-cadherin and Vimentin levels, CXCL1, CXCL2, CXCL3, CXCL8, and CXCL11 mRNA levels, CXCL11 protein level, and extracellular release were assessed. CAFs were transfected with interfering RNA sh-CXCL11 to silence CXCL11 or transfected with CXCL11 overexpression plasmids and treated with OXA to explore the role of CXCL11 in OXA-mediated CRC cells through CAFs. CXCL11 receptor CXCR3 levels in CRC cells and the PI3K/AKT pathway changes were examined. The xenogeneic tumor was transplanted in nude mice. CXCL11 and CXCR3 levels in tumor tissues, tumor volume, shape, size, weight, and Ki67 positive expressions were assessed.

RESULTS

CRC cell growths and epithelial-mesenchymal transformation were stimulated after culture with CAFs-CM, while OXA averted these trends. CXCL11 mRNA level was elevated most significantly, and its protein and extracellular secretion levels were raised, while OXA diminished the levels. CXCL11 silencing weakened the effects of CAFs-CM on promoting CRC proliferation and malignant episodes and CXCL11 overexpression averted OXA property on inhibiting CAFs-promoted CRC cell growth. CXCR3 and PI3K and AKT1 phosphorylation levels were raised in the CAFs-CM group but diminished by OXA. CXCL11 overexpression in CAFs averted OXA property on inhibiting CAFs-activated CXCR3/PI3K/AKT in CRC cells. OXA also inhibited the progression of xenograft tumors by limiting CAFs-secreted CXCL11.

CONCLUSIONS

OXA repressed CRC progression by inhibiting CAFs-secreted CXCL11 and the CXCR3/PI3K/AKT pathway.

NADPH-Oxidase 2 Promotes Autophagy in Spinal Neurons During the Development of Morphine Tolerance

Repeated morphine administration results in analgesic tolerance. However, the underlying mechanism of morphine analgesic tolerance remains unclear. NADPH-oxidase 2 (NOX2) is the first discovered NADPH oxidase, which mainly functions to produce reactive oxygen species. Its specific role in morphine tolerance has not been fully investigated. In this work, we found that chronic morphine administration significantly increased the expression of NOX2 in spinal cord. Pretreatment of NOX2 inhibitor blocked the upregulation of NOX2 and autophagy markers, including LC3B and P62, and consequently the development of morphine tolerance. NOX2 and LC3B were both colocalized with NeuN in spinal dorsal horn in morphine-tolerant rats. Our results suggest that the increased autophagy activity in spinal neurons promoted by NOX2 activation contributes to the development of morphine tolerance. NOX2 may be considered as a new therapeutic target for morphine tolerance.

The circular RNA circSlc7a11 promotes bone cancer pain pathogenesis in rats by modulating LLC-WRC 256 cell proliferation and apoptosis

Treatment of bone cancer pain (BCP) caused by bone metastasis in advanced cancers remains a challenge in clinical oncology, and the underlying mechanisms of BCP are poorly understood. This study aimed to investigate the pathogenic roles of circular RNAs (circRNAs) in regulating cancer cell proliferation and BCP development. Eight differentially expressed circRNAs in the rat spinal cord were validated by agarose gel electrophoresis and Sanger sequencing. Expression of circRNAs and mRNAs was detected by quantitative RT-PCR. MTS assay and flow cytometry were performed to analyze cell proliferation and apoptosis, respectively. Differentially expressed mRNA profiles were characterized by deep RNA sequencing, hierarchical clustering, and functional categorization. The interactions among circRNAs, microRNAs (miRNAs), and mRNAs were predicted using TargetScan. Additionally, western blot was performed to determine the protein levels of Pax8, Isg15, and Cxcl10. Multiple circRNAs were differentially expressed in the spinal cords of BCP model rats; of these, circSlc7a11 showed the greatest increase in expression. The overexpression of circSlc7a11 significantly promoted cell proliferation and repressed apoptosis of LLC-WRC 256 and UMR-106 cells, whereas circSlc7a11 silencing produced the opposite effects. Altered expression of circSlc7a11 also induced substantial changes in the mRNA expression profiles of LLC-WRC 256 cells; these changes were linked to multiple apoptotic processes and signaling pathways, such as the chemokine signaling pathway, and formed a complex circRNA/miRNA/mRNA network. Additionally, Pax8, Isg15, and Cxc110 protein level in LLC-WRC 256 cells was consistent with the mRNA results. The circRNA circSlc7a11 regulates rat BCP development by modulating LLC-WRC 256 cell proliferation and apoptosis through multiple-signaling mechanisms.

Evaluating the Role of CXCR3 in Pain Modulation: A Literature Review

CXCR3 is a well-known receptor involved in immune cell recruitment and inflammation. Pathological inflammation leads to pain stimulation and hence nociception. Therefore, we decided to review the recent research on CXCR3 to identify its precise role in the modulation of pain in a variety of clinical conditions targeting various regions of the body. Studies were selected from PubMed Medline, which relate CXCR3 to the progression of diseases with either bone cancer pain, neuropathic pain, cystitis pain, osteoarthritis and rheumatoid arthritis pain, dental pain, in particular, periodontitis and pulpitis. In all the diseases studied, a high prevalence of CXCR3 and/or its ligand were identified where CXCR3 is a key player in the pathophysiological process of many inflammatory conditions. CXCR3 and its ligands, particularly CXCL10, modulate nociception via actions in the dorsal root ganglia and dorsal horn of the spinal cord, in cases of bone cancer pain, neuropathic, and joint pain. However, with the other studied disease, no direct link to pain has been made, although it contributes to the pathological progression of the diseases and hence would be a causal factor for the pain. Furthermore, CXCR3 appears to play a role in desensitizing the opioid receptor in the descending modulatory pathway within the brain stem as well as modulating opioid-induced hyperalgesia in the dorsal horn of the spinal cord. Further research is required for understanding the exact mechanisms of CXCR3 in pain modulation centrally and peripherally. A greater understanding of the immunological activities and pharmacological consequence of CXCR3 and its ligands could help in the discovery of newer drugs for modulating pain arising from pathogenic or inflammatory sources. Given the significance of the CXCR3 for nociception, its utilization may prove to be beneficial as a target for analgesia.

The endocannabinoid system: Novel targets for treating cancer induced bone pain

Treating Cancer-induced bone pain (CIBP) continues to be a major clinical challenge and underlying mechanisms of CIBP remain unclear. Recently, emerging body of evidence suggested the endocannabinoid system (ECS) may play essential roles in CIBP. Here, we summarized the current understanding of the antinociceptive mechanisms of endocannabinoids in CIBP and discussed the beneficial effects of endocannabinoid for CIBP treatment. Targeting non-selective cannabinoid 1 receptors or selective cannabinoid 2 receptors, and modulation of peripheral AEA and 2-AG, as well as the inhibition the function of fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) have produced analgesic effects in animal models of CIBP. Management of ECS therefore appears to be a promising way for the treatment of CIBP in terms of efficacy and safety. Further clinical studies are encouraged to confirm the possible translation to humans of the very promising results already obtained in the preclinical studies.

Endoplasmic Reticulum Stress in Spinal Cord Contributes to the Development of Morphine Tolerance

Morphine tolerance remains an intractable problem, which hinders its prolonged use in clinical practice. Endoplasmic reticulum (ER) stress has been proved to play a fundamental role in the pathogenesis of Alzheimer's disease, diabetes, atherosclerosis, cancer, etc. In this study, we provide the first direct evidence that ER stress may be a significant driver of morphine tolerance. Binding immunoglobulin protein (BiP), the ER stress marker, was significantly upregulated in neurons in spinal dorsal horn in rats being treated with morphine for 7 days. Additionally, chronic morphine treatment resulted in the activation of three arms of unfolded protein response (UPR): inositol-requiring enzyme 1/X-box binding protein 1 (IRE1/XBP1), protein kinase RNA-like ER kinase/eukaryotic initiation factor 2 subunit alpha (PERK/eIF2α), and activating transcription factor 6 (ATF6). More importantly, inhibiting either one of the three cascades could attenuate the development of morphine tolerance. Taken together, our results suggest that ER stress in spinal cord might contribute to the development of morphine tolerance. These findings implicate a potential clinical strategy for preventing morphine tolerance and may contribute to expanding the morphine usage in clinic.

Upregulation of (C-X-C motif) Ligand 13 (CXCL13) Attenuates Morphine Analgesia in Rats with Cancer-Induced Bone Pain

Background

The aim of this study was to investigate the role of chemokine (C-X-C motif) ligand 13 (CXCL13) in morphine tolerance in rats with cancer-induced bone pain (CIBP).

Material/Methods

We established a rat CIBP model and a rat CIBP-morphine tolerance (BM) model. BM rats were intrathecally administered rmCXCL13, neutralizing anti-CXCL13, and normal saline, while the control group rats underwent a sham operation and were injected with normal saline. The morphine analgesia was assessed by measuring mechanical withdrawal threshold (MWT) and mechanical withdrawal duration (MWD) at various time points. The co-expressions of CXCL13 and NeuN were measured by immunofluorescence double-staining. CXCL13 protein and mRNA expressions were detected by Western blot and quantitative real-time polymerase chain reaction (RT-qPCR), respectively.

Results

Compared to the sham-operation (S) group, the BM group showed obviously decreased MWT and increased MWD on Day 9 after CIBP, but obviously increased MWT and decreased MWD on Day 3 after morphine administration; subsequently, the MWT was decreased and MWD was increased (all P<0.05). In comparison with the S+saline group, increased MWT and decreased MWD were observed in BM rats on Day 3 after anti-CXCL13 administration, and obviously decreased MWT and increased MWD were found in BM rats on Day 3 after rmCXCL13 administration (all P<0.05).

Conclusions

Up-regulated CXCL13 has a negative role in morphine analgesia in relief of CIBP, which may provide a new target for the management of CIBP.

Involvement of Spinal CCR5/PKCγ Signaling Pathway in the Maintenance of Cancer-Induced Bone Pain

Cancer-induced bone pain (CIBP) is a challenging medical problem that considerably influences cancer patients' quality of life. Currently, few treatments have been developed to conquer CIBP because of a poor understanding of the potential mechanisms. Our previous work has proved that spinal RANTES (a major ligand for CCR5) was involved in the maintenance of CIBP. In this study, we attempted to investigate whether spinal CCR5 and its downstream PKCγ pathway is involved in the maintenance of CIBP. Inoculation of Walker 256 cells into the tibia could induce a marked mechanical allodynia with concomitant upregulation of spinal CCR5 and p-PKCγ expression from day 6 to day 15 after inoculation. Spinal CCR5 was prominently expressed in microglia, and mechanical allodynia was attenuated by intrathecal injection of DAPTA (a specific antagonist of CCR5) with downregulation of spinal CCR5 and p-PKCγ expression levels at day 15 in inoculated rats. Pre-intrathecal injection of RANTES could reverse the anti-allodynia effects of DAPTA. Intrathecal administration of GF109203X (an inhibitor of PKC) could alleviate mechanical allodynia as well as decrease of spinal p-PKCγ expression level, but no influence on spinal CCR5 level. Our findings suggest that CCR5/PKCγ signaling pathway in microglia may contribute to the maintenance of CIBP in rats.

Minocycline attenuates bone cancer pain in rats by inhibiting NF-κB in spinal astrocytes

AIM

To investigate the mechanisms underlying the anti-nociceptive effect of minocycline on bone cancer pain (BCP) in rats.

METHODS

A rat model of BCP was established by inoculating Walker 256 mammary carcinoma cells into tibial medullary canal. Two weeks later, the rats were injected with minocycline (50, 100 μg, intrathecally; or 40, 80 mg/kg, ip) twice daily for 3 consecutive days. Mechanical paw withdrawal threshold (PWT) was used to assess pain behavior. After the rats were euthanized, spinal cords were harvested for immunoblotting analyses. The effects of minocycline on NF-κB activation were also examined in primary rat astrocytes stimulated with IL-1β in vitro.

RESULTS

BCP rats had marked bone destruction, and showed mechanical tactile allodynia on d 7 and d 14 after the operation. Intrathecal injection of minocycline (100 μg) or intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced mechanical tactile allodynia. Furthermore, intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced upregulation of GFAP (astrocyte marker) and PSD95 in spinal cord. Moreover, intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced upregulation of NF-κB, p-IKKα and IκBα in spinal cord. In IL-1β-stimulated primary rat astrocytes, pretreatment with minocycline (75, 100 μmol/L) significantly inhibited the translocation of NF-κB to nucleus.

CONCLUSION

Minocycline effectively alleviates BCP by inhibiting the NF-κB signaling pathway in spinal astrocytes.

Rho/ROCK acts downstream of lysophosphatidic acid receptor 1 in modulating P2X3 receptor-mediated bone cancer pain in rats

Background

Lysophosphatidic acid receptor 1 and Rho/ROCK signaling is implicated in bone cancer pain development. However, it remains unknown whether the two signaling pathways function together in P2X₃ receptor-mediated bone cancer pain.

Results

In this study, using a rat model of bone cancer, we examined the expression of P2X₃ and lysophosphatidic acid receptor 1 in rat dorsal root ganglion neurons and further dissected whether lysophosphatidic acid receptor 1 and Rho/ROCK-mediated pathways interacted in modulating rat pain behavior. Bone cancer was established by inoculating Walker 256 cells into the left tibia of female Wistar rats. We observed a gradual and yet significant decline in mean paw withdrawal threshold in rats with bone cancer, but not in control rats. Our immunohistochemical staining revealed that the number of P2X₃- and lysophosphatidic acid receptor 1-positive dorsal root ganglion neurons was significantly greater in rats with bone cancer than control rats. Lysophosphatidic acid receptor 1 blockade with VPC32183 significantly attenuated decline in mean paw withdrawal threshold. Flinching behavior test further showed that lysophosphatidic acid receptor 1 inhibition with VPC32183 transiently but significantly attenuated α,β-meATP-induced increase in paw lift time per minute. Rho inhibition by intrathecal BoTXC3 caused a rapid reversal in decline in mean paw withdrawal threshold of rats with bone cancer. Flinching behavior test showed that BoTXC3 transiently and significantly attenuated α,β-meATP-induced increase in paw lift time per minute. Similar findings were observed with ROCK inhibition by intrathecal Y27632. Furthermore, VPC32183 and BoTXC3 effectively aborted the appearance of lysophosphatidic acid-induced calcium influx peak.

Conclusions

Lysophosphatidic acid and its receptor LPAR₁, acting through the Rho-ROCK pathway, regulate P2X₃ receptor in the development of both mechanical and spontaneous pain in bone cancer.

CX3CR1-Mediated Akt1 Activation Contributes to the Paclitaxel-Induced Painful Peripheral Neuropathy in Rats

Painful peripheral neuropathy is a serious dose-limiting side effect of paclitaxel therapy, which unfortunately often happens during the optimal clinical management of chemotherapy in cancer patients. Currently the underlying mechanisms of the painful peripheral neuropathy remain largely unknown. Here, we found that paclitaxel treatment (3 × 8 mg/kg, cumulative dose 24 mg/kg) upregulated the expression of CX3CR1 and phosphorylated Akt1 in DRG and spinal dorsal horn. Blocking of Akt1 pathway activation with different inhibitor (MK-2206 or LY294002) significantly attenuated mechanical allodynia and thermal hyperalgesia induced by paclitaxel. Furthermore, inhibition of CX3CR1 by using neutralizing antibody not only prevented Akt1 activation in DRG and spinal dorsal horn but also alleviated pain-related behavior induced by paclitaxel treatment. This study suggested that CX3CR1/Akt1 signaling pathway may be a potential target for prevention and reversion of the painful peripheral neuropathy induced by paclitaxel.

Treatment of Cancer Pain by Targeting Cytokines

Inflammation is one of the most important causes of the majority of cancer symptoms, including pain, fatigue, cachexia, and anorexia. Cancer pain affects 17 million people worldwide and can be caused by different mediators which act in primary efferent neurons directly or indirectly. Cytokines can be aberrantly produced by cancer and immune system cells and are of particular relevance in pain. Currently, there are very few strategies to control the release of cytokines that seems to be related to cancer pain. Nevertheless, in some cases, targeted drugs are available and in use for other diseases. In this paper, we aim to review the importance of cytokines in cancer pain and targeted strategies that can have an impact on controlling this symptom.