Response to pregabalin and progesterone differs in male and female rat models of neuropathic and cancer pain

Background: Cancer pain involves nervous system damage and pathological neurogenesis. Neuropathic pain arises from damage to the nervous system and is driven by ectopic signaling. Both progesterone and pregabalin are neuroprotective in animal models, and there is evidence that both drugs bind to and inhibit voltage-gated calcium channels. Aims: This study was designed to characterize the effects of progesterone and pregabalin in preclinical models of cancer and neuropathic pain in both sexes. Methods: We measured peripheral sensory signaling by intracellular in vivo electrophysiology and behavioral indicators of pain in rat models of cancer-induced bone pain and neuropathic pain. Results: Female but not male models of cancer pain showed a behavioral response to treatment and pregabalin reduced excitability in C and A high-threshold but not low-threshold sensory neurons of both sexes. Male models of neuropathic pain treated with pregabalin demonstrated higher signaling thresholds only in A high-threshold neurons, and behavioral data indicated a clear recovery to baseline mechanical withdrawal thresholds in all treatment groups. Female rat treatment groups did not show excitability changes in sensory neurons, but all demonstrated higher mechanical withdrawal thresholds than vehicle-treated females, although not to baseline levels. Athymic female rat models of neuropathic pain showed no behavioral or electrophysiological responses to treatment. Conclusions: Both pregabalin and progesterone showed evidence of efficacy in male models of neuropathic pain. These results add to the evidence demonstrating differential effects of treatments for pain in male and female animals and widely differing responses in models of cancer and neuropathic pain.

xCT knockdown in human breast cancer cells delays onset of cancer-induced bone pain

Cancers in the bone produce a number of severe symptoms including pain that compromises patient functional status, quality of life, and survival. The source of this pain is multifaceted and includes factors secreted from tumor cells. Malignant cells release the neurotransmitter and cell-signaling molecule glutamate via the oxidative stress-related cystine/glutamate antiporter, system x_C^-, which reciprocally imports cystine for synthesis of glutathione and the cystine/cysteine redox cycle. Pharmacological inhibition of system x_C^- has shown success in reducing and delaying the onset of cancer pain-related behavior in mouse models. This investigation describes the development of a stable siRNA-induced knockdown of the functional trans-membrane system x_C^- subunit xCT ( SLC7A11) in the human breast cancer cell line MDA-MB-231. Clones were verified for xCT knockdown at the transcript, protein, and functional levels. RNAseq was performed on a representative clone to comprehensively examine the transcriptional cellular signature in response to xCT knockdown, identifying multiple differentially regulated factors relevant to cancer pain including nerve growth factor, interleukin-1, and colony-stimulating factor-1. Mice were inoculated intrafemorally and recordings of pain-related behaviors including weight bearing, mechanical withdrawal, and limb use were performed. Animals implanted with xCT knockdown cancer cells displayed a delay until the onset of nociceptive behaviors relative to control cells. These results add to the body of evidence suggesting that a reduction in glutamate release from cancers in bone by inhibition of the system x_C^- transporter may decrease the severe and intractable pain associated with bone metastases.

Activation of hippocampal microglia in a murine model of cancer-induced pain

Introduction

Pain is a common and debilitating comorbidity of metastatic breast cancer. The hippocampus has been implicated in nociceptive processing, particularly relating to the subjective aspect of pain. Here, a syngeneic mouse model was used to characterize the effects of peripheral tumors on hippocampal microglial activation in relation to cancer-induced pain (CIP).

Materials and methods

Mice were systemically treated with the colony-stimulating factor 1 receptor inhibitor Pexidartinib prior to intrafemoral (IF) or subcutaneous 4T1 carcinoma cell inoculation. Spontaneous and evoked nociceptive responses were quantitated throughout tumor development, and contralateral hippocampi were collected via endpoint microdissection for RNA analysis. Additionally, IF tumor-bearing animals were sacrificed on days 5, 10, 15, and 20 post 4T1 cell inoculation, and brain sections were immunofluorescently stained for Iba1, a marker of activated microglia.

Results

Ablation of these neuroimmune cells with the CSF1R inhibitor Pexidartinib delayed the onset and severity of cancer-induced nociceptive behaviors in IF tumor-bearing animals, adding to the body of literature that demonstrates microglial contribution to the development and maintenance of CIP. Furthermore, in untreated IF tumor-bearing mice, nociceptive behaviors appeared to progress in parallel with microglial activation in hippocampal regions. Immunofluorescent Iba1+ microglia increased in the dentate gyrus and cornu ammonis 1 hippocampal regions in IF tumor-bearing animals over time, which was confirmed at the mRNA level using relevant microglial markers.

Conclusion

This is the first experimental evidence to demonstrate the effects of peripheral tumor-induced nociception on hippocampal microglial activation. The increase in hippocampal microglia observed in the present study may reflect the emotional and cognitive deficits reported by patients with CIP.

Functional effects of TrkA inhibition on system xC--mediated glutamate release and cancer-induced bone pain

Breast cancer cells release the signalling molecule glutamate via the system x_C⁻ antiporter, which is upregulated to exchange extracellular cystine for intracellular glutamate to protect against oxidative stress. Here, we demonstrate that this antiporter is functionally influenced by the actions of the neurotrophin nerve growth factor on its cognate receptor tyrosine kinase, TrkA, and that inhibiting this complex may reduce cancer-induced bone pain via its downstream actions on xCT, the functional subunit of system x_C⁻. We have characterized the effects of the selective TrkA inhibitor AG879 on system x_C⁻ activity in murine 4T1 and human MDA-MB-231 mammary carcinoma cells, as well as its effects on nociception in our validated immunocompetent mouse model of cancer-induced bone pain, in which BALB/c mice are intrafemorally inoculated with 4T1 murine carcinoma cells. AG879 decreased functional system x_C⁻ activity, as measured by cystine uptake and glutamate release, and inhibited nociceptive and physiologically relevant responses in tumour-bearing animals. Cumulatively, these data suggest that the activation of TrkA by nerve growth factor may have functional implications on system x_C⁻-mediated cancer pain. System x_C⁻-mediated TrkA activation therefore presents a promising target for therapeutic intervention in cancer pain treatment.

Behavioural Effects of Using Sulfasalazine to Inhibit Glutamate Released by Cancer Cells: A Novel target for Cancer-Induced Depression

Despite the lack of robust evidence of effectiveness, current treatment options for cancer-induced depression (CID) are limited to those developed for non-cancer related depression. Here, anhedonia-like and coping behaviours were assessed in female BALB/c mice inoculated with 4T1 mammary carcinoma cells. The behavioural effects of orally administered sulfasalazine (SSZ), a system x_c⁻ inhibitor, were compared with fluoxetine (FLX). FLX and SSZ prevented the development of anhedonia-like behaviour on the sucrose preference test (SPT) and passive coping behaviour on the forced swim test (FST). The SSZ metabolites 5-aminosalicylic acid (5-ASA) and sulfapyridine (SP) exerted an effect on the SPT but not on the FST. Although 5-ASA is a known anti-inflammatory agent, neither treatment with SSZ nor 5-ASA/SP prevented tumour-induced increases in serum levels of interleukin-1β (IL-1β) and IL-6, which are indicated in depressive disorders. Thus, the observed antidepressant-like effect of SSZ may primarily be attributable to the intact form of the drug, which inhibits system x_c⁻. This study represents the first attempt at targeting cancer cells as a therapeutic strategy for CID, rather than targeting downstream effects of tumour burden on the central nervous system. In doing so, we have also begun to characterize the molecular pathways of CID.

Preparation of tetrazine-containing [2 + 1] complexes of 99mTc and in vivo targeting using bioorthogonal inverse electron demand Diels–Alder chemistry

A new ^99mTc-labelled tetrazine for targeted imaging using bioorthogonal chemistry was developed and evaluated in vivo using a trans-cyclooctene derived bisphosphonate targeting regions of high bone turnover and bone lesions.

Chronic Inhibition of STAT3/STAT5 in Treatment-Resistant Human Breast Cancer Cell Subtypes: Convergence on the ROS/SUMO Pathway and Its Effects on xCT Expression and System xc- Activity

Pharmacologically targeting activated STAT3 and/or STAT5 has been an active area of cancer research. The cystine/glutamate antiporter, system x_c^-, contributes to redox balance and export of intracellularly produced glutamate in response to up-regulated glutaminolysis in cancer cells. We have previously shown that blocking STAT3/5 using the small molecule inhibitor, SH-4-54, which targets the SH2 domains of both proteins, increases xCT expression, thereby increasing system x_c^- activity in human breast cancer cells. The current investigation demonstrates that chronic SH-4-54 administration, followed by clonal selection of treatment-resistant MDA-MB-231 and T47D breast cancer cells, elicits distinct subtype-dependent effects. xCT mRNA and protein levels, glutamate release, and cystine uptake are decreased relative to untreated passage-matched controls in triple-negative MDA-MB-231 cells, with the inverse occurring in estrogen-responsive T47D cells. This “ying-yang” effect is linked with a shifted balance between the phosphorylation status of STAT3 and STAT5, intracellular ROS levels, and STAT5 SUMOylation/de-SUMOylation. STAT5 emerged as a definitive negative regulator of xCT at the transcriptional level, while STAT3 activation is coupled with increased system x_c^- activity. We propose that careful classification of a patient’s breast cancer subtype is central to effectively targeting STAT3/5 as a therapeutic means of treating breast cancer, particularly given that xCT is emerging as an important biomarker of aggressive cancers.

Oxidative stress and cancer pain

Breast cancers are the most common source of metastases to bone, of which cancer-induced bone pain is a frequent pathological feature. Cancer-induced bone pain is a unique pain state with multiple determinants that remains to be well understood and managed. Current standard treatments are limited by dose-dependent side effects that can reduce the quality of life of patients. Glutamate is a neurotransmitter and bone cell-signalling molecule that is released via the system x(c)(-) cystine/glutamate antiporter from cancer cell types that frequently metastasize to bone, including breast cancers. In cancer cells, glutamate release is understood to be a side effect of the cellular response to oxidative stress that upregulates the expression and activity of system x(c)(-) to promote the increased import of cystine. Attenuation of glutamate release from cancer cells has been demonstrated to result in reductions in associated cancer-induced bone pain in animal models. This review examines the clinical implications of attenuating cystine uptake and glutamate release in the treatment of cancer-induced bone pain.