Inhibition of breast cancer-cell glutamate release with sulfasalazine limits cancer-induced bone pain

Abstract

Cancer in bone is frequently a result of metastases from distant sites, particularly from the breast, lung, and prostate. Pain is a common and often severe pathological feature of cancers in bone, and is a significant impediment to the maintenance of quality of life of patients living with bone metastases. Cancer cell lines have been demonstrated to release significant amounts of the neurotransmitter and cell-signalling molecule l-glutamate via the system xC(-) cystine/glutamate antiporter. We have developed a novel mouse model of breast cancer bone metastases to investigate the impact of inhibiting cancer cell glutamate transporters on nociceptive behaviour. Immunodeficient mice were inoculated intrafemorally with the human breast adenocarcinoma cell line MDA-MB-231, then treated 14days later via mini-osmotic pumps inserted intraperitoneally with sulfasalazine, (S)-4-carboxyphenylglycine, or vehicle. Both sulfasalazine and (S)-4-carboxyphenylglycine attenuated in vitro cancer cell glutamate release in a dose-dependent manner via the system xC(-) transporter. Animals treated with sulfasalazine displayed reduced nociceptive behaviours and an extended time until the onset of behavioural evidence of pain. Animals treated with a lower dose of (S)-4-carboxyphenylglycine did not display this reduction in nociceptive behaviour. These results suggest that a reduction in glutamate secretion from cancers in bone with the system xC(-) inhibitor sulfasalazine may provide some benefit for treating the often severe and intractable pain associated with bone metastases.

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

“…This finding carries clinical significance, particularly considering recent evidence that SSZ inhibits tumour progression4850 and cancer-induced bone pain37. Our results are consistent with the hypothesis that the primary mechanism of antidepressant-like action of SSZ may be through inhibition of glutamate release via system x c − at the peripheral tumour site.…”

“…Based on these bioavailability data, mean water consumption, and mean weight of mice, it was estimated that 0.3 mg/mL of SSZ would translate into a dose of approximately 8 mg/kg/day. This target dose was chosen to be comparable to a dose that we have previously demonstrated to effectively reduce cancer-induced bone pain37. The SSZ metabolites, 5-ASA and SP (Sigma-Aldrich), were prepared the same way as SSZ to a final concentration of 0.09 mg/mL for 5-ASA and 0.15 mg/mL for SP.…”

Identification of capsazepine as a novel inhibitor of system x_c^− and cancer-induced bone pain

“…When in the bone, these cancers initiate a wide variety of pathological sequelae, with the primary symptom being debilitating pain 2. Once tumors metastasize to the skeleton, they are associated with a dramatic change in the bone microenvironment inducing a physiologically complex pain state, which can arise from a multitude of factors including altered bone remodeling, fracturing of the bone, damage to surrounding nerves, and release of nociceptive factors from the bone tissue itself or directly from the invading tumor 3–7. These skeletal-related effects correlate to a marked increase in patient morbidity and mortality2 with cancer-induced bone pain (CIBP) affecting up to 75% of cancer patients making it a key indicator of patient quality of life 8,9.…”

“…We hypothesize that cancer-specific factors are responsible for the complexity of CIBP and discovered that concentration of the nociceptive factor glutamate is greatly increased in the tumor microenvironment as a result of upregulated antioxidant machinery,6,7,11 namely, the cys-tine/glutamate antiporter, system x c − (xCT). System x c − is upregulated in many tumor types in response to the high concentrations of reactive oxygen species (ROS) produced as a consequence of their rampant cell growth and metabolism.…”

The Bone Microenvironment: a Fertile Soil for Tumor Growth

“…The origin of this pain is reportedly due to both the tumor itself as well as the activity of osteoclasts [89, 90]. Groups have attempted to target specific pathways involved in bone pain such as Nerve Growth Factor (NGF) [91], the receptor P2X7R [92], and glutamate release [93] to help improve quality of life. Additionally, commonly prescribed drugs such as denosumab and bisphosphonates have been shown to reduce bone pain in part through the reduction in osteoclast activity [94].…”