Blood glutamate scavengers increase pro-apoptotic signaling and reduce metastatic melanoma growth in-vivo

Abstract

Inhibition of extracellular glutamate (Glu) release decreases proliferation and invasion, induces apoptosis, and inhibits melanoma metastatic abilities. Previous studies have shown that Blood-glutamate scavenging (BGS), a novel treatment approach, has been found to be beneficial in attenuating glioblastoma progression by reducing brain Glu levels. Therefore, in this study we evaluated the ability of BGS treatment to inhibit brain metastatic melanoma progression in-vivo. RET melanoma cells were implanted in C56BL/6J mice to induce brain melanoma tumors followed by treatment with BGS or vehicle administered for fourteen days. Bioluminescent imaging was conducted to evaluate tumor growth, and plasma/CSF Glu levels were monitored throughout. Immunofluorescence staining of Ki67 and 53BP1 was used to analyze tumor cell proliferation and DNA double-strand breaks. In addition, we analyzed CD8, CD68, CD206, p-STAT1 and iNOS expression to evaluate alterations in tumor micro-environment and anti-tumor immune response due to treatment. Our results show that BGS treatment reduces CSF Glu concentration and consequently melanoma growth in-vivo by decreasing tumor cell proliferation and increasing pro-apoptotic signaling in C56BL/6J mice. Furthermore, BGS treatment supported CD8+ cell recruitment and CD68+ macrophage invasion. These findings suggest that BGS can be of potential therapeutic relevance in the treatment of metastatic melanoma.

Neuronal Cannabinoid CB1 Receptors Suppress the Growth of Melanoma Brain Metastases by Inhibiting Glutamatergic Signalling

“…We consider this latter possibility plausible for several reasons: (i) other metabolites abundant in the central nervous system, such as lactate and ketone bodies, promote melanoma metastasis [53]; (ii) melanoma and other cancer cells establish in the brain ways of communication with neurons and astrocytes, thereby hijacking neuronal and glial signalling pathways [17,18,[20][21][22][23]; and (iii) melanoma cells adopt in the brain a neuron-like, brain-adaptive phenotype that upregulates several genes involved in synapse formation (e.g., SNCA), cell adhesion (e.g., LRRC1), and the sensing of neurotrophic factors (e.g., NGFR) [54,55], all of which strongly supports an interaction with brain components. Interestingly, a recent report showed that treating mice with glutamate scavengers reduces blood and cerebrospinal fluid glutamate concentrations in association with a decrease in brain melanoma cell growth [56]. Thus, glutamate seems an important pro-tumorigenic factor for brain melanoma cells and, logically, glutamatergic neurons represent a potential glutamate source.…”

Electroporation-based proteome sampling ex vivo enables the detection of brain melanoma protein signatures in a location proximate to visible tumor margins

“…We chose the RET mice melanoma cell line [ 35 , 36 ], kindly donated by Dr. Carmit Levi, Tel-Aviv University, since it has been shown that the RET oncogene is mutated in human melanomas, particularly in desmoplastic melanomas which have an increased risk for brain metastasis [ 37 ]. The RET cells were double-labeled with mCherry and Luc2 (pLNT/Sffv-MCS/ccdB plasmid), sorted for a red fluorescence, and selected in culture before they were injected intracranially (i.c.)…”