Breast cancer brain metastases: evidence for neuronal-like adaptation in a ‘breast-to-brain’ transition?

Abstract Brain metastases remain a significant challenge in the treatment of breast cancer patients due to the unique environment posed by the central nervous system. A better understanding of the biology of breast cancer cells that have metastasized to the brain is required to develop improved therapies. A recent Proceedings of the National Academy of Sciences article demonstrates that breast cancer cells in the brain microenvironment express γ-aminobutyric acid (GABA)-related genes, enabling them to utilize GABA as an oncometabolite, thus gaining a proliferative advantage. In this viewpoint, we highlight these findings and their potential impact on the treatment of breast cancer brain metastases

Comprehensive Analysis of the Immunogenomics of Triple-Negative Breast Cancer Brain Metastases From LCCC1419

BackgroundTriple negative breast cancer (TNBC) is an aggressive variant of breast cancer that lacks the expression of estrogen and progesterone receptors (ER and PR) and HER2. Nearly 50% of patients with advanced TNBC will develop brain metastases (BrM), commonly with progressive extracranial disease. Immunotherapy has shown promise in the treatment of advanced TNBC; however, the immune contexture of BrM remains largely unknown. We conducted a comprehensive analysis of TNBC BrM and matched primary tumors to characterize the genomic and immune landscape of TNBC BrM to inform the development of immunotherapy strategies in this aggressive disease.MethodsWhole-exome sequencing (WES) and RNA sequencing were conducted on formalin-fixed, paraffin-embedded samples of BrM and primary tumors of patients with clinical TNBC (n = 25, n = 9 matched pairs) from the LCCC1419 biobank at UNC—Chapel Hill. Matched blood was analyzed by DNA sequencing as a comparison for tumor WES for the identification of somatic variants. A comprehensive genomics assessment, including mutational and copy number alteration analyses, neoantigen prediction, and transcriptomic analysis of the tumor immune microenvironment were performed.ResultsPrimary and BrM tissues were confirmed as TNBC (23/25 primaries, 16/17 BrM) by immunohistochemistry and of the basal intrinsic subtype (13/15 primaries and 16/19 BrM) by PAM50. Compared to primary tumors, BrM demonstrated a higher tumor mutational burden. TP53 was the most frequently mutated gene and was altered in 50% of the samples. Neoantigen prediction showed elevated cancer testis antigen- and endogenous retrovirus-derived MHC class I-binding peptides in both primary tumors and BrM and predicted that single-nucleotide variant (SNV)-derived peptides were significantly higher in BrM. BrM demonstrated a reduced immune gene signature expression, although a signature associated with fibroblast-associated wound healing was elevated in BrM. Metrics of T and B cell receptor diversity were also reduced in BrM.ConclusionsBrM harbored higher mutational burden and SNV-derived neoantigen expression along with reduced immune gene signature expression relative to primary TNBC. Immune signatures correlated with improved survival, including T cell signatures. Further research will expand these findings to other breast cancer subtypes in the same biobank. Exploration of immunomodulatory approaches including vaccine applications and immune checkpoint inhibition to enhance anti-tumor immunity in TNBC BrM is warranted

Effects of Acute Tryptophan Depletion on Brain Serotonin Function and Concentrations of Dopamine and Norepinephrine in C57BL/6J and BALB/cJ Mice

Acute tryptophan depletion (ATD) is a method of lowering brain serotonin (5-HT). Administration of large neutral amino acids (LNAA) limits the transport of endogenous tryptophan (TRP) across the blood brain barrier by competition with other LNAAs and subsequently decreases serotonergic neurotransmission. A recent discussion on the specificity and efficacy of the ATD paradigm for inhibition of central nervous 5-HT has arisen. Moreover, side effects such as vomiting and nausea after intake of amino acids (AA) still limit its use. ATD Moja-De is a revised mixture of AAs which is less nauseating than conventional protocols. It has been used in preliminary clinical studies but its effects on central 5-HT mechanisms and other neurotransmitter systems have not been validated in an animal model. We tested ATD Moja-De (TRP−) in two strains of mice: C57BL/6J, and BALB/cJ, which are reported to have impaired 5-HT synthesis and a more anxious phenotype relative to other strains of mice. ATD Moja-De lowered brain TRP, significantly decreased 5-HT synthesis as indexed by 5-HTP levels after decarboxlyase inhibition, and lowered 5-HT and 5-HIAA in both strains of mice, however more so in C57BL/6J than in BALB/cJ. Dopamine and its metabolites as well as norepinephrine were not affected. A balanced (TRP+) control mixture did not raise 5-HT or 5-HIAA. The present findings suggest that ATD Moja-De effectively and specifically suppresses central serotonergic function. These results also demonstrate a strain- specific effect of ATD Moja-De on anxiety-like behavior

Time Course of Biochemistry Experiment.

<p>Time Course of Biochemistry Experiment.</p

Behavioral data showing time spent in the light.

<p>Only TRP+- and TRP− -treated animals are shown. N = 14/group. +different from TRP+, ♦ different from corresponding group in BALBc mice.</p

Time course of ATD Moja-De in both strains.

<p>(a) Plasma = plasma tryptophan (µg/ml plasma) (b) HPC TRP = tryptophan in hippocampus (µg/mg tissue) (c) HPC-5-HIAA = 5-HIAA in hippocampus (ng/mg tissue). N = 3–4/group for C57, N = 4–8/group for BALBc. * different from Time 0 and ♦ different from corresponding group in BALBc mice.</p

Brain 5-HT.

<p>Brain 5-HT content in ng/mg tissue in (a) prefrontal cortex (b) frontal cortex and (c) hippocampus. Animals were treated as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0035916#pone-0035916-g002" target="_blank">Figure 2</a>. Only vehicle treated animals are shown. N = 5–6/group. * different from Water, +different from TRP+, ♦ different from corresponding group in BALBc mice. 5-HT content was lower at baseline in BALBc in the hippocampus; TRP− significantly decreased 5-HT content in the hippocampus; TRP+ did not consistently increase 5-HT content; TRP− was consistently lower than TRP+ in all regions.</p

Brain tryptophan.

<p>Brain tryptophan content in µg/mg tissue (a) prefrontal cortex (b) frontal cortex and (c) hippocampus. BALBc and C57 mice received two treatments by gavage of TRP+, TRP− mixtures or water vehicle at 30 minute intervals followed by saline or NSD 1015 to inhibit amion acid decarboxylase at 2 hours. Animals were killed 2.5 hours after the first treatment. Data are collapsed for NSD treatment as no significant effects were predicted or observed. N = 11–12/group. * different from Water. +different from TRP+, ♦ different from corresponding group in BALBc mice. TRP+ and TRP− effectively raised and lowered TRP respectively, although the depletion condition was more consistently effective than the control condition. Similar effects were detected in both strains.</p

Time Course of Behavioral Experiment.

<p>Time Course of Behavioral Experiment.</p