Felsberg, J. | bioRxiv Science

bioRxiv2024

Identification and characterization of tertiary lymphoid structures in brain metastases

Brain metastases (BrM) are the most common cancers in the brain. We performed transcriptome-wide gene expression profiling combined with spatial immune cell profiling to characterize the tumor immune microenvironment in BrM from different primary tumors. We found that BrM from lung carcinoma and malignant melanoma showed overall higher immune cell infiltration as compared to BrM from breast carcinoma. RNA sequencing-based immune cell deconvolution revealed gene expression signatures indicative of tertiary lymphoid structures (TLS) in subsets of BrM, mostly from lung cancer and melanoma. This finding was corroborated by multiplex immunofluorescence staining of immune cells in BrM tissue sections. Detection of TLS signatures was more common in treatment-naive BrM and associated with prolonged survival after BrM diagnosis in lung cancer patients. Our findings highlight the cellular diversity of the tumor immune microenvironment in BrM of different cancer types and suggest a role of TLS formation for BrM patient outcome.

cancer biology↗

bioRxiv2024

Direct excitatory synapses between neurons and tumor cells drive brain metastatic seeding of breast cancer and melanoma

Interactions between neurons and cancer cells are found in many malignancies, but their relevance for metastatic organ colonization remain largely unknown. It is also unclear whether any direct synaptic communication between neurons and cancer cells of non-neural tumor types exists, and if so, whether this can support metastasis and thus cancer progression. Here we show that excitatory synapses are formed between neurons and brain-metastatic melanoma and breast cancer cells. This starts at an early microscopic stage after extravasation into the brain parenchyma, during residence of cancer cells in the perivascular niche, a critical step for their survival. These neuron-cancer synapses showed a bona fide synaptic ultrastructure, and generated excitatory postsynaptic currents mediated by glutamate receptors of the AMPA subtype in cancer cells. In accordance, AMPA receptor signatures were consistently detected in preclinical and patient samples of melanoma and breast cancer brain metastases. Genetic perturbation and pharmacological inhibition of AMPA receptors with the approved antiepileptic drug perampanel in models of breast and melanoma cancer reduced the number of brain metastases and overall brain metastatic burden. These findings demonstrate for the first time that neurons can form biologically relevant direct synapses with non-neural cancer cells. In brain metastasis, a particularly challenging complication of many common malignancies, this non-canonical stimulatory synaptic interaction offers novel therapeutic opportunities.

cancer biology↗