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Cholesterol is an essential plasma membrane lipid for the maintenance of cellular homeostasis and cancer cell proliferation. Free cholesterol is harmful to cells; therefore, excessive free cholesterol must be quickly esterified by acetyl-coenzyme A:cholesterol acetyltransferase (ACAT) and exported by scavenger receptor class B member I (SR-BI) or ATP-binding cassette protein A1 from specific cells such as macrophage foam cells, which contain cholesteryl ester-derived vacuoles. Many vacuoles are present in the cytoplasm of Burkitt lymphoma cells. In this study, we observed that these vacuoles are often seen in high-grade lymphomas. Cell culture study using lymphoma cell lines found that esterified cholesterol is the main component of these vacuoles and the expression of cholesterol metabolism-related molecules was significantly upregulated in lymphoma cell lines, with SR-BI and ACAT inhibitors (BLT-1 and CI-976, respectively) impeding lymphoma cell proliferation. Cytoplasmic free cholesterol was increased by ACAT and SR-BI inhibitors, and the accumulation of free cholesterol induced lymphoma cell apoptosis by inducing endoplasmic reticulum stress. Furthermore, synergistic effects of SR-BI and ACAT inhibitors were observed in a preclinical study. Treatment with SR-BI inhibitor suppressed lymphoma progression in a tumor-bearing mouse model, whereas ACAT inhibitor did not. Therefore, SR-BI inhibitors are potential new antilymphoma therapeutics that target cholesterol metabolism.

Glioblastoma is a glioma characterized by highly malignant features. Numerous studies conducted on the relationship between glioblastoma and the microenvironment have indicated the significance of tumor-associated macrophages/microglia (TAMs) in glioblastoma progression. Since interleukin (IL)-1β secreted by TAMs has been suggested to promote glioblastoma growth, we attempted to elucidate the detailed mechanisms of IL-1β in glioblastoma growth in this study. A phospho-receptor tyrosine kinase array and RNA-sequencing studies indicated that IL-1β induced the activation of signal transducer and activator of transcription-3 and nuclear factor-kappa B signaling. Glioblastoma cells stimulated by IL-1β induced the production of IL-6 and CXCL8, which synergistically promoted glioblastoma growth via signal transducer and activator of transcription-3 and nuclear factor-kappa B signaling. By immunohistochemistry, IL-1β expression was seen on TAMs, especially in perinecrotic areas. These results suggest that IL-1β might be a useful target molecule for anti-glioblastoma therapy.

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