Targeting histone deacetylase 6 (HDAC6) to enhance radiation therapy in meningiomas in a 2D and 3D in vitro study.

BACKGROUND: External radiation therapy (RT) is often a primary treatment for inoperable meningiomas in the absence of established chemotherapy. Histone deacetylase 6 (HDAC6) overexpression, commonly found in cancer, is acknowledged as a driver of cellular growth, and inhibiting HDACs holds promise in improving radiotherapeutic efficacy. Downregulation of HDAC6 facilitates the degradation of ß-catenin. This protein is a key element in the Wnt/ß-catenin signalling pathway, contributing to the progression of meningiomas. METHODS: In order to elucidate the associations and therapeutic potential of HDAC6 inhibitors (HDAC6i) in conjunction with RT, we administered Cay10603, HDAC6i, to both immortalised and patient-derived meningioma cells prior to RT in this study. FINDINGS: Our findings reveal an increase in HDAC6 expression following exposure to RT, which is effectively mitigated with pre-treated Cay10603. The combination of Cay10603 with RT resulted in a synergistic augmentation of cytotoxic effects, as demonstrated through a range of functional assays conducted in both 2D as well as 3D settings; the latter containing syngeneic tumour microenvironment (TME). Radiation-induced DNA damage was augmented by pre-treatment with Cay10603, concomitant with the inhibition of ß-catenin and minichromosome maintenance complex component 2 (MCM2) accumulation within the nucleus. This subsequently inhibited c-myc oncogene expression. INTERPRETATION: Our findings demonstrate the therapeutic potential of Cay10603 to improve the radiosensitisation and provide rationale for combining HDAC6i with RT for the treatment of meningioma. FUNDING: This work was funded by Brain Tumour Research Centre of Excellence award to C Oliver Hanemann.

Calcium depletion at high glucose concentration promotes vesicle-mediated NET release in response to Staphylococcus aureus.

The primary immune response against Staphylococcus aureus is mediated by neutrophils. In response to S. aureus and its proteins, neutrophil shows two different kinds of NETosis, viz. suicidal and vesicular NETosis. Glucose is the major energy source of neutrophils for performing NETosis. However, NETosis was found altered in response to high glucose levels. Growth of S. aureus was also found modulated in response to high glucose and they behave differently at different glucose levels. This work was attempted to study NET release in response to S. aureus cell-free culture supernatant at different glucose concentrations. Freshly isolated neutrophils were treated with different concentrations of glucose along with S. aureus cell-free culture supernatant and were analyzed for neutrophil extracellular trap formation, ROS production, and peptidylarginine deiminase 4 activities. Influence of calcium on NETosis was analyzed using calcium chelator (EDTA) and calcium inhibitor (TMB-8). With increasing glucose levels, NET release in response to S. aureus cell-free culture supernatant was increased. Oxidant level was also increased dose-dependently with increasing concentrations of glucose. At very high glucose concentrations (> 15 mM), vesicular NETosis was predominantly observed. At these glucose concentrations, peptidylarginine deiminase activity was found to be decreased. Furthermore, calcium quenching in the medium facilitated vesicular mode of NET release. In conclusion, calcium depletion occurring at high glucose concentrations can reduce peptidylarginine deiminase 4 activity and can thereby promote the vesicular NET release.