Toma stem (brain-tumor-initiating) cells [12] and human glioblastoma cell lines [58]. Notably, in
Toma stem (brain-tumor-initiating) cells [12] and human glioblastoma cell lines [58]. Notably, within the latter study, only one particular (U138MG) and in tendency also a second (T98G) out of five glioblastoma lines have been radiosensitized by disulfiram (7500 nM) when grown in Cu2+ -containing serum-supplemented medium and when utilizing clonogenic survival because the endpoint [58]. Clonogenic survival determines the probability of a treated tumor to relapse, and is consequently believed to be the gold common for the interpretation of drug effects on radiosensitivity in radiation biology [59]. Within the glioblastoma stem-cell spheroid cultures, five Gy irradiation in mixture with disulfiram (one hundred nM) and Cu2+ (200 nM) additional decreased viability (as defined by metabolic activity and when compared with the disulfiram/Cu2+ /0 Gy arm) of only one out of two tested spheroid cultures [12]. Additionally, within the very same study, disulfiram/Cu2+ delayed repair of DNA double-strand breaks (DSBs) of two mGluR5 Activator MedChemExpress Gy-irradiated cells without the need of growing the number of residual (24 h-value) DSBs, as analyzed by the counting of nuclear H2AX (phosphorylated histone H2AX) foci [12]. Considering the fact that only restricted conclusions on clonogenic survival might be drawn in the decay of radiation-induced H2AX foci [60] as well as metabolically defined “viability” of irradiated cancer cells, the reported evidence for a radiosensitizing function of disulfiram in glioblastoma stem cells is restricted. Combined with all the notion that disulfiram radiosensitized only a minor fraction on the tested panel of glioblastoma cell lines [58], and moreover thinking about the results of our present study, it could be concluded that disulfiram may possibly radiosensitize glioblastoma (stem) cells, but this appears to be rather an exception than a common phenomenon. The circumstance is diverse in irradiated AT/RT (atypical teratoid/rhabdoid) brain tumor lines and major cultures, where disulfiram (in Cu(II)-containing serum-supplemented medium) regularly decreases survival fractions in colony formation assays of all tested cell models with an EC50 of 20 nM [61]. 4.3. Cu2+ -Mediated Oxidative Strain The radiosensitizing action of disulfiram possibly is determined by the Cu2+ ion-overloading function with the drug. Ionizing radiation induces beyond immediate radical formation (e.g., formation of OHby ionization of H2 O) delayed long-lasting mitochondrial-generated superoxide anion (O2 – formation which contributes to radiation-mediated genotoxic damage [62]. It can be tempting to speculate that disulfiram-mediated Cu2+ overload and subsequent OHformation (see introduction) collaborates with radiation-triggered mitochondrial oxidative strain (as well as with temozolomide) in introducing DNA DSBs. If that’s the case, the radiosensitizing (and also MMP-2 Inhibitor custom synthesis temozolomide-sensitizing) effect of disulfiram need to be, on the 1 hand, a direct function with the interstitial Cu2+ concentration, and on the other, a function with the intracellular Cu2+ -reducing, Cu+ -chaperoning, -sequestrating, and -extruding capability also because the oxidative defense of a tumor cell [63,64]. The Cu2+ -Biomolecules 2021, 11,17 ofdetoxifying capability most in all probability differs amongst cell varieties, and may well clarify the distinction in reported radiosensitizing activity of disulfiram between AT/RT [61] plus the glioblastoma (stem) cells ([12,59] and present study). In particular, tumor stem cells have been demonstrated to exhibit upregulated drug-efflux pumps, DNA repair, and oxidative defense [65]. 4.4. Does Disulfiram Specificall.