Mechanistic insights into the cytotoxic and apoptotic effects of 1-butyl-3-methylimidazolium bromide and 1-butylpyridinium bromide on human cell lines

Ionic liquids (ILs) are a novel class of salts with growing industrial applications due to their tunable physicochemical properties. However, their popularity has given rise to concerns about their cytotoxic potential. This study investigates the cytotoxic, apoptotic, and cell cycle effects of two ILs, namely 1-butyl-3-methylimidazolium bromide ([Bmim]Br) and 1-butylpyridinium bromide ([Bpy]Br), on three human cell lines: HeLa (cervical cancer), MCF-7 (breast cancer), and HEK293T (human embryonic kidney). Using real-time cell analysis (RTCA), we determined that the half-maximal inhibition concentrations (IC₅₀) for [Bmim]Br were 841.86 μmol/L in MCF-7, 538.38 μmol/L in HeLa, and 654.78 μmol/L in HEK293T cells. Respective [Bpy]Br IC₅₀ values were 341.74 μmol/L, 333.27 μmol/L, and 328.98 μmol/L. Flow cytometry revealed that both ILs induced dose-dependent apoptosis and that [Bpy]Br showed stronger pro-apoptotic effects. At 1000 μmol/L, [Bpy]Br reduced live cell population to 33.86 % in MCF-7 and to 38.32 % in HeLa cells. Both ILs induced the G0/G1 phase arrest and significantly suppressed the expression of cyclin D1, CDK2, and CDK4 at both mRNA and protein levels. MTT and Transwell assays further confirmed inhibited cell proliferation and migration, particularly in MCF-7 and HeLa cells. These findings demonstrate that [Bmim]Br and [Bpy]Br inhibit cell growth by triggering apoptosis and by interfering with cell cycle progression. Stronger effects observed with [Bpy]Br suggest its therapeutic potential, but given the toxicity of both ILs in non-cancerous HEK293T cells, further research is necessary to evaluate their biosafety and long-term effects.