Abstract / Summary
Abstract Background Cutaneous T-cell lymphomas (CTCL) are skin-homing T-cell malignancies characterized by recurrent disease, therapeutic resistance and limited durable treatment responses in advanced stages. Although the proteasome inhibitor bortezomib has demonstrated activity in CTCL, the molecular pathways associated with its antitumour effects remain incompletely defined. This study investigated whether bortezomib modulates SKP2-associated cell-cycle regulation, oxidative stress and apoptosis in CTCL cells and evaluated its activity in combination with cisplatin. Methods H9 and HH human CTCL cells were exposed to increasing concentrations of bortezomib. Cell viability, cell-cycle distribution, apoptosis, mitochondrial membrane depolarization, cellular and mitochondrial reactive oxygen species, and intracellular glutathione were assessed using CCK-8 assays, fluorescence imaging and flow cytometry. Proteins regulating cell-cycle progression, survival and apoptosis were evaluated by immunoblotting. The contributions of caspase activation and oxidative stress were examined using the pan-caspase inhibitor z-VAD-FMK and the antioxidant N-acetyl-L-cysteine respectively. Interactions between bortezomib and cisplatin were quantified using the Chou–Talalay method. Results Bortezomib reduced CTCL cell viability in a concentration-dependent manner, with 24 h IC 50 values of 5.25 nM in H9 cells and 1.82 nM in HH cells. Treatment increased the sub-G0/G1 population and Annexin V-positive cells, promoted caspase-8, caspase-9 and caspase-3 activation, induced PARP cleavage, increased the Bax/Bcl-2 ratio and caused mitochondrial membrane depolarization. z-VAD-FMK attenuated bortezomib-induced apoptosis, supporting a caspase-dependent component. Bortezomib also increased cellular and mitochondrial reactive oxygen species and depleted intracellular glutathione. N-acetyl-L-cysteine partially reduced cell-cycle disruption, apoptosis and caspase activation, indicating that oxidative stress contributes to bortezomib-mediated cytotoxicity. These effects were accompanied by reduced SKP2 and CDK4/6 expression and increased p21 and p27 expression. At selected dose combinations, bortezomib enhanced cisplatin-induced loss of viability and apoptosis, with strong synergistic interactions observed at 5 nM bortezomib plus 10 µM cisplatin. Conclusions Bortezomib induces ROS-associated, caspase-dependent mitochondrial apoptosis in CTCL cells and is accompanied by suppression of the SKP2–p21/p27 cell-cycle regulatory axis. Selected bortezomib-cisplatin combinations further enhance CTCL cell death. These findings identify SKP2-associated signaling as a candidate pharmacodynamic vulnerability and support further validation of this therapeutic strategy in primary CTCL samples and in vivo models.