Modulazione di CD44/xCT come possibile strategia per contrastare la resistenza all'Etoposide di cellule staminali del cancro

The current anticancer therapies for human neuroblastoma (NB) include the use of Etoposide, a drug that exerts its cytotoxic effect by inducing oxidative stress. Although the therapeutic approach with Etoposide is initially efficacious, subsequently, it selects a chemoresistant cell population which is able to adapt to the oxidative environment induced by the drug, increasing the levels of intracellular glutathione (GSH). The chemoresistance is also due to the presence of cancer stem cells (CSCs), which have a low proliferative rate and are less susceptible to therapies acting on highly-proliferating cells. Moreover, CSCs expressing CD44, a PKC-alpha-modulated staminality marker, are able to influence GSH levels by stabilizing xCT, a transporter promoting the influx of cystine, essential for GSH synthesis. Based on this evidence, our aim was to investigate whether targeting CD44/xCT might be a useful strategy to increase neuroblastoma sensitivity to Etoposide. CSCs selected from HTLA-230, a malignant human NB cell line, and from Etoposide resistant HTLA (HTLA-ER), were treated once a week with 1.25 μM Etoposide alone or in combination with 0.5 μM PKC-alpha peptidic inhibitor (C2-4) or 5 μM Sulfasalazine (SSZ), an xCT inhibitor. The treatments were carried out for 2 and 5 weeks. CSC propagation, staminality marker expression (FACS analysis), GSH levels (HPLC analysis) and metabolic parameters were analyzed. The treatment with Etoposide is able to deplete GSH and to reduce proliferation in both sensitive and drug-resistant CSC populations. Notably, sensitive CSCs respond to Etoposide already after 2 weeks while the resistant CSCs after 5 weeks. Interestingly, co-treatments with SSZ or C 2-4, exerted a drug-sensitizing effect in resistant CSCs by anticipating GSH depletion and antiproliferative action and inducing a switch towards an anaerobic metabolism with the consequent increase of lactic acid and the induction of lipid peroxidation, two events responsible for the death of cancer cells. Collectively, our data demonstrates that the modulation of CD44/xCT in association with Etoposide, by reducing GSH levels and increasing lipid peroxidation, could be an effective strategy to sensitize CSCs to Etoposide (Grants from Genoa University).