EARLY DNA DAMAGE DETECTION AND POTENT ANTIOXIDANT PROTECTION RENDER P19 CARCINOMA STEM CELLS MORE RESISTANT TO ANTI-CANCER TREAMENT

Cancer stem cells (CSCs) are pointed out as tumor-initiating cells and responsible for treatment failure.1 Thus, differentiation therapies constitute a promissory strategy against cancer relapse.2 Here, we sought to analyze if alterations in redox status and DNA damage detection/repair during CSCs differentiation affect the outcome of anti-cancer treatment. P19 carcinoma stem cells (P19CSCs) presented higher GSH/GSSG ratio and lower cardiolipin peroxidation when compared with retinoic acid-differentiated cancer cells (P19dCCs). By using the comet assay, we found that P19CSCs treated with cisplatin or etoposide presented lower single- and double-strands breaks than P19dCCs. Furthermore, P19CSCs also showed a G2/M arrest with increased expression of cleaved Parp-1, suggesting that P19CSCs treated with cisplatin and etoposide trigger DNA repair pathways before undergoing cell division. Accordingly, cisplatin and etoposide triggered an early activation of caspases 3 and 9 in P19dCCs. P19CSCs and P19dCCs treated with doxorubicin displayed equal amounts of single- and double-strand breaks, inducing a G0/G1 arrest in P19CSCs and a S-phase arrest in P19dCCs. Despite this, P19dCCs showed an earlier activation of caspase 9 suggesting that, even under similar DNA damage, P19CSCs evade apoptosis activation. Differentiation therapies may counteract antioxidant protection, the activation of DNA repair mechanisms and apoptosis-resistance of CSCs.