Abstract 1011: Quercetin inhibited starvation-induced autophagy to increase apoptosis in CD133+ neuroblastoma stem cells in vitro and in vivo

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA Malignant neuroblastoma is the most common extra cranial solid tumor in children and many pediatric patients with this tumor still face poor prognosis due to therapy resistance and relapse. Malignant neuroblastoma usually occurs in one of the adrenal glands but it may also appear in neck, chest, abdomen, or pelvis. Most of the chemotherapeutic drugs for treating malignant neuroblastoma are used at higher doses that cause severe long-term organ toxicity in the patients. So, it is imperative to find out the most suitable natural compounds as promising therapeutic agents to improve therapeutic outcomes and enhance the survival rate of malignant neuroblastoma patients. Human malignant neuroblastoma SK-N-SH and SK-N-DZ cell lines contain a population of cells that express the stemness marker CD133+. The CD133+ neuroblastoma stem cells (NSC) may represent the underlying mechanism for resistance to conventional therapy and recurrence of this deadly malignancy in the patients. So, it is important to demonstrate that an experimental therapeutic agent is fully capable of inhibiting the growth of CD133+ NSC in vitro and in vivo. Some earlier studies indicated that the natural flavonoid quercetin (QCT) could inhibit autophagy, a potential survival strategy in solid tumors, through upregulation of cytosolic p53 and activation of caspase mediated apoptotic death. In current investigation, we isolated CD133+ NSC cell lines from the parental malignant neuroblastoma SK-N-SH and SK-N-DZ cell lines and tested therapeutic efficacy of QCT at different doses for inhibition of starvation-induced autophagy and promotion of apoptosis in CD133+ NSC in vitro and in vivo. Our results indicated that CD133+ NSC cell lines were more resistant to QCT than the parental malignant neuroblastoma SK-N-SH and SK-N-DZ cell lines. We observed inhibition of starvation-induced autophagy due to upregulation of cytosolic p53, inhibition of AMP activated protein kinase α (AMPKα), decreases in the autophagy promoting markers Beclin-1 and LC3 II, and increase in the autophagy inhibiting marker mTOR. Our results also indicated inhibition of the key molecular markers of cell proliferation (Cdk2 and pRb), unlimited growth (hTERT), and angiogenesis (VEGF) in both CD133+ NSC cell lines. We also found a decrease in mitochondrial membrane potential (Δψm) and enhancement of pro-apoptotic signaling in cell culture and animal models of CD133+ NSC following QCT treatment. Thus, our current results indicated for the first time that QCT suppressed the proliferation of CD133+ NSC by inhibiting autophagic flux and augmenting molecular mechanism of apoptotic death. Notably, QCT at a higher dose very efficiently blocked starvation-induced autophagy and enhanced apoptotic death in CD133+ NSC in vitro and in vivo. In conclusion, our current investigation clearly showed significant anti-cancer effects of QCT for controlling growth of CD133+ NSC in vitro and in vivo. Citation Format: Mrinmay Chakrabarti, Angela Murphy, Swapan K. Ray. Quercetin inhibited starvation-induced autophagy to increase apoptosis in CD133+ neuroblastoma stem cells in vitro and in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1011. doi:10.1158/1538-7445.AM2015-1011