Abstract 1662: Dendrogenin A is a newly identified mammalian steroidal alkaloid that induced autophagic cell death in melanoma cells through an LXRbeta-, Nur77- and Nor1-dependent way.

Abstract

Abstract Dendrogenin A (DDA) is a steroidal alkaloid that we recently discovered in mammalian tissues and normal cells. We did not detect DDA in a panel of melanoma and breast cancer cells, while DDA was present in normal Human Mammary Epithelial Cells and normal Human Epidermal Melanocytes suggesting that a deregulation of DDA metabolism may occur during carcinogenesis. We established that DDA triggered melanoma and breast cancer cells re-differentiation and death in vitro and in vivo, demonstrating its anticancer potency. In the present study, we investigated the molecular mechanisms involved in the cytotoxicity of DDA in melanoma cells. We found that DDA induced a time- and concentration-dependent cytotoxicity with the characteristics of apoptosis in human (SKMEL-28) and mouse (B16F10) melanoma cell lines. DDA induced the impairment of mitochondrial functions and activated the executioner caspase 3. However, caspase inhibitors failed to inhibit cytotoxicity suggesting that other mechanisms were involved. DDA triggered autophagy in melanoma cells and induced an autophagic flux. Genetic and pharmacological inhibition of autophagy inhibited DDA cytotoxicity showing that autophagy was involved in the cytotoxicity, which contrasts with the classical involvement of autophagy in tumor cell survival. In the search for cytotoxic effectors, we found that DDA stimulated the re-expression and re-localization of Nur77 (NR4A1) to the mitochondria, and the re-expression of Nor1 (NR4A3) in melanoma cells. We showed that pharmacological inhibition of the nucleo-cytoplasmic shuttling of Nur77, and the knock-down of Nur77 and Nor1, led to the inhibition of the cytotoxic autophagy. This establishes that Nur77 and Nor1 are involved in the induction of cytotoxic autophagy by DDA. Using a combination of molecular modeling, binding, luciferase gene reporter and transcriptional assays in tumor cells, we showed that DDA was a ligand of LXRα (NR1H3) and LXRβ (NR1H2) and a selective modulator of LXR-dependent gene expression. Interestingly, DDA displayed a specific transcriptional fingerprint compared to prototypical LXR modulators. Finally, we found that LXRβ was required for the stimulation of Nur77 and Nor1 expression by DDA and the induction of a cytotoxic autophagy. Altogether, these data established that the newly identified mammalian steroidal alkaloid DDA is a ligand of LXR that induced cytotoxic autophagy through an LXRβ-,Nur77- and Nor1-dependent mechanism in melanoma cells. Thus, DDA constitutes a promising drug candidate for melanoma treatment through an original mechanism of action. Since Nur77 and Nor1 expression has been found to be repressed in a number of aggressive tumors, DDA may represent an interesting option for the treatment of cancers expressing LXRβ. Citation Format: Gregory Segala, Mathias C. Poirot, Philippe de Medina, Michael Paillasse, Jean-Marc Lobaccaro, Sandrine Silvente-Poirot, Marc Poirot. Dendrogenin A is a newly identified mammalian steroidal alkaloid that induced autophagic cell death in melanoma cells through an LXRbeta-, Nur77- and Nor1-dependent way. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1662. doi:10.1158/1538-7445.AM2013-1662