Abstract 2237: Involvement of Retinoic Acid Receptors RARβ and RARγ in growth, self-renewal and differentiation on mammary cancer stem cells

Retinoids exert different effects on cell differentiation and malignant phenotype reversion through the modulation of Retinoid Acid Receptors (RAR). In this work we have analyzed the involvement of retinoid system induction on proliferation, self-renewal and differentiation of cancer stem cells (CSC) using the triple negative mammary cell line LM38-LP. In order to obtain a CSC enriched culture, cells where cultured under mammosphere conditions. We performed mammosphere cultures in order to enrich in CSC. The treatment with All-trans retinoid acid (ATRA1μM for 96 h) reduced CSC growth rate evaluated as mammosphere diameter (Control: 176±8 μm vs. ATRA: 129±10 μm; p≤0.05). Surprisingly, ATRA pre-treatment for 96 h increased CSC self-renewal evaluated as the number of secondary mammospheres (Control: 313±19; ATRA: 495±21; p≤0.05) and as the clonogenic capacity of LM38-LP CSC (Control: 6±0.5; ATRA: 11±1.2; p≤0.05). Concomitant with these biological effects, the same treatment showed, by RT-PCR, an increase in RARβ and RARγ levels in LM38-LP- CSC. Through the use of specific RAR antagonists, we found that RARγ inhibition impaired ATRA effects on self-renewal but RARβ inhibition increased the number of secondary mammospheres (Control: 382±27; ATRA: 735±11; ATRA/RARγ antagonist: 352±17; ATRA/RARβ Antagonist: 1260±177; p≤0.05). A similar result was observed when clonogenic capacity in RARγ blocked CSC was analyzed. Finally, we performed a matrigel 3D culture using cells from LM38-LP mammospheres. Under these conditions, colonies presented large irregular structures while ATRA treatment led to the formation of differentiated colonies with evidence of lumen. Our findings suggest that RARγ down modulation and RARβ induction could lead to CSC self-renewal inhibition and differentiation in triple negative mammary cancers. Citation Format: Damian E. Berardi, Carolina Flumian, Maria I. Diaz Bessone, Stefano M. Cirigliano, Elisa D. Bal de Kier Joffe, Alejandro J. Urtreger, Laura B. Todaro. Involvement of Retinoic Acid Receptors RARβ and RARγ in growth, self-renewal and differentiation on mammary cancer stem cells. [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 2237. doi:10.1158/1538-7445.AM2015-2237