Abstract 5143: ABCG2 is involved in self renewal of melanoma cancer/initiating cells and major tumor associated antigens are expressed by ABCG2-positive cells
Authors: Porta Caterina Am La , Sigalotti Luca , Covre Alessia , Arosio Beatrice , Pirroni Stefania , Nicotra Maria R. , Taghizadeh Rouzbeh , Maio Michele , Sherley James , Natali PierGiorgio 
Published: February 2011

Abstract
The present model of cancer stem cells (CSC) states that tumors contain a subset of cells capable of self renewing and generating a differentiated progeny. Like normal adult tissue stem cells, CSCs account for a minor tumor cell population being the only capable of maintaining indefinite tumor growth. In melanoma, initiating/stem cells have been recently identified (melanoma CSC, MCSC). In particular, our group characterized MCSC using markers CD133 and ABCG2, a member of the ABC transporter family involved in drug resistance.
Being MCSC the best potential target of therapeutic intervention, herein we have addressed two critical questions: 1) Is ABCG2 involved in MCSC self renewal? 2) Can Tumor Associated Antigens (TAA), currently utilized as target in melanoma immunotherapeutic protocols, be used to target ABCG2-positive (ABCG2+) MCSC?
We have used as in vitro model two melanoma cell lines, IgR39 and IgR37, obtained from the primary and from metastatic lesions of the same patient, respectively. Both of these cell lines are tumorigenic when injected into NOD-SCID mice.
To address the first question, we have sorted ABCG2+ IgR39 and IgR37 cells, demonstrating an increase in the overall tumor mass by 3.00 and 1.75 fold, respectively, as compared to both ABCG2- and WT (WildType) cells. Interestingly, ABCG2+ and WT derived tumors resulted in the same weight. Then we have analyzed the level of expression of ABCG2 in tumor xenografts. According to our previous results, the level of expression of ABCG2 in both IgR39 and IgR37 tumor xenografts were undetectable. Immunohistochemistry analysis further confirmed these tumors expressed melanocyte differentiation markers such as the melanoma associated proteoglycan and HLA class I antigens at high level. HER3 and CD9 were weakly expressed. Among the Cancer Testis Antigens (CTA) NY-ESO-1 was undetectable, while MART-1 expression was documented.
To investigate the second question, RT-PCR analyses for TAA expression were performed. An overlap in the expression profile of the investigated TAA belonging to the CTA family (MAGE-A1, -A2, -A3, -A6, GAGE 1-2, GAGE 1-6, SSX-2, SSX 1-5, and NY-ESO-1) and of HMW-MAA, was observed at mRNA level between ABCG2+ and ABCG2- cells derived from the same parental cell cultures. In addition, the treatment with the DNA hypomethylating agent 5-aza-2′-deoxycytidine was able to induce a de novo expression of MAGE-A3, MAGE-A4, GAGE 1-2, GAGE 1-6 and SSX 1-5 in both ABCG2+ and ABCG2- melanoma cells derived from the same parental cell culture.
All together these results support the role of ABCG2 in self renewal in MCSC, and suggest the potential clinical effectiveness of TAA-based immunotheraputic strategies, alone or combined with DNA hypomethylating drugs, for more effective eradication of MCSC and non-MCSC neoplastic cells in patients with cutaneous melanoma.
Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5143.