The Sonic Hedgehog (Hh) pathway has been implicated in the maintenance of stem or progenitor cells in many adult tissues. Importantly, abnormal Hh pathway activation is also associated with initiation of neoplasia, but its role in tumor growth is still unclear. Here, we demonstrate that cyclopamine, a plant-derived alkaloid product used to inhibit the Hh signaling pathway, reduces the Side Population (SP) obtained by Hoechst 33342 (Ho342) dye measurements. In addition, cyclopamine is able to modulate, along with oxysterols and other products, the ABCG2 transporter by increasing Ho342 and mitoxantrone uptake. Therefore, if the SP is solely measured as a Ho342 dye extruding fraction, this may be significantly modulated by the inhibition of ABCG2 transport fraction, independently from the action of cyclopamine on the Hh pathway. Our results indicate that ABCG2 may act in the upstream regulation of the Hh signaling pathway to protect the stemness of the SP compartment, giving support to the cancer stem cell hypothesis and suggesting that ABCG2 is not only critical for increased resistance to anticancer agents. ' 2011 International Society for Advancement of Cytometry

Neuroblastoma is the most common extracranial solid tumor of childhood. Cellular heterogeneity is a hallmark of this embryonal malignancy, as distinct neural crest lineages can be found within the same tumor sample. The aim of our study was to investigate the presence of a subpopulation of immature cells with features of cancer-like stem cells in 12 neuroblastoma cell lines. RT-PCR and flow citometry were performed in order to analyze different kinds of “stemness genes” such as: NESTIN (NES), CD133, SOX-2, BMI1, c-KIT, MELK1, MUSASHI-1 (MSI1), FAS, CD44 and VIMENTIN (VIM). Also, glial and neuronal markers like NCAM1, GFAP and B-TUBULIN III (TUBB3) were analyzed. Interestingly, we found that neuroblastoma cell lines showed a particular pattern of expression suggesting the presence of a subpopulation of immature stem like cancer cells. Epigenetic changes regarding the CD133 (Prominin-1) promoter gene were also analyzed. This protein has been extensively used to enrich putative cancer propagating stem-like cell populations of different kinds of solid tumors. We found unusual DNA methylation, as 7 of the 12 neuroblastoma cell lines analysed featured a half-methylated state. An increase of RNA and protein levels of CD133 was achieved following demethylation assays using 5-aza-2′-deoxycytidine. Because cancer stem cells are believed responsible for tumor metastasis, escape from anticancer therapies and disease relapse, their therapeutic targeting and analysis is crucial in neuroblastoma. Also, the regulation of CD133 by epigenetic changes may provide an innovative mechanism of CD133 expression as its regulation still remains unclear. 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 5247.

Abstract. Neuroblastoma is the most common extracranial solid tumor in children, accounting for up to 10% of all childhood malignancies. Cellular heterogeneity is a hallmark of this embryonal cancer, as distinct neural crest lineages can be found within the same tumor sample. The aim of our study was to investigate the presence of a subpopulation of immature cells with features of cancer-like stem cells in 10 neuroblastoma cell lines. RT-PCR and flow cytometry were performed in order to analyze different kinds of 'stemness genes' such as: NESTIN (NES), CD133, SOX-2, BMI1, c-KIT, MELK1, MUSASHI-1 (MSI1), FAS, CD44 and VIMENTIN (VIM). In addition, glial and neuronal markers such as NCAM1, GFAP and B-TUBULIN III (TUBB3) were analyzed. Epigenetic changes within the CD133 (Prominin-1) gene promoter were also analyzed. Neuroblastoma cell lines showed a particular pattern of expression, suggesting the presence of an immature cancer stem cell-like subpopulation. The CD133 protein, commonly used to enrich putative cancer propagating stem cell-like populations in different kinds of solid tumors, presented a half-methylated DNA state in 7 of the 12 neuroblastoma cell lines analyzed. An increase in RNA and protein levels of CD133 was achieved following demethylation by assays using 5-aza-2'-deoxycytidine (5-Aza-dC). Since cancer stem cells are believed to be responsible for tumor metastasis, escape from anticancer therapies and disease relapse, their therapeutic targeting and analysis is crucial in neuroblastoma. Moreover, the regulation of CD133 by epigenetic changes may provide an innovative mechanism of CD133 expression as its regulation still remains unclear.

The Sonic Hedgehog pathway (HH) has been implicated in the maintenance of stem cells in adult tissues. Abnormal HH activation is also associated with initiation of neoplasia by cancer stem cells. Cyclopamine has been used as an inhibitor of the HH, with potential effectiveness in several xenograft models, including gliomas. Side Population (SP) cells are stem cells with expression of ABCG2, a multidrug ABC transporter, able to extrude dyes as Hoechst 33342 (Ho342). SP cells, then, present low fluorescence after staining with Ho342. ABC transporters have been identified as drug-resistance proteins. HH regulates the expression of ABC transporters, and promotes multi-drug resistance by increasing drug efflux by the ABC transporters. Different research groups have shown that SP cells can be depleted following cyclopamine treatment, an observation that would support that SP cells are HH pathway-dependent. We hypothesized that cyclopamine might interact with ABCG2 and limit the number of SP cells. Therefore, we analyzed the effect of cyclopamine and temozolomide on the MXRA cell line (KB cells transfected with the full-length ABCG2 cDNA), and on five astrocytoma cell lines, both in the parental cell lines and in their SP cells. We first evaluated the modulatory effect of cyclopamine on ABCG2 function by measuring the intracellular accumulation of two substrates of ABCG2, Ho342 and mitoxantrone. Secondly, we analyzed the effect of these drugs in the phenotype of SP cells (the cells were incubated with only Ho342, or a combination of Ho342 and cyclopamine, or a combination of Ho342, cyclopamine and temozolomide; afterwards we analyzed the number of SP cells). We saw that cyclopamine significantly decreased the fraction of SP cells but not through a depletion of the SP compartment, but as a consequence of the molecular mechanisms involved in the affinity of cyclopamine and Ho342 for ABCG2, as cyclopamine modulated the ABCG2 transporter by increasing Ho342 and mitoxantrone uptake. Temozolomide had no effect on the SP cells. Therefore, cyclopamine, although decreases the SP fraction of cancer stem cells in glioblastoma cell lines, does not deplete the SP compartment, but modulates ABCG2 activity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5049. doi:10.1158/1538-7445.AM2011-5049