Abstract 764: A role for GLI1 in the development of multidrug resistance in rhabdomyosarcoma (RMS) cells

Abstract RMS is the most common sarcoma of childhood. About 30% of patients with localized tumors will recur following treatment. The outcome for patients with recurrent RMS remains poor. Therefore, development of chemotherapy resistance during RMS therapy represents an important problem and novel approaches to prevent or reverse drug resistance are essential. Activation of multidrug transporter genes, including MDR1, MRP1, LRP and TAP1 represents an important mechanism for drug resistance in RMS. However, the mechanism of expression of multidrug resistance genes in RMS is incompletely understood. Recent reports have suggested a role for the Hedgehog (HH) signaling pathway and its downstream mediator GLI1 in acquisition of a multidrug resistance phenotype in esophageal adenocarcinoma, glioblastoma, and myeloid leukemia. Since approximately 60% of embryonal RMS (ERMS) and more rarely alveolar RMS (ARMS) express HH pathway components, we hypothesized that HH pathway activation may up-regulate the expression of multidrug resistance genes in RMS. We demonstrated expression of HH pathway components, including GLI1, in ERMS (RD, Rh18 and Ruch-2) and ARMS (Rh30 and Rh41) cell lines by qRT PCR and/or Western blot. We found variable expression of MDR1, MRP1, LRP and TAP1 by qRT PCR in these cell lines. Treatment of RMS cells with GLI1 siRNA (RD, Rh18 and Rh41) or the GLI1 antagonist GANT61 (Rh18 and Rh30) caused down-regulation LRP and TAP1 expression. In addition, GLI1, MDR1, LRP and TAP1 expression was increased in vincristine resistant UKF Rhb-1 RMS cells compared with parental cells (obtained from Dr. Cinatl) by qRT PCR. Treatment of vincristine resistant UKF Rhb-1 cells with vincristine together with either GANT61 or Cpd#33 (GLI1 inhibitors), each at a dose, which did not reduce cell viability individually, significantly decreased cell viability by MTT assay. Our results suggest that GLI1 up-regulates a subset of multidrug resistance genes in RMS cells and that GLI1-inhibitors may reduce multidrug resistance. Citation Format: Joon Won Yoon, Marilyn Lamm, King-Fu Leong, Stephen Iannaccone, Philip Iannaccone, David Walterhouse. A role for GLI1 in the development of multidrug resistance in rhabdomyosarcoma (RMS) cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 764. doi:10.1158/1538-7445.AM2014-764