Sonic Hedgehog Signaling Pathway as a Therapeutic Target in Diffuse Large B-Cell Lymphoma
JE Kim, RR Singh, C Milito, JH Cho-Vega, M Karanikou, F Kasbidi, LJ Medeiros, R Luthra, F Vega. MD Anderson Cancer Center, Houston, TX
Background: Sonic hedgehog (SHH) signaling is involved in the regulation of cell proliferation and differentiation of embryonic and adult stem cells. Deregulation of this pathway have been reported to result in the initiation and maintenance of a broad range of cancers including basal cell carcinoma, medulloblastoma, prostate cancer, cancers of the digestive tract, lung, breast and liver. However, the role of SHH/GLI signaling in diffuse large B-cell lymphomas (DLBCL) has not been explored.
Design: SHH and GLI-1 were immunohistochemically assessed in a tissue microarray containing 36 DLBCL tumors and by Western blot (WB) analysis of 6 DLBCL cell lines (Pfeiffer, DOHH2, MS, MCA, Ly3 and Ly10). For comparison, tissue microarrays containing cases of follicular lymphoma as well as mantle cell lymphoma cell lines (SP-53 and Z-138) were assessed.The biological effect of inhibition of SHH pathway was assessed using a cell viability (MTT assay) and clonogenicity assays after treatment with the SMO inhibitors, cyclopamine and SANT-1, and after transfection with siRNA specific for GLI1. The presence of extra copies of GLI1 gene was investigated using real-time quantitative PCR.
Results: SHH expression (cytoplasmic) was detected in 32 of 36 (89%) DLBCL tumors and was intense in 15 cases (41.7%). GLI1 expression (nuclear) was detected in 35 of 36 (97.2%) DLBCL and strong nuclear expression was seen in 12 (34.3%) cases. High expression levels of both proteins in DLBCL cell lines were confirmed by WB. In contrast, in follicular lymphomas we found expression of SHH and GLI1 in only 2 of 23 and 8 of 23 cases, respectively. We found a correlation between high expression of GLI1 and lower survival in DLBCL patients. Pharmacologic inhibition of SHH signaling induced cell death (35-80%) and decreased clonogenecity of DLBCL cell lines in a dose-dependent manner in comparison with controls (tomatidine and DMSO). Importantly, cyclopamine treatment showed no effect on colony formation or cell viability in cell lines with no overexpression of SHH signaling or in the cell viability of non-neoplastic B-lymphocytes. Extra copies of GLI1 were detected in 5 of 11 (45.4%) DLBCL tumors analyzed, including 3 cases with 4 or more extra copies of GLI1.
Conclusions: SHH signaling pathway is activated in DLBCL. Our data show that this pathway plays an important role in cell survival and proliferation in DLBCL and that inadequate activation of this pathway may confer a poor prognosis in DLBCL.
Wednesday, March 11, 2009 9:30 AM
Poster Session V # 175, Wednesday Morning