Simultaneous Targeting of SHH/ p53 Pathways in Large B Cell Lymphomas.

Abstract 1730

Poster Board I-756

The sonic hedgehog (SHH) pathway, associated with proliferative stem cell niches of many organs, is frequently deregulated in diverse cancers. We have previously shown that the SHH pathway augments the survival of tumor cells by inducing antiapoptotic molecules including bcl-2 and provides resistance to a number of conventional cancer therapies. Aberrant activation of the SHH pathway has been associated with activation and maintenance of lymphoid malignancies. Additionally, our recent data indicates that p63, a p53 family member and an important marker of stem cells has multiple interacting nodes with the SHH pathway. Based on these observations, we hypothesized i) that there is crosstalk between the SHH and p53/p63 networks in cells and, ii) inhibition of the SHH pathway with simultaneous activation of the p53 pathway would result in increased cell death in cancer cell lines of lymphoid origin. Using SDS-PAGE followed by immunoblotting and RT-PCR we surveyed a panel of 18 leukemia/lymphoma cell lines for components of the SHH pathway and the p53/p63/p73 network. Robust SHH pathway expression was observed in 15 of the 18 cell lines examined. Interestingly, in p53 deficient cell lines there was an increase in p63/p73 expression as compared to cell lines with wild type (WT) p53. A set of the previously analyzed diffuse large B- cell lymphoma (DLBCL) cell lines were selected and were representative of both p53 deficient and WT cell lines and also the activated B-like DLBCL (ABC) and germinal center B-like DLBCL (GCB) subgroups. These cells were treated with cyclopamine, an inhibitor of the SHH pathway and/or nutlin, an HDM2 antagonist. Cell viability (MTS assay) was measured using both compounds at various drug concentrations and time points. In addition we also investigated the effects of the drugs individually and in combination on components of the p53/p63 and SHH axes and their targets. Our findings suggest that treatment of p53 (WT) cell lines with a combination of nutlin and cyclopamine results in reduced cell survival than treatment with either drug alone and at lower drug concentrations and that the p53 status of the cell line may be more important in determining therapeutic response to the selected compounds. In addition the p53/p63 pathway may have a novel role in regulation of specific components of the SHH pathway in cells of lymphoid origin. In conclusion, these observations provide proof of concept that a combinatorial therapeutic approach, targeting both the p53 and SHH axes would provide a more robust and favorable response in large B cell lymphomas.