In Vitro Characterization of Wnt/β-Catenin Pathway Inhibition in Multiple Myeloma Cell Lines Using a Novel Class of Small Molecules.

Multiple Myeloma (MM) is a fatal form of hematologic cancer characterized by the clonal expansion of plasma cells in the bone marrow. Recent finding by several research laboratories have shown that Wnt/β-Catenin signaling pathway is activated in MM leading to the translocation of β-Catenin to the nucleus where it binds to T cell factor (TCF) and drives transcription of genes involved in the progression of cancer (Derksen et. Al., PNAS 2004). The mechanism by which Wnt/β-Catenin signaling is activated in MM is not well understood, however, β-Catenin is expressed in the majority of MM cell lines and inhibition of the pathway with a dominant negative form of TCF4 or the small molecule PKF115-584 have shown anti-proliferative effects in in vitro and in vivo cell line and xenograft models making inhibition of Wnt/β-Catenin signaling a promising modality for the treatment of MM (Sukhdeo et al., PNAS 2007). To this end, Avalon Pharmaceuticals has developed a series of small molecule compounds, lead candidate series-363 (LC-363), with potent inhibitory effects on Wnt/β-Catenin signaling and anti-proliferative effects in colon cancer cell lines and in vivo models (EORTC, 2007). LC-363 compounds down regulate expression of the noted β-Catenin/TCF transcriptional targets c-jun, fra-1, and PPARδ as well as increase expression of the Dickkopf family of secreted proteins 1 and 3 which inhibit Wnt signaling. In this study, we report on the in vitro characteristics of LC-363 in MM cell line models. We show that LC-363 compounds have broad and potent growth inhibitory and cytotoxic effects on MM cell lines. Additionally, these effects are mediated through a G1 phase cell cycle block, apoptosis, and decrease in cytoplasmic levels of β-Catenin. Importantly, we show the relationship between expression level of β-Catenin protein and sensitivity to LC-363 compounds in terms of growth inhibition and apoptosis. Lastly, we describe the gene expression signatures induced by LC-363 in MM cell models across multiple time and dose studies to detail their dynamic effects on expression of genes within the Wnt/β-Catenin signaling pathway. In conclusion, we believe that inhibition of Wnt/β-Catenin signaling is a viable therapeutic alternative for treatment of MM patients with activated Wnt/β-Catenin signaling and to that end; LC-363 compounds are promising candidates currently in pre-clinical development for treatment of cancers with activated Wnt/β-Catenin signaling including MM.