Inhibition of Wnt/ß-Catenin Pathway with ICG-001 Induces Apoptosis in Multiple Myeloma.

Abstract 2951

Multiple Myeloma (MM) is characterized by clonal expansion of malignant plasma cells, which preferentially reside in the bone marrow (BM). It has been previously shown that canonical Wnt signaling plays a critical role in proliferation and differentiation in MM. ICG-001 is a selective Wnt/ß-catenin signaling inhibitor that binds to the amino terminus of CREB, thus preventing ß-catenin/TCF signaling in the nucleus. Here we investigated whether the pharmacological inhibition of canonical Wnt signaling with ICG-001 could affect viability of MM cells and produce anti-myeloma effect.

C-myc and cyclin D1 are known to be downstream target genes of canonical Wnt signaling. MM cells lines treated with ICG-001 revealed down regulation of c-myc and cyclin D1 as compared to control. To investigate the varying sensitivity of cell lines to ICG-001, four cells lines were used: RPMI-8226, NCI-H929, U266, and MM1S. MM cells lines were treated with ICG-001 (1uM – 40uM) and data was collected using MTT assay or flow cytometry (Annexin binding assay). ICG-001 significantly reduced viability in all four cell lines due to induction of apoptosis, with RPMI-8226 showing the greatest sensitivity. We performed cleaved-caspase assays and demonstrated that apoptosis was caspase-3 dependent. We have also evaluated the effect of ICG-001 in BM samples from patients with MM. BM cells were treated with ICG-001 for 24 hours and the level of cleaved-caspase-3 was evaluated by flow cytometry. MM cells were defined as double positive CD138+ and Lambda/Kappa+. Our results demonstrated that MM cells were sensitive to ICG-001, while this drug was not able to induce cell death in non-tumor BM cells.

To test the effect of ICG-001 in vivo we injected SCID/Beige mice with 10 × 10⁵ 8226 cells in 100 μL phosphate-buffered saline (PBS). After 3 weeks when a tumor was measurable, the mice were split into two groups and were treated with either ICG-001 (100 mg/kg) or vehicle control (PBS) daily, for 14 days. Tumor size was consistently monitored during treatment and 3 weeks after treatment. We observed that ICG-001 produced a significant antitumor effect as compared to control group.

These data indicate targeting Wnt/ß-catenin Pathway with ICG-001 could be therapeutically beneficial to patients with MM.