Abstract A74: Targeting the β-catenin oncogene in multiple myeloma disease using locked nucleic acid technology.

β-catenin is an oncogenic transcription factor that lies down stream of the Wnt signaling pathway. Typical of many transcription factors, it has been exceeding difficult to identify small molecule inhibitors of β-catenin. Therefore, we have applied an alternative technology using locked nucleic acid (LNA)-based short antisense oligonucletides (ON) to specifically destroy β-catenin mRNA. Such LNA-ONs to the androgen receptor, HIF-1α, and survivin are currently being evaluated in cancer patients. Previously, we established anti-tumor activity of a β-catenin specific LNA-ON (EZN-3892) in colorectal and lung cancer xenograft models (Dumble, M et al , Poster, EORTC 2010, Berlin.). In the current studies, we have explored the LNA-ONs in experimental models of multiple myeloma (MM) since uncontrolled clonal expansion of plasma cells within the bone marrow, which typifies MM, is highly dependent on stromal secretion of various cytokines (e.g. IL6) and notably several Wnt ligands. Wnt signaling can promote hematopoietic stem cell proliferation and self renewal as well as trigger the proliferation of tumor cells via the activation of -catenin. In addition, -catenin has been shown to be stabilized and in the nucleus of primary patient MM samples as well as many MM cell lines (Sukhdeo, K et al , 2007, PNAS (104), 7516–7521). Finally, several groups have shown that inhibition of β-catenin by siRNA silencing or a natural product small molecule results in decreased MM cell viability and growth, although further development of these molecules has not occurred. The study reported herein describes a novel 16-mer LNA-ON antagonist of β-catenin, EZN-3892, and its anti-tumor effect on a panel of eight MM cell lines. Robust mRNA decrease is measured in all MM cell lines treated with a dose titration of EZN-3892 in 3-day culture without the aid of transfection agents (“gymnotic culture”). As expected, this mRNA decrease results in an inhibition of β-catenin protein. Surprisingly however, inhibition of the β-catenin protein is not sufficient to result in an anti-proliferative effect in all eight cell lines with only 2/8 lines having 25–35% inhibition of growth when treated with 5 M of EZN-3892. Despite moderate anti-proliferative effect in vitro, the anti-tumor effect is much greater when tested in vivo in tumor xenograft experiments. Treatment of mice bearing OPM-2 MM tumor xenografts with a well tolerated dose of EZN-3892 (50 mg/kg EZN-3892, Q3D×4), results in 85% tumor growth inhibition after 10 days. Tumor growth inhibition is associated with an inhibition of β-catenin in the tumor environment (stroma) and tumor cell death. Interestingly, tumor cells that showed no growth inhibition in 2-D culture likewise show no tumor growth inhibition in a xenograft model suggesting the 2-D proliferation assay in vitro is predictive of tumor response in vivo. Similar observations have been made with EZN-3892 and mouse xenograft models derived from human colorectal and lung cancer cells with activated β-catenin signaling. This work raises the possibility that targeted inhibition of β-catenin within the tumors, as well as the stroma surrounding the tumor are critically important in the control of MM. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A74.