Abstract B223: Selective downregulation of interferon regulatory factor 4 by generation 2.5 antisense oligonucleotides induces strong apoptosis and sensitizes multiple myeloma cells to lenalidomide or bortezomib.
Authors: Zhou Tianyuan , Schmidt Joanna , Jerue Ari , Jo Minji , Kim Youngsoo , MacLeod A. Robert 
Published: August 2014

Abstract
Despite significant advances made recently in treating multiple myeloma (MM), MM patients are often either unresponsive to or develop resistance to the standard therapies. Therefore, the disease still remains incurable and new more efficacious therapies are needed. Interferon Regulatory Factor 4 (IRF4) is a transcription factor which plays a critical role in the differentiation of normal B and T cells, and is strongly implicated in the development of hematological malignancies, especially MM. Although recent publications have pointed IRF4 as a key driver in the progression of MM, it is considered an intractable target by convention approaches.
We recently demonstrated preclinical and clinical activity of a next-generation constrained-ethyl (cEt) modified (Gen 2.5) antisense oligonucleotides (ASOs) targeting STAT3 mRNA (STAT3Rx/AZD9150). Systemic delivery of unformulated STAT3Rx/AZD9150 produced robust target RNA and protein reductions in a broad range of xenograft models (AACR 2013). More importantly, STAT3Rx/AZD9150 showed striking clinical activity in the phase I dose escalation study, producing anti-tumor activity in 4 out of 6 patients with advanced treatment-refractory lymphoma (ASCO 2013).
In this study, we describe next-generation .Gen 2.5 ASOs targeting IRF4. We first investigated whether selective downregulaion of IRF4 could lead to the death of MM cells and enhance the sensitivity of the tumor cells to the treatment of either lenalidomide or bortezomib. IRF4 ASOs administered via ‘free-uptake’, (lipid-independent) to cells growing in culture reduced IRF4 levels in a dose-dependent fashion with a concomitant strong induction of apoptosis in multiple human MM cell lines including KMS-11 and H929 cells. c-Myc, a key oncogene in MM and an immediate target gene of IRF4, also decreased significantly following IRF4 knockdown as anticipated. Importantly, MM cells were sensitive to even modest depletion of IRF4 (&lt;50%), suggesting the strong dependence of MM cells on IRF4 for their survival. The effects of IRF4 ASOs on cell death were specific to MM cells as the ASOs had little effect on the proliferation of most of non-MM types of tumor cells, further demonstrating the specificity of the compounds in targeting IRF4. Next, IRF4 ASOs strongly potentiated the antiproliferative effects of either lenalidomide or bortezomib on MM cells. In addition, we established bortezomib-resistant clones of KMS-11 cells from a long-term exposure to drug and these remained sensitive to IRF4 inhibition. Furthermore, the growth of subcutaneously implanted KMS-11 tumors was significantly delayed with the systemic administration of IRF4 ASO compared with control ASO and this activity correlated with IRF4 depletion. Finally, treatment of mice with mouse-selective IRF4 ASOs at 50 mg/kg, twice a week for 4 weeks was well tolerated in normal mice, which is consistent with the lack of phenotypes observed in IRF4 heterozygous animals. Taken together, these results suggest that MM cells rely heavily on the survival pathway mediated by IRF4 and that selective knockdown of IRF4 by ASOs might provide an efficacious option for treating MM either as a mono-therapy or in combination with other drugs currently in clinical use for MM.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B223.
Citation Format: Tianyuan Zhou, Joanna Schmidt, Ari Jerue, Minji Jo, Youngsoo Kim, A. Robert MacLeod. Selective downregulation of interferon regulatory factor 4 by generation 2.5 antisense oligonucleotides induces strong apoptosis and sensitizes multiple myeloma cells to lenalidomide or bortezomib. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B223.