Therapeutic Targeting of Interferon Regulatory Factor 4 with Next Generation Antisense Oligonucleotides Produces Robust In Vivo Antitumor Activity in Preclinical Models of Multiple Myeloma

Despite significant recent advances in therapeutic options, multiple myeloma (MM) remains an incurable disease, and novel agents targeting novel molecular pathways with activity in advanced patients are urgently needed. Interferon Regulatory Factor 4 (IRF4) is a transcription factor involved in immune responses in normal B and T cells, and is strongly implicated in the development of hematological malignancies, especially MM. Although recent publications have pointed to IRF4 as a driver oncogene in the progression of MM, it is considered an intractable target by conventional therapeutic approaches.

Here we describe an antisense oligonucleotide (ASO) approach to selectively target IRF4. Administration of next generation human IRF4 ASOs via 'free-uptake' (without transfection) to a large panel of human MM cell lines resulted in a dose-dependent IRF4 reduction with concomitant induction of apoptosis. ASO-mediated IRF4 depletion also decreased the levels of c-Myc, another key oncogene in MM. MM cells were sensitive to even modest depletion of IRF4 (<50%), suggesting the strong dependence of MM cells on IRF4 for their survival. IRF4 ASOs also enhanced the sensitivity of the tumor cells to the treatment of IMiD (lenalidomide), proteasome inhibitor (Bortezomib) and BTK inhibitor (Ibrutinib) in MM cell, including KMS-11, JJN3 and MM1.R. In addition, Bortezomib-resistant clones of KMS-11 cells established from a long-term exposure to the drug remained sensitive to IRF4 inhibition. Importantly, in two different subcutaneously implanted MM tumor models, systemic administration of 2 independent human IRF4 ASOs depleted IRF4 protein levels in tumors and inhibited the growth of tumors compared to control treatment. Moreover, in a clinically relevant MM mouse model where human MM cells accumulate in the mouse bone marrow, treatment with human IRF4 ASOs substantially prolonged the survival of the tumor-bearing animals along with specific downregulation of human IRF4 and its downstream gene c-Myc. Finally, systematic 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 next generation ASOs is an attractive therapeutic strategy for the treatment of patients with advanced treatment-refractory MM.