Preliminary Results from a Phase 1/2, Open-Label, Dose-Escalation Clinical Trial of IMO-8400 in Patients with Relapsed or Refractory Waldenstrom's Macroglobulinemia

Introduction: Waldenström's macroglobulinemia (WM) is a rare, indolent B-cell lymphoma characterized by lymphoplasmacytic cell infiltration of bone marrow and elevated serum levels of immunoglobulin M (IgM) protein. Despite recent advances in treatment the disease relapses in most patients. About 90% of WM patients harbor the MYD88 L265P oncogenic mutation. MYD88 is an adapter protein in the Toll-like receptor (TLR) pathway. The MYD88 L265P oncoprotein has been shown to amplify TLR 7 and 9 signaling, leading to downstream activation of NF-κB and cytokine signaling pathways that promote tumor cell survival and proliferation (Lim, AACR 2013). IMO-8400 is an investigational oligonucleotide antagonist of endosomal TLRs 7, 8 and 9. In preclinical studies in a human cell line and animal models of WM, IMO-8400 inhibited key cell signaling pathways, including NF-κB, BTK, STAT-3 and IRAK-4, and inhibited tumor growth and tumor IgM production. In Phase 1 and 2 clinical trials in healthy subjects (N=30) and in patients with autoimmune disease (N=35), IMO-8400 was generally well tolerated and demonstrated evidence of clinical activity. Based on these data, we initiated a Phase 1/2 clinical trial of IMO-8400 in WM, the first study of a drug candidate specifically targeting the MYD88 L265P mutation.

Methods: This Phase 1/2 multicenter, open-label, dose-escalation clinical trial continues to recruit adult patients with relapsed or refractory WM (NCT Identifier: NCT02092909). In a classic 3x3 dose escalation scheme, patients are enrolled in one of three sequential escalating dose cohorts and receive subcutaneous IMO-8400 at dosages of 0.6, 1.2 or 2.4 mg/kg per week, respectively, for 24 weeks. The presence of the MYD88 L265P mutation is assessed by PCR-based genetic screening following enrollment. Patients who complete the 24-week treatment period are eligible to enroll in an extension trial. The primary study objective is to evaluate the safety and tolerability of escalating IMO-8400 dosages. Secondary objectives include preliminary evaluation of clinical response based on international guidelines and identification of an optimal dose for further evaluation (Kimby, Clin Lymphoma Myeloma 2006).

Results: Overall, 17 patients (6 female, 11 male) have been enrolled in three dose cohorts to date. Median baseline characteristics include: age 66 years, prior therapies 4 (range 1-13), serum IgM 2,225 mg/dL, serum M protein 0.96 g/dL, and B2-microglobulin 3.42 mg/L. IMO-8400 has been generally well tolerated across all dose cohorts to date, with patient exposure ranging from 2-46 weeks in the Phase 1/2 and extension trials. The most common adverse events reported to date include transient flu-like symptoms and injection site reactions. One serious adverse event of worsening grade 3 arthritis, deemed possibly related to study drug, was reported in a patient with a pre-existing history of arthritis in the 2.4 mg/kg dose cohort. This patient discontinued study treatment. To date, no other patients have discontinued treatment due to treatment-related adverse events. Preliminary evidence of clinical activity for IMO-8400 has been observed in all dose cohorts. In June 2015, an independent Data Review Committee reviewed 4-week safety data from the highest dose cohort and agreed that 2.4 mg/kg was safe for further evaluation. Safety, pharmacokinetics and preliminary activity for all three dose cohorts will be presented.

Conclusions: IMO-8400 is a mutation-targeted therapy in development for the treatment of patients with relapsed or refractory WM. In an ongoing Phase 1/2 clinical trial in WM, IMO-8400 has been generally well tolerated and has demonstrated preliminary evidence of clinical activity. Safety results support continued evaluation of IMO-8400 at 2.4 mg/kg/week in this patient population.