Safety and pharmacodynamics of the PDE4 inhibitor roflumilast in advanced B-cell malignancies

Purpose: In this study, we aimed to validate our extensive preclinical data on phosphodiesterase 4 (PDE4) as actionable target in B-cell malignancies. Our specific objectives were to determine the safety, pharmacokinetics, and pharmacodynamics (PI3K/AKT activity), as well as to capture any potential antitumor activity of the PDE4 inhibitor roflumilast in combination with prednisone in patients with advanced B-cell malignancies. Experimental Design: Single-center, exploratory phase Ib open-label, nonrandomized study. Roflumilast (500 mcg PO) was given daily for 21 days with prednisone on days 8 to 14. Additional 21-day cycles were started if patients tolerated cycle 1 and had at least stable disease. Results: Ten patients, median age 65 years with an average of three prior therapies, were enrolled. The median number of cycles administered was 4 (range, 1-13). Treatment was well tolerated; the most common ≥grade 2 treatment-related adverse events were fatigue, anorexia (≥25%), and transient ≥ grade 2 neutropenia (30%). Treatment with roflumilast as a single agent significantly suppressed PI3K activity in the 77% of patients evaluated; on average, patients with PI3K/AKT suppression stayed in trial for 156 days (49-315) versus 91 days (28-139 days) for those without this biomarker response. Six of the nine evaluable patients (66%) had partial response or stable disease. The median number of days in trial was 105 days (range, 28-315). Conclusions: Repurposing the PDE4 inhibitor roflumilast for treatment of B-cell malignancies is safe, suppresses the oncogenic PI3K/AKT kinases, and may be clinically active.