(661) The PDE4 Inhibitor Apremilast Enhances Benefits of CFTR Modulators in vitro and in vivo

Background: CFTR modulators successfully restore the function of defective CFTR and have significantly improved the disease course in many subjects with CF. However, maximal benefits are not uniformly found, and very few attain physiological CFTR activity levels matching non-CF subjects or CF carriers. CFTR channel gating is tightly regulated by cAMP-dependent signaling pathways suggesting that drugs that increase cellular cAMP levels may increase ion transport. Previously, we have shown that clinically-used PDE4 inhibitor apremilast increases cytosolic cAMP levels and activates CFTR function. Here, we evaluate apremilast in combination with currently used CFTR modulators in patient-derived cells and a humanized G551D CF rat.

Methods: Human bronchial epithelial (HBE) cells isolated from CF patients with F508del-CFTR^+/+ were cultured at an air-liquid interface until terminal differentiation. SD rats expressing hG551D-CFTR^+/+ were treated with oral VX-770 (30mg/kg/day) and apremilast (20mg/kg/day by IP). CFTR function was assessed in vitro by Ussing chamber electrophysiology and in vivo by nasal potential difference (NPD) assay. Micro-optical coherence tomography (µOCT) imaging was used to estimate periciliary liquid (PCL) depth, mucus viscosity, and mucociliary transport (MCT) in cells and rat tracheal explants.

Results: CFTR function was evaluated in F508del-CFTR^+/+ HBE cells pre-treated with either a vehicle, VX-661, VX-445, or VX-661+VX-445, followed by sequential addition of VX-770 and apremilast in Ussing chambers. In CF cells treated with Corrector drugs, apremilast augmented CFTR activity induced by VX-770 (ΔVX-770 in Vehicle, VX-661, VX-445, and VX-661+VX-445 treated cells were 2.22±0.74, 4.74±1.34, 11.94±2.57, and 21.09±5.20 μA/cm² and, ΔVX-770 + apremilast were 8.01±3.41, 15.93±2.50, 28.28±3.17, and 38.34±5.51 μA/cm², respectively). Increased ion transport by apremilast translated to increased MCT by 54% in F508del-CFTR^+/+ HBE cells treated with triple CFTR modulators (ΔMCT in Vehicle, triple CFTR modulators, and triple CFTR modulators + apremilast were 1.10±0.09, 4.89±2.16, and 7.50±3.93 μm/s, respectively). Interestingly, PCL depth was not augmented by apremilast (vehicle, triple combination therapy, and triple CFTR modulators + apremilast were 2.46±0.30, 4.34±0.59, and 4.46±0.46 μm, respectively), suggesting a physiologic ceiling. But, apremilast significantly improved mucus reflectance, a proxy for viscosity (% reflectance in Vehicle, triple combination therapy, and triple CFTR modulators + apremilast were 33.21±5.21, 13.85±5.40, 9.79±6.5, respectively). In hG551D rats, CFTR activity by apremilast was tested on top of VX-770. Baseline CFTR activity by NPD (Δzero cl+forskolin) in hG551D rats was -2.0 mV. With VX-770, transepithelial voltage increased by -5.1mV and increased further by -2.8mV with the inclusion of apremilast.

Conclusions: Apremilast enhances CFTR activation in CF cells and G551D CF rats treated with modulator drugs. Additive effects of apremilast with modulator drugs result in substantial improvements in mucus transport and viscosity. Thus, apremilast (and other clinically available PDE4 inhibitors) represent a novel means to improve respiratory outcomes in CF patients and warrant further evaluation.

Acknowledgements: This work was supported by grants from UAB Research Development Program – ROWE19RO (CFF) CFRC and Research and Translation Core Center (P30DK072482), and NIH/NIAA (RO1AA027528).

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