Evaluation of a new proteasome inhibitor for treatment of lung fibrosis

Background: So far treatment options in lung fibrosis are very limited and lung transplantation still remains the only therapy in severe cases. Proteasome inhibition has been reported to prevent development of fibrosis in several organs like liver, skin, kidney, heart, or bone marrow. Non-toxic doses of proteasome inhibitors effectively reduce deposition of collagens, expression of MMPs, and TGFß signaling. However, the effect of proteasome inhibitors on lung fibrosis is controversial and possibly related to the cytotoxic side effects of the inhibition of proteasomal protein degradation in the cell.

Hypothesis: Local administration of proteasome inhibitors allows efficient drug delivery to the lung and prevents development of pulmonary fibrosis without systemic toxicity.

Methods: ONX0912, a new irreversible epoxyketone inhibitor of the proteasome was evaluated with regard to cytotoxicity, proliferation, and proteasomal inhibition profile in the human and murine lung epithelial cell lines A549 and MLE-12 using MTT survival, BrdU proliferation, and luminescent proteasome activity assays. Moreover, we prepared primary lung fibroblasts isolated from a proteasome reporter mice (ODD-luc mice), which were characterized as mentioned above. The ODD-luciferase reporter accumulates upon proteasome inhibition which can be quantified via bioluminescence and reflects the actual degree of proteasome inhibition in the cell. We were able to establish an optimized inhibitor dose which partially inhibits the proteasome but efficiently blocks fibroblast proliferation and fibroblast function without affecting cell viability. The same dose is less effective in epithelial cells.

Conclusion: ONX0912 provides antiproliferative and possibly antifibrotic effects in murine lung fibroblasts. The therapeutic application of proteasome inhibitors will be further analyzed by local inhalative delivery of ONX 0912 in a mouse model of pulmonary fibrosis.