Mode of action of nintedanib in the treatment of idiopathic pulmonary fibrosis

Abstract

Idiopathic pulmonary fibrosis (IPF) is a progressive and ultimately fatal disease characterised by fibrosis of the lung parenchyma and loss of lung function. Although the pathogenic pathways involved in IPF have not been fully elucidated, IPF is believed to be caused by repetitive alveolar epithelial cell injury and dysregulated repair, in which there is uncontrolled proliferation of lung fibroblasts and differentiation of fibroblasts into myofibroblasts, which excessively deposit extracellular matrix (ECM) proteins in the interstitial space. A number of profibrotic mediators including platelet-derived growth factor (PDGF), fibroblast growth factor (FGF) and transforming growth factor-β are believed to play important roles in the pathogenesis of IPF. Nintedanib is a potent small molecule inhibitor of the receptor tyrosine kinases PDGF receptor, FGF receptor and vascular endothelial growth factor receptor. Data from in vitro studies have shown that nintedanib interferes with processes active in fibrosis such as fibroblast proliferation, migration and differentiation, and the secretion of ECM. In addition, nintedanib has shown consistent anti-fibrotic and anti-inflammatory activity in animal models of lung fibrosis. These data provide a strong rationale for the clinical efficacy of nintedanib in patients with IPF, which has recently been demonstrated in phase III clinical trials.

FIGURE 1

Polypharmacology of nintedanib and the downstream signalling pathways. Nintedanib binds to the intracellular ATP binding pocket of fibroblast growth factor receptors (FGFRs), platelet-derived growth factor receptors (PDGFRs) and vascular endothelial growth factor receptors (VEGFRs) resulting in blockage of the autophosphorylation of these receptors and the downstream signalling cascades. Nintedanib might exert additional activity by directly blocking non-receptor kinases like Src and Lck (not illustrated). Nintedanib was shown to inhibit PDGFR phosphorylation and subsequent protein kinase B (Akt) and extracellular signal-regulated kinase (ERK)1/2 phosphorylation in lung tissue from mice. Vascular endothelial growth factor (VEGF) was shown to stimulate angiogenesis via the VEGFR, but also to bind to the PDGFR on fibroblasts, stimulating proliferation. Inhibition by nintedanib ultimately results in reduced proliferation, migration and survival of fibroblasts and, potentially, also to attenuated angiogenesis in the lung. FAK: focal adhesion kinase; FGF: fibroblast growth factor; FRS2: FGFR substrate 2; Grb2: growth factor receptor-bound protein 2; MEK1/2: mitogen-activated protein kinase kinase 1/2; PDGF: platelet-derived growth factor; PI3K: phosphatidylinositol-4,5-bisphosphate 3-kinase; PIP2/3: phosphatidylinositol-2/3-phosphate; PKC: protein kinase C; PLC-γ: phospholipase C-γ; SOS: son of sevenless, a guanine nucleotide exchange factor that acts on the Ras GTPases.

FIGURE 2

Crystal structure of nintedanib bound to the active site of the fibroblast growth factor receptor-1 kinase domain. The inhibitor and residues that line the active site are shown in stick representation. Hydrogen bonds are depicted as yellow dots. Key residues are labelled.

FIGURE 3

a) Nintedanib inhibits platelet-derived growth factor (PDGF)-BB-stimulated platelet-derived growth factor receptor (PDGFR)-α and β autophosphorylation and proliferation of primary human lung fibroblasts (HLFs). HLFs were incubated with nintedanib at different concentrations and stimulated with PDGF-BB (50 ng·mL⁻¹). PDGFR-α and β phosphorylation was determined by an ELISA specific for the phosphorylated receptors. Proliferation was determined by bromodeoxyuridine incorporation. Concentration-dependent inhibition data are presented as mean±sem (n=3 experiments). Reproduced from [78] with permission from the publisher. b) Nintedanib inhibits basic fibroblast growth factor (FGF) and PDGF-BB-stimulated motility of primary HLF from patients with idiopathic pulmonary fibrosis (IPF-HLF) and without IPF (N-HLF). Human lung fibroblasts were incubated with nintedanib at different concentrations for 30 min before the cells were stimulated with basic FGF (20 ng·mL⁻¹) or PDGF-BB (50 ng·mL⁻¹). Motility of the cells was determined by time lapse microscopy using a Cell-IQ imager (CM Technologies Oy, Tampere, Finland) and manual single cell tracking for 72 h. Mean cell velocity was calculated from three experiments. Inhibition is presented as mean±sem.

FIGURE 4

Current understanding of the mode of action of nintedanib in fibrotic lung diseases. The scheme reflects ongoing processes in the pathology of idiopathic pulmonary fibrosis (IPF). As a result of epithelial damage, alveolar epithelial cells undergo apoptosis and epithelial type II cells transform into myofibroblasts (epithelial–mesenchymal transition (EMT)) to provide mesenchymal cells for the initial repair process. Residual lung fibroblasts in the interstitium start to proliferate and migrate to the site of injury. Excessive fibroblast proliferation, migration and transformation to myofibroblasts (fibroblast to myofibroblast transformation (FMT)), and synthesis and deposition of extracellular matrix (ECM) are hallmarks of the fibrotic pathology in IPF. Nintedanib (yellow molecules) interferes with fibroblast/myofibroblast proliferation, FMT and migration. By limiting the number of fibroblasts/myofibroblasts, the synthesis and deposition of ECM are reduced. Nintedanib was found to have no effect on EMT. The effects of nintedanib on fibrocytes and other structural cells of the lung need further exploration. The inhibitory activities of nintedanib are shown in yellow.