ABSTRACT
SU5416 plus chronic hypoxia causes pulmonary arterial hypertension in rats and is assumed to occur through VEGFR2 inhibition. Cabozantinib is a far more potent VEGFR2 inhibitor than SU5416. Therefore, we hypothesized that cabozantinib plus hypoxia would induce severe pulmonary arterial hypertension in rats. Cell proliferation and pharmacokinetic studies were performed. Rats were given SU5416 or cabozantinib subcutaneously or via osmotic pump and kept hypoxic for three weeks. Right ventricular systolic pressure and hypertrophy were evaluated at days 14 and 28 following removal from hypoxia. Right ventricular fibrosis was evaluated with Picro-Sirius Red staining. Kinome inhibition profiles of SU5416 and cabozantinib were performed. Inhibitor binding constants of SU5416 and cabozantinib for BMPR2 were determined and Nanostring analyses of lung mRNA were performed. Cabozantinib was a more potent VEGFR inhibitor than SU5416 and had a longer half-life in rats. Cabozantinib subcutaneous plus hypoxia did not induce severe pulmonary arterial hypertension. Right ventricular systolic pressure at 14 and 28 days post-hypoxia was 36.8 ± 2.3 mmHg and 36.2 ± 3.4 mmHg, respectively, versus 27.5 ± 1.5 mmHg in normal controls. For cabozantinib given by osmotic pump during hypoxia, right ventricular systolic pressure was 40.0 ± 3.1 mmHg at 14 days and 27.9 ± 1.9 mmHg at 28 days post-hypoxia. SU5416 plus hypoxia induced severe pulmonary arterial hypertension (right ventricular systolic pressure 61.9 ± 6.1 mmHg and 64.9 ± 8.4 mmHg at 14 and 28 days post-hypoxia, respectively). Cabozantinib induced less right ventricular hypertrophy (right ventricular free wall weight/(left ventricular free wall weight + interventricular septum weight) at 14 days post-hypoxia compared to SU5416. Right ventricular fibrosis was more extensive in the SU5416 groups compared to the cabozantinib groups. SU5416 (but not cabozantinib) inhibited BMPR2. Nanostring analyses showed effects on pulmonary gene expression of BMP10 and VEGFR1 in the SU5416 28 days post-hypoxia group. In conclusion, selective VEGFR2 inhibition using cabozantinib plus hypoxia did not induce severe pulmonary arterial hypertension. Severe pulmonary arterial hypertension due to SU5416 plus hypoxia may be due to combined VEGFR2 and BMPR2 inhibition.
ABSTRACT
The platelet-derived growth factor (PDGF) signaling pathway has been found to be activated in human pulmonary arterial hypertension (PAH) and in animal models of the disease. Our study tested the hypothesis that a novel, nonselective inhaled PDGF receptor inhibitor, PK10453, would decrease pulmonary hypertension both in the rat monocrotaline (MCT) model and the rat MCT plus pneumonectomy (MCT+PN) model of PAH. PK10453, delivered by inhalation for 4 (D4)- and 8 (D8)-minute exposures 3 times a day for 2 weeks, decreased right ventricular systolic pressure (RVSP) in both the rat MCT and rat MCT+PN models: RVSP was 80.4 ± 2.6 mmHg in the vehicle MCT group (n = 6), 44.4 ± 5.8 mmHg in the D4 MCT group (n = 6), and 37.1 ± 4.5 mmHg in the D8 MCT group (n = 5; P < 0.001 vs. vehicle); RVSP was 75.7 ± 7.1 mmHg in the vehicle MCT+PN group (n = 9), 40.4 ± 2.7 mmHg in the D4 MCT+PN group (n = 10), and 43.0 ± 3.0 mmHg in the D8 MCT+PN group (n = 8; P < 0.001). In the rat MCT+PN model, continuous telemetry monitoring of pulmonary artery pressures also demonstrated that PK10453 prevented the progression of PAH. Imatinib given by inhalation was equally effective in the MCT model but was not effective in the MCT+PN model. Immunohistochemistry demonstrated increased activation of the PDGFß receptor compared to the PDGFα receptor in neointimal and perivascular lesions found in the MCT+PN model. We show that imatinib is selective for the PDGFα receptor, whereas PK10453 has a lower half-maximal inhibitor concentration (IC50) for inhibition of kinase activity of both the PDGFα and PDGFß receptors compared to imatinib. In conclusion, PK10453, when delivered by inhalation, significantly decreased the progression of PAH in the rat MCT and MCT+PN models. Nonselective inhibition of both the PDGFα and PDGFß receptors may have a therapeutic advantage over selective PDGFα receptor inhibition in PAH.
