Protection against vascular leak in neprilysin transgenic mice with complex overexpression pattern.

Neprilysin (NEP) is a cell surface metallopeptidase found in many tissues. Based mostly on pharmacological manipulations, NEP has been thought to protect blood vessels from plasma extravasation. We have suggested that NEP may protect against pulmonary vascular injury. However, these prior studies did not utilize mice which overexpress NEP. The aims of the present investigation were to develop and characterize doubly transgenic (DT) mice that overexpress NEP universally and conditionally, and to investigate the protective effect that overexpressed NEP may have against plasma extravasation in the vasculature. The duodenum, which is often used to assess vascular permeability, and in which the NEP protein was overexpressed in our DT mice two-fold, was selected as our experimental preparation. We found that substance P-induced plasma extravasation was decreased substantially (3.5-fold) in the duodenums of our doxycycline-treated DT mice, giving independent evidence of NEP's protective effects against plasma extravasation. Transgenic lung NEP protein was not stably expressed in the DT mice, so we were not able to test the effect of NEP overexpression in the lung. Although initially overexpressed nearly nine-fold at that site, pulmonary NEP protein overexpression eventually dissipated. Surprisingly, at a time when there was no lung transgenic NEP protein overexpression, lung NEP mRNA expression was still increased 23-fold, indicating that the expression defect probably is not transcriptional. These studies help to characterize our complex transgenic model of NEP overexpression and further demonstrate NEP's protective effects against plasma extravasation.

Alveolar hypoxia promotes murine lung tumor growth through a VEGFR-2/EGFR-dependent mechanism.

Patients with chronic obstructive pulmonary disease (COPD) are at an increased risk for the development of lung cancer, the mechanisms for which are incompletely understood. We hypothesized that the hypoxic pulmonary microenvironment present in COPD would augment lung carcinogenesis. Mice were subjected to chemical carcinogenesis protocols and placed in either hypoxia or normoxia. Mice exposed to chronic hypoxia developed tumors with increased volume compared with normoxic controls. Both lungs and tumors from hypoxic mice showed a preferential stabilization of HIF-2α and increased expression of VEGF-A, FGF2, and their receptors as well as other survival, proliferation, and angiogenic signaling pathways regulated by HIF-2α. We showed that tumors arising in hypoxic animals have increased sensitivity to VEGFR-2/EGFR inhibition, as chemoprevention with vandetanib showed markedly increased activity in hypoxic mice. These studies showed that lung tumors arising in a hypoxic microenvironment express increased growth, angiogenic, and survival signaling that could contribute to the increased lung cancer risk in COPD. Furthermore, the differential sensitivity of tumors arising in hypoxia to VEGFR-2/EGFR inhibition suggests that the altered signaling present in tumors arising in hypoxic lung might be therapeutically exploited in patients with underlying COPD.

Vascular endothelial growth factor receptor 2-targeted chemoprevention of murine lung tumors.

No clinically effective chemoprevention for lung cancer has been found. Angiogenesis is an early feature of both adenocarcinoma and squamous cell lung cancer. We investigated the effects of vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2) inhibition on lung carcinogenesis in a murine model of adenocarcinoma. The VEGFR-2 tyrosine kinase inhibitor, vandetanib, was given to FVB/N mice in chow for 7 days at varying doses to show pharmacologic activity by inhibition of VEGF-mediated VEFGR-2 and ERK phosphorylation. Plasma levels corroborated adequate dosage. For chemoprevention experiments, mice were injected i.p. with 1 mg/g of urethane, a carcinogen found in tobacco smoke. Chow containing vandetanib, 75 mg/kg/d, or control chow was given to mice, starting 7 days after urethane administration. Sixteen weeks after urethane injection, mice were sacrificed, tumors enumerated and measured. Vandetanib resulted in reductions in tumor multiplicity (6.5 +/- 0.86 versus 1.0 +/- 0.30, P = 0.001) and average tumor volume (0.85 +/- 0.10 versus 0.15 +/- 0.09 mm(3), P = 0.001), but not incidence (71% versus 100%, P = ns), compared with control. As vandetanib has other activities besides VEGFR-2 tyrosine kinase inhibition, we gave the anti-VEGFR-2 monoclonal antibody, DC101, for weeks 11 to 15 of a urethane carcinogenesis protocol with an arrest in tumor volume increase, but no change in multiplicity or incidence. Further investigation of the chemopreventive effect of vandetanib and other VEGF signaling inhibitors is needed.

Chemoprevention of murine lung cancer by gefitinib in combination with prostacyclin synthase overexpression.

INTRODUCTION: We hypothesized that the combination of the EGFR tyrosine kinase inhibitor (TKI) gefitinib with the powerful chemopreventive manipulation of lung-specific transgenic prostacyclin synthase (PGIS) overexpression on tumorigenesis in FVB/N mice would result in augmented chemoprevention. MATERIALS AND METHODS: Wildtype and littermate PGIS overexpressors (OE) were given urethane, 1 mg/kg i.p. followed by thrice weekly i.p. injections of gefitinib, 50 mg/kg or 100 mg/kg, or vehicle. Pulmonary adenomas were enumerated and measured. RESULTS: Gefitinib at either 50 mg/kg or 100 mg/kg administered i.p. three times weekly was effective in inhibiting EGF induced EGFR tyrosine phosphorylation and downstream signaling. The PGIS overexpressors showed significant decreases in tumor multiplicity consistent with prior studies. Gefitinib had no effect on tumor multiplicity or volume in wildtype mice. Among the PGIS overexpressors, a significant reduction in tumor multiplicity was shown in the 50 mg/kg, but not the 100 mg/kg, gefitinib treatment group vs. vehicle control animals (1.13+/-0.29 vs. 2.29+/-0.32 tumors/mouse, p=0.015). We examined the phosphorylation status in selected downstream effectors of EGFR (Erk, Akt, Src, PTEN). The major difference in the 50 mg/kg vs. 100 mg/kg group was an increase in p-Src in the PGIS OE mice receiving the higher dose. CONCLUSION: We conclude that gefitinib alone has no chemopreventive efficacy in this model; it augmented the effect of PGIS overexpression at 50 mg/kg but not 100 mg/kg. Increased p-Src is correlated with loss of efficacy at the higher dose, suggesting the potential for combined EGFR and Src inhibition strategies in chemoprevention.

Neprilysin null mice develop exaggerated pulmonary vascular remodeling in response to chronic hypoxia.

Neprilysin is a transmembrane metalloendopeptidase that degrades neuropeptides that are important for both growth and contraction. In addition to promoting carcinogenesis, decreased levels of neprilysin increases inflammation and neuroendocrine cell hyperplasia, which may predispose to vascular remodeling. Early pharmacological studies showed a decrease in chronic hypoxic pulmonary hypertension with neprilysin inhibition. We used a genetic approach to test the alternate hypothesis that neprilysin depletion increases chronic hypoxic pulmonary hypertension. Loss of neprilysin had no effect on baseline airway or alveolar wall architecture, vessel density, cardiac function, hematocrit, or other relevant peptidases. Only lung neuroendocrine cell hyperplasia and a subtle neuropeptide imbalance were found. After chronic hypoxia, neprilysin-null mice exhibited exaggerated pulmonary hypertension and striking increases in muscularization of distal vessels. Subtle thickening of proximal media/adventitia not typically seen in mice was also detected. In contrast, adaptive right ventricular hypertrophy was less than anticipated. Hypoxic wild-type pulmonary vessels displayed close temporal and spatial relationships between decreased neprilysin and increased cell growth. Smooth muscle cells from neprilysin-null pulmonary arteries had increased proliferation compared with controls, which was decreased by neprilysin replacement. These data suggest that neprilysin may be protective against chronic hypoxic pulmonary hypertension in the lung, at least in part by attenuating the growth of smooth muscle cells. Lung-targeted strategies to increase neprilysin levels could have therapeutic benefits in the treatment of this disorder.

Induction of a high incidence of lung tumors in C57BL/6 mice with multiple ethyl carbamate injections.

Murine pulmonary adenomas progress to malignancy with many similarities to human pulmonary adenocarcinoma, the most common form of lung cancer. Inbred mice vary in their susceptibility to lung tumor development, and induced genetic modifications are a powerful tool for understanding this susceptibility. Many transgenic and null mutations relevant to lung cancer pathogenesis were derived on the highly resistant C57BL/B6 (B6) background. Since the inability to reliably induce lung tumors in B6 mice limits these studies, we systematically examined several carcinogenesis protocols in B6 mice. Ten weekly ethyl carbamate (EC) doses caused a nearly 100% lung tumor incidence with a tumor multiplicity >2; multiple EC dosing is thus an alternative to the time-consuming transfer of transgenes and null mutations to susceptible backgrounds.