Differential and opposing effects of imatinib on LPS- and ventilator-induced lung injury.

Endothelial dysfunction underlies the pathophysiology of vascular disorders such as acute lung injury (ALI) syndromes. Recent work has identified the Abl family kinases (c-Abl and Arg) as important regulators of endothelial cell (EC) barrier function and suggests that their inhibition by currently available pharmaceutical agents such as imatinib may be EC protective. Here we describe novel and differential effects of imatinib in regulating lung pathophysiology in two clinically relevant experimental models of ALI. Imatinib attenuates endotoxin (LPS)-induced vascular leak and lung inflammation in mice but exacerbates these features in a mouse model of ventilator-induced lung injury (VILI). We next explored these discrepant observations in vitro through investigation of the roles for Abl kinases in cultured lung EC. Imatinib attenuates LPS-induced lung EC permeability, restores VE-cadherin junctions, and reduces inflammation by suppressing VCAM-1 expression and inflammatory cytokine (IL-8 and IL-6) secretion. Conversely, in EC exposed to pathological 18% cyclic stretch (CS) (in vitro model of VILI), imatinib decreases VE-cadherin expression, disrupts cell-cell junctions, and increases IL-8 levels. Downregulation of c-Abl expression with siRNA attenuates LPS-induced VCAM-1 expression, whereas specific reduction of Arg reduces VE-cadherin expression in 18% CS-challenged ECs to mimic the imatinib effects. In summary, imatinib exhibits pulmonary barrier-protective and anti-inflammatory effects in LPS-injured mice and lung EC; however, imatinib exacerbates VILI as well as dysfunction in 18% CS-EC. These findings identify the Abl family kinases as important modulators of EC function and potential therapeutic targets in lung injury syndromes.

Novel therapies for microvascular permeability in sepsis.

Sepsis is characterized physiologically by an aberrant systemic inflammatory response and microvascular dysfunction. While appropriate antibiotics and supportive care are essential in the management of the septic patient, therapies targeting specific aspects of the pathophysiology could have a significant impact on the morbidity and mortality associated with both sepsis and its sequlea, including acute lung injury (ALI). We have characterized several mediators of endothelial cell (EC) barrier function that may serve as novel therapies for sepsis-induced microvascular dysfunction including simvastatin, adenosine triphosphate (ATP), sphingosine 1-phosphate (S1P), and activated protein C (APC). Notably, APC is already available for the treatment of severe sepsis, however, to date its mechanism of action has been unclear. While distinct in many ways, we have found that these agonists have in common the ability to induce dynamic rearrangement of the EC actin cytoskeleton that corresponds to barrier protection. In addition, we have extended our in vitro findings to relevant animal models of endotoxin-induced acute lung injury and have confirmed beneficial effects of both simvastatin and S1P which are associated with evidence of decreased vascular permeability in this setting. Moreover, our data also indicate that APC effects in sepsis may be largely due to augmentation of EC barrier function affecting decreased microvascular permeability. We speculate that the administration of direct modulators of EC barrier function and microvascular permeability, such as those described here, may ultimately become the standard of care for the septic patient.

Statins and thrombin.

L-Mevalonic acid is the distant precursor of cholesterol, in contrast to cholesterol, L-mevalonic acid, its distant precursor gives rise to farnesyl and geranylgeranyl pyrophosphates in relatively few metabolic steps. These isoprenyl pyrophophates covalently conjugate with specific G-proteins and serve as membrane anchors enabling them to carry out their function. Although farnesyl-proteins may participate in signal transduction, geranylgeranyl-proteins (e.g., Rho GTP binding proteins) are well known to downregulate signaling pathways by inhibiting L-mevalonic acid synthesis. Such inhibitors include 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, drugs (statins) and isoprenoids of dietary origins, where Rho protein activation appears to be necessary for cellular-mediated thrombin generation. Thrombin and other proteases (e.g., coagulation factor Xa, tryptase) upregulate protease-activated receptor (PAR) synthesis and PAR activation promotes synthesis and expression of other proteins [e.g., tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1)]. With the PAR-1 activating peptide SSFLRNP, we found that either cerivastatin or atorvastatin mitigated platelet stimulation in a time- and dose-dependent manner, as predicted if a statin-mediated Rho pathway is required. We also found that simvastatin decreased prothrombin fragments F1+2 in plasma from type 2 diabetics, demonstrating that statins downregulate thrombin generation. Thus, independent of cholesterol, statins and dietary isoprenoids behave as inhibitors of TF-dependent thrombin generation. Because thrombin has multiple physiological functions, the 20 pleiotropic effects reported for statins may reflect a common mechanism for downregulation of thrombin-mediated events, in particular at the cellular level.

Hepatic chemoembolization combined with systemic infusion of 5-fluorouracil and bolus leucovorin for patients with metastatic colorectal carcinoma: A Southwest Oncology Group pilot trial.

BACKGROUND: Rates of response to systemic chemotherapy among patients with advanced colorectal carcinoma rarely exceed 25- 30%, and complete responses are rare. The liver is the most common site of metastasis; however, regional therapies have not improved survival rates. The Southwest Oncology Group designed a clinical trial combining hepatic arterial chemoembolization with systemic infusion of 5-fluorouracil chemotherapy in an attempt to increase the complete response rate and prolong the time to disease progression. METHODS: Patients with documented liver metastasis from colorectal carcinoma were treated with two or three cycles of chemoembolization using a collagen suspension with doxorubicin, mitomycin C, and cisplatin. Subsequently, systemic chemotherapy with continuous infusion of 5-fluorouracil and weekly leucovorin was initiated. Patients were assessed for response at 12-week intervals, with treatment continuing until disease progression. RESULTS: Thirty-one eligible, evaluable patients were treated. One complete and 8 partial responses were observed, for an overall response rate of 29%. Fifty-eight percent of patients survived 1 year, and the median survival for the whole cohort was 14 months. The median time to progression was 8 months. Seven patients (23%) experienced Grade 4 toxicity and 21 patients (67%) had Grade 3 toxicity. CONCLUSIONS: The response rate in this trial was comparable to that achieved with systemic chemotherapy consisting of a fluorinated pyrimidine-based regimen for patients with this disease. No improvement in complete response rate or time to progression was observed compared with the Southwest Oncology Group's experience with systemic therapy. The authors are not planning to study this regimen further as a treatment for patients with metastatic colorectal carcinoma.