Optimization of irinotecan chronotherapy with P-glycoprotein inhibition.

The relevance of P-glycoprotein (P-gp) for irinotecan chronopharmacology was investigated in female B6D2F1 mice. A three-fold 24h change in the mRNA expression of Abcb1b was demonstrated in ileum mucosa, with a maximum at Zeitgeber Time (ZT) 15 (p<0.001). No rhythm was found for abcb1a in ileum mucosa, or for Abcb1a/b in Glasgow osteosarcoma (GOS), a mouse tumor cell line moderately sensitive to irinotecan. Non-tumor-bearing mice received irinotecan (50mg/kg/day i.v.×4days) as a single agent or combined with P-gp inhibitor PSC833 (6.25mg/kg/day i.p.×4 days) at ZT3 or ZT15, respectively corresponding to the worst or the best irinotecan tolerability. Endpoints involved survival, body weight change and hematologic toxicity. Antitumor efficacy was studied in GOS-bearing mice receiving irinotecan (25, 30 or 40mg/kg/day×4days) and +/-PSC833 at ZT3 or ZT15, with survival, body weight change, and tumor growth inhibition as endpoints. Non-tumor bearing mice lost an average of 17% or 9% of their body weight according to irinotecan administration at ZT3 or ZT15 respectively (p<0.001). Dosing at ZT15 rather than ZT3 reduced mean leucopenia (9% vs 53%; p<0.001). PSC833 aggravated irinotecan lethal toxicity from 4 to ~60%. In tumor-bearing mice, body weight loss was ~halved in the mice on irinotecan or irinotecan-PSC833 combination at ZT15 as compared to ZT3 (p<0.001). PSC833-irinotecan at ZT15 increased tumor inhibition by ~40% as compared to irinotecan only at ZT15. In conclusion, P-gp was an important determinant of the circadian balance between toxicity and efficacy of irinotecan.

Protective effects of angiopoietin-like 4 on cerebrovascular and functional damages in ischaemic stroke.

AIMS: Given the impact of vascular injuries and oedema on brain damage caused during stroke, vascular protection represents a major medical need. We hypothesized that angiopoietin-like 4 (ANGPTL4), a regulator of endothelial barrier integrity, might exert a protective effect during ischaemic stroke. METHODS AND RESULTS: Using a murine transient ischaemic stroke model, treatment with recombinant ANGPTL4 led to significantly decreased infarct size and improved behaviour. Quantitative characteristics of the vascular network (density and branchpoints) were preserved in ANGPTL4-treated mice. Integrity of tight and adherens junctions was also quantified and ANGPTL4-treated mice displayed increased VE-cadherin and claudin-5-positive areas. Brain oedema was thus significantly decreased in ANGPTL4-treated mice. In accordance, vascular damage and infarct severity were increased in angptl4-deficient mice thus providing genetic evidence that ANGPTL4 preserves brain tissue from ischaemia-induced alterations. Altogether, these data show that ANGPTL4 protects not only the global vascular network, but also interendothelial junctions and controls both deleterious inflammatory response and oedema. Mechanistically, ANGPTL4 counteracted VEGF signalling and thereby diminished Src-signalling downstream from VEGFR2. This led to decreased VEGFR2-VE-cadherin complex disruption, increased stability of junctions and thus increased endothelial cell barrier integrity of the cerebral microcirculation. In addition, ANGPTL4 prevented neuronal loss in the ischaemic area. CONCLUSION: These results, therefore, show ANGPTL4 counteracts the loss of vascular integrity in ischaemic stroke, by restricting Src kinase signalling downstream from VEGFR2. ANGPTL4 treatment thus reduces oedema, infarct size, neuronal loss, and improves mice behaviour. These results suggest that ANGPTL4 constitutes a relevant target for vasculoprotection and cerebral protection during stroke.

Angiopoietin-like 4 serum levels on admission for acute myocardial infarction are associated with no-reflow.

BACKGROUND: No-reflow in ST-segment elevation acute myocardial infarction (STEMI) is associated with a poor clinical prognosis. Its pathophysiological mechanisms are not fully elucidated yet but enhanced vascular permeability plays a key role in this phenomenon. Angiopoietin-like 4 (ANGPTL4) has been implicated in vascular permeability in experimental models of acute myocardial infarction (AMI). We therefore sought to investigate whether baseline ANGPTL4 serum levels are associated with no-reflow after primary percutaneous coronary intervention (PPCI). METHODS: We studied a group of 41 patients presenting with a first STEMI within 12h of onset of symptoms and who underwent successful PPCI. Blood samples were obtained from all patients on admission before the start of the procedure, for ANGPTL4 level measurement. No-reflow was assessed by cardiac magnetic resonance imaging (MRI), the reference method. RESULTS: MRI-detected no-reflow was observed in 20 patients (48.8%). Variables independently associated with no-reflow on multivariate logistic regression analysis were: lower ANGPTL4 serum levels (odds ratio 0.82, 95% CI 0.70-0.98, P=0.02), higher troponin T peak (odds ratio 1.03, 95% CI 1.00-1.05, P=0.03), higher incidence of left anterior descending coronary artery (LAD) as culprit artery (odds ratio 14.61, 95% CI 1.24-172.49, P=0.03), and higher C-reactive protein levels (odds ratio 1.18, 95% CI 1.00-1.39, P=0.05). CONCLUSION: ANGPTL4 serum levels predict MRI-detected no-reflow after successful PPCI in STEMI patients. Given the recently demonstrated therapeutic role of ANGPTL4 in diminishing no-reflow and limiting infarct size in pre-clinical animal models, these findings in humans may open up new possibilities in the field of research.