Excessive erythrocytosis does not elevate capillary oxygen delivery in subcutaneous mouse tissue.

OBJECTIVE: Acclimatization to reduced environmental oxygen includes erythropoietin-regulated increase in erythrocytes enhancing the blood's oxygen content. However, increased hematocrit levels result in elevated blood viscosity that might impair microcirculation and tissue oxygenation. To assess this oxygen supply to the skin, the authors used erythropoietin overexpressing transgenic mice (tg6) that develop excessive erythrocytosis in an oxygen-independent manner. These animals have been previously reported to elevate their blood viscosity 4-fold. METHODS: The partial oxygen pressure (pO2) distribution was evaluated in microvessels as well as in subcutaneous interstitial tissue within a dorsal skinfold chamber of resting conscious mice using automated phosphorescence quenching. RESULTS: Compared to wildtype (wt) animals, transgenic blood viscosity increased 4-fold but microvessel diameter was not altered. Despite sharing similar blood pO2 as the wt siblings, tg6 animals nearly doubled their oxygen content. Moreover, tg6 erythrocytes reduced hemoglobin's oxygen affinity by decreased 2,3-DPG levels and an increased Hill number. Transgenic arterioles and venules showed increased pO2 compared to wt controls whereas capillary and tissue pO2 were not altered. CONCLUSIONS: Excessive erythrocytosis does not elevate capillary oxygen delivery.

Topotecan and etoposide as first-line therapy for extensive disease small cell lung cancer: a phase II trial of a platinum-free regimen.

In the treatment of extensive disease of small cell lung cancer (ED SCLC) there is an urgent need for more effective and better-tolerated drug regimens. We report on a prospective phase II trial performed to evaluate the efficacy and safety of a platinum-free regimen--containing topotecan and etoposide--in the first-line treatment of ED SCLC. Between December 1999 and July 2001, 28 chemotherapy-naive patients with ED SCLC were recruited; 9 patients had stage IIIB disease and 19 patients had stage IV disease. Based on phase I results, patients received treatment with intravenous topotecan 1 mg/m2 (days 1-5) followed by intravenous etoposide 75 mg/m2 (days 8-10). Treatment courses were repeated every 28 days for a maximum of 6 cycles. A confirmed response rate of 46.4% with 1 complete response (CR) and 12 partial responses (PR) (95% CI=27.5-66.1%) was observed. Stable disease (SD) was observed in 18% of patients. The median time to response was 7.9 weeks (range: 7.7-15.1 weeks) and median survival was 29.9 weeks (range from 3.3 to 91.4 weeks). Main toxicities encountered were haematological with Grade III/IV neutropenia in 2.6/1.5% of courses and Grade III/IV thrombocytopenia in 1.8%/0.7% of courses. These toxicities were manageable and were not associated with clinical sequels. Non-haematological toxicities were generally mild with no Grade III/IV toxicities reported apart from Grade III alopecia. The combination therapy of topotecan and etoposide is active in first-line chemotherapy for patients with ED SCLC. The regimen showed a tolerable safety profile. Since drug scheduling plays a critical role in the combination of topoisomerase I and II inhibitors, concurrent administration of topotecan and etoposide might increase the efficacy.

Combined inhibition of VEGF and PDGF signaling enforces tumor vessel regression by interfering with pericyte-mediated endothelial cell survival mechanisms.

Destruction of existing tumor blood vessels may be achieved by targeting vascular endothelial growth factor (VEGF) signaling, which mediates not only endothelial cell proliferation but also endothelial cell survival. In this study, however, intravital microscopy failed to demonstrate that targeting of VEGFR-2 (by the tyrosine kinase inhibitor SU5416) induces significant regression of experimental tumor blood vessels. Immunohistochemistry, electron microscopy, expression analyses, and in situ hybridization provide evidence that this resistance of tumor blood vessels to VEGFR-2 targeting is conferred by pericytes that stabilize blood vessels and provide endothelial cell survival signals via the Ang-1/Tie2 pathway. In contrast, targeting VEGFR-2 plus the platelet-derived growth factor receptor (PDGFR)-beta system (PDGFR-beta) signaling (by SU6668) rapidly forced 40% of tumor blood vessels into regression, rendering these tumors hypoxic as shown by phosphorescence quenching. TUNEL staining, electron microscopy, and apoptosis blocking experiments suggest that VEGFR-2 plus PDGFR-beta targeting enforced tumor blood vessel regression by inducing endothelial cell apoptosis. We further show that this is achieved by an interference with pericyte-endothelial cell interaction. This study provides novel insights into the mechanisms of how 1) pericytes may provide escape strategies to anti-angiogenic therapies and 2) novel concepts that target not only endothelial cells but also pericyte-associated pathways involved in vascular stabilization and maturation exert potent anti-vascular effects.

pO(2) measurements by phosphorescence quenching: characteristics and applications of an automated system.

An automated system for pO(2) analysis based upon phosphorescence quenching was tested. The system was calibrated in vitro with capillary samples of saline and blood. Results were compared to a conventional measuring procedure wherein pO(2) was calculated off-line by computer fitting of phosphorescence decay signals. PO(2) measurements obtained by the automated system were correlated (r(2) = 0.98) with readings simultaneously generated by a blood gas analyzer, accuracy being highest in the low (0-20 mm Hg) and medium pO(2) ranges (21-70 mm Hg). Measurements in in vivo studies in the hamster skin-fold preparation were similar to previously reported results. The automated system fits the phosphorescence decay data to a single exponential and allows repeated pO(2) measurements in rapid sequence.