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Patupilone Induced Vascular Disruption in Orthotopic Rodent Tumor Models Detected by Magnetic Resonance Imaging and Interstitial Fluid Pressure

Authors' Affiliation: Oncology Research, Novartis Institutes for BioMedical Research, Basel, Switzerland

Requests for reprints: Paul M.J. McSheehy, Oncology Research, WKL 125.2.05, Novartis Institutes for BioMedical Research, CH-4002 Basel, Switzerland. Phone: 41-61-696-8189; Fax: 41-61-696-5751; E-mail: paul_mj.mcsheehy{at}novartis.com.

Purpose: Evaluation of vascular disruptive activity in orthotopic models as potential surrogate biomarkers of tumor response to the microtubule-stabilizing agent patupilone.

Experimental Design: Mice bearing metastatic B16/BL6 melanoma and rats bearing mammary BN472 tumors received vehicle or efficacious patupilone doses (4 and 0.8-1.5 mg/kg i.v., respectively). Tumor vascularity assessment by dynamic contrast-enhanced or dynamic susceptibility contrast magnetic resonance imaging and interstitial fluid pressure (IFP) occurred at baseline, 2 days (mice and rats), and 6 days (rats) after treatment and were compared with histologic measurements and correlated with tumor response.

Results: In B16/BL6 metastases, patupilone (4 mg/kg) induced a 21 ± 5% decrease (P < 0.001) in tumor blood volume and a 32 ± 15% decrease (P = 0.02) in IFP after 2 days and reduced tumor growth and vessel density (>42%) after 2 weeks (P 0.014). Patupilone dose-dependently inhibited BN472 tumor growth (day 6) and reduced IFP on days 2 and 6 (–21% to –70%), and the percentage change in IFP correlated (P < 0.01) with the change in tumor volume. In both models, histology and vascular casts confirmed decreases in tumor blood volume. One patupilone (0.8 mg/kg) administration decreased (P < 0.01) tumor IFP (54 ± 4%), tumor blood volume (50 ± 6%), and vessel diameter (40 ± 11%) by day 6 but not the apparent diffusion coefficient, whereas histology showed that apoptosis was increased 2.4-fold and necrosis was unchanged. Apoptosis correlated negatively (P < 0.001) with IFP, tumor blood volume, and tumor volume, whereas tumor blood volume and IFP were correlated positively (P = 0.0005).

Conclusions: Vascular disruptive effects of patupilone were detected in situ using dynamic contrast-enhanced or dynamic susceptibility contrast magnetic resonance imaging and IFP. Changes in IFP preceded and correlated with tumor response, suggesting that IFP may be a surrogate biomarker for patupilone efficacy.

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