Abstract A7: Targeting the tumor microenvironment via inhibition of VEGF and PDGF to improve liposomal drug delivery in human non-small cell lung cancer xenografts
Tailor, TD; Hanna, G; Yarmolenko, PS; Dewhirst, MW
Published in: Molecular Cancer Therapeutics
Background: Pathological angiogenesis creates an abnormal microenvironment in tumors, characterized by elevated interstitial fluid pressure (IFP) and hypoxia. Judicious attenuation of angiogenic signals may “normalize” the vascular bed, making it more suitable for drug delivery and radiotherapy. In this work, we investigate the role of pazopanib, a small-molecule inhibitor of vascular endothelial growth factor (VEGF) receptors and platelet-derived growth factor (PDGF) receptors, on normalization parameters of IFP, vascular pericyte coverage, hypoxia, and liposomal drug delivery.Methods: Nude mice bearing A549 human non-small cell lung cancer (NSCLC) xenografts were treated with pazopanib 100mg/kg (n=20) or control (n=20) for 8 days, followed by a single intravenous dose of Doxil (liposomal doxorubicin) 10mg/kg. 24 hours after Doxil delivery, tumor IFP was measured, and tumors were snap frozen and sectioned. In a second study, designed similarly to the previous (n=4 pazopanib 100mg/kg, n=4 control), EF5 (hypoxia marker) was delivered 3 hours prior to tumor harvest. Tissue sections were stained for vasculature and pericytes using anti-CD-31 (endothelial cell marker) and anti-alpha-smooth muscle actin, respectively. Hypoxia was assessed via immunostaining for CA-IX and EF5. High performance liquid chromatography was used to determine tumor doxorubicin concentration ([dox]), and the penetration distance of Doxil from CD-31 stained vessels was calculated using a MATLAB algorithm.Results: Pazopanib treatment resulted in reduction of tumor IFP (116.571 ± 15.174 mmHg control vs. 61.000 ± 7.367 mmHg pazopanib, P = 0.0145) and decreased vessel density (251.228 ± 18.770 vessels/mm2 control vs. 101.313 ± 11.005 vessels/mm2 pazopanib, P < 0.0001). No differences in tumor [dox] were observed between groups (10.849 ± 1.785 ng/kg control vs. 12.274 ± 1.013 ng/mg pazopanib, P = 0.5956), however Doxil penetration improved in pazopanib-treated tumors (18.980 ± 0.687 m control vs. 32.886 ± 1.741 m pazopanib, P = 0.0006). Despite these trends towards normalization, tumor hypoxia, evaluated by CA-IX and EF5 expression, was increased in the pazopanib group (% CA-IX staining, 7.034 ± 0.988% control vs. 16.720 ± 1.728% pazopanib, P = 0.0005;% EF5 staining, 15.992 ± 2.610% control vs. 36.554 ± 4.617% pazopanib, P = 0.0074). Additionally, the proportion of pericyte-coated vessels was decreased in the pazopanib group (0.840 ± 0.0362 control vs. 0.675 ± 0.0495 pazopanib, P = 0.0160).Conclusions: Our results suggest a role for VEGF/PDGF inhibition in modulating functional parameters of the tumor microenvironment and improving drug distribution. However, these changes may be mediated by stromal changes in response to PDGF-receptor blockade, rather than normalization.Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A7.
