Abstract 3269: VEGF inhibitor resistance is associated with stromal EGFR activation and normalized revascularization in an orthotopic model of lung adenocarcinoma

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Therapeutic resistance to angiogenesis inhibitors represents a major obstacle in the treatment of non-small cell lung cancer (NSCLC). Previously, we reported that acquired resistance of subcutaneous murine models of NSCLC to the anti-vascular endothelial growth factor (VEGF) antibody bevacizumab (BV) was mediated by upregulation and activation of the epidermal growth factor receptor (EGFR) signaling pathway in stromal cells. Here, we investigated the effects of BV and dual VEGFR/EGFR inhibition, and the mechanisms of therapeutic resistance in H441 NSCLC orthotopic tumors. Short-term BV treatment (2 weeks) resulted in a significant tumor volume reduction compared with vehicle-treated tumors (p=0.026). For survival analysis, tumor-bearing mice were randomized to receive vehicle, erlotinib (E), BV, erlotinib + BV (E + B), or the VEGFR/EGFR inhibitor vandetanib (V), until moribund. All therapies significantly prolonged survival compared with vehicle (p<0.0001; E vs. vehicle p<0.05). Long-term BV administration improved survival compared with E (median survival 77 vs. 58 days, p=0.00015); however, both E + BV and V treatments (median survival 101 and 91 days, respectively) prolonged survival compared with E or BV alone (p=0.0001 E + BV vs. E or BV; p=0.0004 V vs. E; p=0.022 V vs. BV). Microvessel density (MVD) was strongly decreased in BV-sensitive tumors compared with 2 week vehicle treatment (p=0.0008); however, tumors resistant to BV or dual VEGFR/EGFR inhibition showed revascularization with increased MVD compared with BV-sensitive tumors (p=0.045). In erlotinib-resistant group MVD was significantly lower than in BV-resistant tumors (p=0.034). Levels of p-EGFR increased in BV-resistant tumors compared with controls (p=0.039) and co-localized with the stroma supporting large, normalized vessels. This signaling was suppressed in tumors resistant to VEGFR/EGFR targeting compared with both controls and BV-resistant tumors (p=0.0001 E + BV vs. vehicle; p=0.0008 E + BV vs. BV; p = 0.011 V vs. vehicle; p=0.009 V vs. BV), demonstrating persistent EGFR blockade with treatment. Pericyte coverage increased in BV-resistant tumors compared with controls and BV-sensitive tumors (p=0.003 BV vs. vehicle; p<0.0001 BV progression vs. BV 2 weeks). In tumors resistant to erlotinib or VEGFR/EGFR inhibition, pericyte coverage was reduced to levels comparable to controls (p=0.001 E vs. BV; p=0.054 E + BV vs. BV; p=0.007 V vs. BV). These findings demonstrate that in an orthotopic NSCLC model, resistance to BV is associated with tumor revascularization, featuring large, pericyte-covered vessels with increased perivascular EGFR activation. Dual VEGFR/EGFR blockade abrogates the BV-induced increase in pericyte coverage and delays the emergence of resistance. Stromal EGFR may contribute to VEGF inhibitor resistance through activation on perivascular cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3269. doi:10.1158/1538-7445.AM2011-3269