ASA404, a Tumor-Vascular Disrupting Agent developed at the Auckland Cancer Society Research Centre, is currently undergoing two Phase III clinical trials (Novartis) against non-small cell lung cancer. Its early effects on tumor tissue include increased tumor vascular permeability, increased tumor endothelial apoptosis, decreased tumor blood flow and increased tumor hypoxia. The basis for the selective effect of ASA404 on tumor versus normal vasculature is not clear. We hypothesized that VEGF, produced in tumor tissue in responses to hypoxia and other stresses, played a possible role in this selectivity. We compared the actions of ASA404 and VEGF in vitro and also examined the potential for induction of tumor VEGF by ASA404 treatment in vivo. We grew human umbilical vein endothelial cells (HUVEC) on Matrigel and compared in vitro responses to ASA404 and human VEGF using time-lapse microscopy and image analysis. Both ASA404 (30 and 300 µM; 9.9 and 99 µg/ml) and VEGF (50 ng/ml) stimulated the initial formation of 2-dimensional tubular networks on Matrigel. Both ASA404 and VEGF induced actin stress fiber formation in cultured HUVEC's, consistent with increased migration. To determine if there was an in vivo relationship between ASA404 and VEGF expression, mice with Rif-1 tumors (7-9 mm diameter) were treated i.p. with ASA404 (70 µmol/kg; 21 mg/kg) and mRNA was extracted from tumor tissue 4 hours later. VEGF-A mRNA abundance was measured by co-amplification with endogenous 18S mRNA as standard. VEGF-A relative abundance rose from 0.6 ± 0.1 to 1.3 ± 0.1 (p < 0.01). VEGF-B and VEGF-D concentrations also increased but the changes were not significant. The results are consistent with the following model: hypoxia and other stresses in tumor tissue lead to synthesis by both tumor and host cells of VEGF, which increases vascular permeability and partially compromises tumor blood flow. The administration of ASA404 leads to increased tumor vascular permeability and vascular endothelial apoptosis, possibly by a pathway involving p38 kinase, ceramide synthesis and actin stress fiber formation. The resultant decrease in tumor blood flow further increases hypoxia, potentially providing a positive feedback loop by stimulating further VEGF production. These effects, in combination with other cytokines such as tumor necrosis factor that are induced by ASA404, lead to tumor vascular failure. Thus, endogenous VEGF production by tumor tissue may contribute to the antitumor selectivity of ASA404. Further studies addressing the modulatory role of VEGF in the action of ASA404 are warranted.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1660.