Tumor vasculature is targeted by the combination of combretastatin A-4 and hyperthermia

Background and purpose: Combretastatin A-4 disodium phosphate (CA-4) enhances thermal damage in s.c. BT(4)An rat gliomas. We currently investigated how CA-4 and hyperthermia affect the tumor microenvironment and neovasculature to disclose how the two treatment modalities interact to produce tumor response. Methods: By confocal microscopy and immunostaining for von Willebrand factor, we examined the extent of vascular damage subsequent to CA-4 (50 mg/kg) and hyperthermia (waterbath 44 degreesC, 60 min). The influence on tumor oxygenation was assessed using interstitial PO2-probes (Licox system) and by immunostaining for pimonidazole. We examined the direct effect of CA-4 on the tumor cell population by flow cytometry (cell cycle distribution) and immunostaining for beta -tubulin (cytoskeletal damage). Results: Whereas slight vascular damage was produced by CA-4 in the BT4An tumors, local hyperthermia exhibited moderate antivascular activity. In tumors exposed to CA-4 3 h before hyperthermia, massive vascular damage ensued. CA-4 reduced the pO(2) from 36.1 to 17.6 mmHg (P = 0.01) in the tumor base, and tumor hypoxia increased slightly in the tumor center (pimonidazole staining). Extensive tumor hypoxia developed subsequent to hyperthermia or combination therapy. Despite a profound influence on beta -tubulin organization in vitro, CA-4 had no significant effect on the cell cycle distribution in vivo. Conclusion: Our results indicate that the anti-vascular activity exhibited by local hyperthermia can be augmented by previous exposure to CA-4. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.