ABSTRACT: Background: Cantharidin, an active constituent of mylabris, is believed to have anti-tumor activity. Cantharidin selectively inhibit protein phosphatase 2A (PP2A), a repressor of oncogenic kinase pathways (ERK, JNK, NF-κB, and PKC). Cantharidin represses the growth and metastasis of pancreatic cancer cells in vitro. In the present study, we investigated the effects of cantharidin on pancreatic cancer xenografts in vivo. Methods: Cells stably expressing luciferase were used to establish xenograft models. Xenograft growth was evaluated by living imaging. Gene expression was determined using a microarray, real-time PCR, a RayBiotech antibody array, and the Milliplex assay. Results: Surprisingly, cantharidin significantly accelerated xenograft growth. Living imaging showed a rapid distribution of D-luciferin in cantharidin-treated xenografts, suggesting a rich blood supply. Immunohistochemistry confirmed increased angiogenesis. Microarray and antibody array identified upregulated pro-angiogenic and downregulated anti-angiogenic factors. The Milliplex assay suggested elevated secretion of IL-6, IL-8, TNF-α, and VEGF. ERK, JNK, NF-κB, and PKC pathway inhibitors attenuated the cantharidin-induced changes to pro-angiogenic gene expression. PKC pathway-inhibiting tamoxifen or antiangiogenic therapeutics, including Ginsenoside Rg3, bevacizumab, Apatinib, and Endostar antagonized the pro-angiogenic effect of cantharidin or its derivatives. These regimens presented remarkable synergistic antitumor effects in vivo. Conclusion: Although cantharidin presents anti-tumor effects in vitro and has been applied in clinical practice, we revealed an unfavorable pro-angiogenic side effect. We recommend that the clinical application of cantharidin should be performed on the premise of anti-vascularization therapy.
