Interferon γ-inducible protein 10 selectively inhibits proliferation and induces apoptosis in endothelial cells

Background: Interferon γ-inducible protein 10 (IP-10) has antitumor effects in various murine models. The IP-10 receptor has two distinct splice variants, CXCR3A and CXCR3B, that have paradoxical effects after ligand-receptor interaction. Methods: To characterize the putative antiangiogenic effects of IP-10, we measured proliferation rates and apoptosis in human umbilical vein endothelial cells (HUVECs), fibroblasts, and A375 melanoma or WIDR adenocarcinoma cell lines after exposure to the recombinant protein. CXCR3A (activating) and CXCR3B (inhibitory/proapoptotic) messenger RNA (mRNA) expression levels in fibroblasts, 2 human tumor cell lines, T lymphocytes, and HUVECs of varying cell densities were characterized. Results: IP-10 resulted in dose-dependent and selective inhibition of proliferation and countered the proliferative effects of vascular endothelial growth factor in HUVECs but did not affect fibroblasts or 2 human tumor cell lines. In addition, IP-10 resulted in potent and selective induction of apoptosis in HUVECS but had no effect on fibroblasts or A375 melanoma. Confluent HUVECs had a predominance of mRNA for the CXCR3B splice variant by reverse transcriptase-polymerase chain reaction, and the ratio of CXCR3B to CXCR3A mRNA was > 40 in HUVECs, compared with ≤10 in the other cell types. Moreover, CXCR3B mRNA levels were significantly higher in proliferating compared with confluent HUVECs. In vivo, systemic IP-10 administration resulted in slower A375 xenograft growth rates compared with control-treated animals, and immunohistochemical staining showed decreased microvessel density in xenografts of IP-10-treated mice. Conclusions: IP-10 has antiangiogenic properties and selective effects on endothelial tissue that may be secondary to higher levels of the CXCR3B inhibitory/proapoptotic receptor in that cell type, particularly in its actively proliferating state.