A combination of plasmid DNAs encoding murine fetal liver kinase 1 extracellular domain, murine interleukin-12, and murine interferon-gamma inducible protein-10 leads to tumor regression and survival in melanoma-bearing mice.

The vascular endothelial growth factor (VEGF) and its interaction with the vascular endothelial growth factor receptor 2 [VEGFR2/murine fetal liver kinase 1 (Flk-1), human kinase domain receptor] are an important angiogenic pathway leading to tumor vascularization. A plasmid DNA encoding the complete extracellular domain (ECD) of murine Flk-1 including the endogenous signal sequence was designed as a possible competitor of the receptor to sequester VEGF. The plasmid DNA was used to treat B16F10 cell-induced subcutaneous melanomas in syngeneic mice. The Flk-1 ECD-encoding plasmid DNA injected intramuscularly did not lead to tumor reduction. However, intratumoral injection caused a dose-dependent reduction and significant retardation of tumor growth. Blood vessels analyzed by immunohistochemistry with anti-CD31 antibodies as indicators of vascularization appeared smaller in diameter after treatment. A combination of Flk-1 ECD and DNA encoding murine interleukin-12 or murine interferon-gamma inducible protein-10 improved the effect, leading to tumor regression and long-term survival of the mice.