Impaired blood flow in the
tumor vascular bed caused by structurally and functionally abnormal blood vessels not only hinders the delivery of chemotherapeutic agents but also aggravates tumor hypoxia, making the
tumor cells further resistant to
antineoplastic drugs. Therefore, normalization of
tumor blood vessels may be an important approach to increase therapeutic efficacy in the treatment of
cancer patients. As blood vessels are supplied by sympathetic nerves containing
dopamine (DA), and DA regulates functions of normal blood vessels through its receptors present in these vessels, we investigated the effect of DA on
tumor vasculature. Here we report loss of sympathetic innervation and endogenous DA in abnormal and immature
tumor blood vessels in malignant colon and prostate
tumor tissues. In contrast, exogenous administration of DA normalizes the morphology and improves the functions of these vessels by acting on pericytes and endothelial cells, the two major cellular components of blood vessels. DA acts through its D(2) receptors present in these cells to up-regulate directly the expression of
angiopoietin 1 (Ang1) in pericytes and the expression of the zinc finger transcriptional factor, Krüppel-like factor-2 (KLF2) in
tumor endothelial cells. Importantly, this vessel stabilization by DA also significantly increases the concentration of anticancer
drug in
tumor tissues. These results show a relationship between vascular stabilization and a
neurotransmitter and indicate that DA or its D(2) receptor-specific agonists can be an option for the treatment of
cancer and disorders in which normalization of blood vessels may have therapeutic benefits.