Adenosine is a purine nucleoside and modulates a variety of physiological functions by interacting with cell-surface adenosine receptors. Under several adverse conditions, including ischemia, trauma, stress, seizures and inflammation, extracellular levels of adenosine are increased due to increased energy demands and ATP metabolism. Increased adenosine could protect against excessive cellular damage and organ dysfunction. Indeed, several protective effects of adenosine have been widely reported (e.g., amelioration of ischemic heart and brain injury, seizures and inflammation). However, the effects of adenosine itself are insufficient because extracellular adenosine is rapidly taken up into adjacent cells and subsequently metabolized. Adenosine uptake inhibitors (nucleoside transport inhibitors) could retard the disappearance of adenosine from the extracellular space by blocking adenosine uptake into cells. Therefore, it is expected that adenosine uptake inhibitors will have protective effects in various diseases, by elevating extracellular adenosine levels. Protective or ameliorating effects of adenosine uptake inhibitors in ischemic cardiac and cerebral injury, organ transplantation, seizures, thrombosis, insomnia, pain, and inflammatory diseases have been reported. Preclinical and clinical results indicate the possibility of therapeutic application of adenosine uptake inhibitors.

3-[1-(6,7-Diethoxy-2-morpholinoquinazolin-4-yl)piperidin-4-yl]-1,6-dimethyl-2,4(1H,3H)-quinazolinedione hydrochloride (KF24345) is a novel potent adenosine uptake inhibitor. KF24345 inhibited [3 H]adenosine uptake into erythrocytes from human, mouse, rabbit, and hamster with IC 50 values of 59.5, 130.1, 104.2, and 30.9 nM, respectively. In mice, oral administration of KF24345 at 10 mg/kg almost completely inhibited the [ 3 H]adenosine uptake into sampled blood cells at least up to 10 h of the administration. In this study, to examine whether the adenosine uptake inhibition exhibits anti-inflammatory effects, we determined the effects of KF24345 on lipopolysaccharide (LPS)-induced tumor necrosis factor-␣ (TNF-␣) production and leukopenia in mice. ) also inhibited the decrease of leukocytes after the LPS injection, and 8-(p-sulfophenyl)theophylline, a nonselective adenosine receptor antagonist, completely reversed the inhibitory effect of KF24345. These results demonstrate that KF24345 inhibits LPS-induced TNF-␣ production and leukopenia via enhancing the effect of endogenous adenosine. It is thus suggested that the adenosine uptake inhibitor has anti-inflammatory effects in vivo and represents a novel therapeutic approach to the treatment of various inflammatory diseases.

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These are the first demonstrations that the adenosine uptake inhibitors ameliorate cerulein-induced acute pancreatitis in mice, and these data suggest that adenosine uptake inhibition could ameliorate the severity of acute pancreatitis in vivo.

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