Direct Effects of Caffeine and Theophylline on p110δ and Other Phosphoinositide 3-Kinases

Abstract

We investigated the effects of methylxanthines on enzymatic activity of phosphoinositide 3-kinases (PI3Ks). We found that caffeine inhibits the in vitro lipid kinase of class I PI3Ks (IC 50 ‫؍‬ 75 M for p110␦, 400 M for p110␣ and p110␤, and 1 mM for p110␥), and theophylline has similar effects (IC 50 ‫؍‬ 75 M for p110␦, 300 M for p110␣, and 800 M for p110␤ and p110␥) and also inhibits the ␣ isoform of class II PI3K (PI3K-C2␣) (IC 50 Ϸ 400 M). However, four other xanthine derivatives tested (3-isobutyl-1-methylxanthine, 3-propylxanthine, alloxazine, and PD116948 (8-cyclopentyl-1,3-dipropylxanthine)) were an order of magnitude less effective. Surprisingly the triazoloquinazoline CGS15943 (9-chloro-2-(2-furyl)(1,2,d)-triazolo(1,5-c)quinazolin-5-amine) also selectively inhibits p110␦ (IC 50 < 10 M). Caffeine and theophylline also inhibit the intrinsic protein kinase activity of the class IA PI3Ks and DNA-dependent protein kinase, although with a much lower potency than that for the lipid kinase (IC 50 Ϸ 10 mM for p110␣ , 3 mM for p110␤, and 10 mM for DNA-dependent protein kinase). In CHO-IR cells and rat soleus muscle, theophylline and caffeine block the ability of insulin to stimulate protein kinase B with IC 50 values similar to those for inhibition of PI3K activity, whereas insulin stimulation of ERK1 or ERK2 was not inhibited at concentrations up to 10 mM. Theophylline and caffeine also blocked insulin stimulation of glucose transport in CHO-IR cells. These results demonstrate that these methylxanthines are direct inhibitors of PI3K lipid kinase activity but are distinctly less effective against serine kinase activity and thus could be of potential use in dissecting these two distinct kinase activities. Theophylline, caffeine, and CGS15943 may be of particular use in dissecting the specific role of the p110␦ lipid kinase. Finally, we conclude that inhibition of PI3K (p110␦ in particular) is likely explain some of the physiological and pharmacological properties of caffeine and theophylline.Caffeine and theophylline are naturally occurring methylxanthine compounds that can be found in micromolar concentrations in human circulation as a result of dietary intake or pharmacological use. These compounds have been the subject of intense study to determine how they act at physiological concentrations, and a number of effects have been ascribed to these compounds at such concentrations including stimulation of muscle contraction levels (1), anti-inflammatory and immunomodulatory effects (2), alterations in glucose metabolism (3-8), attenuation of the antilipolytic effect of insulin (3), and induction of apoptosis (9, 10). Several mechanisms of action have been identified for these methylxanthines, and these can explain some of the pleiotropic effects these compounds have on cells at their physiologically achievable concentrations. These include their abilities to directly inhibit phosphodiesterases and thus increase cellular cAMP levels, to directly antagonize adenosine receptors, and to cause increases in cytosolic C...

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