Isoquinolinesulfonamides, Novel and Potent Inhibitors of Cyclic Nucleotide Dependent Protein Kinase and Protein Kinase C

Abstract

Naphthalenesulfonamides such as N-(6-amino-hexyl)-5-chloro-l-naphthalenesulfonamide (W-7) are potent calmoduhn (CaM) antagonists and act upon several protein kinases at higher concentration. When the naphthalene ring was replaced by isoquinohne, the derivatives were no longer CaM antagonists but retained the ability to inhibit protein kinases, and some of the derivatives exhibited selective inhibition toward a certain protein kinase. cAMP-dependent, cGMP-dependent, and Ca2+-phospholipid-dependent (protein kinase C) protein kinases were mhibited significantly by addition of 10-6M N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (H-8) and l-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7). H-8 was the most active of the inhibitors in this series and inhibited more markedly cyclic nucleotide dependent protein kinases, than other kinases, while the derivative with the sulfonylpiperazine residue (H-7) was the most potent in inhibiting protein kinase C. Apparent Ki values of H-8 were 0.48 and 1.2 μM. for cGMP-dependent and cAMP-dependent protein kinases, respectively, and the Ki value of H-7 for protein kinase C was 6 μM. Both the holoenzyme and the catalytic subunit (or fragment), which is active without an enzyme activator, are susceptible to these compounds with a similar concentration dependency, thereby indicating that the inhibitory effect is attributed to the direct interaction of the compound with the active center of the enzyme but not with the enzyme activator. The inhibitions were freely reversible and of the competitive type with respect to ATP and of the noncompetitive type with respect to the phosphate acceptor. Kinetic studies with the catalytic subunit of cAMP-dependent protein kinase indicated that isoquinolinesulfonamides, structurally unrelated to ATP, compete with ATP for free enzyme but do not interact with the same enzyme form as does the phosphate acceptor (i.e., enzyme-ATP complex). The inhibitory potency of these derivatives seems to be dependent on the position and the strength of the plus charge contributed by the terminal nitrogen in the isoquinoline-sulfonamide molecule. This report is concerned with the preparation and inhibitory mechanisms of isoquinoline-sulfonamide derivatives, as possible tools for clarifying the in vitro and in vivo functions of protein kinases. © 1984, American Chemical Society. All rights reserved.