Bảng 24,1 lập bảng IC50 giá trị (tức là nồng độ nM cần thiết để đạt được sự ức chế 50% hoạt động của enzyme) cho ruboxistaurin và chất ức chế không cụ thể PKC, staurosporine, đối với mỗi isoform | 214 SECTION IV- MECHANISMS OF HYPERGLYCAEMIA INDUCED VASCULAR DYSFUNCTION Fig. Structure of ruboxistaurin a macrocyclic bis-indolylmaleimide which is an orally active selective PKC-p inhibitor. Tabulated IC 50 values for ruboxistaurin Kinase IC50 nM ruboxistaurin . Staurosporine PKC-a 360 45 PKC-P1 23 PKC-p2 19 PKC-y 300 110 PKC-0 250 28 PKC-e 600 18 Z 105 X 103 PKC-n 52 5 Cyclic AMP kinase 105 100 Ca2 -calmodulin kinase 8 X 103 4 Casein kinase 105 X 104 Src tyrosine kinase 105 1 Table Tabulated IC50 values . concentrations in nM required to achieve 50 inhibition of enzyme activity for ruboxistaurin and the non-specific PKC inhibitor staurosporine with respect to each PKC isoform and related intracellular kinases. Adapted from Science 1996 472 728-731. CHAPTER 24 EXPERIMENTAL PHARMACOLOGY USING ISOFORM-SELECTIVE PKC INHIBITORS 215 new vessel formation. Thus blocking VPF-mediated retinal permeability is a prime target for therapeutic amelioration of diabetic maculopathy. Studies in rats have clearly shown that intravitreal administration of VPF increases vitreous fluorescein leakage and that pretreatment of these animals for one week with ruboxistaurin 25 mg kg day via oral administrattion ameliorated VPF and phorbol ester-induced vitreous fluorescein leakage Fig. . Furthermore whereas control rats showed a two-fold increase in vitreous fluorescein leakage after intravitreal VPF administration rats pretreated with the PKC-P inhibitor showed no difference in basal vitreous fluorescein leakage but there was a 96 reduction in VPF-induced vitreous fluorescein leakage Fig. . Increased retinal permeability is a hallmark of neovascularization within the diabetic eye as well as being a sight-threatening pathological entity even in the absence of new vessel formation. These experimental data have shown that oral administration of ruboxistaurin is well tolerated and considerably 0 2 0 2 VPF ng eye 0 0 25 25 PKC-p inhibitor mg kg rat day
