The Effects of a Selective CK2 Inhibitor on Anti-glomerular Basement Membrane Glomerulonephritis in Rats

Abstract

Protein kinase CK2 ("casein kinase II") is a protein serine/threonine kinase that plays critical roles in biological processes such as cell growth, cell cycle progression, and apoptosis. So far, we have identified that one catalytic isozyme of CK2, CK2α, is over-expressed in the kidney during the progression of glomerulonephritis (GN). Moreover, we have shown that in vivo inhibition of CK2 by administration of CK2 inhibitors was effective in the treatment of experimental GN. Hence the development of potent CK2 inhibitors should be considered in therapeutic strategies for GN. In the present study we identified compound 13, a pyrazine derivative, as a potent CK2 inhibitor. By performing enzyme kinetics analysis in vitro, we characterized the inhibition of compound 13 toward each CK2 catalytic isozyme. Furthermore, in vivo, we demonstrated that compound 13 is effective in attenuating proteinuria, decreasing the enhanced level of blood urea nitrogen and serum creatinine, and ameliorating glomerular crescent formation in an experimental GN rat model. On the other hand, cellular apoptosis was detected in the rat testis following administration of compound 13. This study provides clues for new strategies for developing applicable compounds into CK2-targeted GN treatments.Key words protein kinase CK2; glomerulonephritis (GN); CK2 inhibitor; testicular toxicity Protein kinase CK2 (formerly called "casein kinase 2") is a serine/threonine kinase ubiquitously distributed in eukaryotic organisms. CK2 phosphorylates more than 300 proteins, 1) and its roles in cells are various, including cell proliferation, cell growth, cell division, and cell apoptosis.2) The CK2 holoenzyme in mammals exists predominantly as a heterotetramer composed of two catalytic subunits (α and/or α′) and two regulatory subunits (β). The two catalytic isozymes of CK2, CK2α and CK2α′, have been well characterized. CK2α and CK2α′ exhibit approximately 90% identity in their catalytic domains, even though they arise from different chromosomes.2) Although they may display similar enzymatic properties (including turnover rates and substrate specificity) in vitro, the two isozymes may play different roles in vivo, since CK2α is widely distributed in various tissues, whereas CK2α′ is mainly expressed in the brain and testis.3) In a report, the deficiency of CK2α in mice caused embryonic lethality, while the knockout of CK2α′ in mice induced spermatocytes to undergo apoptosis and the surviving spermatozoa to exhibit abnormal morphology. 4) Hence, CK2α and CK2α′ may have distinct functions.We have previously identified CK2α, but not CK2α′, as a glomerulonephritis (GN)-related gene using cDNA microarray analysis. 5) In the same study, we observed that administration of either antisense oligodeoxynucleotide against CK2α or low molecular weight CK2 inhibitors effectively prevented the progression of renal dysfunction. Based on this background, we focused on developing novel CK2 inhibitors as a therapeutic agent for GN. We have synthesized a series of pyrazine deriva...