Pyrazolopyridine inhibitors with low micromolar potency for CHK1 and good selectivity against CHK2 were previously identified by fragment-based screening. The optimization of the pyrazolopyridines to a series of potent and CHK1-selective isoquinolines demonstrates how fragment-growing and scaffold morphing strategies arising from a structure-based understanding of CHK1 inhibitor binding can be combined to successfully progress fragment-derived hit matter to compounds with activity in vivo. The challenges of improving CHK1 potency and selectivity, addressing synthetic tractability, and achieving novelty in the crowded kinase inhibitor chemical space were tackled by multiple scaffold morphing steps, which progressed through tricyclic pyrimido[2,3-b]azaindoles to N-(pyrazin-2-yl)pyrimidin-4-amines and ultimately to imidazo[4,5-c]pyridines and isoquinolines. A potent and highly selective isoquinoline CHK1 inhibitor (SAR-020106) was identified, which potentiated the efficacies of irinotecan and gemcitabine in SW620 human colon carcinoma xenografts in nude mice.

Abstract. Secretory defects in abnormal plasma cells, called Mott cells, that appear in lymphoid tissues of spontaneously autoimmune, "viable motheaten" (me°/me°) mice lead to deposition of immunoglobulin in RER-bound vesicles. Such vesicles have been termed Russell bodies. Cells with Russell bodies can also be observed rarely in normal animals, usually as a result of extreme antigenic loads or pathologic states . To understand why these abnormal cells appear commonly in mev/me°mice, we have established a panel of hybridomas that contain Russell bodies . Using immunochemical analysis and immunoelectron microscopy, we have characterized the secretory defects. Although these hybridoma cells synthesize a normal size heavy chain and it associates with light chain, the Russell bodies have many characteristics of inclusion bodies, which commonly appear in cells synthesizing mutant proteins and often are associated with incompletely or abnormally folded proteins . Pulse-chase experiments showed that immunoglobulins M UTATIONS that disrupt biological processes provide insight into the ordering of these processes. Many mutations that affect the immune system cause multiple pleiotropic abnormalities, emphasizing the complexity and interrelatedness of the immune, endocrine, and nervous systems (33) . One of the most deleterious mutations identified is "viable motheaten" (me,),' a spontaneous, single gene mutation that occurred on the C57BL/6J background (34) . me, mice have a mean life span of 9 wk. Autoimmune pulmonary lesions are the proximal cause of death. Homozygotes (me°/me,) develop glomerulonephritis, have multiple autoantibodies, and serum IgM levels are increased 25-to 50-fold above levels found in littermate controls (35) . Abnormal plasma cells, called Mott cells, are found initially at -4 wk of age . These cells have discrete gly-1 . Abbreviations used in this paper: BiP, binding protein ; Endo H, endoglycosidase H; me', viable motheaten; PAS, periodic acid-Schiffs ; SACI, Staphylococcus aureus, Cowan strain I ; TEM, transmission electron microscopy.

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