| In Vitro | In vitro activity: The kinase selectivity of PIM447 is first determined in biochemical assays for a panel of 68 diverse protein kinases that included PIM2 as well as 9 lipid kinases. In this panel, only PIM2 is significantly inhibited by PIM447 with an IC50 of<0.003 1='' 5='' the='' lowest='' sensitivity='' range='' for='' assay.='' pim447='' also='' inhibits='' and='' but='' at='' a='' significantly='' lower='' potency='' with='' ic50='' between='' m=''>105-fold differential relative to the Ki on PIMs). The biochemical IC50 for all other kinases tested in this panel is>9 μM. In follow-up cellular assays of GSK3β inhibition, PIM447 is tested up to 20 μM and is not active. PIM447 is cytotoxic for myeloma cells due to cell-cycle disruption and induction of apoptosis mediated by a decrease in phospho-Bad (Ser112) and c-Myc levels and the inhibition of mTORC1 pathway. PIM447 also inhibits in vitro osteoclast formation and resorption, downregulates key molecules involved in these processes, and partially disrupts the F-actin ring, while increasing osteoblast activity and mineralization.
Kinase Assay: PIM447 (also known as LGH447) is a novel and potent pan-PIM (proviral insertion site of Moloney murine leukemia) kinase inhibitor with Ki values of 6 pM, 18 pM, 9 pM for PIM1, PIM2, PIM3 respectively. It also inhibits GSK3β, PKN1, and PKCτ, but at a significantly lower potency with IC50 between 1 and 5 μM (>105-fold differential relative to the Ki on PIMs).
Cell Assay: PIM447 is cytotoxic for myeloma cells due to cell cycle disruption and induction of apoptosis mediated by a decrease in phospho-Bad (Ser112) and c-Myc levels and the inhibition of mTORC1 pathway. Following treatment of KG-1 cells with PIM447 for 2 h at the indicated concentrations, cells are lysed in RIPA buffer. Protein concentration is determined using a BCA assay, and 50 μg of lysate is separated by SDS-PAGE using 10% bis-Tris gels. Proteins are transferred onto 0.2 μm nitrocellulose membrane, and pS6RP/total S6RP are detected. Following incubation with secondary antibodies, antibody binding is detected using ECL Advance. |
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| In Vivo | Low to moderate in vivo CL is observed for PIM447 across species, as CL values of 20, 28, and 8 mL/min/kg are observed in mouse, rat, and dog, respectively. The volume of distribution is consistently large across species, with Vss of 5.3, 6.4, and 3.6 L/kg observed in mouse, rat, and dog, respectively. Additionally, PIM447 exhibits high oral bioavailability across species, as 84%, 70%, and 71% is observed in mouse, rat, and dog, respectively. The stability of PIM447 in human plasma is high,>90% after a 3 h incubation, and the human plasma protein binding of PIM447 is 95%. With the combination of potent in vitro activity and low to moderate CL, PIM447 demonstrates in vivo target modulation (pS6RP), single agent antitumor activity in a KG-1 AML mouse xenograft model, and druglike properties suitable for development. PIM447 significantly reduces the tumor burden and prevents tumor-associated bone loss in a disseminated murine model of human myeloma. |
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