Monday, September 21, 2015

Drugs in Clinical Pipeline: RN486

RN486 [6-cyclopropyl-8-fluoro-2-(2-hydroxymethyl-3-{1-methyl-5-[5-(4-methyl-piperazin-1-yl)-pyridin-2-ylamino]-6-oxo-1,6-dihydro-pyridin-3-yl}-phenyl)-2H-isoquinolin-1-one] is a potent, selective, reversible inhibitor of Bruton's tyrosine kinase (BTK). In the enzymatic assay, the compound potently inhibited Btk kinase activity with an IC50 of 4.0 nM. RN486 binds the enzyme in a competitive manner as demonstrated in a time-resolved FRET-based competitive binding assay with an IC50 of 0.3 nM. RN486 was shown to be highly selective when tested against a panel of 369 kinases in the Kinomescan. In the assay, the compound exhibited a strong and competitive binding to Btk with a Kd of 0.31 nM and a high degree of selectivity over almost all other kinases, including Syk and Janus kinase (JAK, Kd = 5.1 uM). The enzyme that was most potently inhibited next to Btk was Ste20-like kinase (SLK, Kd = 0.043 uM), for which the compound showed a 139-fold selectivity [1].

The activity of RN486 is as follows:

IC50 (BTK enzyme assay) = 4.0 nM; Kd = 0.31 nM
Kd (JAK binding assay) = 5.1 uM
Kd (SLK binding assay) = 0.043 uM

Common Name: RN486
Synonyms: RN486; RN 486; RN-486
IUPAC Name: 6-cyclopropyl-8-fluoro-2-(2-hydroxymethyl-3-{1-methyl-5-[5-(4-methyl-piperazin-1-yl)-pyridin-2-ylamino]-6-oxo-1,6-dihydro-pyridin-3-yl}-phenyl)-2H-isoquinolin-1-one
CAS Number: 1242156-23-5
SMILES: OCc1c(cccc1n1ccc2c(c1=O)c(F)cc(c2)C1CC1)c1cc(Nc2ccc(cn2)N2CCN(CC2)C)c(=O)n( c1)C
Mechanism of Action: Kinase Inhibitor; BTK Inhibitor
Indication: Various Cancers; Anti-inflammatory Agents; Treatment for Rheumatoid Arthritis
Development Stage: Pre-Clinical
Company: Hoffmann-la-Roche

The production and effector function of antibodies are regulated by distinct immunoreceptors on B cells and innate immune cells. The receptors, termed B cell antigen receptor (BCR) and activating Fc receptor (FcR), belong to a family of Ig-like immunoreceptors containing an intracellular immunoreceptor tyrosine-based activation motif (ITAM). ITAMs act to integrate diverse antigen- or Fc-specific signals into a common pathway regulated by nonreceptor tyrosine kinases including Lyn, spleen tyrosine kinase (Syk), and Bruton's tyrosine kinase (Btk) from the sarcoma kinase, Syk, and Tec kinase families. These kinases relay the signals sequentially from ITAMs to phospholipase Cγ2 (PLCγ2) and thus play a critical and nonredundant role in the signal transduction of BCR and FcR. Consequently, loss-of-function mutation in the Btk gene results in severe B cell immunodeficiency and impaired FcR function in both patients with X-linked agammaglobulinemia and mutant mice with X-linked immunodeficiency.

Together, Btk and Syk regulate the signal transduction of ITAM-containing receptors or adaptors that are critical for autoantibody production, effector function, and osteoclast differentiation. Therefore, pharmacological inhibition of these enzymes may affect multiple steps in the pathogenesis of Rheumatoid arthritis (RA) and represent a useful approach for the treatment of the disease. Rheumatoid arthritis (RA) is an autoimmune joint disease characterized by chronic synovial inflammation and progressive joint destruction. The disease is often associated with the appearance of autoantibodies in both blood and inflamed joints. Several of these autoantibodies have emerged as potential arthritogenic factors. For example, anti-glucose-6 phosphate isomerase and anti-type II collagen antibodies, both of which are highly arthritogenic in mice, can be detected in patients with RA. In addition, anticitrullinated protein autoantibodies, the most prevalent in RA, can bind citrullinated fibrinogen in RA joints to form immune complexes, which stimulate macrophages to produce inflammatory cytokines such as TNFα. Lastly, clinical efficacy of B cell-depleting agents in RA strongly implicates autoantibodies as culprits in the pathogenesis of the disease.

When tested in the rat and mouse, RN486 exhibited an excellent pharmacokinetic profile. In the rat, it reached the maximal concentration of 2.5 µM at 4.5 h when dosed orally at 20 mg/kg and showed a half-life of 9.8 h in the blood when administered intravenously. In the mouse, the compound reached the maximal concentration of 6.0 µM at 3 h and a trough concentration of 1.0 µM at 24 h when dosed orally at 30 mg/kg [1].

Important facts about RN486:

a: RN486 Blocks both BCR and FcR Signaling.
b: RN486 Displays a Selective B Cell Inhibitory Profile in BioMAP Systems.
c: RN486 Displays Efficacy on Immune Arthritis Induced by both Active and Passive Immunization in Mice.
d: RN486 Inhibits Inflammation and Bone Erosions in Adjuvant-Induced Arthritis Either Alone or in Combination with Methotrexate.
e: RN486 Reduces Blood Inflammatory Markers in AIA.

Combination therapy with low-dose methotrexate is an important treatment option for patients with RA. Researchers therefore determined the potential of RN486 for combined therapy with methotrexate. To identify a suboptimal or low dose of methotrexate for combination study, researchers tested methotrexate alone in the AIA model at doses ranging from 0.025 to 0.25 mg/kg. Methotrexate displayed a dose-dependent inhibitory effect on both paw inflammation and splenomegaly in AIA rats, attenuating paw swelling by ~50 and 100%, respectively, at 0.075 and greater or equal 0.15 mg/kg. Researchers then tested RN486 and methotrexate at their respective suboptimal doses, 10 and 0.075 mg/kg, alone or in combination in the AIA model to assess the combined effect. As in the monotherapy studies, both RN486 and methotrexate attenuated paw swelling by approximately 50% when tested alone at the suboptimal doses. When combined, the two compounds completely eradicated paw swelling, splenomegaly, and histopathogical changes of inflammation and bone erosions [1].

1. Xu, D.; et. al. RN486, a selective Bruton's tyrosine kinase inhibitor, abrogates immune hypersensitivity responses and arthritis in rodents. J Pharmacol Exp Ther 2012, 341(1), 90-103.