Molecule

Description

R935788 (Fostamatinib disodium, R788) is a Syk inhibitor with IC50 of 41 nM.

Targets

IC₅₀

In Vitro

R935788 is a methylene phosphate prodrug of R406, which can be rapidly converted to R406 in vivo. R406 (in vitro active form of R935788) selectively inhibits Syk-dependent signaling with EC50 values ranging from 33 nM to 171 nM, more potently than Syk-independent pathways in different cells. ^[1] R406 inhibits cellular proliferation of a variety of diffuse large B-cell lymphoma (DLBCL) cell lines with EC50 values ranging from 0.8 μM to 8.1 μM. ^[2] R406 treatment reduces basal phosphorylation of BLNK, Akt, glycogen synthase kinase-3 (GSK-3), forkhead box O (FOXO) and ERK not only in cells with high (TCL-002) but also in cells with low levels of phosphorylated Syk (TCL1-551). In addition, R406 completely inhibits the anti-IgM induced Bcr signal in TCL1 leukemias. Despite the higher levels of constitutively active Syk in TCL1 leukemias, R406 is not selectively cytotoxic to the leukemic cells. ^[3]

In Vivo

Given that plasma half-life of R406 in mice is less than 2 hours, R935788 is administered in 3 divided doses at 3-hour intervals to provide continuous Syk inhibition during each day of treatment, mimicking the longer plasma half-life in humans (15 hours). Despite the relatively modest cytotoxic effect in vitro, R935788 significantly inhibits the proliferation and survival of leukemic cell in vivo, which is associated with the blocking of antigen-dependent B-cell receptor (Bcr) signaling rather than inhibition of constitutive Syk activity. R935788 treatment at 80 mg/kg/day for 18-21 days potently inhibits tumor growth of TCL1-002, TCL1-551 and TCL1-870 in mice with undetectable leukemic CD5⁺/B220⁺ cells at the last day of treatment, significantly prolongs the survival of the treated mice with median survival increased from 45/46 days to 170/172 days, and completely eradicates the malignant cells in a substantial proportion of mice after a 6-month follow-up period without affecting the production of normal B lymphocytes. R935788 treatment also induces an early and transient migration of both normal and malignant B cells from spleen and lymph nodes to peripheral blood, which is subsequently followed by selective growth inhibition of the malignant B-cell population. In addition, R935788 is also effective against spontaneously developing TCL1 leukemias in Eμ-TCL1 transgenic mice. ^[3]

Clinical Trials

A Phase II study of R935788 in advanced colorectal, non-small cell lung, head and neck, hepatocelluar and renal cell carcinomas and pheochromocytoma and thyroid tumors has been completed.

Features

Clinically used oral formulation of R406

In vitro fluorescence polarization kinase assays

R406 (in vitro active form of R935788) is serially diluted in DMSO and then diluted to 1% DMSO in kinase buffer (20 mM HEPES, pH 7.4, 5 mM MgCl₂, 2 mM MnCl₂, 1 mM DTT, 0.1 mg/mL acetylated BGG). ATP and substrate in kinase buffer are added at room temperature, resulting in a final DMSO concentration on 0.2%. The kinase reactions are performed in a final volume of 20 μL containing 5 μM HS1 peptide substrate and 4 μM ATP and started by addition of 0.125 ng of Syk in kinase buffer. The reaction is allowed to proceed for 40 minutes at room temperature. The reaction is stopped by the addition of 20 μL of PTK quench mix containing EDTA/anti-phosphotyrosine antibody (1× final)/fluorescent phosphopeptide tracer (0.5× final) diluted in FP Dilution Buffer. The plate is incubated for 30 minutes in the dark at room temperature and then read on a Polarion fluorescence polarization plate reader. Data is converted to determine the amount of phosphopeptide present using a calibration curve generated by competition with the phosphopeptide competitor provided in the Tyrosine Kinase Assay Kit. For IC50 determination, R406 is tested at eleven concentrations in duplicate and curve-fitting is performed by non-linear regression analysis using Prism GraphPad Software.

Cell Lines

TCL1-002, TCL1-252, TCL1-551, TCL1-870, and TCL1-540

Concentrations

Dissolved in DMSO, final concentrations ~10 μM

Incubation Time

48 hours

Methods

Cells are exposed to increasing concentrations of R406 (in vitro active form of R935788) for 48 hours. The percentage of apoptotic cells is determined by double staining with propidium iodide (PI) and annexin-A5–FITC conjugate. Ki-67 staining is performed with the FITC mouse anti–Ki-67 set. Samples are analyzed on a FACSCalibur flow cytometer with CellQuest Version 3.3 software.

Animal Models

B6/C3H F1 female mice intraperitoneally injected with TCL1-002, TCL1-551, or TCL1-870 leukemia cells, and Eμ-TCL1 transgenic mice

Formulation

Formulated as a 4 mg/mL solution in 0.1% carboxymethylcellulose sodium, 0.1% methylparaben, and 0.02% propylparaben (pH 6.5)

Doses

80 mg/kg/day

Administration

Intraperitoneal administration in 3 divided doses at 3-hour intervals