MSA-2

MSA-2 in solution exists as monomers and noncovalent dimers in an equilibrium that strongly favors monomers; MSA-2 monomers cannot bind STING, whereas the noncovalent MSA-2 dimers bind STING with nanomolar affinity. MSA-2 exhibits substantially higher cellular potency in an acidified tumor microenvironment than normal tissue, owing to increased cellular entry and retention combined with the inherently steep MSA-2 concentration dependence of STING occupancy.^[1]

MSA-2 is orally available, manifesting similar oral and subcutaneous exposure in mice. In tumor-bearing mice, MSA-2 induced elevations of interferon-b in plasma and tumors by both routes of administration. Well-tolerated regimens of MSA-2 induced tumor regressions in mice bearing MC38 syngeneic tumors. In tumor models that are moderately or poorly responsive to PD-1 blockade, combinations of MSA-2 and anti-PD-1 antibody are superior in inhibiting tumor growth and prolonging survival over monotherapy.^[1]

• Cell lines

  THP-1 cells, mouse macrophages

• Concentrations

  20 μM, 0.16 μM-100 μM

• Incubation Time

  5 h

• Method

  In the primary screen, THP-1 cells are incubated, in 1536-well plates, with test compounds (20 μM) in a RPMI1640-based assay medium in the presence of 5% carbon dioxide at 37°C for 5 hours. IFN-b levels are determined using an AlphaLISA assay and an EnVision Reader and expressed as percentages of IFN-b induced by cGAMP. STING binding activity of compounds is evaluated with a competitive radioligand binding assay using tritiated cGAMP and membrane embedded full-length recombinant human and mouse STING generated in insect cells. STING pathway activation by MSA-2 is assessed by Western blotting, probing phosphorylation status and total protein levels of STING, TBK-1, and IRF3 by using commercially available antibodies.

• Animal Models

  C57BL/6J mice, NSG mice, BALB/c mice, nude NCr mice

• Dosages

  25 mg/kg, 40 mg/kg, 50 mg/kg, 60 mg/kg, 80 mg/kg, 160 mg/kg

• Administration

  intra tumor injection, SC, PO