Loxoribine

Loxoribine is a guanosine derivative and an agonist of toll-like receptor 7 (TLR7).^1,2 It is selective for TLR7 over other human TLRs in a cell-based reporter assay at 1 mM.². Loxoribine induces proliferation, increases the antibody response to sheep red blood cells, and activates natural killer cell activity against Yac-1 lymphoma cells in murine splenocyte cultures (EC₅₀s = 10-50, 3-20, and 13-22 μM, respectively).¹ Loxoribine (250 μM) increases production of IL-12, IL-23, IL-27, and IL-10 by human monocyte-derived dendritic cells (MoDCs).³ Loxoribine-treated MoDCs induce higher levels of IL-17 and IFN-γ secretion by co-cultured allogeneic CD4⁺ T cells compared to control MoDCs. Loxoribine (120 mg/kg) reduces the number of pulmonary metastases in the B16 mouse model of melanoma, an effect enhanced by co-administration of IL-2, and exhibits adjuvant activity in mice immunized with a B16 tumor vaccine.⁴

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1. Reitz, A.B., Goodman, M.G., Pope, B.L., et al. Small-molecule immunostimulants. Synthesis and activity of 7,8-disubstituted guanosines and structurally related compounds. J. Med. Chem. 37(21), 2561-2578 (1994).

2. Heil, F., Ahmad-Nejad, P., Hemmi, H., et al. The Toll-like receptor 7 (TLR7)-specific stimulus loxoribine uncovers a strong relationship within the TLR7, 8 and 9 subfamily. Eur. J. Immunol. 33(11), 2987-2997 (2003).

3. Dzopalic, T., Dragicevic, A., Vasilijic, S., et al. Loxoribine, a selective Toll-like receptor 7 agonist, induces maturation of human monocyte-derived dendritic cells and stimulates their Th-1- and Th-17-polarizing capability. Int. Immunopharmacol. 10(11), 1428-1433 (2010).

4. Pope, B.L., Sigindere, J., Chourmouzis, E., et al. 7-Allyl-8-oxoguanosine (loxoribine) inhibits the metastasis of B16 melanoma cells and has adjuvant activity in mice immunized with a B16 tumor vaccine. Cancer Immunol. Immunother. 38(2), 83-91 (1994).