Anticancer effects of polyadenylic-polyuridylic acid (poly[A:U]) and uncoupling of chemokine receptor signaling: Role of CCR5 and CXCR3

3063 Background: Several tumor cells express toll-like receptors (TLRs) which constitute putative therapeutic targets. Methods: To dissect the clinical outcome of the host versus cell autonomous effects of the TLR3 agonist poly(A:U), we took advantage of two murine TLR3 expressing tumor models (melanoma and glioblastoma) that produced large amounts of CCL5 (a CCR5 ligand) and CXCL10 (a CXCR3 ligand) in response to the poly(A:U) and type I IFN in vitro and in vivo. We tested in vivo a triple combination based on vaccine against tumor antigens (V), chemotherapy (C), and TLR3 agonist (poly[A:U]) (T). Results: Single agents (V, C, or T) and combinations of two agents (VC, VT, or CT) failed to improve tumor progression. However, the sequential tritherapy (VCT) significantly retarded tumor growth and prolonged the survival of tumor-bearing C57BL/6 mice. The antitumor effects of VCT (immunochemotherapy) failed to be observed in nu/nu and TRIF -/- mice, indicating the contribution of T cells and TRIF-dependent signals to the therapeutic effect. Knockout of CCR5 improved the efficacy of immunochemotherapy. The VCT combination induced the recruitment of IFNγ + /CD8 +/ CXCR3 + T lymphocytes supporting the notion that this subset of T cells contributes to the antitumor efficacy of immunochemotherapy. Knockout of the CXCR3 gene annihilated the beneficial effects of VCT. The source of the deleterious CCL5 was the TLR3-activated tumor cells in that stable inhibition of the chemokine production by targeted shRNA CCL5 ameliorated the efficacy of VCT tritherapy. Altogether, 11% of wild-type mice were completely protected from melanoma by VCT sequential regimen. Conclusions: This study supports the notion that poly(A:U) can act on tumor epithelia to promote the release of beneficial CXCL10 for the recruitment of intratumoral CTLs but also the release of deleterious CCL5 acting on host immunosuppressors. Uncoupling chemokine release and/or prior vaccination may enable the CXCR3L-dependent CTL to overrule the CCR5-dependent suppression and may be integrated in future trials using TLR3 agonists. [Table: see text]