Targeting Toll like receptor 3 by double stranded RNA in breast cancer: Results from in vitro studies and randomized trial

Abstract

9619 Background : Toll like receptor 3 (TLR3) is known to be expressed by myeloid dendritic cells (DC) and to induce their maturation following binding with double stranded RNA (dsRNA) or its synthetic homologues polyAU and polyI:C. Several clinical trials have reported that injection of dsRNA is associated with survival benefit in cancer patients. In the present study, we have asked whether dsRNA could act directly on tumor cells through TLR3. Patients and methods : 300 patients with early breast cancer have been included from 1972 to 1979 in a randomized trial comparing post-operative administration of polyAU with no treatment. Results have been reported that showed a trend for a survival benefit in patients with involved axillary lymph nodes (n=200). Tumor biopsies from these patients were stained with TLR3-specific mAb and correlation between TLR3 expression and polyAU efficacy was determined. To investigate directly the effects of dsRNA, both freshly isolated breast tumor cells and cancer cell lines were cultured with polyI:C, and apoptosis was measured. The involvement of TLR3 in cell response was established by TLR3 RNA interference. Results : 182 tumor samples (91%) were available from the 200 pTxN+M0 patients included in this randomized trial. TLR3 was strongly expressed by tumor cells in 18 patients (10%). Table 1 reports the 20-year survival rates according to treatment and TLR3 expression. In vitro studies showed that breast cancer cell lines can express TLR3, and that dsRNA can induce up to 80% apoptosis in TLR3+ tumor cell lines within 48h of culture. This pro-apoptotic effect of double stranded RNA was specifically abolished by RNA interference for TLR3. Conclusion : These data suggest that: i. TLR3 is expressed by breast cancer cells in a subset of patients, ii. its activation by dsRNA could lead to tumor cell apoptosis in vitro and survival benefit in patients with TLR3+ tumors. No significant financial relationships to disclose.