Phosphorothioate-Modified TLR9 Ligands Protect Cancer Cells against TRAIL-Induced Apoptosis

Abstract

Hypomethylated CpG oligodeoxynucleotides (CpG ODNs) target TLR9 expressed by immune cells and are currently being evaluated as adjuvants in clinical trials. However, TLR signaling can promote some tumor growth and immune evasion, such as in multiple myeloma (MM). Therefore, deciphering the effects of CpG ODNs on cancer cells will help in preventing these adverse effects and in designing future clinical trials. TLR activation induces multiple signaling pathways, notably NF-κB that has been involved in the resistance to TRAIL. Thus, we wondered if CpG ODNs could modulate TRAIL-induced apoptosis in different models of tumors. Here, we show that TLR9+ (NCI-H929, NAN6, KMM1) and TLR9− MM cells (MM1S) were protected by CpG ODNs against recombinant TRAIL-induced apoptosis. By using two fully human, agonist mAbs directed against TRAIL receptors DR4 and DR5 (mapatumumab and lexatumumab, respectively), we show that the protection was restricted to DR5-induced apoptosis. Similar results were observed for two colon cancer (C45 and Colo205) and two breast cancer cell lines (HCC1569 and Cal51). The protection of CpG ODNs was mediated by its nuclease-resistant phosphorothioate backbone independent of TLR9. We next demonstrated by surface plasmon resonance that phosphorothioate-modified CpG ODNs directly bound to either TRAIL or lexatumumab and then decreased their binding to DR5. Finally, NK cell lysis of a DR5-sensitive MM cell line (NCI-H929) through TRAIL was partially inhibited by phosphorothioate-modified CpG ODNs. In conclusion, our results suggest that the phosphorothioate modification of CpG ODNs could dampen the clinical efficacy of CpG ODN-based adjuvants by altering TRAIL/TRAIL receptor interaction.

CpG-Oligodeoxynucleotide Inhibits Smad-Dependent Bone Morphogenetic Protein Signaling: Effects on Myeloma Cell Apoptosis and In Vitro Osteoblastogenesis

“…Recently, CpG-ODN with a PTO backbone was shown to protect cancer cells from TRAIL-induced apoptosis by inhibiting binding of TRAIL to its receptor (54). Further, we have, in this study, shown that CpG-ODN with a PTO-backbone prevents BMP-induced apoptosis of malignant plasma cells, and BMP-induced osteoblastogenesis by inhibiting Smad signaling in a TLR9-independent manner.…”

Cell Death via DR5, but not DR4, Is Regulated by p53 in Myeloma Cells

“…However, in contrast to TNF-a receptors, both TRAIL receptors induce cell death. TRAIL differentially binds to TRAIL-R as illustrated by the phosphorotioate-modified CpG nucleotides, which block the binding of TRAIL to DR5 but not to DR4 and similarly bind to lexatumumab and not to mapatumumab (40). TRAIL mutants with selective binding to DR4 or DR5 also showed that binding of TRAIL to DR4 and DR5 involves different amino acids (41).…”

Toll-Like Receptor 9 Is a Novel Biomarker for Esophageal Squamous Cell Dysplasia and Squamous Cell Carcinoma Progression

“…Inverse association was seen with the vascular density suggesting that possible tumor-promoting properties of TLR9 expression are not linked to induction of angiogenesis. Activation of tumor cell TLRs has been reported to promote tumor cell proliferation and resistance to apoptosis [12,31] . In this study, the TLR9 expression showed no association with tumor cell proliferation or apoptosis.…”