Development of immunomodulatory six base-length non-CpG motif oligonucleotides for cancer vaccination

We have previously described a novel family of immunomodulatory synthetic oligonucleotides characterized by a phosphodiester backbone, a length of six bases and a 5'G3xG23' sequence, where x is A, C, G or T. In the present study, we have evaluated whether these 5'G3xG23' oligonucleotides possess additional activities essential for adequate cancer vaccination. Immunization for the treatment of cancer requires an adjuvant, a source of tumor-associated antigen(s), for example apoptotic cancer cells, and a way to overcome the escape of tumor cells from the immune system, for example the up-regulation of Fas ligand (FasL) on the surface of cancer cells. The results show that phosphodiester 5'G3AG23' and 5'G3TG23' oligonucleotides have a direct activity on a number of different cancer cells by inducing apoptosis (release of cytochrome C, activation of caspase-3, cleavage of poly [ADP-ribose] polymerase, degradation of nuclear mitotic apparatus protein and translocation of phophatidylserine at the cell surface). In addition, the 5'G3AG23', 5'G3CG23', and 5'G3TG23' oligonucleotides were found to down-regulate the levels of FasL on the surface of cancer cells. These immunomodulatory phosphodiester six base-length oligonucleotides, which are capable of inducing apoptosis in cancer cells as well as downregulating the expression of FasL at their cell surface, may have application as cancer cell vaccines.