Expression of new antigens on tumor cells by inhibiting nonsense-mediated mRNA decay.

The main reason why tumors are not controlled by the immune system of the cancer patient is that tumors do not express potent tumor antigens that can be recognized by the immune system as "foreign." The current focus in developing immune-based modalities is to potentiate an immune response against the existing, albeit weak, antigens expressed in the tumor. An alternative approach is to express new, and hence potent, antigens in tumor cells in situ. To this end, we have developed an approach to generate new antigenic determinants in tumor cells using siRNA technology to inhibit nonsense-mediated mRNA decay (NMD), a surveillance mechanism which prevents the expression of mRNAs containing a premature termination codon. Targeting siRNA inhibition to tumor cells--an essential requisite because of the constitutive nature and physiological roles of the NMD process--is accomplished by using a novel targeting technology based on using oligonucleotide aptamer ligands. Aptamers or aptamer-targeted siRNA conjugates, unlike antibodies, can be synthesized in a chemical process providing a more straightforward and cost-effective manufacturing and regulatory approval process to generate clinical-grade reagents. In murine tumor models, the aptamer-targeted siRNA-mediated NMD inhibition in tumor cells led to significant inhibition of tumor growth, which was superior to best-in-class "conventional" cancer vaccination protocols. Tumor-targeted NMD inhibition forms the basis of a simple, broadly useful, and clinically feasible approach to enhance the antigenicity of disseminated tumors leading to their immune recognition and rejection. The cell-free chemically synthesized oligonucleotide backbone of aptamer-siRNAs reduces the risk of immunogenicity and enhances the feasibility of generating reagents suitable for clinical use.