Abstract 4417: Activity of novel RNA therapeutics to overcome resistance to immune checkpoint blockade

Abstract

T-cells in the tumor microenvironment can often become exhausted and dysfunctional due to chronic and prolonged exposure to antigen. The resulting condition of T cell exhaustion represents an important mechanism of clinical resistance to immune checkpoint blockade. The transcription factor NR4A1 is known to be upregulated in tumor-specific T-cells and is a mediator of T cell dysfunction including driving exhaustion during chronic antigen stimulation of T-cells. Pro-oncogenic activities of NR4A1 have been observed in various solid tumors, including colorectal and breast cancers, and co-expression of NR4A1 with known immune checkpoint markers such as PD-L1 and B7 family members has also been observed in various cancer cell lines. These findings have identified NR4A1 as an important target for overcoming resistance to cancer immunotherapy. We hypothesize that targeted silencing of the NR4A1 and other immunomodulatory genes can reverse T-cell exhaustion and expand the clinical benefit of immune checkpoint blockade in solid tumors resistant to immune therapy. To reverse T-cell exhaustion with a targeted approach, we developed T cell targeting SeekRsTM, which are chimeric RNA therapeutics containing dual-flanking aptamer binders connected by a double-stranded bridge containing siRNA silencers that can target multiple immunomodulatory genes. First-generation aptamer-siRNA chimeras designed with a CTLA-4 targeting aptamer containing a STAT3 siRNA demonstrated effectiveness in silencing its target. Modifications to the structure included the addition of chemically modified nucleotides to improve serum stability. Additionally, dimerization of the structure to form a SeekR dimer molecule greatly improved internalization and target silencing compared to the monomeric chimera. Newly developed SeekRs targeting T cells and designed to silence NR4A1 have effectively downregulated NR4A1 in model cell lines and activated T cells. These results demonstrate that dual targeting SeekRs can be used to specifically deliver siRNA to T cells for targeted silencing that can reverse exhaustion and potentially overcome resistance to cancer immunotherapy in the clinic. Citation Format: Marvin O'Ketch, Jeffrey A. Kiefer, Dnyanesh Rasale, Warren S. Weiner, Lizette A. Castaño, Nathalie A. Azorsa, David W. Lee, Kerry M. Barnhart, Spyro Mousses, David O. Azorsa. Activity of novel RNA therapeutics to overcome resistance to immune checkpoint blockade. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4417.