Abstract 1709: Cyanobacteria-derived RNA aptamer supports prostate cancer hormone sensitivity

Prostate cancer (PCa) hormone therapy resistance is the second leading cause of cancer death among American men. Multiple mechanisms inherent to the disease can lead to castrate-resistance, including those that mediate lineage plasticity. We have reported that inhibiting AR signaling can increase glutamine (L-Gln) secretion by cancer-associated fibroblasts (CAF). L-Gln-free media significantly limits PCa cell growth. However, targeting L-Gln metabolism or transporters provides limited benefit. On the other hand, non-metabolizable L-Gln analogues like 6-Diazo-5-oxo-l-norleucine (DON) and DRP104 have shown promising antitumor effects. We reasoned that extracellular interruption of L-Gln uptake could be a therapeutic strategy that bypasses metabolic adaptation of a specific enzyme or transporter, especially if it could be tumor-selective. To target L-Gln, we explored cyanobacteria-structured non-coding RNA riboswitches, which are typically associated with metabolite-binding for gene regulation. Riboswitches in cyanobacteria that sense L-Gln through an aptamer motif, glnA, were chosen due to their stability and high specificity. Since L-Gln concentrations in bacteria can be higher than those in the tumor microenvironment, we optimized an RNA aptamer binding affinity through structural analysis, computer modeling, and in vitro and in vivo testing. The optimized aptamer depleted L-Gln from PCa cells by both L-Gln sequestration and the recruitment of extracellular glutaminase activity, serving as an allosteric activator. Glutamine depletion reduced FOXM1 transcriptional occupancy on the FGF8 promoter, known mediator of PCa castrate resistance. Further tumor targeting was achieved by functionalizing gold nanoparticles with the aptamer. The L-Gln-depleting aptamer, with demonstrated serum stability, limited the proliferation, and lineage plasticity of the castrate resistant prostate tumors alone and in combination therapy with AR antagonists, enzalutamide and apalutamide in subcutaneous and orthotopic mouse models. A point mutation in the binding pocket of the 56mer rendered the aptamer ineffective in L-Gln binding, FGF8 regulation, and had a limited impact on tumor growth. Superiority of the functionalized nanoparticle targeting was demonstrated in an orthotopic PCa model over the un-targeted aptamer in reducing tumor weight. The studies demonstrated elevated L-Gln can be necessary and sufficient for castrate resistance, as its depletion sensitizes prostatic tumors to AR inhibition. Citation Format: Carlos David Cruz-Hernandez, Bethany Smith, Sandrine Billet, Manish Thiruvalluvan, Gabrielle Gonzalez, Neil Bhowmick. Cyanobacteria-derived RNA aptamer supports prostate cancer hormone sensitivity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1709.