A Cyanobacteria-derived RNA aptamer resensitizes prostate cancer to hormone therapy

Prostate adenocarcinoma (PCa) resistance to androgen receptor (AR) signaling inhibitor therapy is associated with elevated glutamine (L-Gln). Glutamine sensors, present in conserved riboswitches (glnA), control nitrogen metabolism in many organisms, like cyanobacteria. Iterative in silico modifications of glnA found in Synechococcus elongatus and thermodynamic analysis of a 56mer aptamer resulted in high L-Gln specificity and affinity. The optimized aptamer depleted L-Gln from PCa cells by both L-Gln sequestration and extracellular glutaminase activation, serving as an allosteric activator. Glutamine depletion reduced FOXM1 transcriptional occupancy on the promoter of fibroblast growth factor 8 (FGF8), a known mediator of PCa castration resistance. A point mutation in the binding pocket of the 56mer rendered the aptamer ineffective in L-Gln binding and FGF8 regulation. Accordingly, the L-Gln-depleting aptamer, with demonstrated serum stability, limited the proliferation and promoted cell death of castration-resistant PCa alone and in combination therapy with AR antagonists, enzalutamide and apalutamide, in subcutaneous and orthotopic mouse models. Further selective tumor targeting was achieved by functionalizing gold nanoparticles with either the optimized L-Gln aptamer or the point-mutant aptamer. Castration sensitivity was restored by the L-Gln-depleting aptamer but not by the point-mutant. The functionalized nanoparticle demonstrated superior anti-tumor efficacy in an orthotopic PCa model over the untargeted aptamer. The anti-tumor activity of the aptamer helped support L-Gln as an oncometabolite in PCa that can be targeted to sensitize tumors to hormone therapy.