A Cyanobacteria-Derived RNA Aptamer Resensitizes Prostate Cancer to Hormone Therapy.

Prostate adenocarcinoma 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, such as 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 prostate adenocarcinoma 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 FGF8, a known mediator of prostate adenocarcinoma 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 prostate adenocarcinoma 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 aptamer. The functionalized nanoparticle demonstrated superior antitumor efficacy in an orthotopic prostate adenocarcinoma model compared with the untargeted aptamer. The antitumor activity of the aptamer helped support L-Gln as an oncometabolite in prostate adenocarcinoma that can be targeted to sensitize tumors to hormone therapy. SIGNIFICANCE: Depletion of glutamine, which can mediate hormone therapy resistance in prostate cancer patients, with a cyanobacteria-derived catalytic aptamer blocks FGF8 expression and sensitizes hormone refractive prostate tumors to androgen receptor inhibitors.