A Novel G‑Quadruplex Structure within Apolipoprotein\nE Promoter: A New Promising Target in Cancer and Dementia Fight?

Human apolipoprotein\nE (APOE) is a crucial lipid transport glycoprotein\ninvolved in various biological processes, including lipid metabolism,\nimmune response, and neurodegeneration. Elevated APOE levels are linked\nto poor prognosis in several cancers and increased risk of Alzheimer’s\ndisease (AD). Therefore, modulating APOE expression presents a promising\ntherapeutic strategy for both cancer and AD. Considering the pivotal\nrole of G-quadruplex (G4) structures in medicinal chemistry as modulators\nof gene expression, here, we present a newly discovered G-quadruplex\n(G4) structure within the ApoE gene promoter. Bioinformatic analysis\nidentified 21 potential G4-forming sequences in the ApoE promoter,\nwith the more proximal to the transcription start site, pApoE, showing\nthe highest G-score. Biophysical studies confirmed the folding of\npApoE into a stable parallel G4 under physiological conditions, supported\nby circular dichroism, NMR spectroscopy, UV-melting, and a quantitative\nPCR stop assay. Moreover, the ability to modulate pApoE-G4 folding\nwas demonstrated by using G4-stabilizing ligands (HPHAM, Braco19,\nand PDS), which increased the thermal stability of pApoE-G4. In contrast,\npeptide nucleic acid conjugates were synthesized to disrupt G4 formation,\neffectively hybridizing with pApoE sequences, and confirming the potential\nto unfold G4 structures. Overall, our findings provide a mainstay\nfor future therapeutic approaches targeting ApoE-G4s to regulate APOE\nexpression, offering potential advancements in cancer and AD treatment.