Balancing Affinity, Selectivity, and Cytotoxicity of Hydrazone-Based G‑Quadruplex Ligands for Activation of Interferon β Genes in Cancer Cells

G-quadruplex (G4) ligands are investigated to discover
new anticancer
drugs with increased cell-killing potency. These ligands can induce
genome instability and activate innate immune genes at non-cytotoxic
doses, opening the discovery of cytostatic immune-stimulating ligands.
However, the interplay of G4 affinity/selectivity with cytotoxicity
and immune gene activation is not well-understood. We investigated
a series of closely related hydrazone derivatives to define the molecular
bases of immune-stimulation activity. Although they are closely related
to each other, such derivatives differ in G4 affinity, cytotoxicity,
genome instability, and immune gene activation. Our findings show
that G4 affinity of ligands is a critical feature for immune gene
activation, whereas a high cytotoxic potency interferes with it. The
balance of G4 stabilization versus cytotoxicity can
determine the level of immune gene activation in cancer cells. Thus,
we propose a new rationale based on low cell-killing potency and high
immune stimulation to discover effective anticancer G4 ligands.