Well-differentiated (WD)/dedifferentiated (DD) liposarcomas (LPS), which account for ~60% of all liposarcomas, are characterized by the amplification of the 12q13–q15 region, with consequent aberrant expression of MDM2. Patients have limited therapeutic options, particularly in advanced disease, and their outcomes remain largely unsatisfactory. Hence, there is an unmet need to identify and validate WD/DDLPS-specific actionable targets for developing novel biology-driven therapies. G-quadruplexes (G4s), non-canonical secondary structures that can form in G-rich nucleic acid sequences, have recently been identified and characterized within the inducible MDM2 P2 promoter. In addition, G4 ligand-induced DNA damage can lead to the formation of cytoplasmic micronuclei (MN). Spontaneous rupture of the MN envelope allows its recognition by receptor cyclic GMP-AMP synthase (cGAS), initiating the cGAS-STING-Interferon axis downstream of DNA damage. Therefore, we explored the potential of inhibiting MDM2 expression by targeting its G-quadruplex structures with small-molecule G4 ligands while also assessing the immunomodulatory effects of the G4 ligand in DDLPS cell lines.

We used in-house developed patient-derived LPS cell lines and normal pre-adipocytes. CUT&Tag and RNA-seq were performed to analyze the abundance of G4s in the different cell lines. Cell viability, RT-PCR and Western blot assays, siRNA inhibition and nascent transcript analysis were used to assess the effects of QN-302 treatment on different patient-derived DDLPS cell lines.

A G4 ligand, QN-302, significantly impaired the growth of DDLPS cells in a dose-dependent manner. We found that DDLPS cell lines showed enhanced G4 formation and that QN-302 activity strikingly paralleled cell-specific G4 abundance. QN-302-mediated MDM2 G4 stabilization at the P2 inducible promoter prevented polymerase progression from the constitutive P1 promoter in DDLPS cells, thereby inhibiting the formation of full-length MDM2 transcripts. This resulted in the accumulation of the tumor suppressor protein p53. In addition, QN-302 induced DNA damage in DDLPS cells and increased MN, with a significant fraction marked by γ-H2AX. Concomitantly, exposure to QN-302 led to the upregulation of a subset of interferon-stimulated genes (ISGs), including IFI27, IFI44L, IFI6, ISG15, and MX2, along with an increased release of certain cytokines, particularly IL-6.

We have identified a novel therapeutic strategy to inhibit MDM2 expression and promote p53 reactivation in DDLPS. Additionally, QN-302-induced DNA damage may activate the cGAS-STING pathway in DDLPS cell lines. The G4 multiple-target modality holds potential for further development through the rational design of drug combinations with standard chemotherapy, targeted therapies, and immunotherapy.