G-quadruplex Stabilization Fuels the ALT Pathway in ALT-positive Osteosarcoma Cells

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• Most human tumors use telomerase to maintain telomere length, but 10-15% use alternative lengthening of telomeres (ALT).
• Telomeric G-quadruplex (G4) ligands like RHPS4 show antiproliferative effects in telomerase-positive cancers, but their impact on ALT is poorly understood.

Purpose of the Study:

• To investigate the effect of G4 stabilization by RHPS4 on the alternative lengthening of telomeres (ALT) mechanism.
• To determine if RHPS4 sensitivity is linked to the telomere maintenance pathway in osteosarcoma cells.

Main Methods:

• Compared RHPS4 sensitivity in ALT-positive (U2OS, SAOS-2) and telomerase-positive (HOS) osteosarcoma cell lines.
• Analyzed key ALT hallmarks including telomeric doublets, DNA damage, ALT-associated Promyelocytic Leukaemia-bodies (APBs), telomere sister chromatid exchanges (T-SCE), and c-circles in RHPS4-treated cells.

Main Results:

• RHPS4 sensitivity was comparable in both ALT-positive and telomerase-positive osteosarcoma cells, decoupling sensitivity from the telomere maintenance mechanism.
• RHPS4 treatment significantly induced telomeric doublets, clusterized DNA damage, APBs, T-SCE, and c-circles exclusively in ALT cells.
• RHPS4 appears to induce replicative stress, leading to DNA damage at telomeres and fueling recombination in ALT cells.

Conclusions:

• RHPS4 induces telomeric DNA damage and overactivates telomeric recombination in ALT cells.
• The findings open new avenues for exploring G4 ligands as a therapeutic strategy for ALT-positive tumors.
• RHPS4's impact on ALT mechanisms warrants further investigation for targeted cancer therapies.