Lowering the overall charge on TMPyP4 improves its selectivity for G-quadruplex DNA.

Area of Science:

• Medicinal Chemistry
• Biochemistry
• Molecular Biology

Background:

• G-quadruplex (GQ) DNA structures are implicated in cancer biology.
• Ligands stabilizing GQs are potential anti-cancer agents.
• 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4) is a known GQ ligand.

Purpose of the Study:

• To investigate the interaction of TMPyP4 derivatives with human telomeric DNA (Tel22).
• To evaluate the G-quadruplex stabilizing ability, affinity, and selectivity of these derivatives.
• To determine the optimal charge for TMPyP4 derivatives as GQ ligands.

Main Methods:

• Synthesis of five TMPyP4 derivatives with varying charges (4P3, PN3M, PL3M, PC3M, P2C2M).
• Fluorescence resonance energy transfer (FRET) assays to assess DNA stabilization.
• UV-visible and circular dichroism (CD) spectroscopies for binding and structural analysis.

Main Results:

• All derivatives except P2C2M significantly stabilized Tel22 DNA (up to ~20°C).
• The triply cationic 4P3 derivative exhibited the highest stabilization (16.8°C) and selectivity.
• Binding affinity correlated with charge; triply cationic ligands showed higher affinity (5-9 μM⁻¹) than doubly cationic (1 μM⁻¹) or neutral ligands.

Conclusions:

• Reducing the charge of TMPyP4 to 3+ enhances G-quadruplex stabilization, affinity, and selectivity.
• The 4P3 derivative represents a promising candidate for anti-cancer drug development targeting G-quadruplex DNA.
• Electrostatic interactions and base-stacking are key mechanisms in ligand-DNA binding.