title: Lowering the overall charge on TMPyP4 improves its selectivity for G-quadruplex DNA.
abstract: Ligands that stabilize non-canonical DNA structures called G-quadruplexes (GQs) might have applications in medicine as anti-cancer agents, due to the involvement of GQ DNA in a variety of cancer-related biological processes. Five derivatives of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4), where a N-methylpyridyl group was replaced with phenyl (4P3), 4-aminophenyl (PN3M), 4-phenylamidoproline (PL3M), or 4-carboxyphenyl (PC3M and P2C2M) were investigated for their interactions with human telomeric DNA (Tel22) using fluorescence resonance energy transfer (FRET) assay, and UV-visible and circular dichroism spectroscopies in K+buffer. The molecules are cationic or zwitterionic with an overall charge of 3+ (4P3, PN3M, and PL3M), 2+ (PC3M) or neutral (P2C2M). All porphyrins except P2C2M stabilize human telomeric DNA in FRET assays by ∼20 °C at 5 eq CD melting experiments suggest that 4P3 is the most stabilizing ligand with a stabilization temperature of 16.8 °C at 4 eq. Importantly, 4P3, PC3M and PL3M demonstrate excellent selectivity for quadruplexes, far superior to that of TMPyP4. Binding constants, determined using UV-vis titrations, correlate with charge: triply cationic 4P3, PN3M and PL3M display Kaof 5-9 μM-1, doubly cationic PC3M displays Kaof 1 μM-1, and neutral P2C2M displays weak-to-no binding. UV-vis data suggest that binding interactions are driven by electrostatic attractions and that the binding mode may be base-stacking (or end-stacking) judging by the high values of red shift (15-20 nm) and hypochromicity (40-50%). We conclude that lowering the charge on TMPyP4 to 3+ can achieve the desired balance between stabilizing ability, affinity, and high selectivity required for an excellent quadruplex ligand.
authors.affiliation: Department of Chemistry and Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA, 19081, USA.
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Ruan
authors.affiliation: Department of Chemistry and Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA, 19081, USA.
authors.forename: Supriya J
authors.initials: SJ
authors.lastname: Davis
authors.affiliation: Department of Chemistry and Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA, 19081, USA.
authors.forename: Barrett M
authors.initials: BM
authors.lastname: Powell
authors.affiliation: Department of Chemistry and Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA, 19081, USA.
authors.forename: Cole P
authors.initials: CP
authors.lastname: Harbeck
authors.affiliation: Institute of Chemistry, University of Silesia, 40-006, Katowice, Poland.
authors.forename: Jan
authors.initials: J
authors.lastname: Habdas
authors.affiliation: Department of Physics, Saint Joseph's University, 5600 City Ave., Philadelphia, PA, 19131, USA.
authors.forename: Piotr
authors.initials: P
authors.lastname: Habdas
authors.affiliation: Department of Chemistry and Biochemistry, Swarthmore College, 500 College Ave., Swarthmore, PA, 19081, USA. Electronic address: lyatsun1@swarthmore.edu.
authors.forename: Liliya A
authors.initials: LA
authors.lastname: Yatsunyk
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry* / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D054856:G-Quadruplexes; D006801:Humans; D008024:Ligands; D009691:Nucleic Acid Denaturation; D011166:Porphyrins / Q000737:chemistry* / Q000378:metabolism; D013053:Spectrophotometry; D055672:Static Electricity; D016615:Telomere / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013696:Temperature
chemical_list: D000970:Antineoplastic Agents; D008024:Ligands; D011166:Porphyrins; C021096:tetra(4-N-methylpyridyl)porphine; D004247:DNA
keywords: Binding constants; FRET; Guanine quadruplex; Human telomeric DNA; TMPyP4 derivatives